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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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How do welding shade numbers add up? Eclipse viewing.
I want to look at the eclipse this weekend.
Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike |
#2
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How do welding shade numbers add up? Eclipse viewing.
mike wrote:
I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike A much better idea is to punch a pinhole in the center of one end of a shoebox , and tape a piece of white paper inside the other end . Point the pinhole end at the sun , there will be an inverted IIRC image of the sun on the paper if you've lined it up properly . Similar in principle to a pinhole camers , you might google "pinhole eclipse viewer" or similar for more info . Welding lenses are not really suitable for viewing the sun , though many people do it ...; -- Snag Learning keeps you young ! |
#3
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How do welding shade numbers add up? Eclipse viewing.
"mike" wrote in message
... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? More than the dark factor, for eclipses, is the UV factor, and window glass (and plastic) is fairly opaque to UV. Beer's law would proly indicate that more lenses would be better for UV than one dark lens, regardless of the net tinting. http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law After all the bull****, Absorption is linear with thickness.... LOL Of course, Snag's advice is always good. -- EA Thanks, mike |
#4
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How do welding shade numbers add up? Eclipse viewing.
On Thu, 17 May 2012 15:22:39 -0500, Snag wrote:
mike wrote: I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike A much better idea is to punch a pinhole in the center of one end of a shoebox , and tape a piece of white paper inside the other end . Point the pinhole end at the sun , there will be an inverted IIRC image of the sun on the paper if you've lined it up properly . Similar in principle to a pinhole camers , you might google "pinhole eclipse viewer" or similar for more info . Welding lenses are not really suitable for viewing the sun , though many people do it ...; If you have a room available that's sunny at the time of day of the eclipse, cover up the windows and make a pinhole in the shade. You get a lot bigger solar disk to view, and if you want you can make multiple holes. Because you need to make a tradeoff between brightness and focus, you want a bigger "pinhole": if I recall correctly a 1/16" or even 1/8" is appropriate for a ten foot distance. I remember one solar eclipse where, after leaving the building where us engineering staff had converted a conference room into a solar observatory, I noticed that the little sun-dapples filtering through the leaves of the trees were all little solar eclipse pictures. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com |
#5
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How do welding shade numbers add up? Eclipse viewing.
"Existential Angst" wrote in message ... "mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? More than the dark factor, for eclipses, is the UV factor, and window glass (and plastic) is fairly opaque to UV. Beer's law would proly indicate that more lenses would be better for UV than one dark lens, regardless of the net tinting. http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law After all the bull****, Absorption is linear with thickness.... LOL Of course, Snag's advice is always good. -- EA Arc welding puts out lot's of UV. Why wouldn't a helmet already have UV filters in it? Art |
#6
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How do welding shade numbers add up? Eclipse viewing.
"Artemus" wrote in message
... "Existential Angst" wrote in message ... "mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? More than the dark factor, for eclipses, is the UV factor, and window glass (and plastic) is fairly opaque to UV. Beer's law would proly indicate that more lenses would be better for UV than one dark lens, regardless of the net tinting. http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law After all the bull****, Absorption is linear with thickness.... LOL Of course, Snag's advice is always good. -- EA Arc welding puts out lot's of UV. Why wouldn't a helmet already have UV filters in it? Even better for eclipses! -- EA Art |
#7
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-17, Artemus wrote:
"Existential Angst" wrote in message ... "mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. [ ... ] Arc welding puts out lot's of UV. Why wouldn't a helmet already have UV filters in it? It does -- and the auto-darkening ones block the UV even when they aren't dark. But -- I suspect that the problem with viewing the sun is more a matter of IR than UV -- something which can boil the back of your eyeball. Gas welding glasses have good IR blocking. Arc welding hoods have good UV blocking. Probably you want both at the same time for viewing an eclipse -- if you don't go with the pinhole camera approach, which strikes me as the best -- especially since you can have more than one person viewing the image at once, instead of fighting over the filters. :-) Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#8
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How do welding shade numbers add up? Eclipse viewing.
mike used his keyboard to write :
I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Try These for a better view. http://www.sunguntelescope.com/MAIN.html http://cdn.transitofvenus.org/docs/B...Sun_Funnel.pdf -- John G |
#9
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How do welding shade numbers add up? Eclipse viewing.
"mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Sent my wife today for two 4 x 5 shade 14 lenses. They said they were out, and had sold 14,000 lenses. We are SMACK DAB in the middle of the path here in Toquerville, Utah. My NexGen only goes up to 13. What's up with that? Steve |
#10
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How do welding shade numbers add up? Eclipse viewing.
Tim Wescott wrote in
: I remember one solar eclipse where, after leaving the building where us engineering staff had converted a conference room into a solar observatory, I noticed that the little sun-dapples filtering through the leaves of the trees were all little solar eclipse pictures. I've seen that before. Way cool, isn't it? |
#11
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How do welding shade numbers add up? Eclipse viewing.
"mike" wrote in message
... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Several years ago (20? 25?) we had something like a 3/4 eclipse. I was busy working and didn't have much time to play that day, but I sure found it interesting seeing all the crescent shapes in the shadows when I walked under a mulberry tree in my back yard. I'ld never heard of such a thing before. Oh, I knew about pinhole boxes, and my dad had a reflector for looking at the sun with his telescope, but I never expected to see such a blatant display of it so casually like that. I wished I had a camera handy at the time, but I had work to do, and could only enjoy the site for a few moments. |
#12
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How do welding shade numbers add up? Eclipse viewing.
"mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike If you convert the shade number (S) into something called "optical density' (OD), then the OD numbers do add up when you combine them. the formula is: OD = 0.428 * (S -1) To convert back from OD to shade # the formula is: S = 2.33*OD +1 So a shade number of 7 has an OD of 2.568 . Two of these used together have an OD of 5.136 which is a shade number of 12.96 An OD of 5 or more is usually considered safe enough for sun viewing. I have no idea why the welders shade scale was made different than optical density. |
#13
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How do welding shade numbers add up? Eclipse viewing.
On Thu, 17 May 2012 18:29:31 -0700, "Steve B"
wrote: "mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Sent my wife today for two 4 x 5 shade 14 lenses. They said they were out, and had sold 14,000 lenses. We are SMACK DAB in the middle of the path here in Toquerville, Utah. My NexGen only goes up to 13. What's up with that? Steve Wear sungalsses under the nexgen? Remove 333 to reply. Randy |
#14
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How do welding shade numbers add up? Eclipse viewing.
"anorton" wrote in message m... If you convert the shade number (S) into something called "optical density' (OD), then the OD numbers do add up when you combine them. the formula is: OD = 0.428 * (S -1) To convert back from OD to shade # the formula is: S = 2.33*OD +1 So a shade number of 7 has an OD of 2.568 . Two of these used together have an OD of 5.136 which is a shade number of 12.96 An OD of 5 or more is usually considered safe enough for sun viewing. I have no idea why the welders shade scale was made different than optical density. Assuming your equations for Shade # vs OD are correct. Then, since the equations are linear, you can add Shade #'s too by using S(sum) = S1 + S2 -1. Art |
#15
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How do welding shade numbers add up? Eclipse viewing.
"Artemus" wrote in message ... "anorton" wrote in message m... If you convert the shade number (S) into something called "optical density' (OD), then the OD numbers do add up when you combine them. the formula is: OD = 0.428 * (S -1) To convert back from OD to shade # the formula is: S = 2.33*OD +1 So a shade number of 7 has an OD of 2.568 . Two of these used together have an OD of 5.136 which is a shade number of 12.96 An OD of 5 or more is usually considered safe enough for sun viewing. I have no idea why the welders shade scale was made different than optical density. Assuming your equations for Shade # vs OD are correct. Then, since the equations are linear, you can add Shade #'s too by using S(sum) = S1 + S2 -1. Art You are correct. So I guess that 12.96 number above should really be 13 if not for rounding errors. By the way, the constants in those equations are more accurately 3/7 and 7/3. |
#16
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How do welding shade numbers add up? Eclipse viewing.
"anorton" wrote in message m... "mike" wrote in message ... I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike If you convert the shade number (S) into something called "optical density' (OD), then the OD numbers do add up when you combine them. the formula is: OD = 0.428 * (S -1) To convert back from OD to shade # the formula is: S = 2.33*OD +1 So a shade number of 7 has an OD of 2.568 . Two of these used together have an OD of 5.136 which is a shade number of 12.96 An OD of 5 or more is usually considered safe enough for sun viewing. I have no idea why the welders shade scale was made different than optical density. My SIL called, and was in a tizzy because he could not find one shade 14 lens in all of Las Vegas. So, I went to a local eye doctor, and they had a case of little cardboard glasses for $2 per. My wife musta got the last of the 14's at the welding shop, as I called there today, and they have a list of 38 sold if their special shipment comes in before Sunday evening. I am pretty much at ground zero, about 15 miles south of Kanarraville, the epicenter of it. I am going out tomorrow with my 14 lens on my camera, and try out the settings I googled up, and make a box to shade me somewhat from the sun, even though I won't be looking at it, I'll be facing it full on for a good bit. Gonna have a tripod setup. Gonna be interesting, both the actual event, and the photography. In Kanarraville, population 456, they estimate 40,000 people will come in for this event. There is a lot of farm land around there, so guess there will be room for all. Some of the farmers will probably clean up on renting RV spots and such. There's a public baseball park, but it won't hold all the vehicles, rvs, news satellite trucks, etc. They have 50 portapotties. It's going to be a zoo, and I'm not going near it. I'll watch it from my back yard. Steve, xxtreme SW Utah. |
#17
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-19, Edward A. Falk wrote:
On related note, I've discovered that my auto-darkening welding helmet is not triggered by direct sunlight. How can that be? They are designed for that, it is a feature, not a bug. The idea is to NOT be triggered by sunlight, but to be triggered by welding arcs. This is done for weldors who have to work outside. Just get a old non-electronic helmet to look at the sun. i |
#18
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How do welding shade numbers add up? Eclipse viewing.
"Ignoramus28088" wrote in message ... On 2012-05-19, Edward A. Falk wrote: On related note, I've discovered that my auto-darkening welding helmet is not triggered by direct sunlight. How can that be? They are designed for that, it is a feature, not a bug. The idea is to NOT be triggered by sunlight, but to be triggered by welding arcs. This is done for weldors who have to work outside. Just get a old non-electronic helmet to look at the sun. i The sensor appears to have a high pass filter so the sun and AC-powered lights don't trigger it. My Jackson EQ darkens in sunlight if I wave my hand across it, a quick test to tell if it's turned on. jsw |
#19
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How do welding shade numbers add up? Eclipse viewing.
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#20
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How do welding shade numbers add up? Eclipse viewing.
On 5/17/2012 10:53 AM, mike wrote:
I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Turns out that the weather didn't cooperate. I found the whole thing very boring. Never found any images online that showed anything more than a smooth crescent. I was expecting some corona or something interesting. |
#21
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How do welding shade numbers add up? Eclipse viewing.
I shot the eclipse with my Sony A700, and a Perkin-Elmer 800mm
catadiptric lens. Only thing I had that would cover that were my gold coated full face lenses. I did some test shots in my driveway mid-day to try and get a handle on shutter speeds and such (since the lens is a fixed f/11), and noticed that after only a few minutes of experimenting trying to get an idea where I needed to be for the actual event, my right eye was starting to get that scratchy eyeball feeling most welders have experienced. I ended up shooting through a #13, ISO 160, at 1/4000 sec. Here's 6 of the best: http://www.flickr.com/photos/10986502@N08/sets/72157629865291990/ Obviously late WRT to the eclipse, but for someone wanting to view or photograph the Venus transit, this might give a clue what you're going to need to dim the sun enough to see Venus against a full sun. I don't think a welding lens is going to cut it for the Venus transit. Search ebay for 'solar filter', there's special films available pretty cheaply that blocks 99.9999% of visible light. BTW, a neat tool for photographers, is The Photographer's Ephemeris, a freebie that integrates with Google Earth data. You can specify a date and pick a location, it'll show where the sun and moon will rise and set. You can also use it to determine of there's anything in your line of sight that will interfere with the shot you wish to compose. (well, big things like hills...) I used it to make sure I picked a location where I could get a clear shot at the eclipse. Wouldn't have been able to shoot it from my driveway due to trees. Jon |
#22
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How do welding shade numbers add up? Eclipse viewing.
On Wed, 23 May 2012 11:08:02 -0800
Jon Anderson wrote: snip I ended up shooting through a #13, ISO 160, at 1/4000 sec. Here's 6 of the best: http://www.flickr.com/photos/10986502@N08/sets/72157629865291990/ Nice shots. I used to fool with stuff like this back when I had some ambition. Film, 35mm stuff that is. I have a couple mediocre digital cameras but nothing that can use my old 35mm lenses, nor have much control of the cameras mechanics. Obviously late WRT to the eclipse, but for someone wanting to view or photograph the Venus transit, this might give a clue what you're going to need to dim the sun enough to see Venus against a full sun. I don't think a welding lens is going to cut it for the Venus transit. Search ebay for 'solar filter', there's special films available pretty cheaply that blocks 99.9999% of visible light. If I really wanted to see this I would get a filter that goes over the far end of my old Mead 90mm Maksutov-Cassegrain telescope. Like these: http://www.telescope.com/catalog/sea...d=sun+filte r When I was a kid I had an old Tasco refractor telescope (Dad bought it used for me, a big surprise) that happened to have a Sun filter that screwed on to the eye pieces. It wasn't much, but if you kept the magnification within reason and used the Sun filter, you could actually see sunspots pretty good. I even got to watch a partial eclipse with it -- Leon Fisk Grand Rapids MI/Zone 5b Remove no.spam for email |
#23
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How do welding shade numbers add up? Eclipse viewing.
"Jon Anderson" wrote in message ... I shot the eclipse with my Sony A700, and a Perkin-Elmer 800mm catadiptric lens. Only thing I had that would cover that were my gold coated full face lenses. I did some test shots in my driveway mid-day to try and get a handle on shutter speeds and such (since the lens is a fixed f/11), and noticed that after only a few minutes of experimenting trying to get an idea where I needed to be for the actual event, my right eye was starting to get that scratchy eyeball feeling most welders have experienced. I ended up shooting through a #13, ISO 160, at 1/4000 sec. Here's 6 of the best: http://www.flickr.com/photos/10986502@N08/sets/72157629865291990/ Obviously late WRT to the eclipse, but for someone wanting to view or photograph the Venus transit, this might give a clue what you're going to need to dim the sun enough to see Venus against a full sun. I don't think a welding lens is going to cut it for the Venus transit. Search ebay for 'solar filter', there's special films available pretty cheaply that blocks 99.9999% of visible light. BTW, a neat tool for photographers, is The Photographer's Ephemeris, a freebie that integrates with Google Earth data. You can specify a date and pick a location, it'll show where the sun and moon will rise and set. You can also use it to determine of there's anything in your line of sight that will interfere with the shot you wish to compose. (well, big things like hills...) I used it to make sure I picked a location where I could get a clear shot at the eclipse. Wouldn't have been able to shoot it from my driveway due to trees. Jon I think you have definitely shown your welding filter is not flat enough for full aperture photographic or telescopic use. This site sells a variety of filter types including just the aluminized mylar and black plastic sheets. http://thousandoaksoptical.com/solar.html |
#24
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-23, Jon Anderson wrote:
I shot the eclipse with my Sony A700, and a Perkin-Elmer 800mm catadiptric lens. Only thing I had that would cover that were my gold coated full face lenses. I did some test shots in my driveway mid-day to try and get a handle on shutter speeds and such (since the lens is a fixed f/11), and noticed that after only a few minutes of experimenting trying to get an idea where I needed to be for the actual event, my right eye was starting to get that scratchy eyeball feeling most welders have experienced. Did you do what is recommended for mirror lenses -- make a cover for the front, with a small (say 1" diameter) hole off center so your actual aperture is significantly smaller that f/11. That might have gotten you down to f/32 or so. One reason for this is to minimize the heating of the central mirror which can otherwise be damaged by the heat from all that sunlight. (And it also lets you use a less dense filter -- you might have been able to get away with a #10 or so. I ended up shooting through a #13, ISO 160, at 1/4000 sec. Here's 6 of the best: http://www.flickr.com/photos/10986502@N08/sets/72157629865291990/ BTW -- any idea where the multiple rings on the thin side of the image came from? Obviously late WRT to the eclipse, but for someone wanting to view or photograph the Venus transit, this might give a clue what you're going to need to dim the sun enough to see Venus against a full sun. I don't think a welding lens is going to cut it for the Venus transit. Search ebay for 'solar filter', there's special films available pretty cheaply that blocks 99.9999% of visible light. And -- use that off center aperture to cut it down even more and protect the internal parts of the cat lens. Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#25
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How do welding shade numbers add up? Eclipse viewing.
On 5/23/2012 12:47 PM, anorton wrote:
I think you have definitely shown your welding filter is not flat enough for full aperture photographic or telescopic use. Me and a few others on the Sony/Minolta forum I frequent. Welding filters are nowhere near optically clear enough for fine photography! But it was really a last minute decision I made to just go see what I could do with this lens. I bought it at a yard sale last year and it's just sat. Got some real magnification, and in one or two, one can barely resolve mountains on the left side of the moon. I tried a shot at home the next day, same exact setup sans the filter. I'm shooting on a high end Berlebach tripod, hanging a big weight off the column, mirror lockup, remote trigger. Shot the top of a pine tree that on Google Earth, looks to be about 1/4 mine away. I can count the individual pine needles, but even with Photoshop sharpening, it's a bit fuzzy. Since buying that 800mm, I've found I really like macro and wide angle stuff, so decided last night to see if I can't trade/sell it and get an 8-10mm ultra wide angle. I did just order today some Baader solar film to make a proper filter, going to try to shoot the Venus transit with my best 200mm. Jon |
#26
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How do welding shade numbers add up? Eclipse viewing.
On 5/23/2012 1:56 PM, DoN. Nichols wrote:
Did you do what is recommended for mirror lenses -- make a cover for the front, with a small (say 1" diameter) hole off center so your actual aperture is significantly smaller that f/11. That might have gotten you down to f/32 or so. One reason for this is to minimize the heating of the central mirror which can otherwise be damaged by the heat from all that sunlight. (And it also lets you use a less dense filter -- you might have been able to get away with a #10 or so. I did zero research on the specifics of using this type of lens for solar photography, only looked into filters and saw some folks were using #13-#14 welding filters. BTW -- any idea where the multiple rings on the thin side of the image came from? I am not sure, might be an artifact of the design, or perhaps light reflecting off the back of the welding lens? I know this type of lens does strange things with out of focus highlights, one gets little rings of light instead of smooth bokeh. I bought the lens because the price was certainly right. I saw a couple listed on ebay shortly after I got it, for over a grand, though in the month I watched them, they didn't sell. It's a great lens in the right application, but I'm going to sell/swap it and for an ultra wide angle. And -- use that off center aperture to cut it down even more and protect the internal parts of the cat lens. My main concern and focus on research, was possibly damaging the sensor, and that sure is an issue w/digital. (hmm, wonder how the folks I saw driving by one park, fared with their little pocket digital cameras...) The lens came through it just fine. I've decided if/when I really want to do astro photography, I'll pick my brother's brain and scope out his rig. One thing about the Perkin-Elmer lens, is the optics consist of one solid piece of glass, hence it's name, the Solid Cat. Not sure what might damage it, unless excess heat on the secondary mirror could damage the coating. But it survived! Jon |
#27
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How do welding shade numbers add up? Eclipse viewing.
That's what I've heard - #14 filter. Welding shop volunteered the
story - they sell out whenever there's an eclipse or something like that. Lots of non-welding types come by the welding supplies shop. That was near Cambridge, UK. What with the University, there's a lot of scientific types around. RS |
#28
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How do welding shade numbers add up? Eclipse viewing.
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#29
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-24, Jon Anderson wrote:
On 5/23/2012 1:56 PM, DoN. Nichols wrote: Did you do what is recommended for mirror lenses -- make a cover for the front, with a small (say 1" diameter) hole off center so your actual aperture is significantly smaller that f/11. That might have [ ... ] BTW -- any idea where the multiple rings on the thin side of the image came from? I am not sure, might be an artifact of the design, or perhaps light reflecting off the back of the welding lens? I know this type of lens does strange things with out of focus highlights, one gets little rings of light instead of smooth bokeh. Right -- donut bokeh because of the missing part from the center. I bought the lens because the price was certainly right. I saw a couple listed on ebay shortly after I got it, for over a grand, though in the month I watched them, they didn't sell. It's a great lens in the right application, but I'm going to sell/swap it and for an ultra wide angle. Hmm ... it might be multiple reflections from the front surface of the lens and the rear surface of the filter. Or -- if the filter is multiple layers, and they were not parallel you would get multiple reflections from that. [ ... ] One thing about the Perkin-Elmer lens, is the optics consist of one solid piece of glass, hence it's name, the Solid Cat. Not sure what might damage it, unless excess heat on the secondary mirror could damage the coating. But it survived! I think that it would be that the heat would soften the typical adhesives used to attach the center secondary mirror to the back of the lens. In your case, it appears to have been vacuum evaporated onto the back, so there is no problem. BTW You are thinking of parting with the lens you said? What lens mount? And what are you asking for it? Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#30
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-24, Edward A. Falk wrote:
In article , Leon Fisk wrote: Just something to try... What if you point it at the Sun and then use something like a sparker (torch lighter, Bic lighter) to trigger it to go dark. Will it stay dark then, maybe? Actually, simply waving my hand in front the the sensor was enough to get it to trigger, but as soon as you stop waving, it goes transparent again. Tried to think of some flickering light source I could use that I would trust my vision to, and decided it wasn't a good idea. Stick a small electric motor and a propeller on the front of the hood so the propeller interrupts the light to the sensor. Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#31
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How do welding shade numbers add up? Eclipse viewing.
On 2012-05-26, Jon Anderson wrote:
On 5/25/2012 2:07 PM, DoN. Nichols wrote: Hmm ... it might be multiple reflections from the front surface [ ... ] Used good old duct tape to hold the welding filter to the lens. In retrospect, I noticed it had shifted a bit as my set progressed, and wasn't tight against the hood at the end. That could well account for the multiple reflections. As to selling, I'll PM that discussion. O.K. Beware that my address is "spam-proofed", and the directions on how to fix it are in my .sig below -- which *may* be hidden by some setting in your newsreader client. Also -- any e-mails with large attachments (like photos) just plain won't make it to me. Filtering done on e-mail size to keep viruses out of a couple of small mailing lists which I host. Nothing here yet, so I figured that you should be warned of the limitations in effect. Thanks, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#32
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How do welding shade numbers add up? Eclipse viewing.
On 5/25/2012 2:07 PM, DoN. Nichols wrote:
Hmm ... it might be multiple reflections from the front surface of the lens and the rear surface of the filter. Or -- if the filter is multiple layers, and they were not parallel you would get multiple reflections from that. Used good old duct tape to hold the welding filter to the lens. In retrospect, I noticed it had shifted a bit as my set progressed, and wasn't tight against the hood at the end. That could well account for the multiple reflections. As to selling, I'll PM that discussion. Got my Baader solar filter film today, going to machine up a proper adapter that will thread into my 200mm, insuring it's parallel. Jon |
#33
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How do welding shade numbers add up? Eclipse viewing.
"Jon Anderson" wrote in message news On 5/25/2012 2:07 PM, DoN. Nichols wrote: Hmm ... it might be multiple reflections from the front surface of the lens and the rear surface of the filter. Or -- if the filter is multiple layers, and they were not parallel you would get multiple reflections from that. Used good old duct tape to hold the welding filter to the lens. In retrospect, I noticed it had shifted a bit as my set progressed, and wasn't tight against the hood at the end. That could well account for the multiple reflections. As to selling, I'll PM that discussion. Got my Baader solar filter film today, going to machine up a proper adapter that will thread into my 200mm, insuring it's parallel. Jon I do not think the apparent multiple images are reflections. I think it is just due to the waviness of the filter across the aperture. Each image is formed by a different area of the filter that has a slightly different wedge angle. The film works because even though it is wavy, the front and back surfaces remain very parallel and do not deviate the light. |
#34
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How do welding shade numbers add up? Eclipse viewing.
On 5/26/2012 1:26 PM, anorton wrote:
I do not think the apparent multiple images are reflections. I think it is just due to the waviness of the filter across the aperture. Each image is formed by a different area of the filter that has a slightly different wedge angle. The film works because even though it is wavy, the front and back surfaces remain very parallel and do not deviate the light. What I hadn't noticed, being behind the camera, was that things got warm enough for the little bits of duct tape to start slipping. By the end of my shoot, the welding lens was a couple degrees out, far exceeding any possible waviness in the filter itself. In any case, a proper machined holder for the Baader filter is still a nice thing to have and beats the rolled and glued paper tube the instructions show... Jon |
#35
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How do welding shade numbers add up? Eclipse viewing.
"Jon Anderson" wrote in message ... On 5/26/2012 1:26 PM, anorton wrote: I do not think the apparent multiple images are reflections. I think it is just due to the waviness of the filter across the aperture. Each image is formed by a different area of the filter that has a slightly different wedge angle. The film works because even though it is wavy, the front and back surfaces remain very parallel and do not deviate the light. What I hadn't noticed, being behind the camera, was that things got warm enough for the little bits of duct tape to start slipping. By the end of my shoot, the welding lens was a couple degrees out, far exceeding any possible waviness in the filter itself. In any case, a proper machined holder for the Baader filter is still a nice thing to have and beats the rolled and glued paper tube the instructions show... Jon But if you you have a flat, parallel piece of glass at an angle in front of your lens it will not cause any aberration at all for reasonably distant objects. Even the very dim, double reflection off the inside of the back surface and then inside of the front surface will overlap perfectly with the original image for distant objects. |
#36
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How do welding shade numbers add up? Eclipse viewing.
On 5/26/2012 7:38 PM, anorton wrote:
But if you you have a flat, parallel piece of glass at an angle in front of your lens it will not cause any aberration at all for reasonably distant objects. Even the very dim, double reflection off the inside of the back surface and then inside of the front surface will overlap perfectly with the original image for distant objects. Ah, ok. Well, the new filter will use in part, a 55mm filter ring to thread into the the end of the lens. It's the proper filter, it can be easily stored, and I don't have to worry about it accidentally falling off while taking pictures, which the taped filter wanted to do. That's the main reason for machining a proper setup (as well as keeping a touch of metalwork in the topic G). I liked the images I got enough to invest a bit more time to do it properly in the future. Jon |
#37
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How do welding shade numbers add up? Eclipse viewing.
On Thursday, May 17, 2012 at 11:53:14 AM UTC-6, mike wrote:
I want to look at the eclipse this weekend. Everybody says a #14 welding shade is good. I don't have one. So, how do the numbers stack up when you use 2? I'm guessing it's not linear, so 7+7 doesn't = 14??? What's the math for stacking welding shades? Thanks, mike Relevant all over again for August 21, 2017. So based on A Norton's formula: 4 5 6 7 8 9 10 11 4 7 8 9 10 11 12 13 14 5 8 9 10 11 12 13 14 15 6 9 10 11 12 13 14 15 16 7 10 11 12 13 14 15 16 17 8 11 12 13 14 15 16 17 18 9 12 13 14 15 16 17 18 19 10 13 14 15 16 17 18 19 20 11 14 15 16 17 18 19 20 21 So the first column and row are the shades you are adding. Follow 14 on the diagonal to combine your shades. So a #10 + a #5 is #14. If you want to check the formula the spread sheet link is: https://docs.google.com/spreadsheets...it?usp=sharing |
#38
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How do welding shade numbers add up? Eclipse viewing.
This old thread but applies now with 2017 eclipse...
Someone says the numbers DO add up so I figure using two number 10s from cheap Harbor Freight welding goggles will be okay. I wouldn't plan on staring at it for extended periods in any case. Would be cool to put it on front end of telescope and view, but that's pushing it. Long ago I used 6 polarized filters (crossing two at 90 degrees, then three sets at 120 degrees) which made it almost black (easy to see sun) but don't know if it blocks UV and IR. I was stupid (younger..) and used it to look at the sun through a telescope... didn't take long and image got blurry (I don't remember seeing the sun) so looked at filter and it was MELTING... dumb bass... remember burning leaves with sun using mag glass and a telescope is much more powerful... glad I didn't burn my eyeballs (am 60 now so damage from 40 years ago would be apparent). |
#40
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How do welding shade numbers add up? Eclipse viewing.
On 2017-08-03, wrote:
This old thread but applies now with 2017 eclipse... Someone says the numbers DO add up so I figure using two number 10s from cheap Harbor Freight welding goggles will be okay. I wouldn't plan on staring at it for extended periods in any case. Would be cool to put it on front end of telescope and view, but that's pushing it. With a telescope, the way to go is (assuming that it is on a tripod) is to mount a white piece of cardboard (or white paper supported by cardboard) at a proper distance behind the eyepiece, and adjust the focus so it projects a sharp image onto the cardboard. The more distant, the larger the image if the focus range is enough. If the telescope is smaller than the cardboard, put another piece of cardboard around the back end of the telescope eyepiece, to make sure that the target cardboard is in the shadow. If you have a fairly large diameter, mirror lens telescope (much shorter than the glass refractor only 'scopes for a given power), you can use a smaller filter mounted off center in some opaque cardboard, and mount it off center, so it covers the area between the center mirror mount and the outer rim of the front lens. This reduces the amount of energy coming through the 'scope, so the filter can be weaker and smaller than needed for the full aperture of the 'scope. Long ago I used 6 polarized filters (crossing two at 90 degrees, then three sets at 120 degrees) which made it almost black (easy to see sun) but don't know if it blocks UV and IR. I was stupid (younger..) and used it to look at the sun through a telescope... didn't take long and image got blurry (I don't remember seeing the sun) so looked at filter and it was MELTING... *Always* put the filter at the input end of the telescope. dumb bass... remember burning leaves with sun using mag glass and a telescope is much more powerful... glad I didn't burn my eyeballs (am 60 now so damage from 40 years ago would be apparent). Yes. Good Luck, DoN. -- Remove oil spill source from e-mail Email: | (KV4PH) Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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