On Mon, 21 Aug 2017 15:23:48 -0700 (PDT), wrote:

On Thursday, May 17, 2012 at 10:53:14 AM UTC-7, 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

I'm reading this and I still don't understand how the Shade numbers were created and calculated. In some posts I see users indicating camera filters such as #13 for used as a neutral density filter to photograph the sun. In this case I can see that a #13 filter is cutting the exposure by 13 stops. Is this, in essence, what the shade filters mean? In other words does a shade 13 filter cut the amount of light passing through from 100% down to .0122% ?
Taking 100% as a starting point and cutting it by 1/2 you obviously get 50%. Given this example when you cut 100% 13 time in a roll you get 0122%
If this is the case then an opacity of 4.00 (as measured on a densitomter) would be enough to block the sun's rays when viewing it.


There are MANY...many standards...all of which have #13 in them.
Bolts, welding, photography, stamp collecting and so forth.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus