I've got a lot of old photographs to digitise. The options are to scan or re-photograph, and a website on the topic suggests that for a lot of photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Thanks

On 05/02/2017 13:09, Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to scan or re-photograph, and a website on the topic suggests that for a lot of photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Thanks


I'd try asking in rec.photo.digital


--
Cheers, Rob

Rob Graham wrote:

I've got a lot of old photographs to digitise. The options are to scan or
re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would
prefer to use LED for coolness and lifespan. What light temperature do I
go for - cool white or daylight?

Thanks



My understanding is that a lot of white LEDs have deficiencies in their
spectrum that make colour rendering inaccurate. So maybe you have to
get special ones made for the purpose. My limited knowledge of colour
temperature suggests that it doesn't matter as long as you tell the
camera or (usually nowadays) the camera works it out.

(Just my comments to clarify the question while waiting for someone who
actually knows to come along.)

--

Roger Hayter

On 05/02/17 13:09, Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to
scan or re-photograph, and a website on the topic suggests that for a
lot of photos, re-photographing is quicker, and requiring less
re-processing.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?


Does the camera have white balance adjustment? If so it doesn't matter
really.

Id probably go for daylight personally, but I'd suck it and see.


Thanks





--
"If you dont read the news paper, you are un-informed. If you read the
news paper, you are mis-informed."

Mark Twain

On Sun, 5 Feb 2017 14:33:37 +0000
The Natural Philosopher wrote:

Does the camera have white balance adjustment? If so it doesn't
matter really.

Id probably go for daylight personally, but I'd suck it and see.

That's exactly what I use. A home-modified bird fatballs box, that holds
the slide and the compact camera, and the slide is lit from behind by
window daylight through a piece of white perspex. My tripod tips
forward so that the perspex is touching the window.
Adjust for white balance occasionally, and it works just great.
The box was free, and I had the perspex in stock. Cost:£0.00.

--
Davey.

On Sun, 5 Feb 2017 05:09:19 -0800 (PST), Rob Graham
wrote:

- I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Colour temperature isn't much of an issue as the camera or post
processing can easily alter that. Colour Rendering Index (CRI) is
much more important and the incandescent bulb wins here. CRI is a
quantitative measure of the ability of a light source to reveal the
colours of various objects faithfully in comparison with an ideal or
natural light source. Light sources with a high CRI are desirable in
colour-critical applications such as photography.
https://en.wikipedia.org/wiki/Color_rendering_index

The sun and an incandescent bulb have a CRI of 100 (the highest
possible value), LED about 80 (for good quality LED's, lower for cheap
Chinese ones). You can buy high (90) CRI LED's but they will be quite
expensive.

Correcting for poor CRI is difficult, far more so than correcting
colour temperature. See
https://www.reddit.com/r/photography...s_illustrated/
for some comments on the subject.

CRI isn't a perfect measure and it is possible to get good results
from low CRI lights but you might have to buy a lot to find ones that
suit your subject. Unfortunately few manufacturers disclose CRI
figures for their LED bulbs.

On 05/02/2017 15:21, Peter Parry wrote:
On Sun, 5 Feb 2017 05:09:19 -0800 (PST), Rob Graham
wrote:

- I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Colour temperature isn't much of an issue as the camera or post
processing can easily alter that. Colour Rendering Index (CRI) is
much more important and the incandescent bulb wins here. CRI is a
quantitative measure of the ability of a light source to reveal the
colours of various objects faithfully in comparison with an ideal or
natural light source. Light sources with a high CRI are desirable in
colour-critical applications such as photography.
https://en.wikipedia.org/wiki/Color_rendering_index

The sun and an incandescent bulb have a CRI of 100 (the highest
possible value), LED about 80 (for good quality LED's, lower for cheap
Chinese ones). You can buy high (90) CRI LED's but they will be quite
expensive.

Correcting for poor CRI is difficult, far more so than correcting
colour temperature. See
https://www.reddit.com/r/photography...s_illustrated/
for some comments on the subject.

CRI isn't a perfect measure and it is possible to get good results
from low CRI lights but you might have to buy a lot to find ones that
suit your subject. Unfortunately few manufacturers disclose CRI
figures for their LED bulbs.

I have had to photograph quite a few documents, mainly so I have a back
up copy.
I have tried white light balance which does give an improvment but best
results came from using daylight near a window.

It has been a friends experience that LEDs do not have a smoothe enough
bandwidth. although normal bulbs are biased red, other types of lamps tend
to not be like that with holes in some places in the spectrum like we used
to get on cfls.

Maybe somebody makes photographic grade ones by now.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Rob Graham" wrote in message
...
I've got a lot of old photographs to digitise. The options are to scan or
re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would
prefer to use LED for coolness and lifespan. What light temperature do I
go for - cool white or daylight?

Thanks

On Sunday, February 5, 2017 at 5:27:43 PM UTC, Brian Gaff wrote:
It has been a friends experience that LEDs do not have a smoothe enough
bandwidth. although normal bulbs are biased red, other types of lamps tend
to not be like that with holes in some places in the spectrum like we used
to get on cfls.

Maybe somebody makes photographic grade ones by now.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Rob Graham" wrote in message
...
I've got a lot of old photographs to digitise. The options are to scan or
re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would
prefer to use LED for coolness and lifespan. What light temperature do I
go for - cool white or daylight?

Thanks



Thanks guys - interesting. And I hadn't realised that LED's didn't match either the sun or incandescents. So incandescents it will be, though I believe I have to get the right ones even there.

For the initial project, LEDs would have done as the pictures are sepia and b & w. A 170 strong collection just found in my parent's house, of 1905 and 1912 family photos in two albums. As many of the photos are very nicely set up by someone in the family who knew how to take pictures, I do suspect that there might well have been albums for the intervening years too, but that would have been a bit too much to sort out!!

In article ,
Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to scan
or re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

It's not so much the colour temperature that matters since that can be
adjusted for. It's more the holes and peaks in the light spectrum of
ordinary white LEDs. Tungsten is generally far more benign in this respect
- or fluorescent tubes designed for the purpose.

But surely the life of the lamp isn't important for this job? It will
hardly be on for long periods?

--
*Don't worry; it only seems kinky the first time.*

Dave Plowman London SW
To e-mail, change noise into sound.

"Rob Graham" wrote in message
...
Thanks guys - interesting. And I hadn't realised that LED's didn't match
either the sun or incandescents. So incandescents it will be, though I
believe I have to get the right ones even there.

For the initial project, LEDs would have done as the pictures are sepia
and b & w. A 170 strong collection just found in my parent's house, of
1905 and 1912 family photos in two albums. As many of the photos are very
nicely set up by someone in the family who knew how to take pictures, I do
suspect that there might well have been albums for the intervening years
too, but that would have been a bit too much to sort out!!

If you were copying *colour* photographs, I would suggest using daylight or
incandescent bulb. Both of these are continuous spectrum so will not have
problem with "gaps" in the spectrum, like CFLs and LEDs have.

You'll need to white-balance your camera for whatever light source you use,
and I'd suggest if possible doing a manual white balance off a sheet of
paper that is illuminated by the light source, rather than choosing a preset
for sunlight, shade or incandescent. If you are using incandescent, ordinary
60 W bulbs will be fine (you don't need photographic bulbs) but remember
that bulbs get very hot!

However...

Since your photos are sepia of black and white, colour rendition is not
important. The discontinuous spectrum of CFLs or LEDs won't matter when
there's only one colour that you are trying to reproduce. I wonder whether
it is better to try to preserve the sepia tone or to convert it black and
white. Difficult decision!

If you opt for converting the sepias to B&W, I suggest using any light
source that is available, and either set the camera to B&W or else convert
the photos to B&W in software such as Photoshop or Paint Shop Pro
afterwards. Conversion to B&W is probably better than keeping the photos as
colour and striving to make the light as neutral as possible (ie not too red
or too blue). May as well map this to neutral grey where R, G and B
components are *defined* to be equal.

Whatever light source you use, try to make sure that you minimise any glare
off the surface of the photo (eg if it has a glossy finish) as this will
lead to localised hot spots or else general sheen that will reduce the
contrast and cause you to lose detail in the shadows. Try to angle the light
at about 45 degrees to the photo on either side by placing the lights some
way to the left and right of the lens, rather than having a light that is
very close to the axis of the lens. This is why on-camera flash would be a
bad idea.


As an aside, if you are ever in a situation where you want to photograph
something reflective and *only* viable light is on-camera flash, photograph
it at an angle so the light of the flash doesn't reflect straight back into
the lens, and then use the "parallelogram distortion correction" feature of
Photoshop or PSP to correct for photographing off-axis. Beware that this
will alter the aspect ratio of the photo a bit (ie circles will become oval)
so take a straight-on photo (including the flash glare!) as well, for
reference, then you can stretch the parallelogram-corrected picture back to
its correct shape.

On Sunday, 5 February 2017 18:16:35 UTC, Rob Graham wrote:
"Rob Graham" wrote in message
...
I've got a lot of old photographs to digitise. The options are to scan or
re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing..

A design is given for a small booth. It uses incandescent bulbs - I would
prefer to use LED for coolness and lifespan. What light temperature do I
go for - cool white or daylight?

Thanks



Thanks guys - interesting. And I hadn't realised that LED's didn't match either the sun or incandescents. So incandescents it will be, though I believe I have to get the right ones even there.

For the initial project, LEDs would have done as the pictures are sepia and b & w. A 170 strong collection just found in my parent's house, of 1905 and 1912 family photos in two albums. As many of the photos are very nicely set up by someone in the family who knew how to take pictures, I do suspect that there might well have been albums for the intervening years too, but that would have been a bit too much to sort out!!

Incandescent is a lousy choice. The low blue output of all incandescents causes noise in the blue channel. You really need a cool light colour or blue will be noisy. Daylight is free & often convenient, and has the added advantage of coming at the subject from a range of angles.

You can correct for tilt and off-axis in post processing, but doing so reduces effective resolution some. So if you can get them right when snapping, do. Only go off-axis when you need to lose reflections.

Cool CFLs are generally quite good. Some linear fluorescent is, some not. LEDs are rather poorer than CFL. If you go with incandescent, use huge power halogen, like 1kW, to get a cleaner blue channel.

None of this is critical, you can use anything anyhow, but the above will give a much better result, and give originals you realistically can make good photos from.


NT

On 05/02/2017 18:44, Dave Plowman (News) wrote:
In article ,
Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to scan
or re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

It's not so much the colour temperature that matters since that can be
adjusted for. It's more the holes and peaks in the light spectrum of
ordinary white LEDs. Tungsten is generally far more benign in this respect
- or fluorescent tubes designed for the purpose.

But surely the life of the lamp isn't important for this job? It will
hardly be on for long periods?


Is there any flicker on LEDs? If it's a fairly short exposure, could
that cause problems?

On 05/02/2017 13:09, Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to scan or re-photograph, and a website on the topic suggests that for a lot of photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Thanks



I always choose a cloudy bright day and do it in the greenhouse. Set the
camera colour balance to daylight and be prepared to tweak the balance
in photoshop. Photograph a pure white card when you do the shoot and use
it as a balance reference.

Direct sunlight is a no-no. Erect a screen to remove it if necessary.

Uneven light across the print is a big problem. Hence the greenhouse (or
conservatory).

Be prepared to use large white pieces of card as reflectors to even up
the lighting.

If you're doing a lot it's worth either bracketing the exposures or at
least checking the exposure on 'difficult' prints.

Find the optimum focal length for minimum pin cushion/barrel distortion
and best resolution, if using a zoom lens. It's likely to be a mid-range
focal length.

Each shot should have a generous border which you remove later in
Photoshop. Reasons: it allows you to rotate the picture so it is truly
upright, and it avoids edge-of-frame lens issues.

Assume that you will spend more time editing in Photoshop and
cataloguing than taking the actual shots. Cataloguing is important.
Memories and people fade away.

Put some thought into the resolution you need. There's no point in
having ten pixels span the lens blur of the original.

Bill

Thanks guys - interesting. And I hadn't realised that LED's didn't match either the sun or incandescents. So in

andescents it will be, though I believe I have to get the right ones
even there.

For the initial project, LEDs would have done as the pictures are sepia and b & w. A 170 st

rong collection just found in my parent's house, of 1905 and 1912 family
photos in two album

s. As many of the photos are very nicely set up by someone in the
family who kne

w how to take pictures, I do suspect that there might well have been albums

for the intervening years too, but that would have been a bit too much
to sort out!!


These will probably be very high resolution, especially if from plates.
You will need to match that resolution.

Bill

Brian Gaff wrote

It has been a friends experience that LEDs do not have a smoothe enough
bandwidth. although normal bulbs are biased red, other types of lamps tend
to not be like that with holes in some places in the spectrum like we used
to get on cfls.

Maybe somebody makes photographic grade ones by now.

Clearly the ones used in smartphones must be.

"Rob Graham" wrote in message
...
I've got a lot of old photographs to digitise. The options are to scan
or re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

Thanks

On 05/02/2017 13:09, Rob Graham wrote:
I've got a lot of old photographs to digitise. The options are to
scan or re-photograph, and a website on the topic suggests that for a
lot of photos, re-photographing is quicker, and requiring less
re-processing.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

Thanks




Use diffused flash.
It will be cool and less prone to shake affecting the pictures.

In article ,
wrote:
Incandescent is a lousy choice. The low blue output of all incandescents
causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

--
*Stable Relationships Are For Horses.

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 5 Feb 2017 19:08:28 -0000, NY wrote:

You'll need to white-balance your camera for whatever light source you
use, and I'd suggest if possible doing a manual white balance off a
sheet of paper that is illuminated by the light source, rather than
choosing a preset for sunlight, shade or incandescent.

I doubt this will all be a single session, using the correct preset
for the light source will produce consitent results. A manual white
balance will vary, perhaps not by much but it will. Essential to use
the same sheet of "white" paper (or WHY) for every white balance. Be
careful of the exposure of the white as well, any overload/over
exposure will confuse the white balance circutry.

--
Cheers
Dave.

On Sun, 5 Feb 2017 05:09:19 -0800 (PST), Rob Graham wrote:

I've got a lot of old photographs to digitise. The options are to scan
or re-photograph, and a website on the topic suggests that for a lot of
photos, re-photographing is quicker, and requiring less re-processing.

For a quick copy of a document yes photographing it is quicker but
for archiving photos you want the best possible results you can get.
So you'll need very even illumination from a good quality light
source and some means of holding things flat that doesn't reflect the
light source(s) into the lens or degrade the resolution. They also
need to be held dead parallel to the cameras sensor in both
dimensions.

A scanner solves all those problems... Also think about the required
camera resolution a good quality print could well have a resolution
approaching 1000 dpi 6 x 4 print, 6000 x 4000 camera = 24 Mega
pixels(ish). It's ages since I looked at scanners but my ancient one
can do 1200 dpi. I should imagine modern ones will manage that and be
quicker. Another plus for a scanner is overall consitency in results.

--
Cheers
Dave.

On Sun, 5 Feb 2017 05:09:19 -0800 (PST), Rob Graham wrote:

I've got a lot of old photographs to digitise. The options are to scan or re-photograph, and a website on the topic suggests that for a lot of photos, re-photographing is quicker, and requiring less re-processing.

A design is given for a small booth. It uses incandescent bulbs - I would prefer to use LED for coolness and lifespan. What light temperature do I go for - cool white or daylight?

Thanks


If the booth were bigger, I have four 'photo' CFLs free to a good home. IIRC
they're 20W spiral cone shape - as they're in the loft and it's literally
freezing up there the details will have to wait!
--
Peter.
The gods will stay away
whilst religions hold sway

On Monday, 6 February 2017 00:14:31 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:
Incandescent is a lousy choice. The low blue output of all incandescents
causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

You can get plenty of blue from incandescents if you're willing to throw much of the red/green area of the spectrum away, as was done in photography.


NT

On Monday, 6 February 2017 01:18:45 UTC, Dave Liquorice wrote:
On Sun, 5 Feb 2017 19:08:28 -0000, NY wrote:

You'll need to white-balance your camera for whatever light source you
use, and I'd suggest if possible doing a manual white balance off a
sheet of paper that is illuminated by the light source, rather than
choosing a preset for sunlight, shade or incandescent.

I doubt this will all be a single session, using the correct preset
for the light source will produce consitent results. A manual white
balance will vary, perhaps not by much but it will. Essential to use
the same sheet of "white" paper (or WHY) for every white balance.

No, use the white in the photo itself, or your white will be hit & miss, albeit a lot better than no white balancing.

Be
careful of the exposure of the white as well, any overload/over
exposure will confuse the white balance circutry.

Set the cam to show any saturated areas on the screen.


NT

On 05/02/2017 13:09, Rob Graham wrote:

I've got a lot of old photographs to digitise. The options are to
scan or re-photograph, and a website on the topic suggests that for a
lot of photos, re-photographing is quicker, and requiring less
re-processing.

I would question the veracity of the website!

I use both methods extensively and photography is a faff and only really
worth doing if the source material is in an album and there is no easy
way to get them onto a flatbed scanner. If I can I always scan original
material 600dpi as many as will fit onto the scanner at once.

The problems for photography of old photographs is that they are seldom
flat and controlling reflections and scattered light is hard.

I prefer the reproducibility of scanning if at all possible. Photography
is possible but you will work hard to get it right.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

Shouldn't make much difference. Neither will be a true match for colour
temperature but if the photographs are monochrome it won't matter and if
they are colour then autowhite balance should take care of it.

But seriously consider scanning them on a flatbed - you will get better
results unless you are extremely good at still life photography.

--
Regards,
Martin Brown

In article ,
wrote:
On Monday, 6 February 2017 00:14:31 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:
Incandescent is a lousy choice. The low blue output of all
incandescents causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

You can get plenty of blue from incandescents if you're willing to throw
much of the red/green area of the spectrum away, as was done in
photography.

Of course. Relatively simple filters. Which are possible with a relatively
smooth continuous spectrum light source. But things like LEDs with huge
spikes and troughs in the response are near impossible to correct.

--
*ONE NICE THING ABOUT EGOTISTS: THEY DON'T TALK ABOUT OTHER PEOPLE.

Dave Plowman London SW
To e-mail, change noise into sound.

On 2/6/2017 10:11 AM, Martin Brown wrote:
On 05/02/2017 13:09, Rob Graham wrote:

I've got a lot of old photographs to digitise. The options are to
scan or re-photograph, and a website on the topic suggests that for a
lot of photos, re-photographing is quicker, and requiring less
re-processing.

I would question the veracity of the website!

I use both methods extensively and photography is a faff and only really
worth doing if the source material is in an album and there is no easy
way to get them onto a flatbed scanner. If I can I always scan original
material 600dpi as many as will fit onto the scanner at once.

The problems for photography of old photographs is that they are seldom
flat and controlling reflections and scattered light is hard.

I prefer the reproducibility of scanning if at all possible. Photography
is possible but you will work hard to get it right.

A design is given for a small booth. It uses incandescent bulbs - I
would prefer to use LED for coolness and lifespan. What light
temperature do I go for - cool white or daylight?

Shouldn't make much difference. Neither will be a true match for colour
temperature but if the photographs are monochrome it won't matter and if
they are colour then autowhite balance should take care of it.

But seriously consider scanning them on a flatbed - you will get better
results unless you are extremely good at still life photography.

+1

On Monday, 6 February 2017 11:11:59 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:
On Monday, 6 February 2017 00:14:31 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:
Incandescent is a lousy choice. The low blue output of all
incandescents causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

You can get plenty of blue from incandescents if you're willing to throw
much of the red/green area of the spectrum away, as was done in
photography.

Of course. Relatively simple filters. Which are possible with a relatively
smooth continuous spectrum light source. But things like LEDs with huge
spikes and troughs in the response are near impossible to correct.

Sure, it's swings & roundabouts. I'd sooner go with imperfect but good cfls than filament. I say that from dealing with the resulting issues in both cases.


NT

In article ,
wrote:
Of course. Relatively simple filters. Which are possible with a
relatively smooth continuous spectrum light source. But things like
LEDs with huge spikes and troughs in the response are near impossible
to correct.

Sure, it's swings & roundabouts. I'd sooner go with imperfect but good
cfls than filament. I say that from dealing with the resulting issues in
both cases.

I'd have thought tubes, rather than CFL, would be a better choice for a
light box? And probably a bigger variety too?

--
*Proofread carefully to see if you any words out or mispeld something *

Dave Plowman London SW
To e-mail, change noise into sound.

On 06/02/2017 00:11, Dave Plowman (News) wrote:
In article ,
wrote:

Incandescent is a lousy choice. The low blue output of all incandescents
causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

Along with a thick colour correction filter pack and you needed to
stabilise the mains if you wanted to get decent reproducible results.

Enlarger lamps like photofloods ran a bit hotter for a shorter life and
have the rating on the side of the base rather than end of the bulb for
obvious reasons. The printing exposure time was long anyway.

Home wet chemistry colour printing was quite hit and miss.

--
Regards,
Martin Brown

In article ,
Martin Brown wrote:
On 06/02/2017 00:11, Dave Plowman (News) wrote:
In article ,
wrote:

Incandescent is a lousy choice. The low blue output of all
incandescents causes noise in the blue channel.

Odd. That's exactly what was used in colour enlargers.

Along with a thick colour correction filter pack and you needed to
stabilise the mains if you wanted to get decent reproducible results.

Better enlargers used low voltage lamps. And you would likely be
correcting the colour balance anyway when printing.

Enlarger lamps like photofloods ran a bit hotter for a shorter life and
have the rating on the side of the base rather than end of the bulb for
obvious reasons. The printing exposure time was long anyway.

Home wet chemistry colour printing was quite hit and miss.

But very good fun.

--
*You're just jealous because the voices only talk to me *

Dave Plowman London SW
To e-mail, change noise into sound.

On Tuesday, 7 February 2017 00:49:02 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

Of course. Relatively simple filters. Which are possible with a
relatively smooth continuous spectrum light source. But things like
LEDs with huge spikes and troughs in the response are near impossible
to correct.

Sure, it's swings & roundabouts. I'd sooner go with imperfect but good
cfls than filament. I say that from dealing with the resulting issues in
both cases.

I'd have thought tubes, rather than CFL, would be a better choice for a
light box? And probably a bigger variety too?

I wasn't aware the OP was building a light box. If so, tubes are more diffuse, but the wider range makes more potential to get it wrong. You can always use a monitor as a light box . Just add a sheet of diffuser to lose the pixels. Monitors are lit by either CCFL or LED.

Really though the imperfect CRI is a bit of a red herring in this case. If you're photographing objects then yes, it counts. But when you're rephotograping photos you're at best just recording the 3 colour channels in the original print, making CRI not a significant issue, as long as you've got plenty of all 3 colours to avoid noise. So what matters is to get a cool enough light source, ie preferably not filament.


NT