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08-09-2011, 05:09 AM - 2 Likes   #1
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Colour rendering in lenses and binoculars - good recent Lenstip article

FYI.

Just came across a recent article on Lenstip.com that attempts to explain some of the issues around colour rendering in lenses and binoculars. They mention Pentax several times - eg as the pioneer of lens multicoating and even have a light transmission chart for the DA40 as an illustration of the good work modern multilayer coatings can do.

Colour rendering in binoculars and lenses - Colours and transmission - Lenstip.com

An interesting read.

08-09-2011, 05:28 AM   #2
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Nice read, thanks.
08-09-2011, 05:36 AM   #3
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Here an interesting comments on third party lens producers in that text
QuoteQuote:
Such lenses as the Sigma 50 mm f/1.4 EX DG HSM or the Sigma 85 mm f/1.4 EX DG HSM, launched not so long ago, turn out to be optically better than their equivalents produced by Canon, Nikon, Pentax, or even Zeiss.Also the opinions, repeated from time to time on different sites, that brand name instruments render colours perfectly whereas such lenses as Sigmas, Tamrons and Tokinas give you a distinctly yellowish image, you can treat as an urban legend. A proof? Here you go.
The graph below shows the transmission curves of two 24-70 mm f/2.8 lenses produced by Nikon and Sigma. In this pair the Sigma is the more complex one so its task was more difficult. Despite that fact it lets pass through more light for most of the visible spectrum. Both lenses don’t render colours in a perfect way because both curves are slightly slanted, with the highest transmission level in the red part and the lowest in the purple and blue part of the spectrum. However, the slant in both cases is very similar so if the Sigma gives a yellowish hue so does the reputable Nikkor, which is not only less optically complex but also more expensive.
08-09-2011, 05:48 AM   #4
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Speaking as an almost PhD (nearly completed) in optics, and working as a senior optical designer, I can confirm that this very well written article is quite helpful and accurate. Nice find! Every time I though "this should be explained more completely" they did just that.

Multicoatings are an amazingly complex world, full or art, skill and training (in that order). But what can be done by a competent designer is incredible.

08-09-2011, 06:01 AM   #5
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QuoteOriginally posted by bdery Quote
Speaking as an almost PhD (nearly completed) in optics, and working as a senior optical designer, I can confirm that this very well written article is quite helpful and accurate. Nice find! Every time I though "this should be explained more completely" they did just that.

Multicoatings are an amazingly complex world, full or art, skill and training (in that order). But what can be done by a competent designer is incredible.
Looking at the transmission curves it strikes me that white balance correction will usually do a good job in repairing lens' color transmission variation - is that true in practice do you think?

This implies that the color cast inherent in older lenses is not important if one uses white balance correction.

Dave
08-09-2011, 07:58 AM   #6
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QuoteOriginally posted by bobmaxja Quote
Here an interesting comments on third party lens producers in that text
Yes, they also have some good things to say about Samyang lenses, in that article and in their review section too, confirming that the price of a lens is not always related to it's optical quality.
08-09-2011, 08:15 AM   #7
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QuoteOriginally posted by newarts Quote
Looking at the transmission curves it strikes me that white balance correction will usually do a good job in repairing lens' color transmission variation - is that true in practice do you think?

This implies that the color cast inherent in older lenses is not important if one uses white balance correction.
Yes and no. You could simplify by saying that WB has an effect similar to glass in that it affects the spectral distribution of light. But in fact, WB works as if you had a perfect lens, transmitting uniformly. It shifts the colour temperature, trying to offset any cast created by the light source AND the glass. So in that it's different, the glass will not be affected by the light source.
08-09-2011, 08:38 AM   #8
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QuoteOriginally posted by bdery Quote
Yes and no. You could simplify by saying that WB has an effect similar to glass in that it affects the spectral distribution of light. But in fact, WB works as if you had a perfect lens, transmitting uniformly. It shifts the colour temperature, trying to offset any cast created by the light source AND the glass. So in that it's different, the glass will not be affected by the light source.
Thanks,

I was thinking that manual white balance amplifies R, G, & B channels independently such that white is white - it is different from color temperature adjustment. I'll check that out.

If this is the case then any lens' transmission characteristics might be pretty well compensated by using manual white balance.

If manual wb does not adjust R, G, & B independently (and that might depend on mfg), it wouldn't be hard to do in PP.

Dave

PS Do you have any idea where I might find some numerical color rendering data for particular lenses to use for modelling purposes?

08-09-2011, 08:44 AM   #9
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QuoteOriginally posted by newarts Quote
Thanks,

I was thinking that manual white balance amplifies R, G, & B channels independently such that white is white - it is different from color temperature adjustment. I'll check that out.

If this is the case then any lens' transmission characteristics might be pretty well compensated by using manual white balance.

If manual wb does not adjust R, G, & B independently (and that might depend on mfg), it wouldn't be hard to do in PP.

Dave

PS Do you have any idea where I might find some numerical color rendering data for particular lenses to use for modelling purposes?
actually it makes me think you could easily add color cast correction into adobe lens profiles, and make profiles for your legacy lenses.

If you batch update the exif to show your lenses you used, this would be a snap.

In looking at the article, one thought I had was to take my kodak grey card out on a bright sunny day at noon, and shoot the card with all of my lenses.

If it were done in a short enough time span, you could then consider the daylight as a constant color source, and a color histogram could be used to compare the lenses.
08-09-2011, 09:00 AM   #10
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QuoteOriginally posted by Lowell Goudge Quote
actually it makes me think you could easily add color cast correction into adobe lens profiles, and make profiles for your legacy lenses.....
Good thought! I can't see any reason why it wouldn't work as you described.
08-09-2011, 09:03 AM   #11
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QuoteOriginally posted by Lowell Goudge Quote
actually it makes me think you could easily add color cast correction into adobe lens profiles, and make profiles for your legacy lenses.

If you batch update the exif to show your lenses you used, this would be a snap.

In looking at the article, one thought I had was to take my kodak grey card out on a bright sunny day at noon, and shoot the card with all of my lenses.

If it were done in a short enough time span, you could then consider the daylight as a constant color source, and a color histogram could be used to compare the lenses.
I think shooting indoor under a constant light source (eg. incandescent or halogen) would be better, no?
08-09-2011, 09:41 AM   #12
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QuoteOriginally posted by newarts Quote
Looking at the transmission curves it strikes me that white balance correction will usually do a good job in repairing lens' color transmission variation - is that true in practice do you think?
Speaking merely from experience, I would say no, not if the color rendition of the lens favors some colors at the expense of others. When you correct the white balance for one color, it can have an averse affect on other colors.

Using AWB with old lenses sometimes leads to curious results. AWB with the Pentax K 28/3.5 tends to over-compensate with magenta tint, leading to rich, purplish blues. Of course, these can be corrected in post, where one can achieve distinctive and stunning, if not always fully accurate, results. Another two lenses that affect AWB in non-intuitive ways are the M 50/1.7 and, to a lesser extent, the K 35/3.5. In my experience, both of these lenses cause the AWB to over-compensate with a cooler temperature, giving a slighty cold, bluish cast to the image.
08-09-2011, 10:52 AM   #13
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QuoteOriginally posted by Doanh Quote
I think shooting indoor under a constant light source (eg. incandescent or halogen) would be better, no?
Define constant?

flourescent lights have the color change at 60Hs, in fact, I took a shot once to show the color change along the length of the tube

Incandescent lights have the color temperature change with voltage, so unless they are fed from stabalized CD they are out.

sunlight, taken on a clear day, is somewhat constant for the time it would take, AND, even if you only do 4-5 lenses in a day, if you use 1 lens as a calibration standard, you can still map any daily variations, back to one standard.

Just my thoughts any ways.

In fact, you could probably use a common lens as a standard, across multiple users who all have that lens, let's imagine it is something like a K50F1.4 for example, there are a ton of users out there with that lens.
08-09-2011, 12:34 PM   #14
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QuoteOriginally posted by rawr Quote
they also have some good things to say about Samyang lenses
I thought the Samyag sucked based on those graphs. sure it has a great peak value, but the curve is far from being flat, so colours will be uneven.

QuoteOriginally posted by newarts Quote
I was thinking that manual white balance amplifies R, G, & B channels independently such that white is white - it is different from color temperature adjustment. I'll check that out.
I believe with Pentax you can play with the colour space on 2 axes, which would do something akin to what you propose. But my comments refered to the various auto WB modes. I confess with my K20D Auto WB is so good I almost never play with it.

QuoteOriginally posted by newarts Quote
Do you have any idea where I might find some numerical color rendering data for particular lenses to use for modelling purposes?
Sorry, no idea
08-09-2011, 12:36 PM   #15
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QuoteOriginally posted by northcoastgreg Quote
Speaking merely from experience, I would say no, not if the color rendition of the lens favors some colors at the expense of others. When you correct the white balance for one color, it can have an averse affect on other colors..
If manual white balance adjusts the R, G, and B channels independently it ought to do a good job I think... not perfect of course and it can never correct certain light sources adequately but it ought to do real well on old yellowish cast lenses; ie on coloration which is smooth like due to single or no coatings rather than color casts with sharp peaks like mercury vapor lamps etc.
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