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03-02-2010, 04:57 PM   #16
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QuoteOriginally posted by bdery Quote
Well, I'm an optical designer and completing my PhD in optics, so I can help...Physics are cool

Hi bdery,

you are just the guy to answer a question I've been dying to ask: why is it that a very large proportion of camera lenses (both zoom and prime) make such a hash of rendering red blooms (roses, cacti, etc). The net result is a large red blob with very little detail (microcontrast?). These same lenses will render similar blooms of other colours (white, pink, salmon) almost perfectly.

I notice that some makes of lens appear to render red subjects better than other makes. For example, many of the (very) old German made (consumer range) Voiglander and Contaflex lenses do reasonably to very well, whilst many Japanese made lenses are terrible (in this regard).

What gives???

03-02-2010, 05:21 PM   #17
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Bdery,

After you've discussed the variation in refraction between blue and red wavelengths, you can jump into the wave/particle duality of light. I haven't seen a rousing discussion of that since, umm, Einstein mixed up his stove and block of ice!

Silliness aside, thanks for chipping in.
03-02-2010, 06:07 PM   #18
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QuoteOriginally posted by wildman Quote
Why do my conventional camera lens', with the possible exception of m FA35, seem to suffer so much wide open while my scopes do not?
A great deal of this physics is over my head but, if we take as given that a variable aperture lens will have variable resolution, it seems to me that a lens manufacturer has to decide where in the aperture range to locate the maximum resolution and it would seem that, for the most part, f8 is the default. The next question is how far to extend the range on either side of the "sweet spot" and my sense is that, in some cases, the manufacturer will extend the range into very marginal territory on the wide end, figuring that it gives the photographer the option to go that wide despite the cost in resolution.
03-02-2010, 06:43 PM   #19
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I think a scope has to be designed sharp wide open or nobody will buy it, while a camera lens can be designed to be just as sharp wide open but it is very expensive to do so. I really find no reason to stop down my canon 300 f2.8 except if I want more depth of focus or slower shutter speed. It wasn't cheap though.

03-02-2010, 07:04 PM   #20
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QuoteQuote:
you are just the guy to answer a question I've been dying to ask: why is it that a very large proportion of camera lenses (both zoom and prime) make such a hash of rendering red blooms (roses, cacti, etc). The net result is a large red blob with very little detail (microcontrast?). These same lenses will render similar blooms of other colours (white, pink, salmon) almost perfectly.

I notice that some makes of lens appear to render red subjects better than other makes. For example, many of the (very) old German made (consumer range) Voiglander and Contaflex lenses do reasonably to very well, whilst many Japanese made lenses are terrible (in this regard).

What gives???
I'm not sure about that one, actually (though I don't like admitting it :P ) Part of the answer actually comes from the sensor, not the lens, since CCDs and CMOs both have their peak sensitivity around the green colour (like our eyes) and the sensitivity decreases towards the red colour. Part of the answer lies, I'm pretty sure, in the type of filter used in the Bayer matrix of the sensor (I hope you're familiar with that). The red filter might let less "types" of red pass through. Part of the answer lies in the transmission of the glass, which is not uniform for all colours (for instance, car windows do not let UV light pass through, and a green filter will reject blue and red light). As glanglois puts it, there are differences in refraction for different colours, and this will come into play too, though not very much (it will mainly affect chromatic aberrations).

Not much use am I, don't you think? To give you a good, definite answer, I'd have to compare the lens designs and materials of a "good" and "bad" lens (as far as red hues go, that is). Sorry I cannot be more conclusive.

QuoteQuote:
After you've discussed the variation in refraction between blue and red wavelengths, you can jump into the wave/particle duality of light. I haven't seen a rousing discussion of that since, umm, Einstein mixed up his stove and block of ice!
Gotta love that friggin undecided photon... The thing is, if you accept that the photon is both particle AND wave, everything starts to make sense, and we're able to make predictions. So we physicists just roll along with it.

But then, a cow can be quite nicely approximated as a sphere, too
03-02-2010, 11:01 PM   #21
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QuoteOriginally posted by bdery Quote
I'm not sure about that one...Sorry I cannot be more conclusive.
OK, thanks.

(BTW, I should have mentioned that this seems to aply to film as well.)
03-04-2010, 05:30 PM   #22
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Cow or Cat?

QuoteOriginally posted by bdery Quote

Gotta love that friggin undecided photon... The thing is, if you accept that the photon is both particle AND wave, everything starts to make sense, and we're able to make predictions. So we physicists just roll along with it.

But then, a cow can be quite nicely approximated as a sphere, too
Bustopher Jones looks a great deal like that sphere. Except for the spats, or course.

And while we're at it, was Schrödinger considering a cat or a cow? My memory fades with advancing age.

Maybe Mööö sounds like Meow in German.
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