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03-16-2009, 07:15 AM   #16
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QuoteOriginally posted by estudleon Quote
I think that the filter (UV, SKYLIGHT, POL., etc) can .... NEVER can improve the resolution....
I understand what you are trying to say & it is true at a single wavelength, but not true where the short wavelength components of an image are shifted in location with respect to the longer components; in this case there must be ambiguity about the "true" location of the image, hence visual resolution must decrease.

Dave

Perhaps it would be wise for manufacturers to reformulate "hot mirrors" to block long UV as well as IR?

03-16-2009, 08:14 AM   #17
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QuoteOriginally posted by Ben_Edict Quote
The UV filter in my example (Tamron 60B) does NOT improve colour transmission. It reduces the amount of far Blue and near UV light. The improvement in resolution is a natural and quite logical result of using the filter as you remove "colours" from the image, which cannot be brought to the same focal plane, as the image forming visible part of the spectrum. Just simply physics and no guesswork needed. Ben
Hi, Ben_Edict

Yes, I agree when you limited the question to the beneficts in the blue and UV light case.



But this is only argument to the UV filter, and in this way, my guesswork about the rest of the filters is true.

But the quid that you refer, not the only to have in consideration

In the case of the UV filter, don't forget that you are adding two air-glass surfaces to the existents in the lens, and then the internal reflections and the
ghost images increase.

And with the filter in the front, the optical formula of the lens alters when modifying itself the diffraction and refraction of the optic system, losing something of his contracts and shaprness.
03-16-2009, 09:48 AM   #18
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QuoteOriginally posted by estudleon Quote
Hi, Ben_Edict

Yes, I agree when you limited the question to the beneficts in the blue and UV light case.

But this is only argument to the UV filter, and in this way, my guesswork about the rest of the filters is true.

But the quid that you refer, not the only to have in consideration

In the case of the UV filter, don't forget that you are adding two air-glass surfaces to the existents in the lens, and then the internal reflections and the
ghost images increase.

And with the filter in the front, the optical formula of the lens alters when modifying itself the diffraction and refraction of the optic system, losing something of his contracts and shaprness.
I fully agree with your reluctancy about the general use of filters, as the two additional surfaces need necessarily degrade the image. In my own experience though, this is not visible (to my eyes), if the best filters are used. But I do make some caveats:
i.e.
- I remove filters when shooting against bright light
- never use filters for nighttime shooting
- remove them in the studio
- never combine filters, thus I remove any UV filter, if I need a polariser
. always use a lens hood and (if necessary) additional shielding, to prevent increased flare caused by the filter

Anyway, as filters should be plano-parallel (high quality filters are that within technical limits), then it does not affect diffraction. So the loss of sharpness and contrast, which is absolutely there, can be so minimal, that it is not visible under standard shooting conditions.

Ben
03-16-2009, 10:06 AM   #19
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QuoteOriginally posted by Ben_Edict Quote
In my own experience though, this is not visible (to my eyes), if the best filters are used. But I do make some caveats:
i.e.
- I remove filters when shooting against bright light
- never use filters for nighttime shooting
- remove them in the studio
- never combine filters, thus I remove any UV filter, if I need a polariser
. always use a lens hood and (if necessary) additional shielding, to prevent increased flare caused by the filter


Ben

This must be written in in all the filter's boxes.

03-16-2009, 12:38 PM   #20
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QuoteOriginally posted by blende8 Quote
You are right.
Lenses are not well corrected at the borders of the visible spectrum, especially the UV end, starting at ca. 410 nm. ....

NB: With the UV filter you can of course only reduce the UV light.
You cannot reduce purple fringing that originates from the addition of visible red+blue light.
It looks to me like the 486 or certainly the 486 plus the 420 will kill at least some of the purple.

Does anyone have these filters to try?

Dave
03-17-2009, 03:37 AM   #21
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At least a portion of PF is credited to the image sensor. When overenergetic UV photons strike the photocells they force some electrons to leak out to neighboring cells causing the effect.
So a UV filter can reduce this phenomenon under harsh daylight or fluoresent lamps (rich in UV)
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