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11-16-2012, 12:27 PM   #1
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Naive question of the day: Any benefit to adding a modern filter to an old lens

I know there are debates for and against using filters on a lens, and I'm not advocating sticking a $50 filter on a lens you bought for $4 from a bargain bin, so putting those issues aside, would their be any optical benefit to sticking a modern filter on an older lens that might have no coatings or only a single coating. Could you reduce purple fringing, for example? I don't think you'd bother trying this on a common focal length lens, but if you stumbled onto a cheap telephoto prime, or maybe an old Helios that made your photos all dreamy and creamy, might there be some benefit? If so, what sort of filter would you need?

11-16-2012, 12:29 PM   #2
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A filter is not going to improve any aberration that already exists in the lens.

A good filter is always better than a poor one, it introduces lesss of its own problems.
11-16-2012, 12:35 PM   #3
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Thanks @tim60. I hadn't bothered to look up the source of PF, which I see is a form of chromatic aberration. That said, a suggested way to alleviate PF is to use a Haze-2A filter, if wikipedia is to be believed.
11-16-2012, 12:37 PM   #4
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Yeah, some say that a UV filter or maybe a haze filter can help with PF. I've never actually seen any evidence of that however. But then, haven't really looked for any...

11-16-2012, 01:00 PM - 2 Likes   #5
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The short answer is no. A filter is an additional element to a lens that the designer did not take into account when designing it. As such, it can only degrade the image. Good filters will minimize this degradation, but no filter will improve a lens.

Some filters, under certain conditions, can improve the image taken by the particular lens (and with any other lens). For example, a polarizer will cut reflections and may improve the contrast and saturation of an image. A neutral density can allow slower shutter speeds for creative effect that otherwise will be impossible. A graduated filter may improve capturing a very bright sky while maintaining a good exposure for the rest of the image.

Any filter will potentially add flare and ghosts to a lens because it introduces another reflective surface that was not originally accounted for. Multi coated ones help here, but in difficult scenes (such as night with street lights or other point sources) filters should be avoided to reduce the risk of ghost images from reflections.
11-16-2012, 01:23 PM   #6
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QuoteOriginally posted by demp10 Quote
The short answer is no. A filter is an additional element to a lens that the designer did not take into account when designing it. As such, it can only degrade the image. Good filters will minimize this degradation, but no filter will improve a lens.

Some filters, under certain conditions, can improve the image taken by the particular lens (and with any other lens). For example, a polarizer will cut reflections and may improve the contrast and saturation of an image. A neutral density can allow slower shutter speeds for creative effect that otherwise will be impossible. A graduated filter may improve capturing a very bright sky while maintaining a good exposure for the rest of the image.

Any filter will potentially add flare and ghosts to a lens because it introduces another reflective surface that was not originally accounted for. Multi coated ones help here, but in difficult scenes (such as night with street lights or other point sources) filters should be avoided to reduce the risk of ghost images from reflections.
Still potentially possible that UV or other could lessen PF even at the cost of overall sharpness or whatever, although with a good filter the concern is about image degradation is overstated -- in general you can't tell the difference between filter and no filter. "Filters always degrade" is another thing that is true in theory but not always in practice. PF is a special case as it is a little understood interaction with digital sensors rather than solely caused by the lens as with other kinds of CA. A filter certainly will not help with other kinds of CA -- spherical aberration, etc.
11-16-2012, 01:44 PM   #7
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QuoteOriginally posted by MSL Quote
That said, a suggested way to alleviate PF is to use a Haze-2A filter, if wikipedia is to be believed.
I'd like to read that article...

As an optical designer, I can tell you that adiding glass to the light path will not improve chromatic aberrations. especially since the principal quality of a UV filter is to have no impact on the image.

Chromatic aberration is caused by flaws in the optical design (inevitable, to some extend) that cause different colours to be focused at different distances from the lens. so if one colour is in focus, another one won't be, and will apear as a blurred line won contrasted borders.
11-16-2012, 01:45 PM   #8
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I had wondered about this but for reasons of flare not fringing. A bit of ghosting I understand, but at least one 'element' would have modern coatings.


Last edited by jimr-pdx; 11-16-2012 at 02:05 PM.
11-16-2012, 02:17 PM   #9
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QuoteOriginally posted by bdery Quote
I'd like to read that article...
Here you go:
Purple fringing - Wikipedia, the free encyclopedia

I believe the idea is that by blocking some of the UV/purplish light from coming in, you can reduce the amount of aberration in that part of the spectrum. I have a basic knowledge of optics, but I'm more chemistry bent than physics.
11-16-2012, 04:02 PM   #10
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PF can be removed quite effectively using tools like Lightroom (the latest 4.x version) without affecting the entire image as a filter will do.
11-16-2012, 04:57 PM   #11
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Can LR remove damage to the front element?
11-16-2012, 05:52 PM   #12
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QuoteOriginally posted by tabl10s Quote
Can LR remove damage to the front element?
No, but insurance can take care of it without affecting image quality
11-16-2012, 08:38 PM   #13
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Put a hood of sufficient length on that lens and get the best of all worlds - reduce image compromising stray light AND protect the lens without reducing IQ!
11-17-2012, 01:50 AM   #14
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My personal take on the question of using filters as protection
is that a good filter (along with a hood) may be the right compromise.

Insurance will not save a rare lens that is hard to replace,
or a lens that you need on an assignment right now.

And a hood alone will not protect from aerosol sprays,
like oil in the exhaust from an old engine,
or brine from a wet road in winter.

Unfortunately, purple fringing does not seem to be fully understood.
To the extent that a portion of it may be caused
by sensor elements reacting to UV light,
then a good UV filter would help reduce it.

PF removal in PP is a PITA.
11-17-2012, 05:51 AM   #15
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QuoteOriginally posted by Docrwm Quote
Put a hood of sufficient length on that lens and get the best of all worlds - reduce image compromising stray light AND protect the lens without reducing IQ!
+1 for the hood. Especially a metal one.
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