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02-25-2018, 12:41 PM   #1
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645 FA 35mm filter questions

The FA 35mm wide angle lens has an extreme ray angle (with film cameras) of 45 degrees. This angle should be expected to influence interference filter properties and perhaps influence circular polarizer properties. The lens provides an 82-mm filter mounting thread. Many here have used this lens for landscapes, so your thinking on filtering should be helpful.

UV: Have any of you noticed any effect of undesirable blue sky filtering in the corners when using a UV filter with this lens? (This might be hard to discriminate from intensity fall off in the edges of the field of view. It might be evident as a color shift.) Is there a manufacturer or filter type you would recommend for this purpose?

Polarizer: Have any of you noticed any effects, such as increased sky scattering in the image corners, when using a circular polarizing filter with this lens? If so, is there a recommended manufacturer's product found to work as well as possible with this lens or at least one that you have found satisfactory?

An answer to either question of "Don't bother" based on your experience would be equally valuable.

Thanks in advance.

02-25-2018, 01:12 PM   #2
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I use a circular polarizer frequently on the DFA version of the lens, usually for foliage and water. I would be hesitant to polarize a sky at such a wide-angle unless it is sufficiently broken up with clouds, foliage or buildings, Etc. Good luck.

Last edited by mikeSF; 02-25-2018 at 06:35 PM.
02-25-2018, 01:15 PM   #3
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QuoteOriginally posted by kaseki Quote
The FA 35mm wide angle lens has an extreme ray angle (with film cameras) of 45 degrees. This angle should be expected to influence interference filter properties and perhaps influence circular polarizer properties.
UV: Have any of you noticed any effect of undesirable blue sky filtering in the corners when using a UV filter with this lens?
Polarizer: Have any of you noticed any effects, such as increased sky scattering in the image corners, when using a circular polarizing filter with this lens?
Iʻve been shooting with the SMC Pentax-A 645 35mm F3.5. I am not sure how similar or different than it is to the SMC Pentax-FA 645 35mm f/3.5 AL that I believe you are referring to.

I can say that with B&W film in the high key subjects of the Bonneville Salt Flats in Utah, or fresh snow in the Swiss Alps, even with a thin UV filter there was significant vignetting (not wide open, but f/8). Because of that, if I donʻt want vignetting (and in many cases, I donʻt mind it because I tend to dodge and burn that way), I just wonʻt use any filter, including a thin polarizer which will only be worse than the UV.

However, on the smaller 645D/Z sensor (compared to 645 on 120 film), I wouldnʻt think youʻd have much vignetting with either as long as you didnʻt stack filters and only used thin/slim versions. Vignetting is going to be mostly caused while shooting in the f/3.5-5.6 range.
02-25-2018, 02:49 PM   #4
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Alex645: One difference between the A and FA is that the A has a 78-mm thread and the FA has an 82-mm thread. This larger diameter should reduce vignetting. Useful information, nonetheless, even though my questions were directed at wavelength and angle-dependent material properties subjected to ray angles far from perpendicular.

mikeSF: Thanks for passing on your experience.

02-25-2018, 03:49 PM   #5
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regarding vignetting, i'm on digital so this is moot, but I have a slim 82mm circ pol and there is no detectable vignetting at the corners.
02-25-2018, 04:07 PM   #6
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QuoteOriginally posted by kaseki Quote
my questions were directed at wavelength and angle-dependent material properties subjected to ray angles far from perpendicular.
There are two PF members that registered the 645 FA 35mm on site:
SMC Pentax-FA 645 35mm f/3.5 AL Serial Numbers - Pentax Serial Number Database - PentaxForums.com

@Dougg also registered a 645NII, so you might want to PM him.
03-03-2018, 10:28 AM   #7
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Dougg may not have visited this week. My present feeling is that I might as well avoid buying any filters for that lens while I look more deeply into the subject.

03-04-2018, 05:37 PM   #8
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Been away from the forum for about a month, at sea. And sorry to be of little help with the question, as I have not used any filters with this lens. Suggestions sound reasonable...

Doug
03-05-2018, 09:11 AM   #9
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Thanks.
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