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11-10-2020, 10:39 AM   #1
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Rear mount filters for Arsat 30 fisheye lens

Does anyone know where to get extra 38 x 0.5 filters for this lens? My Arsat only came with the 1 clear filter. Don't want to mess it up since a filter must always be mounted for optimum image quality.

I might also try placing gel filters between filter and lens.

Thanks,
barondla

11-10-2020, 11:00 AM - 1 Like   #2
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QuoteOriginally posted by barondla Quote
Does anyone know where to get extra 38 x 0.5 filters for this lens? My Arsat only came with the 1 clear filter. Don't want to mess it up since a filter must always be mounted for optimum image quality.

I might also try placing gel filters between filter and lens.

Thanks,
barondla
what is the filter diameter? I have an Arsat 300mm f/2.8 in a Nikon mount that has a series of rear mount filters it came with and now curious if they are compatible.
11-10-2020, 11:06 AM   #3
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QuoteOriginally posted by yurihuta Quote
what is the filter diameter? I have an Arsat 300mm f/2.8 in a Nikon mount that has a series of rear mount filters it came with and now curious if they are compatible.
Arsat website lists them as 38mm x 0.5 thread. Not near the lens at the moment, but I believe the filter has male only threads to fit the lens's female threads.

300 2.8 is interesting. How does it perform? Imagine it takes larger than 38mm rear filters.

Thanks,
barondla
11-10-2020, 12:53 PM - 1 Like   #4
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Your lens should have come with a set of four. Try this site...

FilterFind

They have a ton of filters and filter-related stuff. Google might also prove helpful. I did a quick search and found a lot of forum posts, a couple of which suggested swapping in gel or glass from other 38mm or 37mm filters.

BTW...what type of filter are you wanting?


Steve

11-10-2020, 04:32 PM   #5
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QuoteOriginally posted by stevebrot Quote
Your lens should have come with a set of four. Try this site...

FilterFind

They have a ton of filters and filter-related stuff. Google might also prove helpful. I did a quick search and found a lot of forum posts, a couple of which suggested swapping in gel or glass from other 38mm or 37mm filters.

BTW...what type of filter are you wanting?


Steve
I did a quick search before posting and didn't find any exact replacements. Lots of gels and adapting other glass. Unfortunately mine only came with the clear filter. I don't want to jeopardize my only filter ring with mods.

Didn't know about FilterFind. Will check them out. A ND and IR filter would be useful.

Thanks,
barondla
11-10-2020, 08:04 PM - 1 Like   #6
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QuoteOriginally posted by barondla Quote
I did a quick search before posting and didn't find any exact replacements. Lots of gels and adapting other glass. Unfortunately mine only came with the clear filter. I don't want to jeopardize my only filter ring with mods.
The other Arsat filters for the fisheye are normally mounted in a velcro attached plate under the cover of the pouch. The colors are yellow, orange, and blue, and are functionally described in the operating manual, attached.
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File Type: pdf Arax-fisheye.pdf (132.7 KB, 15 views)
11-10-2020, 09:37 PM   #7
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QuoteOriginally posted by kaseki Quote
The other Arsat filters for the fisheye are normally mounted in a velcro attached plate under the cover of the pouch. The colors are yellow, orange, and blue, and are functionally described in the operating manual, attached.
Thanks for the link. The pouch and extra filters weren't included with my lens. The colors wouldn't be a big use, to me, on digital. I'll find a filter ring eventually.

Thanks,
barondla
11-11-2020, 12:26 AM - 1 Like   #8
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Have you checked with Arax directly? Worthwhile to check, even if they don't have the lens anymore.

11-11-2020, 07:50 AM - 1 Like   #9
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QuoteOriginally posted by barondla Quote
... I'll find a filter ring eventually.
Any substitute glass will need to have the thickness and index of refraction be the same as the original filters or clear insert. Just how important this might be could be experimentally tested by taking an image with and without the clear filter. Manual focus will have to be changed, I suspect. I'm guessing that infinity focus would occur with the focus dial set a bit short of infinity.
11-11-2020, 10:38 PM   #10
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QuoteOriginally posted by kaseki Quote
Any substitute glass will need to have the thickness and index of refraction be the same as the original filters or clear insert. Just how important this might be could be experimentally tested by taking an image with and without the clear filter. Manual focus will have to be changed, I suspect. I'm guessing that infinity focus would occur with the focus dial set a bit short of infinity.
Hmm. Perhaps I'd be better off putting a gel between lens and original optical filter. Don't think a gel would throw focus off much.

Thanks,
barondla
11-11-2020, 10:47 PM - 1 Like   #11
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Of course, if you focus with magnified live view, then you will automatically be adjusting anyway for any differences in refractive index (with a margin of error, that would probably apply anyway).

Last edited by Ed Hurst; 11-11-2020 at 10:53 PM.
11-12-2020, 08:21 AM - 1 Like   #12
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QuoteOriginally posted by Ed Hurst Quote
Of course, if you focus with magnified live view, then you will automatically be adjusting anyway for any differences in refractive index (with a margin of error, that would probably apply anyway).
I was also thinking of possible secondary effects such as degrading the correction of spherical or chromatic aberration, or of flatness of field. Such effects, if present, would be magnified by comparing a scene image with and without the clear filter. I'm personally unsure, however, just what type of scene would be good for that kind of test.

I would expect a thin gel to be pretty minimal in effect, but that too could be tested with a suitable target scene.
11-12-2020, 03:35 PM   #13
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Good points - and it would be good to know. Not just for this lens, but for others that have a rear-mount or drop-in filter (with the intention that it's used normally with a plain glass filter in there). For example, the Pentax 25mm DA or DFA lenses. I suspect, in the case of the Arsat fish-eye, that you'd be hard pressed to see any issues as long as you're focused properly, just because the lens is bound to have some uncorrected imperfections anyway, but - as you say - it would be great to know for sure :-)
11-12-2020, 04:48 PM - 2 Likes   #14
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As the Arsat has been designed for film, it may actually perform reasonable well with the digital sensor filter stack, no worse than with the rear filter on film. So it's worth a comparison between with and without filter.
11-12-2020, 06:45 PM   #15
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QuoteOriginally posted by JensE Quote
As the Arsat has been designed for film, it may actually perform reasonable well with the digital sensor filter stack, no worse than with the rear filter on film. So it's worth a comparison between with and without filter.
Interesting idea. Hadn't considered that possibility. Could be fine on digital without filter and awful on film. Will try it someday.

Thanks,
barondla
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