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UltravioletPhotography

Is there one size that fits all?


rfcurry

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I am looking at having a short pass filter made for sale that will provide 90%+ for UV for most of the 300-390 nm range and OD4 for 410-1100nm. Unfortunately, this is a dichroic filter, which means, like filters intended for astronomy (Astrodon, Baader U, etc.), it will only be true to the reflected light if said light is collimated. Hence, I won't be making the filter in a 52mm filter ring for the objective lens; I will only have it made in a size that would allow it to fit in adapters... where the light is collimated or nearly so.

 

Now some questions.

What is the size required for you to place a filter within your most-used adapter?

If you do not use an adapter, do you have another mechanism for using a filter on the collimated light from your lens?

 

In order to have these filters made at a reasonable cost, I need to keep them to one size. Please give your input, even if you would never use such a filter.

 

Thank you for your assistance.

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It's tempting to select say 40.5 mm as this is a pretty common size anyway and from my measurements apparently most m43 adapters could handle it. My second choice would be 39 mm threads.
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That would in practice be 46 mm (43.2 is approx. diagonal). Few m43 adapters could house such a filter, maybe with exception of some F>m43.
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I am not using m43, but APS-C and full-frame Sony mirrorless, hence I am interested in larger diameter adapters. I think the minimum for me woud be 40.5.
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The filter need not be as large as the sensor if mounted close to the rear element of a lens.

 

What is the exit aperture diameter of the 105mm UV-Nikkor and the 60mm UV-VIS-IR Coastal?

 

added:

FYI, 1.25" Astro eyepiece filters work fine inside µ4/3 adapters.

 

added later:

36mm is an unmounted Baader filter size, Astrodon has unmounted 31mm..........

 

added later still:

The IDAS MFA for certain Nikon DXs and Canons is a 37mm threaded filter.

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enricosavazzi

As JCDowdy said, slightly larger than the rear lens element will work in most cases, if mounted close to the rear element. Slightly smaller than the rear element is usually not a problem if the lens is stopped down. Some practical examples from my equipment follow.

 

1.5" - this size sits well inside a Nikon F to Micro 4/3 adapter. This diameter is larger than needed by most lenses, so it may be wasteful if the filter is expensive and one needs it for only one lens. On the other hand, it makes a good "universal" size for rear mounting on Micro 4/3 if you have multiple lenses.

 

Approximate rear element diameters:

25mm - Coastalopt 60mm Apo

10mm - Olympus G.Zuiko 20mm f/3.5. This element is quite close to the focal plane, so the filter should be significantly wider (at least 15-20 mm) as light spreads out in a broad cone. This may be a problem for a dichroic filter.

18mm - El-Nikkor 80mm f/5.6 "old" style

7.5mm - UV Rodagon 60mm f/5.6. This is quite recessed, so the filter should be at least 12-15 mm.

12mm - multiple-brand 35mm f/3.5 "good for UV"

 

Still, I don't think we should give up on using this filter at the front of a lens of relative long focal length. As long as we shelter it within a sufficiently narrow and deep lens shade, which I always do, most off-axis radiation is excluded. For use in front of a lens, I have a variety of filter diameters, most of them ending up in a 37mm male thread (with adapters) or 52mm. The actual filter diameter is usually 25mm or 1", mounted in ordinary 28mm filter rings. I also have a few 1 1/4" astronomic filters remounted into 30mm filter rings. I bought perhaps a dozen each 25mm, 28mm and 30mm UV filters on eBay to slaughter them and re-use the aluminium rings.

 

As a whole, an unmounted filter diameter of 25mm or 28mm would serve most of my needs.

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As JCDowdy said, slightly larger than the rear lens element will work in most cases, if mounted close to the rear element.

I certainly must acknowledge Enrico's guidance on that point, borne out in my applications using 1.25" astro filters for µ4/3. I think also relevant is Bjørn's use of the Teleskop Express filter drawers, available in 1.25" & unmounted 36mm, as well as larger. Obviously wider sensors may require greater diameter filter depending on filter proximity to image plane. In response to Alex H, I saw a photo of a full frame Sony mirrorless with a Canon lens adapter fitted with the IDAS MFS mentioned earlier. Apparently, mounted far enough from sensor in such an adapter that filter is large enough.

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The rear mounted filters act merely as a field stop. Thus they may potentially limit the field of view only. The closer they come the rear of the lens the better in terms of reducing the stop size.
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I never use rear mounted filters. I don't know why. I just don't. Like it's too much of a hassle or something. Maybe because I don't really use adapters either - just try instead to put the lens on a Pentax or Nikon camera it fits. Oh well. I'll pass on this one. (I do have a couple of T2 to F mount adapters. And I will eventually have an Exakta to something adapter if I can ever settle on what the something should be.)
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.... I will eventually have an Exakta to something adapter if I can ever settle on what the something should be.

 

I did not think it possible but here is someone who found a way to mount an Exakta lens on a Pentax-K, with expected limitations of course.

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At one point I took a Dremel to my Nikon D40 and made it possible to take M42 screw mount lenses. Then I converted all my Exakta lenses to M42. I simply removed the stop screw on the lens flange and Gorilla glued a 39mm-42mm step up ring to the flange. I could get infinity on many lenses that way. When I switched to m4/3, a bit of acetone removed the glue, and the lense was exactly Exakta again.
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