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Mounting 25mm filters

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#1 dabateman

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Posted 16 January 2019 - 07:05

Mounting smaller 25 mm filters came up in an other thread but I think it deserves its own topic.

25mm filters are sold with diameters of 24, 24.4, 24,5 and rarely 25mm.

I use these filter frames, the bottom thread size hole is 20mm, and the top thread hole is 24.5mm:
https://www.ebay.com...a-/351817577571

I see the cost as shot up since I first posted about them.

Just unmount the uv filter as its one of the few with an actual retaining ring. Then I either gently sand down the sides of the filter glass if it doesn't easily fall in place. If the filter comes in a metal ring and slightly larger, then I will use a Dremel grinding wheel to grind down the threads of this filter and while still hot, pop in the glass filter with the metal ring. This is a cold weld, as the filter will not come out after this, as the hot filter ring has shrunk around the filters metal ring. You must be careful doing cold welds though, because it is possible to crack the glass if the sizes are too close. Fortunately, I have not had this happen to me.

Here is an image of a cold welded 313bp20 filter in place:
Attached Image: 313bp20_Filter.jpg

Here is an image of 330WB80 improved filter which fit within the UV filter and the retaining ring holds it in place:
Attached Image: 330_WB80improved_Filter.jpg

I found that these 25mm rings just fit in a c-mount part of this adapter:
https://www.ebay.com...d=1928589076018
So you can have the filter close to sensor and add M42 helicoid to get focusing, here is an image inside this adapter:
Attached Image: Cmount_M43rds_M42.jpg

I also use the Raf camera 52mm to 25mm adapters, as they have 52mm threads on both sides, so a hood can be used or it can be used directly behind a M42 lens with other ring adapters:
Attached Image: 52To25To52Adapter.jpg


I have cutting the black plastic from a DVD case, and drilling a 1/2 inch hole in place. Using this, I have used these frames to hold 12.5mm filters like my 300bp10 filter:
Attached Image: 12mmFilter.jpg


25mm filters work well, since many UV capable lenses have small diameter front and rear glass.
Pentax UAT 85mm f4.5, front diameter about 18mm, Rear diameter about 15mm
EL-Nikkor 80mm, front diameter about 18mm, Rear diameter about 20mm.
Steinheil Munchen EDIXA 50mm f2.8 front about 17mm, Rear about 16mm
igoriginal 35mm f3.5 lens front diameter about 23mm, Rear about 12mm
Sigma 30mm f2.8 M43rds Art lens front about 14mm, Rear about 23mm.
Wollensak 1" cine velo stigmat front and rear dameters are about 18mm and this lens has a 25mm front filter thread.

Edited by dabateman, 16 January 2019 - 07:06.


#2 Cadmium

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Posted 16 January 2019 - 07:11

There are also 25.5mm rings. What I have here.