• Ultraviolet Photography

Focotar-2 50mm front filter adaptor

UV Lens
7 replies to this topic

#1 Cadmium


  • Members+G
  • 4,246 posts

Posted 13 April 2017 - 13:06

The Focotar-2 50mm enlarger lens transmits UV very well.
This lens has no front threads to mount filters, so here is one possible solution for mounting filters on the front.
Look for a Leica Leitz 36mm Clamp-on Filter on eBay. These fit the front of the Focotar perfectly.
They come with various filter glass installed in them, but you can remove the glass easily by unscrewing the retaining ring that holds the glass in from behind.
This retaining ring also has 33mm x .5mm pitch female threads on the inside of it. You can screw the retaining ring back into the clamp-on frame without the filter glass,
and those 33mm threads will be available from the front to screw a step up ring into.
In the photo I am showing a 34mm x .75mm pitch to 43mm step up ring, which will work if you need to, but should not be screwed all the way in.
Here is a step-up ring on eBay that has the 33mm x .5mm pitch threads to 52mm.

Focotar-2 50mm with no filter.
Attached Image: Focotar_Clampon_3_800.jpg

Focotar-2 50mm with clamp-on ring and 33mm x .75mm to 43mm step up ring.
Attached Image: Focotar_Clampon_1_800.jpg

Leica Leitz 36mm Clamp-on Filter (filter glass removed), and 33mm x .75mm to 43mm step up ring.
Arrow points at retaining ring inside threads.
Attached Image: Focotar_Clampon_2_800.jpg

#2 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 9,115 posts
  • Location: UVP Western Division, Santa Fe, New Mexico

Posted 15 April 2017 - 23:53

That is a nifty clamp-on filter. I couldn't tell from the photos whether where the screw thingie fits. I have tried a filter fitting similar to this, but the screws were going to scratch the lens barrel where they clamped on, so I did not use it again.

Thank you for the write-up about the Focotar-2 and the step-ring link. Always good stuff to know about.
Andrea G. Blum
Often found hanging out with flowers & bees.

#3 Cadmium


  • Members+G
  • 4,246 posts

Posted 16 April 2017 - 06:39

There is another type, which may be more like what you are referring to, which looks like this:
That kind looks like it has two screws on each side that directly clamp onto the outside of the lens.
Alex is sending me one to compare. He says the front screws off, and there are threads also. I will post a comparison when I get it later this month.

The one I have works more like a clamp, the screw doesn't touch the lens. Here are closer pics showing more detail from the rear of the filter with filter glass installed in it.
You can see the clamp by the screw, and you can see the retaining ring also with threads on the inside of it.
Attached Image: Focotar_Clampon_3_1280.jpg

#4 Cadmium


  • Members+G
  • 4,246 posts

Posted 16 April 2017 - 10:03

Here is my current solution to the Focotar-2 50mm front filter mounting.
This uses two step up rings, when only one is needed, and a better one with the correct threads too (per the eBay the link in my first post), but that one costs more than the helicoid, but I will probably get it later.
Here I have a BG40 52mm x 2mm thick filter (for visual) mounted on the front of the Focotar-2 50mm.
This set up works great. I will see how light-tight it is for shooting UV, I may need to use an O-Ring as a light seal between the clamp-on adapter and the front edge of the Focotar lens, but we will see.

In my opinion, Alex is the best expert on the Focotar for UV macro, and I believe he was the one who first tested this lens as such. He says it is very sharp,
and the few visual-only shots I have experimented with so far are very sharp indeed. So if you have any questions about the Focotar-2 50mm or others, you might want to ask Alex, he knows a lot about lenses.

Right to left: Nikon to M42 mount, M42 extension tube, M42 to M42 helicoid, Focotar-2 50mm, 36mm clamp-on adapter, 33mm to 43mm step up ring, 43mm to 52mm step up ring, BG40 52mm x 2mm filter.
Attached Image: Focotar_with_filter_and_helicoid_2_1280.jpg

Attached Image: Focotar_with_filter_and_helicoid_1_1280.jpg

Edited by Cadmium, 16 April 2017 - 10:07.

#5 Cadmium


  • Members+G
  • 4,246 posts

Posted 08 June 2017 - 06:08

Update to the Focotar-2 50mm filter adapters.
Thanks to Alex for sending me another adapter style, which has standard 44mm threads (.75mm pitch).
The adapter he sent me uses two screws, instead of one screw for an inner clamp ring like the one I have shown above.
The problem with the style above is that the inner thread is not standard. I tried 0.5mm pitch thread which will not fit, and although I could partially screw in the .75mm pitch thread, it didn't screw in very well,
and it would not screw into a second identical clamp that I purchased, they have a slightly different inner threaded rings from one another.
The adapter that Alex sent me threads normally. It also has a nice aperture positioning arm (as shown in the photos below).
I prefer the clamp style, because it is simpler to install, but the thread may not be easy to work with.
Of course some slightly smaller step up ring could be glued into one of the clamp style adapters which do happen to be readily available and inexpensive.

Here are some comparison pics.
Attached Image: Focotar_clamps_top_1200.jpg

Attached Image: Focotar_clamps_back_1200.jpg

#6 JCDowdy


  • Members
  • 1,188 posts
  • Location: Arlington, TN

Posted 13 June 2017 - 19:49

Curios, what is the FFD of this lens? That info is missing in our Lens Sticky.

Never mind - I found it! B)

Edited by JCDowdy, 13 June 2017 - 20:04.

#7 Cadmium


  • Members+G
  • 4,246 posts

Posted 14 June 2017 - 08:26

Yep, Boon had it, no surprise. :-)
Focotar-2 50mm f/4.5, FFD = 44.5mm.

#8 JCDowdy


  • Members
  • 1,188 posts
  • Location: Arlington, TN

Posted 05 July 2017 - 14:41

Here is another filter slip mount to consider.