Blocking Light Leaks from Aperture Windows

[enricosavazzi]

ADMIN NOTE: The first 6 comments in this thread were moved from Enrico's Introduction thread in order to make an independent thread about an important topic.

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Hello Enrico and Welcome to UVP. I hope you enjoy this site. We are very happy to have you here.

 

I have read and enjoyed your site for years and learned so much about UV lenses there. Your recommendations are picked up and included in our Lens Sticky (with links to your site) in which we try to provide a list of UV capable lenses.

 

Your tip about using the UV-Rodagon inside an adapter which would permit infinity focus were great news for me. I had always wanted better use of that lens. BTW, how did you solve the problem of the aperture windows on that lens? Klaus recommended using black fingernail polish in them but I could not quite bring myself to use something so permanent on an expensive lens. "-)

 

A 5 hour daily commute must surely be a ordeal you are looking forward to giving up when you retire. My goodness that is a serious commute!!

 

Hi Andrea,

 

I believe I attached a ring of adhesive-backed Protostar (a flocking film for telescopes) at the rear of my UV Rodagon. I haven't had problems with light leaking through it. Protostar, like most flocking, does have a tendence to release particles that may end up on the sensor, so it is a tradeoff. A ring cut out from a sheet of heavy-duty black drawing paper should also work.

 

For more permanent modifications of this type, or for places where an adhesive foil is not suitable, I often use matt black paint sold in small cans in model shops. When it comes to paint, however, one should test for transparency in the NIR before using it on a lens or to cut down internal reflections. Some types of black paint (and even a type of deep-pile velvet cloth I tested) transmit NIR very well. I have not tested nail polish, so I don't know how it would fare.

 

I wrote most of my book on scientific photography while commuting by train, so the time was not a complete waste. It does help as a motivation not being able to do anything else with that time. The problem with Uppsala is that, apart for the university, there aren't too many technical or IT jobs. Everything else is around Stockholm, which means at least one hour away. I see deer, moose, foxes, waterfowl and other wildlife relatively often during my commute, but just for a fleeting moment, so no chance of taking pictures. Shopping malls are steadily replacing wildlife, though.

[Andrea B.]

Now that is a simple elegant solution using the heavy black drawing paper !! Why didn't I think of that?? B)

 

And I had not heard of the Protostar stuff. Another good solution. I wonder if the Protostar could be sprayed with a fixative to prevent its shedding?

 

Some types of black paint (and even a type of deep-pile velvet cloth I tested) transmit NIR very well.

Good to know, thanks.

 

I think I wouldn't mind trying the black nail polish on one of the Omegaron or Omegar enlarger lenses which I got to test. They were very inexpensive. When I get back home, I'll give it a try.

[enricosavazzi]

...

 

And I had not heard of the Protostar stuff. Another good solution. I wonder if the Protostar could be sprayed with a fixative to prevent its shedding?

 

...

It can be sprayed, but this would probably change its reflective properties - most likely in undesirable ways, since it is designed for very low reflectivity.

[JCDowdy]

ThorLabs has a good selection of blackout materials at not so bad prices.

I think perhaps their High-Performance Black Masking Tape or Black Aluminum Foil Tape might be worth a look.

I like the sound of "Removed Easily Without Leaving Residue" too, but cannot imagine ever needing 80 ft of the stuff.

 

Protostar claims that it "doesn't shed on your optics" but I would still worry.

 

Andrea, I still have not tried the black silicone on my old 75mm Omegaron but will get some today! I recently had a "eureka moment" regarding how to use an EL series-N lens or other windowed type. Since I mount my UV-pass filter between the helicoid and camera adapter, I only really need to block UV coming through the window. I rather doubt much UV is transmitted through those windows & little colored light guides anyway. This should be doable with a good grade of UV-blocking window film, and you can still read the stops. I will keep y'all posted on how it goes.

[msubees]

I just used some JB Welder (a type of epoxy glue with black metal powders inside) last night on my cheap 50mm Rodenstock lens (before I read this)...This morning I tested and much better contrast...

[JCDowdy]

Zach! JB Weld? You are lucky you can still adjust the aperture. :o

Of course with an inexpensive lens it is easier to experiment, but it will be very difficult to ever remove.

 

I just tested my cheap 75mm Omegaron with a rear mounted Andrea-U by shining a red laser through the window.

With the pupil of the lens occluded with black felt and ISO 160 &1000 I could not see anything on the screen.

I will shine a quartz fiber optic from a UV source to test if any UV can get through the window.

 

Andrea, should we move this topic off Enricos intro page?

[JCDowdy]

Good move Andrea!

[JCDowdy]

Here is a quote form an earlier topic that needs to connect here:

 

I have disassembled the newer plastic, EL-Nikkor 80mmF5.6N - M39 Screw Mount, enlarger lens & show here the differences to the older metal EL-Nikkor 80mmF5.6 shown above.

I couldn't open the front element stack with the usual rubber tool. I needed to drill two, 1mm holes in the front ring, in the filter thread recess, so I could open the front element stack.

To stop light leaks into the lens, I turned the back flange 120 degrees, to block the rear window. I 'blacked out', with satin black nail varnish, the white plastic aperture housing, behind the aperture index window.

Cheers

Col

[Andrea B.]

Any tape used for blocking needs to be able to withstand hot sunlight.

You don't want the tape adhesive melting and causing a sticky mess. :o

[msubees]

not a problem...i was careful not to leak it into any movable parts....aperture still works fine.

 

Zach! JB Weld? You are lucky you can still adjust the aperture. :D

Of course with an inexpensive lens it is easier to experiment, but it will be very difficult to ever remove.

 

I just tested my cheap 75mm Omegaron with a rear mounted Andrea-U by shining a red laser through the window.

With the pupil of the lens occluded with black felt and ISO 160 &1000 I could not see anything on the screen.

I will shine a quartz fiber optic from a UV source to test if any UV can get through the window.

 

Andrea, should we move this topic off Enricos intro page?