Toho Extension Tube update

[Scott Schroeder]

Some might recall a post I did some time ago. I was have reduced contrast with my Toho extension tube (4") for my fuji 450C. I wanted to make sure it wasn't the lense so I had another LF user take a few photos with my 450C and his and it was fine. So I followed some advice given here and on another forum. I covered the inside of the tube with black flocking paper and used a rubber lens hood to reduce light.
Well that didn't work. Further advice was to create some baffles like for telescopes. So I created a crude set that only had two baffles that could slide into the tube. Here is a pic
http://tinyurl.com/a3hn5

I also got a Lee compendium shade for my Lee holder. Well that didn't work either, although there was some improvement. You might notice I reduced the image circle using the baffles.

So I posted my dilema on the cameramakers forum and was given some excellent advice: the baffles need to be razor sharp. So I decided to rebuild my baffle set with more baffles and as thin as could be with some rigidity. I had some xray fim and felt it was a great candidate for the job. I made several calculations to make the baffle system snug and to have each baffle progressively larger to reduce the angle of coverage (the 450C is HUGE for 4X5). An exacto knife some super glue and some patience put it all together. The construction has that homemade artisan feel to it, LOL. Anyway, the whole thing was painted with the flattest matte black I could find. The result is here.
http://tinyurl.com/95suz

Inside the tube looking down
http://tinyurl.com/cgshh

By opening the back there was no noticable reflections bouncing around. So I went out and took some photos with the Lee hood on as well. GREAT NEGATIVES!!!

So there is limited movements and it is stretched out a bit (on the rail about the same as my Nikkor 300 M) but I got the reach and it's well worth it. The whole setup isn't that heavy so it isn't unstable. It just takes a bit TLC.

So I thought my fellow TOHO users might be interested as well as anyone wanting some extra reach with an extension tube. I set this up ONLY for the 450C.

[Ron Marshall]

Thanks for the info Scott,

I recently purchased a Toho, don't currently have a 450mm, but it is on my wish list, so your post is very helpful for me since loss of contrast was one of my concerns.

[Hening Bettermann]

Has anybody tried black corduroy, glued onto the inner surface of the tube, the "ribs" of course at a right angle to the optical axis? The tip is from a bird photographer who used this to baffle the inside of homemade 1200 mm lenses. The corduroy could be spray-painted with that matte paint in addition.

[Dan Fromm]

Interesting.

FWIW, some of my Taylor Hobson lenses' rear sections are threaded internally, thread size and form reminiscent of standard filter threads.

More to the point, the late Steve Grimes made an adapter for me to hold my 12"/4 Taylor Hobson Telephoto on a board. The adapter's interior was, as delivered, very, very smooth and the lens' exit pupil is far in front of the adapter. Result? Horrible hot spot. Cure? Steve threaded the adapter's interior like, yes, a filter thread. And the fix worked. It doesn't seem to take much to stop glancing reflections from a tube's interior.

Cheers,

Dan