Reduced contrast, toho extension tube

[Scott Schroeder]

I was hoping for a little help with a problem I am having with my Fuji 12.5/450 C mounted on an extension tube for my toho http://tinyurl.com/68mkr
I have taken about five different photos in different lighting situations and I am quite sure I have a problem with reduced contrast from interna reflections as described below from Kerry's review of the TOHO:

"Originally, I had two concerns about using such a long extender. The first was mechanical vignetting when using movements. I had Steve Grimes make the diameter of the spacers as large as possible to prevent this problem. Testing with the maximum extender length indicates there is absolutely no mechanical vignetting when employing the maximum rise the Toho is capable of achieving, even with the lens wide open. In other words, experimental testing has proven that mechanical vignetting is not an issue. The second concern was reduced contrast due to internal reflections. The 450mm Fujinon C has a HUGE image circle, and that means there is a lot of excess, non-image light bouncing around inside the extender. Due to their mechanical and physical properties, camera bellows do a good job absorbing most of this non-image light. So, on a camera with longer bellows (and no extender) this is rarely an issue. The extender is both smaller in diameter and lacks the geometric advantage of the pleated bellows in absorbing this light. For that reason, I have initially been using a lens shade to help limit the excess light entering the camera. I have also taken a few images without using a shade. So far, I have not noticed any reduction in contrast or other ill effects that could be attributed to internal reflections within the extender. However, before I am ready to declare this a total non-issue, further testing is definitely in order. In the end, it is possible that the use of the extender could cause a very slight reduction in contrast in some lighting situations. In these extreme cases, proper lens shading techniques (always a good idea anyway) might alleviate any problems. Once I have had a chance to further test the extender under a wider variety of lighting conditions, I will post an update. Due to the physical geometry involved, this is absolutely not an issue with the extender in its shortest configuration (as used with the 14" L.D. Artar and the 360mm Fujinon A)."

I am pretty sure it isn't the lens itself b/c I have heard this is a very sharp lens. unfortunately the toho is the only camera I own, so I can't test it without an extender.
My question is how can I reduce the reflections?
I have considered just linind the extender with black cloth. any reasons why not?
Also, the image appears sharp on the GG (albeit less than my other lenses) but I am shocked by lack thereof on the negs.....any reason for this?
Thanks for any help and opinions

[Gem Singer]

Hi Scott,

I have used the Fuji 450C with (approx.) 2 inches of extension tube lensboard. 4 1/2 inches sounds like a lot of extension tube to use. I don't think lining the inside of the tube with an anti-reflective material will solve the problem, but it won't hurt it, either. Are you using an effective lens hood? Perhaps stepping up to a 62 or 67mm. long rubber one would help.

[Gem Singer]

P.S. That's 62-67mm. in diameter, not length. Rubber lenshoods are available in both shorter and longer lenghts.

[Scott Schroeder]

Thanks Eugene. I guess I could cut the thing in half. Are you pushing the bellows focused at infinity with that?
On the lenshood...good idea, not sure what you mean about the 62-67mm diameter. Couldn't I just get a 52mm screw in like one of these? http://tinyurl.com/5h42n

Thanks for the response

[David A. Goldfarb]

You can order black flocking paper from Edmund Scientific to reduce reflections in extension tubes and solid lens shades of all types (www.scientificsonline.com (http://www.scientificsonline.com)). I've used it for a number of different applications. There is a self-adhesive type, and a non-adhesive type that you can apply with Pliobond. The non-adhesive sheets are also handy as background material, when you want a really black background for small still-life setups. I think they are mainly selling this material to people who make their own telescopes.

For this situation, though, what you really want is a compendium lens shade so that you can restrict the image circle to the minimum necessary for the image, since you've got way more coverage than you need with a 450C on 4x5". Alternately, you could just look into a long lens shade, but that gives you less flexibility.

[Scott Schroeder]

Thanks for the tip david, I went ahead and order the black flocking
paper. I will also get a rubber lens hood and proceed from there. The
compendium hoods are a bit pricey so that would be a last resort. I will probably take a shot as is, then with the black paper, then with the lens hood and see the
results. If it is still a problem, I will cut the tube in half and
hopefully I can use my 450!!!!!
Thanks
Scott

[David A. Goldfarb]

Since you'll probably have some extra black flocking paper, you can make a lens shade out of it of whatever length works before cutting down your extension tube. You could even make a few of them for different applications (i.e., a long one for shots with no movements, a shorter one for shots with a little movement, an even shorter one for shots with lots of movement). You could glue the flocking to some flexible plastic material to make it more durable, and attach it to the lens with tape or a rubber band.

Another less costly alternative to a compendium shade would be a rubber zoom lens shade (Hama makes one, and I think there are a couple of others), so you can adjust it as needed.

[Gem Singer]

Hello again Scott,

No need to cut down the extension tube. The Fuji 450C has a flange focal length of (approx.) 425mm. I had (approx.) 50mm. of extension tube available to me. Therefore, I needed at least 375mm. of bellows extension to focus that lens at infinity. The camera I was using at the time had a maximum of (approx.) 400mm. of bellows to work with.Yes, it was stretching it a bit, but it worked.

I recommend stepping the 52mm. screw-in filter size of the Fuji 450C up to 62, or 67mm. because that size rubber lens hood is longer and has a wider opening in the front. Reduces flare and lessens the probability of vignetting.