# Thread: Making Another Expansion Back - 8x20 for 11x14

1. ## Re: Making Another Expansion Back - 8x20 for 11x14

Wow Michael, thanks for this explanation! I really like this approach and I understood you instructions perfectly. This will be hugely helpful!! Definitely adding this to my notebook!!

2. ## Re: Making Another Expansion Back - 8x20 for 11x14

So I'm going over everything thats been discussed so far and I'm looking at Michael's diagram and the instructions he posted. I should be able to make one diagram that will give me all of the information needed to determine the depth of the expansion box needed to prevent vignetting at any focus distance that I'll use with any of my lenses. Essentially, I just take the longest lens I intend to use, 600mm, and extend the bellows to the closest focus distance I intend to use with this lens and use that as the focal length measurement for the diagrams and measurements rather then the focal length at infinity. If I work out the math using the focal length at the closest focus distance for the longest lens then everything else for the same lens at shorter focus distances to infinity and all focus distances for the shorter lens should be covered. Does this sound like a correct assumption to make?

3. ## Re: Making Another Expansion Back - 8x20 for 11x14

Sounds right to me.

4. ## Re: Making Another Expansion Back - 8x20 for 11x14

Originally Posted by Fragomeni
Does this sound like a correct assumption to make?
Yes. The only trouble you might conceivably run into is that if calculating for a 600 at closer-than-infinity focus results in having a box that extends well off the back of the Deardorff's rear standard, you might run into a bellows compression constraint if you decide you want to use a much shorter lens like a 300.

Go ahead and do the calculation - you'll know if you have a potential problem before you start to cut anything.

5. ## Re: Making Another Expansion Back - 8x20 for 11x14

Just a quick update. I've got the camera and the 8x20 back on hand now. I visited with a friend who is going to help me build this. We'll probably use Birch for its light weight and a veneer of some sort for extra strength. Anyway, I made all the measurements and drew up the diagram which is attached (hopefully you can see it as I had to photograph it with my iphone again). In order for my longest lens that I intend to use (600mm Fujinon-C) to focus at infinity the expansion back needs to be 7.5 inches deep. For the lens to focus at the closest focus distance (max bellows draw is 42 inches), the expansion back needs to be 12.6 inches deep. Now we just need to figure out how to make it light weight as to not stress the rear standard. Birch should be a good option I think. Balsa would obviously be the lightest but its so soft that I worry about it.

6. ## Re: Making Another Expansion Back - 8x20 for 11x14

So after looking at the dimensions and assessing them while looking at the camera I think I'm going to nix the project. The problem is that I like longer lenses and longer lenses necessitate a deeper back which is bigger and weighs more. This concern was brought up earlier in the conversation by a few I believe and it has indeed become the deciding factor. I've begun the last minute search to see if I could find an 8x20 camera anywhere but funds are running low at this point. I'll keep the 8x20 back and my friend who was going to help me with the build has agreed to help me build a whole 8x20 camera around it later on. He built his own ULF camera so he has the necessary skills.

Huge thanks to all who contributed to this discussion! Obviously I wish making the back was more feasible but this was a great learning experience! Thank you!!

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