1. ## Bellows extension question.

How do you determine the amount of extension you need for various lens sizes? When I change a lens I unlock and move the front on the rails at something at infinity and lock it in place once I've found my infinity focus. So, if you can't find that with a longer lens, then that means the extension isn't long enough, correct?

Thanks much.

2. ## Re: Bellows extension question.

That's correct. What focal length and camera are you working with?

3. ## Re: Bellows extension question.

I've got a Rodenstock 480mm that I occasionally use on my Century Universal 8x10. It works, but I pretty much have to extend the lens to the front with all the beds extended. Do you know the camera, and, if so, does that seem correct? I think at full extension that particular camera is 30-something inches. So, how do you do the math?

Thanks much.

4. ## Re: Bellows extension question.

A 480mm lens should require something close to 19" (480 / 25.4) of bellows extension. So, something sounds amiss if you are extending to 30" for infinity focus.

5. ## Re: Bellows extension question.

I've only used it on that camera a couple of times, so I'll have to do more exploring. Now, my question is, how did you come up with that lens needing 19" of extension; what's the math?

Thanks much.

6. ## Re: Bellows extension question.

Ralph showed you, there are 25.4 mm per inch.

7. ## Re: Bellows extension question.

I've only used that LENS a couple of times, not the camera, is what I meant to write.

8. ## Re: Bellows extension question.

thanks. i'm tired. bed time. Sorry for the confusion, and thanks for the help.

10. ## Re: Bellows extension question.

Something is weird here. You are right in thinking that your Century Universal has something over 30 inches extension. This should be way more than is required to focus a 480mm lens at infinity. 480mm is only about 19'. The distance from lensboard to groundglass should be something fairly close to that figure. I suspect that your lens has had a cell swapped with some other lens, or that you have only one cell of a convertible lens.

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