Infinity Focus

[Terry Hull]

I have used a Fujinon 180MM successfully, and wonder if there is a longer focal length lens that I might use on my Ebony SW 45 (190mm bellows). More specifically do all general purpose 210MM lenses focus similarly, e.g., (without getting into specifically designed telephotos) do 210MM lens from different manufacturers require the same bellows extension to focus at infinity? I have no interest in adding back extenders, etc.

Thank you.

[Vaughn]

That would be a safe assumption -- you would have to find a telephoto type of 210mm (if there are any) to significantly reduce to the film-to-lens distance.

A "top hat" type of lensboard might be possible -- one that extends the lens forward. It would not have to extend the lens very far...a couple inches. But what one gains going from 180mm to 210mm may not be worth the hassle.

Vaughn

[Eric James]

Your 180mm lens is the limit if you are opposed to using an extension back or "top hat". The Nikkor 200mm M comes close to focusing at infinity on your rig. Do you know the exact maximum extension of your particular SW45 - there is some variation within models.

http://www.ebonycamera.com/articles/lenses.html

[Gem Singer]

Ebony makes extension lens boards. When I had an Ebony, I purchased one from Midwest.

They come in various lengths. You should be able to add enough front extension to use a 210 instead of a 180.

Wouldn't it be easier to move the camera a few feet closer to the subject?

[percepts]

Yes a top hat lens board would do it. But how often do you focus on infinity? Mostly you focus closer which means you need even more extension than 210mm. I think you will run out of extension very quickly. Your camera is simply not designed for lenses of 210mm or longer.

[Ed Richards]

You would also hardly notice the difference in field of view.

[Terry Hull]

Thanks.

[ic-racer]

do 210MM lens from different manufacturers require the same bellows extension to focus at infinity?

When you look at a lens datasheet the "flange focal length" tells you the exact distance from the front surface of the lensboard to the film plane when the lens is focused at infinity. It is also called "flange back."

[Terry Hull]

So all 210MM have the same flange back distance? (other than teles, etc.) I thought lens construction and design differences by manufacturer might cause similar focal length lenses to have different flange back distances

[Dan Fromm]

ic-racer, like all values published for lenses, flange-focal distances or tirages mechaniques or whatever we want to call them are nominal. Real lenses as made don't always exactly meet their specifications, so the published flange-focal distances can't be relied on.

For example, I once bought 20 38/4.5 Biogons made to be fitted to AGI F135 aerial cameras. The lenses are bolted to the body's main casting, which is very precisely machined; the lens is focused to infinity by a spacer that sits between the rear of its flange and the body. Each of my little Biogons had its own focusing spacer with its thickness, to 0.01 mm, and the lens' serial number marked on it. Each lens was marked with its measured focal length (nominal, per Zeiss, is 38.5 mm), to 0.1 mm; the range was 38.3 to 38.8 mm, and the spacers varied accordingly.

Many, not all, process lenses have similar calibrations marked on them.

You really can't believe everything you read.

Cheers,

Dan