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rchouser · Joined: 13 Mar 2003 Posts: 16 Location: northern virginia

I have put the 1 1/2 inch spacer between the XLRF back and the Film back. I am trying for a macro capability and I got it. Short of using my focus back then switching to my film back is there any good way of converting marked lens focus distances to "spacer" focus distances. (Right now, I just put on the ground glass and move in and out until I get a focus, set my tripod, mount the camera, move the tripod in and out until the focus is what I want, change to a film back, then shoot. I am thinking of just tying a premeasured string to the camera and setting the camera while holding the string on the subject. Has anyone used these body spacers? PS The photos are incredibly good, so it's worth the hassel. thanks

45PSS · Posted: Thu May 29, 2003 4:40 pm Post subject:

You may decide to just get one of these Macro Focus Adapters .

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rchouser · Joined: 13 Mar 2003 Posts: 16 Location: northern virginia

And the Answer is a macro focusing rail.

Since I have a macro bellows for my 35mm, you would think that I would have thought of the straight rail focusing mount. Thanks for the answer. Is there a standard formula for shifts in the focusing distances when the lens to film plane distance is increased? I have magnification change tables (ie the 1 1/2 spacer is about 40 mm or 1/2 the lens focal length so my magnification ratio should be about 1:2. I will need the 3.5 inch spacer to get to a true 1:1) What happens to the focal length of the lens is a mystery to me. The focus goes down to about 18". If I go to a 3.5" spacer will the subject to lens "in focus" distance drop again? (ie down to 2"). I know I should know this and I guess I can recon the Macro Sites for an understandable answer, but, sometimes you all seem to "know" the answer that applies to our equipment. thanks for the help.

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

the spacers aren't changing the focal length of the lens, just the distance between the lens and the ground glass.

It would be the same effect as mounting a lens on a recessed board backwards. You gain bellows lenght.

Currently it will focus down to 18" or 457mm. By knowing those two data, I can calculate that the lens to film (image) distance is 97mm.
v=(80x457)/(457-80)

Now your gonna add 3.5" or another 89mm to the bellows or image distance (97mm+89mm=186). So the new object (close focus distance) is a similar formula.

u=(80x186)/(186-80)= 140mm or 5.5"
u=(F•v)/v-F
Where u is the object distance, v is the bellows or image distance to the lens, and F is the focal lenght.

Magnification is image distance (186) / object distance (140) = 1.32:1

[ This Message was edited by: Les on 2003-05-29 14:30 ]