Minimum focusing distance with Fotoman 45PS and Nikon Nikkor 90 SW f8 ...

[nicemate1]

Hello! I am trying to figure out what would be the minimum focusing distance with this combination of camera, helical focusing system and the Nikkor 90 sw f.8 lens.
I appreciate any sort of help!!!
best regards and thanks to anyone who answers! pietro

[Drew Bedo]

If you already have the kit—why not just screw it all the way out and see?

What is your application. What are you trying to accomplish?

[C. D. Keth]

Here you go:

1/F = 1/S + 1/B

F is focal length. S is subject distance. B is bellows draw. Since you want to know minimum focus distance, B is the maximum bellows draw of your camera.

[Mark MacKenzie]

I really wanted to do the algebra on this but just couldn't. Guess my mind isn't so agile. So I took the inverse.

1/90mm = .01111111111111111111
1/135mm = .0074074074074074074 Assume a bellows draw of 5.3 inches or halfway to 1:1.
1/S = .0037037037037037
S = 270mm or about 10.5 inches

Does this sound right? Then 1:1 subject distance is about 7 inches.

Bear with me and lets try another camera. Say a 360mm lens. Bellows draw of 500mm (about 19".)

1/360 = 1/S + 1/500
.0028 = 1/S + .002
.0008 = 1/S
S = 1250mm or 49 inches

I guess that sounds about right. Thanks for the formula, Christopher.

[Oren Grad]

Fotoman HFM Minimum Focus Distance Table

[C. D. Keth]

S = 270mm or about 10.5 inches

Does this sound right? Then 1:1 subject distance is about 7 inches.

I guess that sounds about right. Thanks for the formula, Christopher.

Yup that sounds right. Solved for S, that equation is S=BF/B-F