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View Full Version : Minimum focusing distance using a 360mm (14") Kodak Commercial Ektar lens



Clement
29-Nov-2003, 08:40
On a 4X5 camera, what is the minimum focusing distance between the camera lens and subject using a 360mm (14") Kodak Commercial Ektar lens?

For example, if I were to make a portrait of someone using a 4X5 camera with a 360mm (14") lens, how close could the subject be to the camera such that the subject would be in focus (excluding DOF issues)?

Dan Fromm
29-Nov-2003, 09:06
How long is your bellows?

Clement
29-Nov-2003, 09:21
Dan, the bellows is 20" long. Thanks,

Ted Harris
29-Nov-2003, 09:47
For a 14" lens you need approximately 14" of bellows extension to focus at infinity. For 1:1 you need about double that. So ...... with your 20" of bellows extension you are going to be limited to working distances of around 15 feet (plus or minus a foot or so without doing the math). As long as you have that much distance you will be ok but you will not be able to get much closer with only 20" of bellows. That will limit you in terms of portrait capability ... you will be able to get a full body portrait at best and not likely to get close enough for a head and shoulders shot or head shot. Sooooo ... in your situation you either want a longer bellows or a shorter lens (240 or 300).

Ted Harris
29-Nov-2003, 09:56
Clement,



having now read both of your posts I have another suggestion as well ... there is nothing like real world experience to lear BUT large format photography is a bit complicated and it wouldn; thurt if you got and read one of the basic books or went through a quick primer on the basics.



The two books that arae sort of standards are Strobel's "View Camera Technique" and Simmons "Using the View Camera" you will also benefit greatly by looking at some of the basic articles on the large format home page http://www.largeformatphotography.info/ or the article you can get at the "View Camera" magazine site ... go here: http://www.viewcamera.com/archives.html and downloade the "getting strted" article.



Good luck

wfwhitaker
29-Nov-2003, 10:01
47 inches

Dan Fromm
29-Nov-2003, 12:00
Clement, ignoring the distance from the back of the bellows to the film, you should be able to work at 0.4:1, i.e., 40% lifesize, with your bellows fully extended. The front nodal point (approximate it very crudely by the diaphragm) to subject distance will be 1.25m. This is about the answer that William Whitaker gave you, but with a little detail added. Since the bellows starts a little in front of the film plane, in practice you'll be able to get a tiny bit closer.

Your 4x5 film's image area is 90 mm x 120 mm, so in portrait mode something 300 mm high will fill the frame. This will do, I think, for head and shoulders.

Cheers,

Dan

p.s., if you have the equipment, you'll learn more by asking it the question than by posting the question on a bulletin board.

Michael S. Briggs
29-Nov-2003, 12:17
The answers the others have given are based on simple equations of geometric optics. One internet source of the equations is David Jacobson's Lens Tutorial at http://www.photo.net/learn/optics/lensTutorial.





With f=14 inches and Si=20 inches, one obtains So=46.7 inches and M = 0.43. Using the equations you can work out other cases. Be sure to use the same units (here, inches) for all quantities.

Ted Harris
30-Nov-2003, 09:08
Whoops! Don't know where my brain was when I typed in 15' of working distance above .... my apologies!



Dan Fromm's comment is perhaps the best in taht you will want to ask the questions of yoru equipment in terms of seeing what working distance, within the ealm of the possible, is comfortable for you and a subject.



If you a particular subject in mind you might also want to see how comfortable he/she is with yoru working distances. Sometimes, some people get very uncomfortable being that close to the camera/lens .... generally this discomfort can be overcome in a very shot period of time but you need to find out ...

Cheers

Clement
30-Nov-2003, 10:37
Thank you, Michael.

Upon reading David Jacobson's Lens Tutorial at http://www.photo.net/learn/optics/lensTutorial, I would say the circle of confusion just got exponentially larger. ;-)

This is however a valuable and ueseful resource. Thanks!