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Randy
30-Oct-2013, 13:33
I am in the beginning stage of considering building a hyper-focal 5X7 camera around my Caltar II-N 115mm (Grandagon-N) lens. Otherwise, the lens is just going to sit on the shelf since I got rid of my 5X7 camera a while back. I have tried searching the forum and the web, looking for specifics on this lens. I tried to go to the Rodenstock website but couldn't get the page to load up.

Anyway, I guess what I need to know is:

1 - What will be the best f/stop to use on this lens, 22, 32, 45?
I know f/45 will give me the greatest depth of field, but will my images begin to suffer from diffraction?

2 - What will be the near point in acceptable focus?

3 - What distance should the exact focus be set at?

4 - How do I decide the placement of the lens in relation to the film plane for hyper-focal distance?
Do I design the camera so that the lens aperture is a certain distance from the film plane?

I was going to make a 5X7 pinhole camera but then got to thinking that this may give me more of what I want. I have a 5X7 spring back but I may just forgo that as I really don't want to use a dark-cloth and ground glass. I may just make the camera back like some of the pinhole cameras are - wedge and dowels - for holding the film holder in place. I may just mount a viewfinder on top for fast composing.

Would appreciate any thoughts.

Bob Salomon
30-Oct-2013, 13:38
If you want the Rodenstock curves for the 115mm Grandagon-N I can mail them to you. I do not have them electronically.

Randy
30-Oct-2013, 14:05
Bob, what are "curves"?

Jim Jones
30-Oct-2013, 15:55
A quick and rough estimate of the hyperfocal distance for images viewed at the distance to provide correct perspective is 1000 or 2000 times the apparent diameter of the diaphragm as seen through the front of the lens. It depends on how critical the viewer is. For most subjects, f/45 will cause little diffraction limiting.

Bob Salomon
30-Oct-2013, 16:10
Bob, what are "curves"?

MTF, color, distortion curves.

Randy
30-Oct-2013, 16:58
Bob, do you think any of that info will answer my questions above? If so, yes, I would like access to it.

I did find an on-line calculator that allowed me to plug in 5X7 film size, 115mm lens FL, f/45 aperture, and then by changing the focal point until the far focus output just reached infinity, it gave me a near focus of 1.04 meters if I focus the lens at 2.06 meters. Circle of confusion is .15mm. If that is correct, then I just have to put the lens on a camera and focus the lens on an object at 2.06m and then measure the distance from the back of the lens-board to the ground-glass....I think....and that should help me in figuring the camera dimensions....I think. Thoughts?

Drew Bedo
31-Oct-2013, 06:54
There is a wealth of good information available on this forum. The pool of knowledgeable members here is wide and deep.

With that said, I suggest that another approach to your question is to experiment. Why not mount this lens temporarily on a 4x5 or 8x10 camera (coverage is not an issue here) and see what happens when stopping down?

Bob Salomon
31-Oct-2013, 08:06
Bob, do you think any of that info will answer my questions above? If so, yes, I would like access to it.

I did find an on-line calculator that allowed me to plug in 5X7 film size, 115mm lens FL, f/45 aperture, and then by changing the focal point until the far focus output just reached infinity, it gave me a near focus of 1.04 meters if I focus the lens at 2.06 meters. Circle of confusion is .15mm. If that is correct, then I just have to put the lens on a camera and focus the lens on an object at 2.06m and then measure the distance from the back of the lens-board to the ground-glass....I think....and that should help me in figuring the camera dimensions....I think. Thoughts?

Randy,

We are talking two different things here. One is depth of field or maximizing it by focusing at a specific distance at the optimal aperture. That is what you have found.
The other is the optical performance of the lens. How well does it perform, what is its fall off, how much distortion does it have, how accurately does it resolve colors, etc. Those are the graphs that I have. If you would like a set just email me your mailing address and we will mail them to you.

The optimal aperture on the 115mm is diffraction limited at f22. You will have to decide if the diffraction that occurs beyond that is a problem for you or not.

bob@hpmarketingcorp.com

wombat2go
31-Oct-2013, 08:26
Randy, If you can't read this quick hand calculation, I can email it to you.
Hope the camera works out!

Randy
31-Oct-2013, 08:30
Bob, I sent you my address. Thanks.

You will have to decide if the diffraction that occurs beyond that is a problem for you or not.I hate decisions.

Why not mount this lens temporarily on a 4x5 or 8x10 camera (coverage is not an issue here) and see what happens when stopping down?I can do that, as I have the lens mounted to use on my 8x10 camera at present. I just wonder how much I will actually be able to deduce by looking at a 100 year old ground-glass through a loupe when the lens is stopped down to f/22, f/32, f/45...?...but, before I begin construction of the camera I will experiment.

Randy
31-Oct-2013, 08:37
Randy, If you can't read this quick hand calculation, I can email it to you.
Hope the camera works out!Well, I can read it fine, but if you could pretend that I am a 3rd grade child and tell me what all those numbers and letters mean, that might help :) as I honestly don't know how use what you have done to answer my questions.

wombat2go
31-Oct-2013, 08:50
I dunno either !

But it is telling us that if you set the lens to f/22, the hyperfocal distance is about 7 metre
And everything from the near Depth of field of 3.6 metre to infinity should be in focus with a circle of confusion of 1/1500 th of your film height.

To set the hyperfocal focus point, the lens N2 plane has to be 116.88 mm in front of the film plane. That needs to be as accurate as you can get it.

No I don't know the position of N2 of that lens in relation to the physical flange, perhaps Bob has that in a data sheet.

Randy
31-Oct-2013, 09:18
OK. Looks like I will need to put the lens on a camera and do some testing, as drew suggested.

wombat2go
31-Oct-2013, 09:32
Yes, the camera I built was for lenses with a fixed and known register ( Takumar 6 x 7 ) so it was easier.

For moving lenses, better by trial and error, I think. Or use a lens bench to get the approximate position
http://www.surplusshed.com/pages/item/i1483.html