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RichS · Posted: Fri Feb 25, 2005 4:03 am Post subject:

I was running some lens tests today. Focusing on a wire fence about 250 feet away. This turned out to be perfect as I could see the difference in resolving power between various lenses on the GG.

Then this question came to me... If the 1/8 inch wire is just barely resolvable on the GG at 250 feet, that must equate to a calculable resolution? Anyone know how?

And a side thought. If the wire is 1/8 inch, and at a bellows draw of twice the focal length it is also 1/8 inch on the GG, what size is on the GG when bellows and focal length are equal (infinity setting)?

And if these questions are either easily answered, obvious, stupid, or make no sense at all... Well, I'm under the influence of drugs for a bad tooth and less than half of my brain is working... In this state, these are interesting questions that I can't answer...

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"Ya just can't have too many GVIIs"

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shootist · Joined: 05 Nov 2002 Posts: 14 Location: Pocono Mts. PA

Rich, Go to Norman Koren's website. Scroll down and find the section "lens testing".
Download and print the 5mm frequency based test chart,on photo paper at high res.You can inpect the images with a loop,stereo microscope or project through an enlarger and use a grain focusser. You will get actual resolution numbers in line pairs/mm and you can compare lenses more systematically than the subjective method that you are now using. You can email me if you need any help.
TONY

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

actually you are getting the resolution of the ground glass not the lens.

You'll need to focus on the aerial image of the lens rather than some glass between the lens and you. The easiest is a loupe. Or you can shoot film.

RichS · Posted: Sat Feb 26, 2005 3:27 am Post subject:

Thanks guys...

I already have lens charts if I wanted to do scientific lens testing...

What prompted this was a new lens. I set up and focused using the lens on the camera to simply get it in a good position. Then I switched to the new lens. There was an obvious difference in resolving power. I went from there to mounting several other lenses for the comparison. Which prompted the above questions.

I know that the GG can not resolve what the lens is capable of laying down on the film. But there is an obvious difference on the GG that can be seen with a loupe.

I'm not one who cares in the least what the actual resolving power of any particluar lens may be. Especially mine, considering most of them are over 50 years old ( some 100) and not even the best in their time. It all just seemed like an interesting subject... Maybe not when the drugs wear off?