Testing coverage of lenses

[r.e.]

I want to test two lenses for 8x10 coverage (which requires an image circle of about 315mm) at various magnifications and f stops.

The lenses are:

Nikkor 120mm AM ED f/5.6 (specs say 250mm at f/22 at 1:1)

Doctor/Docter Tessar f/4.5 210mm (specs say 250mm at f/22 at infinity, although Arne Croell has suggested that the real number may be 219mm)

I have already done some quick checks through the ground glass, but I would like to do a series of 8x10 photographs that will tell me exactly how these lenses are behaving, not just at f/22 but at larger apertures.

This will require fairly high magnification. About 2:1 for the Nikkor at f/22, not sure yet about the Doctor because my checks on it through an 8x10 ground glass have been cursory. But the latter, at f/22, is probably somewhere between 1:3 to 1:2.

I'm looking for suggestions on what kind of subject I should use to carry out these tests. Will it confuse things too much if I use a three dimensional object and, if not, what kind of object would be best? I'm interested in three dimensional objects because I'd like to see the concrete results for apparent depth of field as well.

[vinny]

depth of field? what depth of field?
I've shot some 8x10 with the 120 nikkor with good results as contact prints. Not 2:1 though, that's frickin' close and doesn't leave much room to work.

oh, you can use newsprint for the tests.

[r.e.]

Vinny,

Yes, for the Nikkor at 2:1 it's about 7 inches/18cm. At what distance/aperture were you getting coverage, or we're you vignetting and OK with it?

Got a kick out of your line: What depth of field? :)

[Jim Jones]

Lens testing can become complex, and requires careful technique. Vinny's suggextion of using newsprint may be suitable for your application. The 1951 USAF resolution chart is a favorite for determining resolution in line pairs/mm. This lets you compare different lenses and center to edge sharpness. You might find copies on a google search. The below chart can be replicated and printed out at original size (from DPI) to avoid introducing artifacts. If your test is for comparison only, the LP/mm data isn't needed.

[E. von Hoegh]

Vinny,

Yes, for the Nikkor at 2:1 it's about 7 inches/18cm. At what distance/aperture were you getting coverage, or we're you vignetting and OK with it?

Got a kick out of your line: What depth of field? :)

You do know that testing the lens at 2:1 will give a larger than infinity image circle, right? Meaning that they may both be quite useable at that ratio.

[r.e.]

You do know that testing the lens at 2:1 will give a larger than infinity image circle, right? Meaning that they may both be quite useable at that ratio.

Yes, thanks, I understand that. The Nikkor will definitely cover at 2:1. My question to Vinny was how much short of 2:1 on the Nikkor he was getting coverage without vignetting, and at what f-stop.

[r.e.]

Lens testing can become complex, and requires careful technique. Vinny's suggextion of using newsprint may be suitable for your application. The 1951 USAF resolution chart is a favorite for determining resolution in line pairs/mm. This lets you compare different lenses and center to edge sharpness. You might find copies on a google search. The below chart can be replicated and printed out at original size (from DPI) to avoid introducing artifacts. If your test is for comparison only, the LP/mm data isn't needed.

Thanks Jim.

[ic-racer]

If you are studying vignetting, then I'd photograph a uniform target like the sky or a white card. If you are determining the falloff of resolution as a function of the distance from the optical center then I'd just go with the manufacturer's specs; they already did it for you.