Maximum practical aperture for nikkor 90mm f8 SW on 6x9 fomat??

[JDP]

Hello All,
I have a rather obscure question regarding the nikkor 90mm f8 SW. Currently I have a Rodenstock Grandagon 90mm f4.5 which I use on a Fotoman 6x9. This lens has a large curvature of field meaning it needs to be stopped down f16 or smaller to get a sharp image, even at 6x9, and this does not always suit my shooting style (particularly for night shots). I have calibrated the focus, in case you are wondering. My other Grandagons (65 & 45mm I use at f8 and get great results).

So my question to anyone in the know is, would changing to the Nikkor 90mm f8 SW lens (which seems to have a rather good reputation re sharpness, and a smaller curvature of field) allow me to shoot at wider apertures - preferably at f8 on the 6x9 format?

Any comments much appreciated.

[Dan Fromm]

Something isn't right here. You're shooting 6x9 straight ahead -- if I'm mistaken in believing that your Fotoman has no movements, please correct me -- with a lens that covers 5x7 and that, according to Rodenstock's propaganda is pretty good centrally and you have bad curvature of field problems. This calls for having the lens and focusing mount checked not, not fobbing it off on the next victim and replacing it.

[ic-racer]

I agree with what Dan posted. It seems odd to have those issues. One thought is that the lens spacing is off. I can get pretty good edge-to edge focus and sharpness near wide open with the Horseman f5.6 90mm 6x9 (150mm circle) lens on 6x9.

[JDP]

Something isn't right here. You're shooting 6x9 straight ahead -- if I'm mistaken in believing that your Fotoman has no movements, please correct me -- with a lens that covers 5x7 and that, according to Rodenstock's propaganda is pretty good centrally and you have bad curvature of field problems. This calls for having the lens and focusing mount checked not, not fobbing it off on the next victim and replacing it.

According to Rodenstock information the working aperture of the 90mm f4.5 lens is f16-f22, and when used as such it produces very sharp results. Therefore I am not convinced there is a problem with it. Do you use one of these len's, and, if so, what is the max aperture you shoot with??

[Dan Fromm]

The recommended aperture range is needed to get full coverage. You don't need full coverage. The MTF curves given here http://www.rodenstock-photo.com/medi...7-42__8226.pdf are for f/11. They suggest that you should have no problems shooting straight ahead on 6x9 at f/11.

To ask the question again, since I'm not acquainted with Fotoman cameras, does your 6x9 Fotoman allow movements? And does it allow you to put on a ground glass for focusing? If it does, check focus on the ground glass. Its easy to blame a lens in a focusing helical for problems due to its not being collimated to the camera.

I don't have a 90/4.5 Grandagon N, do have a 58/5.6 Grandagon and a 35/4.5 Apo Grandagon. I shoot both on 2x3 Graphics, focus both on the ground glass, shoot the 58 between f/8 to f/16, the 35 between f/5.6 and f/16, don't have your problem with either.

[Barry S]

I've never used the Grandagon, but I have both the Nikkor 90mm SW f/8 and 90mm SW f/4.5 lenses. The 90mm SW f/8 is extremely sharp at f/11, better than most lenses at any aperture. I've only shot it at f/8 a couple of times, so I can't be definitive, but it was still excellent. The 90mm SW f/4.5 is a fine lens and much much easier to focus under dim conditions, but it's not as sharp as the f/8 lens at any similar aperture.

[JDP]

Following the comments above about the performance of my 90mm F4.5 Grandagon I thought I should check the lens to see if there were any obvious problems. It appears there was a problem. The rear element set was seated onto the retaining ring, and not the shutter barrel flange. I found a thinner retaining ring which did not protrude above the shutter barrel flange. With this fitted, and viewing on a ground-glass, there does appear to be a much improved edge-to edge sharpness at all apertures than before, though a curvature of field effect is still clear at f4.5. So I am optomistic of better results in future! (Test film to confirm will be next).

So thanks to all respondees to my querie, its been a real help.

P.S. Dan Fromm : No, my Fotoman does not have movements. I believe there was a version with shift available. Shame they are no longer made.

[Maris]

Field curvature in a large aperture wide angle lens like the Grandagon 90mm f4.5 is critically influenced by the spacing between the front and rear lens groups. Lens design is always a compromise and the two main aberrations, astigmatism and field curvature, are traded off against each other by tweaking the spacing. A fraction of a millimetre error or a missing spacing ring is all it takes to hurt lens performance. That's my guess!

[ruilourosa]

you have a missing spacing ring or a dented screw! i have made 4x5 velvias with my grandagon at 8 and even at 5,6 with excellent sharpness and no curvature of field...