Pentax 6x7 Lenses on 645n

I have been shooting 6x7 for a while now but really miss the ratio of 35mm. I picked up a Pentax 645n and adapter to use my Pentax 6x7 lenses. I shot a few rolls using the 105mm and I don't know exactly how to explain it but the images don't "look right". A more experienced shooter at the darkroom said that even thought the 6x7 lenses work they were not meant for the 645 and so they would not create proper images. He mentioned that they did not compress the image correctly for the format.

Could anyone elaborate on this or explain the science behind it.

Should I bother trying my 55mm or just bite the bullet and buy a 645 lens?

I'd be interested in comments on this. And what was meant by "compress" the image correctly for the format....?

The compression comment is confusing to me. All the adapter does is get the registration. distance right the image should be in effect a crop due to the smaller negative size. Relating it to 35mm terms it would compare to a 68mm lens an odd size.One question is it a actual pentax adapter or a third party item.If you have a spare roll of film you might try the 55mm since the 645 has a 55mm it should give a crop from 6x7 but look normal.I'm unsure what doesn't look right means . Is it more or less contrasty out of focus not centered like you thought it would be?

It seems as though you would get a "better" quality image,as you are not using the outside perimeter of the lens as you would on 6x7.I have made images on a 4x5 camera with a 6x7 back and the images seemed to get the best out of the lens for the same reason.

A couple of questions and comments.

Pentax 6x7 lenses are designed to cover a larger frame than 6x4.5. So when you mount a lens designed for 6x7 on the 645N, the camera and film will only make use of the centre of that coverage.

That centred part of the coverage will expose the film in the 645N in the exact same way as it will expose an identical portion of the film in the 6x7 camera. It is just that the 6x7 camera will have additional exposed film outside that centre area.

When it comes to field of view and depth of field a 55mm lens designed for the Pentax 6x7 will give you essentially the same results on film on the 645N as a 55mm lens designed for the 645N. The lenses will differ as to size, and may differ as to maximum and minimum aperture. They also may differ as to sharpness and resolution and contrast and colour response - depends on the individual lenses.

Neither series of lenses "compress" the images. They just cover the angle of view that they cover, depending on which format they are used on.

By the way, the 6x7 has a different aspect ratio to the 6x4.5, and both are quite different from the aspect ratio obtained with 35mm film. Maybe that is what was (somewhat confusingly) meant by "compressing" the images.

105mm is 105mm is 105mm. The size of the film doesn't matter. If you're using it on a 6x7, it's a normal, on a 645 it's a short tele.
The only thing that I can think of (besides the aforementioned 'aspect ratio' theory) is that by 'compressing' they're talking about the different lengths in this way, ie on 35mm a 105mm gives a lot more 'field compression' because it's a 'longer' field of view (whereas on 4x5" a 105mm gives a very wide 'uncompressed' ratio).

Either way, the 105/2.4 makes a beautiful portrait lens on 645, this one shot from across the table (on a Mamiya 645, but same as using it on a Pentax 645). On EPP, and desaturated a bit after scanning because the faces were a bit red.

Heck, I even use P67 lenses with a Nikon adapter sometimes. But everything depends on the specific lens and application. For some applications, certain 6x7 lenses are reputed to work better on the 645 than the original 645 lenses.

Glad I'm not the only one confused about the compression comment.

Adapter is fotodiox but meant for this specific application. Edit No glass elements.

Best way I can explain the images is that they look a bit stretched out/fuzzy

The images were C prints from fuji400H negitives. I did it myself so I checked all the equipment with known good negs and used negs from different rolls.

For 645 format, I think the lens would function at 68mm. No?

gzhuang said:

For 645 format, I think the lens would function at 68mm. No?

Click to expand...

Please don't start with me!

I don't think you can tell without seeing the print but since folks are asking here is a picture.