[MrA]

Can someone with more knowledge of the mathematics behind optics clear something up for me. There are adaptors on the market accepting medium format lenses (e.g pentacon six), which fit cameras with a more current mount e.g pentax k. Companies like arsat make shift adaptors, for instance, which do this.

If one uses such a setup, are there any issues with focal lengths / lenses not reaching infinity, which are immediately going to be encountered, or does the existance of the product imply it will more or less "just work" if you attach one to the other?

I understand that lenses expect to focus on the sensor, which clearly would be in a different (but known) position for a mf camera to a aps-c setup.

I know that people have "made" their own shift lenses using bellow-contraptions, but that all seems a bit involved if there is an easier solution.

I'd also be interested to know what happens to the angle-of view if you use (say) a wide angle mf lens (say 40mm) on an aps-c system - presumably it performs like a 40mm lens on an aps-c, ie a fairly normal length lens.

[Groundloop]

Can someone with more knowledge of the mathematics behind optics clear something up for me. There are adaptors on the market accepting medium format lenses (e.g pentacon six), which fit cameras with a more current mount e.g pentax k. Companies like arsat make shift adaptors, for instance, which do this.

If one uses such a setup, are there any issues with focal lengths / lenses not reaching infinity, which are immediately going to be encountered, or does the existance of the product imply it will more or less "just work" if you attach one to the other?

I understand that lenses expect to focus on the sensor, which clearly would be in a different (but known) position for a mf camera to a aps-c setup.

There can be issues, if the adapter isn't made correctly. Your best bet is to check the FAQ of the manufacturers website (if there is one), or email/phone them to find out if they allow infinity focus. If never used them, but I would assume that the Pentax adapters for the 645 and 67 lenses would allow infinity focus.

I'd also be interested to know what happens to the angle-of view if you use (say) a wide angle mf lens (say 40mm) on an aps-c system - presumably it performs like a 40mm lens on an aps-c, ie a fairly normal length lens.

Terms like wide angle, tele and normal are only relevant to a particular format, so a 40mm lens is a 40mm lens is a...etc. The angle of view that gets recorded is dependent on the sensor or film size. For example, a 300mm lens is normal on an 8x10, short tele on a 4x5, mid tele on a 6x7, long tele on a 35mm, and extreme tele on an APS-C sensor. It helps to visualize an image on an 8x10 ground glass, and then masking the ground glass with black paper that has windows corresponding to other format sizes cut out of the centre. Nothing about the lens or it's characteristics is changing. The only change is the angle of view, which is caused by the size of the "window" you're looking through.

One thing to be aware of though. Medium and large format lenses resolve less detail than lenses designed for APS-C are capable of, but they retain more detail when printed because they don't have to be enlarged as much.

[Ole]

Can someone with more knowledge of the mathematics behind optics clear something up for me. There are adaptors on the market accepting medium format lenses (e.g pentacon six), which fit cameras with a more current mount e.g pentax k. Companies like arsat make shift adaptors, for instance, which do this.

If one uses such a setup, are there any issues with focal lengths / lenses not reaching infinity, which are immediately going to be encountered, or does the existance of the product imply it will more or less "just work" if you attach one to the other?

An adapter for a medium format lens will in all likelihood allow for infinity focus. It's only an issue with 35mm lenses, where one brand may be designed for a different distance from mount to sensor than the other brand, and/or there isn't "room enough" for the adaptor without moving the lens too far out from the body.

With medium format lenses there is plenty of room for the adapter.

The Pentax 645 and 67 to k-mount adapters allow for infinity focus. I have both and can testify to that.

[Abbazz]

Nothing about the lens or it's characteristics is changing. The only change is the angle of view, which is caused by the size of the "window" you're looking through.

Of course, but lenses designed for large format need to have much more covering power than those designed for crop format DSLRs. The 50mm lens on my Fuji G690 camera is a large beast that only goes to F5.6, but it's a superwide angle lens covering an angle of 91° on 6x9 format. On a crop format camera, it would be a rather uninteresting portrait lens with a max aperture of F/5.6. These are the main drawbacks of medium format lenses when used on DSLRs: the lenses are bulky and have a modest maximum aperture, compared to lenses designed specially for the smaller format.

One thing to be aware of though. Medium and large format lenses resolve less detail than lenses designed for APS-C are capable of, but they retain more detail when printed because they don't have to be enlarged as much.

Medium and large format lenses do not necessarily resolve less detail than smaller format lenses. Many medium format lenses outperform consumer grade zooms designed for crop cameras...

Cheers!

Abbazz

[Abbazz]

There are adaptors on the market accepting medium format lenses (e.g pentacon six), which fit cameras with a more current mount e.g pentax k. Companies like arsat make shift adaptors, for instance, which do this.

Arax also makes a very interesting tilt adapter.

If one uses such a setup, are there any issues with focal lengths / lenses not reaching infinity, which are immediately going to be encountered, or does the existance of the product imply it will more or less "just work" if you attach one to the other?

I have both adapters (shift and tilt) and there is no problem with infinity focusing whatsoever. I have posted some pictures taken at infinity with a Vega-12 90/2.8 lens mounted on a tilt adapter here on a previous thread.

I'd also be interested to know what happens to the angle-of view if you use (say) a wide angle mf lens (say 40mm) on an aps-c system - presumably it performs like a 40mm lens on an aps-c, ie a fairly normal length lens.

Yes, as stated by Groundloop, the focal length remains the same when you switch from medium format to APS-C. Only the field of view changes. The Vega-12 90mm lens is a normal lens on a 6x6 camera, offering the same field of view as a 50mm lens on a 24x36 camera. When mounted on a crop format camera, the lens will have a much narrower field of view, due to the small image sensor. Its field of view becomes the same as a 135mm on a 24x36 camera, which corresponds to a small telephoto lens. But the lens is still a 90mm lens, with the depth of field of a 90mm lens.

Cheers!

Abbazz

[Groundloop]

Medium and large format lenses do not necessarily resolve less detail than smaller format lenses. Many medium format lenses outperform consumer grade zooms designed for crop cameras...

Cheers!

Abbazz

Well, I did say "capable of", not "all lenses designed for APS-C are sharper than all medium and large format lenses". I left out the all important "All things being equal" that would have implied an apples to slightly different apples comparison.

[MrA]

Thanks, as ever, for the replies.

Arax also makes a very interesting tilt adapter.
I have both adapters (shift and tilt) and there is no problem with infinity focusing whatsoever. I have posted some pictures taken at infinity with a Vega-12 90/2.8 lens mounted on a tilt adapter here on a previous thread.

I was pondering the tilt adaptor, actually, yes, although being an architecture student the shift one has an obvious appeal. But I'm more interested in the creative potential than simple PC work, so I think the tilt might be the way to go.

Just a case of getting hold of a respectable lens. The MF lenses seem to go for quite wild prices sometimes on ebay, yet sometimes not. Not sure if I could be lucky and pick up a 50mm or 65mm or something. Also noted that Arsat did a 30mm fisheye. Wonder how a tilted fisheye lens cropped to aps-c would turn out...!

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Last edited by MrA; 05-11-2008 at 02:04 PM.

[Abbazz]

Not sure if I could be lucky and pick up a 50mm or 65mm or something. Also noted that Arsat did a 30mm fisheye. Wonder how a tilted fisheye lens cropped to aps-c would turn out...!

For tilt work, I recommend the Vega-12 90/2.8 lens. It's available for cheap (Arax has new old stock lenses for $69) and the image quality is quite good. For architecture shots with the shift adapter, the Flektogon 50/4 would be more suitable and it's a very good lens available for less than $100 (a bit more for the last multicoated version). I have heard that the Mir-26 45/3.5 was not as good, but I have never tried it. The widest of the bunch is the Zodiak-8 30/3.5, which is a fisheye, thus normally not very suitable for architecture work, but the fisheye effect shouldn't be too pronounced on a crop format camera and straightening the lines in Photoshop should be pretty easy.

Cheers!

Abbazz