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04-18-2020, 01:47 AM   #16
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Join Date: Mar 2020
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35mm 645 lens

Pepperberry farm

You are right. It is the larger format lens that I am interested in.

stevebrot

The frame diagonal is precisely the crucial factor. I will only find out by testing. If I could temporarily attach the lens to be Pentacon Six, at infinity focussing distance, I would be able to find out. Obviously, for closer focussing, the image circle will be larger.

Some people would dispute your comment that the Pentacon Six mount is a dead mount. Lenses are still being made with this mount, not only for the Pentacon Six and Exakta 66, but also because adapters from the Pentacon Six mount to a wide range of 645 format and 35mm format cameras, both digital and film-based) are so easy to make and so easy to find. For decades, the Pentacon Six was the most-used medium format camera in large sectors of the world.

If I make any progress, I'll report on it here.

Trevor

04-18-2020, 02:19 PM - 1 Like   #17
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Join Date: Aug 2015
Posts: 46
Original Poster
QuoteOriginally posted by TrevorA Quote
Thank you, kypfer, for your suggestion. I will investigate the 35mm Fujinon 1.9 lens for 35mm “full-format” use.

Rob
Thank you for letting me come back to “haunt” you about a post you made five years ago, if I remember correctly. Thank you, also, for all the good, practical tips.

I was not familiar with SK Grimes, and will investigate.

Using this lens on the Sony A7Rii is an interesting bonus for me, but the real aim is to use it on “6×6” (2¼” square) film format, if it adequately covers the format, which is, strictly-speaking, 54mm × 54mm. If it does the job, it would be the widest rectilinear lens for this format and I would be keen to use it principally on a Pentacon Six, if making a suitable mount is possible.
Trevor, I don't think your plan is going to work. The image circle on an SMC Pentax-A 645 35mm f/3.5 lens is nominally 72mm (assuming 58mm x 43mm of film area on the negative). It's actually around 75mm, but the "extra" image circle is poor quality and was never designed to make good images. I know this empirically from shifting the lens on my GFX 50R sensor. I can shift 12mm in portrait orientation (which requires a 75mm image circle), but the far-shifted side of the image is dodgy.


Rob
04-19-2020, 01:24 AM - 1 Like   #18
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Join Date: Mar 2020
Posts: 12
Using a Pentax 645 35mm lens for other formats

Hello Rob

Thank you for this. It is this sort of factual information and the results of tests that I need. Perhaps I should have obtained this before buying the lens!!

As so-called “6x6 format” is not a 6cm × 6cm square, I hope that I may be able to get away with it – always assuming I can get the lens far enough back into the camera to obtain infinity focus!

Hasselblad specified the intended usable dimensions of the film image in “6x6 format” at 54mm × 54mm – even though the image recorded on the film is slightly bigger than this, generally 56mm × 56mm and sometimes a little larger, depending on the camera manufacturer and model.

For a square 54mm × 54mm, the diagonal is a little under 76.4mm, so it might be worth trying – if, as I say, making a suitable mount is possible.

If I am prepared to crop a little off two opposite sides, to create a rectangular image, I might be there. For instance, with a usable area of 54mm × 50mm, the diagonal is fractionally under 73.6mm. Considering the usable area to be 54mm × 48mm, the diagonal is 72.25mm, and for 54mm × 45mm, the diagonal is just under 70.3mm.

I could thus use a Pentacon Six camera to create images in either portrait or landscape orientation – and without needing to turn the camera through 90°.

The manufacturers of shift lenses often specify the limits to shifts, in order to obtain images with acceptable quality into the corners, and some shift lenses for “6x6” cameras specify that beyond a certain amount of shift, 10mm, for instance, a reduced area of the image (for instance, 6 × 45) should be used. See for instance here: Wiese Fototechnik shift & shift/tilt lenses

On the basis of these calculations, I am prepared to explore the possibilities further.

I will report back here, but given the current situation, several weeks may need to pass before I can take the next step!

Thank you again for your help!

Trevor
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