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05-10-2014, 03:12 PM   #1
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a "crop" factor question

I am hoping to get an answer that clears things up for me. I am shooting a 645D. with regular cameras if you put a ff lens on a dx camera you get a 1.5 crop factor most times. with the 645d sensor =44x33mm. the 645=56x41.5mm and the 6x7=56x70mm , what would be the crop factor using a 645 or 6x7 lens on a 645d camera?

05-10-2014, 03:28 PM   #2
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It's 1.27x. See this chart for a field of view reference:

https://www.pentaxforums.com/forums/54-pentax-lens-articles/93714-field-view-...d-645-6x7.html

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05-10-2014, 03:30 PM   #3
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1.3x compared to 645 film.
05-10-2014, 03:35 PM   #4
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For the 6x7 lenses it would be 1.62x if you use the 67 frame size of 55 x 70mm, which it is. The 645D diagonal distance is 55mm; the 67 diagonal is 89mm.

05-10-2014, 05:27 PM   #5
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QuoteOriginally posted by Adam Quote
thanks guys that helps a lot, now I can concentrate on how to get real wide angles without spending near $5000.00
05-12-2014, 04:08 AM   #6
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Are you looking for something wider than 35mm? I guess it would have to be a third party lens and adapter of some sort. But are such things available cheaply, considering that it would have to be a medium format lens to avoid vignetting?
05-13-2014, 07:37 PM   #7
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There’s the 25mm/4 Pentax DA 645 ultrawide, and that is about $5000 US.
05-14-2014, 12:16 AM   #8
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Read the OP's comment right before mine. The whole point is to not spend $5000.

05-14-2014, 07:16 AM   #9
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I don’t think it’s possible to get anything worthwhile, and compatible with the Pentax 645 family, that's wider than the available 33-55mm or 35mm, for less than you would spend on the 25mm/4, unfortunately. Concentrate on saving your money I guess.
05-14-2014, 02:43 PM   #10
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QuoteOriginally posted by bull drinkwater Quote
thanks guys that helps a lot, now I can concentrate on how to get real wide angles without spending near $5000.00
even the 35mm 645 doesn't seem to be that wide on a 645D. to avoid the $5000.00 route, I am using a 0.16 and a 0.05 screw on lens on my 45-85mm zoom. I got a few that were ok so far. I am going to devote a session to do more research. another route on stationary objects I to use the 45mm f2.8 and stitch 3-5 shots together.
05-14-2014, 06:00 PM   #11
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I don't know what quality the screw-on gives but would think that stitching would probably be quite effective.
05-16-2014, 04:29 AM   #12
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QuoteOriginally posted by revdocjim Quote
I don't know what quality the screw-on gives but would think that stitching would probably be quite effective.


you are right , stitching is better. I have done a number of panoramas even in hdr with good results. the blessing is that it is hard to find a bad 645, or 6x7 lens.
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