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bull drinkwater · 05-10-2014, 03:12 PM

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?

Adam · 05-10-2014, 03:28 PM

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

**boriscleto** · 05-10-2014, 03:30 PM

1.3x compared to 645 film.

desertscape · 05-10-2014, 03:35 PM

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.

bull drinkwater · 05-10-2014, 05:27 PM

Originally posted by Adam

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

thanks guys that helps a lot, now I can concentrate on how to get real wide angles without spending near $5000.00

revdocjim · 05-12-2014, 04:08 AM

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?

SDK · 05-13-2014, 07:37 PM

There’s the 25mm/4 Pentax DA 645 ultrawide, and that is about $5000 US.

revdocjim · 05-14-2014, 12:16 AM

Read the OP's comment right before mine. The whole point is to not spend $5000.

SDK · 05-14-2014, 07:16 AM

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.

bull drinkwater · 05-14-2014, 02:43 PM

Originally posted by bull drinkwater

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.

revdocjim · 05-14-2014, 06:00 PM

I don't know what quality the screw-on gives but would think that stitching would probably be quite effective.

bull drinkwater · 05-16-2014, 04:29 AM

Originally posted by revdocjim

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.

05-10-2014, 03:12 PM	#1
bull drinkwater Loyal Site Supporter Join Date: Nov 2011 Location: pontiac mi. Posts: 392	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
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,609	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 Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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05-10-2014, 03:30 PM	#3
boriscleto Loyal Site Supporter Join Date: Dec 2009 Location: North Syracuse, NY Photos: Gallery Posts: 16,477	1.3x compared to 645 film.

05-10-2014, 03:35 PM	#4
desertscape Pentaxian Join Date: Feb 2009 Location: Arizona Posts: 1,272	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
bull drinkwater Loyal Site Supporter Join Date: Nov 2011 Location: pontiac mi. Posts: 392 Original Poster	Originally posted by Adam 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 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
revdocjim Veteran Member Join Date: Jan 2011 Location: Mt. Akagi, Gunma Prefecture Posts: 374	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
SDK Inactive Account Join Date: Apr 2014 Posts: 2	There’s the 25mm/4 Pentax DA 645 ultrawide, and that is about $5000 US.

05-14-2014, 12:16 AM	#8
revdocjim Veteran Member Join Date: Jan 2011 Location: Mt. Akagi, Gunma Prefecture Posts: 374	Read the OP's comment right before mine. The whole point is to not spend $5000.

05-14-2014, 07:16 AM	#9
SDK Inactive Account Join Date: Apr 2014 Posts: 2	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
bull drinkwater Loyal Site Supporter Join Date: Nov 2011 Location: pontiac mi. Posts: 392 Original Poster	Originally posted by bull drinkwater 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
revdocjim Veteran Member Join Date: Jan 2011 Location: Mt. Akagi, Gunma Prefecture Posts: 374	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
bull drinkwater Loyal Site Supporter Join Date: Nov 2011 Location: pontiac mi. Posts: 392 Original Poster	Originally posted by revdocjim 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.

a "crop" factor question

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