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05-19-2014, 04:36 PM   #16
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Yup! I looked it up as I was writing my previous post and saw that whopping 180 degree FOV. It would be interesting to see what happens if you mounted it on the cropped 645D.

05-19-2014, 06:33 PM   #17
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QuoteOriginally posted by revdocjim Quote
I'm fully aware of the crop factor of the 645D and how it affects the FOV. But if I read your earlier post correctly you said that the 6x7 35mm lens and the 645 35mm lens would give different results on the 645D. And that is the mistake I was trying to point out and correct. A 35mm lens is always a 35mm lens. The only difference between the 6x7 35mm lens and the 645 35mm lens is that the former has a larger image circle and that the former is a fisheye. Of course, depending on what camera the 35mm lens gets attached to and what frame size that camera captures the resulting FOV will be different. So the 645D with it's 44mm x 33mm sensor will crop out a larger percentage of the 6x7 35mm lens than it will when using the 645 35mm lens, but what remains in the captured image will be identical in terms of FOV.

If you want to think about in terms of full frame vs. aps-c, if I attach a Minolta 50/1.4 lens to my A77 camera and take a picture, and then with the help of a mount adapter, attach a medium format 50mm lens such as the Zenza Bronica Zenzanon-S 50/3.5 to the aps-c camera and take a picture, the two pictures will be identical, because a 50mm lens on an aps-c body always yields the same FOV.

Take a look at this table for the actual FOV numbers in degrees. The far left column is the focal length in mm. The subsequent columns show the FOV in degrees for each frame size. According to this chart a 35mm lens on the 645D will yield a FOV of 64.3 degrees. And that is all I am saying. Regardless of whether the lens was originally designed for the 6x7 frame or the 645 frame, or for large format for that matter, it makes absolutely no difference. On a 645D they will all yield 64.3 degrees. I hope this helps.

we are so far on different pages,we may never come close to eachother.as for the difference between aps-c and full frame, using a full frame 100mm lens and a sony a-850, I took one picture in ff mode and one in aps-c mode. the fov was different.. I an baseing my concclusions of the pictures I have actually taken.

---------- Post added 05-19-14 at 09:45 PM ----------

QuoteOriginally posted by texandrews Quote
I also shoot with the A850, and now the A7R. OT, I'd like to hear about your experience contrasting the A850 against the 645D, file -wise.

I never try to compare the two, they are both great cameras. I am happy with the a-850, I just wanted to go medium format and the pentax 645d was my best way to go in both camera and lens cost. I am having a lot of fun with them. when I post my opinions or experiences I get in trouble. maybe i'll spend more time out in the field.
05-19-2014, 07:14 PM   #18
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Yes, that is exactly as it should be. Same lens, different frame size (FF vs. APS-C) yields different FOV as I've been saying all along. In your earlier post you said something completely different though.

Here's the quote.
"from what I've been told, normal for the 645D is 55mm, the 6x7 35mm is 56mm for the 645d. that's normal. the 645 35mm is 44mm for the 645D you have to get down to 20mm or 25mm to really call it wide angle."

The final phrase is accurate. On a 645D you do need something like a 20mm or 25mm to get ultra-wide.
But in the first part, with the attempted application of the crop factor you got your numbers all backwards.
Correct application of the crop factor shows that a 35mm lens on the 645D looks like 55mm on the 6x7 or 45mm on the 645. That gives you an accurate picture of how wide a 35mm lens will be on the 645D if you are accustomed to using 6x7 or 645. And maybe that is in fact what you were trying to say but it just didn't sound or look that way.

A rectilinear 35mm lens will not yield a "normal" FOV as you seem to indicate in this phrase: "normal for the 645D is 55mm, the 6x7 35mm is 56mm for the 645d. that's normal." It will yield a FOV of 64.3 degrees, which isn't ultra-wide but is reasonably wide.

Unless I've said something that is clearly mistaken, I don't think there is anything to really argue or debate and that certainly isn't my intention. And as was pointed out earlier, the whole discussion is confused by the fact that the 6x7 35mm is a fisheye with a 180 degree FOV at infinity on its native mount and I don't really know what the resulting FOV on the 645D would be, other than to say it would probably be somewhat more than 64.3 degrees. But the 645 35mm lens should be exactly 64.3 degrees.
05-19-2014, 07:47 PM   #19
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with the 645d I am also going by frame size. the 6x7 and 645 lenses are matched to different size sensors. the 645d is 44x33mm, the 645 is 56x41.5mm and the 6x7 is 56x70mm. so both lenses should have a similar type crop factor when paired with the 645d sensor. maybe the way I phrased it originally was misleading. I was just surprised that pentax didn't make the sensor the same as the film size.


Last edited by bull drinkwater; 05-19-2014 at 07:52 PM.
05-19-2014, 09:12 PM   #20
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I think they will work fine, I have read a lot on these lenses being a great 645D option.
05-19-2014, 09:59 PM   #21
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QuoteOriginally posted by bull drinkwater Quote
with the 645d I am also going by frame size. the 6x7 and 645 lenses are matched to different size sensors. the 645d is 44x33mm, the 645 is 56x41.5mm and the 6x7 is 56x70mm. so both lenses should have a similar type crop factor when paired with the 645d sensor. maybe the way I phrased it originally was misleading. I was just surprised that pentax didn't make the sensor the same as the film size.
Got it! Stated that way makes it clear that we are in complete agreement! Sorry to be so long-winded in my replies. And I also am one who shares the hope/desire that Pentax will someday release a REAL 645 digital camera instead of the cropped version.
05-20-2014, 01:04 PM   #22
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QuoteOriginally posted by revdocjim Quote
It would be interesting to see what happens if you mounted it on the cropped 645D.
My guess on the FOV of the 35mm Fisheye (P67) used on the 645D is 111 degrees. Very wide indeed. The fisheye needs to be cropped a bit due to soft edges and the 33 X 44 sensor does just that.
05-20-2014, 06:28 PM   #23
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I would love to see a photo from that combination!

05-21-2014, 02:24 AM   #24
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QuoteOriginally posted by desertscape Quote
My guess on the FOV of the 35mm Fisheye (P67) used on the 645D is 111 degrees. Very wide indeed. The fisheye needs to be cropped a bit due to soft edges and the 33 X 44 sensor does just that.
I will be taking my 654d and my 45-85mm plus a 0.5 and a 0.16 screw on lens out for a run soon, I will try to post some photos.
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