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Thread: Pentax 634Z

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    Pentax 634Z

    Let me preface this thread with: So Thanksgiving has just past, enjoyable weekend and it's a lazy Sunday afternoon...

    So the Pentax 645Z has a 51.4MP CMOS Sensor - 43.8 x 32.8 mm, so why is it not called a P634Z. I'm sure the camera merits a lot in the Digital Medium Format world, and I'm sure calling it a 645 bothers absolutely no one, 'including myself!'

    Yup, I know crop sensors and the 645D before the Z have smaller sensors than the IQ180/280 (53.7 x 40.4 mm) for example, but PhaseOne have not stuck the well know 645 on their camera backs, just simply the IQ series.

    However, why not call it for what it is. Hence in 135 world, why not call all APS-C full frame then!

    So why am I bringing it up? Well, I find it rather amusing and only really paid attention to it more recently since I also find it a rather desirable camera to eventually have, as soon as the leaf shutters come!

    In the meantime, I'm waiting for my Fujifilm GA 645 to arrive!
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    Re: Pentax 634Z

    Because that is the product line Pentax has used and kept the name for branding. It also can use the lenses for that product line and the lenses are branded 645.

    Why do people can 35mm-size sensors "full frame" when every camera is full frame? There was nothing special about 35mm and other formats were not made in reference to that.

    But if you want to be precise, a Rollei SL66 should be a Rollei SL5656. And you GA is not 6x4.5, but something smaller.

    And follow your "logic," you would be wrong in the naming. It should be a Pentax 4535Z. I am sure that would be less confusing for customers...

    Also, the 645Z is not a crop sensor. It is a full 43.8x32.8mm sensor.
    Last edited by Shashin; 30th November 2014 at 14:30.
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    Subscriber and Workshop Member MGrayson's Avatar
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    Re: Pentax 634Z

    And try to work out why a 1" sensor is so named. Forget diagonal, its height PLUS its width add up to less than 1".

    --Matt

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    Re: Pentax 634Z

    The sensor might not be 645 size but the body is, well at least the lens mount and flange focal distance is identical to Pentax 645 film bodies. That is why one can use old Pentax 645 lenses on the 645D and the 645Z.

    I think of the medium format SLR solutions only the Leica S is designed specifically for its digital format and hence takes advantage of the smaller than 645 film sensor by having a smaller and lighter body with a shorter flange focal distance (which makes it very easy to adapt all other medium format lenses)
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    Re: Pentax 634Z

    Quote Originally Posted by MGrayson View Post
    And try to work out why a 1" sensor is so named. Forget diagonal, its height PLUS its width add up to less than 1".

    --Matt
    Particularly small sensors started life in video cameras, and so they use video camera based sizing convention for sensor area, which itself stems all the way from the days when cameras used cathode ray tubes to capture images and the tube diameter was measured. Obviously the area captured by the tube was smaller than it's outer diameter, so there was a formula for figuring out how large the actual imaging area was, and for some reason this archaic system is still in use.

    Quote Originally Posted by Ken_R View Post
    The sensor might not be 645 size but the body is, well at least the lens mount and flange focal distance is identical to Pentax 645 film bodies. That is why one can use old Pentax 645 lenses on the 645D and the 645Z.

    I think of the medium format SLR solutions only the Leica S is designed specifically for its digital format and hence takes advantage of the smaller than 645 film sensor by having a smaller and lighter body with a shorter flange focal distance (which makes it very easy to adapt all other medium format lenses)
    Two of the new Pentax lenses, the 25mm and 28-45mm have image circles that I believe only cover the 33x44 format, while the 55mm and 90mm cover full format 645 as tested by film users, so it's hard to say what Pentax's strategy for the future is, but at least there is room to grow. Even so, this doesn't stop me from wanting that 28-45...

    It also didn't stop me from becoming a 645Z owner either, so I guess I'm finally together in hell with you guys. Whatever the sensor size, this camera is just all kinds of awesome.
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    Re: Pentax 634Z

    Quote Originally Posted by Kolor-Pikker View Post
    Two of the new Pentax lenses, the 25mm and 28-45mm have image circles that I believe only cover the 33x44 format, while the 55mm and 90mm cover full format 645 as tested by film users, so it's hard to say what Pentax's strategy for the future is, but at least there is room to grow. Even so, this doesn't stop me from wanting that 28-45...
    Actually, there are two versions of 25mm lens: DFA 645 25mm/4 and DA 645 25mm/4. According to Pentax, the only difference is the hood.

    I have the DFA 25mm and it's perfect on 645Nii. So the image circle does cover 645 "full frame“ of 56*42mm.

    I don't know about the new 28-45mm though.

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    Re: Pentax 634Z

    Quote Originally Posted by laopai View Post
    Actually, there are two versions of 25mm lens: DFA 645 25mm/4 and DA 645 25mm/4. According to Pentax, the only difference is the hood.

    I have the DFA 25mm and it's perfect on 645Nii. So the image circle does cover 645 "full frameď of 56*42mm.

    I don't know about the new 28-45mm though.
    Ok, I didn't know that, so it's good to know... there might be some bit of misinformation out there.

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    Senior Member Ed Hurst's Avatar
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    Re: Pentax 634Z

    My understanding is that the original 25mm f4 DFA - which covered full frame 645 - was found to have a little more fringing that such an expensive lens should (in some situations, principally shooting into the light), so the 25mm f4 DA version was produced which has a longer hood (and, according to some sources, other minor differences to internal baffles, etc.) - and as a result only covers the crop sensor of the 645D and 645Z. For a time, both were available side-by-side (presumably due to stocks already existing of the first version), especially in Japan where there are still lots of 645 film users, who need the first (full frame) version. But the more recent version is effectively there to remedy issues with the lens and is aimed at digital users.

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