645D is a 1.3x crop from 645 format? do FA lenses work?

kmccanta · Aug 24, 2006

I suppose this is a stupid question, but if the new medium format digital is also a cropped sensor format, then is it really a "full-frame" camera?

if so, why the huge mirror box etc? Can we use FA, D-FA and old 645 (and 6x7 w/adapter) lenses?

Will the mount be KAF3? or the 645 mount?

*isteve · Aug 24, 2006

Put it this way - its a lot bigger than a compromised full frame 35mm sensor with better resolution.
--
Steve
Measurebating makes you short sighted.
http://www.pbase.com/steve_jacob

Lance B · Aug 24, 2006

kmccanta said:
I suppose this is a stupid question, but if the new medium format
digital is also a cropped sensor format, then is it really a
"full-frame" camera?

FF refers to whether it is FF for the particular lenses that that the particular format uses. So, FF for 35mm lenses means that a digital sensor needs to be the same size as film or 36mm x 24mm and similarly, FF for 645 lenses would mean that the sensor needs to be 60mm x 45mm.

So, if the 645D sensor is a 1.3x crop of the film 645(60mm x 45mm), then the 645 sensor @ 46mm x 35mm is still bigger than 35mm film @ 36mm x 24mm.

Therefore you could not use the any of the film 35mm lenses on a 645D without significant vignetting.

kmccanta said:
if so, why the huge mirror box etc? Can we use FA, D-FA and old
645 (and 6x7 w/adapter) lenses?

The huge mirror box of the 645D is used due to the size of the digital sensor being 46mm x 35mm and not like the relatively small sensor of the APS C sized DSLR's or even 35mm film for that matter.

kmccanta said:
Will the mount be KAF3? or the 645 mount?

It will be the 645 mount, UNLESS Pentax decide to make lenses specially for the 645D system, which I doubt.

--
Lance B

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GMT +10hours

Robert Chow · Aug 24, 2006

----
rc

Lance B · Aug 24, 2006

My sources say the sensor is 48mm x 36mm.

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Lance B

http://www.pbase.com/lance_b
GMT +10hours

Robert Chow · Aug 24, 2006

Lance B said:
My sources say the sensor is 48mm x 36mm.

I still want one. ;^)

Roland Mabo · Aug 24, 2006

The 645D is a "medium format digital" and as such it uses a larger sensor than 35mm full frame, so lenses for Pentax 35mm system will not work - they're too small.

The lens mount will be the 645 AF mount and current FA lenses for the 645 will work fine (yes, the lenses for the medium format system is also called 'FA', but they can't be used on 35mm system without adapter).

Take care
R

James O'Neill · Aug 25, 2006

Roland Mabo said:
The 645D is a "medium format digital" and as such it uses a larger
sensor than 35mm full frame, so lenses for Pentax 35mm system will
not work - they're too small.

Also because the 645 mirror box is bigger you'd get a similar effect to adding extension tubes to the 35mm lenses - they would be able to do great macros but wouldn't be able to focus anywhere near infinity. In fact the extra distance would enlarge the image circle - possibly enough to reach the edges of a medium format "part frame" Sensor.

Full frame is really just a question of does the sensor go all the way across the mirror box. 35MM full frame is smaller than Medium format "part frame".

justin23 · Aug 25, 2006

I think we'd all like one. I'm sure it will be the cheapest medium format digital available, but i'm also sure it will have a hefty price tag...

Of course if they got it to a price to compete with the Canon 1D price then maybe thats how pentax plans to tackle the top end Canons....

phenri · Aug 25, 2006

That's still twice the size of a "FF" 24x36.

JensR · Aug 25, 2006

Hi Lance!

Lance B said:
The huge mirror box of the 645D is used due to the size of the
digital sensor being 46mm x 35mm and not like the relatively small
sensor of the APS C sized DSLR's or even 35mm film for that matter.

Well, because the 645 film format is so large, the camera needs a large mirror. A large mirror needs a large mirror box. A large mirror box causes a large registration distance. Now, even if the digital sensor is smaller (and thereby the mirror is smaller, too), it still makes sense to keep the registration distance intact. Adapting the mirror box for the smaller mirror would shave off a few millimeters off the registration distance, which would still be too long for small format (135 film) lenses.

Cheers
Jens

--

'Well, 'Zooming with your feet' is usually a stupid thing as zoom rings are designed for hands.' (Me, 2006)
http://www.jensroesner.de/

D W · Aug 25, 2006

1. The mount is the Pentax 645 AF mount. All 645 lens will mount and function as the lens is designed to with the exception of differnt FOV. 67 lens with the adapter will work as well.

2. Sensor size 48X36mm. Nothing more about 18mp or 22mp.

3. Only one new lens announced so far P645-DFA 55/2.8. There was a manual focus 55/2.8 but Pentax did not upgrade this lens and produces an AF version. Most likely it is the same lens design.

4. There are new wide lenses in the works. Nothing as to how wide is known outside the lab.

DW
Professional P645/N user for 20yrs

--
Retired commercial photog - enjoying shooting for myself again.
Hoping to see/shoot as much as I can before the eyes and legs gives way

Lance B · Aug 25, 2006

JensR said:
JensR said:

The huge mirror box of the 645D is used due to the size of the
digital sensor being 46mm x 35mm and not like the relatively small
sensor of the APS C sized DSLR's or even 35mm film for that matter.

Click to expand...

Well, because the 645 film format is so large, the camera needs a
large mirror. A large mirror needs a large mirror box. A large
mirror box causes a large registration distance. Now, even if the
digital sensor is smaller (and thereby the mirror is smaller, too),
it still makes sense to keep the registration distance intact.
Adapting the mirror box for the smaller mirror would shave off a
few millimeters off the registration distance, which would still be
too long for small format (135 film) lenses.

Yes, I realise about the requirement of a large mirror and pentaprism, but I didn't bother to mention the registration distance as I thought all of the above would have been taken for granted and understood.

JensR said:
Cheers
Jens

--
'Well, 'Zooming with your feet' is usually a stupid thing as zoom
rings are designed for hands.' (Me, 2006)
http://www.jensroesner.de/

--
Lance B

http://www.pbase.com/lance_b
GMT +10hours

RevRat · Aug 25, 2006

48x36 is 57.6mm corner to corner.
60x45 is 75mm corner to corner.
75/57.6=1.3.

Greg Erker · Aug 25, 2006

Regarding #3: they may have tweaked the design or coating if the old one was prone to flare due to the sensor being more shiny than film.

Greg

Greg Erker · Aug 25, 2006

I have a bunch of medium format 6x6 cameras and the film gates are about 55x55 or 56x56mm. I don't have any 645s so I can't measure them so I googled.

On this page it appears 645 size is 56x42mm ( http://medfmt.8k.com/mf/formats.html and search for 41.500 on the page).

So the crop factor will come out different if you use these numbers.

Do we know the actual sensor size Pentax is using?

Thanks - Greg

Greg Lovern · Aug 25, 2006

RevRat said:
48x36 is 57.6mm corner to corner.
60x45 is 75mm corner to corner.
75/57.6=1.3.

According to the Pythagorean theorem, 48 x 36 would be 60mm corner to corner:

(48 * 48) + (36 * 36) = (60 * 60)

75 / 60 = 1.25 crop factor.

Greg

Greg Lovern · Aug 25, 2006

Greg Erker said:
On this page it appears 645 size is 56x42mm
( http://medfmt.8k.com/mf/formats.html and search for 41.500 on the
page).

Thanks for the link.

56 x 42 is 70mm corner to corner:

(56 * 56) + (42 * 42) = (70 * 70)

That would make the crop factor only 1.07:

75 / 70 = 1.07

But wait, there's more interesting information at that link:

Greg Erker said:
Don't forget that there is usually some cropping when you splash the image on the paper easel, unless you are a fanatic, it would be difficult to get the entire image on the paper without getting a bit of black edge.

So, the "60 x 45" film frame is really only 56 x 42, and some of that is virtually always of necessity cropped when making a print. Sounds to me like for all practical purposes, the 645D's useable image will be AT LEAST AS LARGE as 645 film's useable image. Here's hoping the legacy 645 glass doesn't vignette on the 645D! ;-) But even if it does, no worries, because you can always use your legacy 6x7 glass on your 645D.

Greg

Greg Erker · Aug 25, 2006

Less than a 1.1x crop factor is pretty darn good.

Has Pentax officially stated the sensor size?

Greg E.

Robert Chow · Aug 26, 2006

Greg Lovern said:
RevRat said:

48x36 is 57.6mm corner to corner.
60x45 is 75mm corner to corner.
75/57.6=1.3.

Click to expand...

According to the Pythagorean theorem, 48 x 36 would be 60mm corner
to corner:

(48 * 48) + (36 * 36) = (60 * 60)

75 / 60 = 1.25 crop factor.

Greg

Hookay,

I get a crop factor of 1.21 based on the info that sensor size will be 46 x 35 for 645D and film size being 56 x 42:

645D: (46 * 46) + (35 * 35) = (57.8 * 57.8)

645: (56 * 56) + (42 * 42) = (70 * 70)

Crop factor: 70/57.8 = 1.21

Therefore, the information for the 645D's sensor size is consistent with the February(?) announcement about the 645D's crop size. I'd say that 1.2 crop ain't too shabby.

645D is a 1.3x crop from 645 format? do FA lenses work?

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