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02-10-2014, 01:32 PM   #136
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QuoteOriginally posted by Paul MaudDib Quote
Even with a "crop" format you still have to fit the mirror in there, and that's going to be longer than the flange focal distance of K-mount lenses. The only way it would work is if you designed the body as a mirrorless, and made an adapter to 645. Medium format advances slowly and hasn't gotten the feature set of the newer mirrorless bodies, like phase-detect AF. You could add that back in with a translucent-mirror type adapter like Sony did with the LA-EA4 adapter, but that has disadvantages too. It's a huge engineering problem and really unnecessary when there's piles of old 645 lenses floating around.

It could be done, it just wouldn't be likely with a simple swing arm. It's only 33mm... so 4.5mm longer than a 36*24. Not a ton but certainly enough to have to redesign the mirror-swing mech.

02-10-2014, 02:47 PM   #137
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But Ron, that bright yellow K-01 might introduce a color cast on the scans, whereas the 645D's body is pleasingly neutral. I mean, a lady could wear a basic black dress to the White House, but bright yellow?
02-10-2014, 02:54 PM   #138
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QuoteOriginally posted by jon404 Quote
But Ron, that bright yellow K-01 might introduce a color cast on the scans, whereas the 645D's body is pleasingly neutral. I mean, a lady could wear a basic black dress to the White House, but bright yellow?


02-10-2014, 03:31 PM   #139
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QuoteOriginally posted by ElJamoquio Quote
It could be done, it just wouldn't be likely with a simple swing arm. It's only 33mm... so 4.5mm longer than a 36*24. Not a ton but certainly enough to have to redesign the mirror-swing mech.
K-mount register distance is 45.45mm, Pentax 645 register distance is 70.87mm. So the lens would need to protrude 25.42mm into the mirror box (impossible) or you need to get rid of the mirror box, that's all there is to it (if you want the camera to focus at infinity).

In the latter case you would also need to come up with a system of adapters, from your new 645-Mirrorless to K mount and from 645-Mirrorless to Pentax 645. This is not a trivial task because the lens stopdown works the opposite way: 645/67 systems force the aperture closed to shoot and springs open it back up to frame and meter, K-mount lenses are forced open by the camera to frame and meter and the lens stop down under spring force. You would have to build these mechanisms into the adapter, or require manual stopdown.


Last edited by Paul MaudDib; 02-10-2014 at 03:40 PM.
02-10-2014, 03:59 PM   #140
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QuoteOriginally posted by Paul MaudDib Quote
K-mount register distance is 45.45mm, Pentax 645 register distance is 70.87mm. So the lens would need to protrude 25.42mm into the mirror box (impossible) or you need to get rid of the mirror box, that's all there is to it (if you want the camera to focus at infinity).
Even with a simple four-bar you could take off quite a bit of register distance req'mt. You would be giving up cheapness/speed but a mechanism design to take a 45 deg mirror and translate it within the ~42mm space req'd is trivial.

We haven't yet spoken about the protrusion that already exists on many lenses, but you could still design a mirror to move in the space req'd. It's just whether or not the result would be worthwhile.

(Heck you could even just translate the mirror).


QuoteOriginally posted by Paul MaudDib Quote
645/67 systems force the aperture closed to shoot and springs open it back up to frame and meter, K-mount lenses are forced open by the camera to frame and meter and the lens stop down under spring force. You would have to build these mechanisms into the adapter, or require manual stopdown.
In the thought experiment above we haven't yet imposed the requirement of being able to use both 645 and k lenses. It's possible of course but would be more complex.
02-10-2014, 04:24 PM   #141
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QuoteQuote:
Even with a simple four-bar you could take off quite a bit of register distance req'mt. You would be giving up cheapness/speed but a mechanism design to take a 45 deg mirror and translate it within the ~42mm space req'd is trivial.

We haven't yet spoken about the protrusion that already exists on many lenses, but you could still design a mirror to move in the space req'd. It's just whether or not the result would be worthwhile.

(Heck you could even just translate the mirror).
So... translate the mirror where? Farther backwards? You know, where the sensor is supposed to be?

It's not even just the mirror. Fine, the mirror is magic and we can make it shrink when we want to shoot K-mount lenses. What are the K-mount lenses being mounted on? If it's the 645 mount, that's 25mm too far forward, you lose infinity focus. The only alternative is to have a mount at the proper register distance (where the mirror is supposed to be), which means that all your lenses have to have a smaller diameter than the 645 mount so that they can fit inside the throat of the camera.

The idea of putting short-register lenses on long-register cameras is patently unworkable, and every workaround has already been investigated in depth by the crowd who adapt manual-focus lenses (alt glass) to digital cameras. You can lose optical quality and get a longer focal length (glass-type adapters), you can modify the lens (expensive and only good for a few mm tops), or you lose infinity focus (non-glass type adapters). The main solution is that you buy a body with a shorter register distance - which is why mirrorless are popular in those crowds. That's why I keep talking about a 645 mirrorless as the only solution to this problem.

QuoteOriginally posted by ElJamoquio Quote
In the thought experiment above we haven't yet imposed the requirement of being able to use both 645 and k lenses. It's possible of course but would be more complex.
Using 645 and K mount lenses interchangeably (via an adapter) was the original point of this discussion.

QuoteOriginally posted by jon404 Quote
Back to the lenses. You know, that 645D sensor is smaller than the 'normal' 6 x 4.5 size (54x40mm, Mamiya Leaf Credo 80 back)... only 44x33mm (same as the Mamiya Leaf Credo 40 back, BTW). Larger than full-frame's 36x24mm, but not by much. Point is, you could probably use many of the K-mount lenses on the 645D without getting objectionable vignetting. Making an adapter would take a bit of engineering, to handle the flange distance, etc... but what a payoff if it worked. Would be fun to manage a rapid-development project to pull this off!
I suppose there's nothing stopping you from making a mirrorless K-mount camera with a crop 645 sensor, that would basically be the "645 mirrorless" I described.

Last edited by Paul MaudDib; 02-10-2014 at 05:03 PM.
02-10-2014, 04:41 PM   #142
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QuoteOriginally posted by jon404 Quote
So... do you think they'll sell off the existing 645Ds for under US $2,000?
If it drops that low original 645D users who paid $10,000 are not going to be happy but I am sure it will sell well at that price.
02-10-2014, 05:27 PM   #143
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QuoteOriginally posted by FrankC Quote
I've just noticed that the FA 25mm lens, once at $4,999 is being sold on eBay for $3,985. A few other dealers have lowered the price as well, but Adorama is still at MAP.

Pentax D SMC FA 645 25 mm F 4 Al If SDM AW Lens New 027075215177 | eBay
Exchange rate to the Yen is in our favour now. Would be a big driver to it appearing cheaper now. Makes me really consider one now...

02-10-2014, 06:43 PM   #144
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QuoteOriginally posted by Paul MaudDib Quote
So... translate the mirror where? Farther backwards? You know, where the sensor is supposed to be?
Nope, to the side.


QuoteOriginally posted by Paul MaudDib Quote
Fine, the mirror is magic
It's not magic. I've designed many mechanisms that are similar. If you need to know more just ask politely!


QuoteOriginally posted by Paul MaudDib Quote
and we can make it shrink
Again, just normal engineering.

QuoteOriginally posted by Paul MaudDib Quote
when we want to shoot K-mount lenses.
We're always shooting K-mount on this thought experiment.


QuoteOriginally posted by Paul MaudDib Quote
What are the K-mount lenses being mounted on? If it's the 645 mount, that's 25mm too far forward, you lose infinity focus.
We're always shooting K-mount on this thought experiment. 45ish mm.

QuoteOriginally posted by Paul MaudDib Quote
The only alternative is to have a mount at the proper register distance (where the mirror is supposed to be), which means that all your lenses have to have a smaller diameter than the 645 mount so that they can fit inside the throat of the camera.
It's not the only alternative. Have the register at the correct register distance.

QuoteOriginally posted by Paul MaudDib Quote
The idea of putting short-register lenses on long-register cameras is patently unworkable
It is not a feasible option in the market. If you have $2m I'll have a working prototype for you by the end of the year!
02-10-2014, 07:36 PM   #145
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@RonHendriks1966 -- ooohh, she looks SO GOOD in yellow! Bet they have a K-01 just like yours, too. Forget that basic black!
02-11-2014, 03:44 AM   #146
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QuoteOriginally posted by jon404 Quote
@RonHendriks1966 -- ooohh, she looks SO GOOD in yellow! Bet they have a K-01 just like yours, too. Forget that basic black!
Orange is also good...........


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02-12-2014, 02:12 PM   #147
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QuoteOriginally posted by ElJamoquio Quote
Nope, to the side.
I get what you're saying now. Yeah, you could just stick a 645 crop sensor behind a K-mount no problem. 6x4,5 crop sensors (specifically the required mirror) are only a little bit bigger, there's probably enough wiggle room with a multi-segment mirror. Bronica did something like that with the S2 camera. You won't get a whole lot extra but it's probably enough.

The only concern there would be that the angle of incidence isn't too high near the edges of the sensor (because of the larger sensor relative to the register distance), which probably wouldn't be an issue, and is a sensor characteristic that's getting better all the time. There's plenty of coverage in a lot of 35mm lenses, IIRC the 17mm fisheye covers ~45mm and the 35/3.5 covers closer to 55mm. Some lenses are mechanically vignetted to hide this "extra" coverage and prevent reflection inside the camera body (some large format lenses for sure).

And from there you could also make an adapter that would allow the 645K to mount traditional 645/67 lenses. Of course this would work in stopdown mode only since the aperture levers work the wrong way, unless you made a crazy bellcrank system or something.

Last edited by Paul MaudDib; 02-12-2014 at 02:19 PM.
02-13-2014, 08:42 AM - 2 Likes   #148
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645D 2014
02-13-2014, 09:01 AM - 1 Like   #149
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Thanks for the video, hajiaru, could you explain in English some highlights of what is being said in that video?
02-13-2014, 09:30 AM   #150
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QuoteOriginally posted by gazonk Quote
Thanks for the video, hajiaru, could you explain in English some highlights of what is being said in that video?
I speak only English
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