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01-13-2018, 11:25 PM   #1
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Behind-the-Mount 20-40 for K-01

Just dreaming...
About a pancake zoom that fits a 20 or 16 minimum to 40-45 maximum into the space no longer needed for the mirror and those chunky retro-focus designs it requires.

I love my K-01 but hate carrying a 21 DA with the 40 XS. Let me have a super compact pancake zoom that fits the body.


Last edited by squareeyes; 01-14-2018 at 10:44 AM. Reason: 20_>21
01-14-2018, 12:34 AM   #2
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The retractable 18-50mm zoom is very compact.
K-01 had made more sense if that lens had been available as kit zoom for K-01.
01-14-2018, 05:05 AM   #3
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I'm perfectly happy of having purchased my K-01 with its matched lens.
It's a lens that I can squeeze in most kits with an insignificant size penalty, covering a focal length for almost no space.

I usually go 10-20/3.5 + 40mm XS + 100/28 SMC-M, but one could go 15mm LTD + 28/3.5 SMC-M + 40XS + 100/2.8 and have a really compact, low-light capable prime set.

There are issues with the K-01, but its kit pairing isn't, IMHO, one of them.
01-14-2018, 10:42 AM   #4
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QuoteOriginally posted by Fogel70 Quote
The retractable 18-50mm zoom is very compact.
K-01 had made more sense if that lens had been available as kit zoom for K-01.
I had forgotten the 18-50. It does retract so it stores smaller: just bigger than the 21 DA. Thanks for mentioning it.

I Still think there is a big place for pentax to introduce a compact mirrorless with widely compatible lenses that enter the mirror box space.


Last edited by squareeyes; 01-14-2018 at 10:48 AM. Reason: 20—>21
01-14-2018, 10:57 PM - 1 Like   #5
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QuoteOriginally posted by squareeyes Quote
I had forgotten the 18-50. It does retract so it stores smaller: just bigger than the 21 DA. Thanks for mentioning it.

I Still think there is a big place for pentax to introduce a compact mirrorless with widely compatible lenses that enter the mirror box space.
That is not a way to design lenses for mirrorless if mirrorless is a system designed for the future users.
K-mount will just be a severe limitation on lenses designed for mirrorless, and much of the point of using K-mount is lost if lenses are designed not being compatible with K-mount.

And designing lenses that protrude into the lens mount will also put severe limitation on optical and mechanical design. So it can only be used on very slow lenses, but once the lenses get very slow they can be designed very compact without protruding into the mount.

It's not by chance all manufacturers of mirrorless have choosen a new mount for mirrorless. It is the only way that make sense on a future proof system. It's only on a new mount that lenses can be fully optimised for mirrorless.

Last edited by Fogel70; 01-14-2018 at 11:13 PM.
01-22-2018, 12:24 PM   #6
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QuoteOriginally posted by Fogel70 Quote
once the lenses get very slow they can be designed very compact without protruding into the mount.
Until I saw what the 08 could do on a Q-7 or Q-S1,
I used to wish Pentax had done something like the Voigtlaender Heliar 12/5.6 for the K-01:


Would have made a great compact kit for real estate photographers.
And without protruding into the mount, this would be a bulky retrofocus lens.
01-22-2018, 09:45 PM   #7
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QuoteOriginally posted by lytrytyr Quote
Until I saw what the 08 could do on a Q-7 or Q-S1,
I used to wish Pentax had done something like the Voigtlaender Heliar 12/5.6 for the K-01:


Would have made a great compact kit for real estate photographers.
And without protruding into the mount, this would be a bulky retrofocus lens.
Lens design like that would not work well for digital as it would lead to lost IQ in the corners and severe vignetting.
On digital the rear lens element must be big to avoid problems like that, which means the lens mount must be close to the sensor if to design ultra compact wide angle lenses.

With a short register mount APS-C 12/5.6 lens would be quite compact.

Does the above lens even have any focusing mechanism? I can imagine it would be difficult to fit inside a tiny lens barrel like that.

Last edited by Fogel70; 01-22-2018 at 11:00 PM.
01-23-2018, 08:23 AM   #8
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Curve the sensor to minimize vignetting

Somewhere there is a series of posts regarding a rumored curved sensor by Sony.

Surely a 90mm radius would give better access to the sensor pixel wells, but the camera is beginning to look like a softball rather than a brick.

But seriously, each digital-enhanced lens has a collimating element at the rear to minimize the angle of rays as they hit the sensor. A 18mm diameter element would likely give enough spread to cover full frame curved sensors.

01-23-2018, 03:04 PM   #9
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QuoteOriginally posted by Fogel70 Quote
Lens design like that would not work well for digital as it would lead to lost IQ in the corners and severe vignetting.
Actually less of a problem for digital, as you don't need to mess with graduated filters to correct.
Photozone tested a Leica-mount version on a Sony E-mount camera,
and it did OK for a really compact ultra-wide.
QuoteOriginally posted by Fogel70 Quote
On digital the rear lens element must be big to avoid problems like that
A lot of satisfied DA 15 Ltd users would disagree.
QuoteOriginally posted by Fogel70 Quote
Does the above lens even have any focusing mechanism?
Yes, the Heliar has a helicoid!
01-23-2018, 11:37 PM   #10
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QuoteOriginally posted by lytrytyr Quote
Actually less of a problem for digital, as you don't need to mess with graduated filters to correct.
Photozone tested a Leica-mount version on a Sony E-mount camera,
and it did OK for a really compact ultra-wide.
I would say it performes quite bad. A f/5.6 FF lens that performs that bad on APS-C is not what I would call OK. If you want a compact 12mm lens for APS-C mirrorless, Zeiss Touit seems to be a better choice. The Zeiss is a little larger, but it is f/2.8 and has AF.

QuoteQuote:
A lot of satisfied DA 15 Ltd users would disagree.
I don't see any rear lens element protruding a couple of centimeter into the mount on DA15. As you know the problem increase the closer the rear lens element sits to the sensor.
01-24-2018, 03:39 PM   #11
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Whatever, as I posted earlier, the 08 on a Q-7 is now my solution to the compact wide-angle question.
01-24-2018, 11:00 PM   #12
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Just received a 18-50 Retractable DA lens.
Somewhat disappointed with the chunky size and the sticky retraction mechanism
The electric focus is fantastic, though.
Still waiting for additons to the XS line...come the messiah
01-25-2018, 07:37 PM   #13
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QuoteOriginally posted by squareeyes Quote
Just received a 18-50 Retractable DA lens.
Somewhat disappointed with the chunky size and the sticky retraction mechanism
If you give the front of the lens
a gentle inward push to start the retraction,
it actually works quite smoothly.

For a kit lens, the rendering is very pleasing,
much better than the muddy DA 18-55 II.
02-27-2018, 11:25 AM   #14
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QuoteOriginally posted by Fogel70 Quote
So it can only be used on very slow lenses,
wrong

QuoteOriginally posted by Fogel70 Quote
but once the lenses get very slow they can be designed very compact without protruding into the mount.
wrong

---------- Post added 02-28-18 at 01:28 AM ----------

QuoteOriginally posted by Fogel70 Quote
I don't see any rear lens element protruding a couple of centimeter into the mount on DA15. As you know the problem increase the closer the rear lens element sits to the sensor.
It's not the rear element, it's exit pupil position... which people constantly confuse
02-28-2018, 02:43 AM   #15
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QuoteOriginally posted by alliumnsk Quote
wrong
Then why do you not explain how to design fast pancake lenses with help of an protruding rear of the lens.

QuoteQuote:
wrong
Are you saying that lenses like DA21 is not possible?


---------- Post added 02-28-18 at 01:28 AM ----------
QuoteQuote:
It's not the rear element, it's exit pupil position... which people constantly confuse
So what is the relation between exit pupil position and vignetting/color shifts?
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