Some mirrorless options for Pentax

Started Aug 25, 2018 | Discussions thread
Barry Pearson
OP Barry Pearson Veteran Member • Posts: 8,723
Re: Some mirrorless options for Pentax

Fogel70 wrote:

Barry Pearson wrote:

Fogel70 wrote:

.... There are many points of making a new mount as a short register distance mount have to be designed differently to best support short register distance lenses. A larger mount would be better as short register distance lenses have large rear lens elements. K-mount is not large enough for this.

See my post above:
https://www.dpreview.com/forums/post/61554148

I believe a lens with rear elements of about 30mm diameter could fit within the body of a mirrorless K-mount camera. That is quite a substantial proportion of the 44mm image circle of an FF lens.

It is not only the rear lens element that would habe to be fitted inside the protruding tube. Several lens elements with lens fittings and focus mechanism would have to be fitted inside which will limit the image circle to less tham 30 mm.

Did you really mean "image circle" in that statement?
Not "rear element diameter"?

Ideally a rear element very close to the sensor would have to cover the whole image circle so the the light hit the sensor in a straight angle. I believe this is what Nikon has planned with the new Z mount.

Are Nikon intending to have a rear element for their ultra-wide lenses of 44mm diameter, which is the FF image circle diameter? (Or 1.7 inches in old money?)

I would like to see evidence for that!

And, of course, the image typically doesn't emerge as parallel lines from the rear of a photographic lens. I found plenty of counter-examples here:
https://www.google.co.uk/search?q=light+path+through+a+photographic+lens

For DSLR lenses the rear element can be smaller as there is a long distance to the sensor. So 30mm is enough for a DSLR lenss but on mirrorless it risk creating problems and may only be enough for APS-C. I believe that is the problem for Sony on FF as they have the same sized mount as K-mount. Although they has less parts inside the mount that limit rear element size.

Mirrorless lenses will not use screw drive or mechanical aperture control, so why fit them in the camera with an added cost? Would it even be room to fit them in a short register distance mount?

Those are good points. My measurements (at the link above) were based on the D FA* 50mm f/1.4 lens.

The screw drive and mechanical aperture control have to be fitted in the adapter for those wanting to adapt AF K-mount lenses. For those adapting manual focus lenses do not need adapter with screw drive and aperture control.

Why re-used the extra complexity of having electrical connectors on the mount surface? For mirrorless new a brand new communication protocol will be introduced between camera and lens. So new pibs will probably gave to be introduced. With a larger mirrorless mount the connector will be designed like on 645-mount or Q-mount for less complexity.

Re-using K-mount will only introduce extra cost and complexity, and will cripple lens design for a mirrorless system.

I think it would be cheaper to design and develop, and it could share existing components in manufacturing. (And it wouldn't risk alienating existing users of Pentax K-mount cameras who have a substantial investment in K-mount lenses).

The design on the mechanical mount is a couple of hours work after they decided what specification it should have. The problem with K-mount is that it is combined electrical and mechanical interface and include a lot of extra features not needed on a mirrorless all electrical mount.

The real extra cost is that the K-mount require extra components and extra assembly time on each produced camera.

It obviously wouldn't cripple lens design for longer lenses!
Whether it would significantly impact lens design for wide angle lenses depends on how much of a constraint that "30mm rear elements with a 35mm tube" would be. (Assuming that is the real constraint).

On many wide angle lenses for mirrorless the rear lens element is larger than the front lens lement. But the camera need a lens mount that support this, FI like MFT, Fuji and now Nikon do. And it is only Nikon that has large enough mount to support this design on FF.

That ratio isn't what is important. What is important is the diameter of the elements inside the camera body. Not the diameter of elements outside the camera body.

Fuji X use same sized mount as K-mount but for them it is only large enough for APS-C.

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Ricoh WG-6 Panasonic LX100 Ricoh GR III Pentax K-7 Pentax K-3 II +27 more
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