Why use a 135format lens mount?

Why did Pentax and most other brands hold their 135format mount for the digital aps-c sensor?

Since everything is smaller they could easily make the register distance smaller so that faster lenses are easier to make and the camera is smaller.
Since the lenses specially make for APS-C cameras won't work on 135 format anyway why didn't they make the jump?
If you still want to use 135format lenses you should easily be able to extend the mount to the correct register distance.

From all the brands only Minolta made a special mount for APS I believe.
They call it the V-mount and the Vectis S series cameras used it.

Does someone know a good reason or have insight into this?

because they wanted people who already had film slr's and lenses to buy a new body without feeling they had to start from scratch. And because there was no need to spend considerable engineering resources on developing a new and potentially problematic mount when they already had one that was tried, tested, and thoroughly known.

Canon did go this way with their EF-S mount, which is "digital (crop) only" - and doesn't have many lenses at all. But what would Canon be if they didn't force their users to throw everything away and start again at regular intervals...

That's an interesting question.

Presumably this is effectively what the manufacturers who use micro 4/3 did.

My guess would be that, for the manufacturers who chose to use ther existing mount, it saved a significant amount of engineering work.

In addition to the effort required to develop the mechanical aspect of a new mount, there would have been a need to develop/adapt a range of lenses to fit the new mount when the first DSLR bodies were released. While many members of forums such as this one may be prepared to use an adapter to use lenses designed for film with a DSLR, I can't imagine it would have been a very attractive marketing proposition for less dedicated users at the time the first DSLRs were released.

Why must someone get that feeling that they need to start all over again?
Since the mount register is smaller you can easily make an adapter for that so I don't see the problem.

The engineering part isn't all that hard, you simply take the existing K-mount, make the register shorter and make the connection of the mount slightly different and presto, you've a new mount which can support faster lenses and make the camera smaller.

The EF-S mount is a slightly different beast, the mount is the same but the EF-S lenses protrude inside the mirror housing, that isn't a problem for APS-C cameras but for the 135format ones you can hit the mirror.

Pentax can't do this because the mount isn't as wide as that of Canon.

Btw you can use EF leneses on the EF-S mount so what do you mean with throw everything away?

In a way but it differs because the micro 4/3 doesn't have mirrors inside the body so it's not a good comparison since the camera is different. But the normal 4/3 are indeed like that. They make a mount specially for that sensor size.

The effort into making a new mount will pay off because it makes it far easier to design faster lenses, just look at the 4/3 mount.

They could off course ship the first series of these camera's with an adapter standard so that you can use the lenses you've straight away.
Maybe the word adapter might scare off some people but it doesn't need to be and some might appreciate the smaller size camera.

When you look at the KM, K-X and the K7 you see Pentax is aiming at making smaller camera's a different mount is one that could make a difference.

I wonder if the world would be shocked if they would come with a new mount with the K-8.
You could see it as a blessing since you could make adapter so you can use the lenses of all the other brands besides the 4/3.
I still want the Minotla/sony 135mm stf lens for example, the bokeh of that lens is just amazing and some members here would love a Macro lens Canon make.
If Pentax could pull it off to make such an universal mount with adapters it would be exciting I think.

I can see the benefits of a new mount if Pentax where to enter the mirrorless market, indeed sticking to the K mount would make no sense as it would restrict the size that the cameras could be built down to.

With the existing line of DSLRs I don't think Pentax lost much by keeping the K mount (indeed they gained in terms of customer loyalty) because when you look at the original (non-micro) FourThirds standard it's hardly any smaller.

The only mount to compare it with is the Minolta Vectis, that's design for the APS so APS-H also, that one has register of 36.00 mm.
The K-mount is 45.46 mm so you can gain around a centimetre.
4/3 is on 38.67mm so that's a good indication what such a mount can do, f/2 zooms anyone?

The maxium aperture of a K-mount at a register of 36mm would be 36mm divided by 42mm is 0.86 just to give an idea what can be done. 35mm f/1 lens wouldn't be just a dream anymore.

To my knowledge there has never been a lens adaptor which worked well, the best anyone has managed is the K-M42 adaptor and Tamron's Adaptall system.

M42 is a very basic system and Adaptall was designed from the ground up to be adaptable, yet it is still a pain in the behind to swap lenses on unless you have one mount per lens.


For Pentax to change mounts at this stage would be most unwise, they have invested a lot in backwards compatibility

Mongoose an adapter wouldn't be the right word for it if they used a mount very similar to a k-mount it would be like an extension tube.

I don't know how good the adapter is for the Micro 4/3 to make it into a normal 4/3 mount but it would be like something like that.

Pentax using a new mount when the Pentax K mount was designed so well in the first place would be crazy. It's proved itself over 35 years and has been up to being developed further as the electroics have taken over.

The K mount is wide enough to design 50mm f1.2 lenses, so I reckon it's good for a while yet.

If Pentax did design a smaller format for mirrorless cameras and needed a special small mount for them, my bet is that they would from the start design an appropriate K adapter to go with it. This would be possible if the design was a radical rethink especially.

Think of the alternative designs of the past and imagine cameras with different sorts of shutter, exchangeable front cells with a fixed rear cell design, Shutter/aperture mechanisms such as the film 110 design, and lots more. Pentax are capable of thinking outside the box (witness all the unusual lens designs)so we could be very surprised yet.

Yes indeed it's a fine mount I don't say it isn't but it has some limitation and with the smaller APS-C format there is potential that they aren't using.
Pentax already have said they don't have ambition to go 135 format so why hold on to a mount that isn't optimized for the sensor size they are using?

The standard lens for the APS-C is 35mm but it would be extremely hard to make that a f/1.2 for the K-mount if it can be done and you have the problem that the dof is greater at that range so actually you need an f/1 to get the same effect.

I surely hope they do that but I hope they will keep SLR for a long time therefore I'm hoping they will optimize the mount to get the most out of it in the long run.

That's what they have been doing all along.

Yes they they improved the existing k-mount but what I meant they should make a mount optimized for APS-C since the K-mount is optimized for 135 format.

I know I said something differently but that's what I meant

With the long run I mean that they can make faster lenses and smaller cameras that can compete with the mirrorless cameras for a longer period of time then when they hold onto the K-mount.

The sensor can already move rotationally. Hypothetically, could the shake reduction unit be designed to move the sensor forwards to reduce registration distance when the camera detected one of these new smaller lenses? (Would be rather awesome if it could tilt to correct vertical perspective too!) This way Pentax DSLRs and microDSLRs could use the same lenses while retaining the K-mount lol

Will, I don't think we would see something like that because it sounds very complicated.

What do you mean with MicroDSLR btw?