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04-13-2013, 03:29 PM   #1
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Why not genuine interchangeable focusing screens?

I remember my old MX had genuine Pentax focusing screens available. It was part of the design plan of the camera to offer interchangeable screens so the change method was easy to do, and the camera was set up to that no shimming and testing of correctness of shims was necessary.

So, why not offer an improved design of the screen holder in DSLRs and offer a range of screens machined to exactly the same thickness as the default screen, so there is no need to change shims and design them so they work properly with the metering, but offer a range of focusing methods (split image, microprism, ground surface, and a range of markings to assist composition or for using in camera metering).

This would greatly help those of us who like to do manual focus work.

For economy, and to improve the economics of the distribution channels, once a design is settled, keep it across a long series of bodies.

04-13-2013, 03:35 PM   #2
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Doesn't the K-5 already support interchangeable screens? Cheaper cameras don't to encourage advanced users to upgrade.

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04-13-2013, 03:38 PM   #3
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Recently Pentax committed to 100% viewfinders. If they also commit to a certain magnification, they probably could keep it standard across all their DSLRs and sell focusing screens that would fit all their cameras. But probably they don't think it would be profitable. And they want people to buy their "digital" lenses, which are made for AF, with short focus throw and without distance scales. And to buy their top tier camera instead of just accessorize their mid tier camera. I know, it doesn't really make sense, but as long as they thing it does..

Pentax could also make filters and all sorts of stuff for their cameras, but they stopped making most accessories. Or never bothered to start. Its too bad, but there are probably reasons for it
04-13-2013, 05:10 PM   #4
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QuoteOriginally posted by tim60 Quote
screens machined to exactly the same thickness as the default screen, so there is no need to change shims
The need for shims is not a matter of the screen thickness. The plane of focus is at the face of the screen. Shimming is required due to lax tolerance in manufacture of the mirror box. As mentioned on another thread, AF has disincented camera makers from giving much attention to accurate manual focus. As a result, critical focus is all but impossible with lenses faster than about f/3.5.


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04-13-2013, 09:34 PM   #5
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QuoteOriginally posted by stevebrot Quote
The need for shims is not a matter of the screen thickness. The plane of focus is at the face of the screen. Shimming is required due to lax tolerance in manufacture of the mirror box. As mentioned on another thread, AF has disincented camera makers from giving much attention to accurate manual focus. As a result, critical focus is all but impossible with lenses faster than about f/3.5.


Steve
This is where I look back to the MX. There was no need for shimming because it was made to the right tolerance - which shows the technology to do that exists.

The evidence in this forum is that lots of people like to manual focus lenses that have AF capabilty. (Quite apart from thos os us who like to use legacy lenses.)

And given inflation since 1981 (when I got my MX), the prices in general have increased about 4 times, so the $320 I paid for the MX now maps to about $1300, a mid priced (not entry level) DSLR. I remember the MX was marketed as an extendable system that would suit most professional needs, except waist level viewfinder ( a feature of the much more expensive LX introduced here in late 1981. One of my classmates got one soon after first release - maybe a present in anticipation of graduation. And the DSLR now has much less precision mechanical work than the old cameras.
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