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01-24-2017, 12:21 AM   #1
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Not just speculation, the new 35 mm FF

Let's have a quick look on lens design. After designing a lens with a given focal length it is fairly straight forward to derive a lens with larger image circle and smaller f-stop or vice versa. Pentax did so when producing the 2.8/55 mm for 645 system. The DA* 1.4/55 mm came a little later for APS-C.

Now let's check out the latest 645 lens which is a 3.5/35 mm. Pentax' rodmap shows a FF wideangle to be released first. Best guess would be a 35 mm lens with moderate f-stop - maybe f/2 or f/1.8. My guess for the next FF lens is a 1.8/35 mm. It could very well be un updated 1.8/31 mm, but I don't think so.

The 2.8/90 for 645 could become a 1.4/90 mm for FF.... but macro vs. very large aperture is not easy, especially with today's competition. This would be the medium tele lens from the roadmap.
The normal angle lens will be a derivative of the existing 55 available for APS-C and 645.

I wonder about the lens drawaing of future Pentax lenses for coparison :-)

01-24-2017, 02:20 AM - 3 Likes   #2
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Topic title is very confusing.
01-24-2017, 06:01 AM   #3
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Pentax already sells DA 35mm f2.4, DA 35mm f2.8 macro, FA 35mm f2. And there is steep 35mm competition from Sigma 35mm Art, Samyang 35mm f1.4.. maybe even Mitakon (affordable) and Zeiss (super expensive)
Some time ago Pentax sent out a questionnaire about 24mm and 28mm primes, so I think that will be the next prime they release. But we don't yet know whether it will be compact (slow aperture, but small lens) or super fast (big lens, lots of corrections), though. Basically, in the next two years Pentax will release lots of stuff.

But specifics are speculation, so...
01-24-2017, 07:17 AM   #4
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IMHO Pentax needs a *24 and a D FA 28 first. Then they could replace the FA35/2 with a D FA35/2 WR DC (PLM?) Limited.


Last edited by monochrome; 01-24-2017 at 07:34 AM.
01-24-2017, 07:45 AM   #5
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The Sigma 28mm f1.8 is FF, and very nice on ASPC, I haven't seen it tested on the K1. I'd think with a 35 already available, something wider like a 24mm or even 20mm would be more attractive. Particularly a FF capable pancake 21mm lens would be quite fun on the K1.
01-24-2017, 08:22 AM   #6
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QuoteOriginally posted by TER-OR Quote
Particularly a FF capable pancake 21mm lens would be quite fun on the K1.
Fun? Yes!

But looking at the Pentax M 20/4 (which I have used on FF film and APS-C digital),
and the Voigtlaender Color Skopar 20/3.5 (which I've steered clear of),
I don't think that a 21mm pancake would be able to meet the demands of the modern market.
01-24-2017, 08:29 AM   #7
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QuoteOriginally posted by lytrytyr Quote
Fun? Yes!

But looking at the Pentax M 20/4 (which I have used on FF film and APS-C digital),
and the Voigtlaender Color Skopar 20/3.5 (which I've steered clear of),
I don't think that a 21mm pancake would be able to meet the demands of the modern market.
Why don't you think there is a market for something like the M20/4? I'm curious because it never leaves my bag since the K1, but it would nice to have aperture control and AF.

01-24-2017, 09:38 AM - 1 Like   #8
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QuoteOriginally posted by zapp Quote
Let's have a quick look on lens design. After designing a lens with a given focal length it is fairly straight forward to derive a lens with larger image circle and smaller f-stop or vice versa. Pentax did so when producing the 2.8/55 mm for 645 system. The DA* 1.4/55 mm came a little later for APS-C.
Sorry, but this is just plain wrong. The DA* 55/1.4 for APS-C is not a straight forward modification of the 55/2.8 for 645.

The design issues in creating larger image circles are different from the design issues in creating larger apertures because the different kinds of aberrations affecting the two. Moreover, in the context of DSLR lens design, the issue of flange focal length forces further differences in lens design for different formats. Sure, you can easily adapt any lens designed for the 645 to go on K-mount, but the result is an excessively long lens compared to what possible with a different design specifically for that mount. And there's no way that a 55mm f/1.4 for K-mount APS-C can be tweaked to operate on the deeper 645 mount with a larger image circle even if one sacrifices aperture.


The only fairly straight forward connection between designs for different image circles is direct scaling in which focal length and all the element sizes and element distances are all multiplied by some factor (with the result that the f-stop aperture remains constant). A 55/1.4 for APSC could be scaled by 1.833 to become a 100/1.4 for crop-645 although the result would be a huge expensive beast of a lens.
01-24-2017, 11:29 AM   #9
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Their hottest lens in the APS-C wide angle is their 15mm f4. SO very like a 24/f4 or 24/f2.8. I hope they maintain the starburst feature of the non-HD 15mm.
01-24-2017, 11:41 AM   #10
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There are different ways of "scaling" when starting from a given design. Using a simple Kipon 0.7x adapter, you will change focal length and effective aperture 1:1. Starting with a working lens design you have mroe degrees of freedom or parameters to play with flange focal distance is important.

The early Hasselblad medium format lens 5.6/60 was scaled to 35 mm Format 4/35 mm as Zeiss reports. This is one of the first reports on lens scaling and re-use of designs. (Hasselblad 60 mm on the right).
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Last edited by zapp; 01-24-2017 at 11:48 AM.
01-24-2017, 12:28 PM   #11
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QuoteOriginally posted by zapp Quote
There are different ways of "scaling" when starting from a given design. Using a simple Kipon 0.7x adapter, you will change focal length and effective aperture 1:1. Starting with a working lens design you have mroe degrees of freedom or parameters to play with flange focal distance is important.

The early Hasselblad medium format lens 5.6/60 was scaled to 35 mm Format 4/35 mm as Zeiss reports. This is one of the first reports on lens scaling and re-use of designs. (Hasselblad 60 mm on the right).
Yes, that's an example of scaling that I mentioned at the end of my post -- multiply every dimension in the design by a factor of c, and the focal length, image circle, and flange focal length all change by that factor. But that can't turn a 55/2.8 for 645 into the DA* 55/1.4 for APS-C.

And, yes, you can use supplementary optics like the Kipon 0.7x adapter to change FL and aperture. But that can't turn a 55/2.8 for 645 into the DA* 55/1.4 for APS-C. Maybe you could use a 55/2.8 for 645 with a Kipon 0.7X to get a 39/2 for APS-C or make a 28/1.4 with a Kipon 0.5X but the lens would be very large and very expensive (the 55 for 645 is bigger in every way that the 55 for APS-C and costs twice as much and that's before adding the Kipon). Worse, the result would probably be soft wide open.
01-26-2017, 08:09 PM   #12
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QuoteOriginally posted by GeneV Quote
Why don't you think there is a market for something like the M20/4?
Because reviewers, technogeeks and pixel-peepers would pan it.
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