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06-07-2011, 07:12 AM   #61
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QuoteOriginally posted by bdery Quote
They choose not to, but they certianly can.



You'd have to ask them... that's marketing again.



It's true that all things being equal a telecentric lens will be better with digital sensors. It,s also true that it particularly applies to fast, long glass. But we've seen countless examples showing that older glass still performs well on digital. I believe that older lenses on full frame digital sensors would be worse, however.



That's quite probably true.



I have to suggest that we can either

-believe all decision makers at Pentax are fools, or

-they know what they are doing, and have more information than any of us (all we have regarding marketing is speculation)

Pentax is profitable, growing, and constantly improving their products. I'd trust them to know how to keep making profits. I'm not working in photography, but in a large photonics company, and I can attest that here, at least, the marketing guys are very much aware of where their market is going, and how to turn a profit.
I won't call them fools, but if the court jesters at Pentax know what they are doing, hopefully they are resolving the SDM failure problem in some of those DA* zooms.

06-07-2011, 08:06 AM   #62
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I would guess that part of the issue is that Pentax has limited resources and they are very focused on the Japanese market where small is important.

I also have my doubts about the speed and reliability of SDM on lenses like an 85mm f/1.2. Then there is the question of AF accuracy and consistency with really fast glass. The room for error is pretty small. Pentax needs smaller AF points and more of them for more accurate work.

Pentax has come a long way with the K-7/K-5, but they still have several areas that need to improve.
06-07-2011, 09:50 PM   #63
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QuoteOriginally posted by Blue Quote
but Nikon's is only slightly different than the Pentax mount dimensions so looking at the fast glass in the Nikon catalog both present and past should give a rough idea of the possibilities. Cost is a separate issue
true, anyone who has looked at the going price for aspherical Ai-S 58mm f/1.2 noct-nikkor these days - I paid a bit more than 3K for mine*, but mine was in its original box


*I paid $150 for a Pentax K 50mm f/1.2 a few years ago - which was(still is) in mint condition.
06-08-2011, 07:00 AM   #64
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QuoteOriginally posted by Blue Quote
There have been several A and K 50mm 1.2 lenses show up with the aperture lever cut off to clear the mirror on those damn full frame canon bodies.
I got a K50/1.2 for a decent price, previously owned by an m4/2 shooter who had 'trimmed' the aperture flag. Just a little; not severely; it still works on both my K20D and K1000. Those neutered victims are the work of demons. TRIM MIRRORS, NOT LENSES!

06-08-2011, 08:05 AM   #65
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Is it worth all the hassle to go from f1.4 to f1.2?
06-08-2011, 08:13 AM   #66
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QuoteOriginally posted by RonHendriks1966 Quote
Is it worth all the hassle to go from f1.4 to f1.2?
With the advent of faster sensors the need for faster glass is moderated quite a bit.

Cutting F-number by half is equivalent to quadrupling ISO; I think there is at least another factor of two available for ISO improvement.
06-08-2011, 08:26 AM   #67
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QuoteOriginally posted by RonHendriks1966 Quote
Is it worth all the hassle to go from f1.4 to f1.2?
yes.

06-10-2011, 08:28 AM   #68
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QuoteOriginally posted by newarts Quote
With the advent of faster sensors the need for faster glass is moderated quite a bit.

Cutting F-number by half is equivalent to quadrupling ISO; I think there is at least another factor of two available for ISO improvement.
There are other creative advantages to faster glass. APS-C needs lenses that are faster and peak in sharpness at wider apertures than lenses for larger sensors.

The other issue facing Pentax is that they seem to be having more QC problems while Sigma seems to be improving their quality. Sigma is currently making more fast glass for the K-mount than Pentax is.

30mm f/1.4
50mm f/1.4 HSM
85mm f/1.4 HSM
150mm f/2.8 macro HSM OS
300mm f/2.8 HSM OS

24-70 f/2.8 HSM
70-200 f/2.8 HSM OS
120-300 f/2.8 HSM OS

06-10-2011, 08:44 AM   #69
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So on the subject of lensdesign placing a question here aswell.

As Digitalis says that some front elements do look alike. But are they also alike? Do for instance DA*300mm/f4 and DA*200mm/f2.8 who both have a 77mm front element have the excact same front element? This because if this is true there is some joint R&D in making lenses that can share some of their parts.

For instance a 500mm/f5.6 takes a 90mm front element, but when you could use that same front element to design a 400mm/f4.5 then it is cheaper to develop both.

Any ideas on this?

QuoteOriginally posted by Lowell Goudge Quote
they can, but if you consider your AD of 111.11 mm, it is not the lens barrel that limits the aperture, but the lens diameter that drives the barrel.

and yes it is because of the size and cost of the front element.

the aperture is placed in the light path where it is convenient to constrict the light further from the wide open case, and is also put in a place where the size of the actual diaphram can be reduced to an economical and practical size for fast response.
QuoteOriginally posted by Digitalis Quote
Three of the fastest pentax lenses I use these days. note that the front elements on all three of these lenses are very similar in size.

( I know the FA*85mm f/1.4 should be in there but I prefer the smaller FA77 f/1.8)
06-10-2011, 08:47 AM   #70
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QuoteQuote:
Originally posted by newarts
With the advent of faster sensors the need for faster glass is moderated quite a bit.

......

QuoteQuote:
There are other creative advantages to faster glass. APS-C needs lenses that are faster and peak in sharpness at wider apertures than lenses for larger sensors.
I certainly agree, but the K-x's ISO improvement over my K100D made my DA 55-300mm lens practical for indoor sports, nighttime sports, theater, birds in the forest, etc. This was a huge practical gain for me and might be for many people.
06-10-2011, 09:34 AM   #71
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QuoteOriginally posted by newarts Quote
I certainly agree, but the K-x's ISO improvement over my K100D made my DA 55-300mm lens practical for indoor sports, nighttime sports, theater, birds in the forest, etc. This was a huge practical gain for me and might be for many people.
I agree that high ISO has it benefits. Take the 55-300 at 300mm f/5.6 - how many usable stops do you have before diffraction starts to impact image quality. As sensors increase pixel density diffraction will become more of an issue at smaller apertures. F/11 is already showing signs of diffraction and with the next APS-C Sony sensor expected to be 24MP I would guess that some loss of IQ will be visible at f/8.

Diffraction is not a brick wall for IQ, but slower glass will become softer as pixel density increases, and slow zooms like the 55-300 already sacrifice some IQ for size and zoom range.

Future technologies like sensors without AA filters or color filters will change things, but we will burn those bridges when we get there.

There are several reasons for Pentax to focus on faster glass that peaks in sharpness at larger apertures.
06-10-2011, 08:25 PM   #72
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QuoteOriginally posted by RonHendriks1966 Quote
As Digitalis says that some front elements do look alike. But are they also alike? Do for instance DA*300mm/f4 and DA*200mm/f2.8 who both have a 77mm front element have the excact same front element? This because if this is true there is some joint R&D in making lenses that can share some of their parts. For instance a 500mm/f5.6 takes a 90mm front element, but when you could use that same front element to design a 400mm/f4.5 then it is cheaper to develop both.
that was actually my point really. For instance Leica used elements from the old Leica-M 50mm f/1.2 Noctilux ASPH in the Leica-M 50mm f/1.0 Noctilux they made in 1975 - though the glass they were using was incredibly hard to make and wasn't available from the catalogues of known glass manufacturer at the time*.


*the glass Leica used in the Noctilux 50mm /1.2 ASPH is called 900/1 - has a refractive index of 1.9005 (abbe index = 40.5) and it contains Lanathum oxide 55.5% 18.6%Tantalum oxide, 8% boron trioxide,5.30% Zirconum and other materials were used to raise the refractive index. The glass was made in platinum crucibles at 1,700K under stringent conditions, the glass blanks were made in batches of 900 and nearly 30% were thrown out because of defects.

Last edited by Digitalis; 06-10-2011 at 08:34 PM.
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