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12-13-2019, 06:07 AM - 1 Like   #31
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QuoteOriginally posted by Jonathan Mac Quote
By that logic all lenses should be FF compatible: twice the size, twice the weight and twice the price. APS-C is about being smaller and lighter and if it can be cheaper too then all the better.
Twice the size? You mean like how the DA 35 f2.4 is basically the same size as the FA 35 f2? DA 50 1.8 is larger than the FA 50 1.7? If we're talking about super-wides, like the DA 15 vs... K 15? Yeah, you're right there, but things start to equalize pretty soon after as focal length increases. I'm not an optical designer at all but I don't think there are a lot of examples that support your theory after 25mm or so.


Another thing that cannot be forgotten is that Pentax offers a pretty convincing line-up of APS-C-only glass and does not offer a very convincing line-up of full-frame glass. They need to keep developing glass for the K-1 or the whole exercise will be a waste. The use case for APS-C camera & 85mm glass isn't very obvious, not that it wouldn't get used, but they're already offering good 77mm and 100mm options as well as many zoom lenses that hit 85mm.

12-14-2019, 01:59 AM   #32
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In the majority of cases a FF lens is larger than an APS-C lens. The DA 50/1.8 is not bigger than the FA 50/1.7, I am looking at them right now. In many cases there are PS-C lenses that could be made smaller than they actually are, though that might increase vignetting to the level often seen on FF lenses, but for equivalent vignetting an APS-C lens will always be smaller than a FF one.

I've nothing against a FF 85mm and believe one is in development, but the whole "just make it FF" arguement annoys me as it passes on extra size, weight and cost to APS-C users. Why shouldn't APS-C users be entitled to their own lenses, designed for their format, regardless of focal length?
12-14-2019, 06:03 AM   #33
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QuoteOriginally posted by hypermodern Quote
Well, the Samyang 85mm f1.8 for APS-C only weighs 350g compared with 510g for a FF 85mm f1.4 and 740g for the same specs (new design) in Nikon Z mount, so a weight saving of 30-50%. A lot lighter than to 50-135 which is covering this range at the moment.
Considering that at 85 mm, f1.8 requires a minimum objective of 47mm and f1.4 needs a 61 mm objective, 68% larger front lens area, the weight difference is easily explained. It has nothing to do with the coverage, and everything to do with the size of the front element,

The myth that crop sensor lenses should be lighter is just that, a myth. The minimum diameter of the lens barrel is determined by the size of the mount at the back and the size of the objective lens at the front.

Size and weight are largely driven by these two factors. Sure there may be some oddities out there, and things vary a lot more in the wide angle lenses with lens design, but once the focal length exceeds the registration distance things are pretty straightforward. Faster = heavier, and within the image circle limits of the mount itself, full frame or crop means very little
12-17-2019, 08:11 AM   #34
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What I would like is a plastic fantastic 85mm f1.8 or 2.0 AND a DFA* 85mm f1.4. one would be 300-400 dollar ish and the other is the high end one. But I understand that Pentax may only do one.

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