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Forum: Pentax SLR Lens Discussion
12-23-2017, 07:24 AM
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I really love the second shot. Great composition.
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Forum: Pentax SLR Lens Discussion
12-21-2017, 03:06 PM
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Jim - I wast trying to point out that the fall off performance data given was in response to this claim by you. The other data may or may not be relevant - I don't know personally but I do know that many other very well respected full frame lenses have worse fall off on even APSC than this. That said - that's not the only factor in lens selection.
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Forum: Pentax SLR Lens Discussion
12-21-2017, 07:06 AM
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Jim, I think the main point made was that apsc vignette numbers aren't very clear indications of performance on full frame. That was demonstrated in measured numbers.
Your observations of da 50 performance in general may in fact be relevant but the level of vignette doesn't seem worse than many lenses rated excellent on full frame.
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Forum: Pentax SLR Lens Discussion
12-13-2017, 03:00 PM
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Yes - I got that but you singled out Nikon which made me curious as it implied that was an outlier to me. However virtually every 200 f/2.8 seems to fit this model. Even the venerable Canon FD SSC f2.8 had a 77mm filter. And then there's the Canon USM II 200mm f/2.8 which has a 72mm filter thread. That seems like a likely candidate for slightly overstated specs.
What's more interesting to me are people who create hoods out of filter and step down rings and then refuse to see that they may have created a light restricting baffle in some cases and claim improvements that actually may be strictly due to more restrictive f/stops.
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Forum: Pentax SLR Lens Discussion
12-13-2017, 02:40 PM
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There are a lot of 200mm f/2.8 lenses with the 77mm filter size. DA* 200, D FA 70-200, etc.
What am I misunderstanding about your comment?
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Forum: Pentax SLR Lens Discussion
12-09-2017, 10:04 AM
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Thanks guys - that was helpful info and helpful to find that link again.
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Forum: Pentax SLR Lens Discussion
12-08-2017, 04:20 PM
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If your point is that the lack of good info is hurting K-1 sales... well, perhaps you are correct in a few cases but honestly the sales have been so strong I'm not sure that's true. Some buyers may not be aware of the site and may have trouble finding out that information - but I'm not sure how anyone could get Ricoh to change their stance. They have obviously set some criteria (border/corner sharpness, vignetting, combo of the two) that governs which lenses available today are considered Full Frame. They also likely factor in costs and profits and since the FA 50 f/1.4 exists and they may not be entirely happy with the DA 50 f1.8 on FF they don't recommend the latter. The same may also be true of the DA 40 since the FA 43 exists alongside the FA 31 and FA 35 f/2. Similarly why tell people to buy the DA 70 when the FA 77 is still sold?
Just between us Forum folks - I can't understand how they keep their website so out of date and inaccurate. For example under K mount Telephotos they list the FA* 645 300mm... sigh.
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Forum: Pentax SLR Lens Discussion
12-08-2017, 07:31 AM
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I can't find the info now but the site I used for information claimed that pre-A series lever distance traveled was proportional to aperture diameter, whereas lever distance traveled in the A series is proportional to aperture area. When I said complex that's a slight misuse of the word, the physical action is simple; calibration and correlation to exact aperture is complicated.
---------- Post added 12-08-17 at 09:36 AM ----------
Sure, sadly few offer this. One approach is to dedicate an adapter for each lens and slowly map the aperture to the specific lens and adds marks on the adapter to indicate the stops. One way to do this is to use a consistent light source lighted scene, meter wide open, then slowly stop down until you see a 1 stop difference in the meter result, then repeat this until you have enough stops marked. Of course this still doesn't give tactile feedback and the need to look to see what aperture is set is annoying.
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Forum: Pentax SLR Lens Discussion
12-08-2017, 06:54 AM
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@pathdoc it isn't just video that drives this, the way Pentax aperture works requires a complicated lever action to accurately reflect f stops; in part this is due to the fact that the travel distance to aperture ratio changed between K/M series and A series so accuracy is complicated by this. Most - if not all adapters are stepless. The m43 adapter I have for DA lenses is also stepless and while it makes picking a particular aperture a bit more difficult it works ok.
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