[Vitalii]

Originally posted by stevebrot Circle of confusion does not determine sharpness. It is a convenient constant. There seems to be some confusion (circular and otherwise) regarding what constitutes image quality. Here are a few bullet points:

Setting focus on ethernity - your detail is determined by the f/ - anything smaller than f/ won´t appear. thats where my confusion is comming from. i´m looking at a shot, not only as light reflection, but a gathering of such single light points.
At any point but Ethernyty, those light spots aren´t equal big- they are going from endlessly big to endlessly small which makes the sharpness and unscharpness - the difference between sharp and unsharp circles is determined by the focus length - far away focus is small difference, making everithing same "sharp", near focus - big difference, which makes more detailed pictures and more bokeh.

smallest detail is detrmined by the circle of confusion - because, smallest detail is as big as the circle or the pixel. thats why most details you get at near focus -f5.6 and less - pixel pitch is nearly as big as circle of confusion. at least in macro%)

ok, than back to reading, what really determine sharpness, focusing everithing else, but ethernity.

[stevebrot]

what really determine sharpness

Resolution + contrast

[Vitalii]

Resolution + contrast

haha, keep mocking.)
no answer is better than smartass answer.

[Dartmoor Dave]

How to decide if a "full frame" lens will work well on your APS-C camera:

1: Go to a camera shop that stocks the lens in question. Mount the lens on your camera and take a few quick shots from the shop doorway.

2. Go home and look at the shots on your computer.

3. If the quality is acceptable to you, return to the shop and buy the lens.

4. If the quality is not acceptable to you, don't buy the lens.




How to decide if an APS-C lens will work well on your "full frame" camera:

1. It'll give the same quality results as it gives on APS-C, but it won't cover the "full frame" image circle.

[stevebrot]

haha, keep mocking.)
no answer is better than smartass answer.

That is not a smartass answer, it is the serious answer and was not intended to mock.

That being said, I think you may be over-thinking all of this. In the real world, what will be driving your lens purchase decisions? I would expect that image quality would be a big consideration. As a person who regularly shoots FF lenses on an APS-C camera and those same lenses on FF, and also APS-C lenses on that same APS-C camera,I can assure you that I don't get crummy results from either format or lens image circle combination.

So here is a real world scenario. Say you want a tele-range zoom with FOV the same as the traditional 70-210 range on 35mm film. Pentax makes the optically excellent DA* 50-135/2.8 which satisfies the FOV requirement. You are ready to pull the trigger on the DA* until someone suggests that the Steveon 45-150/2.8 (made up lens) has good reviews at the same price point as the Pentax and WILL COVER FF!! On examination, you notice that the Steveon is half again larger and twice as heavy.

For me that is a no-brainer, regardless of whether you intend a future purchase of a FF body and regardless of whether that body supports crop mode. The DA* goes into the shopping cart and then I start worrying about SDM failure.

OTOH, I own the FA 77/1.8 Limited. I bought the lens for use on APS-C and happily, it also fits my film cameras. It is a usable focal length on both, is compact, handles nicely, and is full of pixy dust. Am I going to agonize over the DOF difference?* I don't think so.


Steve

* The only real difference, BTW for a comparable composition uncropped.

[Vitalii]

ok - where am i now
Pentax k-x 12 mp, really many FF a/m primes from, old sigma 90mm f2.8 macro, to FA 50mm 1.4 / many macro techniques - good results.

going back to your resolution + contrast
tried out same techniques on K3 - 2xResolution, 0.1% - change, exactly same results, same details, same sharpness.


What i´m aiming at - getting the most of the equipment i can get.
i could get myself k5lls or k3, but will probably wait for ff, or any else real improovement which will get me a real edge.

I have still to grow, there are photographers, which achieve lot more details by same magn.. - question how? and here comes the DXO with its confusing DXO P-megapixels. FFl on FFb or Apas-c lense, on aps-c body, which brings you more details, etc.

i have no dumb issues, which format is better, hell, i really like om-d´s with mft, and their toy looking lenses - the photographer is making most of the shot, and not the gear.
but aparently, i´m starting to hit on edges of my equipment. - Solution - better equipment or better knowledge. i´m trying to pick on second one.