In theory a perfect lens would be sharpest wide open, so a really good lens would be sharpest close to wide open. If it takes 4 or 5 stops to sharpen up a lens, its probably not that great. As for good rules of thumb, I find f5.6 or f8 to usually work pretty damn good....
----------------- J.C.O'Connell hifis...@gate.net ----------------- -----Original Message----- From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of Mark C Sent: Monday, June 04, 2012 8:06 PM To: Pentax-Discuss Mail List Subject: Re: How much difference does optimizing the aperture make? On 6/4/2012 6:22 PM, Larry Colen wrote: > I was thinking about my quest for sharpness, and was considering trying to do some research into what the aperture "sweet spot" is for each lens, and was wondering if anyone had already made a chart of them. > > Then I wondered how much it really matters. I've heard "a couple of stops down from wide open", "anywhere between f/8 and f/16", and a couple other rules of thumb. I do know that on some lenses, particularly the FA50/1.4, that stopping it down a couple of stops from wide open, makes a huge difference. And I suspect that if you look on an MTF chart, you might be able to easily see the difference between f/4 and f/8, but is there a practical noticeable difference? > > There is also the question of sharpness at the critical focus distance, and overall sharpness. That a lens might be sharper at f/4 than f/16 at the focal distance, but with a lot more depth of field, more of the photo will be sharper at f/16, than at f/64. > > I'm primarily interested in answers based on personal, practical experience, rather than theory. My hunch is that as long as I'm not too close to wide open, or pushing diffraction limits, optimizing aperture for sharpness is not the most productive place to spend my time and energy. That I'm generally best optimizing the aperture for the picture, and not trying to optimize the aperture for MTF. > > -- > Larry Colen l...@red4est.com sent from i4est > To a large extent it depends on the lens - I've seen some that benefit hugely from being stopped down one or two stops and others that show less of an improvement. My A 50 1.4 benefits form being stopped down, my FA 50 1.7 is almost as good wide open as it is at f 4 or 5.6. Back when I had the Rikenon 55MM F1.2 it was noticeably less sharp wide open (and also had a fair bit of light fall off.) My Tokina 400 f5.6 is not so sharp at f5.6 but improves tremendously at f8. Most macro lenses I've tried benefit from stopping down but are very good wide open as well. What it boils down to (for me) - in theory any lens would benefit from stopping down one or two stops, but unless I see a difference I don't worry about it. Stopping down = slow shutter speed or higher ISO, either of which would probably offset the benefit gained by shooting at the optimum f stop. I do notice a loss of sharpness when stopping down to f16 or beyond, I assume due to diffraction. So, as a general rule of thumb I try to stick with f8 or at the most f11 . Makes for nicer backgrounds as well. For general shooting I find f5.6 to usually be fine for DOF. You really just got to try out your lenses and see what you experience. MCC -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
