AF Calibration charts
Posted 27/04/2013 - 00:03
Link
Mannesty wrote:
You now, once you download stuff, it's good to read it
The instructions say "minimum focus distance, then back a bit".
When and if I do download a test chart I certainly will but as I haven't as yet downloaded anything (and not sure where you got the idea I had?) I thought I'd just gather as much info as possible both for myself and any other interested parties... Thanks for your response, I shall hope the condescending tone was unintentional as the information was at least relitavely useful, if a little vague...
You now, once you download stuff, it's good to read it
The instructions say "minimum focus distance, then back a bit".
........................................................................
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
https://www.flickr.com/photos/daveholmesphotos/
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
https://www.flickr.com/photos/daveholmesphotos/
Posted 27/04/2013 - 09:04
Link
JAK wrote:
What I am failing to grasp is how some lenses can focus OK on the viewing screen yet be out of focus on the sensor and hence need adjustment, but not others.
An explanation would be interesting and useful.
John K
I can't find the link now but I remember reading about this a year or two back. I think it's something to do with the focus point not necessarily being the same at different f-stops on some lenses, due to various aberrations. AF and visual focus confirmation is done with the aperture wide open, then the shot is taken at a smaller aperture usually, so there's the problem waiting to happen.
What I am failing to grasp is how some lenses can focus OK on the viewing screen yet be out of focus on the sensor and hence need adjustment, but not others.
An explanation would be interesting and useful.
John K
Posted 27/04/2013 - 09:07
Link
You can set it to vibrate when you switch off on the K-30, which is less annoying.
Posted 27/04/2013 - 10:47
Link
sbrads wrote:
I can't find the link now but I remember reading about this a year or two back. I think it's something to do with the focus point not necessarily being the same at different f-stops on some lenses, due to various aberrations. AF and visual focus confirmation is done with the aperture wide open, then the shot is taken at a smaller aperture usually, so there's the problem waiting to happen.
Thanks. I will say though that my test was at full aperture, f2.8, so there wouldn't have been a shift of focus point. Another oddity, I repeated the test on the K-m with the 100mm macro and focus was spot on, not that I could do anything about easily it if it wasn't. Perhaps there were some quirks with the original K-5 that needed ironing out.I can't find the link now but I remember reading about this a year or two back. I think it's something to do with the focus point not necessarily being the same at different f-stops on some lenses, due to various aberrations. AF and visual focus confirmation is done with the aperture wide open, then the shot is taken at a smaller aperture usually, so there's the problem waiting to happen.
John K
John K
Posted 27/04/2013 - 11:36
Link
sbrads wrote:
I can't find the link now but I remember reading about this a year or two back. I think it's something to do with the focus point not necessarily being the same at different f-stops on some lenses, due to various aberrations.
residual spherical aberration, quite common on some older Nikon primes.I can't find the link now but I remember reading about this a year or two back. I think it's something to do with the focus point not necessarily being the same at different f-stops on some lenses, due to various aberrations.
John
Posted 27/04/2013 - 16:53
Link
Quote:
JAK wrote:
... I don't recall any talk of this issue back in the film camera days.
I remember having the lens mount shimmed on one of the film cameras I owned back in the early 70's. Amateur Photographer produced a series of test charts from which you determined the best lines/inch that could be seen in various parts of the chart. Armed with this you shimmed one side of the mount to 'improve' the clarity of the lens. I've still got some of the charts somewhere.JAK wrote:
... I don't recall any talk of this issue back in the film camera days.
regards
Bernard
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7671 posts
16 years
Smegland
When using these test charts do you focus from the minimum focus distance of the lens you're testing or is there a set distance for the chart being used?
Or does it not matter?
Lenses: Pentax DA 10-17mm ED(IF) Fish Eye, Pentax DA 14mm f/2.8, Sigma 17-70mm f/2.8, Pentax-A 28mm f/2.8, Sigma 30mm F1.4 EX DC, Pentax-A 50mm f/1.2, Pentax-A 50mm f/1.4, Pentax-FA 50mm f/1.4, Pentax-A 50mm f/1.7, Pentax DA* 50-135mm f/2.8, Sigma 135-400mm APO DG, and more ..
Flash: AF-540FGZ, Vivitar 283