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+--- Thread: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? (/showthread.php?tid=76123)
Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - space-time - 04-10-2009
I had a Pentax *istD for a long time (I bought it new in 2004). I was never able to get those sharp photos you see in magazines.
I finally did the focus test (http://focustestchart.com/chart.html). I used a 50 mm f/1.4 lens, I shot using a tripod, 10s delay (which locks the mirror up and also eliminates any vibrations), using Auto-focus, and here is the result.
What do you think? (picture is about 900 kb)
http://img23.imageshack.us/img23/1279/focus.png
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - Spock - 04-10-2009
Looks OK to me.
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - mattkime - 04-10-2009
would be a better test at middle aperture
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - pRICE cUBE - 04-10-2009
At that magnification, 1.4 is going to look like that. Also, it looks underexposed so it may look less peppy than you expect.
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - space-time - 04-10-2009
mattkime wrote:
would be a better test at middle aperture
but the DOF would be larger, making judgement more difficult... I think you want to have a shallow DOF to see only what is in the focus, right?
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - pRICE cUBE - 04-10-2009
There are several other factors in play here. What sharpness setting is it? It is underexposed. The lens looks like it focuses fine to me.
Re: Calling Photo Experts: focus test chart: do you think my camera is OK or has a back focus issue? - Don Kiyoti - 04-10-2009
space-time,
It does look like it could be be back focused just slightly. That lens is known to be rather soft wide open but it looks like it might be focused at the 2mm line.
But - are you set up properly for this test? You should have the camera at a 45º angle from the test chart and it doesn't look like you're lined up properly. The test should be done with the lens wide open by the way.
I used the chart here when I tested my K10D:
http://pentaxdslrs.blogspot.com/2008/06/part-1-autofocus-adjustment-for-pentax.html
That site gives a lot of useful instructions and the chart itself presents a 45º angle when you have it folded up so you can rig the test so the camera is on a level surface. I used the method there to adjust the focus on my K10D (you have to have a certain firmware version and then get the camera into a "debug" mode.) I don't know if that's possible for a user to do with the istD. By the way, the K20D is user-adjustable and will remember settings for a number of different lenses.
I also rigged an outdoor test using a ladder and beer bottles. I laid the ladder on the ground and put a bottle at each rung and did a bunch of shots focusing on one bottle or another. It was very helpful and a bit more "real worldly" than shooting a focus chart.