All Forum Comments
Comment by bobrapp posted on AF Calibration on the K20D at 13/11/2010 - 00:32
Yes, the LoCAs are caused by spherical aberrations which can induce focus shifts as a lens is stopped down. See:
http://diglloyd.com/articles/Focus/FocusShift.html
For setting the AF adjustments of my Pentax bodies, I use a Pentax-A 50mm f2.8 macro.
Bob
http://diglloyd.com/articles/Focus/FocusShift.html
For setting the AF adjustments of my Pentax bodies, I use a Pentax-A 50mm f2.8 macro.
Bob
Comment by bobrapp posted on AF Calibration on the K20D at 10/11/2010 - 14:48
Here is a test from Photozone. At the bottom of the analysis page, there is section on LoCa. The lens is in a fixed position and the apertures form f1.4 to f4 are shown. Mouse over 1.4 on up to 4 and you will see the effect. This lens back focuses as it is stopped down.
If it was my lens, I would calibrate at F4 (unless I used it wide open all the time).
http://www.photozone.de/canon-eos/392-sigma_50_14_canon?start=1
Bob
If it was my lens, I would calibrate at F4 (unless I used it wide open all the time).
http://www.photozone.de/canon-eos/392-sigma_50_14_canon?start=1
Bob
Comment by bobrapp posted on AF Calibration on the K20D at 09/11/2010 - 23:59
By using the 50mm f1.2 may be the problem. Whilst I don't have that lens, I have encountered severe focus shift (back focus) on some Sigma fast primes (30 and 50mm). This phenomenon is also suffered by some Canon and Nikon lenses as well.
For that reason, I check the focus adjustment of my fast lenses by stopping the lens down to F5.6 and verify my adjustment. If there is a significant focus shift, I will re-calibrate the lens at f5.6.
The theory that fast primes focus easier should be taken with a lump of salt.
YMMV
Bob
For that reason, I check the focus adjustment of my fast lenses by stopping the lens down to F5.6 and verify my adjustment. If there is a significant focus shift, I will re-calibrate the lens at f5.6.
The theory that fast primes focus easier should be taken with a lump of salt.
YMMV
Bob
Comment by bobrapp posted on AF Calibration on the K20D at 09/11/2010 - 21:50
Smeggypants wrote:
This caused another problem. The 17-70 andn 135-400 sigma lenses now needed more than +10 so I had to compromise with the 50/1.2 and set the overall AF on the K20D to -100um too allow those sigma lenses to work at +10
At -100um the DA* 50-135 AF'd at 0
Conclusion: +/- 10 is not enough a rnge to cater for all lenses.
bobrapp wrote:
Regarding AF adjustments on the K20 - perhaps the K7 as well - The AF adjustment through the MODSET function adjust the AF globally.
I have one lens that I could not bring into focus through the function settings. All of my lenses needed a + 9 or better to bring them close to accurate focus.
I used a manual focus lens to adjust the MODSET AF adjustment and then went about adjusting all my lenses through the custom function. Now they are all within plus or minus 4!
Bob Rapp
I've just had to do this with my K20D. I recently purchased a manual focus 50mm/1.2 which the K20D's +/- 10 wouldn't accommodate. I had to go into debug mode on the K20D and set it to -250um for the manual lens to caliberate it's focusRegarding AF adjustments on the K20 - perhaps the K7 as well - The AF adjustment through the MODSET function adjust the AF globally.
I have one lens that I could not bring into focus through the function settings. All of my lenses needed a + 9 or better to bring them close to accurate focus.
I used a manual focus lens to adjust the MODSET AF adjustment and then went about adjusting all my lenses through the custom function. Now they are all within plus or minus 4!
Bob Rapp
This caused another problem. The 17-70 andn 135-400 sigma lenses now needed more than +10 so I had to compromise with the 50/1.2 and set the overall AF on the K20D to -100um too allow those sigma lenses to work at +10
At -100um the DA* 50-135 AF'd at 0
Conclusion: +/- 10 is not enough a rnge to cater for all lenses.
Comment by bobrapp posted on AF Calibration on the K20D at 09/11/2010 - 21:34
jps wrote:
I've just been trying to open images from the K5 in Silkypix (version 3). Strangely enough, I can see thumbnails of all the files, but I can only open a few of them. All the files were recorded as DNG RAW files, and I'm a bit confused as to why I can only view some of them - has anyone got any ideas?
Thanks for any help,
Jonathan
You have to got to version 4 for support of the latest cameras (DNG may work in 3). The high cost of the upgrade kept me from upgrading after 3 years with version 3.I've just been trying to open images from the K5 in Silkypix (version 3). Strangely enough, I can see thumbnails of all the files, but I can only open a few of them. All the files were recorded as DNG RAW files, and I'm a bit confused as to why I can only view some of them - has anyone got any ideas?
Thanks for any help,
Jonathan
Bob
Comment by bobrapp posted on K5 and Silkypix at 09/11/2010 - 04:06
Regarding AF adjustments on the K20 - perhaps the K7 as well - The AF adjustment through the MODSET function adjust the AF globally.
I have one lens that I could not bring into focus through the function settings. All of my lenses needed a + 9 or better to bring them close to accurate focus.
I used a manual focus lens to adjust the MODSET AF adjustment and then went about adjusting all my lenses through the custom function. Now they are all within plus or minus 4!
Bob Rapp
I have one lens that I could not bring into focus through the function settings. All of my lenses needed a + 9 or better to bring them close to accurate focus.
I used a manual focus lens to adjust the MODSET AF adjustment and then went about adjusting all my lenses through the custom function. Now they are all within plus or minus 4!
Bob Rapp
Comment by bobrapp posted on AF Calibration on the K20D at 09/11/2010 - 03:56
I don't understand. AF calibration changes or can change from lens to lens, or do you mean you set the internal debug mode AF setting with that lens and then offset the other lenses as required with the menu settings.
With the later lenses and the digital SLR, it seems that the lens provides some feed-back in the focusing system.
In the US, when focusing issues were an issue, Pentax USA asked the owners to send in their lenses and camera body for adjustment.
Bob Raapp