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Forum: Pentax K-S1 & K-S2 05-30-2017, 11:52 AM  
K-S1 + AF Fine Adjustment + Sigma
Posted By stv
Replies: 9
Views: 1,595
Dear Steve,
I made many attempts to adjust AF using printed scales and different procedures, including the one published on this site. My Sigma was giving different adjustment values for focal range from 18 to 200 mm. And finally, at a real distance I had always blurred shots.


The procedure to test the whole AF Fine adjustment range from -10 to +10 is the only method that permitted to me to make sharp shots beyond 135mm (including handheld!)


Regards
Nikolay

---------- Post added 05-30-17 at 12:04 PM ----------


Correction:
The procedure to test the whole AF Fine adjustment range from -10 to +10 at the maximum focal length of 200mm is the only method that permitted to me to make sharp shots beyond 135mm (including handheld!). In fact, at smaller focal lengths the DOF is much bigger and Back/front focus is nearly invisible.

Nota: I am interested in the the 170-200mm focal length because I would like to shoot birds and small planes.
Forum: Pentax K-S1 & K-S2 05-27-2017, 10:19 AM  
K-S1 + AF Fine Adjustment + Sigma
Posted By stv
Replies: 9
Views: 1,595
I beg your pardon. The sample photo was 170mm not 200!


New rapid test is shown below : 200mm, AV f6,7, ISO100, 1/400s. The target was at 50-60m. Left is « -8 » AF Fine adjustment, right is zero adjustment. Each sample is one best from a series of 3 shots.


The result is obvious. I agree with your DOF estimation. My test shows that an incorrect adjustment (“0” instead of “-8”) moves the right focus by more than 13m (further, I think).


I think the best method to adjust AF should be taking 3 photos at each adjustment step (-10...+10 in the case of K-S1) and compare them. In such a way there is no mess with the adjustment direction.


Bu the way, I was surprised by the sharpness of 170mm shot compared to 200mm one at the same distance. To be continued...
Forum: Pentax K-S1 & K-S2 05-27-2017, 02:18 AM  
K-S1 + AF Fine Adjustment + Sigma
Posted By stv
Replies: 9
Views: 1,595
Hi pjv,
I set: 200mm, AV f7.1, ISO100, 1/400s. The target was at 60-70m : a wall well lit by the sun (11am). I attach the crop with -8 AF Fine correction.
Nikolay

---------- Post added 05-27-17 at 02:26 AM ----------

I forgot to say that this shot was made nearly handheld (camera put on the loggia barrier).
Forum: Pentax K-S1 & K-S2 05-26-2017, 01:20 PM  
K-S1 + AF Fine Adjustment + Sigma
Posted By stv
Replies: 9
Views: 1,595
Hi,


It have been maybe mentioned before but I have discovered a strange behavior of the AF Fine Adjustment on K-S1 with Sigma 18-200 DG. In fact, I did never succeed with AF adjustment until I tried to apply the correction in the inverse direction (not in the direction that the user manual suggests). Now it works and my Sigma gives sharp photos at 200mm.


It is connected to the fact that the focal ring on my Sigma turns in the inverse direction with respect to the Pentax’s lenses ?


Regards,
Nikolay
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