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09-19-2013, 07:23 AM   #16
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QuoteOriginally posted by alamo5000 Quote
I am having a tough time dialing the thing in.
I also have an FA 50/1.7 and have had exactly the same experience. I haven't found a solution and suspect its the K-5's PDAF that's not designed with work very well with fast lenses in low light, and that the problem has been fixed in the K-5II/s (but you'll need confirmation from K-5II owners). The K-5's live view CDAF works very well with this lens.

09-19-2013, 07:56 AM   #17
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QuoteOriginally posted by alamo5000 Quote
maybe I am expecting too much out of the AF of the K5 and the lens... if I stop down at all I don't have a problem... and if I manual focus in live mode then I can nail the shots with a sharp lens.
Well, there you have it.


Steve
09-19-2013, 08:29 AM - 1 Like   #18
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SouthLander,
That is indeed a nice shot of the loco.
Sometimes it is difficult for me to get the upper parts of those engines sharp against the sky, I am not sure if it is the hot air or the rocking motion.
09-19-2013, 10:40 PM   #19
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QuoteOriginally posted by wombat2go Quote
SouthLander,
That is indeed a nice shot of the loco.
Sometimes it is difficult for me to get the upper parts of those engines sharp against the sky, I am not sure if it is the hot air or the rocking motion.
Thank you. It was one of those shots that looked good the moment it was loaded onto the computer - the sharpness and clarity really caught my attention. I'd only used the F50/1.7 briefly about 12 months ago on a wet low contrast day and it seemed ok, but nothing stunning. I also wasn't entirely convinced I knew exactly where it lay in terms of focus adjustment on my K-x. Decided I needed to give it another go in better light. Took a bit of a guess for last weekend at +40um and it looks to be spot on in real life use. Really keen now to use it some more.

My lenses seem to come out in a small band of focus adjustments, but there is still enough improvement to chase down the minor variations, eg

Tamron 17-50/2.8 +50um
Pentax DA 55-300 +30um
F50/1.7 +40um
FA77/1.8 Limited - still not exactly sure, either +20um or +30um, more likely +30um.
My manual M lenses - using focus confirm light when adjustment is +50um seems pretty well right.

Unfortunately with K-x, only have global adjustment via debug menu, and I forget to change adjustment settings sometimes when swapping lenses. Although it a close band of adjustments, I can still see the difference when I forget. My next camera WILL have lens by lens adjustment capabilities. Hopefully Pentax will announce what that camera is in the next two-three weeks!

I think that the sharpness against the sky was helped by the loco being shaded under the trees. I'm wondering if the problem you describe is caused by the curved upper edges of loco boilers picking up glare/reflections in full sunshine and lowering the local contrast/saturation towards the intersection of the loco and the sky?? A polariser could well do wonders if that is indeed the problem. The shot I posted I think was 1/400th at F7.1 so it would have largely taken motion out of the equation in my specific example.

In this thread I posted back in January of the same loco https://www.pentaxforums.com/forums/groups/84-railroad-photography/2271-steam...kle-train.html, image 2 shows what I think you are describing. Look there and it can be seen how the sunlight reflecting of the top of the boiler is destroying any chance of a sharp high contrast line between engine and sky. I think I had the polariser on for that shot, so I imagine the reflection would have been a lot worse without. It was a VERY strong and UV intense light that day (it had been 45 degrees C/113F two days earlier!!! Bloody hot even for Oz). Image 4 on the other hand is fine with the sun to my back.

09-20-2013, 06:46 AM   #20
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Southlander,
Your January photos are all very good, I don't know how I missed them.
What aperture and shutter do you use for the moving loco?
A stop down is needed to get the length of the train in focus.
It won't let me repost here a photo I put in MF thread of a stationary loco with the Takumar 6 x 7 90mm at f/16.
I see some large format guys spend a long time to set up by the railroad track and then get frustrated by the blur
(of wheels is OK but blurred funnel is definitely not ! )
in their photo of the loco thundering past, shaking and swaying
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