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04-04-2012, 09:11 PM   #1
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100mm f2.8 macro wr not focusing sharp

I have a SMC Pentax-D FA 100mm F2.8 Macro WR that I use to take photos of teeth for my dental lab work .I am on the 2nd floor and I have have a window I can open and a tree just out side the window ,the branches are as close as 6 feet away, I have been taking pictures of birds in the tree with my 70- 300 mm lens and my 18-55 kit lens the auto focus is nice and sharp with the lens and the camera k10d seems to be right on the money with the focus, but when I use the SMC Pentax-D FA 100mm F2.8 Macro WR lens I noticed at a distance of about 10 feet that the photos I took of a bird and some branches and the tree it's self that in auto focus mode the bird and branches and trunk of the tree were not in focus after I took the photo, the camera was beeping as if it was focused and at first I didn't notice until I looked at the photos on the computer . all the photos were on a tripod with good shutter speed 180 and 250 . so I took a few photos of a bird and made sure the red square was in the middle of the bird and then I took one with in manual focus mode all the ones of the bird in auto focus was slightly out of focus and the one I took with manual focus was perfect ,so I though maybe the focusing was not picking up the bird some how so I tried it on a big branch and sure enough with the red square not moved I took some with auto focus and with out it on and the auto photos were out of focus every time but the manual focus was perfect. so then I let the auto focus do its thing and once it though it was in focus I looked really close and I moved the focus ring to see if it was in focus and it was not I moved it till the trunk of the tree was in perfect focus and then touched the auto focus again to see if it would move or stay where I put it , it moved to a out of focus point again, its not a lot but enough to make it out of focus . up close at a distance of 2 feet or less it seems to be focusing in auto perfectly I cant get it any sharper that what it picks . would some one that has this lens do this test at about 10 feet and let me know what happens .focus on something that will not move and use a tripod and a wireless shutter control or the timer in the camera .take a few pictures in auto then move the switch to manual with out moving any thing and take a few that you focus your self and let me know what happens .thanks for your help Steve

04-05-2012, 12:36 AM   #2
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No offense, and I really don't want to come across as a jerk but....

The use of paragraphs would make what you have to say readable.
04-05-2012, 06:56 AM   #3
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I "kind of" read your post through. Sorry it is very diffucult to understand because of the way it is written out.
Probably why you only have 1 response in 9 hours.

I am thinking possibly you may need AF adjustment for your DFA100 if the other lenses seem to lock AF accurately. (I think you can do it on a K10D?? somebody correct me )

But first check the following.....

I assume you had SR turned off whilst using the tripod. Using SR when on a tripod can create blur regardless of using AF or MF.

Often when using AF to try to focus on birds perch among branches the AF may tend to lock onto the branches (which often have sharply defined edges) instead of the bird itself.
With a long tele lens which can have a very narrow depth of field, focussing on the "wrong" subject even if it is only 6" or 1ft away from your intended subject may lead to your subject being noticably out of focus.
I would suggest you test the lens out with another subject which is "easier" to AF on. Perhaps a lamp post or object which stands by itself with no other nearby object which it may mis-focus on. If it does not focus accurately in that situation then maybe you need AF adjustment.
04-05-2012, 09:15 AM   #4
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I used to have the same issue with the K10 camera, some lenses were spot on, but a couple were not. When the camera hack called debug mode showed up, I installed it in my camera, and it helped with some of the lenses. The problem with the Dbug mode It would only do one lens at a time, I upgraded to a Pentax K20 which can do I believe 10 or more lenses. The camera has more pixels better image quality and less noise in the photos. You can pick one up, quite cheap now, and the interface is nearly identical to the K10.

04-05-2012, 12:11 PM   #5
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Taking a picture of a bird in a tree is the absolute classic example where you simply cannot trust AF to guess where you want to focus - it can choose any old branch it wants. In other words, neither your lens nor your camera likely has a problem; you are just talking about a situation where AF doesn't work well. It,s kind of ramdom chance which branch the camera will choose to focus on. This would be just as true with the kit lens, but you be less likely to notice because of the wider field of view and larger depth of field.
04-05-2012, 03:59 PM   #6
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Original Poster
thanks everyone for you help ,I know neil I am the worse writer ever , your not being a jerk .I shouldn't even tried to type what I did but I did the best I could .I did have my sr on steve1307 I forgot about that I remember reading about that in my manual thank you I'll try it again with it off .I tried different distances today and it focused on every thing really good . so it must have just been the darkness if the tree with all the leaves blocking the sun. your right Marc Sabatella .seems like that's the only place it has trouble focusing .
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