Go Back   Steve's Digicams Forums > Post Your Photos > Photo Critiques

Reply
 
Thread Tools Search this Thread
Old Jan 21, 2010, 10:23 PM   #1
Senior Member
 
Join Date: Nov 2009
Posts: 589
Default Sharpness Don't understand

Ok, I'm learning my first DSLR a Pentax K7. I shot this with a 55-300 DA lens at 300mm. Is it normal for the left side of the image to look so soft? I know the depth of field will be very shallow, but the difference in distance from his head to his tail is not that great in that plane.
Attached Images
 
tony3dd is offline   Reply With Quote
Sponsored Links
Old Jan 21, 2010, 10:41 PM   #2
Senior Member
 
mtngal's Avatar
 
Join Date: Nov 2005
Location: Frazier Park, CA
Posts: 16,052
Default

Possibly not normal. It's impossible to tell from this picture because there's nothing on the right side to compare the left side to, but its possible that your lens is decentered (something mis-aligned inside where one side and center is sharp and the other side is blurry). I've used two different methods to test a lens - one is to take pictures of a brick wall, using a variety of focal lengths and distances (including one where the lens was at infinity). Make sure the camera is square to the wall, especially at larger apertures. Use a tripod or a firm surface and turn off stabilization, so there's no question of camera shake or the anti shake system influencing the shot.

The other method I used was to tape a newspaper classified ad page up and shoot that, both with and without flash (this worked well when I was testing a wide angle lens, harder to do with a longer lens like the 55-300). You'll get a better idea if there's something wrong with the lens, because the right and left sides will be the same distance (assuming the camera is square and level to the subject). Use several different focal lengths. If nothing else, you'll find those "sweet spot" focal lengths/aperture combinations where the lens is sharpest.

While this lens has a very good reputation, there's always the occasional lemon. I sent my first 55-300 to Pentax for warranty repair for this problem, and they promptly sent back a new lens that's fine. So shoot some brick walls or classifieds and make sure, then send it in for warranty if one side shows signs of being blurrier than the other.
mtngal is offline   Reply With Quote
Old Jan 21, 2010, 10:48 PM   #3
Senior Member
 
Join Date: Nov 2009
Posts: 589
Default

Here is another shot with the same lens shot the same day.
Attached Images
 
tony3dd is offline   Reply With Quote
Old Jan 21, 2010, 11:05 PM   #4
Senior Member
 
Join Date: Nov 2009
Posts: 589
Default

Here's one more shot on a different day. The bottom left and right looks about the same right?
Attached Images
 
tony3dd is offline   Reply With Quote
Old Jan 21, 2010, 11:44 PM   #5
Super Moderator
 
Hards80's Avatar
 
Join Date: Nov 2004
Location: Cleveland, OH
Posts: 9,046
Default

you really need to shoot something perfectly flat to have any idea. as the dof is confounding everything in these shots.

i would follow mntgal's suggestions. i usually use the brick/block wall method myself, but the newspaper could work too.
Hards80 is offline   Reply With Quote
Old Jan 21, 2010, 11:47 PM   #6
Super Moderator
 
Hards80's Avatar
 
Join Date: Nov 2004
Location: Cleveland, OH
Posts: 9,046
Default

however, i am not sure that there is any decentering here. the 2nd and 3rd shots just not flat enough to make any comparisons.

but looking at the first shot, it appears you might have missed focus a little bit. it looks like you got the focus about halfway through the post, or slightly behind the squirrel. and since the left side of the squirrel is closer than the head, it is even further out of the focal plane.
Hards80 is offline   Reply With Quote
Old Jan 22, 2010, 12:19 AM   #7
Senior Member
 
Join Date: Aug 2009
Posts: 629
Default

I think hards might be right. If you look along the back of the squirrel, it seem to be more in focus (although not completely) The tail and hip is closer and for sure out of focus. The head in the mid line is the same as the back but closer its out of focus.

back to the tail..the hairs closer to the mid line are sharper.

That's what these inexperienced eyes see..
littlejohn is offline   Reply With Quote
Old Jan 22, 2010, 7:36 AM   #8
Senior Member
 
Join Date: Nov 2009
Posts: 589
Default

Thanks everyone. I'm going to do some flat image testing today. I'll post those images.
tony3dd is offline   Reply With Quote
Old Jan 22, 2010, 8:38 AM   #9
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

It's probably normal. You're going to see more softness in the corners with the aperture wide open with most lenses, and you had a very shallow DOF for a shot like that squirrel (with the head a bit further away compared to the rest of the body). Stopping down the aperture a bit would help that (for example, use f/8 instead, keeping an eye on your shutter speeds to reduce blur from camera shake or subject movement).

If you want to use a newspaper type approach, just make sure the lens is perfectly square to it using a tripod. Then, make sure all 4 corners are equally soft to rule out a centering defect (and you can expect them to be a bit softer compared to the center at wide open apertures with most lenses).
JimC is offline   Reply With Quote
Old Jan 22, 2010, 9:06 AM   #10
Senior Member
 
mtngal's Avatar
 
Join Date: Nov 2005
Location: Frazier Park, CA
Posts: 16,052
Default

Looking closer at your squirrel picture does make me think it's more of a focus problem than a centering problem. If you are interested, you can find some pictures that I took with my faulty lens.

This link goes to the first picture that got me thinking I had a problem with my DA55-300, but wasn't definitive. The power lines are far enough away that the focus is infinity, and I would have thought the sharpness should have been the same between the right and left sides. http://mtngal.zenfolio.com/img/v1/p594385645-4.jpg for a reduced version of the picture. And here's one of my brick wall pictures that convinced me to send the lens back: http://mtngal.zenfolio.com/p691012471/e11f494fc . If you follow the link you can download the original, full sized file so you can compare it to your brick wall (the lens normally has a certain amount of barreling, so don't get distracted by that). Mine were taken with the K20 so the file size will be the same as your K-7.

Another thing about shooting test photos - use ISO 100 if at all possible - noise at high ISOs will affect sharpness. Also remember that you are looking for side to side comparison - it doesn't have a centering problem if it is fuzzy across the whole picture.

If you suspect the lens isn't focusing right (i.e., back focusing) there's a totally different process to figure that out. And the good news is that the K-7 has a way of adjusting back/front focus issues within the camera, and it can be adjusted for just that lens.
mtngal is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 1:02 PM.