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Old Jan 28, 2007, 7:03 PM   #1
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Hello again :}

Just bought a brand new Pentax FA 50/1.4 for my K100D. At first it had back-focusing problems. These were fixed (incredible, but it's true) with firmware update to 1.02. After that the lens inherited some slight front focusing. Anyway, since I am suspicious about it I thout maybe you guys could help me out. I added an image here which shows the whole scene and a 100% crop of the focus area. So the questions are: is it sharp enough at 1.4? What do you tink about the focus? Since I am thinking of returning this lens your opinions are welcome!

Thanks in advance!
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Old Jan 28, 2007, 8:42 PM   #2
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Verloc wrote:
Quote:
Hello again :}

Just bought a brand new Pentax FA 50/1.4 for my K100D. At first it had back-focusing problems. These were fixed (incredible, but it's true) with firmware update to 1.02. After that the lens inherited some slight front focusing. Anyway, since I am suspicious about it I thout maybe you guys could help me out. I added an image here which shows the whole scene and a 100% crop of the focus area. So the questions are: is it sharp enough at 1.4? What do you tink about the focus? Since I am thinking of returning this lens your opinions are welcome!

Thanks in advance!
Congratulation on your new lens.

I would believe it is sharp for f1.4 which gives you only paper thin DoF. When taking test shot make sure you do that on a tripod or at least brace for some support.

There are two example of my shots at F1.7 & F2.

http://www.stevesforums.com/forums/v...mp;forum_id=80

Enjoy the newfound power of a fast lens

Daniel
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Old Jan 28, 2007, 8:48 PM   #3
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Hard to tell. Was it taken handheld?

From what I read on other forums, this lens exhibits some back-focus/front-focus issues wide open (F1.4). I could not tell you for a fact since I do not care what so ever. I never used mine at F1.4 and I do not see the need.

Virtually all fast lenses exhibit softness and CA when wide open. The other thing to consider is the DOF which is ridiculous at F1.4 and can give you softness galore.

Use some DOF calculator to figure that out (distance to object, camera sensor size, focal length and aperture need to be feed in).

As a side note, here are some other lenses I tried wide open and which exhibit softness and CA: FA 35mm F2, Takumar 135mm F2.5, F28mm F2.4, A 70-210mm F4.

Bottom line: returning it might not solve the "problem".
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Old Jan 28, 2007, 8:50 PM   #4
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As Daniel has mentioned above, DoF at 1.4 is very shallow. This condition is at it's most extreme, the closer you are to your subject. Try taking some pictures where the subject is at a further distance and check for sharpness.

Jay
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Old Jan 28, 2007, 10:17 PM   #5
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Verloc

You know what. This probably gives you a better idea the degree of acceptability of the pict you showed above at F1.4.

I belong to a photo club in Toronto called TPMG.ca and there was a posting ofsome low light shots. This fellow Dave had a live music shot in a club of equally challenging lighting situation (like what you had ) and his setting waswith Canon EF 50mm f/1.8 wide open at ISO 1600 on a Canon EOS 30D.



The rest of the shot are at


http://www.flickr.com/photos/concret...7594494942769/

The consensus of the photo club is thathis shots were very good.

Yours is really not bad at all

Daniel




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Old Jan 29, 2007, 9:15 AM   #6
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Once post processed. it looks OK:

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Old Jan 29, 2007, 4:59 PM   #7
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I use the lower right focus point when using anything larger than f2 as my K100D has in accurate focus points. This is not very noticable untill you use something like the 50mm 1.4 which really shows that my center focus point is not the most accurate. A lot of people believe they have front or back focus problems as they af using spot focus when in fact they just have a slightly misaligned set of focus points. I lock focus and recompose and it works fine that way for me.
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