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11-14-2010, 06:30 AM   #1
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FA31Ltd: soft wide-open or pixel peeping ?

Beginning of 2010 I bought the FA31Ltd for my K10D and was never really happy with the results, even after calibration of the combo at the local Pentax service center.

The K5 arrived a couple of days ago and I decided to spend the weekend to sort this out once-and-for-all.

I started with a AF calbration on friday. Newspaper against wall, f/1.8, distance approx 1.3 meters, tripod, 2 sec delay, no remote, AF steps from 0 to +10. Conclusion was that +3 (or possibly +2) was optimal.
1) Is this the correct approach?

For the following it might be important to know that I use a 23" monitor. By default (landscape) images are displayed at approximately A4 size (24% of a K5 full res image) and using the viewer in full screen the photos are displayed at approximately A3 size (31% of a K5 full res image) and I view them at approximately 70cm distance.


Saterday morning I took shots with the +3 setting in the garden. Subject distance approx 11 meters, tripod, 2 sec delay and cable release. At f/1.8 it looks either OOF or soft; at that distance however, DOF should take care of OOF so I think it's just soft.
2) Is this a conclusion that can be drawn?

At other apertures (f/2.8 and higher) I'm happy with the results unless I pixel peep.

This is the scene (at f/8.0) and the main subject is the bush with the white and purple flowers.


F/1.8 resized crop


F/2.8 resized crop


Below are links to the photos; resized photos at different apertures unfortunately don't seem to show the problem that I think I'm having, hence the links below.

F/1.8
crop (600kB; ~ 580x800)
crop 100% (3MB; 1450x2000)
full size (12MB)

F/2.8
crop (600kB; ~ 580x800)
crop 100% (3MB; 1450x2000)
full size (12MB)

F/4.0
crop (600kB; ~ 580x800)
crop 100% (3MB; 1450x2000)
full size (12MB)

F/5.6
crop (600kB; ~ 580x800)
crop 100% (3MB; 1450x2000)
full size (12MB)

F/8.0
crop (600kB; ~ 580x800)
crop 100% (3MB; 1450x2000)
full size (12MB)


Below is a (resized) crop of a flower at short distance at F/1.8. I'm quite happy with it (specially if I look at the 100% crop)



crop 100% (1.5MB)
full size (9MB)

I hope some people with no limit on their internet capacity will to download the full size samples and give their opinion. Is it me pixel peeping or is there actually something wrong with this FA31.

PS Images are resized/cropped from camera jpeg; camera settings +1 for both sharpening and contrast, other settings neutral (0).

11-14-2010, 07:31 AM   #2
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Those tiny white flowers look over-exposed and have lost detail. The highlight areas 'glow' or 'bleed' a bit at f/1.8 but is it any worse than you would expect from a fast lens wide open? Looks pretty OK to me.
11-14-2010, 10:54 AM   #3
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Thanks for the reply; I forgot about that. I have experienced that the FA31Ltd is a bit of a 'bitch' when it comes to incorrect exposure (also with regards to purple fringing).

I will try to do the shots again next weekend (weather permitting for the same conditions).
11-18-2010, 04:24 AM   #4
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When I got the FA 31 I also had the same concerns. I think the main issue is the dazzling reputation of this lens - people have very very high expectations of it, i.e. pictures taken wide open to be bitingly sharp while the background to be creamily OOF-ed. I have other fast lenses (i.e. below f2) and seldom find them to be bitingly sharp wide open. That only comes at abt f2.8 and above.

With reference to your shots above, the lighting was quite harsh, and the subject was white in colour - there's a lot of light bouncing about. The resulting effect when you take the shot wide open is that the image would look soft, due to a sort of 'halo' effect from the white colour of the subject reflecting the harsh sunlight. That's my experience with these shots.

However, there will be some occasions where you can use the FA 31 wide open to great effect - usually in low / muted lighting conditions:





11-18-2010, 04:29 AM   #5
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and to add, I've always found that the FA 31 does wonders with film - i enjoy the results better than digital shots (I'm on the K20D).

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