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10-08-2008, 07:06 AM   #1
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FA50 f/1.4 Back Focus

I just have a quick question - I've noticed about an inch of back focus (things further away than what i focused on are in focus - center focus point, and afs) with my FA50, but the same problem doesn't exist with my DA18-55 or my DA50-200. Is this possible to have the lens be at fault - or am I imagining it? the lens is still under warranty, but wanted to check here before I call and speak with Pentax.

10-08-2008, 07:14 AM   #2
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QuoteOriginally posted by mitchkramez Quote
I just have a quick question - I've noticed about an inch of back focus (things further away than what i focused on are in focus - center focus point, and afs) with my FA50, but the same problem doesn't exist with my DA18-55 or my DA50-200. Is this possible to have the lens be at fault - or am I imagining it? the lens is still under warranty, but wanted to check here before I call and speak with Pentax.
BF/FF for lenses like FA50/1.4 is nothing strange... if you have K20D it is easy to find a proper adjustment value(s) /remember - you need to test it under the daylight and under the tungsten light/... if you have K10D (not K200D) it is also possible, but w/ more hassle (for example : rarWebWorks - Pentax K10D Debug Mode Instructions - - )... if you camera is under warranty you can mail both camera and lenses (Pentax lenses) to Pentax service center and they will take care about it.
10-08-2008, 07:30 AM   #3
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I'm curious if this change will only take effect on my fa50, or will it mess up my other lenses which appear to be fine?
10-08-2008, 07:56 AM   #4
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QuoteOriginally posted by mitchkramez Quote
I'm curious if this change will only take effect on my fa50, or will it mess up my other lenses which appear to be fine?
winter is coming - send all three, just in case... my uneducated guess is that if pentax service technician will be doing actually any mechanical adjustments (through infamous 3 screws) then may be (again - somebody will correct me) you can get issues w/ other lenses...

10-08-2008, 08:15 AM   #5
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QuoteOriginally posted by mitchkramez Quote
I just have a quick question - I've noticed about an inch of back focus (things further away than what i focused on are in focus - center focus point, and afs) with my FA50, but the same problem doesn't exist with my DA18-55 or my DA50-200. Is this possible to have the lens be at fault - or am I imagining it? the lens is still under warranty, but wanted to check here before I call and speak with Pentax.
Which camera? You can bias the Af for individual lenses on the K20.
10-08-2008, 08:16 AM   #6
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QuoteOriginally posted by Wheatfield Quote
Which camera? You can bias the Af for individual lenses on the K20.
even for K20D some people find out that +10 / -10 adjustments are not enough.
10-08-2008, 08:21 AM   #7
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QuoteOriginally posted by mitchkramez Quote
I just have a quick question - I've noticed about an inch of back focus (things further away than what i focused on are in focus - center focus point, and afs) with my FA50, but the same problem doesn't exist with my DA18-55 or my DA50-200.
Does it happen with the FA50 even when stopped down to f/5.6, or only when relatively wide open? If the latter, I'd be inclined to assume the camera is at fault, and the larger DOF of the other lenses is masking the problem. If the problem persists at all apertures with the FA50, then the lens may have an issue. Either way, as others have mentioned, you may be able to work around it yourself with the K20D, since it can store individual adjustments for different lenses. But if the FA50 problem goes away at f/5.6, I'd assume the camera really is just off and DOF is hiding the problem with the other lenses - meaning that sending the in for service would not "break: your other lenses (they are already "broken", but have to much DOF to show you that).
10-08-2008, 09:57 AM   #8
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Check lighting, the FA50 HATES incandesant lighting and likes to FF or BF.

10-08-2008, 10:21 AM   #9
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QuoteOriginally posted by Alfisti Quote
Check lighting, the FA50 HATES incandesant lighting and likes to FF or BF.
not FA50, but stupid SAFOX...
10-08-2008, 11:37 AM   #10
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I had to lens stopped down to 2.8, which is supposedly supposed to be sharp. I have pentax K10d.

I'm contemplating reverting back to firmware 1.10 and using the debug menu to adjust it myself rather than send it in. I just got it back for some other issues i was experiencing and it took almost 4 weeks.

Will the changes i make in the debug menu apply to only that lens? or will they apply to all?

The pentax rep told me if i send it in, it will only apply to that lens, but I assume they'll just be using the debug menu as well.

Also, my test shots were taken outside, so the lighting is not to blame, and as i stated before, my other two lenses were spot on.
10-08-2008, 11:42 AM   #11
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QuoteOriginally posted by mitchkramez Quote

Will the changes i make in the debug menu apply to only that lens? or will they apply to all?

.
for K10D must be for ALL lenses...
10-08-2008, 01:03 PM   #12
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QuoteOriginally posted by mitchkramez Quote
The pentax rep told me if i send it in, it will only apply to that lens, but I assume they'll just be using the debug menu as well.
The Pentax Rep was right. There are 'memory locations' for several lenses (not sure how many) but the "debug hack" can only access one of them. If Pentax does it, they have the proper tools to be able to access all of them...

Sorry I can't substantiate this, but a search should pull it up - that's how I found it a few months ago...
10-08-2008, 01:30 PM   #13
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Backfocusing is signature of this lens. Again, some people will say to you that every photographer manual focuses their lenses in the old days
10-08-2008, 02:27 PM   #14
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if it's a K10D

I'm inclined to say it's the camera. It seems to be very common. If it's still under warranty, send it to Pentax with the FA 50mm.

The smaller aperture of the other lenses is masking the problem.

I think the notion the camera focuses under different lighting to be bogus. It was printed on blog some where and it keeps getting repeated. I nearly convinced myself of this phenomenon, but I think nonsense.

When you're indoors under incandescent lighting you're focusing on things that are closer to you (it's just a smaller space). . .which shrinks the depth of field even more. Go out side and focus on the nearest flower or tree trunk and magically the problem seems to resolve its self or get better. . .because the object is probably farther away than what you were pointing at indoors.

If the camera is not under warranty, it's pretty easy to use the debug mode on the K10D to fix the problem. Per this already posted link

rarWebWorks - Pentax K10D Debug Mode Instructions - -

My K10D likes +um60. Sharp as a razor all the time now with all lenses no matter what the lighting.

Get a focus chart like this one

http://focustestchart.com/focus21.pdf

follow the instructions and keep adjusting the camera until the focus is right.

Then test it out on real objects and things in different lighting -- tweak it until just right.

Oh, and adjust wide open and as close as possible. Make that DOF as tight as possible to really zero in on the proper focus adjustment.
10-08-2008, 02:44 PM   #15
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QuoteOriginally posted by konraDarnok Quote
I think the notion the camera focuses under different lighting to be bogus.
nope - it is not... my prev K10D, current K20D do focus differently under the daylight vs pure tungsten... I spent enough time finding AF adjustment values for my body/lens combos

QuoteOriginally posted by konraDarnok Quote
When you're indoors under incandescent lighting you're focusing on things that are closer to you
I kept the distance the same - the testing was done near the window, I have daylight during the daytime and tungsten during the nighttime, sorry to disappoint you.
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