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06-22-2009, 09:29 PM   #1
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DA 16-45 Questions

Just got my DA 16-45 today and noticed soft focus in the center at 1/60 sec and f4.0. At f5.6 it's perfect. These shots are indoors at night with built in flash. Should I return it or adjust focus on my K20D. I had heard that the edges could be soft at f4.0, but the center? What to do....

06-22-2009, 10:35 PM   #2
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QuoteOriginally posted by fccwpe Quote
Just got my DA 16-45 today and noticed soft focus in the center at 1/60 sec and f4.0. At f5.6 it's perfect. These shots are indoors at night with built in flash. Should I return it or adjust focus on my K20D. I had heard that the edges could be soft at f4.0, but the center? What to do....
Are you auto-focusing under tungsten light?
06-22-2009, 11:02 PM   #3
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Can you post an example so we can see?
06-23-2009, 06:16 AM   #4
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Yes, please post one for us.

If you use the K20D adjustment for that lens to make the center sharp at f4, then would the slight edge softness be what you expected at that focal length? My 16-45mm was back-focused when I got it (used) and required about half of the available adjustment before the center was where I wanted it. So no big surprise to me if yours needs an adjustment also.

06-23-2009, 06:18 AM   #5
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But if it's sharp at f/5.6 it may not be a FF/BF issue. It may just be soft at f/4.
Need some examples to check it out further.
06-23-2009, 07:09 AM   #6
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Yes, Ash is correct. I was focused only on the f4 issue. Would want to look at the whole range.

Keep me straight Ash....keep me straight!
06-23-2009, 10:39 AM   #7
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QuoteOriginally posted by asdf Quote
Are you auto-focusing under tungsten light?
No, it is under the eco-friendly light bulbs that fit into a normal socket but are fluorescent.

I think it may be a low light issue, but I'm not sure...
06-23-2009, 02:02 PM   #8
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Those compact fluorescent bulbs often have a similar color temperature profile to incandescent bulbs (intentionally -- so it doesn't seem like cold, harsh light). I have similar focusing issues under both kinds of artificial light sources, where it's perfect in natural light.

I suggest you re-test in sunlight.

That having been said, my lighting-dependent focal issues are really only apparent at f/1.4-2ish, so you may just need to dial in some adjustment regardless of the light source.

06-23-2009, 02:48 PM   #9
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QuoteOriginally posted by Quicksand Quote
I suggest you re-test in sunlight.

That having been said, my lighting-dependent focal issues are really only apparent at f/1.4-2ish, so you may just need to dial in some adjustment regardless of the light source.
Hello Mr. Quicksand, This whole focusing different depending on light source is a new topic for me and one I was unaware of when I adjusted for my BF 16-45mm lens. Can you point me to a thread or refererence or something for more info?
thanks.

I KNOW you don't mean f/1.4-2ish with the 16-45mm lens.
06-23-2009, 07:53 PM   #10
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OK, got it figured out. Outdoors with lots of light the lens is perfect in every respect. I change the program to high speed when indoors and if needed, change the aperture to f5.6 with the rear e-dial. Usually with this setting, under the low ambient lighting and when using the built-in flash the K20D will select 1/60sec and f7.1 Using this technique, the focus issue is a non-issue.

Thanks for all the help you guys! I am always impressed with the amount of expertise here, as well as the willingness to share it.
06-24-2009, 03:04 AM   #11
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QuoteOriginally posted by imtheguy Quote
Hello Mr. Quicksand, This whole focusing different depending on light source is a new topic for me and one I was unaware of when I adjusted for my BF 16-45mm lens. Can you point me to a thread or refererence or something for more info?
thanks.

I KNOW you don't mean f/1.4-2ish with the 16-45mm lens.
In no particular order,

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44459-front-focus-could-bad.html

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44949-poll-who-has...-lighting.html (The majority probably shoot at smaller apertures and because of the wider depth of field don't notice the problem.)

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44548-proposed-sol...ont-focus.html

This is a problem with many DSLRs, not just Pentax's. frank pointed out that K-7's AF is accurate under tungsten.
06-24-2009, 06:25 AM   #12
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QuoteOriginally posted by asdf Quote
In no particular order,

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44459-front-focus-could-bad.html

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44949-poll-who-has...-lighting.html (The majority probably shoot at smaller apertures and because of the wider depth of field don't notice the problem.)

https://www.pentaxforums.com/forums/pentax-dslr-discussion/44548-proposed-sol...ont-focus.html

This is a problem with many DSLRs, not just Pentax's. frank pointed out that K-7's AF is accurate under tungsten.


Many thanks for pulling together the references. I was not yet a forum member when those threads were hot so I missed out. I have lots of catch-up reading to do. Maybe a little re-evaluating my adjustments also
06-24-2009, 11:55 AM   #13
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QuoteOriginally posted by imtheguy Quote
I KNOW you don't mean f/1.4-2ish with the 16-45mm lens.
Heh, no, you're right. I didn't mean that!

I have this focusing issue with my FA 50mm f/1.4, and for a while I thought it might be specific to that one lens. But as asdf pointed out (and I had to ask around here also, sometime last year), this topic has come up a bunch of times in the past, so I eventually figured out it's probably only visible to me at large apertures, and masked by DOF otherwise. That's the only autofocus fast lens I have.

The 16-45mm mentioned in this thread, being f/4, caused me to wonder whether the lens needed adjustment *beyond* the warm-lighting issue. And if that's the case, in my opinion it's best to do that adjustment in natural light.

My FA 50mm autofocuses perfectly outdoors and needs no compensation, so the frontfocusing under artificial light is just an unfortunate fact of life. On the other hand, I have a Sigma 24-60mm f/2.8 that front-focuses in all light conditions, so that one gets compensation.

Boy am I glad my K20D has that function!
06-24-2009, 01:51 PM   #14
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Now I get to recalibrate my 16-45mm but this time in natural light as I the big adjustment I made was using mixed lighting, mostly compact flourescent that you guessed it, is about a tungsten wavelength when I do WB setting. Now I get to see if all that hub-bub about wavelenght and focusing smacked me in the kisser or not.

And we call this fun??
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