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06-07-2009, 10:46 AM   #1
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K200d low EV AF treshold, solutions?

At what approximate EV value AF on k200d becomes theoretically unusable and i should stop trying to use it (use mf, use flash+smaller F/hyper focal).
Yesterday shooting under fluorescent light i couldn' t get it to lock. Tried both 30/1.4 and 70/2.4. After several fail's went MF route, since both lenses were fast for it.

It was hunting back to back and wouldn' t stop when it was 1/15s+f/2.4+iso800~ 4EV - dim lit room. I've also noticed that if the subject has even a slight movement the camera goes crazy, because i can get a reasonable speed and CORRECT lock in pitch black with only some sodium street lights visible far far at the horizon.
But it often fails to lock in daylight if the subject is slightly moving (not running or riding a bike).

Why is this so if the camera can precisely confirm the focus if focus it manually, but hunts or mis-focuses with AF. Apparently the AF sensor can " see" well enough to confirm my, quite fast turning, manual focusing.

How do you usually shoot when AF fails completely and you need to take GOOD pictures FAST.

ISO1000,1/10,F2.8+Boosted ~0.5Ev in PP. M28/2.8, Hand-held, clear focus confirmation:

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06-07-2009, 12:17 PM   #2
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I've shot in basically that same lighting many, many times with no unusual difficulties whatsoever (K200D with DA70/2.4 and DA40/2.8). However, almost never under *fluorescent* light at that low a level. Maybe the color of the light or its cyclical nature complicates AF at low levels?
06-07-2009, 12:51 PM   #3
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Maybe. Duno.. what you do when AF stops working? I usually put my camera aside since i'm rarely shooting anything THAT important it wouldn't be enough with a few flash shots at worst.

What surprised me was that the perceived brightness trough viewfinder was enough to focus manually. Usually it is the other way around, when the AF starts having problems it is already far too dark to distinguish enough detail to focus manually.

I'm guessing that since those were pretty cheap flo. bulbs they have very discrete spectrum. Maybe AF sensors maximum sensitivity fell somewhere in empty part of the light spectrum. But that goes against the flawless ability to confirm focus when in manual mode.

Anyway there always will be a situation where you have to do without AF, what is the best way to work with modern cameras, which has next to none MF capabilities.
06-07-2009, 01:00 PM   #4
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I've never actually shot in any real life situations where AF *stopped* working, although it certainly can get slower and less reliable. So I focus manually. No big deal to me since most of my "fast" lenses for low light are MF anyhow. But the DA70 and DA40 never let me down; they either nail it quickly enough, or else I take over (thanks to quick shift and my thumb on the "cancel AF" button!) and do it myself.

06-07-2009, 02:09 PM   #5
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My k20 refuses any cooperation much below EV metering level i always trying to choose some contrasty points like harsh shadow, reflections of light, white things on black backgrond or light spots even. However the best results one is able to obtain wit AF Aux beam from the flashgun. For instance: Lens f2.8, 5sec exp and iso100 (aperture and shutter indicator blinks so the EV level is below the limit of the metering - that limit for k20 is 0EV i guess) i'm stilll able to focus but ofcours without some additional light the picture would be blurred....
06-07-2009, 02:32 PM   #6
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Are there any seperate aux AF beam devices for reasonable price, you can use simulteniously with manual flash? Google and ebay Search didn't returned anything usefull.
06-07-2009, 03:54 PM   #7
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there are some el cheapo manual flashes with aux beam something like YN-462 or YN-460 - it has aux beam i guess... at least you can assume after look.... there is some red device at the front of it.
06-08-2009, 03:24 AM   #8
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Hi
As a new member to the K200D forum I just wrote (few days ago) that I've noticed a draw back from the K100D on the focus sensitivity, seems like the K100D can do in almost total darkness a perfect focus while the K200D needs stronger light. As for the thread, Since I had this issue on my old Fuji 602zoom (back in 2003-2004), Ive used a single LED spot light the kind that comes as a key holder, just holding it under the lens. Now I am using the AF360 flash just for the AF assist. In case of a city /landscape picture I do go manual. As I stated in 2 different threads + Email to Pentax service , a firmware upgrade that will take care of the focus issues will be welcomed!

06-08-2009, 07:16 AM   #9
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Some day ago, at the school end-of-year party I got some problem with the AF... there was enough light to shot at f3.5 1/60 iso1600. Despite this I got the AF searching for the focus (children was performing "Grease" so black jackets and no still action in the scene; because this wasn't enough the lighting was also poor)... and when this happened I stopped trying to focus, so I search for a high contrast area at the same distance where I can focus and when I get it I'll back on the original composition.
I can't figure another solution... so that's IMHO the limit of AF: with lower light I would go manual... if taking photos in that context has a meaning yet.

Have to say that my K200D performed very well in that situation (I'm absolutely happy of the camera). To be honest I think I couldn't ask more.

Bye
Jenner
06-08-2009, 07:31 AM   #10
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From the picture you posted, it seems like you are shooting through a window. The AF will try to focus on the window, but can't lock on because it's too close. Try opening the window!
06-08-2009, 12:27 PM   #11
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I was not, it is just an example of AF confirm low light capability with MF.
But i must note that the 30/1.4 had UV filter. Only problem is why 70/2.4 had the same problems then.
I think of selling my 30/1.4 since it is of no use in low light anyway. Sometimes it takes up to few seconds for it to focus uncorrectly daytime. Unfortunately M28/2.8 is only 2.8.

Last edited by ytterbium; 06-08-2009 at 12:48 PM.
06-08-2009, 01:01 PM   #12
ntx
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@ytterbium:
I remembered now that many of the problem I got from the AF were caused by the small DOF. It's not only a matter of how much the subject is moving but I see it's even caused by the camera handheld.
Maybe you should check if you have such AF problems when the camera is on a tripod.

Bye
Jenner
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