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12-28-2009, 09:40 PM   #1
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AF in low light of 31 Limited

Hi:

A happy and a merry.

I recently acquired a new 31 Limited. I have been playing around with it for a couple of weeks.

I used the 31 tonight in a shoot and had trouble focusing under lower light. Not sure I really would call it low light (I was using a 750 watt to light up a large basement room. I ended up bringing over a 250 watt extra light). I use these lights for ambient. I use small off camera flashes for "lighting."

I also used my recently fixed DA*16-50. It was at Pentax for about 7 weeks. It had the AF problems widely reported. So far so good. It had an easier time focusing in the lower light.

Has anyone else had this issue with the 31? I was shooting around f/5.6, ocassionally a bit more open, but nothing wide open and nothing beyond f/8.

Thanx so much.

Gregg

12-28-2009, 10:19 PM   #2
Ash
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Hmm, tough one to gauge.
In the same lighting conditions the 31 should handle AF at least as well as the 16-50.
How close were the ambient light sources from the subject?
Does the 31 have trouble in AF function in any other conditions, low-light or otherwise?
12-28-2009, 10:30 PM   #3
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Hi

Hi Ash:

Thanx for the reply. The initial light was perhaps 6 feet away. It was not as bright as my upstairs home studio gets with the same light, but it was not too dark--or at least I did not think so. When I tried the newly fixed 16-50 it worked very well with one or two attempts that seemed to have a slight hunt for focus.

So, the lighting was not great, but what struck me was the difference in AF performance between the lenses. I have not experienced any other problems with the 31, but I guess I may not have been on the edge of necessary light. Perhaps the new AF in my 16-50 lens works extremely well given all of the problems the 16-50 lenses have had.

Anyway, a bit disappointed. I am looking at the pictures I took with the 31 and the 16-50 and find them to be very comparable. No real IQ difference, at least at mid apertures. I know that should not be surprising, but I guess I had some hopes for the lens.

I have the 55 and find that to be a very good prime.

Gregg
12-29-2009, 04:16 AM   #4
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Isn't the purpose of the 16-50 to have a zoom lens that approaches the IQ of the primes?
Especially between 5.6 and 8.

I have never experienced any problems with AF and the FA31 in low light - compared to other lenses, that is.

I suppose you know the AF is always performed wide open? So, FA31 at 1.8 and DA 16-50 at 2.8.
The 16-50 result in pretty contrast full images. Perhaps that aids the AF?

12-29-2009, 08:20 AM   #5
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Thanx Bart

Bart:

I got the 31 to have a second "wider" lens after my 16-50 was in the shop for so long. I tried a Sigma 24 and the 18-55 WR as "backup" lenses to meet this need, but was not happy with them. The 31 clearly was very expensive, but I thought I would treat myself to having such a nice lens and hopefully would come to use it over the years, as well as to be able to fully appreciate it over time.

I tend to process my images a lot so perhaps I just do not need the extra "pop" of the 31, though I am not sure I really have seen it yet. I also thought it would be nice to have an f/1.8 at 31mm since I use my DA*55 f/1.4 a great deal in low light situations.

Anyway, I defienely had trouble with the AF on the 31 in the lower light. I popped on the newly fixed 16-50 and it did very well.

Gregg
12-29-2009, 09:00 AM   #6
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I just put my 31mm on the K20D to give it a try in a dim room. AF was quick and sure. Just to give a sense of light conditions, I was in AV mode @ f/f3.5: ISO came in at 3200 at 1/50s.
12-29-2009, 09:42 AM   #7
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QuoteOriginally posted by Bart Quote
Isn't the purpose of the 16-50 to have a zoom lens that approaches the IQ of the primes?
Especially between 5.6 and 8.

I have never experienced any problems with AF and the FA31 in low light - compared to other lenses, that is.

I suppose you know the AF is always performed wide open? So, FA31 at 1.8 and DA 16-50 at 2.8.
The 16-50 result in pretty contrast full images. Perhaps that aids the AF?
I believe it does help, but that it is only part of it. f2.8 also yields greater depth of field, making the final position of the focusing elements less critical for the camera to perceive focus.
12-30-2009, 11:46 AM   #8
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I used my 31ltd on Xmas party from work. I was bouncing the AF280T off the walls/ceiling so I didn't have any AF assist (280T doesn't have AF spot beam and I couldn't raise built in flash). The lens hunted but not more than I'd expect. Generaly, out of 120 pics, I had 117 spot on. Truth is, it took really low light for the lens to give up and fail to AF. I'd say considering the situation the AF of 31ltd proved very adequate. I can't ccompare it to the DA* you have, but comparing to lenses I own, 31 is no worse than any other.

12-30-2009, 05:16 PM   #9
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Thanx all

Hi:

Thanx all for the rep[lies. I will play around with the 31 and my 16-50 tomorrow and Friday and think some more about whether to keep it.

Though not exactly an old hat, I have realistic expectations, I think, of the lens. Having my 16-50 fail so early on and then take 7 weeks to get it fixed, however, makes me a bit nervous re the 31 since it definitely was hunting in the "lower" light. And, when I put of the 16-50--no more hunting. Maybe it was just an odd lighting situation. My firmware is up to date.

So...I am bit "gun shy" given I have not seen the "magic" yet with the lens or any real appreciable difference--but to be fair I have shot at mid apertures and I bought the 31 in part to have a lens to go below f/2.8.

Gregg
12-30-2009, 06:44 PM   #10
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I think the bottom line of this for you so far is not the fact that the FA31 performs badly, rather it shows just how good a lens the DA* 16-50 is. Its my favourite and most used lens as it is great over all the focal range and keeps giving me stellar results in all sorts of conditions

The 31 is a magic lens, gives wonderful results in low light and I use it for special occasions that suits my needs.


Cheers

Neil
12-30-2009, 07:15 PM   #11
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QuoteOriginally posted by lawjbm Quote
I am bit "gun shy" given I have not seen the "magic" yet with the lens
Understandable. It seems there are two questions: 1) whether you have a good copy (I couldn't replicate the AF issue) and 2) whether you find the "magic". I hope it works for you.
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