Low Light auto focus

JohnKSA · 02-26-2010, 12:50 AM

Hi, I am struggling to focus in low light situations. This applies to auto and manual focus where I am using a dedicated (PTTL) flash. I have a K20 and generally in these situations use a Schneider 18-55 kit lens that I bought with a Samsung G1L (*ist equivalent) - I believe the lens is a rebranded Pentax kit lens. Would an upgrade to an SDM lens make my life easier? In film photography I had a very accurate split screen Minolta manual focus which worked well. I nowstruggle with older eyes and no split screen on the K20. Any suggestions? Thanks!

sterretje · 02-26-2010, 01:54 AM

Does the flash have infrared AF assist? An SDM lens will not help. A faster lens (f/2.8) will help a little.
And you can buy split focus screens from several companies. I have just ordered from katzeye optics, but there are other ones. You can do some research here in the forums and on the net.

WimS

RioRico · 02-26-2010, 07:43 AM

Your kit lens is probably f/3.5-5.6 which is rather slow. For low light you definitely need something faster, but fast f/2.8 AF zooms are not cheap. SDM will make the AF quieter but not necessarily more accurate in low light. You might consider one or more fast primes, an old favorite being the FA 50/1.4. Check here [ Pentax Lens Review and Specification Database - Main Index ] for user reviews of new or used DA and FA lenses, then see what's available that you find affordable. Good luck.

bymy141 · 02-26-2010, 08:18 AM

My flash (a Metz 58) has a red AF support light. Doesn't your flash have any?

As Sterretje says, you can replace your matte with a split screen.
It is not expensive.

Another option is the K-7, same sensor but so much better AF!
Comes with an assist light as well.

sterretje · 02-26-2010, 08:28 AM

Originally posted by bymy141

As Sterretje says, you can replace your matte with a split screen.
It is not expensive.

That's relative

2x katzeye with optibrite and shipping around 400 US$. In local currency around ZAR3000. If I'm lucky, no import duties (might add another ZAR1000, not sure).

That's also why I mentioned that there are other companies that make them

Alfisti · 02-26-2010, 10:25 AM

Everyone is gonna blame the lens being slow but TBH those early model Pentax's had woeful AF in low light.

Those recommending a good manual focus screen have the right idea.

JohnKSA · 03-10-2010, 04:19 AM

In answer to BYMY141 above: I have a Pentax AF-360-FGZ flash which I have just found out does purport to have AF assist red light but there is no way I can get it to work on my K20. According to the instructions one should set it to "PB" mode, the camera to AF, half press the shutter release and........-nothing!! Any ideas? This flash was bought before the K20 was launched but I can't get it to work on my *ist Samsung equivalent either.

John

02-26-2010, 12:50 AM	#1
JohnKSA Inactive Account Join Date: Nov 2009 Location: Pietersburg, South Africa Posts: 26	Low Light auto focus Hi, I am struggling to focus in low light situations. This applies to auto and manual focus where I am using a dedicated (PTTL) flash. I have a K20 and generally in these situations use a Schneider 18-55 kit lens that I bought with a Samsung G1L (*ist equivalent) - I believe the lens is a rebranded Pentax kit lens. Would an upgrade to an SDM lens make my life easier? In film photography I had a very accurate split screen Minolta manual focus which worked well. I nowstruggle with older eyes and no split screen on the K20. Any suggestions? Thanks!

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02-26-2010, 01:54 AM	#2
sterretje Veteran Member Join Date: Dec 2008 Location: Roodepoort, South Africa Photos: Gallery \| Albums Posts: 3,561	Does the flash have infrared AF assist? An SDM lens will not help. A faster lens (f/2.8) will help a little. And you can buy split focus screens from several companies. I have just ordered from katzeye optics, but there are other ones. You can do some research here in the forums and on the net. WimS

02-26-2010, 07:43 AM	#3
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Your kit lens is probably f/3.5-5.6 which is rather slow. For low light you definitely need something faster, but fast f/2.8 AF zooms are not cheap. SDM will make the AF quieter but not necessarily more accurate in low light. You might consider one or more fast primes, an old favorite being the FA 50/1.4. Check here [ Pentax Lens Review and Specification Database - Main Index ] for user reviews of new or used DA and FA lenses, then see what's available that you find affordable. Good luck.

02-26-2010, 08:18 AM	#4
bymy141 Veteran Member Join Date: Aug 2007 Photos: Gallery Posts: 1,563	My flash (a Metz 58) has a red AF support light. Doesn't your flash have any? As Sterretje says, you can replace your matte with a split screen. It is not expensive. Another option is the K-7, same sensor but so much better AF! Comes with an assist light as well.

02-26-2010, 08:28 AM	#5
sterretje Veteran Member Join Date: Dec 2008 Location: Roodepoort, South Africa Photos: Gallery \| Albums Posts: 3,561	Originally posted by bymy141 As Sterretje says, you can replace your matte with a split screen. It is not expensive. That's relative 2x katzeye with optibrite and shipping around 400 US$. In local currency around ZAR3000. If I'm lucky, no import duties (might add another ZAR1000, not sure). That's also why I mentioned that there are other companies that make them

02-26-2010, 10:25 AM	#6
Alfisti Veteran Member Join Date: Mar 2007 Location: Toronto (for now) Posts: 1,748	Everyone is gonna blame the lens being slow but TBH those early model Pentax's had woeful AF in low light. Those recommending a good manual focus screen have the right idea.

03-10-2010, 04:19 AM	#7
JohnKSA Inactive Account Join Date: Nov 2009 Location: Pietersburg, South Africa Posts: 26 Original Poster	In answer to BYMY141 above: I have a Pentax AF-360-FGZ flash which I have just found out does purport to have AF assist red light but there is no way I can get it to work on my K20. According to the instructions one should set it to "PB" mode, the camera to AF, half press the shutter release and........-nothing!! Any ideas? This flash was bought before the K20 was launched but I can't get it to work on my *ist Samsung equivalent either. John