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08-14-2009, 11:29 PM   #1
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low light lens for K-m?

Hi all,

Recently bought the K-m (body only) and the 18-55 (AL, not AL II). Having fun . Doesn't have the reach on the long end, obviously, but I made due on a recent trip to NYC.

I was seriously looking at a walkaround lens (probably Pentax 18-250, though I had poked around for an FA 28-105 3.2-4.5, which seems like a nice compact lens and a good match for the K-m, though lacking in the tele end), but recently went to my daughter's dance recital and realize there is no substitute for a fast indoor lens for those kinds of venues.

My question: how fast is fast enough in these settings? The 50-135, while a chunk of change, covers a lot of the focal ranges that folks would shoot in primes in that sort of context, but it is 2.8 at widest aperture. Wide enough to stop motion in low light?

If not, what would seem to be the best prime lens option? The FA 50s have wider apertures, but I'm not sure they have enough reach. 77? 85?

thanks for any suggestions!


08-14-2009, 11:46 PM   #2
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but it is 2.8 at widest aperture. Wide enough to stop motion in low light?
That's as wide an aperture as you'll go in any zoom lens (Olympus does feature some f/2 zoom lenses, but... those are huge and freakishly expensive... and not to the point )
Is it fast enough? It all depends, really. A fast lens is not going to guarantee you frozen motion - you have to choose shutter speed fast enough so that motion is "frozen", but with everything there's a different appropriate speed - with slow stuff, maybe even 1/100 will suffice, with dancing? I'd guess 1/400 is a good starting point to try out and see if there is ghosting. Indoors and fast shutter speed don't go together that well, though, so you will have to crank up ISO.
The rest is aperture - which should be whatever the smallest you can get with the best combination of shutter speed and ISO (i.e. lowest ISO, lowest shutter speed that freezes motion).
08-15-2009, 05:26 AM   #3
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I shoot mainly indoors so low light is always a factor. f/2.8 is decent enough but you'd probably end up having to shoot with ISO 800-1600 @2.8 the majority of times (handheld) with some ISO400 shots capable. For anything better you'd need f/1.4-2.0 for ISO 320-800. This is all without flash/handheld for me hence why i moved from K200D to K-7

My current fav lens on K-7 are Pentax 35mm 2.8 macro LTD and Pentax 35mm 2.0 lens for indoors low light followed by Pentax 50mm 1.4 (not wide enough for most of my indoor shots though). For everyday I have Sigma 18-50mm 2.8 EX DC Macro lens which handles low light better than my Tamron 17-50mm 2.8 lens (at each level of same aperture/iso settings for both lens, Sigma allows faster shutter speed and end result photo more brighter while Tamron had slower shutter speed and under exposed images).
08-15-2009, 05:37 AM   #4
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Indoor events need a fast telephoto.
50-135's great if you can get reasonably close.
In order for me not to be too intrusive to the audience, I've opted for the Tamron 70-200 with a 1.4x AF TC on hand in case I need the extra zoom. Even shooting at f/2.8, I've sometimes resorted to ISO 1600 to avoid camera shake, but the images clean up well in PP.
Such a fast telephoto zoom is a very valuable asset in this regard.

Without the availability of an SDM TC, you are limited to 135mm with the DA*, so best to know the focal lengths you need if you're doing such shooting on a more regular basis.

08-15-2009, 07:30 AM   #5
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Although f/2.8 isn't as wide as you'd *like* actually stopping motion, realistically, you'll probably settle for only partially stopping it, or getting good at timing your shots for moments when there is little or not motion (the high point of a jump, low point of a bend, etc). Because there are no faster zooms, and once you get past 85mm, there really aren't any primes available much faster than f/2.8, either. So f/2.8 is what people use.

50-135 would seem ideal for dance if you can swing the price. A longer zoom like a 70-200 might be nice sometimesfor closeups, but they are a *lot* bigger, and really, for dance, it seems you usually want more of the body anyhow.

If the price is hard to swallow, consider used manual focus primes in that focal length range - you could get a 50, a 100, and a 135 that combined would be far less than half the price of the 135. And yes, it is perfectly possible to shoot dance with MF, with practice. Again, you're aiming for points here there is relatively less motion, not trying to freeze someone running across the stage.

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