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05-19-2010, 09:23 AM   #1
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Asahi SMC 50mm lens on my K2000

OK, Ive got a stupid question: Ive been using this lens since picking it up off the bay a couple weeks back. AWESOME lens, but I have an issue or two:

When I put it on, the camera wants me to put in the focal lenght. 50mm, no problem, but I can only use the lens in "M" or "AV" mode, and I cant use the flash with it because the lens wont shoot faster than 1/180th with the flash on. If I put it on "M" mode, same thing. If the flash is open, I cant get it over 1/180th when having the camera on f1.7. I cannot understand why, in manual mode, I cannot use the flash with a fast shutter speed. For that matter, I dont understand why in AV mode it wont shoot faster than 1/180th with the flash on either.

05-19-2010, 09:26 AM   #2
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Your camera's flash sync speed is 1/180th of a second, and anything above that would theoretically be like using no flash at all! Also keep in mind that newer Pentax bodies don't have TTL flash, so you'll have to manually fiddle with the aperture value to get the correct exposure. High-speed sync >1/180s requires an automatic lens AFAIK.

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05-19-2010, 10:44 AM   #3
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QuoteOriginally posted by DuaneV Quote
I can only use the lens in "M" or "AV" mode
Actually, you can only use the lens fully in M mode. It will successfully take a picture in Av mode, but only wide open - the aperture ring is ignored. See the sticky thread at the top of the beginner's forum for more on using manual lenses.

QuoteQuote:
and I cant use the flash with it because the lens wont shoot faster than 1/180th with the flash on.
As mentioned, that's the maximum flash sync speed. But why would you need it to be any faster? Flash photography generally doesn't depend on fast shutter speeds - it depends o short flash flash bursts. Shooting at 1/60, 1/180, or 1/1000 would all take essentially the same picture when shooting with flash.

I'm guessing you're thinking a faster shutter speed would help because your pictures are overexposed. That's because when using manual lenses, the flash always fires full power. Speeding up the shutter would *not* help - you're still getting full flash power no matter how fast the shutter. What you need to go is stop down the lens to let in less light. Google the term "flash guide number formula" for information on how to determine the proper aperture to use.
05-19-2010, 12:36 PM   #4
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Have a look at this, it's a flash aperture table for a sync-speed of 1/60s and a guide number of 16, which is close enough to that of the K-m (13 I believe, you can probably just do +1/2 ev to compensate for the difference):





From our accessory review database:

https://www.pentaxforums.com/accessoryreviews/showproduct.php?product=634&cat=112


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05-19-2010, 01:01 PM   #5
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I'm guessing you have the k version of the SMC 50mm. However, if you had the SMC m42 version etc., you could set the A-M switch to M and stop down in Av mode.
05-20-2010, 03:39 PM   #6
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Adam: OK, flash sync speed, gotcha! And I appreciate you posting that table.

Marc, Ive been using it in M and doing what you suggest with stopping down. Works like a charm, just wasnt really thinking about all this. Lots on my mind lately. I recently lost my dog and I just havent been myself.

Thanks guys, Duane
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