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02-20-2009, 12:37 AM   #1
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Shutter speed with M42 lens.

Hi!

I have noticed that, when using Av mode on my K200D along with a M42 lens, if I pop up the flash, the shutter speed "locks" to 1/180 sec. Also, if I go to M mode, the fastest shutter speed I can set is also 1/180 sec. Does anybody has an idea why is this?

Thank you.

02-20-2009, 12:59 AM   #2
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I don't know about the K200D, but likely not different from the K10D, which I have.

Why do you pop up the flash? When you do, the camera body (rightfully) assumes you want to use the flash.

The onboard flash does not support high speed flash.

The "normal" sync speed is 1/180. That's why the camera does not want to go faster.

K10D manual says, "(In Av mode) the shutter speed is locked at 1/180 sec. when lens other than DA, D FA, FA J, F or A is used..... (In M mode) set the shutter speed (...) so that proper exposure is obtained in under 1/180 sec."
02-20-2009, 02:04 AM   #3
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The maximum sync speed is 1/180 sec. With the flash up, you can't go any higher
If you close the flash. then you can get to the maximum speed - 1/4000 sec, I think
02-20-2009, 02:11 AM   #4
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Some hot-shoe flashes support high speed sync which allows for faster shutter speeds.

02-20-2009, 05:24 AM   #5
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Now every thing makes sense...

If I want to use the built-in flash with a M42 lens I will really have to stop it down and lower the ISO until I find the correct exposure. Not that I want to do this with an 1.4 Super Takumar, but i was experimenting with it and eventually arrived to this situation.

Thanks to all of you!
02-20-2009, 10:13 AM   #6
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QuoteOriginally posted by hahifuheho Quote
If I want to use the built-in flash with a M42 lens I will really have to stop it down and lower the ISO until I find the correct exposure.
And there's a time-honored formula to do this without all the guesswork. Most flash units (including the built-in flash) have a published "guide number" that is given in terms of a specific ISO and either in feet or meters for exactly this purpose. Set the ISO to what it says to set it to, then find the distance to the subject in feet or meters as apprpriate. Divide guide number by distance, and there's your recommended aperture.

Built-in flash on the K200D is guide number 13 (in meters) at ISO 100. So if you set ISO 100 and your subject is 2 meters away, the aperture should be 13/2 = 6.5 (close enough to 6.7, so you'd just use that). You can of course raise the ISO and thereby get away with a smaller aperture if you like - at ISO 140 you could go f/8, etc.
02-20-2009, 11:19 AM   #7
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QuoteOriginally posted by hahifuheho Quote
Now every thing makes sense...

If I want to use the built-in flash with a M42 lens I will really have to stop it down and lower the ISO until I find the correct exposure.
Thanks to all of you!
You wont have to change it much because the flash is too feeble anyway.

It's quite normal for flash to be limited in this way. It's to do with the fact that at faster shutter speeds the two blinds that comprise the shutter are never fully open. This means if you take a picture at 1/360 for instance half the picture will be blacked out. Take a picture at 1/500th and even less of the picture is recorded. So under most circumstances the camera stops you making that mistake. I'm not sure what difference the type of lens makes?
02-20-2009, 11:41 AM   #8
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QuoteOriginally posted by kevbirder Quote
I'm not sure what difference the type of lens makes?
The deal with the lens is that with "modern" lenses (ones with exposure automation A, F, FA, FA-J, D-FA, and DA, with or without "*"), the system can automatically figure out the optimum aperture to use, and can also read the current aperture if youv'e set it yourself and figure out how much to scale back the flash if you've got a large aperture selected. So you don't need to experiment with stopping down the lens yourself and either guessing or using the guide number formula - that's all automated. With m42 and other older lenses, the flash *always* fires full power, and the camera has no way of setting an aperture for you, so you've got to figure it out yourself.

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