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03-22-2011, 07:39 AM   #1
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Why is flash sync locked at 1/180 sec with "A" lens?

I normally shoot indoors on AV with flash gelled for tungsten. I have the flash at -1.5 to -2.0 EV for fill in. The shutter speed varies according to different lighting conditions because I have the flash set for slow sync. Yesterday I decide to experiment with my A50/1.7 and the speed locks at 1/180 sec. Look up the manual and sure enough that's what it's supposed to do. My question is why and is there a work around to this? Thanks

03-22-2011, 08:07 AM   #2
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nope, no work around

Its a limitation of the shutter assembly mechanism. The curtains can only move that fast. If you want the whole sensor exposed so that the whole thing sees the flash, you have to be 1/180 or slower. If you were able to go faster, you would start having black bars in your shots where the curtains blocked the light from the flash.

You could get a nice hotshoe flash and shoot with high speed sync -- this allows shutter speeds faster than 1/180 by emitting a burst of flashes instead of one single flash. But you cannot do this with the pop up flash.
03-22-2011, 08:12 AM   #3
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I know I can't go any faster than 1/180 sec. My question is why does it lock at that speed and doesn't allow me to go slower to shoot slow sync. I want to shoot for ambient light and fill in with the flash!
03-22-2011, 08:18 AM   #4
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QuoteOriginally posted by alexcam Quote
I know I can't go any faster than 1/180 sec. My question is why does it lock at that speed and doesn't allow me to go slower to shoot slow sync. I want to shoot for ambient light and fill in with the flash!
I'm guessing there is enough ambient light to max out the shutter speed. Stop the aperture down, or lower the ISO, until the shutter speed lowers.

03-22-2011, 08:27 AM   #5
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Only if your flash support HSS, not sure if the built-in flash support that (depending on the model). I am sure the hot-shoe mount AF360FGZ or AF540FGZ do. Sorry, I misread your post... you want slow sync, which perhaps also depends on which mode you are shooting.
03-22-2011, 08:29 AM   #6
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It doesn't happen with my other lenses. The speed varies with the light. The manual states: The shutter speed is locked at 1/180 sec. when lens other than DA, D FA, FA J, FA or F is used. I wanted to know why?
03-22-2011, 09:10 AM   #7
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QuoteOriginally posted by alexcam Quote
I normally shoot indoors on AV with flash gelled for tungsten. I have the flash at -1.5 to -2.0 EV for fill in. The shutter speed varies according to different lighting conditions because I have the flash set for slow sync. Yesterday I decide to experiment with my A50/1.7 and the speed locks at 1/180 sec. Look up the manual and sure enough that's what it's supposed to do. My question is why and is there a work around to this? Thanks
what camera are you using and what settings. As far as I know, you can set the sync speed anywhere you want, below 1/180 BUT in some auto modes the pentax engineers set it to 1/180 because they do not link the focal length input with manual focus lenses, to the shutter speeds .

If you put a zoom lens on the camera and change focal length the sync speed follows the 1/FL line to insure that in fill flash mode you have enough shutter speed to avoid ghosting from camera motion. It could be linked as well with MF lenses but does not seem to be.

I shoot in manual mode and set the shutter where I want it to be, it is not forced upon you, but is set there in auto modes as a starting point

Note, this only applies to Av mode.

In TV and manual modes you can change the shutter where ever you want. That is, up to the K7 any way. Can't answer for newer bodies
03-22-2011, 10:12 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
pentax engineers set it to 1/180 because they do not link the focal length input with manual focus lenses, to the shutter speeds .
This is what I wanted to know! I figured that when the camera asked for the focal length of the lens, it would link it to the shutter speeds as you described.
I can set the shutter speed in TV and manual, I was just hoping there was a trick I didn't know about to do this in AV mode.
Thanks for answering my question!

03-22-2011, 10:45 AM   #9
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QuoteOriginally posted by alexcam Quote
This is what I wanted to know! I figured that when the camera asked for the focal length of the lens, it would link it to the shutter speeds as you described.
I can set the shutter speed in TV and manual, I was just hoping there was a trick I didn't know about to do this in AV mode.
Thanks for answering my question!
This should really get fixed but then most people who shoot flash shoot manual. The auto modes are OK I guess for fill flash but I prefer, with flash to have total control. I judge the background against he subject based upon the meter reading displayed in manual to determine if the foreground will be blown away by trying to illuminate the background
03-22-2011, 03:33 PM   #10
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When I shoot indoors, sometimes I'm going from room to room and don't have time to adjust flash output. I'm always shooting my family at events and don,t want them to "pose", I'm after candids.

Just in case anyone wants to know, the camera is a K10d and the flash a Metz 48.

After some more experimentation I discovered that the sync speed gets locked at 1/90 sec if you use 2nd curtain sync in AV.

HSS will work in TV with the "A" lens.

Thank you Lowell and everyone else who responded
03-22-2011, 04:40 PM   #11
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Just a note for second curtain sync

It always has cut sync speed by half on pentax cameras. At least between my PZ-1'and today this is because of the combination of flash duration and the actual sweep speed of the curtains
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