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05-29-2011, 07:19 PM   #1
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A-series lenses vs. FA

I have a Pentax-A 28mm F2.8 (manual focus, auto aperture) from KEH that I can still return. It is a very nice lens, except that it seem to lack some functionality with slow-sync flash.

My FA-50, when set to slow sync flash, maintains ambient light from the room with a little fill in. The A-28, at the same setting, uses the full flash power and overwhelms the ambient light. I can duplicate the FA's behaviour by using the manual mode, but that's too many settings for casual use--I'm buying the 28 as a pub lens. Any idea if the 28 is defective, or is this is normal for an older generation of lens?

Thanks in advance!

05-29-2011, 07:22 PM   #2
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From what I remember, it worked well with TTL... is the aperture ring set to "A"?

Edit: For my own reasons, my memory is not to be trusted .
05-29-2011, 08:00 PM   #3
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You haven't provided enough specific information for a complete answer but generally the A-lenses should accommodate slow speed sync with both built-in flash and the AFxxxFTG class flashes.

Note that the A lenses do not pass focal length information so any settings dependent on FL would be problematic regardless of camera.

Consult the manual for your camera and/or external flash for a complete flash/lens matrix.

H2
05-29-2011, 08:22 PM   #4
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Rtfm

Mystery solved. Page 61, KX manual, chart of lens issues ("Lens Compatibility with Built In Flash"):

"FA Soft 28mm f2.8 /Built-in Flash Always Discharges Fully"

Thanks!

05-29-2011, 09:52 PM   #5
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QuoteOriginally posted by LouD Quote
"FA Soft 28mm f2.8 /Built-in Flash Always Discharges Fully"
But you are using the A 28mm f2.8... not the soft version...

none of those A-contact lenses have little chips inside of them... no lens specific issues I would like to think...

So you have the same problem with an on-board external flash?
05-30-2011, 08:38 AM   #6
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Haven't tried the external flash--it defeats the purpose of a small easy to carry kit.

Just to clarify, the KX "discharges fully" with the 28 MM A series on slow sync in AV mode. It also resets the shutter speed higher. In contrast, the FA50 adds just a little fill flash and doesn't muck with shutter speed.
05-30-2011, 09:51 AM   #7
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I'm not going to be of much help I'm afraid, but I don't think your problem has anything to do with the 28mm lens specifically... I think it has more to do with all A series lenses.
05-30-2011, 10:08 AM   #8
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If your flash does not have a zoom head and/or a wide angle diffuser, then it's normal that your light distribution looks different.

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