A-series lenses vs. FA

LouD · 05-29-2011, 07:19 PM

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!

paperbag846 · 05-29-2011, 07:22 PM

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

.

**pacerr** · 05-29-2011, 08:00 PM

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

LouD · 05-29-2011, 08:22 PM

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!

paperbag846 · 05-29-2011, 09:52 PM

Originally posted by LouD

"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?

LouD · 05-30-2011, 08:38 AM

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.

paperbag846 · 05-30-2011, 09:51 AM

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.

bdery · 05-30-2011, 10:08 AM

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.

05-29-2011, 07:19 PM	#1
LouD Inactive Account Join Date: Feb 2010 Photos: Albums Posts: 39	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, 08:22 PM	#4
LouD Inactive Account Join Date: Feb 2010 Photos: Albums Posts: 39 Original Poster	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!

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05-29-2011, 07:22 PM	#2
paperbag846 Veteran Member Join Date: Jul 2010 Photos: Gallery Posts: 2,395	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
pacerr Loyal Site Supporter Join Date: Jan 2008 Location: Paris, TN Photos: Gallery \| Albums Posts: 3,350	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, 09:52 PM	#5
paperbag846 Veteran Member Join Date: Jul 2010 Photos: Gallery Posts: 2,395	Originally posted by LouD "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
LouD Inactive Account Join Date: Feb 2010 Photos: Albums Posts: 39 Original Poster	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
paperbag846 Veteran Member Join Date: Jul 2010 Photos: Gallery Posts: 2,395	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
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,362	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.