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06-01-2011, 11:09 PM   #1
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Any way to do p-ttl through Pentax K 55/1.8 lens?

I know that in manual mode it always fires the pop up flash at full power. But I figured in Av mode (just leaving the lens wide open) it would do p-ttl .. but it appears to fire at full power in that mode as well.. any mode for that matter.

Will a pentax-a lens work with p-ttl?

06-01-2011, 11:27 PM   #2
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Yes, A lenses support p-ttl. It doesn't work with manual lenses because the camera doesn't know the aperture. You need real TTL for such lenses (which is only available on the ist D and DS unfortunately).
06-02-2011, 04:08 AM   #3
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Easiest solution is an off camera flash with an auto mode. Older ones can be had for cheap (just make sure the voltage is safe), and new ones for $100 or so.
06-02-2011, 05:06 AM   #4
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QuoteOriginally posted by geekette Quote
I know that in manual mode it always fires the pop up flash at full power. But I figured in Av mode (just leaving the lens wide open) it would do p-ttl .. but it appears to fire at full power in that mode as well.. any mode for that matter.
It will work if you fool the camera into thinking the lens is an A type. some people fool the camera by putting a ball of aluminum foil over the depressed contact on the camera's mount - I've never been successful trying that.

I've modified my cameras to think that all lenses are A type by putting a small piece of aluminum foil over the depressed pin and holding it in place with the lens mount ring itself:

Remove the mount ring- put foil over the A pin-replace the mount ring.

This is not a risky mod & is easy to un-do. It makes the camera think that all lenses are type A.

EDIT - this is no panacea. It is best used with m42 lenses or K type lenses wide open. Set the f-stop shown in the viewfinder to wide open - then the camera will not try to stop down the lens; therefore exposures set by the camera are not bad. This method is most useful to me for flash macro photography.


Last edited by newarts; 06-02-2011 at 07:37 AM.
06-02-2011, 07:20 AM   #5
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although the modification by newarts works it is not for every body

there are other ways to get metered flash with K mount lenses.

1) Get a flash with Auto Capability.

These flashes have their own sensor, and you set the aperture and ISO you are shooting on the flash (some, like the AF540FGZ will read ISO from the camera) and the sensor will take reflected light back from the scene and control the flash for you

2) Get an early DSLR and SHoot TTL flash with a TTL capable flash

The *istD, DS and DS2 all have both P-TTL and TTL capabilities, and will automatically shoot in TTL mode using a built in sensor reading reflected light off the main image sensor to control the flash. This works much more reliably than Auto mode, because the flash sensor only looks at the image not a wide angle scene, and with longer lenses the wide angle view of the flash sensor in auto mode can be fooled. It can also be shaded by long lenses giving false readings.


You can also go "old school" and use manual flash, taking the flash guide number (usually in metrers at 100ISO) and calculating the aperture needed based upon distance, ISO, and guide number
06-02-2011, 08:00 AM   #6
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QuoteOriginally posted by Jodokast96 Quote
Easiest solution is an off camera flash with an auto mode. Older ones can be had for cheap (just make sure the voltage is safe), and new ones for $100 or so.
Yeah I have one of those... just wanted my pringles can on camera macro flash to work with my older lenses
06-02-2011, 08:07 AM   #7
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Very strange!

None of my A lenses work with P-TTL on my Kr, K7 or K5, AND Pentax US told me P-TTL works only with auto focus lenses as stated on p.26 on their AF540fgz manual. The on- or off- camera flashes will output full power with all my A lenses on P-TTL, disregarding any aperture setting.
06-02-2011, 08:08 AM   #8
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QuoteOriginally posted by geekette Quote
Yeah I have one of those... just wanted my pringles can on camera macro flash to work with my older lenses
See the edit addition I made to my post above. Fooling the camera into thinking the lens is an A type is useful for macro.

Another approach for macro is to get a cheap PKA teleconverter, remove the optics (easy), and force its A pin to the on state (easy...just make it stick out.)

06-02-2011, 08:16 AM   #9
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QuoteOriginally posted by MJL Quote
Very strange!

None of my A lenses work with P-TTL on my Kr, K7 or K5, AND Pentax US told me P-TTL works only with auto focus lenses as stated on p.26 on their AF540fgz manual. The on- or off- camera flashes will output full power with all my A lenses on P-TTL, disregarding any aperture setting.
Hmmm, works with my K100D and K-x... maybe they changed the software?

I wonder why they would disable it for non-autofocus lenses?
06-02-2011, 09:49 AM   #10
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QuoteOriginally posted by newarts Quote
I wonder why they would disable it for non-autofocus lenses?
right, even I asked this sometime back about p--ttl & auto-iso, I couldn't find any reason to disable p-ttl for non-A lenses.
06-02-2011, 11:31 AM   #11
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QuoteOriginally posted by MJL Quote
Very strange!

None of my A lenses work with P-TTL on my Kr, K7 or K5, AND Pentax US told me P-TTL works only with auto focus lenses as stated on p.26 on their AF540fgz manual. The on- or off- camera flashes will output full power with all my A lenses on P-TTL, disregarding any aperture setting.

Page 180 of the K-r manual clearly states that built in and external P-ttl is available with A lenses (see note 1).
http://www.pentaximaging.com/images/temp/63440632054595281761237manual_k-r_en_official.pdf
06-02-2011, 12:30 PM   #12
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QuoteOriginally posted by newarts Quote
Page 180 of the K-r manual clearly states that built in and external P-ttl is available with A lenses (see note 1).
http://www.pentaximaging.com/images/temp/63440632054595281761237manual_k-r_en_official.pdf
I know, ditto in the K7 & K5 manuals. If I turn off and on the cameras, sometime I can get excellent P-TTL with my A lenses (Pentax & Zeiss). A mystery still.
06-02-2011, 12:35 PM   #13
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QuoteOriginally posted by MJL Quote
None of my A lenses work with P-TTL on my Kr, K7 or K5... The on- or off- camera flashes will output full power with all my A lenses on P-TTL, disregarding any aperture setting.
Any aperture setting? Have you try setting the lens's aperture ring at A?
06-02-2011, 12:35 PM   #14
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QuoteOriginally posted by MJL Quote
Very strange!

None of my A lenses work with P-TTL on my Kr, K7 or K5, AND Pentax US told me P-TTL works only with auto focus lenses as stated on p.26 on their AF540fgz manual. The on- or off- camera flashes will output full power with all my A lenses on P-TTL, disregarding any aperture setting.
QuoteOriginally posted by newarts Quote
Hmmm, works with my K100D and K-x... maybe they changed the software?

I wonder why they would disable it for non-autofocus lenses?
QuoteOriginally posted by yusuf Quote
right, even I asked this sometime back about p--ttl & auto-iso, I couldn't find any reason to disable p-ttl for non-A lenses.
QuoteOriginally posted by newarts Quote
Page 180 of the K-r manual clearly states that built in and external P-ttl is available with A lenses (see note 1).
http://www.pentaximaging.com/images/temp/63440632054595281761237manual_k-r_en_official.pdf
QuoteOriginally posted by MJL Quote
I know, ditto in the K7 & K5 manuals. If I turn off and on the cameras, sometime I can get excellent P-TTL with my A lenses (Pentax & Zeiss). A mystery still.
they work on my K7, are you sure you are in A on the lens?

Tested Vivitar 85/1.4 (A mount samyang 85) using K7 and AF540.

Unless you have a failure somewhere it should work
06-02-2011, 01:07 PM   #15
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QuoteOriginally posted by newarts Quote
It will work if you fool the camera into thinking the lens is an A type. some people fool the camera by putting a ball of aluminum foil over the depressed contact on the camera's mount - I've never been successful trying that.

I've modified my cameras to think that all lenses are A type by putting a small piece of aluminum foil over the depressed pin and holding it in place with the lens mount ring itself:

Remove the mount ring- put foil over the A pin-replace the mount ring.

This is not a risky mod & is easy to un-do. It makes the camera think that all lenses are type A.

EDIT - this is no panacea. It is best used with m42 lenses or K type lenses wide open. Set the f-stop shown in the viewfinder to wide open - then the camera will not try to stop down the lens; therefore exposures set by the camera are not bad. This method is most useful to me for flash macro photography.
The best thing about this method is that I can use K/M lenses like A lenses in Tv/Av. You can meter and focus wide open, and stop down. To do this, you set the lens to the smallest aperture setting (e.g. f22).

The only exception is the max aperture that is reported is wrong so when it reports it as f1.4 on say a f2.8 lens, , setting it to f2.0 shoots it at f4.
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