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07-11-2011, 04:36 PM   #1
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Using TTL Flash with old lenses

I'm curious about using old Pentax manual and/or A type lenses on a KR or K7/5. If I have the camera set to manual, does the flash still control itself automatically, or do I have to use the flash like it was an old auto flash on a manual camera?

Situation 2. If I have an A series lens, does everything work normally.

I am trying to weigh my options before pulling the trigger on a DSLR. I'm now a happy K1000 owner with a lot of manual and/or A type lenses.

07-11-2011, 05:15 PM   #2
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I have a Pentax-A 50 1.7 and everything works, including the internal/external flash, just like with a normal AF lens. On K/M lenses I think everything is manual, including the flash.
07-11-2011, 05:16 PM   #3
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The K-r, K-7 and K-5 all do not have TTL flash capabilities. They do have P-TTL, the pentax proprietary TTL flash metering.

So, if you want to use a flash and have it auto meter through the lens, it must be capable of p-ttl or it won't work. If the flash has its own light meter, it will work on its own without using p-ttl.

With SMC-A lenses, you should be able to use p-ttl, but the zoom head might not work if it has a p-ttl auto zoom head (A lenses didn't pass focal length data through).

Older lenses will not work with p-ttl. Newer lenses (F, FA, FA-J, D-FA, DA, DA-L...) work perfectly with p-ttl.
07-11-2011, 05:17 PM   #4
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First off, none of the current Pentax cameras (or any other brand) supports TTL. The most "advanced" mode is p-TTL. TTL and p-TTL may look similar, but they are not. If the flash is set at TTL, since the camera does not talk in TTL language, the flash will fire one strobe at full power.

For p-TTL to work, the camera needs to control the aperture of the lens. In other words, if the lens has an aperture ring, there must be an "A" setting on the aperture ring, and the lens must be set at "A."

If the aperture ring exists and is not set at A, the camera does not control the output of the flash (except for the flash sync. signal of course). If the flash is set at p-TTL, it will fire one strobe at full power.

There is a way to trick the camera to think that all lenses are of A-type. But I don't use that trick. All of my flash units have auto mode, which I find very reliable.

07-11-2011, 05:19 PM   #5
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A lenses work with p-ttl

Non-A lenses do not work with p-ttl unless you trick the camera into thinking it is an A lens - not hard to do.
07-11-2011, 05:19 PM   #6
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I could be very much mistaken, but isn't pTTL limited to the center meter point/AF Point when using older A lenses ?
I think the easier rule of thumb would perhaps be - If the lens supports Multi-Matrix Metering (i.e, it'll work outside of the center point) then it *should* work with pTTL - excepting as mentioned on the Zoom settings as the flash wont know what your current Focal Length is (so on short lenses will probably over-expose and on long lenses underexpose)
Outside of that - it may work limitedly (based on Centre-Spot), or not at all...

Last edited by adr1an; 07-11-2011 at 05:26 PM.
07-11-2011, 05:20 PM   #7
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The built-in flash is controlled automatically with lenses with an A setting on the aperture ring. And you don't have to set the camera to manual exposure to achieve this, you can use all exposure modes.

The built-in flash will fire at full intensity with M and K lenses, so in this case you will have to calculate and set the f-stop on the lens based on the distance and guide number, and you'll have to use the M exposure mode. You also have to set custom function 22 (use aperture ring) to permitted. You can leave this custom function at permitted, in other words you only have to set this once.

07-11-2011, 05:28 PM   #8
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QuoteOriginally posted by adr1an Quote
isn't pTTL limited to the center meter point/AF Point when using older A lenses ?
I did some testing and found that p-TTL metering, with ANY lens, is NOT spot-metering. The flash metering was not affected by the metering setting on the camera body.

I can't tell whether the metering is matrix or center-weighted. But it is definitely not spot.
07-11-2011, 08:28 PM   #9
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Thanks for the responses. I guess I will be eliminating my non-a lenses. I've started accumulating various lenses that are duplicates. I'd like to have a collection of A type so I don't have to fool with the stop down and manual exposure as well as the flash issues.
07-13-2011, 03:35 AM   #10
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QuoteOriginally posted by njpentax Quote
Thanks for the responses. I guess I will be eliminating my non-a lenses. I've started accumulating various lenses that are duplicates. I'd like to have a collection of A type so I don't have to fool with the stop down and manual exposure as well as the flash issues.
You don't need to stop getting Non A lenses to use flash.

There are 3 ways you can still use flash with Non A lenses.

1) Pick up a used *istD, DS, or DS2. All of these bodies support both TTL and P-TTL flash. Let me explain the difference.

TTL flash has a sensor that reads light reflected off the film (the bad old days) or sensor (digital) and controls the duration of the flash directly by the light reflected off the recording surface.

P-TTL (and I wont go into what the P stands for) does not read the light produced by the flash during exposure at all. P-TTL uses the camera's metering and sends a preflash out to read the light reflected back from the flash and the uses the cameras normal metering to measure the light from the flash, plus background ambient. It then calculates the flash duration required, knowing the shooting exposure (shutter, aperture and ISO, existing light) and when the shutter opens, it produces a flash duration to meet the exposure requirements. THe P is for Predictive, Pre flash, Pentax or what ever you pick.

The problem with P-TTL and older lenses is that it does not know the difference between the wide open aperture (when focusing etc) and the shooting aperture, so the camera shoots the flash at full power. TTL has a problem that has been around since the beginning of potential over exposure if if there is a lot of background light, because even though theflash stops the shutter is still open gathering light. But TTL, since it reads directly the light hitting the sensor from a flash, can meter with old lenses because it is the real light during exposure it is measuring.

2) the second method is to purchase a flash that supports AUTO flash, where the flash itself has a sensor, to control duration. The AF540FGZ is one such flash, and can work in auto mode.

3) learn manual flash calculations, and adjust aperture and flash power (if possible) based on ISO, shooting distance, and flash power to get the correct exposure. After All, that is how it was done in the beginning
07-13-2011, 10:19 PM   #11
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Thanks for the explanation. I have a Promaster Flash I use with my K1000 that works with the built in auto sensor. This would probably work with a newer camera in the manual mode.
07-14-2011, 04:34 AM   #12
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QuoteOriginally posted by njpentax Quote
Thanks for the explanation. I have a Promaster Flash I use with my K1000 that works with the built in auto sensor. This would probably work with a newer camera in the manual mode.
providing that the flash trigger voltage is low enough to prevent damaging the camera, yes it can work in both manual and Auto modes
07-15-2011, 06:09 AM   #13
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How would I find out the flash trigger voltage? I wouldn't want to damage an expensive DSLR.
07-15-2011, 06:14 AM   #14
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QuoteOriginally posted by njpentax Quote
How would I find out the flash trigger voltage? I wouldn't want to damage an expensive DSLR.
what you need is a good volt meter.

you need one that presents a very high resistance (more than 20 million ohms) to the flash pin. Measure between the central pin and the contact on the sides of the shoe.

If you only have a cheap meter measure the voltage using the highest rannge first. Then step down through the ranges and see whether the reading changes or not.

Even the cheap meter will have somewhere on it, an internal resistance, usually stated in ohms per volt (of full scale)

with a cheap meter, measure the voltage on each range and plot on log paper, it will approach an asymtote as resistance goes to infinity.
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