photography, engineering, tomfoolery

Flash with the Pentax dSLRs

2005 legacy content

Pentax *ist D, DS, DS2, DL, DL2, K100D, K110D, K10D,...
Samsung GX-1L, GX-1S, GX-10
also useful for other brands


  Some background on flash photography

  1. Manual Flashes: These always fire at a certain power. Simple ones will only have a 100% mode, others offer three steps or in some modern flashes, up to 25. The flash only has one contact in the middle of the foot - and ground contacts on the sides. These are shortened/connected by the camera and the flash discharges.
  2. Auto Flashes: These have a light meter integrated in the flash with an electric/electronic circuit that ends the flash when enough light should have reached the film/sensor. For this, you have to set on the flash the camera's aperture and ISO. Still, only two contacts are necessary. This gives surprisingly good results when the subject is within the normal range.
  3. TTL flashes: The camera has a special light meter inside the mirror box that meters the light reflected from the film/sensor and if the camera decides that enough light was captured, the flash receives the order to stop emitting light. The flash needs at least one additional contact for information exchange with the camera. Modern TTL flashes have another "digital" contact for communicating aditional data like ISO, Focal Length, Aperture which increase ease of use and reliability of the exposure.
  4. Smart Auto Flash: On modern (TTL and later) bodies that support digital communication between flash and camera, Auto Flash becomes Smart Auto Flash: The camera tells the flash which settings it uses. You do not have to adjust anything, it is truely "Auto". Exposure Accuracy is nice and you need no TTL sensor or a preflash (see next paragraph). This is so far only confirmed with the Metz SCA 3000 system on the DS, K100D and K10D.
  5. Preflash flash: The problem with TTL flashes is that they rely on the reflectance of the film/sensor. Now, CCD and CMOS sensors are covered by a protective IR cut/Anti-Alias filter. This surface has very different reflective properties than film. Thus, TTL is not without problems. Nearly all manufacturers have therefore switched to some sort of preflash technology. Light is recorded by the standard metering sensors during a brief preflash. This means that the manufacturer can get rid of the extra TTL sensor: Cheap! The information gathered by the metering flash is used to adjust the flash for the exposure. For this, P-TTL needs lenses with aperture automation (A, and later): It has to know how much darker the stopped down lens is than the wide open one. The metering flash has to happen wide open, otherwise the energy drain would be too much. If you watch exactly, you can see both flashes. If you look through the viewfinder of a dSLR, you can see the first (metering) flash through the viewfinder, whereas as for the second (exposure) flash the mirror is already up.

As of this 2019 update, all digital camera manufacturers have stopped supporting TTL flashes. Pentax supported it probably for the longest but stopped supporting it after the *ist D/DS series and switched to their preflash system named P-TTL (back in film times). You can find more info about the flash technology of Pentax on RiceHigh's page.
NB: There have been many reports of inconsistent TTL flash exposure with the Pentax dSLRs. I cannot report anything like that. Exposure and exposure consistency is excellent with my SCA Metz 300 and 3000 flashes and adapters. There are also reports about inconsistencies with P-TTL, which I cannot comment on, as I do not have an external P-TTL flash.

  Flash Reach Table for the DS

The internal P-TTL flash of the Pentax *ist DS is ok, but when you use it with older lenses (pre "A"), it always fires at 100%. (On the D, the internal flash changes to TTL in this case). The manual lists the guide numbers (Thanks!) and a formula to compute reach or aperture (also good). But I wanted a table like on the back of external flashes. So I did one:

You can download the Excel spreadsheet, too.

  Pentax *ist series flash technology

The flash technology has changed in the various incarnations of the *ist series. You can find more info about flash technology of Pentax on RiceHigh's page.

  How to measure the flash trigger voltage

> The trigger voltage is the voltage that runs from the flash through the camera and back into the flash to trigger the flash bulb. Basically, the camera is a light switch. Modern flashes (since the 80s or so) have at least two circuits: A flash bulb voltage and a trigger circuit. In this case, the camera is no longer an electric switch, but a relay (->Wikipedia) The high voltage of older flashes (upto around 500V) can damage or destroy your camera once they run through it.
I have the confirmation of Pentax Germany that the Pentax *ist DS is safe up to flash trigger voltages of 30Volts. Many pages quote some officials who "think" or "assume" that the DS can cope with the same high voltage (>100V) as the AF film cameras. Are you willing to risk your camera by using an old high-voltage flash because someone "thinks" or "assumes" your camera can cope with this voltage? Me certainly not!
Reports from users indicate that they were told by Pentax that the K10D is only safe to about 6.5V. Some people have used 30V flashes without a problem, but I cannot guarantee that the K10D is able to withstand this.

In any case you should Measure Flash Trigger Voltage if you plan to use an older flash!
Here's how: You set your multimeter/voltmeter (15$ at your local hardware store) to about 600 Volts DC and measure the voltage between the flash's centermost pin and the contact within the side of the flash shoe. If you get a reading that does not indicate an error, choose the next lower measuring range until you get a good reading. If the readings vary between the voltage ranges, this means that your voltmeter has a too low input impedance "resistance". Buy a better one, then.
It is known that manufacturers have changed the flash trigger voltage within a series, without indication on the flash (contradicting reports on some Vivitar flashes are enough proof for me). So, to be safe, I strongly recommend not relying on tables as you can find them. They are good enough to decide about an ebay purchase, but not exact enough for mounting the flash on your 500+$ camera. I will not publish trigger voltages for exactly this reason. I recommend that you measure each flash yourself, a cheap voltmeter costs less than 15 USD and is useful anyway.
If your flash has more than one contact at the bottom, you should isolate the extra ones unless it is a flash known to work with your manufacturer's camera. The problem of short circuiting is mentioned for example here:

  General use of external flashes on the *ist series

First, switch flash and camera off before mounting the flash onto the camera. Even if you are in a hurry, be very sure to switch off the flash: When handling a charged flash you must always be extra careful not to hit the "test" button of it. A medium-sized flash firing a full-power test shot right into your face while you are close to it will make you blind. No kidding.
Once the flash is mounted, switch it on. If you are in P or A mode, your camera will now detect the flash and set the shutter speed to roughly 1/(equivalent focal length). Its behaviour in M-mode also depends on other stuff, as we will see.
If you are using an AUTO flash (all cameras with a hot-shoe), set your camera to A mode and dial in the same aperture that you set at the flash's control panel. Also, make sure the ISO settings are the same. That's it. --------
Auto flash can get much more powerful! If you have a modern flash like the Metz SCA 3000 system that can be set to AUTO, the camera will automagically tell the flash both the ISO and aperture value! It needs the extra contacts for that. AUTO flash has never been easier and it works very fast and very reliably unless you have some weird scenes. AFAIK, this "Smart Auto Flash" was first reported by me in May 2006. The term has since been used in the Pentax forum. Even flash exposure compensation will work nicely (Richard reports that using the adjustment on the flash if it has such is better.) and you can use such a modern AUTO flash in P-mode, too. In P-mode with a modern flash, your camera behaves in a rather intelligent way. The camera knows the focus distance if you use an AF lens. The information of focus distance is used to close down the aperture for near subjects, so that the flash does not overpower the scene. Clever, huh? Please note that cameras up to the K10D disable "Auto ISO" for flash shots. The K10D does not, but interestingly fails to communicate the current ISO to the flash when "Auto ISO" is activated. Overexposure in "Smart Auto" mode can be the result.
Using a TTL flash (D,DS,DS2,GX-1S only), does not require a specific lens. It even works without a lens, though with slightly reduced functionality - no lens-flash interaction possible.
I prefer to use TTL flashes in A mode. In this case, set the desired aperture and you are done. You can easily use flash exposure compensation now.
If you stay in P mode, though, your camera behaves in the same way as described above: The camera knows the focus distance if you use an AF lens. The information of focus distance is used to close down the aperture for near subjects, so that the flash does not overpower the scene. Clever, huh?
When you use the TTL flash in M-mode, you should manually set the shutter speed to roughly 1/(equivalent focal length) and the aperture to your desired one. If the combination of ISO, focus distance and aperture is within the limits of the flash, a correct exposure will result. Be careful with the AE-L button. It serves to take a stop-down meter reading. If you have set the custom option "AE-L bttn on M expsr" to something else than "TV shift", the camera will meter the available light and forget that there's a powerful flash attached. Most often, that is not what you want! If you set the option to "TV Shift", a push of the button will set the shutter speed to roughly 1/(equivalent focal length). Please note that this option was introduced in the firmware 2.00! Browse to a Pentax site to get the free download, which enables continuous AF and auto ISO as other features.
If you are using a P-TTL flash (all Pentax/Samsung dSLRs), the info about TTL flashes apply. P-TTL needs a P/K-A lens or newer and its aperture ring must be set to the "A" position.

  The Metz/Braun/Regula/Cullmann/... SCA 300 system

The SCA system was developed in the 1980 IIRC, and major manufacturers like german Braun and Metz produced flashes for this system. The early SCA 100 system was very basic, but things soon got much more intelligent with the SCA 300 system. Today, only Metz remains as an SCA manufacturer - and what great flashes they produce! Their current flashes use the SCA 3000 and now the SCA 3002 system. The idea remains the same: You have a flash and an exchangeable adapter. So, when you switch the camera, you just have to replace the SCA adapter and then you can fully use the flash on the other camera.
Anyway, if you have an old SCA 300 flash, I was told by Metz that you should not use the dedicated Pentax (or Canon, or Nikon, or...) flash shoe, but step "down" to the standard shoe. Reason: "The old flash expects analog signals at the dedicated extra pins, but the modern cameras (the *ist DS in this case) only communicate by digital impulses." However, many users, including myself have found that SCA 300 flashes work nicely as do older dedicated Pentax flashes, made by Pentax, Vivitar and others. The matching SCA adapters are the 372 and 374. The latter offers AF assist light, but I found it to be quite weak. Also, the 374 offers second-curtain flash on the DS. Nice, but I'd stick with the 372, it is much smaller. Overexposure will occur with higher ISO than 200 or 400 as stated in the pentax manual, but you usually can adjust flash exposure.

  The Metz SCA 3000 and SCA 3002 systems

The SCA 3000 system superseeded the SCA 300 system in the 1990, AFAIK. It offers ISO transmission, motor-zoom reflectors and some other features more. The line up of Metz flashes is very vast and philzucker has written up a nice overview, giving you a head start:
Around 2004 or therabouts, Metz introduced the SCA 3002 series which among other things offers updateable software in the adapter. Currently the 3702 adapter is the adapter for Pentax and should be used on the DS in second-curtain mode. Users have found that it works in standard first-curtain mode, too. More info in this thread by philzucker:
I own the predecessor to the 3702, the SCA 3701. With my Metz 40 MZ-3 it offers ISO transmission and motor zoom, first and second curtain flash and the flash exposure compensation trick. TTL flash still only works correctly for ISO 200 and ISO 400, but you just have to dial in -1 flash exposure compensation for each ISO step above 400 and you are ok. This means that ISO 3200 will not work, because for ISO 1600 you already need the full -2 flash compensation the DS offers. I can only recommend the 3701 if you are really not willing to spend the extra money for the 3702. One benefit of the 3702 is the integration with newer flashes like the 54 MZ-3: The 3701 will not fit those (physically), whereas the 3702 will fit all SCA 3000 flashes.

Recently, we found an issue with Metz's 3701 and 3702 series adapter in Auto mode, with the flash tilted and at high ISO, which results in very inconsistent exposure: / The newer 3702 adapter does have less of this problem: It works nicely in Auto mode with the SCA 3002 flash 54-MZ (thanks to Richard and awaldram) but it does still not work with the SCA 3000 flashes like the 40MZ (thanks to Richard and awaldram, confirmed by myself and PhilZ). Apart from the 3702, using a basic 301 centre-contact or 372 analog TTL adapter will allow consistent Auto flash performance with any Metz flash&camera, but without the extra comfort described in the following paragraph(s).
In August 2007, Christian K. notified me of a method he found that corrects the problem. I don't really understand why it works, but it works. Push the "Prog." button on your MZ40 series flash, then push the "+" button until "P 4" is indicated. Then push the "P" button to load the "programme" stored there. With the flash set to Auto, it now properly fires, independent from ISO. Usual restrictions on flash reach and Auto flash exactness remain, but no erratic behaviour. Depending on your flash, you may have to turn off the beeper now. You need to redo this after you turned off the flash. Christian tell us that this setting must be done, too, when the secondary reflector is used. Thanks for the info!
In November 2007, Mehmet mailed me about a problem with his K100D and 3701 adapter, when manual lenses (pre-A) are used with the flash set to Auto. The flash fires (almost?) full power and proper exposure cannot reliably be obtained. To remedy this, either insulate the extra contacts on the foot of the adapter or use the simple 301 adapter, which only has one contact (plus ground).

  Are there any external P-TTL flashes?

Yes, all recent Pentax flashes of course. Steve has compiled a nice overview of how they act in various modes:
Probably the most important third-party P-TTL flashes are the Sigma flashes. The 500 and the 530 (since 2007) flashes can do P-TTL.
Since 2007, a P-TTL adapter by Metz is available, the 3702-M2. It works with the newest flashes of Metz.
Phil made me aware of the Soligor flashes which, since early 2007, are certified to do P-TTL. The flashes sold as Soligor and Digital Concepts have been reported as working okay with the Pentax dSLRs. Please note that these simple flashes do not offer high-speed snyc or wireless P-TTL. Please also note that there were identically looking non-P-TTL flashes sold under this brand. This makes it risky to buy one somewhere without a proper description.
Promaster has a Pentax P-TTL module since 2006, too. Promaster assured me that the module is capable of proper P-TTL communication. This considerably increases P-TTL choices for Pentax and Samsung users, especially as Promaster offers a rather neatly looking macro flash. In 2007, the adapter was unavailable for a while, when Promaster adapted them to the new K10D firmware.
With all third-party flashes, you may experience incompatibility when a new camera generation is introduced. Sigma for example did free flash-firmware upgrades when Pentax introduced the K100D camera. But there is no guarantee that this will always work.

  Force P-TTL flashes into TTL mode

P-TTL flashes do a preflash. Some people being photographed are fast enough to close their eyes completely or partly ("lazy eyes" phenomenon) for the main flash, which looks a bit stupid on the photo, of course. This, plus the inherent shutter lag caused by the P-TTL flash is enough for some people to not want P-TTL. If you have a dSLR that supports TTL flash, you can use a P-TTL flash as a TTL flash: Set your camera to M mode and set the aperture ring of the lens to another position than A - that means, your desired aperture. You need to have to set "Using Aperture Ring" to "permitted". Using the aperture ring will make your lens behave like a a manual K or M lens - which do not support P-TTL because of missing lens-camera communication. You now may need to set the shutter speed to the rough 1/(equivalent focal length) value as mentioned before. Thanks to Greg for confirming this method: Greg mentions that the flash will still show P-TTL but works as a TTL flash. Michael informed me that on some bodies with some lenses, this does not work, as the camera will still know the aperture even if the lens is off the A-position. I do not have a P-TTL flash to test further. We assume that this phenomenon is due to data being transmitted across the P-KAF mount's digital port. Obviously, some auto focus lenses use this to transmit precise aperture data, even if the lens is off the A-position. My Pentax DFA 100 Macro does NOT do this. If a lens does it, this means that the trick does not work. You'd need to cover the digital port with thin plastic tape or so. However, I doubt many will do that. For those intersted, please visit Bojidar's Pentax page in the section about the KA-mount and KAF-mount. More info on this interesting topic is very welcomed!

  Use P-TTL flashes with manual lenses

As I tried to explain in my introduction, P-TTL needs A and later lenses. However, there's a work-around. Try at your own risk ;)
Ok. Prelude: "P-K/A" lenses transmit their aperture range to the body in electric resistor registers: The P-K/A mount allows changing aperture from the body and open aperture metering. The older K and M lenses use a lever to tell the K/M body how far the lens will be stopped down. No numerical absolute values are transmitted - they are irrelevant for metering anyway. #But# this only works if you use a matching body. Modern bodies cannot read that lever (So called "crippled KAF" mount). The work-around is to use stopped-down metering (green button or AEL button).
I now remotely remember some people tricking the camera into believing that there's an "A" lens attached if a pre-A lens is mounted. How? You must short-circuit the body's "*" contact with the lens, for example by inserting a thin strip of aluminium foil (be careful!). Have a look at the detailed view of the mount here
The lens will short circuit at least another one of the pins. And there you have it: The body thinks that it has an A lens attached. You can now change the aperture on the body and the lever that stops the lens down will change the distance it travels and thereby change the aperture of the lens.
However, there's a reason why this isn't implemented: On K and M lenses, the lever movement is proportional to the diameter of the aperture, on the A and later lenses, it is proportional to the area (or the other way round, I always forget), a difference of ()^2 - noteworthy. As the body expects an A lens, this method only gives correct exposure (P-TTL flash or no flash) with an A (or later) lens attached to a pre-A attachment, like my Panagor Macro Converter
So, why do I want to do this? Because it enables P-TTL flash with my non-A macro attachments. All the newer bodies by Pentax only support P-TTL (a bad decision, IMO) and this is a possibility to continue to use some really nice accessories should I upgrade to one of those modern crippled bodies.

Please note that
  1. When using an A or later lens on a non-A macro, it will transmit the correct stopping down action to the mounted A lens but the recorded EXIF aperture will likely be incorrect and it just tells you how far you stopped down. For this you should short circuit the correct amount of pins to give the correct range, but I found this works quite nicely with a rather random short circuiting-
  2. When using a genuine pre-A K-mount lens, set your lens to the narrowest aperture it allows, this gives maximum flexibility for the stop-down lever. There will be an exposure error, but you should be able to correct it with FEC. Again, the recorded EXIF aperture will likely be incorrect and because of that linear/square difference, it is also only a rough guide. This is obviously less comfortable.
  3. (Just for fun.) If you want to use P-TTL with M42 lenses, that's not easy, as the body cannot control the M42 lens. Here's a work-around, use aluminium foil to trick the body into thinking that M42 lens is an A lens. Then, set your camera to the 2 second timer release. Have the M42 lens wide open, hit the shutter, the preflash fires, stop down to the dialed-in f-stop during the 2 second delay, main flash fires. Re-iterate until you get good at it ;)
  4. The metal trick works for non-flash photos, too.

  A great tip for flash exposure compensation

This tip was , to my knowledge, first documented by me on September 4th, 2005: ../forums/read.asp?forum=1036&message=14899758.
Normally, the flash exposure compensation (FEC) is set via a menu on the DS. On the D, you can use the command wheel that normally controls camera exposure compensation _if_ the flash is popped up. Interestingly, this works similarly for the DS. If the *ist DS is used with flash (internal P-TTL / external (P-)TTL / smart Auto) in Av mode, the exposure time is changed to roughly 1/focallength (up to 1/180) upon fully flash charge _and_ exposure compensation dialed in via the command wheel will now serve as flash exposure compensation. This makes adjusting flash exposure simpler than in M mode, where you have to go through the menu. So, if I do not need to adjust exposure time for my flash shots, I will use Av mode.
I found that if you have dialed in -1EV via the menu and +1EV via the command wheel, the exposure will be identical - obviously the two compensations get combined (as long as the flash can provide enough light).
Here are some samples:

0 EC / 0 FEC

+1 EC / 0 FEC = brighter

+1 EC / -1 FEC = exposed as the first picture

Please note: This works in P-TTL, TTL and even smart Auto mode!

Another feature is described in the manual: Charge the external or internal TTL/PTTL flash until the camera (in A mode) recognizes there's an active flash. Now, dial in EC (which becomes FEC) on the command dial. You can see the +/- symbol appearing. Now, go into the menu, and set FEC (which gets added to the compensation you dialed in). The +/- symbol now flashes/blinks very rapidly. Now, remove the compensation you dialed in via the command dial - the +/- symbol flashes slowly. So, by looking at the symbol you'll know whether you have dialed in EC, FEC or both. This works similarly in P, A, S, M modes. So:

FEC EC +/- symbol
passive passive invisible
passive active displayed
active passive blinks
active active blinks fast

  Focus Assist without flash

Pentax dSLRs do not feature a dedicated AF assist light. If you mount an external flash, that supports "spotbeam", the camera will tell the flash to send out a usually red pattern that the camera can focus on.
If you do not have an external flash mounted, the onboard flash can help: It sends out a pulse of small flash pulses, which help the AF to lock. So far, so good. But what do you do if you do not want to use flash, but want the focus assist?
  1. Raise the onboard flash, let it do the pulses until focus locks, then close the onboard flash.
  2. The old Metz SCA 374 adapter works as an SB adapter when used without a flash mounted to it. If a flash is mounted, you can switch the 374 to "SB" mode.
  3. The newer Metz SCA 3000/3002 adapters do not offer a stand alone adapter with SB mode, AFAIK. But those SCA 3000/3002 flashes that do offer a spotbeam can be switched to "only spotbeam" via a small slider on the 3701/3702 adapter.
  4. *isteve found a great way to get focus assist without having to use flash lighting. It works with the K10D, and I suspect it might work with the original *ist D, too:
    Set the onboard flash to wireless controller mode. It will do the focus assist pulses, and then will send out the command to a wireless slave. Normally, this slave flash would provide the light for the exposure, but as there is no flash now, the camera will only use and meter the ambient light.

Now that we have covered how flash works, why not check out how to make flash pictures less "flashy"?

copyright 2005..06 by Jens Roesner