Pentax *istD underexposed with AF-360FGZ


Anonymous

Link Posted 03/01/2004 - 14:02
Hi,
I have been reading this thread with interest and has prompted me to join.
Just got the *1st D and now the 360 flash.
The camera is OK but the flash is under exposing by up to 3 stops.
The confirmation flash ok does not blink in the camera or the P-ttl on the gun.
Before I take the gun back please can you help as I dont want to seem a clot at the shop.
I have boosted iso , stood 2 metres away from the subject in a room , all sorts but it is still 2-3 stops under.
Any ideas please will be welcome.
Bryan

Anonymous

Link Posted 03/01/2004 - 17:10
Guest,

Malcolm and Matt have been doing the most work with the testing of this problem, but I can say that you seem to be experiencing the same problem that I have been.

I have found that the flash works very well off-camera, in wireless mode, as a slave flash using the built in camera flash as the master. I have yet to get a correct exposure from the camera-flash combo with the flash attached to the camera.

What I have resorted to doing is cranking up the flash compensation to +1.0. This seems to take care of 'most' of the problem, 'some' of the time.

Lenses - So far my conclusion is that any lens below f3.0 will work with this flash reasonably well. It is when I try to use a lens in the range of f3.5 - f6 that the underexposure problem seems to really take control.

So, if I am in a situation where I must use the AF360 with this camera and a lens of f3.5 or above, I have just learned to:

-- Set the camera to spot metering and focus on the desired area.
-- Set the flash compensation to +1.0
-- Set the quality setting to RAW mode

This is all very hard for me because I am, in general, a natural light person, but I have been finding myself in many situations lately where a flash is necessary. Using the settings above is at least giving me a decent starting point for my photos.

Anonymous

Link Posted 03/01/2004 - 20:24
Well I just ordered both this flash and a 1.7 lens, so I am hoping I do not experience this problem!

Anonymous

Link Posted 04/01/2004 - 10:13
Hi Thanks,
Yes the lens will not open more than f4.0 to f5.6 according to zoom ( the lens came with the camera ) position but then surely if you stand a metre away you should get an exposed shot ?
Bryan

Malcolm Riches

Link Posted 05/01/2004 - 15:39
At
http://www.aaka92.ukgateway.net/Flash/
are two photos taken of my bookcase(!) using the *ist D's built-in flash.

Both were taken using the Green settings - 18-35mm FA-J lens - 1/45 at f/5.6 - ISO 400. One is correctly exposed, the other grossly underexposed.

The only difference between them is that the underexposed one was taken "full on" and the other when on my knees and looking up. (Perhaps prayer helps?)

I'm sure that the metering system of the camera has been fooled by the
bright reflections from the book spines in the full-on shot.

I have repeated this experiment many times with the same results.

Beware of reflections fooling the metering!

Anonymous

Link Posted 05/01/2004 - 16:36
Hi,
You may have hit the nail on the head, my shots were at a new y party where on the wall were white plates hanging, these could have given a bounced light and mucked up the metering.
I will try again.
Thanks,
Bryan

Anonymous

Link Posted 07/01/2004 - 22:03
I don't yet have a *ist D, so forgive my lack of detailed knowledge.

Which device is doing the metering, the camera or the flash? If the former, what metering mode is set? If it's spot, it could well give entirely inappropriate results.

If the flash is doing the metering, then what is the angle of view of the sensor? If it is rather narrow it could be fooled.

Are you using modern lenses which are supposed to work fully with the *ist D? Are you following all the guidelines for use of the flash in auto mode?

I am surprised that Pentax could have brought out a camera with such a fault, and wonder if somebody is missing something fundamental. Does the film *ist have this problem?

MattMatic

Link Posted 08/01/2004 - 06:29
Hello Guest,

It is the camera doing the metering - in P-TTL flash mode. That is, a preflash is fired from which the camera does the metering, adjusts the exposure appropriately then fires the main flash.
Regarding the metering, it is true that spot metering could affect things, and indeed it does (depending on the subject of course).
Yes, modern lenses are being used. Yes, the guidelines are being followed.

Overall, the *istD produces beautiful results, and the exposure and control are far better than the film based SLRs I already use. I am very pleased with the camera itself and the images it produces. It is been a real help to stick with the equipment I had invested in, and to continue to have digital and film compatibility (maybe my gallery will help in showing that).

However, this is not a simple problem. In the real world, the *istD seems to "randomly" mis-expose some shots. I am of the opinion that it is not random at all. Yet the factors affecting the issue are complex - much more complex than a film camera. So far, these are the findings in trying to work out what is going on (mostly from my experiments, but also from others' comments):
* It appears the metering issue is not just down to the flash. From what I can see, there are differences in exposure (due to factors that I haven't entirely pinned down yet) - if the non-flash exposure is under, then the flash exposure appears to be over exposed (and vice-versa).
* Auto white balance makes testing confusing, since the camera is trying to correct the image post-shutter close.
* Auto sensitivity is a great feature. In some 'real world' situations, I thought it was this feature creating the flash issue. However, after testing, I cannot say conclusively either way. The issue certainly occurs without AS enabled.
* The ISO setting has a bearing
* The zoom setting on the lense has a bearing
* The lens itself has a bearing.

Some theories as to the cause:
* The exposure sensor is sensitive to non-visible wavelengths, or sensitive in selected wavelengths.
* The camera is trying to compensate for something (zoom, lense type etc) which is throwing the exposure off with the kit I have (though I have tested a genuine Pentax lens with similar results)
* There's a little bug in the firmware (indeed, as a firmware developer myself, we have a saying that "the size of the fault is inversely proportional to the size of the bug". ie. make a small mistake in coding and the result will probably look catastrophic. We call this "Golding's law" after the MD who coined the observation.)

To be fair, this is Pentax's first commercial DSLR, and I didn't for one minute expect perfect firmware on the first release. As I mentioned, the issues are not simple ones, and the factors are many, and exposure to the wider market always yields situations that haven't been coded correctly in the firmware.

All that said, I am confident that Pentax will resolve the issue, and maybe add some extra features in the firmware too In the meantime I am taking a little more care (bracketing exposure, double checking results etc) when taking important shots. I wouldn't let this issue put you off considering the camera - it has some great features that stand it apart from the mainstream competition (small body, large clear viewfinder etc) that should not be ignored

Hope that clarifies things a little
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

Anonymous

Link Posted 08/01/2004 - 12:18
Thanks for a comprehensive reply. I hope nobody felt insulted that I thought it might be user error rather than the camera, but it is a very complex instrument, and there are many variables to consider.

Recently I had the dubious pleasure of using one of the better Minolta Dimage cameras. Despite lots of experimentation we could not get the white balance right, but I am sure it was due to the ludicrous user interface and appalling manual, rather than a fault. Who buys these things beats me. The camera was "given" to a model I know in lieu of payment for a shoot. I suspect the photographer couldn't get rid of it fast enough.

I know the *ist D is much more user-friendly, but it must still be easy to overlook some important setting that perhaps the manual doesn't make clear.

I understand that the flash has some kind of zoom facility, but I am not sure how this works. It is presumably another area to investigate.

Assuming it does turn out to be the camera's fault, is the "firmware" upgradeable, or will you have to await a revised model?

MattMatic

Link Posted 08/01/2004 - 13:32
Hi Guest,

No, not insulted
When I first decided to go digital, I considered the Dimage 7. Specification wise it looked great, but the handling - eurgh. Having a proper DSLR is just fantastic. Don't think I could go back now. Even film seems daunting having got used to the advantages of pure digital

Yes, some of the flashes have zoom (the ones ending FTZ - AF360FTZ etc). The zoom on the flash can be overridden, but this seems to make little, if any, difference to me.

The firmware is always upgradeable these days (the code is stored in a flash memory chip inside the camera). In developing the code for such devices you always need to throw new code at a device quickly to bugfix. Such benefits also extend to the end user too Normally a little Windows application will fire the data via USB, or you load up a CF card with the appropriate files on and shove it in the camera which upgrades itself. (That all assumes it is a firmware bug, and not something more fundamental.)

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

Anonymous

Link Posted 08/01/2004 - 17:10
Hi,
Yes,
The 360 flash has a a zoom facility that is adjusted according to where you turn the lens and I suppose that they `talk ` to each other, as you turn the lens zoom the flash zoom will change if you have the camera button half pressed.
It`s like cars they are getting too techy you cant service them yourself.
Bryan

MattMatic

Link Posted 09/01/2004 - 11:09
Hi all!

I've just upgraded my *istD to firmware 1.10, as released today on the Pentax US website.

Initial tests look wonderful. Took some AF360 shots of a boring Dell box we had (no offense to Dell ) with four of my lenses. All look great, with minor variations in exposure. The Tokina 28-70/f2.8 that I was having flash problems now looks wonderful

Now, Pentax didn't mention any bug-fixes in the firmware release (only extra features - better DPOF and EXIF support, Adobe RGB change, and better support for M lenses). It would be nice to know if they have actually done something regarding these issues, especially if it was in response to these threads.

However, time will tell - I've got a burst of photographic enthusiasm again and I'm going snapping

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

Anonymous

Link Posted 09/01/2004 - 11:27
I must get round to joining this forum. Half the time I forget to type in my name and appear as guest.
The firmware news is excellent. I was particularly interested in the "better support for M lenses", as I have a couple myself.
I had thought that Pentax were actively trying to get away from supporting older lenses (new "crippled" cameras, etc). It's great for us to have backward lens compatibilty, but not for Pentax, which must sell fewer lenses as a result.
Here's the link to the upgrade page:
http://www.pentaxusa.com/products/cameras/istd/istd_fw_110.htm

malcolmk

Link Posted 09/01/2004 - 12:09
Just done the update myself. I would never bother replacing all my lenses totally of course but it could be argued that the M upgrade has saved me about 4000. Certainly my idea of buying the 31mm 1.7 Limited goes on the back burner, my 28mm F2 will do just fine until I get fed up with no auto-focus.

As for the 360 flash issues. When I first bought it I did what most of us would do and fire off a few test shots indoors. Several were underexposed and they all had one thing in common - reflections from glass. I never did think of that as being a fault as the reasons looked so obvious, however I didn't do any serious tests so maybe I'm being naive. I'll do some more flash tests after dark. Meanwhile I'm off out into the sunshine to try out my rejuvenated 300mm * F4.

Anonymous

Link Posted 12/01/2004 - 08:24
It depends on "how much white is in the pic". A white wall or a lot of other white things in the picture will cause underexposed images.

The same problem is discussed in German-Pentax-forum.

Best regards from Germany
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