sfxn flash questions

Hi all, i've been pondering on this for a while and hope you might be able to help..........

I've been experimenting with the following equipment:

sfxn
af400ftz
50mm f1.7 smc-f

On the cameras program setting and with the flash set to TTL auto, the camera selects 1/60 and f4 regardless of whether the subject is close or far away. Now i understand that flash exposure is determined by aperture alone - if so, surely the f-stop up close should be larger than for a subject further away. Is it that on TTL auto the flash shuts off quicker for a close subject, and that the camera can safely choose f4 in the 'knowledge' that the flash won't overexpose the picture? (I can't think of another explanation!)

Also, when I set the camera to shutter priority (ie. leave the aperture ring on A but adjust the shutter speeds manually), the camera overides whatever speed i have chosen, even if it is below the synch speed of 1/125. The only way to manually adjust the shutter speeds is to have the camera on full manual mode - this is the only way i have been able to experiment with 'slow synch' exposures.

And finally, is there any way of firing the flash as a fill light without resorting to full manual mode with the above set-up? I know the flash has a manual low setting, but if i use it will the flash fire every time regardless of ambiant light, and will the camera take this into account in the exposure calculation?

So many questions! Guess i need to get out there and experiment some more, but i'd be really grateful for any clues you can give me.

Karol

Hi Karol,
The whole purpose of TTL flash metering is that the camera turns the gun of when there is sufficient light. It sets F4 to give you a good range.

Once the flash is charged, the camera recognises it and will override any shutter speed to the flash synch speed. This is to prevent inadvertant exposures in case you forgot and had a high speed set. It's not intelligent enough to know there is a slow speed set.

Not sure about the fill in. If you need the manuals for both the camera and flash, they are here www.pentax-manuals.com

Regards
Kim

Hi Kim,
thanks for your answer, think i've got the TTL flash bit cleared up now. Presumably my camera would select 1/125 instead of 1/60 if more ambient light was available.

I've got manuals for both the camera and flash, and unfortunately the references to contrast control (fill) flash aren't very helpful. In summary, they do say that in programme AE mode the flash can be used for "daylight synch flash" to compensate for underexposure in backlit situations. They also say that in very bright areas, the flash may not fire in which case manual flash mode should be used. Just how bright this has to be isn't stated.

I'm still not sure whether the flash will fire every time when set to one of the manual settings (either manual high or low).......

Regards,
Karol

Hi,
I know. Sometimes the manuals are not very helpful. The best thing to do is "play". Wait till you have finished the film and then try various settings and lighting conditions with no film. Get to know when it fires and when it doesn't. When you are happy you think you know what is happening, try it with film and record the details of each shot. When you get the results back, analyse them against your notes. The manuals are a good start place but there is no substitute for getting to "know" your camera.

Regards
Kim

In response to my earlier post about fill flash on the sfxn, i now have the results of some trial shots which go some way to answering my questions.

On a bright sunny day I took advantage of a passing model (my mum!) and positioned her so that the camera was facing into the sun. I was using my newly acquired Tamron 90mm F2.5 manual focus lens and popped up the built in flash. The camera selected the faster of the flash speeds available (1/125th), but i don't recall the aperture - judging by the out of focus background it must have been somewhere around f8/f5.6 i think. I presume it wasn't far below that since at a distance of 2meters the flash might have blown out the highlights, which wasn't the case. To my eye, the exposures were spot on and use of the flash gave a very pleasing 'catchlight' in each eye.

I realise that the automated processing during film development may have altered the effects of the original exposure to a certain extent. Nevertheless i am reassured that the camera can cope with fill flash against a bright backlight when left to it's own devices, and i am certainly encouraged to continue experimenting. A couple of weddings coming up should provide more opportunities....

Oh, and I am very impressed with the Tamron lens: Very sharp results, lovely smooth focussing and it balances the weight of the camera body perfectly.

This is a good reason for using slide (transparency) film for experimentation. What you take is what you get and it is easier to judge what has been happening.

The reduced exposure latitude of slide film is also a good discipline.