A question of compensation

I could do with a bit of guidance from the experts, please.
Compensation, as I understand it is the change in exposure value against that set by the exposure meter.

Exposure Compensation :
When this is active, is it
a) the aperture that is modified
b) the shutter speed that is modified
c)neither of these!

Flash compensation :
When this is active, is it
a) the aperture that is modified
b) the shutter speed that is modified
c) the flash output that is modified
d) none of these?

Graham

I'd guess that it depends whether you are in Shutter priority or Aperature Priority mode, which I think is confirmed by my reading of Page 151 of the K10D manual, which says (in relation to Tv mode)

"* Turn the front e-dial whilst pressing the +/- button to chnage the EV Compensation value
* Set the shutter speed in increments of 1/2 or 1/3 EV. Set in [EV Steps] in the [C Custom setting] Menu"

Flash Compensation is the adjustment of the output (Page 47 of the AF360FGZ manual)
"Flash Amount Correction -3.0 to +1.0 levels (EV) (0.5 Steps)"

I could be wrong, though!

Graham,
Exposure Compensation: if you are in "P" mode, then the compensation is performed according to the current program line selected. So, generally it will be a combination of Av and Tv adjustment.

In the other modes, it depends on where the priority is. For instance, in TAv mode, it will be the ISO that will change because the user selects the Av and Tv.

Flash Compensation: again this depends on the mode somewhat, but remember that the flash speed is (generally) much faster than the shutter speed so it's always Av that's adjusted to expose. (Varying the shutter speed only varies the amount of ambient light, not flash light.)

Hope that helps!
Matt

Thanks Tim & Matt
Does it help? Well yes and no.

I understand what you are saying, but there appears to be a slight conflict with regard to Flash compensation. However, Tim is presumably talking about an external flash.

Also, with reference to Matt's explantion of Flash Comp. I see little difference between Flash and Exposure modes. If I understand you correctlly and set the Tv to the flash sync speed, then both flash and exposure comp will adjust the aperture in the same way.

The istD does not have flash comp, so can I achieve the same result by setting the Tv to flash sync speed? In fact, if I use the on-board flash the shutter speed is automatically set to 1/150 sec. anyway.

This is where I get confused

I seldom use flash and when I do it seldom produces the result I am looking for.

Graham

Ooops
Forgot also with flash that the power of the flash is adjusted as well...

In fact, with the pop-up flash and AF360/540 you can use fully manual on the camera (ie meter for the bits you want) and the P-TTL flash will sort itself out automatically

To be honest, you have little control over pop-up flash, even on the ones with flash compensation. With the *ist-D there is no control - except "on" or "off" Adjusting the Tv speed won't make jot of difference.

Bear in mind this too: when the metering is done for flash the camera will take into consideration all reflections. For example, if you take a shot in a room and accidentally get a reflection from a window or mirror opposite you will find the shot looks massively underexposed. Also, if you try taking a shot of someone with even a small reflective strip on their coat - it will be underexposed.



Flash isn't that difficult really - it's just that automatic flash makes it seem tricky because it's not always predictable To explain my comments further:

The flash speed is very, very fast. The reason you have a sync speed for flash is to do with the two-curtain nature of the shutter. On slower speeds the first curtain opens the shutter, waits the time, then the second curtain lowers. On fast speeds, (1/150 - 1/4000) the second curtain follows the first curtain - exposing a moving "strip" onto the film or CCD. This effectively reduces the exposure time for that little strip (when you think about it - how could you get a mechanical shutter to shift itself in 250 microseconds?? It's not possible).

Now, if you could use a normal flash on a fast shutter speed then you'd only expose a portion of the CCD/film. On the AF360/540 they have a special HS mode which creates a very fast pulse of flashes so that the "strip" is still exposed correctly as the curtains move in the shutter.



Back to normality... because the shutter speed doesn't matter (at least not in terms of getting correct exposure, the above information notwithstanding), you can only control the aperture and flash power. You can, of course, also vary the distance between the subject and the flash - but only if the flash is remote.

Now, CCDs absolutely hate being overexposed. They are linear, and you just blow out the image completely if you overexpose. When dealing with flash you are very likely to blow out the image... hence the camera errs on the side of caution when exposing.

However, if you have studio conditions, then it's a cinch to setup fully manual flash - the camera doesn't have to work out what you need properly exposed in the image because you've done all the work first.

If you're not going down that route and you are using flash for "ad-hoc" stuff, then bouncing or diffusing the flash is the best thing to do. A Stofen Omnibounce on an AF360 is really excellent. It's even better if you move the flash off camera (great with the *ist-D wireless).

If you're stuck with just the pop-up flash and want to take short-range portraits etc, then holding a piece of thin tissue paper over the flash will go a long way to making a more flattering image... and lowering the risk of reflections too.

(Phew!) Hope that helps!
Matt

Many thanks Matt, especially for your patience. That was some reply and confirmed much of what I suspected plus adding a few new bits as well.

As you have probably gathered from my various posts over time, my photography is not in the same league as some of the rest of you. I find the subject, and its practice, both stimulating and challenging. That said, I am more an enthusiastic amateur than keen exponent of the art.

My photographs are more of the "record" variety to provide memories of times, places, people, etc. as well as some of the oddities that I come across in life. I cannot be doing with carrying loads of gear around, which is why I use a 18-200mm lens as an almost permanent fixture (sometimes my 28-300mm lens). No flash, no Tripod, no supplementary lenses, nothing but the camera set up before I set off.

Which brings me back to Flash. I depend on the built-in flash (unless someone brings out a mini portable unit about the size of a match box) which I use as fill-in. For close-up work - eg unusual fungi, an insect, leaf or whatever - this is always too powerful, and any attempt to correct it using aperture simply results in grossly underexposed surroundings.

I think I mentioned somewhere else that my Minolta A2 bridge camera allows me to adjust the strength of the in-built flash. Most external units also allow this facility. I had hoped that Flash Compensation was merely posh SLR-speak for achieving this result but apparently not. I guess not even the K10 will do that.

I have tried the tissue paper idea, and the handkerchief, and the muslin, but they do not fit with my casual/impulsive approach.

Still, thanks for your reply and now that you know the real problem, if there are any other bright suggestions let me know. You might even know of a matchbox sized external unit
Graham

Hi Graham,

for diffusing the pop up flash, you might want to look at one of these..

http://cgi.ebay.co.uk/LUMIQUEST-SOFT-SCREEN-BRAND-NEW-PRODUCT_W0QQitemZ270078842...

They clip into the hotshoe, and when you need it, just fold it up and over the flash.. it attaches with velcro on the front if needed.

Cheers

Liam

Hi Graham,

I think you're misunderstanding what's being said. Yes "flash compensation" on the K10 does change the power of the flash.

If you are using it as fill in, then the natural lighting must be sufficient to give full exposure without the flash. If it isn't, you'll probably end up with a picture which is underexposed by the flash compensation you dialled in.

If you are relying on the flash for full or a substantial part of the exposure, then the camera will use both the power of the flash and the aperture to adjust the exposure.

Adding to Tailety's comment:

If you are too close, or the ambient light is too high, then you'll have problems with overexposure. The flash can only be powered down so far, and beyond that it won't cope.

However, for macros you are better off trying this with the popup:
* Set camera to "M"
* Set shutter speed to 1/150 (or lower)
* Set the aperture to f16
* Take a shot

If it's still too bright, reduce the aperture (larger f-number). If it's too dark (flash isn't powerful enough), then open the aperture (larger f-number).

The pop-up flash will compensate for you and do its best
Matt

Hi Taliety
That sounds interesting and I must follow it up further to make sure I really understand and that it achieves my objective. Also a bit more experimenting is called for.

Thanks Liam
The Lumiquest screem might do the trick - something else to follow up

Meanwhile....
Apparently Sunpak have just released a new flashgun - PF20XD - about the size of a fag packet and relatively low power with 5 different power ratios. That seems to be just the job only it is so new that I cannot find it on sale anywhere. It is $70 in the US so I guess that will be £70 in the UK - a bit steep for me

Graham

Just found out that they are due for release in UK in about 3 weeks - price £60. Its times like this that I wish I had a relative in USA

Just looked up the relevant bit in the manual and there does seem to be a small limitaition
"Compensating to the minus(-) side may not effect the image if the subject is too close, aperture is low or sensitivity is high"

Still, it is probably not the end of the world

Graham

Graham - see my last post above (I think we posted at the same time)

Thanks Matt et al

I have certainly learnt a few things and hopefully some other members of similar innocence might have picked up something.

The problem of shutting down the pop-up flash light using the aperture is that of course it darkens everything.

I have been trying a few experiments with an old low powered Sunpak which is only slightly larger than the PF20XD I mentioned above. It seems to offer the solution I am looking for except that I need to reduce the flash with bits of paper. Having a switch would be much better.

I am simply looking for some method/device to provide low level fill-in light that I can carry around in my shirt pocket. If push comes to shove, I guess even an ordinary flash light would do if I could attach it to the camera. - here comes the araldite - only joking.

Anyway, thanks for your attention. Perhaps I will post the final so;ution when I have found it!
Graham