Flash Exp Comp or camera exp comp?

[Big Bob]

Trying to figure out which to use or both. If you're using the onboard flash and you want for example +1 stop, should you set the flash exp comp, or the camera exp comp. Within the camera is there any connection between the two. Would a combination of both ever be advisable - say in a fill flash situation?

Any light you can shed (no pun intended) on this would be greatly appreciated.
Thanks.

 

[Tom Caldwell]

Bob

The original GRD had only EV compensation and I proved that with the flash in use the EV controlled the flash output as well - only emitting enough flash to correctly expose the image (according to the EV set). But there was a lot of "discussion" over the lack of FV compensation and in the every last firmware upgrade for the GRD it was included but buried in the menu. I am not sure whether this was good or bad.

This left me wondering as you are wondering on just what takes the priority - for instance what happens if the camera EV is -3.0 and you turn up the flash full tilt? Or the reverse? I guess we could experiment a bit to see what effects we might create.

I have rationalised that the camera EV is the broad brush and the FV is the fine tuning. For example a little fill flash might be needed for a backlit subject and should not disturb the overall EV "coarse" setting on the camera. But I do not consider myself a flash expert and I would also like to know the inter-action of these two settings - perhaps someone with more precise knowledge might chip in and assist?

Tom

 

[Blow-in]

Bob,

This is a good question and I suppose the answer lies in trying to understand what the various compensations are actually doing.

I think (but stand to be corrected please) that the camera exposure compensation control is really a sort of light meter adjustment. The camera metres the scene but you then tell it via the compensation whether you want more or less light and if you are shooting in AP for example, the camera will resolve this by adjusting the shutter speed (or possibly the ISO if you are using auto ISO). You can test this by a series of half presses where you read the shutter speed as you adjust the exp comp.

If you try the same experiement but with auto flash selected and half press a few times with different flash exposure compensations you will find that the shutter speed & aperture doesn't change so what the flash compensation is doing (I think) is adjusting the amount of flash that you get (the camera will switch off the flash either earlier or later with compensation using through the lens metering).

I don't see why you couldn't use both together. Exp comp to set your general light setting then flash comp to adjust for fill-in on your subject. Personally for fill-in I use manual flash where the adjustments are fractions of full power.

Have a play - it's almost free with digital.

Richard

 

[Big Bob]

Tom and RIchard thanks for your replies, they have helped me think the issue through. I started to use the flash for fill purposes in backlighted, bright contrasty situations with pretty good results. I did notice that foreground sometimes still needed a little more exposure, and this is where the question arose - should I use a little ev boost, or try to pump up the flash a little. Seems like either, or a combination of both might work.

Thanks,
Bob

 

[Tom Caldwell]

Bob

I think the "experts" are no more expert I am not a great user of flash and my flash attempts are usually no more than a tap of low power fill flash using the useful manual flash value settings. In this case it works much the same as the original GRD where the EV setting controls the base exposure value.

I told my little story because the GRD 10 years ago worked fine using EV only to drive regular flash use to provide correct required exposure merely using the amount of flash power necessary - the GRD had ttl metering for flash but the R4 which didn't and both cameras could quite easily produce a whisper of flash when needed or crack! and fill the room with light if suitably provoked. Someone noticed that other cameras had a separate FV control and all of a sudden there was a great deficiency in the GRD and quite a campaign to have FV compensation on the GRD or some sort of world calamity would ensue. So Ricoh added a FV control to satisfy the raging and nothing much has been said about it since.

It does make sense in a sort of way but the only way it could work is in a ratio with the normal EV control to achieve exposure. The EV control is the primary control - + or - is an indication of how YOU wish the camera to adjust the reading of of its exposure metering. If the flash is enabled the strength of the FV selected is also adjusted into the metering to try and achieve what YOU wish the adjusted EV to be.

Therefore if you are in (say) Aperture Priority and your subject is backlit you might dial in a little positive EV to compensate and the shutter speed selected will become slightly slower. Enable the flash and the amount of regular flash will be available and the shutter speed will rise. Reduce the FV setting and there will be less flash and the shutter speed will slow again but will not be as slow as if no flash were used.

I don't know if I am correct in these assumptions but am simply trying to use some common sense first principles. However it is a basis for some testing to see if what I am postulating is actually true in practice.

It cannot work if the controls are independent of each other as you would certainly get some queer results if you simply turned up the FV with no reference to the EV. Presumably over-flashing is still possible and can just as easily blow the subject away. If this truly happens then one might wonder what use a FV control might be.

Therefore us "not knowers" really need the input of someone who knows exactly what the inter-relationship of the EV and FV settings are - or better still simply work it out ourself by experimentation. Maybe there is something on this subject in an article on the web?

Tom

 

[Blow-in]

I've done a small trial with my GRD4 (if anyone would like to lend a me a GR I'd be more than happy to repeat this!).

For all these shots I've used AP, ISO 80 and F4.0 with DRC off.

So for the first shot (217) I've selected EV0 and no flash:



As you can see the view through the window is completely blown out. The camera selected 1/17 shutter speed.

For the next shot (218), I selected EV-0.7 to correct the window exposure (a bit at least) and no flash:



So there is a bit more window detail and as you would expect the camera selected a slightly faster shutter speed - 1/26

So for the 3rd shot (219), I kept EV-07 but selected auto flash with 0 compensation.



Interestingly the camera selected a slightly faster shutter speed. I couldn't work out whether that was due to a bit more daylight or anticipation of the flash so I tried a similar couple of shots in a darker area forcing the non-flash speed to 1/12...with flash selected it jumped to 1/32. So clearly the camera will select a 'shake free' speed when the flash is selected.

Next (220) I adjusted the flash compensation to - 2.0



The only obvious effect was to reduce the amount of flash.

And lastly (221) is changed the flash compensation to + 2.0



And here the effect was to increase the amount of flash.

So the only small surprise was that the camera increased the shutter to 1/32 in anticipation of the flash (helpful). Otherwise it worked as I expected in 2 posts above. In a situation like this I think you can use flash & EV compensation together with EV used to adjust the exposure beyond flash range and flash compensation to adjust the close range 'flashed' item.

Having said all this, outside in normal daylight auto flash hardly ever fires so I still prefer to use manual flash and flash amount for fill-in in the great outdoors.

Richard

 

[Blow-in]

OK - three more (no more after this, I promise).

Here I've been more agressive with the EV compensation using EV - 2.0 throughout to give good colour through the window.

First one (237) has no flash:



Second (235) has auto flash with FV 0:



Last one (236) has FV - 1.0



Richard

 

[Big Bob]

Richard,
Your little experiment, I think, answers my question completely. I am going to experiment with outdoor situations where the sunlight is harsh and the subject is backlit. I will set the camera exposure for the background conditions, and set the flash compensation for the subject exposure.

Thanks for the examples.

bob

 

[Tom Caldwell]

OK - three more (no more after this, I promise).

Here I've been more agressive with the EV compensation using EV - 2.0 throughout to give good colour through the window.

First one (237) has no flash:



Second (235) has auto flash with FV 0:



Last one (236) has FV - 1.0



Richard

Richard

I think you really nailed it with this last experiment. The EV can adjust to bring in the over-exposed background and the FV gets the foreground right. Brilliant - thanks for taking the trouble.

Tom

 

[Blow-in]

Tom,

Thanks very much for the comments. I suspect fewer people use fill-in flash in the digital world compared to film days as we now have access to such high ISOs and can PP up under exposed areas. Some have even suggested deleting the built-in flash. Now for the real world outside. I took these 2 today in really quite harsh sunlight. There was no way the auto flash was going to fire so I used full manual on the shot with flash....it has helped a little bit I think but also produced a cooler picture.

First without - Mollie is mainly in shadow



Then with - some more detail of Mollie's coat



Obviously the range of the built-in flash is limited and I should have helped by opening-up the aperture.

Richard

 

[Tom Caldwell]

Richard, obviously lots of backlighting. By the time you get the foreground right the sky would be washed out and any camera flash would have to work really hard to compete with bright daylight. I suppose that in instances like this dynamic range bracketing might have helped.

I rarely use flash but I keep thinking that I should use fill flash more often. The day that they are no longer supplied with camera will probably be the day I will start pining for one.

Perhaps you should train Mollie to be your assistant and carry a reflector around for you ...

Tom