[Lucad]

Hello all, I'm new to the forum and have just purchased the Pentax KP and an learning to use it. My question is regarding the on camera flash and ISO. I have the ISO range set to 100 - 6400. When I use the flash in Auto or P more and I believe in TVA mode the ISO the camera chooses is at 6400 or 5000 range. Shouldn't the ISO be much lower when using the flash. I guess I can use manual or set the ISO to a reasonable number. Just surprised at the settings the camera uses. Will the noise be less at a high ISO when flash used?
Your thoughts would be appreciated.

Thanks,
Luca

[enoeske]

The flash is done at exposure. So, the camera is still metering for the scene its looking at. It tries to get a decent amount of ambient exposure. Then when you go to take the picture, it pre-flashes to tell the flash what exposure to use and takes the real shot with the flash at that power. If you want a different ambient-to-flash ratio, then you have to take control and set the camera according to what you want. Its not a mind reader.

[photoptimist]

First, a flash isn't going to reduce the noise inherent in a high ISO image although a better-lit subject might end up looking less noisy after post processing.

Second, on-camera flashes are not very powerful. In a large room or outdoors, the flash simply cannot light the whole space which forces it to use a high ISO.

Third, even in smaller rooms this kind of issue can happen if the subject is very near to the camera relative to the walls of the room. To avoid the "deer-in-the-headlights" look, the camera can't use the flash at a power level suitable for the room without blow-out the nearby subject. Thus, the camera will use the flash at lower power and pick an ISO that's appropriate for the dim background and the flash sync shutter speed.

[UncleVanya]

The default is to essentially use flash as fill lighting to make it look natural. A quick change of iso should force it to a more flash centric exposure. On my k3 I have a dedicated flash setting (X). I don't have a KP so I'm not sure if you have that option. That setting also sets the shutter speed to sync speed.

[stevebrot]

Welcome to the Pentax Forums!

Shouldn't the ISO be much lower when using the flash.

I am not a fan of auto ISO. One of its quirks is that the ISO is not calculated until after the pre-flash when using P-TTL flash. If the metered reading from the pre-flash is bright (close subject), the ISO will be lower than if the subject is farther away. The on-board flash on the KP is pretty weak (GN 6), hence the a tendency to higher auto-ISO in general with flash than might be expected, except at moderate distances or with bright ambient light.

A good exercise might be to use the on-board flash in combination with manually set ISO and various subject distances. The limits should be pretty obvious.


Steve

[CarlJF]

With flash, on-board or not, it’s usually better to set the iso manually. As many said above, the camera can’t know what you want exactly... Thus it just uses a combination of settings that will get a usable exposure for most of the scene. Which can or not be yo your liking even if technically right.

[clackers]

Take control, Lucad, it's why you bought a DSLR, to micromanage this stuff!

Get the exposure for the background right first ... take a pic beforehand without flash to confirm your settings, and in manual, make sure they stay that way before popping up the flash.

Then use the flash exposure compensation dial to light the subject according to taste. It is easy, by the way, to be too close or too far from the subject for the compensation to be enough.

[C_Jones]

I would also recommend being in Manual mode for flash operation. Being able to set your own effective ISO and other settings is something you have some control over when in Manual mode. When/if you get for example a flash such as a Pentax or Yongnuo YN-585EX, if you use the P-TTL (Pentax TTL) feature of the flash, to have more certain control over the use of the flash, you will want to be in Manual mode, due to the TTL feature of the flash being able to decide itself the appropriate flash power to be used. Then from there, as Clackers iterated, you can choose the flash compensation plus or minus to further modify what you would like to be used relative to that light.