Quick Preflash Question

Simple hypothetical question.
Is there any reason why in the flash menu there couldn't be a Disable Preflash mode?

Because the pre-flash determines the exposure in p-ttl

Yep!

No pre-flash > No flash metering > Wrong exposure

Sadly not like TTL where the flash was metered by light bouncing off the film so only needed a single flash.

That's progress ... isn't it :

I think part of the problem is that TTL sensors didn't meter off the sensor correctly as it doesn't behave like film and this was the easiest option.

If you use pre A series or soft lenses, the on board flash discharges 100% as it cannot be controlled/regulated. It's also possible (needs testing) that you won't get the pre-flash either.

If you need to prevent the pre-flash from firing, fit an older Pentax flash to your hot shoe. There are plenty of old flash models to choose from.

Or just set the flash to M mode and use fully manual.

Thanks everyone. This is what I've been doing. I've got a couple of old Pentax flashguns. I just wondered though why, as the built-in flash is there already, there couldn't be a setting in the flash mode menu to discharge without preflash? You don't always want or need auto P-TTL flash.

The built-in flash is to be avoided at all costs.

You can disable pre-flash by using manual mode on any flashgun. The onus is then on you to get the exposure right, but that isn't difficult with a DSLR.

You can either take a series of trial pictures until you get one right, or you can work out the correct settings from the guide number.

I far prefer manual flash, with A-flash as second choice. By A-flash I mean the flashguns with their own built-in exposure sensor, like the AF400-T.

link

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It is a total mystery to me as to why a DSLR comes with a built in flash, anyone who buys one must be striving towards a level of photographic skill which makes such a contrivance a nonsense.

It can be handy for the odd snap when travelling light.

The built in flash is highly useful for me. There are plenty of occasions I want some fill in light without having to carry my main flash around. I've even built a tiny bubble wrap diffuser to stick over the top of it condom style

try this sometime... light a couple with hard lighting, have your female posed a little closer to the camera...
now use the built in (or optional ringflash) as on axis contrast control... you'll knock a few years off her by diminishing wrinkles while maintaining a harder lighting look on him....(due to flash light fall off, even a few inches makes for darker shadows)

or anybody with deep set eyes....
it's there, might as well use it...
as for the op... I guess they don't let you disable preflash 'cause they want you to buy a seperate flash?

+1, on the beach, shooting into the sunset and you can't be arsed to load up a GN50 beast (even if you have it stuffed in your welly) and miss the decisive moment. Press the little button and problem solved.