Fill flash

desmobob

Senior Member
Yesterday I was snowshoeing with friends and set up a quick photo on a hilltop with the background bright with snow and back-lit. I had my AF-S 24mm f/1.8G stopped down to f/2.2 to get the shutter speed down to 2000 and popped up the camera's flash for fill. It didn't go off. When I stopped down further, it did. I didn't review the images at the time so I didn't notice I didn't get the much-needed fill until it was too late to try again.

I was just getting some casual snapshots so it was no big deal, but it is something I'll be more aware of in the future. I had inadvertently left the Auto ISO enabled and I don't know if that had anything to do with it.

I got the flash fill (and busy background in focus) here:
_02-26-22_79.jpg

But not here:
_02-26-22_84.jpg

I guess with that lens I couldn't have softened the background focus much at f/2.2 anyway, but I wanted to try.

Just another reminder for me to slow down and check all settings before I push the shutter release... 99% of the time that I screw up photos it's because I don't notice a single thing other than the subject when I look in the viewfinder. All the valuable information is there and I have to make myself remember to look at it!
 
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BF Hammer

Senior Member
I don't know if you were in M mode or A mode, but the flash should work the same either way. I see ISO 100 in your exif data so really auto ISO was not interfering. The D750 manual does not indicate it would either in the flash section.

Reading further into the manual, here is why no fill-flash happened. The built-in flash is not going to work on a shutter speed that fast, but an external speedlight can. With the pop up you need to be down at 1/200 or 1/250.
 

Roscoe Primrose

Senior Member
Reading further into the manual, here is why no fill-flash happened. The built-in flash is not going to work on a shutter speed that fast, but an external speedlight can. With the pop up you need to be down at 1/200 or 1/250.

An external flash may fire above the max sync speed, but you're not going to be happy with the results. Maximum sync speed is based on the physical characteristics of the shutter. Above the maximum sync speed, there is no instant that the shutter is fully open, so the flash won't light up the whole frame....

Roscoe
 

desmobob

Senior Member
Reading further into the manual, here is why no fill-flash happened. The built-in flash is not going to work on a shutter speed that fast, but an external speedlight can. With the pop up you need to be down at 1/200 or 1/250.

Ah ha! The pop-up doesn't do fast synch! Thanks for solving the mystery!

I like using balanced fill flash outdoors so I'll start bringing my SB-800 along.
 
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