Nikon TTL / Metering with speedlights and macro lenses

[andy-xr]

Had something that confused the crap out of me yesterday and trying to work out what the camera was thinking I wanted to do. I fancied trying some macro work as I've never really done any before, so went off to hunt out a local bee thing in the garden. SB600 on camera (D300), Tamron 90mm, Aperture Priority, set at F32, camera exposure compensation set to +0.7, flashgun set to 85mm, TTL (no BL) with +0.7 compensation, camera metering set to centre weighted average, single point A/F. Should be fire and forget really.

So all looking good so far til the first shot. Badly underexposed. Look at the settings and I've got 1/60th @ F32 but the flash has decided to dial -2.7 EV in. Change to spot metering, focus on the beasty, add a stop of flash compensation in to the speedlight, same thing again. Change to matrix metering, and it dials -3.0 in (or out)

Go into the flash menu on camera and it all looks sensible - no bracketing set up, max sync @ 1/320th and no red eye or slow sync etc set in.

Go Manual, 1/160th, F32, ISO400 and put the flash on half power at 50mm zoom and it's looking fine from some chimping. I see flash catchlights and shadows that would be indicative of what a speedlight would do, and leaving the flash on the same power I've got some freedom in shutter speed and aperture to brighten/darken things as light changes, so thats how I carried on

I've never seen this before as I tend to roughly work out what the settings should be in my head as a base starting point, so never really have the camera make decisions for me.

So, I probably dont have the right tools for the job with an SB600 on the hotshoe, I'll take that. But I'd have thought why it was happening still needs working out. Is it because with a flash on camera and a lens with close focus ability that the camera thinks the flash cant really get close enough to affect things? Or trying to meter for something else (ie shadows) in the photo? Have I missed something somewhere? Do you want a picture? Shall I RTFM?

[Simpo Two]

Ah, you're mkaing the mistake of trying to understand how a Speedlight works!

Try something easier first and work up, eg:

1) War and Peace
2) Fermat's Last Theorem
3) Speedlight Manual


Add the Speedlight to the camera and the fun really begins... sorry, can't help

[SamHH]

When you say that you set the flash to +0.7EV but that it dialled in -2.7EV, what exactly do you mean? I'm not familiar with Nikon flash, but if you've instructed the flash to flash 0.7 stops over the metered exposure, how can it decide to do anything but that?

Anyway, the way I set things for macro flash is to have the camera in manual mode with a shutter speed around 1/180th, an aperture of about f16 and the ISO set at 200 or 400. I then set the flash to fully automatic, and adjust the exposure by changing the flash exposure compensation.

Aside from the confusion about the flash "dialling in" odd exposure values, my only thought about what's going wrong is that maybe, because of its position on the hotshoe, the flash can't 'see' the subject. By manually setting the zoom to 50mm (instead of the 90mm it would presumably have selected itself), it could have spread the light just wide enough to illuminate the subject.

[andy-xr]

SamHH said:

When you say that you set the flash to +0.7EV but that it dialled in -2.7EV, what exactly do you mean?

I set it to TTL and added +0.7 exposure bias into it on the back of the flash by pressing the Up arrow twice. It's supposed to slightly overexpose

SamHH said:

I'm not familiar with Nikon flash, but if you've instructed the flash to flash 0.7 stops over the metered exposure, how can it decide to do anything but that?

Thats what I thought! However, shoot something and the flashgun blinks -2.whatever as what it just metered.

SamHH said:

maybe, because of its position on the hotshoe, the flash can't 'see' the subject.

This is where I think it's gone wrong. The Tamron 90mm is a lengthy bugger at full macro and may well be that the sensor from the flashgun being way back on the camera cant see what the lens is seeing, so is going for an evaluation of what it can get to. Interesting stuff

[Simpo Two]

andy-xr said:

Thats what I thought! However, shoot something and the flashgun blinks -2.whatever as what it just metered.

Gottit (I thought you were tkaing it from EXIF). The blinking signal is trying to tell you that the flash CANNOT give as much light as it wants to, and by how much. It was the f32 that did it. It was trying to do what you wanted but couldn't achieve the correct exposure.

It's in the manual you know