Nikon ISO problem in Aperture Priority Flash

[pzirnis]

Nikon D610 - Auto Flash works fine. Aperture or Shutter priority overexposes by increasing ISO three to four times over what it should be. Auto: 1/60, F4, ISO 800 APERTURE PRIORITY: 1/60, F4, ISO 6400. Camera Settings: ISO Sensitivity settings: 200, Auto ISO ON, Maximum Sensitivity 6400, Minimum Shutter Speed 1/60. Any ideas ? Thanks, Peter

[Manfred M]

Hi Peter - welcome to CiC.

I'm not totally sure quite what you are doing here; are you using the camera's built-in flash or are you using an external flash, and if so are these CLS compatible Nikon flash units or third-party flashes?

Just a first guess here. The built-in flash and external Nikon flashes are integrated into your camera;s computer and when using a Nikon Creative Light System (CLS) flash, these units fire a pre-flash to get a light reading and adjust the flash output for proper exposure. If you are using a non-CLS flash, the camera will not see any pre-flash signal and will assume the ambient light that has returned is correct and will increase the ISO to compensate, so when the flash goes off, the exposure gets really overexposed, via auto-ISO.

You would get a similar result if your CLS flash is set to manual, rather than TTL.

[GrahamS]

In "Auto" mode, the camera will use the flash as the primary light source. If you have the flash set for "Fill flash," in Aperture or Shutter priority the camera will base the exposure on the ambient (and increase iso accordingly if "Auto ISO" is set to "On") and use the flash only for fill.

[pzirnis]

built in flash - have had camera for a couple of months but hardly used flash and then just in AUTO - have just noticed while checking that even in non-flash using same F stop as Auto and shooting in Aperture Priority the numbers don't match. Auto non-flash 1/20,F4,1600 vs Aperture Priority 1/50, F4 6400. Slightly overexposed. Possible I set some indicator that is causing this ? Thanks GrumpyDiver for the quick reply.

[Manfred M]

built in flash - have had camera for a couple of months but hardly used flash and then just in AUTO - have just noticed while checking that even in non-flash using same F stop as Auto and shooting in Aperture Priority the numbers don't match. Auto non-flash 1/20,F4,1600 vs Aperture Priority 1/50, F4 6400. Slightly overexposed. Possible I set some indicator that is causing this ? Thanks GrumpyDiver for the quick reply.

In auto the camera will pick what it things are appropriate shutter speed, aperture and ISO, while if you shoot aperture priority, you choose the aperture, while the camera adjusts the other paramters. A similar thing happens in shutter priority (where you set the shutter speed and the camera adjusts the aperture and ISO), but things will go a bit strange with Auto-FP mode, once you exceed the sych speed of your camera (I don't know the D610, but on my D800, Auto-FP High speed sych is limited to 1/250th sec for the built in flash, while I can get up to 1/8000th with my SB-900).

[pzirnis]

D610 has 1/200 sec max flash sync - but that can't be the problem as the sync speed is low as you can see: 1/60 since ISO is 6400! I did notice that I had center weighted metering on, but changing this to matrix had only a slight effect. Checked with my 'old' D40 (which has max sync speed of 1/500th by the way) and also saw a variation between Auto and A or S priority but these were minor. Assume it is some setting I changed in the guts of the options - at least I hope so.

[RustBeltRaw]

Assume it is some setting I changed in the guts of the options - at least I hope so.

If you're not sure which setting it could be, most cameras allow you to reset them to factory configurations. I'm afraid I've never done it on a Nikon, so I can't provide specific instructions, but if necessary, that should get you back to a workable baseline.

[ajohnw]

I think this may be the same problem I had a long time ago.

Flash makes up the light needed to provide the correct exposure So say you set the camera to manual. shutter speed 1/250 if that is max flash sync speed and aperture to F4 the flash will make up any extra light that is needed. I am not at all sure what would happen if the camera is in auto iso but if sensible it will drop to a low value. The key is using the camera in manual mode.

The reason for working this way comes down to providing fill flash etc. Here some one might might select a shutter speed / aperture that was some stops short of achieving the correct exposure so that the flash will make up the difference. I haven't done this on a Nikon ( or any camera) for some time but might for instance set a manual exposure that was lower than needed and leave the rest for the flash to remove or weaken shadows from any side lighting. When used like this the shutter speed can't be any higher than max flash sync speed.

: Just watch that you haven't left any negative exposure compensation on in inadvertently as I did very recently. Made me think that the flash wasn't working correctly.

The flash needs to be in the creative(?) mode as Manfred mentioned. In some camera modes that option may not be available in the menu's.

John
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[pzirnis]

Hello All and thank you for your comments. After spending a few hours shooting, changing settings etc I finally got my over exposure in A/S Priority problem under control. It was a mix of not understanding Nikon's various focus modes, using center area metering with Spot focus plus a strongly backlit subject etc etc. On the upside I have a handle now on what the various options do and how they interact with each other - the downside was I had a few bad moments yesterday thanks again.
Peter

[shreds]

Glad you got it sorted in the end!

Anyway welcome Peter.

It would help the rest of us if you could put your first name and approximate location in the profile section. Since we have members from all parts of the globe, it can assist in providing the answers and has generally been a positive feature of CiC since its inception. (Also explains why you haven't had a reply as they may be asleep!).