I have a Nikon SB-28DX which I am using with an F5. I understand from the instructions how to turn the AF-assist illuminator off. But, how do I verify that it's working? Does it still work with the flash in standby? If no, how do I ensure that the unit will perform AF-assist only, and not fill flash?

In case it makes a difference, I'm activating AF using the AF-on button (that is, custom function 4 is set to 1).


2 Answers 2


Try it in a very dark room. If you can focus, and there's no flash, it's working.

I haven't used an F5 (only much more primitive SLRs), but I assume it will let you shoot with no film loaded so you're not wasting anything.

You've edited the question to emphasize the part about ensuring the unit will perform AF-assist only, which is pretty different from the question of verifying if it is working. From the manual (note the DX and non-DX are identical for film cameras), this flash does not appear to have a mode that does what you want — activate the AF assist light but not actually flash. Some flash makers call this "Spot Beam mode"; Nikon, for flash units that have it, calls it "AF-Assist Illuminator only" (AF-ILL ONLY) or, somewhat confusingly, "Firing canceled". I don't have an SB-28DX, but since the manual doesn't mention this as an option, it's probably not. You can still verify this with the test mentioned above.

  • \$\begingroup\$ I did some experiments today. Trying a variety of flashes in a dark room, I started with an SB-800 in AF-assist-only mode (to get this, you hold down SEL, scroll down and set the FIRE menu option to OFF). In a completely darm room the F5 wouldn't focus at all (with a 35mm f/2). Likewise with low light levels (I gradually opened the bathroom door). It worked with the light on of course. So I was unable to find a light level at which the camera would focus with AF-assist but not without it. This is not to say that it's useless, it may improve AF accuracy. \$\endgroup\$ Mar 18, 2012 at 11:01
  • \$\begingroup\$ Trying also an SB-28DX and an SB-24, I obtained similar results (in particular, I could see no vertical red lines). I was unable to find a way to leave AF-assist on but turn off flash firing for the SB-28DX or the SB-24, though as I mentioned above this is possible with an SB-800. Thanks Matt and Alen for your help. \$\endgroup\$ Mar 18, 2012 at 11:02

But, how do I verify that it's working?

If you are using Continuous AF, I believe, AF-assist will not work. But don't quote me on that, it's been a while since I used F5. Also, see if you can access SB-28DX's menu and check if AF-assist is on. Not sure how to do this, never used that flash. I know on my SB-800 there is such option.

Does it still work with the flash in standby?

Pressing the shutter button half way down, or in your case pressing AF-on button, should "wake up" the flash from stand-by mode, if mounted on the hot shoe on top of the camera. If you are using any kind of remote triggering system this might not be the case so make sure you test it.

You can always refer to the manuals and see what it says for both flash and the camera. Or if all else fails, like Matt said, go into very dark room and play with settings.

Look trough the viewfinder if you can see vertical red lines when you activate your AF then it's working.


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