What is FV Lock?
Keywords: nikon, speedlights, lighting, flash
I've written in previous Speedlight articles about the fact that the Nikon flash metering system measures only the center of the frame. This means that if the subject is not in the center of the frame, the brightness of the subject will likely be wrong. Below is an example of a subject that is not in the center. I used FV Lock to make sure the subject was exposed properly by the flash.
I was outdoors at a reception on a pitch dark night, so there was zero ambient light, and I wanted the very dimly lit waterfall to come out in the background, so I used my DSLR handheld in manual mode, ISO 400, 1/8 sec, f/2.8 and my flash in TTL.
I first pointed my flash at the subjects and pushed the FV Lock button to fire the pre-flashes and lock in the correct flash power. Then, I recomposed the shot to place the subject on the left 1/3 line (rule of thirds), and released the shutter. Notice that the subject is sharp despite the very slow 1/8th second shutter speed, because the flash stopped any motion. But, look at the waterfall. There is definite motion blur there, but I used f/2.8 to make sure it was out of focus so the motion blur from handholding the camera wouldn't show.
If I had just framed it as above to start with and taken the shot without using FV Lock, the flash would have metered the center of the frame, which was the waterfall about 70 feet (approx. 21m) away, and it would have set a very high power. The subjects would have been totally blown out.
One very important thing to know when using FV Lock is that once it is pushed the flash value remains locked at that power setting until one of three things takes place:
- FV Lock is pushed a second time
- the camera is turned off, or
- the light meter in the camera times out.
Since the default light meter reset time is very short (only 6 seconds on my D200), you need to use your camera menus to extend the light meter timeout to as long as possible when you are using FV Lock.
Don't forget to return the light meter timeout to its default time after you are finished with FV Lock, or it will run your camera batteries down faster than normal.
FV Lock is very useful for shooting a series of shots of a group of people, so that all the images will look exactly the same from one shot to the next.
It is also useful for those rare people who are 'fast blinkers'. A fast blinker can blink at the pre-flash and their eyes will be closed by the time the main flash happens. Lots of animals are fast blinkers, so FV Lock is also good for them.
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Originally written on July 1, 2013
Last updated on January 24, 2021
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13 comments
User on July 18, 2013
Hi Russ Thank you for your awesome tips and for the amount of time and energy you put into explaining them. You have made me a better photographer. Eric Beal
Michel Raguin (raguin) on July 17, 2013
Very useful article. Now I understand why some of pictures using the flash were too dark or too light
Traugott Bartels (tangobravo) on July 17, 2013
Thanks a lot for this usefull tip.
Allen Henderson (AAHNikon) on July 5, 2013
Nice article Russ. Thank you!
Charles Strong (cwstrong) on July 3, 2013
I found this on the web. Focus Value lock button needs to be setup. The answer to Morton’s question is to use the FV Lock function built into your Nikon dSLR. Everyone needs to know that using Nikon flashes in TTL or TTL BL or even Manual will always result in pre flashes if you are operating in the Nikon CLS. What I mean is that if you have an SB-800 Commander (or a camera’s pop-up Commander like the D90, D300, D700) communicating with the remote flashes in channels/groups, then the preflashes are used to communicate between Commander/Remotes and can’t be turned off. However, there is a great workaround solution that is called FV Lock. You can program one of your camera’s buttons to activate the FV Lock function so that when you press the button, it causes all the flashes in the system to do the preflash at that moment. Then, the camera remembers the Flash Value (FV) and allows you to take the real shot without the preflashes. I do this when photographing pets or kids with fast reflexes who are prone to blinking. To program the FV-Lock capability into your camera, you’ll need to go to your Custom Settings Menu (the pencil icon) and find the FV Lock menu item. On some Nikon models like the D70/D80/D90 you can program the AE-L/AF-L button to activate FV Lock. On other Nikon models like the D300/D700/D3/D90, you can program the Func button or the AE-L/AF-L button to activate FV Lock.
Charles Strong (cwstrong) on July 3, 2013
I found this on the web: The answer to Morton’s question is to use the FV Lock function built into your Nikon dSLR. Everyone needs to know that using Nikon flashes in TTL or TTL BL or even Manual will always result in pre flashes if you are operating in the Nikon CLS. What I mean is that if you have an SB-800 Commander (or a camera’s pop-up Commander like the D90, D300, D700) communicating with the remote flashes in channels/groups, then the preflashes are used to communicate between Commander/Remotes and can’t be turned off. However, there is a great workaround solution that is called FV Lock. You can program one of your camera’s buttons to activate the FV Lock function so that when you press the button, it causes all the flashes in the system to do the preflash at that moment. Then, the camera remembers the Flash Value (FV) and allows you to take the real shot without the preflashes. I do this when photographing pets or kids with fast reflexes who are prone to blinking. To program the FV-Lock capability into your camera, you’ll need to go to your Custom Settings Menu (the pencil icon) and find the FV Lock menu item. On some Nikon models like the D70/D80/D90 you can program the AE-L/AF-L button to activate FV Lock. On other Nikon models like the D300/D700/D3/D90, you can program the Func button or the AE-L/AF-L button to activate FV Lock.
Alan Dooley (ajdooley) on July 3, 2013
My impression was that the button shown in the graphic is the Fn button and can be assigned a number of functions. Do we have to "assign" this Focus Value Lock to it? This look like a wonderful use for it!
Gustaf Risling (nussika) on July 3, 2013
Absolutely news to me - thanks - I'll try it soon!
Jackie Donaldson (bhpr) on July 3, 2013
I never knew this. I will have to try it now :) Thanks!
Bill McGrath (wfmcgrath3) on July 2, 2013
It might be a good idea to explain how to access the FV lock feature using one of the buttons configured in the menus. I realize it differs a little bit from camera to camera, but it would provide a starting point to people who have never used it.
Tom Feazel (tfeazel) on July 1, 2013
I use a Metz SCA 3000 system flash. Does this flash work in a similar manner?
User on July 1, 2013
Thank you! :)
Zita Kemeny (zkemeny) on July 1, 2013
Good tips. Thanks.