Flash and auto ISO

I never had a compatible Nikon flash before so of course I always shoot flash in manual and no auto ISO. Just bought a SB-800 yesterday and I will try to find out how the camera/flash behave when auto ISO is on. Anyone tried that before?

It works in auto ISO on my D750, but

 

1) The camera will boost the ISO higher than necessary to illuminate the main subject which introduces noise.

2) Due to the increased ISO the background will bee properly illuminated. When I take flash images, I usually want the subject properly illuminated and the background subdued to enhance subject separation.

 

I usually set the ISO to between 200 and 400 and let the flash do the illumination. But it depends upon the image I am taking and whether the background is important. Of course with the SB-800 you can set the flash to BL, balanced, limit the ISO, and still illuminate the background.

 

The SB-800 is a great flash, and as a bonus, it also works on my F100 film body.

The D850 has separate control (menu e4) over whether the auto-ISO is trying to expose the background assuming the flash won't illuminate it, or whether it's exposing the foreground with the flash's benefit. I don't think my previous bodies had this as an option.

 

Generally I turn auto-ISO off when I'm using flash (and shoot at base ISO if I can). If the camera doesn't get confused, I do. But then I'm not necessarily trying to do a lot of dynamic lighting with balanced flash and natural lighting.

The D850 has separate control (menu e4) over whether the auto-ISO is trying to expose the background assuming the flash won't illuminate it, or whether it's exposing the foreground with the flash's benefit. I don't think my previous bodies had this as an option.

 

Generally I turn auto-ISO off when I'm using flash (and shoot at base ISO if I can). If the camera doesn't get confused, I do. But then I'm not necessarily trying to do a lot of dynamic lighting with balanced flash and natural lighting.

If it were to ignore the background then which ISO would it pick?

Auto ISO is set according to the illumination of the scene sans flash. The flash is set according to the pre-flash measurements, after the ISO, shutter and aperture are set. Auto ISO would have the effect of rendering fill flash (slow flash).

Auto ISO is set according to the illumination of the scene sans flash. The flash is set according to the pre-flash measurements, after the ISO, shutter and aperture are set. Auto ISO would have the effect of rendering fill flash (slow flash).

So it's not usable for me. Thanks.

In most cameras you can adjust exposure compensation for flash and ambient light independently. You could reduce the exposure for ambient light, but your flash exposure would be based on the ISO (and aperture) at the time of exposure. You can also set a compensation value in the flash itself. Edited May 5, 2020 by Ed_Ingold

If it were to ignore the background then which ISO would it pick?

 

To quote the manual entry:

 

e4 Auto (flash) ISO sensitivity control

Subject and background

Subject only

Choose whether auto ISO sensitivity control for flash photography is adjusted to correctly expose both the subject and background or the main subject only.

 

The camera works out what the "main subject" is (I've no idea whether it does this relying solely on the selected metering point or matrix identification of the scene, whether it works out what the flash is actually illuminating, or some combination). If the flash can illuminate it at base ISO, you get that. If you're trying to illuminate a distant subject with a small flash (or if your flash power is reduced by auto-FP HSS, or if you manually set the flash to a low output) I'd expect the camera to boost the ISO to get the right foreground exposure.

 

I could believe this would be useful behaviour. It's effectively the difference you get from slow sync, except choosing whether the exposure varies by ISO instead of extending the shutter speed. If you want a sharp foreground subject that's flashlit and grain free, you probably want slow sync off and auto-ISO affected by the subject only (or just trust that you have enough flash power). If you want a reasonably-exposed background as well, you probably want some combination of slow sync and auto-ISO allowing for the background turned on - but you'll get some noise and/or blur in your foreground subject as a consequence.

 

I think, anyway.

I personally have tired of the "natural" look of fill and bounced flash. Give me the old "cup of flour in the face" look of the Brownie days ;)

With the Auto ISO range of 100 to 12800 when the flash is ready to fire the camera switch to ISO400 regardless of aperture chosen or the amount of ambient light. This is on the Df.

With the Auto ISO range of 100 to 12800 when the flash is ready to fire the camera switch to ISO400 regardless of aperture chosen or the amount of ambient light. This is on the Df.

 

Interesting. I just tried my D810 (with the integrated flash). Auto ISO, manual mode. Pointing the camera out of the window, it stays at ISO 64 and the flash does a reasonable job of exposing the window frame. Pointing into the darkest corner of my study, it drops to ISO 4000 (and still fires the flash). Auto ISO seems to be vaguely working as I'd expect under those circumstances.

 

I do recall there being something odd about ISO400, though. Apparently we did discuss this a couple of years ago.

 

Ah, there's this. It might be specific to program mode - on a D810 in manual, the ISO behaviour definitely matches with both the integrated and a hotshoe flash; I'd not registered that the post was talking about program mode until I'd put the camera away again, and forgive me if I don't get everything out again. Also I think the description is backwards: according to the images, it's the integrated flash which uses a higher ISO, which I assume might be some combination of not overloading the integrated flash's cooling ability and wanting to get better CIPA numbers for battery life when flash photos are taken (cynical? moi?) Even so, since the Df can't possibly be using an internal flash, it wouldn't explain a jump to ISO 400.

 

There's a note in the Df manual about the auto-ISO minimum shutter speed being ignored in flash photography in favour of the flash sync speed. It definitely couldn't be that?

 

My D810 memory cards are still full of some not very aesthetic images of a trip to the Tutankhamun exhibition in London shortly before the lockdown. I was grumbling to myself about how much longer it takes to scroll through all the images to delete both the SD and CF versions (JPEG and RAW respectively in my case) of my test images (the D850 is both much faster at showing them and lets you scroll faster because of the touch screen) when I discovered that you can jump between them if you go to the minimum zoom (lots of images on screen - which I never normally do because it takes several seconds to populate) and then zoom out one more time. Apparently I failed to RTFM on that one. Learn something new every day...

Interesting. I just tried my D810 (with the integrated flash). Auto ISO, manual mode. Pointing the camera out of the window, it stays at ISO 64 and the flash does a reasonable job of exposing the window frame. Pointing into the darkest corner of my study, it drops to ISO 4000 (and still fires the flash). Auto ISO seems to be vaguely working as I'd expect under those circumstances.

 

I do recall there being something odd about ISO400, though. Apparently we did discuss this a couple of years ago.

 

Ah, there's this. It might be specific to program mode - on a D810 in manual, the ISO behaviour definitely matches with both the integrated and a hotshoe flash; I'd not registered that the post was talking about program mode until I'd put the camera away again, and forgive me if I don't get everything out again. Also I think the description is backwards: according to the images, it's the integrated flash which uses a higher ISO, which I assume might be some combination of not overloading the integrated flash's cooling ability and wanting to get better CIPA numbers for battery life when flash photos are taken (cynical? moi?) Even so, since the Df can't possibly be using an internal flash, it wouldn't explain a jump to ISO 400.

 

There's a note in the Df manual about the auto-ISO minimum shutter speed being ignored in flash photography in favour of the flash sync speed. It definitely couldn't be that?

 

My D810 memory cards are still full of some not very aesthetic images of a trip to the Tutankhamun exhibition in London shortly before the lockdown. I was grumbling to myself about how much longer it takes to scroll through all the images to delete both the SD and CF versions (JPEG and RAW respectively in my case) of my test images (the D850 is both much faster at showing them and lets you scroll faster because of the touch screen) when I discovered that you can jump between them if you go to the minimum zoom (lots of images on screen - which I never normally do because it takes several seconds to populate) and then zoom out one more time. Apparently I failed to RTFM on that one. Learn something new every day...

First it does switch to flash sync speed. Second I didn't point the camera at a bright subject like the windows so that the ambient exposure for the aperture chosen doesn't need to be ISO 400 or higher. When I point the camera at various scene that would need higher ISO than 400 to properly expose for the ambient light it switched to ISO400 and exposed correctly.

One thing it bothers me is that even in M and auto ISO off it switched to flash sync speed when the flash is ready. I normally shoot flash with the Df at 1/125. I have to set the flash sync speed to 1/125 now instead of the default 1/200. Even then it wouldn't let me chose the shutter speed at will in M.

Any way ISO 400 is OK to me for flash. I actually use ISO800 for flash with the Df quite often as the noise isn't a problem at that ISO and it gives me assurance that I have enough flash power to bounce and the recycling time not too long.

You've confused me a bit, BeBu (it sounds like when you need more than ISO400 it gives you ISO400, and you didn't point the camera at a bright scene but it still didn't need a high ISO?) - but so long as it's doing what you want, I'm glad! If there's a Nikon camera for which unnecessarily high flash is acceptable, it's the Df. Well, it's the D5 or any of the D3 generation (which gain a lot less from lower ISO than other sensors), but the Df certainly holds up well to moderate ISOs.

You've confused me a bit, BeBu (it sounds like when you need more than ISO400 it gives you ISO400, and you didn't point the camera at a bright scene but it still didn't need a high ISO?) - but so long as it's doing what you want, I'm glad! If there's a Nikon camera for which unnecessarily high flash is acceptable, it's the Df. Well, it's the D5 or any of the D3 generation (which gain a lot less from lower ISO than other sensors), but the Df certainly holds up well to moderate ISOs.

Yes when the ambient light is low and ISO higher than 400 is needed to give correct exposure without flash then it will give me ISO400 and the flash would expose for ISO 400.

Yes when the ambient light is low and ISO higher than 400 is needed to give correct exposure without flash then it will give me ISO400 and the flash would expose for ISO 400.

 

Ah, so it doesn't expose for the background but it boosts to ISO400 anyway if the foreground needs it for the flash?

 

I barely understand flash on a D810 (with auto ISO, arguably anyway). I think I'm going to say my brain is too full of other useless information to learn how to do it on a Df. :-) (Unless someone donates me a Df, obviously. But there are more worthy recipients.)

Ah, so it doesn't expose for the background but it boosts to ISO400 anyway if the foreground needs it for the flash?

 

I barely understand flash on a D810 (with auto ISO, arguably anyway). I think I'm going to say my brain is too full of other useless information to learn how to do it on a Df. :) (Unless someone donates me a Df, obviously. But there are more worthy recipients.)

First thought I think there are a lot more worthy recipients than you. Second thought you have 1 thing that makes you a bit worthy. You want to use one to be sure why you hate it.

Since it costs nowt to shoot digital, maybe the best way to find out how your camera and SB-800 'play' together is just to shoot some flash scenarios that are typical for you.

 

Nikon's i-TTL flash defaults to 'BL' (Balanced Lighting) mode when the camera's using matrix metering. So it'll try to balance the flash, and presumably the chosen ISO, with ambient unless the ambient lighting falls below some undisclosed threshold, or the shutter speed gets too long.

 

Personally, I gave up on i-TTL flash quite some time ago. It's vaguaries were quite beyond my fathoming. So good luck trying to make sense of what the camera and flashgun decide between them.

 

I suspect you'll revert to manual mode, or AA mode if you want some understandable and reliable flash automation. Although the camera will still choose whatever ISO speed pops into its mechanical little brain.

 

BTW. Attaching a charged flash to a Nikon camera has automatically switched the shutter speed to X synch since the days of the FE. In fact it's not even the maximum synch speed that's automatically set on modern Nikon DSLRs, but some lunatic default speed like 1/30th, unless you dig into the menu and set a sensible option.

Edited May 7, 2020 by rodeo_joe|1

I can't test TTL performance with my F5 unless I put film in it. If I try to measure the flash output with the flash meter the pre flash triggers the meter.

I can't test TTL performance with my F5 unless I put film in it. If I try to measure the flash output with the flash meter the pre flash triggers the meter.

Cancel the pre-flash by either tilting the flash head down 7 degrees or selecting rear curtain sync..

Since it costs nowt to shoot digital, maybe the best way to find out how your camera and SB-800 'play' together is just to shoot some flash scenarios that are typical for you.

 

Nikon's i-TTL flash defaults to 'BL' (Balanced Lighting) mode when the camera's using matrix metering. So it'll try to balance the flash, and presumably the chosen ISO, with ambient unless the ambient lighting falls below some undisclosed threshold, or the shutter speed gets too long.

 

Personally, I gave up on i-TTL flash quite some time ago. It's vaguaries were quite beyond my fathoming. So good luck trying to make sense of what the camera and flashgun decide between them.

 

I suspect you'll revert to manual mode, or AA mode if you want some understandable and reliable flash automation. Although the camera will still choose whatever ISO speed pops into its mechanical little brain.

 

BTW. Attaching a charged flash to a Nikon camera has automatically switched the shutter speed to X synch since the days of the FE. In fact it's not even the maximum synch speed that's automatically set on modern Nikon DSLRs, but some lunatic default speed like 1/30th, unless you dig into the menu and set a sensible option.

 

Well when the camera is in M and no auto ISO it doesn't switch to flash sync speed which is good for me. TTL exposure is good. Checking the power output at 35mm it came out to about GN110 which is as expected lower than the rated GN125 but better than my Metz 60CT4 which is rated at GN197 but actually is only GN160. So overall I do like it.

Because I hit a lunch break, and for completeness, I just tried P mode with auto-ISO on my D810.

 

Auto ISO max sensitivity set to 6400 (actually set to 80, but ISO explicitly set to 6400 because that's easier to change and it has the same effect until I turn off auto-ISO and don't notice). P mode pointing out of a window chooses ISO6400, 1/2000s, f/16. Yargh (speaking as someone who starts worrying about diffraction and dust on my sensor at f/8). A flash (the internal one and added a hotshoe one seems to have the same behaviour) drops the shutter speed to the flash sync speed, tweaks the aperture a bit, and adjusts the ISO to balance (so 1/250s, f/11, ISO320 I think I saw, give or take a bit). The reported D7000 "on-camera flash behaves differently" thing seems to have gone away, possibly because someone called them on it if it was really a CIPA battery rating hack (or I'm still very cynical). I didn't try the dark so much, since the ISO selected was the question.

 

I remember why I don't use P mode except when I'm handing the camera to people who don't know how to change settings. Now I know the auto-ISO interaction works like that, I'm going to be a lot more careful about doing so.

Because I hit a lunch break, and for completeness, I just tried P mode with auto-ISO on my D810.

 

Auto ISO max sensitivity set to 6400 (actually set to 80, but ISO explicitly set to 6400 because that's easier to change and it has the same effect until I turn off auto-ISO and don't notice). P mode pointing out of a window chooses ISO6400, 1/2000s, f/16. Yargh (speaking as someone who starts worrying about diffraction and dust on my sensor at f/8). A flash (the internal one and added a hotshoe one seems to have the same behaviour) drops the shutter speed to the flash sync speed, tweaks the aperture a bit, and adjusts the ISO to balance (so 1/250s, f/11, ISO320 I think I saw, give or take a bit). The reported D7000 "on-camera flash behaves differently" thing seems to have gone away, possibly because someone called them on it if it was really a CIPA battery rating hack (or I'm still very cynical). I didn't try the dark so much, since the ISO selected was the question.

 

I remember why I don't use P mode except when I'm handing the camera to people who don't know how to change settings. Now I know the auto-ISO interaction works like that, I'm going to be a lot more careful about doing so.

Please confirm this. What is your minimum ISO and what is the Max ISO set at when you set auto ISO?

If the minimum ISO is 80 and max is 6400 then when you point the camera at the window I expect it to set to something around f/4.5 1/125 ISO80 unless you have longer lens than 125mm.

Edited May 7, 2020 by BeBu Lamar

Since it costs nowt to shoot digital, .

 

:eek: Come on someone - Take the bait!

Since it costs nowt to shoot digital, maybe the best way to find out how your camera and SB-800 'play' together is just to shoot some flash scenarios that are typical for you.

 

Agree with RJ. Back in the day the photographers I knew, mostly gifted nerds but with little to no income would sell plasma once a week. That was $20 that would buy a couple rolls of grey market film and processing. For less than the price of 100 roles of film or a basic N70 film camera from the mid 90s you can buy a D3XXX and shoot all day long with image quality that will knock your socks off compared to tight grained Velvia and Provia.

 

I have been shooting manual flash for a few years now and enjoy the control that manual settings give.

I shoot auto ISO with my speed cameras and moving objects but for scenics and macro revert to full manual everything.

This thread piqued my interest and I have a few days on hand before traveling to back to work.

After all its not like there is a highlight button like in Photoshop that allows me to light scenes differentially with a single flash and and single exposure.

Wait a minute I can actually do that in Photoshop cant I ??

So yesterday I pulled out my D500 aging 28-105 D lens and SB800 to try and make sense of it all..........................

I will leave it at that and go back to shooting manual.

Stay frosty.

I think you're a decade late to that rant, Stuart. I've upgraded my dSLRs three times during the time I've had some film sitting in the fridge waiting for me to feel it was worth the expense of getting it developed.

 

Please confirm this. What is your minimum ISO and what is the Max ISO set at when you set auto ISO?

If the minimum ISO is 80 and max is 6400 then when you point the camera at the window I expect it to set to something around f/4.5 1/125 ISO80 unless you have longer lens than 125mm.

 

There is no "minimum ISO" to the best of my knowledge. In auto-ISO, the ISO always varies between the (native) camera base ISO and the set maximum. The set maximum is whichever is higher of the explicitly set ISO and the auto-ISO "Maximum sensitivity". I see the same behaviour whether I set ISO 64 and maximum sensitivity 6400, or maximum sensitivity 80 (you can't set 64) and manually set ISO to 6400. I now do the latter - I have to remember to change ISO when I switch to manual ISO, but at least I don't need to dive into a menu to change the upper limit for auto-ISO.

 

Pointing out of the window with a 50mm lens, apparently it's sunny outside. I just checked again, and P mode selects ISO 6400 (my set upper limit), 1/6400s, f/16.

 

...ah. Okay. So the user-selected ISO is used to choose other parameters in P, S and A, and the camera will increase it if need be, if and only if the auto-ISO sensitivity maximum is higher. In manual mode, you get the ISO needed to match the other two parameters, and both explicit ISO and auto-ISO set only the upper limit - they're interchangeable. If explicit ISO is set to something between the camera minimum and the explicit sensitivity limit, it's ignored in manual mode. I normally shoot with M, so I'd missed the distinction. (I'd have met it if I shot aperture priority, but util Nikon give us a fast way to shift the shutter speed limit/auto-shift without going into a menu, it's limiting.)

 

I probably switched to using ISO the way I do for manual mode relatively recently, recently enough not to realise the interaction. In which case, the "auto ISO limit/native ISO independence" slide on the Nikon requests should better have said "provide a better way to set maximum ISO in auto-ISO". I'd have said use the front and rear dials for the native and upper limits, but then you need another way to toggle auto-ISO on and off (perhaps push and release ISO without turning anything?)

 

I don't mind learning new things every day, I just don't like it when I'm learning old things that I've forgotten.