Flash power 'used' data

[Stagecoach]

Question.......................

Does anyone know if there is a way of reading the actual flash power used (e.g. 1/2, 1/32 power etc) when a Nikon was used with a speedlight in TTL mode within the meta/exif data?


Reason for question........................

I want to try and confidently determine the number of shots in a burst sequence using my flash I am able to take at a specific aperture and ISO setting that was used for the below pic. It's the location of a full marathon very early morning start that's going to be in the dark apart from the very limited ambient light from some streetlights.

D800, 1/250s, f/4, ISO800, SB600 in TTL, with basic PP to improve.


Grahame

[William W]

Not anywhere near a comprehensive response to the exact question but:

"within the meta/exif data" - my guess is the metadata would have that detail but you'd need to know which line and the key to the code.

"if there is a way of reading the actual flash power used" - shoot one frame in situ and use a flash meter to read the exposure of the flash and then work backwards using the Guide Number of the flash to calculate the approximate power used for the one shot for the Flash in TTL Mode. (but I suspect you already knew that and perhaps you don't have easy access to a Flash Meter.

A third option is to make maybe three or four trial runs in similar/same lighting conditions and simply average the number of bursts you actually do get, erring on the conservative side.

Also (not intimately acquainted with of Nikon Gear) watch out for the automatic cutout most Speedlites have (HEAT TRIGGERED) - for example it was, with a bit of effort possible to fry a Canon 580 when shooting in bursts, the MkII version had a much quicker heat sensing cutout - so, what I mean is - whilst you might calculate or extract from experiment that you can shoot 6 bursts - that might be so for a series of 8 lots of six bursts and then you might not be able to shoot any at all.

WW

[William W]

... in fact, thinking about it for a few minutes - the simplest way to make a reasonable guess is simply use the Guide Number of the Flash; the intended Aperture used; the intended ISO - from that you can calculate the the MAXIMUM DISTANCE the Flash will have (i.e. that will be "Full Power") and substitute the actual Subject Distance and thus calculate what fraction of Flash Power will be used.

However I am not sure that will accurately tell you how many bursts you will get - it could be that the flash will attempt to recycle even if it does has enough power to make a shot (for example at 1/32 power) if 1/32 power is all that is required.

(trust myu speed typing makes sense - didn't have time to proof read it)

Bill

[Stagecoach]

Not anywhere near a comprehensive response to the exact question but:

But it's all useful Bill.

"within the meta/exif data" - my guess is the metadata would have that detail but you'd need to know which line and the key to the code.

That's what I need ideally.

"if there is a way of reading the actual flash power used" - shoot one frame in situ and use a flash meter to read the exposure of the flash and then work backwards using the Guide Number of the flash to calculate the approximate power used for the one shot for the Flash in TTL Mode. (but I suspect you already knew that and perhaps you don't have easy access to a Flash Meter.

I have actually got a flash meter, about 40 years old which has remained in its case unused for about 39 years

Unfortunately I'm unable to get back to the location before the race on Saturday morning for more testing but I might have a play with it tonight using similar distances. Then again it would be easy to simply take some shots with the flash in manual at different settings, determine power necessary for the rough subject distance that give a reasonable workable exposure and work back from that.

A third option is to make maybe three or four trial runs in similar/same lighting conditions and simply average the number of bursts you actually do get, erring on the conservative side.

Agree with this.

Also (not intimately acquainted with of Nikon Gear) watch out for the automatic cutout most Speedlites have (HEAT TRIGGERED) - for example it was, with a bit of effort possible to fry a Canon 580 when shooting in bursts, the MkII version had a much quicker heat sensing cutout - so, what I mean is - whilst you might calculate or extract from experiment that you can shoot 6 bursts - that might be so for a series of 8 lots of six bursts and then you might not be able to shoot any at all.

I'm only going to be attempting the 'burst flash' for a short period, roughly the time it takes for 80 runners to pass me at the start on this width of road (I'm still guessing the time). My Nikon has a setting where I can set the rate of burst shots in 'CL' mode between 1/sec up to 5/sec so I will use this to assist.

Grahame

[Stagecoach]

... in fact, thinking about it for a few minutes - the simplest way to make a reasonable guess is simply use the Guide Number of the Flash; the intended Aperture used; the intended ISO - from that you can calculate the the MAXIMUM DISTANCE the Flash will have (i.e. that will be "Full Power") and substitute the actual Subject Distance and thus calculate what fraction of Flash Power will be used.

Good idea Bill.

However I am not sure that will accurately tell you how many bursts you will get - it could be that the flash will attempt to recycle even if it does has enough power to make a shot (for example at 1/32 power) if 1/32 power is all that is required.

If calcs from the above indicate say 1/2 power I can then simply set the same manual settings on the camera, flash manually at 1/2 power and experiment for recharge/cycle results without having to worry about ambient lighting. I have a pile of fresh batteries.[/QUOTE]

My logic for wanting to go manual flash is for consistency rather than relying upon what could be variable return light to determine exposure.

Grahame

[dje]

Grahame

If you look at an nef file with View NX, you can view the Metadata when in the edit screen. It gives some info on the flash settings used.

eg this one shows a manual power setting of 1/4.

Not sure about ttl mode though.



Dave

[Stagecoach]

Grahame

If you look at an nef file with View NX, you can view the Metadata when in the edit screen. It gives some info on the flash settings used.

eg this one shows a manual power setting of 1/4.

Not sure about ttl mode though.



Dave

Dave, ViewNX seems to only give the flash power setting in flash manual mode unfortunately.

Perhaps it's not recorded in TTL because it would not be a 'set' data but vary depending upon return light measurement.

[dje]

Dave, ViewNX seems to only give the flash power setting in flash manual mode unfortunately.

Perhaps it's not recorded in TTL because it would not be a 'set' data but vary depending upon return light measurement.

Fair enough Grahame. Yes the power level used is not a setting with ttl but ultimately the camera does tell the flash what power level to use. Perhaps it's too complicated to record this value in metadata.

Dave

[george013]

http://www.sno.phy.queensu.ca/~phil/...mes/Nikon.html

An overview of the used tagnames by exiftool. Do a search on flash and look if there is something in it you can use.

I think it's called flashoutput.

George

[Stagecoach]

http://www.sno.phy.queensu.ca/~phil/...mes/Nikon.html

An overview of the used tagnames by exiftool. Do a search on flash and look if there is something in it you can use.

I think it's called flashoutput.

George

Thanks for that George, I'll have a browse through it and see if it's lurking in there.

[William W]

I want to try and confidently determine the number of shots in a burst sequence using my flash I am able to take at a specific aperture and ISO setting that was used for the below pic. It's the location of a full marathon very early morning start that's going to be in the dark apart from the very limited ambient light from some streetlights.

. . . If calcs from the above indicate say 1/2 power I can then simply set the same manual settings on the camera, flash manually at 1/2 power and experiment for recharge/cycle results without having to worry about ambient lighting. I have a pile of fresh batteries.
My logic for wanting to go manual flash is for consistency rather than relying upon what could be variable return light to determine exposure

Ah! OK. Everything MANUAL – I think I now better understand what you want to do, I think that there is a much easier way to set this up.

Let’s assume that your sample image will be the settings that you want to use, i.e. F/4; ISO800, 56mm Lens on a D800.

Have a look at page 35 in your SB 600 User Manual.Note the GN Table and also the ISO Factor Table.

You need to know the typical SD (Subject Distance) and I assume that you will be using a pre focus point and a reasonably smallish aperture to accommodate an adequate DoF.

So for this example I will assume that the Subject Distance will typically be about 8 metres – that provides a DoF from about 6.5 to 10.5meters if you use F/4 and a 56mm lens.

So we know that GN = A x SD (Guide Number = Aperture x Subject Distance)

So if we want a MANUAL FLASH exposure using F/4 at 8m we need a guide number of about 32.

In your SB 600 User Manual look down the FL = 50mm column and multiply all the (metric) Guide Numbers by 2.8 (because you choose to use ISO800). Note that ⅛ Power fits the mark (12.7 x 2.8 = 35.56)

So put the flash into ⅛ Power and test away to see how many you can get.

***

But before you do that, have a look at page #38 and read the warnings about Flash in Burst Mode and also the procedure about the 10 minute down time. This goes to my warning about automatic overheat cut-outs on modern Speedlites. I have no idea about how the SB600 will function when it gets hot or even if it has an automatic thermal cut out.

If I understand the User Manual correctly- the suggestion are:

> 1. the total of any one burst is four shots (4) at ⅛ Power

> 2. the total of number of frames across a set of bursts is 40 at ⅛ Power.

But who knows how that would pan out if you were shooting in bursts of four with a minute in between each burst?

So, if I understand you aim correctly, I don’t think it is about you having enough batteries but the main consideration is whether or not the SB600 will overheat.

WW

[Stagecoach]

Ah! OK. Everything MANUAL – I think I now better understand what you want to do, I think that there is a much easier way to set this up.

I like easy and planned

Let’s assume that your sample image will be the settings that you want to use, i.e. F/4; ISO800, 56mm Lens on a D800.

Have a look at page 35 in your SB 600 User Manual.Note the GN Table and also the ISO Factor Table.

You need to know the typical SD (Subject Distance) and I assume that you will be using a pre focus point and a reasonably smallish aperture to accommodate an adequate DoF.

So for this example I will assume that the Subject Distance will typically be about 8 metres – that provides a DoF from about 6.5 to 10.5meters if you use F/4 and a 56mm lens.

So we know that GN = A x SD (Guide Number = Aperture x Subject Distance)

So if we want a MANUAL FLASH exposure using F/4 at 8m we need a guide number of about 32.

In your SB 600 User Manual look down the FL = 50mm column and multiply all the (metric) Guide Numbers by 2.8 (because you choose to use ISO800). Note that ⅛ Power fits the mark (12.7 x 2.8 = 35.56)

So put the flash into ⅛ Power and test away to see how many you can get.

I undertook exactly the above this afternoon and came up with 1/8th power at around 8 metres for the estimated subject distance. It had been many years since I had used Guide Nos and distance calcs.

***

But before you do that, have a look at page #38 and read the warnings about Flash in Burst Mode and also the procedure about the 10 minute down time. This goes to my warning about automatic overheat cut-outs on modern Speedlites. I have no idea about how the SB600 will function when it gets hot or even if it has an automatic thermal cut out.

If I understand the User Manual correctly- the suggestion are:

> 1. the total of any one burst is four shots (4) at ⅛ Power

> 2. the total of number of frames across a set of bursts is 40 at ⅛ Power.

But who knows how that would pan out if you were shooting in bursts of four with a minute in between each burst?

So, if I understand you aim correctly, I don’t think it is about you having enough batteries but the main consideration is whether or not the SB600 will overheat.

WW

This is where it gets interesting because I find a bit of confusion at the actual number of bursts (allowing for necessary recharge time) as opposed to the actual number possible before overheat.

But, I have just this minute since reading your reply undertaken a test outside in the dark at similar subject distance, f/4, ISO1000, 50mm, 1/8th flash power and took 10 frames timed in CL mode at 1 sec between each and all have exact same acceptable exposure.

This ties roughly with my guess that it will take the runners about 10 seconds to pass me after they start. There is then plenty of time for cooling as I shoot individual shots over the next hour using flash before sun up (although it's looking like it will be rain).

For info my test was done with a used set of batteries.

Thanks for your help with this one Bill,

Grahame

[William W]

I undertook exactly the above this afternoon and came up with 1/8th power at around 8 metres for the estimated subject distance. It had been many years since I had used Guide Nos and distance calcs.

haha! - serendipity - there must be some telepathy happening.

*

I have just this minute since reading your reply undertaken a test outside in the dark at similar subject distance, f/4, ISO1000, 50mm, 1/8th flash power and took 10 frames timed in CL mode at 1 sec between each and all have exact same acceptable exposure.

This ties roughly with my guess that it will take the runners about 10 seconds to pass me after they start. There is then plenty of time for cooling as I shoot individual shots over the next hour using flash before sun up

Thanks for your help with this one Bill,

It was fantastic. I love puzzles.

Cheers for now.

Bill

[Stagecoach]

Bill,

I thought I would let you know my findings on the day for interest.

On arrival I took a few test shots with the layout for the start arrangement that was now set up and decided I would go at 1/250s, f/4.5, ISO1250, 55mm and 1/8th power on the flash set. A burst rate of 1/sec was set in CL mode.

At the start of the full marathon 5:30 am in the dark I got three shots at 1 sec intervals before someone stood in my line of fire with a b****y camera phone. By the time I had sorted that they had all passed but what I had was good.

At 6:30 am 10 mins before sunrise I shot the half marathon start and decided to push my luck and set a camera burst rate of 2 frames/sec with 1/8th manual flash power. Results were 10 firings with good even exposures then every other one with good even exposure up until the end on the 19th frame.

So it appears the SB-600 is capable of firing 10 times at 1/8th power at a rate of 2 frames/sec, and more times when reduced to a frame rate of 1 frame/sec.

And it did continue working for the next hour whilst I experimented using fill light

[george013]

Bill,

I thought I would let you know my findings on the day for interest.

On arrival I took a few test shots with the layout for the start arrangement that was now set up and decided I would go at 1/250s, f/4.5, ISO1250, 55mm and 1/8th power on the flash set. A burst rate of 1/sec was set in CL mode.

At the start of the full marathon 5:30 am in the dark I got three shots at 1 sec intervals before someone stood in my line of fire with a b****y camera phone. By the time I had sorted that they had all passed but what I had was good.

At 6:30 am 10 mins before sunrise I shot the half marathon start and decided to push my luck and set a camera burst rate of 2 frames/sec with 1/8th manual flash power. Results were 10 firings with good even exposures then every other one with good even exposure up until the end on the 19th frame.

So it appears the SB-600 is capable of firing 10 times at 1/8th power at a rate of 2 frames/sec, and more times when reduced to a frame rate of 1 frame/sec.

And it did continue working for the next hour whilst I experimented using fill light

Can you show an example with 1/8 flash?

George

[Stagecoach]

Can you show an example with 1/8 flash?

George

I certainly can George. These are from the RAW files.

No 1 1/250s, f/4.5, ISO1000, flash SB600 1/8th power


No 2 1/250s, f/4.5, ISO1000, flash SB600 1/8th power (1 second after No 1 shot above)


No 3 Above image has had Blacks raised by 25% in ACR and basic sharpening nothing else.


No 4 And a possible final edit


There is more scope to 'play' but the biggest problem is the fluorescent strips on the jackets

Here's a better example of what was possible with the 1/8th power of the flash

No 5 One of the shots in the second sequence where the flash did not fire.


No 6 The shot 1 second after No 5 where the flash fired.


I have done a bit of playing with pulling the shadows on No 5 and although its possible the end result is noisy and flat (to me) and does not have the punch I prefer. Strangely I got the best result in PSCC rather than in ACR.

[William W]

Thanks!

1 and 2 certainly show exposure consistency.

It's interesting that when over the limit, each second shot was "OK".

My other comment - assuming that your Subject Distance was accurate for the lead runner and was calculated correctly to suit the GN and the ISO, - image 2 appears a little under-exposed?

Which seems understandable, because most Flash Manufacturers 'exaggerate' the ability of their units.

I mainly use Canon 580 and I haven’t done a comprehensive test to assure myself that the GN is correct for reduced power output – but I do know that Canon exaggerate the full power GN for that model – well at least for the two that have.

***

I have not used on camera flash like that (i.e. manual via GN /bursts / reduced power) - but I have fried a a Vivitar and also Canon shooting a lot of frames in succession (maybe 2 or three seconds apart) - maybe I should have used reduced power and bumped the ISO!

Thanks again.

Bill