PDA

View Full Version : Auto ISO Canon vs Nikon



Mircula
14-09-2010, 10:41am
Hello,

I just had a Nikon in my hands a couple of days ago and noticed the great flecibility with auto iso.

I did not have this feature on my 20D but just upgraded to a 40D. I am honestly really disappointed that I cannot set things like minimum shutter speed or the exact range of the auto ISO.

Why does Canon not implement that?
Do other (newer or pro) canon models have this feature more advanced?

Does anybody know how the camera decides what shutter speed prevents camera shake? (As stated in the manual on page 60) Does it consider focal lengths here?

Auto iso could be such a powerful feature if it would be more customizable….


Anyway would love to hear your story about auto ISO, from both Canon and Nikon users!


Cheers,

Mirc

pgbphotographytas
14-09-2010, 11:05am
I think "most" people prefer to set the ISO manually rather then letting the camera decide, early on with my Nikon D40 I had it set to "Auto ISO" and this produced some "interesting" photos :(

When out taking photos unless the weather / light changes a lot then you normally don't need to change the ISO that much.

Paul

Wayne
14-09-2010, 11:21am
Auto ISO on the D3/700 is great for getting the desired shutter speed when shooting sports at night or where there is large variance in light say at different ends of a field.

Simply set the max ISO you want the camera to use.

ricktas
14-09-2010, 11:30am
I agree the Nikon system works well, but i never use it. I always set ISO manually

kiwi
14-09-2010, 11:32am
I find autoiso very useful for all sorts of shooting, including weddings where I know the lighting will be changing from good to bad often. I just choose the creative options of shutter speed and apperture, put on manual, activate autoiso, and presto....Nikon magic

Old Skool
14-09-2010, 12:57pm
Canon 50D & 7D both have Auto ISO. As with any settings depends on the circumstances of your shoot. Handy to have as an option though on a camera.

campo
14-09-2010, 1:03pm
I just choose the creative options of shutter speed and apperture, put on manual, activate autoiso, and presto....Nikon magic

re: put on Manual...

That's what I hate most about Auto ISO on my Nikon. It's great in A/S modes, but when I flick to Manual mode, I want full manual. Nine out of ten times I switch to M, it's because the camera's meter is not exposing the subject how I want or i want consistent exposures. Having the ISO change automatically based on what the camera thinks is right when in Manual mode is very frustrating to say the least!

kiwi
14-09-2010, 1:05pm
using autoiso isnt really manual though is it, you are still letting the camera decide something.....what's the difference using apperture or shutter priority and fixing the other two variables ?

if you want full manual, go full manual

tanz
14-09-2010, 1:06pm
I have been leaving my ISO on auto as I am learning and this all doesn't come naturally to me yet, but think I am going to start making more of an effort and start setting it manually.

Tannin
14-09-2010, 1:12pm
1: Auto ISO is not particularly useful.

2: Nevertheless, Nikon do it lots better. Canon don't take it seriously and have never really tried to make it useful. Last time I looked at the Nikon version, it was almost good enough to be something you'd want to use. It may have improved further since then. The Canon version is just one of those pages in the manual you glance at once when the camera is new, shrug, and turn the page, thinking "what's the point of that feature? I'll never use it".

kiwi
14-09-2010, 1:16pm
why dont you think its useful Tony ?

campo
14-09-2010, 1:20pm
using autoiso isnt really manual though is it, you are still letting the camera decide something.....what's the difference using apperture or shutter priority and fixing the other two variables ?

if you want full manual, go full manual

agree, what I want though is to be able to use AutoISO in any semi automatic mode (ie. A/S/P) but when i 'turn the dial' to M mode, I want the camera to turn AutoISO off. I don't have time at a wedding to drive through the menus to turn AutoISO on/off everytime I need to flick to Manual mode.

kiwi
14-09-2010, 1:29pm
You can put in on the quick menu (which is what I have done)....you could even program it to a function button I suppose

But I also use autoiso in A and S mode also, so, wouldnt want it to turn off and therefore change automatically. I hate when machines do that, if I want it on, i'll turn it on, if i want it off, i'll turn it off

Tannin
14-09-2010, 1:29pm
I find autoiso very useful for all sorts of shooting, including weddings where I know the lighting will be changing from good to bad often. I just choose the creative options of shutter speed and apperture, put on manual, activate autoiso, and presto....Nikon magic

What you are doing is essentially elevating ISO to be the equal of aperture and shutter speed - in other words, making a new mode to stand alongside Av (camera decides shutter speed, you decide everything else), and Tv (camera decides aperture, you decide everything else) - call it "Iv" (camera decides ISO, you decide everything else).

And why not? If it works for you in your situation, do it!

Mircula
14-09-2010, 1:33pm
lots of interesting comments here.

I think it could be very very useful if more customizable in Canon...

I repeat my question from the first post, maybe some canon users who use it could answer this question :) :

Does anybody know how the camera decides what shutter speed prevents camera shake? (As stated in the manual on page 60) Does it consider focal lengths here?

kiwi
14-09-2010, 1:34pm
Yeah, that's the appeal to me I suppose

kiwi
14-09-2010, 1:35pm
lots of interesting comments here.

I think it could be very very useful if more customizable in Canon...

I repeat my question from the first post, maybe some canon users who use it could answer this question :) :

Does anybody know how the camera decides what shutter speed prevents camera shake? (As stated in the manual on page 60) Does it consider focal lengths here?

Not speaking about anyone else, but I have no idea what you are going on about here

ving
14-09-2010, 1:45pm
I had it on my nikon d40 and used it quite a bit. all I did was set a minimum shutter speed and max iso (usually 1/160 and 800) and i was set. it worked quite well really :)

my new d90 is even better with this :D

as to why canon dont have it... who knows. they just arent as good as nikon i guess :p

...this said i dont always have it on, in fact i only have it on when the situation dictates that i might need it, but its bloody great :D

campo
14-09-2010, 1:50pm
You can put in on the quick menu (which is what I have done)....you could even program it to a function button I suppose

I tried the quick menu, but takes my eye away from viewfinder. I'm pretty sure i found you can't program it to a function button as that would be a decent compromise for me :)

I can see why it's of benefit in M mode for some shooters - set A&S to get desired effect and let AutoISO do the rest but it turns "M" into another semi automatic mode where the shooter has little control over the final exposure. Maybe there should be another mode on cameras for autoiso: P / A / S / I / M - that would solve it!

kiwi
14-09-2010, 1:54pm
yeah, sure, that would solve it

Mircula
14-09-2010, 1:56pm
Not speaking about anyone else, but I have no idea what you are going on about here

So, with the 40d it is not possible to set a minimal shutter speed or the iso range for the auto iso.

In the manual of my 40d it says (if used in AV mode):

"The iso speed will be set automatically within iso 400-800 so that a shutter speed preventing camera shake will be set ..... "

What is this shutter speed? How does the camera calculate the minimum shake - less shutter-speed and does it consider focal lengths for instance?

Does that make it a bit clearer? Was a bit confusing maybe without reading the manual, sorry english is not my mother tongue.....

kiwi
14-09-2010, 2:02pm
on the nikon you can set a minimum, but it has nothing to directly with camera shake, camera doesnt care how good your technique or what lens you are ysing in this regard, it just says I dont want the camera to go below that iso, but I suppose, indirectly then it will mean that if you start underexposing camera will next start reducing the shutter speed and that fact might start introducing motion blur

Mircula
14-09-2010, 2:10pm
I think there is either a fixed value shutter speed for non shaking set inside the camera or some sort of algorithm considering other factors like focal lengths which have an effect on how low the speed can be without shaking.

I am just wondering if anybody knows this number or algorithm.

I guess the camera first lowers the shutter speed to this number or algorithm and then upps the iso.....but it is kind of vital to know that number to decide if this auto iso feature on a canon is at all useable.....

fillum
14-09-2010, 2:11pm
I find it extremely useful for sport in keeping the shutter speed fast. I've also recently found it to be useful in general shooting situations (after forgetting to turn it off :o), particularly in those situations where I'm not concentrating too well on what I'm doing (at a bbq for example).


Does anybody know how the camera decides what shutter speed prevents camera shake? Are you asking how the camera would know to increase ISO to get a shutter speed to prevent blur due to camera shake? The answer to that is that the camera doesn't know - the photographer sets the minimum shutter speed (when shooting aperture priority) as one of the parameters for auto-ISO. When the meter calculates that the shutter speed will be below your value, it starts boosting the ISO till the shutter speed is back to your minimum parameter setting (if possible). So if you were shooting with a 70-200 for example you might set the minimum s/s to say 1/200, but when using a 17-50 set the minimum s/s to 1/60. You might also use different minimum s/s values if the lens has image stabalisation.



Cheers.

Mircula
14-09-2010, 2:19pm
hello,

that is tv on a canon camera.

In av i set the aperture and my camera decides what the shutter speed will be.

fillum
14-09-2010, 2:23pm
agree, what I want though is to be able to use AutoISO in any semi automatic mode (ie. A/S/P) but when i 'turn the dial' to M mode, I want the camera to turn AutoISO off. I don't have time at a wedding to drive through the menus to turn AutoISO on/off everytime I need to flick to Manual mode.
Campo have looked into using the shooting banks? I haven't used them so don't know what the capabilities are. Downside would be that you probably still need to take your eye away from the viewfinder to change settings.


Cheers.

kiwi
14-09-2010, 2:24pm
camera decides only based on the exposure reading (it wants to create a "good" exposure when it decides what shutter speed to choose for any particular scene), it couldnt care less what other issues it might cause, such as camera shake

Mirculam have you been through the NTP program yet ?

Tannin
14-09-2010, 2:25pm
why dont you think its useful Tony ?

I think my post just above more or less addresses that but in reverse, Darren (I wrote that before I saw your question) - grafting an auto ISO function onto one of the existing major modes (Av for eg) just confuses the issue and winds up giving you less control instead of more.

But using it as you are - as a fully-fledged mode in its own right, to stand alongside Av and Tv - is a different matter.

Then there is the way that I would like to use it: this would need a significantly more complex decision rule system that I can program for my particular needs. Not just a min shutter speed, more like a scripted set of responses to light conditions that mimics what I'd actually do myself. For example, for bird work:

Use ISO 400 to start with, and f/8.

If the shutter speed drops below 1/1000th, go to f/5.6.

If the shutter speed is still below 1/1000th, go to 800 ISO.

If the shutter speed is still below 1/1000th, go to f/4

Go to 1/250th if needed.

If you can't get 1/250th, go to 1600 ISO.

And so on.

Why? Because 1/1000th @ 800 ISO will generally get you a better result than 1/500th @ 400i if you are working with smaller, fast-moving birds. The camera needs to know that. And it needs to know what the next thing to sacrifice is too, and the thing after that.

All of which leads me back to the point that I started with: EITHER we need a much smarter auto ISO (and other things too) system which is fully programmable, OR we just fall back on the old Mark One Human and do it the present way.

Am I making sense?

pgbphotographytas
14-09-2010, 2:26pm
Not speaking about anyone else, but I have no idea what you are going on about here

Basically the OP wants to know how a Canon decides what ISO to use to get a "safe" shutter speed and if this is based on the focal length (as we know with a longer focal length you need a higher shutter speed to avoid camera shake) it is a good question that I think only Canon could answer as I guess it would be buried deep in the firmware.

Paul

kiwi
14-09-2010, 2:28pm
yeah, makes sense

You tried jailbreaking the Canon OS yet ?




I think my post just above more or less addresses that but in reverse, Darren (I wrote that before I saw your question) - grafting an auto ISO function onto one of the existing major modes (Av for eg) just confuses the issue and winds up giving you less control instead of more.

But using it as you are - as a fully-fledged mode in its own right, to stand alongside Av and Tv - is a different matter.

Then there is the way that I would like to use it: this would need a significantly more complex decision rule system that I can program for my particular needs. Not just a min shutter speed, more like a scripted set of responses to light conditions that mimics what I'd actually do myself. For example, for bird work:

Use ISO 400 to start with, and f/8.

If the shutter speed drops below 1/1000th, go to f/5.6.

If the shutter speed is still below 1/1000th, go to 800 ISO.

If the shutter speed is still below 1/1000th, go to f/4

Go to 1/250th if needed.

If you can't get 1/250th, go to 1600 ISO.

And so on.

Why? Because 1/1000th @ 800 ISO will generally get you a better result than 1/500th @ 400i if you are working with smaller, fast-moving birds. The camera needs to know that. And it needs to know what the next thing to sacrifice is too, and the thing after that.

All of which leads me back to the point that I started with: EITHER we need a much smarter auto ISO (and other things too) system which is fully programmable, OR we just fall back on the old Mark One Human and do it the present way.

Am I making sense?

kiwi
14-09-2010, 2:28pm
Basically the OP wants to know how a Canon decides what ISO to use to get a "safe" shutter speed and if this is based on the focal length (as we know with a longer focal length you need a higher shutter speed to avoid camera shake) it is a good question that I think only Canon could answer as I guess it would be buried deep in the firmware.

Paul

what's safe ?

Mircula
14-09-2010, 2:33pm
camera decides only based on the exposure reading (it wants to create a "good" exposure when it decides what shutter speed to choose for any particular scene), it couldnt care less what other issues it might cause, such as camera shake

Mirculam have you been through the NTP program yet ?

Yes been through the ntp. Should i go through it again?

I know that the camera tries to expose correctly, but if auto iso is on it has two options doing so, iso and shutter speed.....

I dont think you get my point....in the manual it basically says that it upps the iso to prevent camera shake. That indicated that the camera must have some sort of index or value or algorithm which tells it how high the shutter speed must be to stop camera shake.

Do we agree on that?

If so, i would be interested in what that minimum camerashakestopping shutterspeed is.

fillum
14-09-2010, 2:34pm
hello,

that is tv on a canon camera.

In av i set the aperture and my camera decides what the shutter speed will be.I think you missed what I wrote (probably could have been worded better):

the photographer sets the minimum shutter speed (when shooting aperture priority) as one of the parameters for auto-ISO

The photographer sets the desired aperture on the camera then the camera adjusts the ISO till the shutter speed is at least the minimum set parameter value.


Cheers.

kiwi
14-09-2010, 2:38pm
Yes been through the ntp. Should i go through it again?

I know that the camera tries to expose correctly, but if auto iso is on it has two options doing so, iso and shutter speed.....

I dont think you get my point....in the manual it basically says that it upps the iso to prevent camera shake. That indicated that the camera must have some sort of index or value or algorithm which tells it how high the shutter speed must be to stop camera shake.

Do we agree on that?

If so, i would be interested in what that minimum camerashakestopping shutterspeed is.

No, we dont agree.....the camera doesnt determine at what point you get camera shake, you do based on your settings you are primarly determining. There is no index, smarts, or algorithm, you set all the parameters

By the way

http://www.youtube.com/watch?v=YJGYShZNDYY&feature=related

Mircula
14-09-2010, 2:39pm
what's safe ?

Safe = eliminating camera shake



Paul said want i want to know!

kiwi
14-09-2010, 2:41pm
I'll ask again ? what is safe for you ?

Mircula
14-09-2010, 2:42pm
No, we dont agree.....the camera doesnt determine at what point you get camera shake, you do based on your settings you are primarly determining. There is no index, smarts, or algorithm, you set all the parameters

By the way

http://www.youtube.com/watch?v=YJGYShZNDYY&feature=related

I dont do.

My camera does in the auto iso situation.

At least it claims to do that in the manual of my 40D!

Mircula
14-09-2010, 2:44pm
I'll ask again ? what is safe for you ?

it is not about what i think is safe, it is about what my camera thinks is safe.

kiwi
14-09-2010, 2:44pm
my point is that even in autoiso you are determining the minimum shutter speed for it to kick in at. So, you control it.

kiwi
14-09-2010, 2:45pm
so, what's a safe shutter speed ?

what's yours Paul ?

Mircula
14-09-2010, 2:52pm
I use 1/ focal lengths if i want to eliminate camera shake from holding my camera photographing something non-moving as a general starting point.

That is without IS and factoring in the 1.6 crop of my 40D......

pgbphotographytas
14-09-2010, 2:53pm
what's safe ?

1/ focal length was what I have always been told...

Mircula
14-09-2010, 2:54pm
my point is that even in autoiso you are determining the minimum shutter speed for it to kick in at. So, you control it.


I disagree. If I am in av and auto iso is turned on the only thing i decide is the aperture. And maybe a bit of +/- ev.

fillum
14-09-2010, 2:56pm
Sorry Mircula, I missed your posts at 1:56pm and 2:33pm as I was typing a response both times. I understand what you are asking now.

I don't know the answer but perhaps you could find out by running some test shots. Decrease the amount of light till you see the ISO increase. The s/s displayed when the ISO starts to increase will be the minimum s/s value. You could try different lenses to see if that makes a difference to the minimum s/s value.


Cheers.

pgbphotographytas
14-09-2010, 3:01pm
I disagree. If I am in av and auto iso is turned on the only thing i decide is the aperture. And maybe a bit of +/- ev.

Correct.

Case 1:
Camera on AV, F8, ISO 100 you might get a shutter speed of 1/50

Case 2:
Camera on AV, F8, Auto ISO the camera needs to work out what ISO to give it a "safe" shutter speed or else it would pick a random value for the ISO.

What the OP was asking is how it sets that value? With a 30mm lens it might say 1/50th is "Safe" where as on a 300mm lens it might need to set it to 1/300th.

Paul

Art Vandelay
14-09-2010, 3:11pm
This threads a bit confusing. :D

In Shutter mode, it can't keep a higher speed as it'll stay at whatever you set.
In manual mode it will also keep the shutter you've set.

Out of interest, just had a fiddle with mine (7D) on auto ISO in AV mode while reading this.

It doesn't have an automatic lower limit stop for shutter speed. Tried a few scenarios and focal lengths and it let the shutter go way down beyond hand holdable.

Mircula, I don't understand what the manual is suggesting.

arthurking83
14-09-2010, 10:45pm
I'm an ISO base or lower type of person, but I find Auto ISO to be one of the handiest features of the modern age.

I use it a lot in 'full manual mode', and set it's range from lowest to highest(200-6400) with varying shutter speeds to suit the lens I'm using at that point in time.

Basically.. I'm more like Darren.

My two methods of ISO usage are: lowest(ISO100) or Auto

Campo! if you have a Dxxx or Dx series camera, you're use of Auot ISO in full manual mode is quite easy to control. Use the memory banks for when you want, or not want to, use Auto ISO in manual mode.
I created a [Portrait_Auto ISO] memory bank where the camera is set to use AutoISO as a part of the set of parameters. Other settings in there too, like faster burst rate and 14bit capture, where normally I only use 12bit.

The only really annoying things about Nikon's implementation is that you can't use the ISO ranges below base(Lo-1..etc) and that you can't set AutoISO using the dedicated ISO button and the command wheel. You can only access AutoISO via the menu system, but as Darren said, that's still easy using the Quick Menu(I set it to the top of the menu too! :D). I still think, it's not an ideal way to set it.

I suppose the argument Campo made about having the option to turn AutoISO mode off when using full manual mode kind'a makes sense.
But then again that would complicate things a bit too much in simply wanting to switch to manual mode... and that's what the memory banks are there for anyhow! .. as long as you name them appropriately, and they makes sense.
I normally don't use Auto ISO when I use aperture priority mode, and as I don't use shutter priority mode... these two modes coupled with Auto ISO don't really interest me all that much.

For the D300, Nikon only addressed a few silly shortcomings with Auto ISO too. It used to be limited in selecting shutter speeds, and with a new firmware update they basically allow almost all (reasonable) shutter speeds, that the camera is capable of in some cameras.
ie. minimum shutter speeds from 1s to 1/4000s! :D

1s??? :confused: .. I suppose this is handholdable with a UWA lens with VR :th3:
1/4000s!! :eek: JeeeZ!! .. my brain hurts just thinking of situations for that setting.

Mircula
15-09-2010, 6:59am
This threads a bit confusing. :D

In Shutter mode, it can't keep a higher speed as it'll stay at whatever you set.
In manual mode it will also keep the shutter you've set.

Out of interest, just had a fiddle with mine (7D) on auto ISO in AV mode while reading this.

It doesn't have an automatic lower limit stop for shutter speed. Tried a few scenarios and focal lengths and it let the shutter go way down beyond hand holdable.

Mircula, I don't understand what the manual is suggesting.

Hmmm....so if it does not even have that it is completely useless....I will play around a bit with it tonight....

It astonishes me a bit that nobody knows that. Apparently all canon users really dont use auto iso at all....

etherial
18-09-2010, 2:18pm
I'll try and clear this up, I think some Nikon users don't understand the question because they have the flexibility of setting a minimum shutter speed when in Av mode - Canon does not (I wish it did!)

So here I am with my 7D and 70-200 lens, I point it at a blank wall only a metre or so away from me.

Av mode, F2.8, Auto ISO.
at 70mm it gives me a shutter of 1/100 and ISO of 1250
at 200mm it gives me a shutter of 1/250 and ISO of 3200

So clearly the camera is making a determination of a suitable minimum shutter speed and then setting the ISO to suit. It appears that it is looking for the first increment faster than 1/focal length. In my mind it is not fast enough though, and therefore I don't use it.

When shooting dog shows where I want a fast shutter and wide aperture, I flick mine to Manual mode, set the Aperture and shutter and use Auto ISO to automatically deal with the variations in light. So it is useful, but not as flexible as the Nikon method.

pgbphotographytas
18-09-2010, 8:07pm
I'll try and clear this up, I think some Nikon users don't understand the question because they have the flexibility of setting a minimum shutter speed when in Av mode - Canon does not (I wish it did!)

So here I am with my 7D and 70-200 lens, I point it at a blank wall only a metre or so away from me.

Av mode, F2.8, Auto ISO.
at 70mm it gives me a shutter of 1/100 and ISO of 1250
at 200mm it gives me a shutter of 1/250 and ISO of 3200

So clearly the camera is making a determination of a suitable minimum shutter speed and then setting the ISO to suit. It appears that it is looking for the first increment faster than 1/focal length. In my mind it is not fast enough though, and therefore I don't use it.

When shooting dog shows where I want a fast shutter and wide aperture, I flick mine to Manual mode, set the Aperture and shutter and use Auto ISO to automatically deal with the variations in light. So it is useful, but not as flexible as the Nikon method.

Thanks for the info, it makes a lot more sense now :)

RaoulIsidro
18-09-2010, 9:20pm
Once the Auto ISO on Canon is set/chosen, (5D, 5D2) it seems it isn't programable or changeable. The camera thinks for itself.
The Auto ISO on Nikons have a set up where you choose the highest ceiling the ISO will go, and the slowest shutter speed the camera will select.

ricktas
18-09-2010, 9:29pm
The Nikon Auto ISO system and the Canon one are completely different, you cannot compare what happens on a Canon to that which Nikon allow. The Nikon auto ISO system is much more programmable by the photographer. I think some of the Canon users in this thread haven't realised that.

I @ M
20-09-2010, 5:54pm
The entire subject of auto ISO made me have a think from the Nikon point of view.
We have used auto ISO ( in the limited range of 100 - 800 on D200 bodies ) in conjunction with manual control of the camera in every other aspect as a handy aid when shooting birds in varying and unpredictable light conditions and it has proved worthwhile.

The weekend just past and memory of this thread made me wonder how auto ISO in conjunction with a flash would work ( Nikon ) so I experimented.

To say I am confused is an understatement, there seems to be no predictability with the way the camera chooses to either increase flash output or to increase ISO or a combination of both.

My rather rough and very unscientific testing seems to indicate that the camera chooses to apply an ISO increase and a flash output increase at the same time very very accurately to obtain a correct exposure ---- but --- the manner in which it does the calculations seems to be heavily dependant on distance between subject, flash and camera.

Any thoughts.

zollo
20-09-2010, 6:00pm
canon users are weird:pirbaffled:D

I @ M
20-09-2010, 6:07pm
As a rough example, this shot was taken facing West ( into the sun through the scrub ) and from memory before the flash and auto ISO were brought into play it metered at around 1/30 F/8 ISO 3200 @ 200mm without the flash.

With auto ISO and the flash engaged ( +1/3 flash ev ) and the camera set in manual at 1/640 F/8 @ 200mm the camera chose an ISO of 5400 and pretty dammed good flash exposure to produce the image below.

http://dl.dropbox.com/u/9582534/Crimson.JPG

Harves
20-09-2010, 6:44pm
I use a D300 and use the auto iso for birding. I find it quite useful with the camera set on aperture priority, usually around f/4 or f/5.6, with the minimum shutter speed of 1/1250, along with the auto iso constantly adjusting the third element of producing the correct exposure, can't (shouldn't) go wrong.

Works for me anyway.:pircool:

RaoulIsidro
20-09-2010, 10:43pm
The Auto ISO on Nikons are more sane and predictable, by my experience with Nikons.
On the Canon, it's just crazy.
Auto ISO on my Canon 40D chose ISO100 for this and proceeded to OVERIDE my f4 setting to f5.6!
(I think I forgot to disable the Safety Shift function)


http://www.ausphotography.net.au/gallery/files/9/6/3/0/img_5146xs.jpg

fillum
21-09-2010, 4:51am
My rather rough and very unscientific testing seems to indicate that the camera chooses to apply an ISO increase and a flash output increase at the same time very very accurately to obtain a correct exposure ---- but --- the manner in which it does the calculations seems to be heavily dependant on distance between subject, flash and camera.

Any thoughts.
At 1/640 I assume that you are using auto FP high speed sync? With auto FP, max effective flash power is significantly decreased and consequently effective flash distance also decreases. My guess is that the camera will increase ISO when it calculates that flash power is insufficient for the distance. I'd assume that flash output would remain constant in auto FP for any particular shutter speed.


Cheers.

I @ M
21-09-2010, 7:19am
Phil, yep the reduced "full power burst" of flash is not available with auto fp on at high shutter speeds particularly when at any significant distance.
Even when using high speed synch, you are usually aware of the amount of power being chucked out by the flash from the sound of the discharge/s and the recycle time to "ready" for the next shot and only a couple of times when I was experimenting did I hear and see that a full power drain had occurred in the flash.
Back in the laboratory ( kitchen :D ) I tried some very simple shots at close distances where power needs wouldn't be compromised even with a high shutter speed and the result was that a correctly exposed shot was taken at 1/800 F5.6 400 ISO. Taking the same shot again but dialling in +1 flash ev saw a brighter shot as one would expect but instead of the camera increasing the ISO by a full stop to 800 it increased it to 720. This and other shots made me think along the lines I have about the camera , flash and the auto ISO combination working in different ways.

Likewise with another shot, straight at the subject about 3 metres away at 1/800 F/5.6 it chose 400 ISO with no sign of high flash discharge. Then simply lifting the flash head to about 45 degrees and bouncing the light from the very non reflective ceiling to light the same subject saw the ISO go straight to 6400 but still a properly exposed image and no sign of the flash working hard. :confused013