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Thread started 08 Jul 2017 (Saturday) 03:31
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Flash at ISO400 issue

 
Gel
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Jul 08, 2017 03:31 |  #1

I'm a bit stumped.

I've recently started to use my 5D4 in the following mode:

AV + auto ISO. With the minimum shutter speed set in the auto iso section of my camera at 1/125 second minimum.

However when I occassionally need to turn the flash on it defaults to ISO400 every damn time and the shutter speed plummets to 1/10 sec or thereabouts.

Is this something others have got around, the camera is good to ISO6400 IMHO and it'll use much less flash power. Why it defaults to 400 is beyond me and I'd prefer to rely on the auto iso function as moments are fleeting and I don't want to change the ISO setting every time I need to pop the flash.

Thanks in advance!
Chris


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Ramon-uk
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Jul 08, 2017 05:18 |  #2

I think you will find that is normal for auto ISO with flash.
Why not set up one of your custom modes (C1,C2 or C3) to be manual ISO then you can just switch to that if you want to use the flash.




  
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Bassat
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Jul 08, 2017 08:22 |  #3

On most Canon cameras you have 3 choices for shutter when in Av mode with Flash on:

Normal (what you are getting).
1/60 - 1/(sync)
1/sync.

I leave mine on 1/sync ALL THE TIME. If I want a different shutter speed while using flash, I put the camera into MANUAL mode. IMHO, auto-ISO with flash is almost always a bad idea. It will always be 400. How often is that what you want?




  
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gonzogolf
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Jul 08, 2017 12:24 |  #4

At some point you have to control some of the parameters yourself if you don't like what auto gives you. If you have auto iso and auto flash going on you can't really dial in compensation if you have two moving targets for each shot.




  
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Wilt
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Jul 08, 2017 13:20 |  #5

Part of the 'intelligence' behind flash ISO defaulting to ISO 400 is the range of distances for different power levels at an f/stop ISO 400 permits, with f/2.8 it can control from 2'-96' at full power (to 1/256 power under eTTL) and 'normal' FL , Higher ISO selection would mean that near photos can be overexposed because the flash cannot cut its output by more than 1/1256 power. Particularly, P mode has programmed behaviors with flash...ISO 400 1/60 f/4.

Separate from flash automation is the Auto ISO function, which is intended primarily for ambient exposure shooting. But because the flash power range is inherently more limited that ambient exposure shooting, the flash apparently gets 'first dibs' at what gets set. Av is somewhat like P mode in terms of defaulting to ISO 400, with the selected aperture and the automatically set shutter speed, but shifting to lower ISO if the shutter speed otherwise would need to exceed X-sync speed (when CFn option set to 1/60-1/250 allowable Av speed range)


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John ­ Sheehy
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Jul 08, 2017 14:21 |  #6

Bassat wrote in post #18396990 (external link)
On most Canon cameras you have 3 choices for shutter when in Av mode with Flash on:

Normal (what you are getting).
1/60 - 1/(sync)
1/sync.

I leave mine on 1/sync ALL THE TIME. If I want a different shutter speed while using flash, I put the camera into MANUAL mode. IMHO, auto-ISO with flash is almost always a bad idea. It will always be 400. How often is that what you want?

That's precisely the problem. Canon assumes that if you are choosing auto-ISO, that you are totally clueless, when in fact, it is Canon that is totally clueless, as they don't seem to understand the concept of "fill flash". Fill flash means "I want a little bit of extra light from the flash system"; not, "help, camera, I have no idea what I'm doing so why don't you take over and automate more than just the ISO, and give me more flash than I really want, and ruin the ambient part of my exposure if I'm in M mode"..

There is no reason why fill flash should work any different with auto-ISO than with manual ISO. The camera already knows what the ISO target is before it fires the flash. Canon has replaced a potentially valuable function with something that already exists on the camera; flash with manual ISO.

There is sort of a workaround. You can set the custom function on recent Canons for exposure safety shift to "ISO", and ISO will drop when ISO is set manually, to avoid over-exposure. This works as a sort of auto-ISO, but it does not work in M mode, which is what I always use. Unless the Av and Tv limits that the camera provides in its auto-ISO setting are to your liking, M mode is difficult to simulate, or. On my cameras, I can not set the min and max Av value to the same value, and the values available are few, same for Tv values. It's like there are sadists working in Canon's firmware dept.




  
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John ­ Sheehy
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Jul 08, 2017 14:26 |  #7

gonzogolf wrote in post #18397149 (external link)
At some point you have to control some of the parameters yourself if you don't like what auto gives you. If you have auto iso and auto flash going on you can't really dial in compensation if you have two moving targets for each shot.

Not at all.

Auto-ISO with flash should be no different than auto-ISO without flash, except that the flash fires, and its intensity honors your FEC setting, just as if you had chosen that ISO yourself, manually.

I don't understand why people make this such a complicated thing, to justify Canon's horrible decision.




  
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John ­ Sheehy
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Jul 08, 2017 14:41 |  #8

Wilt wrote in post #18397187 (external link)
Part of the 'intelligence' behind flash ISO defaulting to ISO 400 is the range of distances for different power levels at an f/stop ISO 400 permits, with f/2.8 it can control from 2'-96' at full power (to 1/256 power under eTTL) and 'normal' FL , Higher ISO selection would mean that near photos can be overexposed because the flash cannot cut its output by more than 1/1256 power. Particularly, P mode has programmed behaviors with flash...ISO 400 1/60 f/4.

Separate from flash automation is the Auto ISO function, which is intended primarily for ambient exposure shooting. But because the flash power range is inherently more limited that ambient exposure shooting, the flash apparently gets 'first dibs' at what gets set. Av is somewhat like P mode in terms of defaulting to ISO 400, with the selected aperture and the automatically set shutter speed, but shifting to lower ISO if the shutter speed otherwise would need to exceed X-sync speed (when CFn option set to 1/60-1/250 allowable Av speed range)

That type of nanny-ing should be left to things like P and full auto. No such nanny-ing should exist in M, Av, or Tv mode (except user self-nanny-ing with Av and Tv limits, and safety shifts) . If I get blown-out flash in M mode with auto-ISO, it is ultimately my choice of Av and Tv values which precipitated it, and if I manually chose that ISO for the ambient, I would have the same problem. What you say is more likely with fast lenses, but there are whole worlds of photography where lenses are operating at f/5.6 or slower, and fast shutter speeds are used with high-speed-sync which has a much lower guide number.

There could also be a user-selectable feature to not fire flash if it is deemed to blow out the exposure at minimum power, rather than altering the ambient exposure.




  
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Wilt
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Jul 08, 2017 14:49 |  #9

John,
As I have already posted, Canon's logic is driven primarily by the range of distances for which the eTTL flash can control via power output (-6.5 levels). The minimum distance assumption (at ISO 100) is 1.6' with f/1.4 lens, so using 'normal' FL GN135 (for the 580EX) that is 1.5' - 96' flash range; the flash autofocus assist is good as close as 2'.

Assuming our ambient light level mandated 1/50 f/4 at autoISO 3200 (a reading just taken indoors in my home), the 580EX would have a Guide Number of 756 at ISO 3200...I would need flash output cut from an effective range of 189' (at GN3200, f/4) by -7EV to shoot as close as 1.5'...beyond the range of flash output control.


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John ­ Sheehy
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Jul 08, 2017 15:17 |  #10

Wilt wrote in post #18397255 (external link)
John,
As I have already posted, Canon's logic is driven primarily by the range of distances for which the eTTL flash can control via power output (-6.5 levels).

Yes, and I conceded that taking that into account for P mode or full-auto is somewhat acceptable.

The minimum distance assumption (at ISO 100) is 1.6' with f/1.4 lens, so using 'normal' FL GN135 (for the 580EX) that is 1.5' - 96' flash range; the flash autofocus assist is good as close as 2'.

Assuming our ambient light level mandated 1/50 f/4 at autoISO 3200 (a reading just taken indoors in my home), the 580EX would have a Guide Number of 756 at ISO 3200...I would need flash output cut from an effective range of 189' (at GN3200, f/4) by -7EV to shoot as close as 1.5'...beyond the range of flash output control.

Many of us often shoot in situations where we are never close to the subject, never use f/1.4, and use HSS, with very low guide numbers. Why should our flash/auto-ISO functionality be crippled because of what *could* happen if we we shooting close subjects with direct normal-sync flash at low f-numbers?

Even when I shoot indoors with a fast, wide lens, I aim the flash head at a white surface, above, but preferably, behind me, and flash has a lot more area to cover and is less likely to blow out.

I don't see why everyone who wants fill flash with auto-ISO needs to suffer because of people who shoot up close with direct flash with fast lenses, especially when there is P and full-auto mode for those people to use, and the chance of flash blowing the picture is no worse than if I chose that same ISO manually. Plus, I can use HTP giving me a stop of extra highlight headroom for flash.

Too much kindergarten, IMO. You can have kindergarten and PHD on the same camera, but Canon pushes out the PHD program for the kindergarten.




  
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Gel
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Jul 08, 2017 17:09 |  #11

Thanks for the comments everyone.

For me the main times I use is are church exits when I'm walking backwards and about to head outside. I'd prefer to be all set up for outside before the walk, flip on the flash, blat, blat, then switch it off as I approach the door.

The other is if I'm shooting a tipi wedding where I'm inside and outside at a moments notice. I don't use flash a lot, but when I do the scenarios are such that I just want a little fill quickly.

It would be nice of Canon to give the option to set it at a higher default ISO, because when it does fire at ISO400 it's more pawerful than it needs to be and just increases the recharge time.


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Bassat
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Jul 08, 2017 17:54 |  #12

Gel wrote in post #18397373 (external link)
Thanks for the comments everyone.

For me the main times I use is are church exits when I'm walking backwards and about to head outside. I'd prefer to be all set up for outside before the walk, flip on the flash, blat, blat, then switch it off as I approach the door.

The other is if I'm shooting a tipi wedding where I'm inside and outside at a moments notice. I don't use flash a lot, but when I do the scenarios are such that I just want a little fill quickly.

It would be nice of Canon to give the option to set it at a higher default ISO, because when it does fire at ISO400 it's more pawerful than it needs to be and just increases the recharge time.

You are aware that you can set ISO to anything you want, right?




  
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Jul 08, 2017 18:12 |  #13

John Sheehy wrote in post #18397232 (external link)
That's precisely the problem. Canon assumes that if you are choosing auto-ISO, that you are totally clueless, when in fact, it is Canon that is totally clueless, as they don't seem to understand the concept of "fill flash". Fill flash means "I want a little bit of extra light from the flash system"; not, "help, camera, I have no idea what I'm doing so why don't you take over and automate more than just the ISO, and give me more flash than I really want, and ruin the ambient part of my exposure if I'm in M mode"...

I agree completely that fill flash should be just as you say. The camera should compute the exposure exactly the same way it normally does, but then fire the flash.

By selecting auto ISO, however, you are asking the camera to take over and automate something for you. Why would you even shoot in M mode for shutter speed and aperture but let the camera choose the ISO? With or without fill flash, unless you know what your ISO setting is, how can you even select the shutter speed and aperture?

Mike


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John ­ Sheehy
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Jul 08, 2017 18:35 |  #14

mcoren wrote in post #18397411 (external link)
I agree completely that fill flash should be just as you say. The camera should compute the exposure exactly the same way it normally does, but then fire the flash.

By selecting auto ISO, however, you are asking the camera to take over and automate something for you. Why would you even shoot in M mode for shutter speed and aperture but let the camera choose the ISO? With or without fill flash, unless you know what your ISO setting is, how can you even select the shutter speed and aperture?

In limited ambient light, all I am interested in is a wide-open lens and a certain shutter speed. ISO is meaningless to me. If I add flash, I want it to add a little light and not dominate. I'm not sure what it is that you don't understand.




  
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Wilt
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Jul 08, 2017 18:36 |  #15

mcoren wrote:
Why would you even shoot in M mode for shutter speed and aperture but let the camera choose the ISO? With or without fill flash, unless you know what your ISO setting is, how can you even select the shutter speed and aperture?

A. I would! I can see the selected ISO value in the viewfinder (and top LCD), as well as my predetermined aperture and shutter speed. I know what shutter for motion control (the subjects and/or my camera) and aperture for DOF control...and I can see what ISO the camera has chosen for me. This is simply a different parameter (out of the triad of exposure controls: shutter, aperture, and ISO) compared to Tv or Av. Unlike automatic selection of Av and Tv, however, letting the ISO float does invite (too readily) getting high ISO noise. But having a menu setting for max ISO in auto ISO mode can overcome that issue somewhat.

As an aside, I have long thought that Pentax has a better way than Canon, in offering a mode on the dial for auto ISO with M selection of aperture and shutter, rather than having the 'A' setting on the ISO dial...Pentax's TAv mode.

ISO 12800 is 5EV more sensitive that ISO 400...the flash first needs to have sufficient range of control that it works properly at more typical distances that 100+ ft and can regulate its power level back to be successful at 20'.


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