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Thread started 01 Oct 2015 (Thursday) 09:20
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ISO on 70D When Using Flash

 
tspencer1
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Oct 01, 2015 09:20 |  #1

I had some flash shots come out very dark - set up was as follows:
Shutter Priority
ISO Auto
Shots taken at night under street lighting.

Non-flash shots were fine - ISO varied between 3000 - 8000.

However, when I activated the flash, the ISO reset to 400 and stayed there. All flash shots came out very underexposed. I COULD adjust the ISO upward manually and then everything was fine. But why would it go to 400 and underexpose? I did not see anything in the manual about this.

Thanks,

Tim




  
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Frodge
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Post edited over 2 years ago by Frodge.
     
Oct 01, 2015 10:10 |  #2

Manual flash or ettl? Exposure compensation?


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tspencer1
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Oct 01, 2015 10:12 |  #3

No exposure compensation - and used the attached pop-up flash - which is eTTL, correct?

Thanks-




  
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Frodge
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Oct 01, 2015 10:14 |  #4

I think I remember complaints about underexposed shots with the flash on the 70D. Do a search....


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John ­ from ­ PA
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Post edited over 2 years ago by John from PA. (4 edits in all)
     
Oct 01, 2015 10:42 |  #5

If you have Auto ISO set then when the internal flash is used the ISO defaults to 400. This is discussed on page 122 of the current user manual. You should review that page as there are at least four other conditions dependent on other settings that may apply and affect the end result.

It is also suggested you review the other pages in close proximity to 122. Page 124 for instance shows how to set up an Auto ISO range, i. e., the upper and lower limits.

Why would it underexpose at ISO 400? Quite simply the flash is only capable of putting out so much light and the lower the ISO the lower the maximum distance of proper exposure. If you were beyond that distance, and it is about 22 feet for ISO 400 (outdoors even less) images would be underexposed. Run the ISO up, that maximum distance increases. A table of range vs. ISO is shown on page 187 of the manual. Take note as well that the distance varies as a function of what lens (wide angle or telephoto) is mounted.

AS you can see here most of the questions you posed could be answered by going through the manual. I suggest you download a PDF and put it on a smartphone or tablet that you might commonly have with you. Great to have it handy and usually you can readily search the PDF version.




  
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MakisM1
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Oct 01, 2015 10:42 |  #6

I believe that setting aperture or shutter (Av/Tv) priority mode sets the flash to fill in mode. As a result, the combination of shutter/aperture provides the lighting and the AutoISO the ISO 400. I believe than in any auto mode the ISO goes to 400.


Gerry
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rrblint
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Oct 01, 2015 10:44 |  #7

Yes, the camera automatically sets ISO 400 for Auto ISO when flash is used.



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tspencer1
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Oct 01, 2015 10:58 |  #8

Thanks for the info! The subject was further away than 22 ft - which explains the underexposure. The take-away for me will be that I have to set ISO manually for dimly lit flash shots.

I'm left wondering why Canon would have that setting in the first place - why force flash shots to be ISO 400 instead of letting the ISO float to expose properly?




  
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tspencer1
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Oct 01, 2015 10:59 as a reply to  @ John from PA's post |  #9

Great info - thanks!




  
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Frodge
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Oct 01, 2015 11:12 |  #10

I would just get a flash for the hotshoe. You won't be disappointed.


_______________
“It's kind of fun to do the impossible.” - Walt Disney.
Equipment: Tokina 12-24mm, Canon 40mm 2.8, Tamron 17-50 2.8 XR Di, Canon 18-55mm, Canon 50mm 1.8, Tamron 70-300VC / T3I and 60D

  
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gossamer88
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Oct 01, 2015 11:14 as a reply to  @ Frodge's post |  #11

Start with Yongnuo. They have'em at B&H.

http://www.bhphotovide​o.com …d/3857973351/N/​4294255798 (external link)


Canon 5D Mark IV | Tamron 24-70mm G2 | Tamron 70-200mm G2 | 85mm 1.8 | 50mm STM | 35mm f/2 IS | Powershot G9 X | iPhone 6s
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tspencer1
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Oct 01, 2015 11:19 as a reply to  @ Frodge's post |  #12

That is next on my list - thanks.




  
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gqllc007
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Post edited over 2 years ago by gqllc007.
     
Oct 01, 2015 11:24 as a reply to  @ tspencer1's post |  #13

I posted the exact same issue when I was taking flash pics outside. The issue is Auto ISO and Shutter priority. You have to set your own ISO and M mode It drove me nuts having it revert to ISO 400. On my 5Dmk3 I can set ISO to 800 or higher and shoot Av and/or M mode. I am pretty sure you can do it in Av mode and for indoors set 1/60-1/200




  
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BlakeC
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Oct 01, 2015 11:24 |  #14

Shoot in M with flash. It will make everything more consistent and leave no surprises.


Blake C
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tspencer1
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Oct 01, 2015 11:38 |  #15

Blake/gqllc007: Thanks! I think it will do the same thing in Av mode. Quirky - I don't get the logic behind it. Will try M mode for flash.




  
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ISO on 70D When Using Flash
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