ISO on 70D When Using Flash

Any recommendations on where to look for decent used Canon speedlites?

The for sale section here...ebay, craigslist

With auto ISO in P mode, the camera will select ISO 400 if you aim the flash at the target, but ISO 1600 if you intend to bounce the flash. On the reasonable assumption that bouncing is less efficient.

tspencer1 wrote in post #18461360
Any recommendations on where to look for decent used Canon speedlites?

DreDaze wrote in post #18461370
The for sale section here...ebay, craigslist

Agreed. I've purchased from all three. Be CAREFUL with CL.

apersson850 wrote in post #18461506
With auto ISO in P mode, the camera will select ISO 400 if you aim the flash at the target, but ISO 1600 if you intend to bounce the flash. On the reasonable assumption that bouncing is less efficient.

Too simple an answer. The manual says P w/Auto ISO will vary the ISO from 400-1600 (not either/or) when bouncing flash. If I set my 80D to P, auto-ISO, and use direct flash, I can get the ISO to run anywhere from 100 to 16,000. Seems a bit like Canon doesn't know how their camera works. Or the engineers aren't talking to the tech-writers.

I also believe that in ANY mode, if a flash exposure will result in OVEREXPOSURE, ETTL will drop the ISO to as low as 100 trying to get you a decent result.

Thanks Andre, Anders and Tom!

tspencer1 wrote in post #18461543
Thanks Andre, Anders and Tom!

You are welcome.

Please allow me to add one thing about flash with P mode. If you shoot in P mode, with auto-ISO, and ETTL flash, you are controlling exactly NONE of the exposure parameters. Don't be surprised by ANY of the results you get. Flash is best done, and easiest to control, in Manual mode. Av works well, if you let the shutter speed float, but it will surprise you on occasion. Tv with flash just seems wrong to me.

Thanks. I have never used P mode. I don't even understand the concept - that is - when used and how different from straight auto.

Why no Tv with flash?

For the shots I'll do this weekend, likely will be ISO 800 or 1600 (based on distance to subjects), shutter at 1/200 or so and let the aperture float. Any surprises likely?

tspencer1 wrote in post #18461553
Thanks. I have never used P mode. I don't even understand the concept - that is - when used and how different from straight auto.

Why no Tv with flash?

For the shots I'll do this weekend, likely will be ISO 800 or 1600 (based on distance to subjects), shutter at 1/200 or so and let the aperture float. Any surprises likely?

P lets you have some input on aperture and shutter speed. Just roll the front dial.

Tv with flash seems weird to me because shutter speed has negligible impact of flash exposure. And you are letting the things that DO control flash exposure (aperture and ISO-in auto) float. With both floating you have no idea if you are going to get f/8 and 800, or f/2 and 100. You are not controlling the outcome. Why bother?

Please remember that you asked the last question. ISO 800-1600, and the pop-up flash, is going to give you a bunch of really poor photographs. Keeping the shutter at 1/200 will make them worse. You really are working outside the parameters of good results here. That doesn't make it wrong. Just don't expect top-notch results.

Caveat: my wife is always reminding me that I am way too picky. I don't cull my own photos anymore. My wife knows diddly about cameras. Folks seem to like my photos that she chooses to print.

Bassat wrote in post #18461542
Too simple an answer.

Well, considering the equipment and skill level of the OP, I thought it was detailed enough. But it's not all the details, no.

apersson850 wrote in post #18461601
Well, considering the equipment and skill level of the OP, I thought it was detailed enough. But it's not all the details, no.

Apologies. I do tend to go overboard from time to time. Or daily!

tspencer1 wrote in post #17728816
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.

Canon seems to be dead from the neck up on the subject of flash fill in a user-selected ambient exposure and auto-ISO. The idea that someone might want to shoot at 1/400, stop the lens down 2/3 stop and use -2 FEC with high-speed-sync (HSS), all with auto-ISO, seems to be foreign to Canon. There is no way around this unless your camera offers the custom function of ISO safety shift. If you set safety shift to ISO, then you can set the camera to the highest ISO that you'd be willing to happen, then if the limits of Av and Tv value ranges that you've set for P, Av, and Tv modes do not prevent over-exposure, then the ISO will drop based on ambient exposure just before the flash does its pre-exposure test flash, and will operate just as if you had manually set that ISO. So basically, the camera is choosing manual ISO for you, automatically.

ISO safety shift does not work in M mode, though, so you have to rely on the other modes (Tv and Av) to simulate it as best as you can. You can also wind up in a situation where the weakest flash that the flash can produce is too strong for the ambient-based ISO result, so you have to look at for that. That is more likely with stronger flashes, closer distances, and very fast lenses.

Please report if the 70D has this custom function and how it works for you if it does. Others may benefit from your experience.

John Sheehy wrote in post #18461671
Canon seems to be dead from the neck up on the subject of flash fill in a user-selected ambient exposure and auto-ISO. The idea that someone might want to shoot at 1/400, stop the lens down 2/3 stop and use -2 FEC with high-speed-sync (HSS), all with auto-ISO, seems to be foreign to Canon. There is no way around this unless your camera offers the custom function of ISO safety shift. If you set safety shift to ISO, then you can set the camera to the highest ISO that you'd be willing to happen, then if the limits of Av and Tv value ranges that you've set for P, Av, and Tv modes do not prevent over-exposure, then the ISO will drop based on ambient exposure just before the flash does its pre-exposure test flash, and will operate just as if you had manually set that ISO. So basically, the camera is choosing manual ISO for you, automatically.

ISO safety shift does not work in M mode, though, so you have to rely on the other modes (Tv and Av) to simulate it as best as you can. You can also wind up in a situation where the weakest flash that the flash can produce is too strong for the ambient-based ISO result, so you have to look at for that. That is more likely with stronger flashes, closer distances, and very fast lenses.

Please report if the 70D has this custom function and how it works for you if it does. Others may benefit from your experience.

It seems like you are basically asking if the 70D has EC in Manual mode. It does not. My 80D does. IIRC, so does the 7D2. I will assume the 5D3/4, 1DX/2 also have it. If you shoot a 1D3/4, you can force it with Custom Functions limiting Av/Tv/ISO values. I agree with you. EC should be a basic function available on any SLR, in any mode. I can make my own decisions, Canon.

Bassat wrote in post #18461717
It seems like you are basically asking if the 70D has EC in Manual mode. It does not. My 80D does. IIRC, so does the 7D2. I will assume the 5D3/4, 1DX/2 also have it. If you shoot a 1D3/4, you can force it with Custom Functions limiting Av/Tv/ISO values. I agree with you. EC should be a basic function available on any SLR, in any mode. I can make my own decisions, Canon.

I was talking about a possible custom function that allows ISO to drop from a manual setting to avoid over-exposure. Canon started including this a few years ago.

It is not available in M mode in the cameras I have that have it.

John Sheehy wrote in post #18462025
I was talking about a possible custom function that allows ISO to drop from a manual setting to avoid over-exposure. Canon started including this a few years ago.

It is not available in M mode in the cameras I have that have it.

I'm pretty sure every Canon camera I've ever had does that, but I'm not sure about Manual mode. Let me check my 6D/80D.