Looking for an answer

I am shooting airshows this year with a Canon 1DM4 and 100-400 EF L II. This past weekend at Ft. Worth Alliance practically all shots ground to air are severely underexposed. Attaching two unprocessed JPEG from the same show here so maybe someone has an idea where the problem is. Thanks in advance if somebody knows.

Without knowing what you were expecting it is hard to say. To my eyes the 2nd image is in the ballpark and the first is quite underexposed unless you are going for a silhouette. Both of your shots are 1/2000 F/5.6 ISO 100 but they represent very different lighting/exposure scenarios. The first shot would have to be shot much further to the right than the second for a properly exposed subject. If my understanding of your question is correct it appears that you calculated exposure correctly for the second shot but not for the first.

They were both shutter priority... I posted the 2nd one to show the difference....

bandfan wrote in post #18949999
They were both shutter priority... I posted the 2nd one to show the difference....

So then look at your settings. Your aperture is wide open and you are at ISO 100 (I assume you are not using auto ISO). Shutter priority is a semi-automatic mode that changes the aperture to adjust exposure but at F/5.6 you are maxed out. If your camera needs to increase your exposure it has nowhere to go. You may still have to dial in some compensation for a shot like this but giving the camera some latitude to do its job would be a good place to start.

A combination effect from not using the correct metering mode and/or EC, which are both critical when using automated modes like Tv or Av modes. Check metering and your EC settings...

The photo may look underexposed to you but the sky looks properly exposed. The EXIF data says you used spot metering. You may have Spot metered the sky and not the aircraft. Spot metering is good in this situation, but only if you meter the right spot.

But, as Trvlr323 said above, even if the Spot metering was on the correct spot, the shutter speed was locked at 1/2000 and the aperture was wide open at f/5.6

That means it would have been impossible to get a backlit aircraft properly exposed.

You're shooting a backlit subject so you have compensate accordingly. To expose the aircraft in such a way as to reveal fuselage details, you will have to overexpose the sky to some degree.

My five cents worth, from what I see:
you've chosen a high shutter speed to freeze the fast-moving aircraft = good
The lens you're using has an aperture that has a maximum opening of 5.6 when zoomed out to 400mm
You've chosen to use ISO 100

for the first shot with those settings, the camera cannot let enough light in to properly expose the aircraft given it's effectively in shadow.
You would need to either lower the shutterspeed somewhat, or increase the ISO to get the subject properly exposed.

The second shot is in full sunshine, so with the same settings, gets enough light to properly expose the subject.

Even if you do lower the shutterspeed or increase the ISO, with a backlit subject like the first shot, there is always a good chance that the camera may guess wrong which part of the frame you want to properly expose, so probably better to use full manual rather than Tv, and work out what settings need to be prior to the shot.

msowsun wrote in post #18950040
The photo may look underexposed to you but the sky looks properly exposed. The EXIF data says you used spot metering. You may have Spot metered the sky and not the aircraft. Spot metering is good in this situation, but only if you meter the right spot.

But, as Trvlr323 said above, even if the Spot metering was on the correct spot, the shutter speed was locked at 1/2000 and the aperture was wide open at f/5.6

That means it would have been impossible to get a backlit aircraft properly exposed.

This leads to the discussions of safety shift functions using ISO priority. ... and auto ISO implementations of newer cameras ... and using higher ISOs without fear of noise or having the ability to combat it.

ISO 640, 1/2500, f5.6 (so almost the same settings except raising the ISO over 2 stops makes a difference, but I used auto ISO)

msowsun wrote in post #18950040
The photo may look underexposed to you but the sky looks properly exposed. The EXIF data says you used spot metering. You may have Spot metered the sky and not the aircraft. Spot metering is good in this situation, but only if you meter the right spot.

But, as Trvlr323 said above, even if the Spot metering was on the correct spot, the shutter speed was locked at 1/2000 and the aperture was wide open at f/5.6

That means it would have been impossible to get a backlit aircraft properly exposed.

Nice to see you still lurking around Mike.

I agree with the others your lens needed to go to a wider aperture than it could for that ISO & SS combo. What I do as a Tv shooter is to set the SS I want then zoom out to the long end & pick an ISO that will put the aperture at F 8 to F 11 when looking at the empty sky. I then lower the lens until I have whatever the background is for the low level shots such as take offs & landings to verify the camera settings still work with the lens now having to go wide open or very close to wide open. I re check roughly every hour or so & rely on EC for the rest as I fine tune throughout an event.