Remote shutter release won't consistently work with my EOS Rebel T6i

[alb84100]

I have had occasions where my remote shutter release would not function.  In trying to take telephoto shots of the sky, using a 200mm lens, the remote worked when AF is turned off but not when on. The focus was set on infinity.  This is with my T6i Canon.

[Tronhard]

Hi and welcome to the forum:
When AF is on, the system must find something that is distinct enough to provide a focus lock.  If you are focusing on the sky, it is likely that the system does not find that level of contrast.

[alb84100]

That makes sense.  The shot I was trying was last night when the moon and Jupiter were close to each other.   So you are saying that if the lens doesn't see something enough, the autofocus will not try and therefore the shutter release won't function?  I thought the moon would have been something to focus on. 

[Tronhard]

You would think so, but not necessarily.  There are some variables here:
- the mode of autofocus - are you using single point, all points etc.
- If the moon is actually blown out to white, it can also fool the focusing system because the white bleeds across other photosensors.
I have shot the moon a few times and I get my best results by using spot focus on the moon - the moon is very bright but the Field of View is mostly black - so the camera will try to over-expose the whole image.
Tweaking focus if necessary with manual focus, switch to Manual focus having got it (to avoid the camera re-focusing), and then compose, and shoot.EOS 80D, Sigma 150-600c@ 600mm, f/8, 1/250sec, ISO-200

[alb84100]

Thank you for answering.  I learn something every day.  Hard to adequately troubleshoot when outside in 20 degree evening in the dark.  Something about preparation.....