Using Auto ISO with 'M' Mode
One of the problems with Auto Focus, is it doesn't work quickly or accurately if your exposure is too low ie. too dark. The system just doesn't have enough light to manage!
If you are photographing small creatures that have the potential to move, you often miss the shot.
Missing too many Shots
This happened too often for me recently while I was trying to photograph little brown birds called Thornbills, that were in dense bushes, in low light and they were almost always moving. They would stop occasionally to taunt me and then, while the camera was trying to focus, it hopped away!
Aim - to Reduce my Movements to 2 - 3 moves
Ideally, I would like to only frame, focus & shoot
So I decided to experiment.
I like to use manual as I can select the shutter speed and f-stop without the camera applying something I don't want. I would then adjust the ISO to get the correct exposure. So I thought the camera could do that faster than me.
It worked! and the exposure was mostly in the right ball park
As always there are exceptions to everything, so there were some instances when you have to adjust the exposure. You do this with exposure compensation (the +/- button). There are of course some situations where it can't cope well eg. a back lit bird in the tree tops with a bright sky behind. You can fix this with spot exposure or going back to full manual.
Check the ISO of your Images
While you may be getting the correct exposure, in low light particularly at this time of the year, you may end up with ISO's that are very high. This is OK if you don't want to crop or enlarge the image too much. If you want a lower ISO (even 1 stop can make a difference) you can lower your shutter speed or f-stop. This will automatically lower your ISO.
If you don't want to do that - or can't, then it is time to get out the tripod, add a flash or add another light source.
It is your choice of how you want you image to look
I am using these settings more often now and finding my hit rate much improved in a quicker time.