Hi,
Firstly really loving having bees and working with them. Being new to the game I do have some questions. Firstly,
“When do you know a frame is full” I harvested all but the two outside frames about 2 weeks ago. I left the two outside as I could see empty cells at the back. The centre ones were all full, looking from behind. Now the centre ones appears to be full or almost full, again looking from behind. How do you know when the frame is full and can be harvested again?
Thanks
Mark.
Welcome Mark.
The rear window in your photo isn’t a bad guide, but the only way to really know is open the top and pull a frame out.
Each individual hive will have it’s own way of filling the frames and even then will probably do it differently each time.
Our recent harvest saw almost nothing in the rear window but pulling out a frame showed they had filled and capped all but the rear few columns of cells. I think they were on to us. 
I agree with Clint. You have to look directly at the frames, but there is a slight shortcut. You can lift every second frame and look at the exposed sides of the frames either side. That way you see four sides for each lift.
Mike
Thank you Mike and Clint. I will open the super this weekend. Trying to disturb them as little as possible but also need to see if I need to add a second super. Possibly replace two brood frames at the same time.
Cheers
Mark