I've never heard of that before Martyn but it makes sense now you say it, something to consider.Problem with doing that is the warm air leaving the house through the window can cause a heat haze effect to your images, especially when it is a lot colder outside than it is inside.
The Chaffinch is my favourite of the three.
I've never heard of that before Martyn but it makes sense now you say it, something to consider.
Nice set of shots, BT looks like it's just had a bath!