Want to tell you about my newest toy. This isn't an adaptor to fit your camera to a scope, but it fits on the end of your camera lens to make it a scope.
As you might know, I lug around my 3-800 sigmonster when I don't have too far to walk, trouble is I then can't really lug around my Nikon Fieldscope with me and while having 800mm is great, it really can't show the detail a proper scope can at distance, even with a multiplier on the cameras viewfinder is not designed for that.
So I finally got one of these scope converters off e-bay. They are no longer made (why, I don't know) I paid just over a hundred quid for it. They come up from time to time on e-bay.
On the back of my lens it makes it a 30x - 80x scope (10x for every 100mm of FL) and I was dubious that it would be a compromise but it is not. Today I was looking at Dunlin over 1/4 mile away and I could easily make out all it's features. I've also tried it on my 80-400 (4.5-5.6) nikkor and it is still miles better than my fieldscope.
This really is a fantastic option as I always want a camera with me as I need to keep record shots, and now with a pocket sized adaptor I have a super scope too.
I have never seen these for Canon or other makes of lens but it is such a useful item I cannot believe they do not exist.
It unbalances the lens on the tripod as it doesn't have the weight of the camera there so you need to be able to slide the lens back. I have my lens on a long Arca Swiss mount so this is easy.
The lens must have a manual aperture ring as the attachment won't open the iris for you.