I have a 42 mm Nikon Monarch gold and find it does a good job for gathering light at low light conditions. I think any Nikon Monarch would work just as well. One scope that you could check into is the Zeiss 3-9 x 40 mm. Although I haven’t had the opportunity for field testing this scope, it has been getting lots of attention and good reviews. Looking forward in getting my Zeiss as soon as possible. Another scope that I have been very impressed with is the Weaver Grand Slam but this scope is not very popular and the eye relief is a little short...