The difference of 50mm, every body will tell you is more light: true. But: I just read in a magazine and my expence with photo work ( where calculation of light is important) can change the way you look at it.
A variable scope will transmit less light at maximum magnafication.
The amount of light transmited through a scope a lower magnification and absorbe by your eye will be more or less the same with a 40mm or 50mm.
To get the full advantage of a 50mm lens, you would need to use it at high magnification and low light condition.
Another factor, other then cost is the size: will be high and long. Plus the additional weight. I really liked a 50mm scope but considering all these factors and the type of hunting I do, I got a 40mm.
Evaluate your needs to get something for you. You indicated that you hunt in the sunshine, then a 40mm would do the job.
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