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David,
This can be a difficult target if you have never observed it before. Under less than favourable conditions you could sweep straight past it with a 10" scope and not realise you had just bypassed it. Once you see it for the 1st time you will know what your looking for and it becomes progressively easier to locate. It is a large galaxy so its best to use the lowest power eyepiece that provides a dark sky background with good contrast. You need to make sure that you don't use an eyepiece creating too large an exit pupil under less than pristine skies. Your 40mm eyepiece creates an 8mm exit pupil in an F5 scope and I would consider this virtually useless under any sky conditions. An oversized exit pupil causes the sky background to appear a little milky and images lose contrast making it impossible to find dim targets, the worse the light pollution the smaller the exit pupil you need to limit yourself to. From Mag 5 skies I limit myself to about a 5mm exit pupil and from dark skies of Mag 6 and better I limit myself to a 6mm exit pupil which in my F5 scope is a 30mm eyepiece. With you being a little younger than me (I am 46) you may be able to use a slightly larger exit pupil than I can but it certainly won't be a lot greater. As you age the eye loses its ability to fully dillate under dark conditions.
I suggest that you use your 25mm eyepiece as your finder and you will need reasonable conditions. Under poor conditions I have trouble finding it in my 10" scope, under fair to good conditions it is a lot easier to spot.
CS-John B
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