The hartmann has 3 triangle holes in it, allowing for precise focusing of the telescope. The aperture mask I use (4.25") is mainly for cutting back on glare from a bright object. also, by making the objective smaller in a refractor... it lengthens the focal length of the telescope, thus cutting back on chromatic abberation that is produced by an achromatic refractor.
I also made a 3 holed mask for the 12.5" that I swear by. It effectively cancels out diffraction spikes as seen in a newt reflector, also as a glare cut back on bright objects. Yep, the trade off is less light grasp because your cutting the aperture back considerably. On jupiter, it works great though.
Sweet image, I had a good look at Venus last night at our club viewing, it was very crisp and clear very much like your image only white hot in colour.
