Quote:
Originally Posted by doppler
I'll have to give that a try. So if I cut the centre out of a lens cap, then make some cardboard inserts with different sized holes in the centre to find the "sweet spot".
Anyway back to the diffraction spikes here is a pic of m45 with a 135mm f2.8 lens stopped down to f5.6
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Yes, a perfect set of direction spikes
Not everyone finds these offensive of course and I personally don't mind them but they can become an issue with reflections though when there is a particularly bright star in the field of view (such as Rigel or Sirius). It could still be that the issue that Raymo is having is due to reflections caused by the diffraction spikes from a bright star. It is worth experimenting with the aperture mask and seeing if you are happy with the results.
The other benefit from using an aperture mask is when attaching a Canon or Nikon lens to a CCD (a QSI683 in my case) as you cannot use the DSLR electronics to stop down the lens. It can be done with a bit of trickery but using the aperture mask makes things a little easier.