Expert: Paul Wagner - 10/29/2005

Question
Hi:
I just bought my second telescope, it is a reflector 114mm, f/4.4. The problem that I have encountered is that at the moment I try image projection with my Nikon N65 I cannot achieve focus. I have tried everything and the only thing that works is the afocal method. Is there anything I can do to achieve focus without using the afocal method?
Thank you for your time.

Answer
Direct image projection on these scopes is tough, because the focal length is so short, and the f/ratio so fast, that it is hard to get the camera close enough to the telescope to focus it.  The only solution is pretty drastic--changing the length of the telescope tube, then position the eyepiece and focuser farther off the axis---and then increasing the size of the secondary to make sure you're not missing any light.  


You are better off using a 25mm eyepiece and projecting with that...Start by just using a piece of white paper, and projecting the moon onto that.  That will give you a rough idea of where the focal plane is.  Adjust that a bit with the paper, until you get something that should work with the camera.  

Your best shots will be of brighter objects...so start with the moon.  Once you get the focus dialed in, you can start doing longer and more complicated exposures.

Paul Wagner