In this early foray into naked astrophotography I have just two optical surfaces – my red devil’s 150mm diameter primary and 44mm  fat secondary mirror. As you can see it seems to work pretty well. Especially when you learn that this fifty year old Edmund Optics newtonian  cost me fifty quid (you can find out more about this telescope in this vid). Normally the big problem with Newtonians is an aberration called coma which get progressively worse the further away from the centre of the image you go. To correct coma I would recommend getting a very expensive coma corrector like Tele Vue’s paracorr. But at F6.3 the red devil is quite slow and its hard to notice the coma until you get quite far from the center of the image. In fact if you use a small sensor camera like wot I did ( the zwo asi585mc) then coma doesn’t even make an appearance.

Without coma you don’t need a coma corrector and that leads to maximising the biggest benefit of mirror based telescopes – which is that they handle the red, green, blue and infra red wavelengths just the same. In short a Newtonian is like superpowered super expensive apochromatic refractor.

And as the asi585mc camera is very sensitive in the infra red I was able to leave its sensor naked (without a Luminance filter) to gather all the photons it could from UV right down to the infra red wavelengths.

Being able to gather light from such a broad band of wavelengths means that this slow telescope actually gathers photons quite quickly and combined with the asi585mc’s extremely low read noise meant that I was able to take 30 second exposures which in turn meant I didn’t need to bother guiding. This is music to the ears of folks who can’t afford super accurate mounts or can’t be bothered to set up guiding.

Advantages:

• No expensive coma corrector
• No need for guide camera and guide scope
• No need for a super expensive mount
• No need for filters
• Easy

EDIT: QUICK NOTE ON THE MOUNT

Because I polar aligned my mount quite poorly (due to the tripod to mount head adapter locking up the polar alignement adjustment knobs) I was limited to 30 second exposures. At this pixel scale (900mm focal length, 2.9micron pixels, 0.66″ per pixel ) 30 second exposures is pretty impressive but I felt it prudent not to bang on about the fact that the mount had been tuned by Dave from Dark Frame Optics because I knew I could have gotten longer exposures if I had nailed the polar alignement. I was worried that folks would think that Dave’s mounts can only manage 30 second exposures. But Dave thinks I should have mentioned his stellar drive  upgrade bc even with my cock ups its performed pretty well. So sorry bud. Here you go! (But your mount could have gone longer if I had  properly polar aligned it).