Quote:
Originally Posted by MattT
I'm going to add:
#12. Use a long focal length Achro.
I tried again on Saturday night and got the Pup in the 10" no problems. The E+F stars in the Trap were visible too.
So onto the 70mm f13 Achro. Yep this 70mm is well in the Conrady scale for CA at about 4.5. Sirius was a white star, shown as an Airy disc with a couple of diffraction rings, dimmer and a lot less scatter than the 10".
I got a result that was surprising to me but more on that later as I need to try it again on another night.
In the meantime read this article by Neil English...love him or otherwise 
http://www.cloudynights.com/page/art...-fiction-r2452
This is turning into an epic thread. |
I'm a Neil English fan -so glad you brought this up.
My favourite scope type ever is a long f/ratio Refractor. I can well remember the images Of Mars etc in my now sold 4" F/15 Unitron -Never seen better since, except maybe Mars one night in May back in a 7" Mak; it was that good.
Just had a quick read, and he talks about the greater DOF, less spherical aberration, height above ground of the objective , and greater encircled energy per given strehl, all adding to a STEADIER image than say an ED doublet, but less so for a triplet and he says contributing to less eyeball strain in these long F/ratios.
HOW GOOD THIS WILL BE FOR OBSERVING DOUBLES ;WE MAY SOON FIND OUT FROM YOU MATT!
Wishing you goodluck with this!
bigjoe.