NGC2467 in Puppis is a rather small emissions nebula and I recent imaged this object with two different scopes that I own; one a RC08 f8 and the other a 10" f5 imaging newt (that I built); both of these scopes use GSO optics. The idea here was to get a handle on the differences in image quality between the two scopes. The same camera was used on both (my Canon 450D full spectrum, cold finger modified). The images were taken from my observatory, on my pier mounted NEQ6 Pro, and all shots were guided. The camera cooling was set for 2C at the sensor back. The focuser (a Moonlight on the RC and GSO R&P on the Newt) was locked after using a Bahtinov mask to focus precisely. Seeing conditions were similiar. ISO 1600 was used for the RC subs and ISO800 for the Newt Subs. Processing was equally minimal in Photoshop.
I realise a 8" f8 RC may not be an equivalent performance benchmark with a 10" f 5 imaging Newt, but for novice buyers they are in the same price band. The RC will always need more light for a longer time to provide a similiar data set, but some things can be determined from my test.
A series of 10 subs were taken with the RC, and with the Newt. Both were sets were stacked with darks and bias offsets taken at the same sensor temperature (2C) as the lights. For the RC I shot 360" subs at ISO 1600, and for the Newt 240" at ISO800. Now right away people will point out that for there to be good comparative signal quality I would need to push the RC subs out to probably something like 500-600" and I accept that. But doubling the ISO does help. What I am showing here, more than equal signal total time, is the relative contrast, resolution, etc and ease of use.
I have attached the two downsized jpg images that came from this test, and be aware that downsizing for the web reduces the apparent quality. Obviously the RC gets in much closer to the object due to a longer focal length, the newt being the wider field of view. Draw your own conclusions about your preferences. For me, the newt is the winner in terms of image enjoyment, with better contrast (smaller central obstruction) and simply the speed with which it can gather light. The RC while great for getting in close, suffers from a slight collimation issue (still), bloated stars, and lacks the snap of the newt photo. I realise it's not apples to apples but I wanted to do this. I will reshoot the RC series on NGC2467 with much longer sub times to get a better comparative signal result.
These images don't need a subjective analysis by the experts, they are simply put here to demonstrate the differences I have noticed and give people some perspective on scope performance on the same target.
