Categories: Astronomy Astrophotography Behind The Scenes Photography Posted by: Martin
First Light: Astrophotography of Jupiter with SCT & APO Telescopes
After much deliberation, and in an effort to do more stargazing and astrophotography instead of virtual stargazing on the iPad, I decided it was time to get a new telescope!
Finding the right telescope is a tough task as they vary so much in both size, weight and quality and some are easier to setup than others. So I thought I’d blog my findings and my first attempt at planetary imaging in case anyone else finds themselves going down a similar route.
Finding The Right Telescope
Many moons ago I started out with a 60mm refractor, and although it’s cheap lenses gave imperfect views and false colours, I kept it for years & really got to know my way around the sky using a planisphere & Patrick Moore’s pocket astronomy guide. No computers back then!
I eventually upgraded to a 200mm/8″ newtonian reflector, a huge tube with mirrors on a wooden tripod with heavy equatorial mount & manual controls. I had some amazing views through that scope but it was a beast to setup, awkward to use, and not very portable.
So after a while I swapped it for a 200mm/8″ Schmidt-Cassegrain Telescope (SCT) on a computerised equatorial goto mount, thinking it would be more portable and easier to setup. But as we live in a light polluted area, the SCT scope has been gathering dust and I’ve gone back to using a small refractor. A large SCT can be a great all rounder for viewing both deep sky objects like galaxies and planets. But to realise it’s full potential it really needs to be used away from light pollution, and you have to be prepared to spend time re-aligning the mirrors if you move it about a lot.
Refractors Are Go!
We do a lot of camping and I need a scope that travels well to dark sky sites, so a few years ago I ended up going back nearly full circle to a 72mm / 3″ semi-apochromatic refractor, which is small, portable and quick to setup. It’s ok visually and views through it are very clear indeed, but they’re also quite small. It’s mainly designed for fast wide field astrophotography, so I’m now swapping my old SCT for a more modern 102mm/4″ apochromatic (APO) refractor. I’m hoping it will be a worthy replacement as it should give similar views, and the lenses should stay collimated so it’ll be more suited to travelling, quicker to setup & should produce more consistent results… that’s the theory anyway!
8″ SCT vs 4″ APO
Jupiter was well placed, but given that it was near a full moon & our back garden is awash with orange glow from sodium street lights, I was expecting fairly poor results. In this case, the APO faired rather better due to the poor seeing and light pollution, but if you live in an area with little light pollution and don’t need a portable scope, then the SCT might suit you better.
Luckily we had a few clear nights after the new scope arrived, so I set about doing some tests and some planetary imaging for the first time. I’d read that a 4″ APO refractor should give an 8″ SCT a run for it’s money, so it was time to find out…
Through The Eye
Visually with both at the same magnification and using both scopes on the same night, the 4″ APO produced slightly sharper views in the eyepiece than the 8″ SCT on both Jupiter and the Moon, despite it having half the aperture of the larger scope.
There was less distortion and a bit more contrast in the view through the 4″ APO. This is probably due to the SCT having a central obstruction for the secondary mirror which reduces contrast, the SCT mirrors not being collimated as perfectly as the APO lenses, and more air moving about in the larger tube which caused the image to ripple slightly.
I did collimate the secondary mirror, but don’t think I could align them as perfectly as the lenses in the APO. If the mirrors were perfectly aligned and we could have waited another hour for the SCT tube to cool down, it may have been a better view through the bigger scope. But I don’t usually have that much time, which is why I’ve gone back to using a refractor, albeit a much bigger one than my first scope.
Through The Camera
From an astrophotography point of view, the larger scope performed much better than it did visually. It’s hard to make a true comparison photographically as they were taken on different nights, in different seeing conditions, and using a different number of frames. But as only the best frames are selected in post processing, it shows how astrophotgraphy reduces the effect of poor seeing in the larger scope, with both the 8″ SCT and the 4″ APO producing similar quality images.
Anyway enough rambling, here’s what I came up with… it’s a million miles from the NASA photos you see from the Cassini spacecraft and the Hubble Space Telescope. But hopefully better results will follow with more practise and a dedicated astrophotography imaging camera. I just find it amazing that fairly small telescopes can take these types of images of a planet about 500 million miles away.
For anyone who wants to have a go at planetary imaging, I definitely recommend researching it online to get ideas. I found Trevor Jones’ AstroBackyard astrophotography website very inspiring, and the Cloudy Nights & Stargazers Lounge forums are particularly helpful. You do have to read between the lines though as everyone has a different opinion. Sky At Night Magazine and Sky & Telescope also have tutorials on how to get started.
The planetary images being produced by amateur astronomers these days are amazing and much better than my first efforts here. The trick it seems with this sort of “lucky imaging” is finding clear skies with good seeing and mastering the various image processing apps to enhance the details. So maybe not for the faint hearted, but I can definitely recommend giving it a go if you like astronomy and photography. The hardest bit is getting your head around how the software works and how to align, stack and enhance the image to look anything like a planet! ?
Clear skies & happy stargazing! ?