M56 Calibration Frames

Capturing calibration frames as planned.  Wow, did it get bright early!  At 3.50am the sky was blue in the east, which was too bright to continue imaging, so covered the scope and took dark frames.

Unfortunately I didn't buy the 250 quid Pink Floyd tickets I was offered....

Blooming CCD Camera

Computer says no blooming (after 300s)

While waiting for the clouds to clear, or the mist at least, I decided to see if I can make my CCD chip on the QHY8L bloom, which means over exposing the image so that electrons leak from the wells on the chip and drain off into other parts of the chip.  Apparently the QHY8L has anti-blooming - not sure how it works, but a 300s exposure of Arcturus might do the trick.
Lets try 600s.

This is pointless.  If the camera can't do 10 minute exposures of a bright star without blooming, then I have really bought a dud.  The guiding went AWOL during the exposure, so this will be interesting...  PHD (guiding) has gone off the scale again, so I've left the last minute to the mount to guide.

Not what I expected, little zig-zags...

Setting Up for Flats

C8 with cameras and cables (I always tidy the cables if I am going to image,  but with the clouds, it wasn't necessary)

The clouds have returned, as forecast, but I set up anyway as I needed to take some flats to enable calibration of the images I took yesterday of M13.  I took care not to change focus, or to turn the camera, or make any other changes to the telescope.  I have found the skyflats plugin for MaximDL written by John Winfield to be an excellent little tool for getting flats at dusk.  The plug-in automatically adjusts exposure length to compensate for the declining brightness of the sky so the average ADU of the flats are within the range required (approximately 25,000 ADU for my QHY8L).

 I also find sky flats better than the light box I built; probably something to do with the LED light source I used not having the right spectrum of light.

After the flats were taken, the sun lit up the clouds over south east London:

C8 at Sunset

I've left the telescope set up as there is a possibility that the clouds will clear at 11pm, and behind the strom front could be a window of opportunity... Until then I will process the shots of M13 I took last night.

Normal Guiding Service Resumed

A little less drift, but again, seeing conditions not ideal, so I am just happy to be imaging M13 again...

I've just noticed PHD was set to not guide on declination, so recalibrating with it set to north.

After getting enough data on M13, although it's late, M57 (the Rin Nebula in Lyra) came up into view, above the dirty grey zone of the horizon.  This is one of the joys of imaging where an image seemingly so bland as a grey smudge, will turn into a beautiful nebula once enough data is captured.  Yes, the grey smudge in the middle is what I am so excited about...

When I zoom in, this is what the camera is capturing, a planetary nebula 2,300 years from earth:

Once the image is processed, although it won't be nearly as good as the colour image below (from Stellarium), it's one of the personal rewards of astrophotography.

Below is one 120 second image converted to colour.  No other processing...

I wish I had more time to get more data, but as is often the case, M57 will have to wait for another day until I and my equipment can do it justice.

Apart from the odd blip, as below, (probably caused by "stiction" (static friction in the gears) - the CG-5 mount is reknowned for it), guiding has been good tonight, just a pity I have to close up shop...  The clouds are due to descend for a few days however, so at least I have plenty of data to process.

My Telecope - Celestron C8 Schmidt-Cassegrain Telescope (SCT)

There are 3 main groups of optical telescopes - refractors (the oldest type, as used by Sir Isaac Newton), reflectors, and catadioptrics.  (For more detail see this excellent wikipedia page). The SCT is one of the latter types, and I chose this because of the size and aperture.  Basically, the greater the aperture (light gathering ability), the greater the number of objects that can be seen. I went for an 8 inch based on a simple price to performance equation:  this is how much I wanted to pay, and this is the performance I got.  For the same aperture, refractors are vastly more expensive.  The big downsides to getting a larger scope (apart from cost obviously) are portability, size, and attachments - the bigger your scope, the bigger the other attachments (eyepieces, filters, etc.) seem to need to be (at least to compliment the scope, or to not become the limiting factor in its use), and consequently the greater the cost. The 8 inch version was a happy medium for me - 6 inches seemed too small - I felt like I could have picked it up and run with it, and worried I would regret not getting something bigger, but the 9.25 and 12 inch versions induced mumblings of, "what a beast" "where will I hide that from the wife - I couldn't even get it in the garden shed".  So the 203mm C8 was a compromise of reasonable aperture, performance, portability, and cost.  It still feels like a good price to me, and is probably why Celestron have sold so many of these pieces of kit.  They are really popular, and I can see why.

Would I buy it again?  Maybe.  I'm still relatively new to this, and the only other scope I've really looked through is a cheap 80mm refractor (pictured above attached to my C8, which I'm using as a guide scope), so I haven't got much to compare, or got the best out of it yet, but so far it's been money well spent, and the optical tube is certainly fantastic; the detail I saw on the moon in the first week was gobsmacking.  Yes, I literally spent a week looking at the moon awestruck.

Seeing Saturn and rings with your own eyes for the first time is also a memorable experience. More distant, smaller or fainter objects ("faint fuzzies") take more skill, such as good polar alignment and averted vision, to get the best out of the scope, and you own eyes, but the C8 delivers in spades if you give it time to learn it's nuances.

The mount (CG-5) I have my doubts about - more on that later, but suffice it to say that for Goto functionality (slewing to objects in the database) it's great, but for long exposure astrophotography, you will be battling the mount, as much as all the other things that have to be just right.

I read a huge amount before shelling out my hard-earned on the scope, and one of the best sources of information I came across was this site by Ted Kurkowski.  Some of the content (for example on models, software and technology) is quite dated, but the guys knowledge and experience shines through. One of the great tips I picked up was to cut a disk with a hole over it and place it over the focuser, to enable finer control of focussing - always a tricky thing, especially with the standard focus knobs supplied on most scopes, and especially the C8. I cut a hole in an old plastic credit card sized rectangle (it was in fact a National Trust Membership card) and slotted it over the focussing knob.  Not only was fine control much better, but it also reduced vibrations induced by touching the scope.

The first few accessories I bought were a moon filter (good for viewing when the moon is near full) and a Neodyniun "light pollition" filter (don't bother).

Next was adapting an old webcam I had lying around to enable me to take stills and video of the moon.  Then USB cables to connect the mount to my laptop, so I could control it whilst sitting at my kitchen table, and not have to be out in the cold.  When it was minus 6 degrees every night, this became a neccessty...

After about 6 weeks of being a telescope owner, I went a bit mad and spent the same amount as I had on the scope and mount, on a focal reducer, guide scope, guide camera, and CCD camera.  Yes, I had really caught the bug, and my bank statements are the proof.  But if I wanted to take long exposure shots, I need a camera that could do this, and the focal reducer to increase the speed (and reduce the f number from f/10 to f/6.3, and reduce the focal length (from approximately 2000mm to  1400mm), thereby reducing the required exposure time by a factor of 3.  For long exposures I also needed a guide scope and camera to keep the telescope tracking my target objects.

Looks neat doesn't it?



Note the above picture includes the Celestron C8, with 80mm Skywatcher piggybacked on top as a guide scope (without eyepiece or camera attached).  The red cap on the end of the C8 covers the focal reducer and extender - it is here the CCD camera goes.  Just the other side of the focal reducer is the focusser (it was a standard focussing knob, but I replaced it with a feathertouch focuser and stepper motor).  The above picture also does not conain cameras or the plethora of cables requires to power and operate the mount, focussing and cameras. 

First Astrophoto



M3 Globular Cluster - 20 x 60s exposures taken with a C8 SCT. Darks and bias frames, but no flats


It's took me 6 weeks from getting my telescope in late January 2011, and a few weeks later a new QHY8L camera, to produce a reasonable astrophotograph.

During this time, I did a lot of reading about polar alignment, light pollution, exposures, guiding, set up, and all the other skills required for astronomy and astrophotography. I learnt it all from practically zero knowledge beforehand, and it has been a difficult but very rewarding experience.

It was only on Monday 7th March that the skies were clear enough in London for me to take 20 or so images of this globular cluster (M3), which I then processed and stacked in MaximDL.

Even 3 months ago I never would of thought I'd be taking images of globular clusters in the freezing cold March weather. It's an addicitive pastime that has grown on me very quickly.

More about my telescope and setup in the next post, but briefly:
Celestron 8 inch telescope - C8 SCT XLT on CG-5 Mount
f/6.3 reducer / Astronomik CLS-CCD filter / QHY8L camera
20 x 60s stacked in Maxim, curves and levels in Photoshop
Guided on PHD (although possibly not required on such short exposures if my polar alignment was any good!)

The main lesson I have learned, apart from the huge amount of patience required, is that you have to choose your target carefully, and then set up everything for the evening with this in mind.  For the first few nights out I often took few images of very many different objects, and for astrophotography this is absolutely no good, as a lot of data (images) are required to get the desired end result.  Images are processed and stacked to reduce noise and increase signal.