My astrophotography journey continues

Now that I have my own website, I feel that I am always looking for more material to post online – which is great as a motivator for me to do many of the different interests/hobbies that I have. So there should be something which will interest most if not all people. Recently, a few things have happened which have refuelled my interest in astrophotography and spurred further investment of time and money.

The things that have happened recently are following on in a sequential order, with each step making it possible for the next step of improvement in my imaging system. It did take me about a night each to do the various adjustments to the mount after installing it on the pier – with some testing of imaging following the adjustments, to see if the adjustments did improve the imaging process or results.

The steps are:

1) Purchase of the Celestron Starsense Auto-align system, which made using the Celestron CGEM mount so much easier (Link here). Hence I am interested in getting back into the garden to set up my telescope; the 2 star alignment was a real killer for me prior to using the Starsense autoalign, and deterred me from using it.

2) The fact I am happy to use the CGEM again, led to me to install a telescope pier in my garden, which has served to truly stabilise my mount and also provide a more permanent and level area to work around (Link here).

3) With such a stable permanent system, I am able to get my polar alignment as accurate as possible using drift alignment (a one-off investment of time and effort). In fact in declination (DEC), when using my 5mm Reticle eyepiece on my 1600mm Astrotech 8″ Rithchey Chretien telescope I did not notice any movement of the western star El Nath from the vertical line for over 13 minutes; after 13 minutes had gone by, I decided to swap to adjusting the right ascension (RA) instead, which also was good for at least 8 minutes bearing in mind the periodic error. Now I do not need to adjust the polar alignment unless there is noticeable drift in the future.

4) With the polar alignment as close to true as possible and a stable system, I am able to do a batch training of periodic error correction with Celestron PECTOOL on the laptop and get my CGEM’s original +/- 9 arc seconds periodic error curve down to just under +/- 3 arc seconds.

Periodic Error Curve from PECTOOL after batch training
Periodic Error Curve from PECTOOL after batch training

5) With all the benefits afforded by all the changes above, I am able to get unguided 2 minute subs with round stars with my 1600mm telescope and full spectrum Olympus E-PL5 (2x crop factor).  To put things in to perspective, I previously required guiding to even achieve 2 1/2 min subs with my Canon 500D on this telescope. But I do have to accept that there are still a fair few unguided 2 minute subs which need to be discarded, due to suboptimal stars.

6) The next step will be to do auto guiding and get all light frames to have pinpoint stars, and allow for lower ISO imaging.

Workmen blaming their tools:

he Now at this point I do have to say something in defence of the Celestron CGEM mount, which may have been unfairly criticised by many people over the years. Mine was purchased many years ago, and certainly one of the first ones to be shipped after its initial release. It remains fully functional and this despite (or perhaps as a result of) it being left outside through the many years since, albeit covered by the Telegizmo 365 scope cover. As a side-note, I can’t give the Telegizmo scope cover higher praise as it is a great cover and highly recommended as it remains fully functional without any wear or tear despite many years of exposure to the wind, sun, rain and snow.

I suspect that those who have rated the CGEM poorly have at least one of these problems below:

Problem 1: Used the original tripod with their CGEM, which will likely have flexure to a certain extent and affect the stability of their mount/scope ( and perhaps the perceived/recorded periodic error of their mount).

Solution: Pier mount the CGEM to be as stable as possible.

Problem 2: They have moved the CGEM about so much and may have accidentally stripped the gear or adversely affected the moveable parts of the mount.

Solution: Permanently pier mount the CGEM so it is no longer moved about, or at least minimise/take extra care when moving the mount about.

Problem 3: Polar alignment has not been done as accurately as possible (or worsened by Problem 1).

Solution: Pier mount the CGEM to be as stable as possible. Then do the All Star Polar alignment to get it as close as possible, prior to doing the drift alignment. Then the periodic error correction can be trained into the system to reduce the periodic error down to as low as possible.

I am sure there must be a fair few disillusioned CGEM owners out there, who have read over the years about the various faults on astronomy forum about the mount they have spent their precious money on for astrophotography. But take heart, as I hope to show that there are some CGEM out there which still work just fine (like mine), even without Hypertuning the CGEM.

Proof of the pudding:

Now the night I finished doing the drift alignment, I decided to test out the mount by doing 1 minute subs at ISO 3200 and  6400. I managed most frames with round stars. But stacking the images revealed that it had failed to capture much of the details of the deep space objects, which meant I needed to do longer exposures.

The following night, I did the PECTOOL batch training to correct the periodic error as much as possible. Then I tested imaging with 2 minute subs, just to see how well my mount would cope with an exposure of that length when left unguided. Anyway, the following images below were taken using my Olympus E-PL5 shot in RAW, using high ISOs (3200 and 6400) with unguided 2 minute subs. These were then stacked in Deep Sky Stacker (DSS) 3.3.4 and final adjustments done in Capture One Pro 7 to produce the final image.

For M51 it was near zenith when I shot these images. As you can see, the 2 minute subs have managed to capture a fair amount of the detail of M51, particularly with the ISO 6400 subs.

Whirlpool Galaxy M51 ISO 3200 - 7x 2 minute subs stacked in DSS
Whirlpool Galaxy M51 ISO 3200 – 7x 2 minute subs stacked in DSS
Whirlpool Galaxy M51 - 12 x 2 minute subs at ISO 6400 stacked in DSS
Whirlpool Galaxy M51 – 12 x 2 minute subs at ISO 6400 stacked in DSS

But it is when all the images from ISO 3200 and 6400 are combined that much more detail is revealed from M51 without blowing the highlights.

Whirlpool Galaxy M51 - stacked from all images ISO 3200 & 6400 in DSS
Whirlpool Galaxy M51 – stacked from all images ISO 3200 & 6400 in DSS

The images for the Bode’s nebula were 2 minute subs at ISO 6400, with it being towards the North-West not too far from the North Celestial Pole. It was interesting that the stars of every single light frame was pinpoint, and hence all images captured were useable i.e. periodic error was kept easily at bay for each 2 minute sub. I should probably have shot at ISO 3200 as well, to capture the details in the center of the Bode’s nebula better.

Bode's nebula - 2 minute subs at ISO 6400 stacked in DSS
Bode’s nebula M81 – 2 minute subs at ISO 6400 stacked in DSS

In short, I am well chuffed with the capabilities of my imaging system. Now that I have ironed out the stability issue and polar alignment, as well as made it easy to set up and autoalign the mount to the stars, I can envisage more time imaging Deep Space Objects (DSO) than previously.

As it is possible to get images like the ones above unguided on the CGEM, imagine what could be possible when it is guided (and lower ISOs used). I will do a thread about my Lacerta MGEN autoguider when I have the time, as well as the various settings I’ve found which seems to work for me.

Boon