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Froeng

Simple astrophotography...

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Posted (edited)

Hello everyone,

I wanted to share some thoughts and experience regarding astrophotography and its required equipment.

First of all I am mostly a visual observer. As such I have about 30years of experience, although I was not constantly very active during the whole time due to education/work/family reasons. After a few attempts in the late nineties, early 2000s with film and some later DSLR equipment (Olympus E-1, then E-5), I have recently started to pay more attention to astrophotography again. Partly, as my back garden is heavily light polluted (both local from street lamps, as well as generally from the proximity to central London). As a visual telescope I use a mid-80s Celestron C8 on a Vixen Super Polaris DX, both of which have been in my possession from new, together with my Vixen SP60l Fraunhofer refractor, which was my first telescope and was later used as a visual guide scope.

I go with the principle of using what I have already, rather than splurging on new equipment without maxing out my current kit. To cut a long story short, over the last five years I got frustrated with banding in my otherwise (to me at least) excellent Olympus E-5 DSLR. The banding is almost impossible to remove in post-processing, hence after about 5 years of struggling with this camera, I thought about what’s good and what’s bad about it...

The good points I came up with were:

1.       4/3 sensor size is a good match for a C8 with the f6.3 reducer, as almost the entire field is reasonably well illuminated

2.       Liveview and being able to use it with up 14x magnification is brilliant for focussing

3.       MySet preset modes user definable is a big plus in the dark

4.       Ability to blank off the viewfinder to avoid stray light getting in form behind (local lamps)

The bad points:

1.       Noise and more noise (in particular banding)

2.       Quite Heavy

As I had until recently used this camera with manual guiding (using my 60/910mm refractor with a Vixen GA-4), I did not really want to start overcomplicating my setup any further.

So, my thinking was as follows:

1.       What is the simplest setup I can use with my existing equipment?

2.       What is the lightest camera I could use and retain the good points above?

3.       I do not want to have a laptop outside having to fiddle around with IT problems

4.       I don’t want excessive cabling and the associated build up/strip down time

I first started researching some of the ASI cameras and the associated controller, the ASI air. Interestingly the popular ASI 1600 camera uses a 4/3 sized chip and the results are remarkable. But once you start putting an equipment list together, I realised this would be too much of a hazzle and too much money to spend for occasional use. As said above I most of all enjoy visual observing.

Hence I started looking at simpler solutions. Again, I thought about some conditions/requirements that would need to be met.

1.       Ideally I  would not want any guiding – that meant I would have to keep exposure times to a minimum! Fortunately, my mount has an old Boxdoerfer MTS3 controller, which allows PEC training and storing of this data in the controller. From previous tests, I reckoned 1-2mins of exposure time should be possible with polar alignment via the polar scope and with PEC enabled to avoid star trailing. This means I could keep my refractor in the closet for this purpose, ie not having a dedicated imaging setup when I build up the scope, but the exact same setup as for visual!

2.       If I was to stick to a DSLR or similar, I would not need a laptop or some other electronic box with cables, converters, adapters and the like, hence keeping it simple.

3.       To keep the weight down, was also important, so could keep strain on the mount as low as possible, which should improve its performance further.

So, I started looking a different camera types, but like most people I stuck with what I knew already, hence I bought a used Olympus E-PL5 and a fitting m4/3 T adapter, plus a couple of spare batteries – and a simple aftermarket remote cable and that was it.

The camera has a 4/3 sized sensor with 16mp, similar in size to the ASI 1600, so I should be okay with the C8 in terms of image scale and sampling as many images on the web demonstrate. The camera is also incredibly light, it has no viewfinder, but only works with liveview which can be magnified to 14x and it has NO banding and MUCH better noise performance than the older E-5. I am aware a bigger sensor is generally considered “better”, but my my standards described above, this seems to be quite good!

I started with training the PEC as well as I could using a 3x barlow (that is part of the GA-4) with the C8, giving an effective focal length of about 6m(!). You only need to guide for about 8mins on the SP-DX as this is as long as it takes for the worm gear to do a full turn.

Then I thought, let’s start with something bright and easy. So I aimed at one of the bright stars in UMa, used a Bahtinov mask to focus with the Liveview magnifier, then slewed the short distance to M81, and enabled the serial exposure function. This allows a maximum no. of ten exposures, slowest shutter speed of 60sec. And off it went snapping pictures.

First inspection already showed a nice amount of spiral structure appearing on the little screen, so off it went for the next round of 10 exposures. I repeated this for multiple times with the occasionally break for re-focussing , then again over a few nights, added some darks and flats and bias frames and couldn’t believe what I was suddenly able to capture from my light polluted back garden, with hardly any effort!

For post processing I used the free DeepSky Stacker and then Adobe Lightroom, which I already have for general photography.

The results speak for themselves. All of it with no laptop, no cables, no extra battery, no guidescope and hardly any extra setup time.  If I want visual, I just replace the camera with an eyepiece and vice versa. This shows to me even if you are a visual observer, you can make use of those occasions where you don’t have optimal transparency, darkness, etc, by taking some nice images...

The second image below is even shot at f/10!

Some might say, but the stars are not 100% round or the flats are not optimal or the noise is still quite high and these are all valid points. The argument that counts to me however is to not drown in electronics and software and being able to enjoy the simplicity of a visual setup, with the occasional photo being taken when I feel like it. Some food for thought, YMMV...

ps: I have no affiliation with any of the manufacturers or companies mentioned above.

M81_20200420_002.jpg

M51_20200529_003.jpg

Edited by Froeng
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Thanks for that great write up, and very nice results. With your dslr, you don’t need a computer outdoors. Just make sure you have enough fresh batteries when it gets cold, or invest in a mains adapter for your camera. You can also add an intervalometer, to allow more exposures in a series.

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