My last post about my adventure with Astrophotography suggested that I might be able to get my first pic in the last week but that never happened. The moon in all its glory and a thunderstorm stopped that. I have to be able to find the South Celestial Pole (CSP) as it is used to do polar alignment and, well, frankly, that is hard to do. I should say almost impossible with the naked eye using the Star Adventurer’s eye piece when there is any light around. Some people have offered suggestions and the best way of doing polar alignment was mentioned in the last post where you use a camera, a guide scope and SharpCap. Easy, eh? Well, there are about as many options for picking the right camera and guide scope as there are days in the year and if you want quality, you pay for it big time.
The simplest method (perhaps I should say the best value) costs about $400 AUD. I looked at a ZWO camera called ASI120MC-S for about $250. The maths then come into the equation. What would I use this camera for? A guidescope to help me find the CSP. Then what? Take pictures? What of? That last question is the tricky one. I want to have a go at Deep Sky Imaging (DSI). It seems that this particular camera is good for planetary imaging and quite reasonable for solar/lunar imaging. But the camera is very average when it comes to DSI. The important thing is that DSI requires large sensors and interestingly, large pixels. My choice has neither. It has a sensor diagonal size of 6.09 mm and a pixel size of 3.75 microns. The Sensor Dimensions (pixels) are 1280×960. My choice seems to work well for imaging planets and small deep-sky objects.
So what should I buy? Should I start small and grow later? How long is a piece of string? Let’s say money was no object and I chose the ASI128MC-PRO. The name is not all that different to my ASI120MC-S right? It has a sensor diagonal size of 43.3 (versus 6.09 mm) and a pixel size of 5.97 mm. The Sensor Dimensions
(pixels) are 6032×4032. There would be no change for $6400 AUD.
It would be a shame if I didn’t like it right? I have seen a second hand camera (but still in the box) ZWO ASI224MC for $300 AUD plus postage (retail is $379 and no postage). It has the same fundamentals as the ASI120MC-S but it has a slightly bigger Sensor Dimensions (pixels) of 1304×976. It also has a Sony IMX224 sensor. Some forum contributors have not been all that kind to this camera but there are some nasty ill tempered people out there who just like to disagree with everyone. I think that if I realise its limitations as an entry level camera, I shouldn’t be too upset if it has less than stellar (pun intended) performance.
Some one suggested I look at the QHYCCD cameras especially the QHY5II-C. It’s specs are pretty much the same as the ASI224MC. Pixel size is 3.75um, resolution is 1280*960. The optical format is 6 mm which I expect is the sensor diagonal size mentioned with the ZWO cameras. It gets a bit more complex as it talks about quantum efficiency and it is around 74. The ZWO 224 has a TBD in its measurement of quantum efficiency. High Quantum Efficiency means that the sensor is more efficient at turning incoming light into an electrical signal = % of photons converted to light information. If you believe all the scientific marketing information, the ZWO would be in the 75% or higher range. Again, that same marketing suggests the ZWO 224 is very suitable for planetary astronomy and also for small DSO imaging.
There is no doubt that a quantum efficiency of 100% provides a very clear image and 60%, well, its pretty bad. So settling for 75 to 80% offers an image that could be better but the price might be ok. Again, its all about the money.
ZWO push the fact that these cameras probably work better with lots of smaller exposure subs than longer exposure mainly to do with the low noise they seem capable of capturing at low exposure times.
Let’s see where this leads us. My advice to myself is to start small and then see what happens. I can easily spend heaps and not be excited with the results.
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