The ZWO ASI 533mc Pro is a cooled, one-shot colour dedicated astronomy camera. Featuring an extremely sensitive sensor and two-stage cooling. This sub £1000 camera can help take your astrophotography to the next stage.
Taking the step up to a dedicated astronomy camera can be daunting and if you’re looking at getting the ZWO ASI 533mc Pro as your first camera, or maybe second or third, then in this article I’ll be sharing my thoughts and feelings about this cooled one-shot colour astro camera.
The first question people often ask is if you should go Mono or One Shot Colour. I’ve tried both and whilst mono definitely had some upsides, I’ve resorted back to OSC. If nothing else than for the convenience. This camera was graciously loaned to me from First Light Optics for review.
So let’s get into this review!
ZWO are a popular brand of astronomy cameras and most likely have a camera for everyone. The ASI 533mc Pro is more on the entry level side as stated on their website. Nether-the-less, it may be “entry level” but this camera certainly pulls its weight and has a lot to offer the discerning astro imager.
It has two-stage cooling, a very sensitive colour sensor and pixel sizes that allows it to be used in a variety of applications. All of which I’ll delve into soon.
I want to start at the business end of any camera though, and what gives the ASI 533mc Pro its charm and adds to its interest: the square imaging sensor.
The Square Sensor
So as mentioned the 533mc Pro features a square CMOS “ColdMos” sensor. A bit unconventional certainly. It appears most cameras use 3:2 or something similar, whereas this camera is 1:1. So why would you pick a camera with a square sensor? There has to be some advantage, right?
There is. One thing with square images is the ability to crop them into any further aspect ratio you may want. The camera starts at 1:1, but if you want to change to 3:2, or 16:9 and so on – you can.
As you can see, it adds an extra layer of versatility to your photos when you can make it any size that your heart wishes. But this comes at a cost of eating away at your pixels.
The sensor also is very sensitive. Boasting a pretty high quantum efficiency of 80%. This is a fancy way of saying how effective the camera is at using the light it gets. But high efficiencies are never a bad thing and means that you get more bang for your buck with your exposure times and photos. Be it being able to use a shorter exposure, easier narrowband photography or better Signal to Noise Ratio (SNR).
The sensor also boasts nice sized pixels which measure 3.76µm, and a full resolution of 3008 x 3008. The active area of the sensor measures 11.3mm x 11.3mm – despite the claims of a 1″ (25.4mm) diagonal, the actual diagonal section of the sensor is more like 0.6″ (16mm).
The 1″ diagonal is accurate if you measure the clear window, but not the sensor – the bit that’s actually doing the photography!
Imaging With Squares
I thought that getting used to a square sensor would be difficult. At the beginning I spent some time in Stellarium with my telescope and the ASI 533mc Pro selected trying to work out framing and composition. After that, it was actually very easy and simple to get used to.
In fact, I almost feel like the square sensor was easier to compose images with.
I couldn’t find anything written down about the bayer pattern though. So I took an educated guess and rolled with RGGB. This worked well and appears that this camera does indeed have an RGGB bayer pattern.
The 3008 x 3008 images were easy to use and were relatively small and wieldy for stacking and processing. Als0 the size of the sensor means that the image circle of my Sky-Watcher Evostar 80ED covered it perfectly and I saw absolutely no star trails at the edges of my images. Granted I am using the genuine flattener but the small sensor makes this even more forgiving.
The field of view afforded me with more opportunities than I was used to with my 80ED. Being able to fit smaller targets in like the Bubble Nebula and the entire Leo Triplet. Also with a longer instrument I was able to get Venus looking nice, and some good close ups of the Lunar surface.
The camera definitely has a lot of use cases under its belt.
Focal Length Suitability
At 3.76µm pixels this camera is best suited for telescopes between 388mm and 1163mm focal length. Under normal seeing conditions this gives you the best sampling rate.
If you go deeper, you’ll begin to over sample. But this should still be fine for high resolution planetary imaging.
The picture above gives you some real salient points about this camera. However, there are some things that need clarification. Since I’m still talking about the sensor, I’ll start there.
Read Noise & Full Well Depth
So the ASI 533mc Pro boasts low read noise of 1.0 electron and full wells of 50000 electrons. These seem really attractive.
As a sidebar – read noise is a measure of grain and noise that every picture will have (lower is better), and full wells is basically how much light each pixel can take before its full and becomes white.
However it shouldn’t be taken at face value. To get access to the super low read noise or the deep full wells you need to be at completely opposite ends of the gain values!
Let’s look at the performance charts and we’ll see why. (Be sure to click to see a larger view).
Okay, so the chart on the left is from ZWO and the one on the right are measurements I took.
On the top row where it says Full Wells, the 50k depth is right at gain 0. So if you want those deepest wells you need to shoot there. Gain can be likened to sensitivity of the camera, so you’ll have the lowest sensitivity selected and you’d need to overcome that with exposure time.
To get to 1 electron read noise, notice it’s all the way at gain 500 (which is the maximum for this camera). So you’d be losing all your full well depth and dynamic range and other things.
Finding a gain setting somewhere between these two numbers that suits your requirements and that your equipment can handle is the challenge. When I was using the 533mc Pro I initially chose gain 95, and then I used gain 110 also. Both worked quite well. If you’re planning on taking really long exposures with this camera though, I’d recommend using a lower gain for those deeper wells.
Downsides To The Sensor
During my time with this camera I found some areas that didn’t sit right with me. A camera is judged by its sensor, so I’m going to start there.
The ASI 533mc Pro’s 9 megapixel sensor, which is plenty for web images, is a little on the short side for my taste. Considering the camera “below” this in ZWO’s range (the 183 sensor) has a crazy 21 megapixels on a similar sized sensor (13.2mm x 8.8mm, but it does have smaller pixels). You can make and crop your 1080p full HD images.
But I enjoy being able to print my photos. And with the 3008 x 3008 resolution, you and me will be limited to 10″ x 10″ prints. Before any cropping.
If you’ve studied the graphs above, you’ll also have noticed how the Full Well drops of very quickly. This is another reason why I suggest using low gains if you’re all about them really long exposures. But going from 0 gain to 100 gain (which is unity) nets you a loss of 68% of the total well depth!
In order to use the two-stage cooling on this camera, you need to use an external power source. A centre-tip positive DC power cable is required. Required, but not supplied. I don’t understand why ZWO don’t put power cables in their boxes and it really bothers me.
The camera can function without a power lead (though mine never would download images from the camera for some reason). But since you’re looking at the Pro version of the camera (even though the 533mc doesn’t have a non-pro version). I assume you’re interested in cooling the camera.
So using an external power source that either runs from the
mains, or battery power. Or alternatively
using the new ZWO ASI Air Pro can power the chiller on this camera. Enabling you to take full advantage of that ColdMos sensor!
Speaking of cooling the camera. The fact this is a ColdMos camera and has two-stage cooling means you can really chill that sensor and get cleaner images.
From looking at the chart, the best gains are to be had between 0° and -5° Celsius. As well as -10° and -15°c.
I ran the ASI 533mc Pro at -15°c and found that to give some very nice and clean images. I feel like going colder would yield not much in the way of cleaner pictures. There’s also a limit to worthwhile cooling determined by your read noise as well as your light pollution anyway. I have a video from Dr Glover (of Sharpcap) on camera cooling.
Video mode, or more like planetary mode. This camera can be used not only for Deep Sky Objects but handles Solar System work quite well also.
I used this camera alongside SharpCap Pro to take some Lunar photos. I teamed it with my Sky-Watcher Evostar 80ED. As well as a Sky-Watcher SkyMax 180 Mak. In both cases the ASI 533mc Pro worked really well, supplying me some very nice final images.
I did use it on Venus, but due to my own idiocy, I managed to delete those files! (doh!).
When shooting the Moon, I found using a lower gain setting in order to keep those wells and dynamic range to be advantageous. I used gain 60 and controlled the rest via the exposure time. I used 150-300ms to capture these images.
Dynamic Range is what you’ll be wanting when imaging the Moon. So gains 0-60 or 100-120 is what I’d recommend using for Lunar photography. Especially if you’re wanting to capture it during its crescent stage.
ZWO says the ASI 533mc Pro can get 20 frames per second in video mode. Great, right? Well like the full well and read noise we need to look a bit deeper. When I was imaging the Lunar photos, I was using USB3 with Sharpcap. At the RAW 14bit depth and 3008 x 3008 resolution I was getting about 1-2 frames per second.
This is simply down to transfer speeds I think. Whilst the camera has a 256mb frame buffer built into it, there’s a limit to how fast you can transfer video.
In order to get closer to the advertised FPS, you’ll need to down the sensor to 8-bit mono, or use ROI (Region of Interest) to use a smaller part of the sensor. This allows for smaller file sizes and faster transfer rates. I used this in mono mode at half resolution and was getting about 10 frames per second instead. Much faster.
No review of a camera would be complete without showing you the images I’ve captured with it. I used this not only in broadband mode with a Skytech L-Pro Max filter, but also in narrowband using an Optolong L-eNhance multi-bandpass filter.
All in all, this camera has served me very well during my time with it. It has proven itself a very effective and capable DSO camera as well as working well on Lunar photography as well. It finds itself slap bang between two big names. The ZWO ASI 183mc Pro and the ZWO ASI 294mc Pro. Both are very popular cameras and the ZWO ASI 533mc Pro slots perfectly in the middle.
The price reflects that as well. The ASI 533mc pro is cheaper than the 294mc pro and more expensive than the 183mc Pro.
At the time of this review the camera costs £856.
I feel that if you’re torn between a DSO camera and a high resolution planetary camera, then the ASI 533mc Pro will have you covered. It’s very versatile and can cater for a variety of focal lengths. Even more so if you’re using it for planetary.
Whilst I would like to have seen more mega pixels and there’s a couple of other
bits mentioned I dislike. I can also happily recommend this camera to people. It’s effective, efficient and fun to use. I felt the square sensor would take more getting used to, but after a couple nights it was straight forward. In fact I almost feel like the square sensor makes framing and composition that much easier.
I feel this camera will do you right.
If you’re interested in buying the ZWO ASI 533mc Pro: http://bit.ly/2GjkzTD