ZWO ASI 533mc Pro Review

In fact I almost feel like the square sensor makes framing and composition that much easier.

The ZWO ASI 533mc Pro Is a cooled, one-shot colour dedicated astronomy camera. Featuring an extremely sensitive sensor and two-stage cooling. This camera costs just over £1000 and can help take your astrophotography to the next level.

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 your second or third, this article is for you. Within I’ll be sharing my thoughts and feelings about this cooled one-shot colour astronomy camera.

So let’s get going!

The first question people often ask is if you should go mono or one-shot colour (OSC). I’ve tried both – in fact you can find my review for the ZWO ASI 533mm Pro on my website also. Whilst mono certainly has its place and its advantages, you can’t beat the convenience of an OSC. Especially when you have uncertain skies like I do in the United Kingdom. This camera was graciously loaned to me from First Light Optics for review.

ZWO ASI 533mc Pro Review

ZWO are a popular brand of astronomy gear manufacturer. From cameras to filters, mounts and computers they have a lot. Their ASI lineup also most likely has a camera for everyone. The ZWO ASI 533mc Pro is more on the entry level side as stated on their website. However even if they call it “entry level”, the performance this camera produces is anything but entry level. Being able to pull its weight and offer a lot to the discerning astrophotographer.

The ‘Pro’ part of the camera’s title refers to the fact that this is a cooled dedicated astronomy camera. Featuring two-stage PEC cooling. It also has a very sensitive colour sensor and pixel sizes that allow the camera to match a variety of applications. All of which I’ll delve into soon.

The ASI 533mc Pro finished in ZWO's signature red
The ASI 533mc Pro finished in ZWO’s signature red

Though to begin with, I want to start with the business end of any camera, and what gives the ZWO ASI 533mc Pro its charm and adds to the interest: the square imaging sensor.

That Square Sensor

As mentioned above: the ZWO ASI 533mc Pro features a square CMOS sensor created by Sony. Affectionally known as a “ColdMOS” due to the cooling. A bit unconventional certainly as a lot of cameras on the market use 3:2 aspect ratio sensors. Whereas this camera has a 1:1 aspect ratio. So why would you pick this camera, with the square Sony IMX533 sensor in it? There must be some advantage, right?

There is! One major advantage with square sensors is the ability and flexibility to crop into any further aspect ratio that 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.

Top Left to Bottom Right – 1:1 ratio, 3:2 ratio, 16:9 ratio and 10:8 ratios

As you can see this adds an extra layer of versatility to your photos when you can make it any size your heart wishes. The downside of this though is you pay with the pixels. As you crop into different aspect ratios it eats into your image’s pixel resolution. If you have enough data you can try to negate this by performing a 2×2 drizzle.

Sensor Size & Sensitivity

The sensor is very sensitive as I’ve already alluded to. Boasting a pretty high quantum efficiency of 80%. Quantum efficiency being a fancy way of saying how well a sensor uses the gathered light. Higher efficiencies are, logically, better. As it means you get more bang for your buck with your exposure time and photos. This means you can use shorter exposure times, or a better result with narrowband filters on a colour camera and generally better Signal to Noise ratios (SNR).

The sensor also boasts nice sized pixels which measure 3.76um and a full pixel resolution of 3008×3008. The active area of the sensor measures 11.3mm x 11.3mm. Giving a diagonal measurement of 15.99mm or 0.6″. Despite the described diagonal of 1″.

The 1″ diagonal is accurate if you measure across the clear window. But it doesn’t relate to the sensor’s diagonal – the bit that’s actually doing the photography!

One thing to note is that the sensor size on the ZWO ASI 533mc Pro gives this camera a 2.7x Crop Factor. This means that if your telescope is 1000mm, then you’d actually see an equivalent field of view of a 2700mm instrument. Just bare this in mind when selecting a telescope to pair this camera with!

Illustrating the sensor size of the ZWO ASI 533mc Pro
The square sensor measures 11.3mm by 11.3mm

Imaging With Squares

I thought getting used to a square sensor would be difficult. At the beginning I spent some time in Stellarium. Using my telescope and the ZWO ASI 533mc Pro selected I experimented with framing and composition. After that bit of research it was actually very easy and simple to get used to.

In fact I almost felt like the square sensor was easier to compose images with.

I couldn’t find any information about the bayer pattern of this camera though. I took an educated guess and rolled with RGGB. The results of stacking within Deep Sky Stacker would end up confirming this camera does have an RGGB bayer.

The 3008 x 3008 pixel images were easy to use and the file sizes were relatively small. Weighing in at 17.6 megabytes a file. This means stacking also wouldn’t ruin my laptop even when stacking large sets of data.

Also the sensor size meant the image circle of my Sky-Watcher Evostar 80ED covered it perfectly and I saw absolutely no star trails, coma or field rotation at the edges of my images. Granted I was using the genuine reducer/flattener for my telescope, but the small sensor certainly makes this even more forgiving as it uses only the central very best glass.

The field of view gave me many more opportunities to image than I was used to with the 80ED. The ZWO ASI 533mc let me fit much smaller targets in such as the Bubble Nebula and the entire Leo Triplet. Previously with my DSLR I would never have been able to get a field of view that permitted this.

Also with a longer instrument – the Sky-Watcher SkyMax 180 Maksutov-Cassegrain, I was able to get some nice views of Venus and some great close up images of the Lunar surface.

This camera definitely has a lot of use cases under its belt!

Focal Length Suitability

At 3.76um 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 before you hit under/over sampling issues. Whilst not always the end of the world, it is best practice to stay within a well sampled region.

Over-sampling however – where you use a longer focal length – is best suited for Lunar, Solar or Planetary high resolution imaging.

Let’s quickly talk about some examples of what you may see with this camera at different focal lengths before moving onto more technical specs of the sensor.

400mm

At 400mm focal length you could see targets such as NGC 2244 The Rosette Nebula and M33 the Triangulum galaxy. These round, circular targets really lend themselves well to the square image format!

600mm

600mm gives you nice framing on targets like IC 410 the Tadpoles Nebula and M16 the Eagle Nebula

IC410 – not taken with the ASI 533mc Pro (illustrative purpose only)

750mm

Using the ZWO ASI 533mc Pro at 750mm gives you a wonderful opportunity to capture the entire Lunar and Solar discs, as well as targets like the Helix Nebula

The Moon with the ZWO ASI 533mc Pro and the Sky-Watcher Evostar 80ED

1000mm

Finally 1000mm will give you nice framing on beautiful galaxies, and visually smaller nebulae such as M20 – The Trifid Nebula as well as The Crescent Nebula

M20 – Trifid Nebula taken from Stellarium

Read Noise & Full Well Depth

ZWO ASI 533mc Pro Specifications from ZWO’s website

The picture above gives some real salient points about this camera. You can click it to see a larger image. However, there are some things to talk further about and as I’m still going on about the sensor, I’ll carry on with that.

The ZWO ASI 533mc Pro boasts a low read noise of 1 electron and full wells of 50000 electrons. These numbers seem really attractive, but to get the full picture we need to look a bit closer. Particularly at the published charts. To get access to those super low read noises, or the deepest full wells, you have to be at complete opposite ends of gain value!

As a sidebar – read noise is a measure of graininess that every picture will have. The lower this number the better. Full well describes how much light each pixel can take before it’s saturated and becomes just white date. Higher is better here.

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).

Sensor specs: Left is from ZWO, right is my measurements. Click for full size

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.

The full sensor analysis can be found on this chart.

Demonstrating the Sensor Analysis of the ZWO ASI 533mc Pro using SharpCap
ZWO ASI 533mc Pro Sensor Analysis from SharpCap

Drawbacks To The ZWO ASI 533mc Pro

During my time with this camera, I of course 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 is the ZWO ASI 183. That camera has a crazy 21 megapixels and a similar sized sensor (13.2mm x 8.8mm, but it does have smaller pixels). Once you put both against each other, you realise the ZWO ASI 533mc Pro really could benefit from more pixels.

I enjoy being able to print my photos. Unfortunately with the 3008 x 3008px resolution, 10″ x 10″ prints (25cm x 25cm) are the best you can get at 300DPI. But if you decide to then crop in, or worse yet change the aspect ratio as mentioned above, you’ll lose even more pixels. One way to mitigate this is to perform a drizzle to the image. A 2x drizzle will increase the resolution to 6016 x 6016px but if you don’t have a lot of high quality data, it will magnify the noise in the image.

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. Going from 0 gain to 100 gain (which is unity) nets you a loss of 68% of the total well depth!

Full Well loss going from 0 gain to Unity gain (100) on ZWO ASI 533mc Pro
Full Well loss going from 0 gain to Unity gain (100)

Powering The ZWO ASI 533mc Pro

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 understand why ZWO don’t supply cables with their cameras – it’s a localisation issue where they’d have to package each box individually for each country they sell to. But other manufacturers do. It bothers me even though I understand the rationale.

The camera can function without a power lead, though mine never would download images from the camera for some reason. You can get a ZWO ASI 533mc uncooled camera which would circumvent this problem. But we’re talking about the Pro version of the camera.

So an external power source will be required. There are various options available these days. You can use a mains power plug such as the Lynx Astro 12v DC power supply which is the same that I’ve used in the past to power ZWO ASI cameras as well as mounts. You could also use a deep cycle battery but be mindful that the cooling will drain the battery faster. Or finally you can use the ZWO ASI Air Plus and Pro to power the camera, which is what I do these days.

An external power plug can be used to power the ZWO ASI 533mc Pro

Cooling

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.

ZWO ASI 533mc Pro Cooling Chart from ZWO

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. Bare in mind also that the harder you cool the camera the more it’ll drain battery power if you’re using batteries to cool the camera. Also the more susceptible you will be to dewing issues, even though the camera has an anti-dew heater on it.

Video Mode On The ZWO ASI 533mc Pro

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.

ZWO ASI 533mc Pro and Sky-Watcher Skymax 180 in Video Mode

I really could’ve improved the image with the Skymax 180 by nailing the collimation of the instrument. I really liked the tight close up details that the ZWO ASI 533mc Pro and the Skymax gave me. I’ve never really had a setup to be so tight like that and the resolution to resolve sharp details on the lunar surface.

Though when I shot the full disc with the ZWO ASI 533mc Pro and the Sky-Watcher Evostar 80ED I didn’t have to worry about the collimation, thanks to it being a refracting telescope!

Image of the Moon with the ZWO ASI 533mc Pro
ZWO ASI 533mc Pro and Sky-Watcher Evostar 80ED

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.

Video Framerate

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. Now this can also be impacted by your computer’s hardware also, and that may be what happened with me.

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.

Sample Images

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. You can click any of the images to see a larger version.

Leo Triplet shot with the ZWO ASI 533mc Pro
The Leo Triplet
Bubble Nebula with the ZWO ASI 533mc Pro, Sky-Watcher Evostar 80ED and Optolong L-eNhance
Bubble Nebula with the ZWO ASI 533mc Pro, Sky-Watcher Evostar 80ED and Optolong L-eNhance
The Rosette Nebula NGC 2244 from the ZWO ASI 533mc Pro, L-eNhance and no dark frames
The Rosette Nebula NGC 2244 from the ZWO ASI 533mc Pro, L-eNhance and no dark frames
M81 & M82 in HaRGB shot with the ZWO ASI 533mc Pro
M81 & M82 in HaRGB shot with the ZWO ASI 533mc Pro

Summary

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 ZWO ASI 533mc pro is cheaper than the ZWO ASI 294mc pro, and more expensive than the ZWO ASI 183mc Pro.

At the time of the original review the camera costs £856. During this update the camera now costs £1022. It’s unfortunate the price has increased, but so has everything lately.

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 are a couple of other bits mentioned I dislike. I can also happily recommend this camera to you. It’s effective, efficient and fun to use. I thought 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.

Video Review

If you’re interested in watching my video review of the ZWO ASI 533mc Pro on YouTube, you can find it here:

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