ZWO recently surprised everyone by announcing a camera no one thought would arrive. A new micro 4/3 sensor based mono camera called the ZWO ASI294MM-Pro. This camera is based off the similar color sensor camera ZWO ASI294MC-Pro. In this review, I’ll cover what’s new, what’s better, and what could have been as I compare and contrast it with its predecessor the ZWO ASI1600MM-Pro.
What’s new, and what’s better…
This camera uses a newer generation Sony IMX492 sensor. This sensor is actually a single generation behind ZWO’s other newest cameras the ASI6200MM-Pro, and the ASI2600MC-Pro, but it’s at least 5 generations newer than what was released in the ZWO ASI1600MM-Pro camera. So, what can you get with five generations of change?
A larger 4/3 sensor (by a few mm) 19.1 x 13 mm
Resolution of 4144 x 2822
14bit ADC
Full Well capacity 66ke
QE around 90%
Pixel Size 4.63um
AR/UV sensor window
See the update at the bottom of this article showing a new mode of operation with this camera that can now offer 8192 x 5556 px resolution with 2.314 um pixels at a cost of slightly lower 12 bit-depth color.
So, what do these specs mean, and how are they improved over the ASI1600? To start, the slightly larger sensor means you can see just a bit more in your field of view. The resolution is actually slightly lower by a touch, but mainly because the pixel size is larger. Larger pixels typically offer better light gathering capability and a better degree/pixel ratio on your telescope, helping to keep those images sharp even during moderate seeing. 14bit ADC is going to give you two more stops of bit-depth. This is better color fidelity for a given area of imaging on the histogram. You’ll capture more color than you could on the 1600. The full well capacity has increased to 66ke from 20ke on the 1600. This means you can image longer subs without saturating the pixels of extremely bright areas (specifically stars). And the QE of 90% compared to 60% means that in a single image, you’ll capture and retain 90% of the total light that comes across the sensor, where on the 1600 you would only capture 60%. So, given the same integration time on a given DSO image, the ASI294 will gather 30% more light than the ASI1600.
A few issues.
One thing I noticed right away when comparing to the ZWO ASI1600 camera is that the sensor itself on the ASI294 has some mottling over the sensor. I’m not sure what has caused this. Surely, it’s part of the manufacturing process. While the photo shows some minor mottling on the 1600 sensor (TOP), this can’t be seen well with your eyes, as it appears smooth. The 294 sensor has some clear discoloration visible (BOTTOM) that you can see with your eyes, and is clearly visible in the photo.
ZWO ASI1600MM-Pro sensor at the top, and ZWO ASI294MM-Pro at the bottom.
Unfortunately, this appears in your flats AND images. While worrying, it 100% corrects out of all your images, but flats will be necessary to do this. I set my flat ADU value to 32,000 ADU, and every frame perfectly corrects out. Interestingly, this only appears on narrowband filters like HA and SII, but in OIII and LRGB it’s absent.
Luminance flat on the left, and HA flat on the right for the ASI294MM-Pro.
What could have been…
Unfortunately, ZWO has opted to maintain the existing form factor without any real change. The down side of this, is that there’s no built in tilt adjuster like this camera’s bigger brothers. It only uses the original OAG and filter wheel that’s been out for years. This would have been an ideal time to update this form factor, along with the OAG and filter wheel to have bolt on options that keep the parts well aligned and minimize tilt from the poor connection method used in these devices. An improvement similar to the ZWO 2” filter wheel and M68 OAG would have been welcome.
All is not lost though. This makes the upgrade path very straight forward if you have an ASI1600 that you’re ready to upgrade. The one benefit of this camera using the older style filter wheel and OAG, is that if you currently own them for your 1600, they can be used here as well. This definitely keeps the costs down, and makes upgrading an easier choice. This camera is really the spiritual successor to the ASI1600, and is better than it in every respectable way.
So, how does the ZWO ASI294MM-Pro perform?
I decided to pair this camera with my Celestron EdgeHD 11” telescope and .7x reducer. This puts me at a small, but still respectable pixel scale of .49”/pixel. This is really pushing the limits of my system under moderate seeing conditions. Images have been turning out on the softer side, and I think I prefer using the ASI6200MM-Pro set to Bin 2x2 to achieve a .79”/pixel scale, which results in crisp, sharp images. On telescopes with a shorter focal length, you can expect even better results with the ASI294, and I plan on trying it on my Sky-Watcher Esprit 100 in the near future.
My first target is something I’ve been wanting to image for some time. The core of the Heart Nebula. It’s really a wonderful area with a contrasting blue background that makes the center nebulosity really pop.
With my first image squared away, I took a small break to image with the ZWO ASI6200MM-Pro on my Sky-Watcher Esprit 100. Eventually I made my way back this week, and snapped a few more images.
The moon at dawn. I snapped this real quick about 6:00am one morning when I got up to shoot some flats for the nights imaging session. This was a single L R G B set of frames stuck together with no processing. It has a very nice low contrast yet detailed look.
The Blue Snowball planetary nebula, NGC 7662.
The Heart of the Soul, IC 1871. 10.3 hours exposure with the Edge HD 11” and ZWO ASI294MM-Pro.
NGC 7331. Just 6 hours of exposure from a bortle 7/8 zone.
I’m very happy with the results of this camera. All these images were taken from my back yard in Pearland Texas. Bortle 7/8 skies. Finally the gallery below shows a few images I took with this camera and my Sky Watcher Esprit 100 telescope.
UPDATE: New camera mode now available
When this camera was released, and ZWO revealed it would use the Sony IMX492 sensor, users looked to the Sony website for details on this image sensor, and revealed that it can operate in a sub pixel mode with 2.315 um pixels, offering 8192x5556 pixel resolution with a cost of lower bit rate at 12-bit color. Many were left wondering why the sensor was locked at 4.62 um pixel size with only 4144x2822 resolution at 14 bits per pixel color. While the latter mode does provide better color depth and larger pixels which are more suitable for a larger range of telescope sizes, ZWO “unlocked” this new mode through an updated driver. Many new users to the hobby have smaller refractor telescopes, and this new mode is very suitable for those telescopes with the smaller pixel size. The bit depth difference can be become a non-issue through the stacking process which naturally adds all the pixel color variations on top of each other thus increasing the bit depth for the final image.
What ZWO has provided now, is a very versatile camera. You can operate in Bin 1x1 mode with the smaller pixels and large resolution of 8192x5556 at 12-bit color, or you can operate in Bin 2x2 mode the larger pixels at 4144x2822 and 14-bit depth color. Because the pixels are so small in the 1x1 mode you may or may not see an improvement in your image resolution due to seeing effects of the atmosphere slightly blurring your image. But in very good seeing, you should be able to fully realize the potential of this camera. Or if you live in an area with moderate seeing and high humidity like myself, you may find the Bin 2x2 mode is the best option. But now you have a choice.
Over the last 4 nights, I tried out this new Bin 1x1 mode of the camera while shooting the Jellyfish Nebula IC 443. I think the results were great. See the full resolution image at my Astrobin page here.
The Jellyfish Nebula, shot with the ZWO ASI294MM-Pro with the new Bin 1x1 mode 8192x5556 px resolution on a Sky Watcher Esprit 100..
Some more recent images taken with this camera:
