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So many cameras from so many different brands. Reflex camera or dedicated for astrophotography, sensor type, pixel size, resolution, full well capacity. How to select the right camera for your telescope?
This article tries to answer the most frequent questions for deep sky astrophography.
Camera type
Camera type
Digital camera or dedicated one? Here is just a short comparison between the 3 main types
Digital camera
Digital camera
Daily use and astrophography
Manual and remote control
Screen available
Low to medium thermal noise
RGB Bayer filter
Longer back focus
Medium to high price
Wireless
Uncooled camera
Uncooled camera
Moon, planets, guider, allsky
Remote control
No screen
Low thermal noise
RGB or monochrome
Short back focus
Lower price
Usually not wireless
Cooled camera
Cooled camera
Deep sky, faint objects
Remote control
No screen
Very low thermal noise
RGB or monochrome
Short back focus
High to very high price
Usually not wireless
Digital camera of dedicated for astrophotography?
Digital camera of dedicated for astrophotography?
The main advantage of a digital camera is its portability and its ability to take "normal" pictures. We used high quality digital cameras during our first 5 years of astrophography mainly because we still did a lot of "regular" photography, and invested significantly in camera bodies and lenses.
Let's be honest: smart phone cameras are so good today, that 90% of our pictures are made with them. Therefore, it was less important to have a good digital camera, leaving more budget for astrophotography. This is the time we decided to purchase our first cooled camera, a ZWO ASI 1600MM we still have today.
Though, our digital cameras are sometimes used for a portable setup mounted on a Star Adventurer, and it still makes fun, but we use them in rare occasions.
Color or monochrom?
Color or monochrom?
Bayer filter
It depends on the application!
We use a monochrome camera for our main 200mm Newtonian telescope, since we mostly do narrow band pictures. The guiding camera and the indoor allsky cameras are also monochrome, in order to keep the exposure at short as possible.
Today, the only RGB camera is the outdoor allsky, mostly because it's fun to see the dusk and dawn colors, but also because it gives an indication about the light pollution. We noticed that the sky turns orange when there is lots of sand or pollen in the air. During humid of foggy nights, the western horizon tends to become reddish, due to the lights of the hospital located 1km away. When a storm approaches, the clouds take on a yellow tint.
My children also like to observe the red and green flashing lights of aeroplanes :-)
Wifi and screen?
Wifi and screen?
If you have a mobile setup and you are permanently monitoring the camera, a WIFI camera is nice. Less cables, and therefore less chance to have guiding problems due to cable snagging. Oh and... less chance to forget the cables at home :-)
However, we always prefer wired solutions for unmanned astrophotography. Provided that you have high-quality shielded cables, it is a very reliable solution.
The same logic applies to the screen. It's a very convenient feature for mobile astrophotography (especially during the focus) but almost useless in an observatory. The light disturbance of a lit screen may also have a negative effect on long exposures.
ZWO ASI 2600 MC Air Wireless
You said Backfocus?
You said Backfocus?
As you may know, the backfocus is the distance between the back of an optical train (including coma corrector) and the image plane (sensor). In our case, the back focus distance is reasonably long: 55mm. This distance is sufficient to accommodate different items such as a filter wheel and a manual rotator.
Filter wheel, rotators, camera and their adapters consume backfocus distance. Therefore, the shorter the "consumed" cameras backfocus is, the more space it leaves for the other items.
In the example below, 55mm of backfocus leaves enough space for the filter wheel, but it would be too short for a rotator with a 20mm thickness rotator.
Pixel and sensor size
Pixel and sensor size
As shown below, 800mm focal length and 3,76um pixel size correspond to 0.97 arcsec/pixel. This value is ideal for good seeing conditions (FWHM between 1 and 2 arcsec) which corresponds to 0.33 to 1 arcsec / pixel.
A too large pixel size leads to undersampling, and too small pixel size leads to oversampling.
Of course, oversampling is less critical, but be careful with too high sensor resolutions: Stacking 200 files of 100MB each may or may not be a pleasant experience for your computer.
https://astronomy.tools/calculators/ccd_suitability
Camera driver
Camera driver
Rarely mentioned in forums, the driver's reliability is a fundamental criteria, even more if you run a remote observatory. We learnt this the hard way.
In 2015, we purchased a ToupTek guider camera. The camera was perfectly working... when it was working. For no obvious reason, we regularly lost several frames, and sometimes even the driver's communication, leading to a crash of the entire session. Usually, the system collapsed just a few moment after we went to the warm room and we lost several hours of imaging.
Is is possible that the drive is of better quality meanwhile but psychologically, we couldn't purchase any of those cameras anymore.
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