We need to rethink how we take sub-exposure with a CMOS camera. Here is why.
We have seen the introduction of CMOS technology over the past year, which has entered the Astronomy field.
Beforehand CMOS technology was limited to 8-bit, then grew to 12-bit and now is 16-bit. What does this mean?
An 8-bit camera only allows you to capture 256 levels of light, and now with 16-bit, you have 65,536 levels, which allows you to capture very faint objects, which is needed for astronomy. This had been previously the exclusive advantage of CCD sensors.
Depending on the sensor, CMOS cameras also have a low noise profile, between 2 and 5 times lower than a CCD. Why should I worry about noise? This means you can capture more light in less time.
A good example is if you have a CCD, you might need a 600 to 300-second sub-exposure to get enough light into the camera to see the deep space object. However, with a CMOS sensor, you can get the same amount of signal between 60 to 180 seconds.
Additionally, if setup correctly, e.g. the GAIN and OFFSET levels of the CMOS sensor (our job), you can capture far more star light into the CMOS sensor vs a CCD. Sometimes, the CMOS sensor can be 20% to 80% more efficient.
It is far better to shoot shorter sub-exposure times and align and stack your images, producing a far better outcome. WHY?
- Telescopes have to track for a given exposure time, the less tracking they need to do, the less chance of error (non-round stars), which can be caused by wind, misalignment, gear errors, moments of bad seeing, satellite tracks, etc.
- Sometimes, you can eliminate auto-guiding. Making things less complex always yields a better result, as you don't have to worry about those tracking errors in point 1.
- In post-processing, you have more sub-exposure, you can eliminate ones with bad seeing, poor tracking and satellite tracks.
If you are working on a telescope with a CMOS sensor and wideband filters (LRGB or VBRI) or a single shot colour camera, we strongly suggest you try shorter exposure times of 60 to 180 seconds. This should yield optimal results in most cases.
If you are working with narrowband filters (Ha, SII and OIII), we recommend 180 to 300 seconds as these filters let in far less light.
As of August 2022, the following telescopes have CMOS sensors: T02, T68, T69, T18, T70, T71 and T80
Please visit our main website for telescope information or the following support websites:
Here is a single sub-exposure from T02, a single-shot colour camera with a 120-second sub-exposure. If you stack a few of these together, you will have an amazing image.
Please join our webinars if you want to learn how to process images. https://www.itelescope.net/webinar