RASA 11 vs C11HD - Galaxy Season - Forums

Topic starter

Jan 31, 2023 · Edited: Jan 31, 2023

=Y2IQFcHello everyone!
Now, during the galaxy season, I was wondering what the difference is, in terms of quality, between taking pictures with RASA11+ASI294mm, resolution 0.77"/pixel vs C11HD-f/7+ASI6200mm bin2x2, resolution 0.79"/pixel.
As an advantage, obviously RASA is 10 times faster than C11HD@f/7, that's why I wonder if the more important focal length for C11HD adds value to a picture? Thanks in advance

RASA 11-M106: https://www.astrobin.com/ftbr73/D/
C11Edge-M106: https://www.astrobin.com/m6mjzc/B/

andrea tasselli

Frequent contributor

Jan 31, 2023

On the balance I'd say the RASA might have the edge as the overall noise profile should be lower.

alexbb

Jan 31, 2023

Adrian Criss:
=Y2IQFcHello everyone!
Now, during the galaxy season, I was wondering what the difference is, in terms of quality, between taking pictures with RASA11+ASI294mm, resolution 0.77"/pixel vs C11HD-f/7+ASI6200mm bin2x2, resolution 0.79"/pixel.
As an advantage, obviously RASA is 10 times faster than C11HD@f/7, that's why I wonder if the more important focal length for C11HD adds value to a picture? Thanks in advance

RASA 11-M106: https://www.astrobin.com/ftbr73/D/
C11Edge-M106: https://www.astrobin.com/m6mjzc/B/

A telescope is faster than another when it has more aperture than the other, but both have the same focal length.
Reducing a system doesn't make it faster, it just reduces focal length.
The term faster is used by telescope vendors for marketing purposes. In the photography world you do exactly what I described above, you close or open the diaphragm, but keep the same focal length, thus taking a shot with the same amount of light faster or slower.
In this case both telescopes provide the same amount of light coming from an object, but they spread the light wider or tighter so you need to adapt the pixel size, which is what you achieved in the 2 examples.
You also need to adapt the exposure time as the full well of the bin1x1 294 is shallow so you need many short exposures in order to achieve a high dynamic range eventually, while the 6200 binned takes advantage of a longer exposure as the light is more spread out and full well is deeper.

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Adrian Criss

Topic starter

Jan 31, 2023

Adrian Criss:
=Y2IQFcHello everyone!
Now, during the galaxy season, I was wondering what the difference is, in terms of quality, between taking pictures with RASA11+ASI294mm, resolution 0.77"/pixel vs C11HD-f/7+ASI6200mm bin2x2, resolution 0.79"/pixel.
As an advantage, obviously RASA is 10 times faster than C11HD@f/7, that's why I wonder if the more important focal length for C11HD adds value to a picture? Thanks in advance

RASA 11-M106: https://www.astrobin.com/ftbr73/D/
C11Edge-M106: https://www.astrobin.com/m6mjzc/B/

A telescope is faster than another when it has more aperture than the other, but both have the same focal length.
Reducing a system doesn't make it faster, it just reduces focal length.
The term faster is used by telescope vendors for marketing purposes. In the photography world you do exactly what I described above, you close or open the diaphragm, but keep the same focal length, thus taking a shot with the same amount of light faster or slower.
In this case both telescopes provide the same amount of light coming from an object, but they spread the light wider or tighter so you need to adapt the pixel size, which is what you achieved in the 2 examples.
You also need to adapt the exposure time as the full well of the bin1x1 294 is shallow so you need many short exposures in order to achieve a high dynamic range eventually, while the 6200 binned takes advantage of a longer exposure as the light is more spread out and full well is deeper.

Thank you!
=Y2IQFcThe RASA has a focal length of 620 mm with a focal ratio of f/2.2 and the C11Edge has 1960 at f/7. So the 2 telescopes do not have the same focal length...

alexbb

Jan 31, 2023

Adrian Criss:
Adrian Criss:
=Y2IQFcHello everyone!
Now, during the galaxy season, I was wondering what the difference is, in terms of quality, between taking pictures with RASA11+ASI294mm, resolution 0.77"/pixel vs C11HD-f/7+ASI6200mm bin2x2, resolution 0.79"/pixel.
As an advantage, obviously RASA is 10 times faster than C11HD@f/7, that's why I wonder if the more important focal length for C11HD adds value to a picture? Thanks in advance

RASA 11-M106: https://www.astrobin.com/ftbr73/D/
C11Edge-M106: https://www.astrobin.com/m6mjzc/B/

A telescope is faster than another when it has more aperture than the other, but both have the same focal length.
Reducing a system doesn't make it faster, it just reduces focal length.
The term faster is used by telescope vendors for marketing purposes. In the photography world you do exactly what I described above, you close or open the diaphragm, but keep the same focal length, thus taking a shot with the same amount of light faster or slower.
In this case both telescopes provide the same amount of light coming from an object, but they spread the light wider or tighter so you need to adapt the pixel size, which is what you achieved in the 2 examples.
You also need to adapt the exposure time as the full well of the bin1x1 294 is shallow so you need many short exposures in order to achieve a high dynamic range eventually, while the 6200 binned takes advantage of a longer exposure as the light is more spread out and full well is deeper.

Thank you!
=Y2IQFcThe RASA has a focal length of 620 mm with a focal ratio of f/2.2 and the C11Edge has 1960 at f/7. So the 2 telescopes do not have the same focal length...

I tried to simplify things a bit, as the term faster exists and makes sense, but is misleading in this case.
To put it in fewer words, you have the same aperture for both and, in combination with the pixel size, that's the only relevant thing.
If you end up with the same pixel scale, both setups collect the same amount of light/pixel so you then get similar results at similar total integration.
In this case, the difference is the field of view and how long the subs should be (shorter in the RASA at F/2.2, longer in the Edge HD at F/7).

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