Everyone loves M31, but what about M33?

[jhayton]

M33 has been one of my favorites since last November. I had just gotten my 8" and didn't have much time behind it before M33 slipped beyond my viewing.  I've been wafting patiently for its return.   Now it is high enough above the horizon for me to catch it, I still needed to wait until after midnight for it to clear obstructions.  I still managed to capture ~4hr on target.

 

74x180s

ASI2600MC-P
Sky-Watcher EQ6-R Pro
Sky-Watcher 200P-DS
Starizona Nexus x0.75
SVBONY UV / IR CUT

[newbie alert]

Done it proud... Really nice that

[StuartT]

totally agree! It's lovely. Coincidentally I am imaging it right at this moment!

[MichaelBibby]

On 07/08/2022 at 04:28, jhayton said:

M33 has been one of my favorites since last November. I had just gotten my 8" and didn't have much time behind it before M33 slipped beyond my viewing.  I've been wafting patiently for its return.   Now it is high enough above the horizon for me to catch it, I still needed to wait until after midnight for it to clear obstructions.  I still managed to capture ~4hr on target.

 

74x180s

ASI2600MC-P
Sky-Watcher EQ6-R Pro
Sky-Watcher 200P-DS
Starizona Nexus x0.75
SVBONY UV / IR CUT

Great image. Nexus .75x brings an F5 down to F3.75, 1.78x the amount of light per unit of time, great upgrade (you can almost halve your exposure times for the same gain settings). I do still see a bit of coma on the edges of your image, did you get exactly 55mm of back spacing?

[ollypenrice]

7 hours ago, MichaelBibby said:

Great image. Nexus .75x brings an F5 down to F3.75, 1.78x the amount of light per unit of time, great upgrade (you can almost halve your exposure times for the same gain settings). I do still see a bit of coma on the edges of your image, did you get exactly 55mm of back spacing?

This is incorrect. There is no increase in the amount of light per unit time because the available light from M33 goes into the front of the telescope and cannot, therefore, be increased by a lens at the back. What the reducer does is put the same amount of light onto fewer pixels, exchanging intensity for scale and resolution. Your calculation applies when the aperture is increased so as to reduce the F ratio. When the focal length is reduced to increase it, all you get is a smaller, less resolved, but brighter image in the time.

This debate is an old one and is usually called The F Ratio Myth, which will Google.

Olly

[andrew s]

It would be correct to say "light per unit time per pixel" ignoring transmission loss through the corrector. Regards Andrew 

[MichaelBibby]

3 hours ago, ollypenrice said:

This is incorrect. There is no increase in the amount of light per unit time because the available light from M33 goes into the front of the telescope and cannot, therefore, be increased by a lens at the back. What the reducer does is put the same amount of light onto fewer pixels, exchanging intensity for scale and resolution. Your calculation applies when the aperture is increased so as to reduce the F ratio. When the focal length is reduced to increase it, all you get is a smaller, less resolved, but brighter image in the time.

This debate is an old one and is usually called The F Ratio Myth, which will Google.

Olly

Thanks for the technical corrections, because it doesn't do anyone any good to be clumsy and imprecise with a technical language, every use of it should be a practice of it's precision, especially on forums were people augment so much of their knowledge (learning both good and bad habits).

Edited February 6, 2023 by MichaelBibby