M74 Take 2

[MarsG76]

Hi All,

After discovering that my first imaging session of Galaxy M74 on the pier in the obsy was slightly out of focus, I decided to give it a bit more time, this time double checking the focus. 

I figured that since I already had the OAG setup with the DSLR on the scope, I might as well try to get more data of this Galaxy. The moon is at 1st quarter so I won't be doing any DSO until around new moon.

This was taken with a full spectrum modded Canon 40D on Nexstar 8SE on a CGEM mount at F6.3.

55 x 450sec and 11 x 210 sec at ISO800. All RGB through a IR cut filter.

Thanks for looking, clear skies.

Mars

[lux eterna]

I like your processing, the faint outer parts of the spiral arms look very natural.

How did you double check the focus ? It looks to me the focus is still a little off. Personally I like using a Bahtinov mask, I think that works very well.

Ragnar

 

[MarsG76]

16 hours ago, lux eterna said:

I like your processing, the faint outer parts of the spiral arms look very natural.

How did you double check the focus ? It looks to me the focus is still a little off. Personally I like using a Bahtinov mask, I think that works very well.

Ragnar

 

Hello Ragnar,

I double checked before the exposure start each night using a bahnitov mask. The diffraction spikes were exactly symmetrical before starting the exposure.

The focus is definitely not off this time... I'm guessing that with a DSLR at 1280mm and the Galaxy being 35 degrees at the highest position that's the most detail my kit will capture. 

 

[tooth_dr]

That's actually pretty cool, and a big improvement over the last effort.  If you dont mind be saying something still doesnt look totally right with the shape of the stars.  Was that taken right in the middle of the camera FOV or in one of the corners?

[MarsG76]

2 minutes ago, tooth_dr said:

That's actually pretty cool, and a big improvement over the last effort.  If you dont mind be saying something still doesnt look totally right with the shape of the stars.  Was that taken right in the middle of the camera FOV or in one of the corners?

It was in the center of the frame, there was some kind or chromatic abberation in the subs... that said, last night I was observing the moon through my 14" dob and the 8" SCT and I noticed that the SCT had a lot less contrast compared to the dob, especially at high magnification. Looking into the visualback with out the EP and into the corrector lens, there seems like there's some kind of film or substance at the back of the corrector INSIDE THE OTA!!! That could be causing the loss of contrast and the abberation effect in my subs...

I'll research that and I hope I don't have to be pulling off the corrector plate.

[lux eterna]

3 hours ago, MarsG76 said:

Hello Ragnar,

I double checked before the exposure start each night using a bahnitov mask. The diffraction spikes were exactly symmetrical before starting the exposure.

The focus is definitely not off this time... I'm guessing that with a DSLR at 1280mm and the Galaxy being 35 degrees at the highest position that's the most detail my kit will capture. 

 

Maybe I was wrong regarding focus being off. But anyway - you may have nailed exact focus before starting the exposures, but you also need to fine tune the focus several times during the night. Different OTA:s behave differently, but my experience is that I need to refocus most frequent at the start of an astro session. After several hours it is almost static and I can leave it alone. 

Ragnar

[MarsG76]

17 minutes ago, lux eterna said:

Maybe I was wrong regarding focus being off. But anyway - you may have nailed exact focus before starting the exposures, but you also need to fine tune the focus several times during the night. Different OTA:s behave differently, but my experience is that I need to refocus most frequent at the start of an astro session. After several hours it is almost static and I can leave it alone. 

Ragnar

Yeah you might be right, especially with a SCT mirror moving to achieve focus. That said tho, I always reach focus with the mirror moving up against gravity which minimizes the chance of mirror flop, and I never had a issue with focus slipping...

The first thing I need to do is get rid of the hazey residue on the inside on my corrector plate... caused by internal outgassing apparently... and that should improve the performance of the scope and quality of the subs.