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  #41  
Old 21-10-2018, 09:09 PM
Cimitar (Evan)
Evan Morris

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Hi Ryan,

My imaging rig is an 8" Meade LX200 ACF.
I mainly flick between f/10 and f/7, depending on targets.
I'm really happy with the scope and like you mentioned, I love a challenge.

On a side note, I really enjoy getting up close and personal with my targets. Having a longer focal length is one way of achieving this. I particularly enjoyed this aspect when I captured the black hole jet in M87.
Note: all images were taken at f/10, except Trifid and NGC 253. They were shot at circa f/7 using the same equipment. Mars was captured at circa f/20 (eyepiece projection).

Cheers, Evan
Attached Thumbnails
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Click for full-size image (Mars_BEST_007.jpg)
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Click for full-size image (Moon Base (SouthPole).jpg)
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Click for full-size image (Ghost of Jupiter.jpg)
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Click for full-size image (Pillars4_AF-75pc.jpg)
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Click for full-size image (Trifid Nebula.jpg)
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  #42  
Old 21-10-2018, 09:17 PM
Cimitar (Evan)
Evan Morris

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In addition to what I wrote above,

After re-reading the thread I noticed you posted a Tarantula shot. This is mine I took a few years back. My processing skills were fairly ordinary at that stage so I'm keen to have another crack soon.
It's at f/7, still on the same equipment though. Just thought I'd share in case it's useful
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  #43  
Old 21-10-2018, 11:25 PM
RyanJones
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Hi Evan,

You have some incredible images there. I'm a big fan of Tarantula as an object and I'd have to say yours is simply inspirational ! The detail in the moon is also incredible.

I've really enjoyed the challenge of the f/10 and after 2 nights now with the f5, I'd have to say I'm struggling it just picks up too much sky glow. I know the moon is lighting up the sky like Times Square but my f/10 could deal with that within reason.

Anyway Evan, thank you very much for sharing.
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  #44  
Old 22-10-2018, 09:30 AM
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cometcatcher (Kevin)
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Yes, F10 does deal with sky glow somewhat better than F5. Baader make a Moon and skyglow filter that helps a little.
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  #45  
Old 22-10-2018, 01:32 PM
RyanJones
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You know sometimes you get yourself into a rabbit hole thinking about all the different things that could be contributing to your problem and suddenly the problem seems a whole lot worst? .......

I've been thinking about the challenges I had when I first started ( not that long ago really ) and how knowing nothing meant that I could only deal with one thing at a time. The title of this thread is reflecting and I think I need to do a bit of that. Have a look at some old data and remind myself how far from that I got to with my SCT and then accept that making the f/5 sing in my skies can be done, it's just another challenge.
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  #46  
Old 22-10-2018, 01:45 PM
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Personally, I don't shoot colour in more than 50% moonlight. Doing so just makes everything harder. I've tried filters in full moonlight with OSC and they help a bit, but nothing matches a dark sky.

With narrow band imaging, it's possible to shoot Ha in full moonlight with little degradation.
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  #47  
Old 22-10-2018, 09:41 PM
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Ok, so for those that are interested, here are the results of my ISO exposure test on the f/5.

I ran the ISO at 800 for all subs and took 20 of each

At 22s, 20s and 18s the sky glow was too high but interestingly the star count in DSS didn't change.

At 16s the sky glow became almost acceptable and the star count dropped by about 10%

Finally at 14s the sky glow was acceptable but the star count had now dropped by a huge 50% !

It would seem that there's a cliff that the image drops off at a certain point.

Interesting.....

Am I right in saying that an f/5 gathers light 4x as fast as the f/10 ? So in theory a 15s sub would be roughly the same as a 60s sub on the f/10 ?
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  #48  
Old 23-10-2018, 08:05 PM
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Quote:
Am I right in saying that an f/5 gathers light 4x as fast as the f/10 ? So in theory a 15s sub would be roughly the same as a 60s sub on the f/10 ?
For extended objects like nebula, yes. For stars, aperture is what makes a difference.
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  #49  
Old 23-10-2018, 10:01 PM
Cimitar (Evan)
Evan Morris

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Quote:
Originally Posted by RyanJones View Post
Hi Evan,

You have some incredible images there. I'm a big fan of Tarantula as an object and I'd have to say yours is simply inspirational ! The detail in the moon is also incredible.

I've really enjoyed the challenge of the f/10 and after 2 nights now with the f5, I'd have to say I'm struggling it just picks up too much sky glow. I know the moon is lighting up the sky like Times Square but my f/10 could deal with that within reason.

Anyway Evan, thank you very much for sharing.
Thanks mate
I'd imagine your f/5 scope will throw up some different challenges than what you've been used to. The sky glow will certainly become an issue more quickly.

Quote:
Originally Posted by RyanJones View Post
At 16s the sky glow became almost acceptable and the star count dropped by about 10%
Can a single 16sec exposure show much detail in a nebula? If you use that approach will you need to take hundreds of images and stack?

Have you considered guiding your f/10 scope? If your mount allows it, you could get longer exposures by guiding.
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  #50  
Old 23-10-2018, 10:51 PM
RyanJones
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Quote:
Originally Posted by Cimitar View Post
Thanks mate
I'd imagine your f/5 scope will throw up some different challenges than what you've been used to. The sky glow will certainly become an issue more quickly.


Can a single 16sec exposure show much detail in a nebula? If you use that approach will you need to take hundreds of images and stack?

Have you considered guiding your f/10 scope? If your mount allows it, you could get longer exposures by guiding.
Hi Evan,

No doubt the sky glow is an issue but it always has been. You're correct that the refractor makes a monster of it quite quickly. The 16 seconds was purely part testing sequence. With the moon almost full, it's about as bad as it gets. I ran 350 subs on Helix at ISO 800 for 16 sec and I was surprised I could make it out at all. The main reason I choose Helix was the stars around it are very faint and the moon was only about 10degrees away. As I said, the absolute worst case scenario. Regarding the stacking, I'm pretty used to stacking upwards of 600 subs to only get 3 odd hours of intergation. Yes it is time consuming but it's the only way I could manage it with my mount which takes me to your last comment. Yes, I believe tracking on the mount is possible but there's very like information available. I guess it's because most people don't do what I am trying to with such a basic setup. The actual mount gets jitters as it moves around. It's driven by a plastic spur gearbox so it is never going to be smooth although I do have some modifications in mind. Time will tell if I actually do it. Regardless though, we come full circle and get back to sky glow. On the f/10 at ISO 3200, a 22sec sub ( being all the mount could reliably do cleanly ) was underexposed but I made it work so an extent. Often I would take longer shots to frame the object but anything above 40 seconds had too much sky glow anyway. With the f/5, that's theoretically only 10sec. Now iso3200 is noisey so maybe 20 sec at 1600 might work. I just have to find a new sweet spot. I'll get there, it all a part of the challenge. I must say that I'm enjoying the data collection and analysis and understanding why things work the way they do.
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  #51  
Old 24-10-2018, 08:00 PM
Cimitar (Evan)
Evan Morris

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Hi Ryan,

I see your dilemma! Given the situation it sounds like you're doing an incredible job to make it all come together in one sense or another

Given that you're limited with the mount and f/10 exposure lengths, guiding probably isn't worth it at this stage. I think someone else has already mentioned narrowband imaging, which is always an option further down the track, if you can't get away to a dark site.

I currently image with an unmodified DSLR and exposures are generally 3mins at ISO 1600. I typically take 25 images and stack them together. I've never done anything with a total integration time longer than 2 hours. I know I really should drop the ISO to 800 and take more subs to get a cleaner image, however, at the moment I'm a tad impatient and just want to "see everything". After I've finished doing that I'll go back and actually dedicate the appropriate time to each target.

Cheers, Evan
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  #52  
Old 24-10-2018, 09:13 PM
RyanJones
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Thank you Evan,

I think a lot of my efforts have been driven by a combination of a never give up attitude and also being told that what I was doing would be incredibly hard or wouldn't work...... Challenge accepted

Regarding your efforts, being a tad impatient seems to be working incredibl well for you. I wouldn't change a thing lol. I can't wait till the day I'm producing stuff like yours..... I just went back and had another look at your tarantula.....

I'm sure with persistence, I'll get this new setup producing something half reasonable but it looks like it is going to consume some of my dark sky time in between moons and the poor C5 will have to take a back seat for a bit
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