Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

The "No EQ" DSO Challenge!


JGM1971

Recommended Posts

On ‎16‎/‎09‎/‎2017 at 10:11, happy-kat said:

@Nigel G has I think tried his ed80 on the star discovery mount but off to of head I can't recall the exposure length he managed. 

 

I used both 80ed @ 500mm FL and 150p @ 750mm FL, both within the weight limit and max exposure length about 90s but about 60% keep, the 80ed was a little bit better but that would be expected. I would say with 30s around 80 % keepers and 60s around 60-70 %. Many things can reduce the keepers, the alignment, balance, wind, stability of the tripod, hanging cables, position of the target, occasionally everything seemed right but just would not track well so I would start again from the beginning. Re align and balance the scope, sometimes everything worked perfect and would have 99% keep at 45s or so.

Every night was different :) 

I would balance the scope a little on the camera heavy side.

Nige.

  • Like 2
Link to comment
Share on other sites

31 minutes ago, Nigel G said:

I would balance the scope a little on the camera heavy side.

I recall Joseph Ashley making that observation about Alt-Az imaging and certainly with my Startravel 102 being back-heavy has not done any harm in imaging, I think it helps damp down vibrations.

Good luck.

Cheers,
Steve

  • Like 1
Link to comment
Share on other sites

great thread, im just waiting to get a camera to start getting images like these, the images on here are very inspiring and give me the confidence knowing i can get images like these with our set up, we have a celestron 8se and im looking at getting a canon 600d, budget is tight as my camera died after a water leak.

Link to comment
Share on other sites

40 minutes ago, Petehog72 said:

great thread, im just waiting to get a camera to start getting images like these, the images on here are very inspiring and give me the confidence knowing i can get images like these with our set up, we have a celestron 8se and im looking at getting a canon 600d, budget is tight as my camera died after a water leak.

Hi, always good to see new faces :) shame about your camera packing up.

Your scope is a 2mtr focal length F10. You might struggle to get long enough exposures with Alt-AZ unless you can guide the mount. ( I see in the specs the mount can be guided )

I hope you can prove me wrong though :) 

Most Alt-AZ imagers use scopes between 500mm and 750mm focal length and low F ratio - F4 - F6.5, faster scopes to gather the required photons in a short time.

I'm no expert so don't take my word as the law :) 

I look forward to seeing your images.

Cheers

Nige.

  • Like 2
Link to comment
Share on other sites

Welcome to having a go with what you have. Several members here have your mount and either use a refractor or DSLR with camera lens for DSO. You can pick up vintage lenses quite cheaply and you don't need auto focus anyway. Using just a camera initially may be easier to start with anything from the kit lens to 200mm.

Link to comment
Share on other sites

2 hours ago, Petehog72 said:

great thread, im just waiting to get a camera to start getting images like these, the images on here are very inspiring and give me the confidence knowing i can get images like these with our set up, we have a celestron 8se and im looking at getting a canon 600d, budget is tight as my camera died after a water leak.

As Nigel says, you'll find that imaging on a mount designed for visual and a scope with a long focal length is a ... shall we say painful experience. I've tried it and whilst I was pleasantly surprised that I got an image, it's an experience I would never repeat.

Here's my take on M1 with a 9.25 SCT.

It's worth noting I used a very fast/sensitive camera so the limited and short exposures sort of worked. I don't think it would have been possible with my Canon 60D. I now image with a 500mm focal length scope and it's a breeze in comparison. 

Give it a go but be prepared to switch to a camera/lens combo :)

 

  • Like 4
Link to comment
Share on other sites

Nice Crab!

As for balancing, I find that as the target rises or sets, the scopes balance changes from front to back.

I see what you mean a little front heavy, it's like being East heavy on an EQ, to keep the pressure on the gears. I'll try and make it a little front heavy in the East, and back heavy in the West now. 

 

I took some more subs of M45, and didn't constrain DSS to process only an intersecting area this time. It's not as bright and overly stretched as the last one, but has more detail. Still struggling to remove this grainy noise though.

 

Also this SW 0.9 coma corrector is a PITA. The draw tube sticks into the scope and makes the stars look like "D"s. Also I can't seem to get that "crisp" focus I could without it, I have the appropriate T mount.

 

21951072_10155084774783247_9187678165667

Edited by Shaun_Astro
  • Like 3
Link to comment
Share on other sites

34 minutes ago, Shaun_Astro said:

Also this SW 0.9 coma corrector is a PITA. The draw tube sticks into the scope and makes the stars look like "D"s.

I don't think this is specific to the SW CC, they all mean you have to wind the tube in further because of the way they work.

I took a slice off my draw tube.

  • Like 1
Link to comment
Share on other sites

Thanks for the advice folks, I kinda expected these answers and the photography side came in after the wife bought the scope, the scope is great and loving the observing, I will still chip away and wont expect the images to be great but hopefully wet my feet in the world of astrophotography 

  • Like 1
Link to comment
Share on other sites

On 19/09/2017 at 16:05, Nigel G said:

Hi, always good to see new faces :) shame about your camera packing up.

Your scope is a 2mtr focal length F10. You might struggle to get long enough exposures with Alt-AZ unless you can guide the mount. ( I see in the specs the mount can be guided )

I hope you can prove me wrong though :) 

Most Alt-AZ imagers use scopes between 500mm and 750mm focal length and low F ratio - F4 - F6.5, faster scopes to gather the required photons in a short time.

I'm no expert so don't take my word as the law :) 

I look forward to seeing your images.

Cheers

Nige.

thanks Nige, as soon as i get fixed with a camera i shall post some images, I will give it a try and do the best i can and see what happens

  • Like 1
Link to comment
Share on other sites

On 9/19/2017 at 15:11, Petehog72 said:

great thread, im just waiting to get a camera to start getting images like these, the images on here are very inspiring and give me the confidence knowing i can get images like these with our set up, we have a celestron 8se and im looking at getting a canon 600d, budget is tight as my camera died after a water leak.

After seeing some of the images people were getting with Alt-Az mounts, I decided to give it a go with the Celestron 8SE, the long focal length makes it quite difficult, but also makes it very useful for going after the smaller objects e.g. planetary nebulae, smaller galaxies, so long as they are bright enough!

I'm able to get 30s exposures when the object is close to polaris, e.g. M81, but for anything else, only 5-10 seconds is all I can do!

Here's the ring nebula from a week ago, taken with a Nikon D610 through an 8SE at f/10. It's made of 1719x5s (!) exposures at ISO 6400 (So that DSS can see the stars) - only 2 and a half hours of data, but 60GB of files. Not the most efficient way of doing things, but it's a start.

M57 V5.png

  • Like 14
Link to comment
Share on other sites

Thanks! The nice part about using 5 second exposures is that you can rack up a huge number of subs, I think I was getting 450 an hour! Also the keep rate was actually 97% which was a nice change. It kind of hurts to almost double the shutter count on the camera overnight, but I'm looking into shorter focal length scopes so that I can increase the exposure time. This thread just goes to show that it's definitely worth having a go - field rotation will be the least of my issues for quite some time!

  • Like 2
Link to comment
Share on other sites

First, what a great Ring Nebula and looks like you caught quite a nice spiral galaxy to the right. IC1296 maybe? Dare I say a little noisy and you may need a few more subs :) Just kidding. You're now facing that same dilemma anyone taking short exposures faces, whether to archive all those subs so you can add more at a later date! 

6 hours ago, profdann said:

I'm able to get 30s exposures when the object is close to polaris, e.g. M81, but for anything else, only 5-10 seconds is all I can do!

This surprised me. I always thought it was easier to push longer subs the closer you image to the horizon (though this is counterbalanced by atmospheric disturbance) and the closer you image to east and west. Imaging at the zenith is all but impossible and imaging to the north or south difficult other than at very short exposures. I found my ideal targets were usually crossing east or west between 30 and 60 degrees above the horizon. These allowed me to consistently achieve longer exposures.

  • Like 1
Link to comment
Share on other sites

I think that would be true Ken if field rotation was the limiting factor, but my guess is that in profdann's case it is just that the mount's general tracking isn't sufficiently good for such a long fl. Even at ~600mm fl I get a good proportion of 30s subs showing star streaking over the whole frame.

Ian

Edited by The Admiral
  • Like 1
Link to comment
Share on other sites

Yes, that's it - the azimuth tracking seems to be dead on all night, but the altitude has a huge error causing the object to drift more than half way out of frame over about 10 minutes before returning to the centre. It seems to be fairly periodic, but I don't think the SE mount allows that to be corrected. Pointing near to Polaris means that the object isn't moving very fast, so the error occurs over a longer time period, so the star trails are smaller. 

15 hours ago, Filroden said:

Imaging at the zenith is all but impossible and imaging to the north or south difficult other than at very short exposures. I found my ideal targets were usually crossing east or west between 30 and 60 degrees above the horizon. These allowed me to consistently achieve longer exposures.

I've thankfully been saved from this discovery by the fact that the camera hits the mount at anything above 65 degrees altitude!

This is a crop of one of the worse 5 second exposures, the camera was tilted by this point so the trails are in the altitude direction and it's from the centre of the frame, so probably not field rotation.

Trails.png

Link to comment
Share on other sites

25 minutes ago, profdann said:

Yes, that's it - the azimuth tracking seems to be dead on all night, but the altitude has a huge error causing the object to drift more than half way out of frame over about 10 minutes before returning to the centre. It seems to be fairly periodic, but I don't think the SE mount allows that to be corrected. Pointing near to Polaris means that the object isn't moving very fast, so the error occurs over a longer time period, so the star trails are smaller. 

That makes perfect sense. What a horrible combination to have to navigate through - the periodic tracking issue wants you to point to areas of the sky not liked for field rotation. I guess the one advantage you can take from lots of 5 second exposures is it really helps the S/N ratio :) And with so many subs, throwing away even 10% is not much of an issue.

  • Like 1
Link to comment
Share on other sites

If it wasn't for the fact that DSS takes 12 hours to stack the images, and that I can't use any other method than just the standard average (no Kappa-Sigma satellite trail removal for me!) because it takes too much disk space during the stacking process, 5 second exposures would actually be quite nice!

Link to comment
Share on other sites

6 hours ago, profdann said:

If it wasn't for the fact that DSS takes 12 hours to stack the images, and that I can't use any other method than just the standard average (no Kappa-Sigma satellite trail removal for me!) because it takes too much disk space during the stacking process, 5 second exposures would actually be quite nice!

There is actually a trick to get around this problem.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.