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Equipment Discussions >> Mounts

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Jon Rista
Carpal Tunnel


Reged: 01/10/14

Loc: Colorado
Re: Buying a telescope...how important is the mount? [Re: Chuckwagon]
      #6362311 - 02/07/14 04:14 PM

Quote:

Quote:

A note on stacking. A 10-minute exposure is a 10-minute exposure. Take 50 of them and stack, and it is still a 10-minute exposure because stacking is an averaging process, not an additive one.




That is generally true, however, you can stack and ADD while stacking. It also adds the noise, so in places where the noise overlaps, it gets worse. As does the sky fog. And you can easily blow out saturated areas very quickly. So adding while stacking may not generally be the best way to do things, but you can do it.

Cheers,
Charles




My proprietary technique is to do both, actually. In my Orion Nebula shot on my blog, I took 50 or 80 frames, and stacked them (as smart objects in photoshop) in batches of 10 with median averaging. I then stacked those stacks additively, to improve the signal strength. The result was less noisy than a single frame, and had more overall signal. It was, as GDD stated, able to be stretched farther. Even with that, though, while you can get some more contrast, you really don't get much more detail in nebulosity and dust. There is an upper limit on detail that is bound by the initial signal strength, it seems. The only way to do better would be longer exposures for each sub.

Edited by Jon Rista (02/07/14 04:14 PM)


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davebuechler
professor emeritus
*****

Reged: 08/21/11

Loc: Red River Gorge Kentucky
Re: Buying a telescope...how important is the mount? new [Re: Jon Rista]
      #6362991 - 02/07/14 09:45 PM

Quote:

The thing about the G11 is, while it seems it can be tuned and upgraded to get closer to the performance of higher end mounts (<2" P2P PE w/ PEC+guidng), the upgrades are costly. Just the improved worm is $500, and I've read a number of articles about people installing them on their own, and they end up fiddling with it forever trying to get it installed exactly right. If it isn't exactly right, then there can still be a little bit of quirky periodic error. So, you can pay someone to install it, but that only increases the cost even more. After you've paid for all the necessary upgrades and tuning, you've spent as much as an LX850 or CGE Pro, and both of those seem to be able to achieve the same level of performance as a G11 after upgrades with nothing more than PEC, and <2" P2P PE tracking with guiding.




You can also get one out of the box that takes unguided 3 minute exposures at 2000mm F/L like this
http://www.astrobin.com/29589/

Quote:

I am really curious to see how this 600mm lens with 150mm aperture works for astrophotography. A 150mm aperture on a refractor is pretty big (I mean, if one were to buy an actual high end 150mm APO refracting telescope, like the Officina 152mm, it still costs about twelve grand! Even Orion's 150mm APO is $6500), but when I use it as a visual scope, I can only see andromeda's core, and it's just a faint gray blob. There are a lot more glass elements inside this lens than in the average APO refractor (I guess you have anywhere from two to four elements, my lens has 16). I think part of it is due to the fact that I'm using a DSLR as an eyepiece, the mirror is half-silvered, so I'm probably getting less light than one would with a normal scope and a normal eyepiece. But even when imaging with a 1 second exposure, I get a faint grayish-yellow blob for the core, and that's it. I'm really hoping that once I am tracking and doing longer exposures, my results will change dramatically.




I think it will be amazing!!! I for one can't wait to see what you get.


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Per Frejvall
sage


Reged: 09/28/12

Loc: Saltsjöbaden, Sweden
Re: Buying a telescope...how important is the mount? new [Re: davebuechler]
      #6363257 - 02/08/14 01:48 AM

Gale,

A short exposure stack can be stretched much further due to the increase in s/n, so that is the key factor. There are, however, diminishing returns as you go up in numbers. I sometimes stack 50-100 10 to 20 minute exposures just for the heck of it, but there really isn't much improvement over 25-30 subs. The good thing is if you use a sigma rejection algorithm in the stacking process. All satellites and airplanes gone. Poof!

Back on track, now... Mounts...

/per


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: Buying a telescope...how important is the mount? new [Re: Jon Rista]
      #6364044 - 02/08/14 01:15 PM

You'll be setting that aside. What you really need to do is go open-choke on the f/# and get that camera sensitivity up. Play with all of the parameters and set aside what you've learned in the past. You should be able to get a MUCH deeper image on the orion nebula than that one, and do it in shorter exposures.

And take some of the pressure off yourself. Even when you get to be an old hand, you're going to have nights where every single frame turns out to be flawed.

-Rich

Quote:

Quote:

Quote:

A note on stacking. A 10-minute exposure is a 10-minute exposure. Take 50 of them and stack, and it is still a 10-minute exposure because stacking is an averaging process, not an additive one.




That is generally true, however, you can stack and ADD while stacking. It also adds the noise, so in places where the noise overlaps, it gets worse. As does the sky fog. And you can easily blow out saturated areas very quickly. So adding while stacking may not generally be the best way to do things, but you can do it.

Cheers,
Charles




My proprietary technique is to do both, actually. In my Orion Nebula shot on my blog, I took 50 or 80 frames, and stacked them (as smart objects in photoshop) in batches of 10 with median averaging. I then stacked those stacks additively, to improve the signal strength. The result was less noisy than a single frame, and had more overall signal. It was, as GDD stated, able to be stretched farther. Even with that, though, while you can get some more contrast, you really don't get much more detail in nebulosity and dust. There is an upper limit on detail that is bound by the initial signal strength, it seems. The only way to do better would be longer exposures for each sub.




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Jon Rista
Carpal Tunnel


Reged: 01/10/14

Loc: Colorado
Re: Buying a telescope...how important is the mount? new [Re: Starhawk]
      #6364214 - 02/08/14 02:38 PM

Quote:

You'll be setting that aside. What you really need to do is go open-choke on the f/# and get that camera sensitivity up. Play with all of the parameters and set aside what you've learned in the past. You should be able to get a MUCH deeper image on the orion nebula than that one, and do it in shorter exposures.

And take some of the pressure off yourself. Even when you get to be an old hand, you're going to have nights where every single frame turns out to be flawed.





Well, I'm looking forward to it all. I've ordered an Astronomik light pollution filter for EOS, so hopefully I'll be able to get a lot more use of this equipment without having to drive far all the time. The LP here is going to intrinsically limit my maximum exposure times, hopefully with the CLS clip filter I'll be able to do longer exposures even than I would with a tracking mount, and still have darker background sky. I'm ok with unlearning techniques I've learned so far, if that's what it takes.


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