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Unguided astrophotography

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#1 SpeySnglMlt

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Posted 13 April 2021 - 07:29 PM

I have a Celestron c8 with a focal length of 2000mm. Realizing this is not the right scope for astrophotography, but can this scope be used to take DSO with no auto guiding/tracking features. I have a basic mount. I have the f/6.3 reducer. What would be my max exposure with dslr and would any pics turn out with stacking?

#2 rj144

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Posted 13 April 2021 - 07:30 PM

What's a basic mount?  Alt/Az?



#3 bobzeq25

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Posted 13 April 2021 - 07:35 PM

No, it can't.

 

Even autoguided on a good mount, it's a bad choice for learning DSO imaging.

 

"I regret spending the first 6 months trying to learn imaging with an 8" Edge, with that scope it was a losing effort. Fortunately got a nice little refractor, and not only have the quality of my images improved but I'm actually enjoying the process of learning how to do it!"

 

15 minutes spent watching this video (you really only have to look at the first 5 or so) could save you a _lot_ of wasted time, money, and frustration.

 

https://www.youtube....h?v=MNQU1hdqz4M

 

Good visual scopes are _often_ not good scopes to learn DSO imaging with, however unintuitive that may seem.  These are two _completely_ different activities.

 

If you want to use that setup, I suggest you look into electronically assisted astronomy, which is a separate forum.  It's in between visual, and traditional imaging.


Edited by bobzeq25, 13 April 2021 - 07:37 PM.

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#4 kathyastro

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Posted 13 April 2021 - 07:41 PM

It is possible to take unguided DSO images with a fast scope on a good equatorial mount, if you keep the exposures short enough.  But an SCT is not a fast scope, so it needs longer exposures.  If your "basic" mount is alt-az, it will be next to impossible to get any reasonable images.

 

By all means, give it a try, since it is what you have.  You will quickly learn the limitations of that rig for imaging.


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#5 Stelios

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Posted 13 April 2021 - 08:01 PM

First, define "basic mount." 

 

Second, WHY don't you want to guide this scope? Cost? 



#6 PirateMike

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Posted 13 April 2021 - 08:12 PM

Every job requires the right tools for it to be performed correctly.

 

Maybe you need to define the job that you want to do and the tools required to get it done properly.

 

HINT: Astrophotography is made much easier with a decent electronically controlled EQ mount and a short focal length telescope... for starters.

 

If you can't acquire the right tools then maybe it would be better not to attempt the job. If you can then maybe it is time to start planning the purchase of those particular tools.

 

Either way, you can always make an attempt with what you have available, there is nothing to lose by doing so except maybe your time and there is a good chance that you may learn something useful along the way.

 

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Edited by PirateMike, 13 April 2021 - 08:21 PM.


#7 bridgman

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Posted 13 April 2021 - 08:13 PM

As others have said, a bit more information on the mount would really help.

 

If you have no drive at all then you are probably limited to somewhere around 1/2 second (rule of thumb is 500 over focal length, so 500/1250 with reducer).

 

If you have an alt-az mount with star tracking but no wedge then the scope can follow stars but (a) you will get trails from field rotation and (b) some alt-az drives move in large enough steps that getting a good image with a long focal length is unlikely. I don't remember the rule of thumb for this but IIRC somewhere around 10 seconds should be OK depending on which direction you are pointing. Because of the stepping you might want to take a sequence of short exposures anyways so that you can discard the ones that get "stepped in".

 

If you have an equatorial mount with drive then you might be able to take 30-60 second exposures and have enough of them come out to get a good image. You'll need fairly good polar alignment for that, but you can use your camera to help figure out the alignment.

 

That's about as far as it's worth guessing smile.gif

 

I should mention that people took great pictures with manual guiding for a lot of years... this auto-guiding thing is very convenient but it's not the only way to image.


Edited by bridgman, 13 April 2021 - 08:15 PM.

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#8 ravenhawk82

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Posted 13 April 2021 - 08:16 PM

I'll preface this by saying that you won't really want to use any of the sub exposures by themselves. The SNR will be garbage and you'll end up with a very noisy image, so stacking is virtually a necessity (as it is in most forms of astrophotography). 

Now with that out of the way, the answer to whether or not you can get results without guiding is a solid maybe depending on a few factors. I took this image using an early 90's era 10" Meade SCT on an Atlas/EQ6 mount without any guiding and an F6.3 reducer. It's made up of just shy of 2 hours worth of 60s exposures. So unguided imaging IS possible with your scope. However, it's a difficult option for a few reasons:

1. You need a well aligned equatorial mount that can handle the weight of your scope and then some. I polar aligned to within ~19" using an ASIAir for this one. I don't know what your basic mount is, but if it's less than at minimum an EQ5/Sirius or equivalent you'll run into stability issues. If it's alt-az without a wedge you'll be unlikely to get good results at any exposure due to field rotation.

2. You will be limited to different exposure times depending on the target's proximity to the equator. I can manage up to about 90s unguided subs pointing near the pole if my alignment is spot on but 30s is pushing it out toward the equator. 60s was the most I could manage for this image before stars started to trail. 

3. You'll lose a lot of subs due to breezes, periodic error, mirror flop, and any other little abnormality that an OAG (or at least a guide scope) would help to smooth over. I had quite a few unusable frames from this session but the overall results were worth a few missed shots. The benefit of short subs is that messing one up isn't all that big of a deal.

So I'd say give it a go. It'll be more difficult, no doubt about it, but trying is how we learn things best. I recommend taking notes of what you do and what effect they have so you can better hone in on what does and doesn't work, and down the line when you're looking to upgrade you'll have a much better idea of what you need and what questions to ask to get it. 

Good luck! And if you do try this I'd be interested in seeing the results!



#9 Mr. Pepap

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Posted 13 April 2021 - 08:27 PM

SCT?

 

On a basic mount?

 

With no guiding?

 

Ouch. It's not impossible, just impossibly difficult. I managed to pull it off (I think) on my C8 with some practice and a lot of patience. First of all, no idea what you mean by "basic mount." If it's the one that came out of the box and you are serious about doing this, you need to get a new mount ASAP. One that is sturdy, well-built from a trusted manufacturer, and can carry a lot of weight. SkyWatcher's EQ6-R Pro is great.

 

Second: if you plan on doing this without autoguiding, not only are you going to get lower-quality images, it's going to take more effort to get them. You are at the mercy of field rotation and drift without guiding, so you are limited to extremely short exposures, which will make whatever the final product is appear really dark. Conversely, to make it brighter, you'd need to jack up the ISO on your camera by a ton, which unfortunately means that the SNR will be garbage and makes your photos grainy.

 

Furthermore, to take said short exposures, you need a fast f/stop scope, which yours is not. This limits you to longer exposures, which as I mentioned, will make your photos grainy. Oh and did I mention that without guiding, mirror flop, focus, vibrations, etc. are also going to be a problem without a guiding solution to fill in the cracks?

 

TL;DR is that it is going to be living hell making things work with your current setup.

 

In other words, if you are serious about this hobby, please consider investing some money into better equipment.


Edited by Mr. Pepap, 13 April 2021 - 11:21 PM.

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#10 Jared

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Posted 13 April 2021 - 10:21 PM

I have a Celestron c8 with a focal length of 2000mm. Realizing this is not the right scope for astrophotography, but can this scope be used to take DSO with no auto guiding/tracking features. I have a basic mount. I have the f/6.3 reducer. What would be my max exposure with dslr and would any pics turn out with stacking?

 

For an experienced imager? It would be really hard to get something decent. Hard meaning, frankly, impossible. OK, maybe not quite impossible--don't want someone to see this as a challenge to take on just because people here on the forum said it was impossible. Instead, I'll say not at all rewarding. It would be like asking if one could build a skyscraper with hand tools. It might be possible, but it would be needlessly difficult and the result would be. Well. You get the picture.

 

For a beginner? Worse.


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#11 dclt

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Posted 13 April 2021 - 10:27 PM

I have a Celestron c8 with a focal length of 2000mm. Realizing this is not the right scope for astrophotography, but can this scope be used to take DSO with no auto guiding/tracking features. I have a basic mount. I have the f/6.3 reducer. What would be my max exposure with dslr and would any pics turn out with stacking?

Don’t listen to people who try to tell you that is not a good scope for astrophotography. That said, guiding is a must. Most people who claim a longer focal length is “too hard” haven’t done it much. I began with a 1900 focal length scope. When reduced with a 0.63 reducer it is about 1200mm & F9. I have gotten very good results. You just have to be smart about which targets you choose.

I strongly recommend auto guiding with that or any scope, but particularly that one. You have a good telescope, particularly for things like galaxies...with guiding. Without guiding you are going to be limited to mostly solar system objects. With guiding there’s a lot you can do.

Edited by dclt, 13 April 2021 - 10:28 PM.

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#12 Jared

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Posted 13 April 2021 - 11:44 PM

Don’t listen to people who try to tell you that is not a good scope for astrophotography. That said, guiding is a must. Most people who claim a longer focal length is “too hard” haven’t done it much. I began with a 1900 focal length scope. When reduced with a 0.63 reducer it is about 1200mm & F9. I have gotten very good results. You just have to be smart about which targets you choose.

I strongly recommend auto guiding with that or any scope, but particularly that one. You have a good telescope, particularly for things like galaxies...with guiding. Without guiding you are going to be limited to mostly solar system objects. With guiding there’s a lot you can do.

The problem isn't the C8. Lots of good astrophotography has been done over the years with C8's. In fact, they were once the most popular platforms going for astrophotography, though you have to go back to the 70's or 80's for that. The problem is the combination of long focal length and a basic mount (no guiding or even tracking the OP says) I'm assuming it's on a Super Polaris or equivalent--Celestron used to sell it that way. That's not a recipe for success in astrophotography. 


Edited by Jared, 14 April 2021 - 12:05 AM.


#13 bobzeq25

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Posted 14 April 2021 - 12:20 AM

Don’t listen to people who try to tell you that is not a good scope for astrophotography.

Let me be very clear.  It's a fine scope for an experienced imager to DO AP with.  It's a horrible scope for a beginner to LEARN AP with.  For example, they end up:

 

Spending so much time and effort on trying to control the scope, that they have little attention left for learning basic techniques.  Things like "lights only" posts are common.

 

Being confused about issues.  The SCT makes it hard to diagnose them.  "What am I doing wrong?" posts from beginners with SCTs are common here, and it's often extremely difficult to answer the question.  Especially in a way which will put them on a good path.

 

I've been advising beginners for years, and have seen this story has played out over and over again here.  There are 3 general outcomes.

 

They simply disappear.

 

They get a small refractor, and are amazed to find out they actually CAN do AP.  A lot more common than the third outcome.  I have referenced a couple of cases of outcome 2 in #3, and have _many_ more.

 

They succeed with the SCT.  It happens, and it's rare.  Moreso than outcomes 1 and 2.

 

If people's goal are to image small DSOs with an SCT, they are virtually guaranteed to reach it faster/better/cheaper if they start with a small scope and big targets.  Those are simply far better things to learn on and with.  They're the right tools for the job.  Time for a quote.

 

"I started out with a CPC 800.  In hindsight, I'd have started with an 80mm refractor.  I would have saved a lot of money and gotten up the learning curve a lot quicker."

 

Not distinguishing learning imaging, from doing imaging, is a real problem on CN.  Note the words "learn" and "learning" in the first quote in post #3.


Edited by bobzeq25, 14 April 2021 - 12:40 AM.

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#14 Jared

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Posted 14 April 2021 - 12:36 AM

Let me be very clear.  It's not a bad scope for an experienced imager to DO AP with.  It's a horrible scope for a beginner to LEARN AP with.  For example, they end up:

 

Spending so much time and effort on trying to control the scope, that they have little attention left for learning basic techniques.  Things like "lights only" posts are common.

 

Being confused about issues.  The SCT makes it hard to diagnose them.  "What am I doing wrong?" posts from beginners with SCTs are common here, and it's often extremely difficult to answer the question.  Especially in a way which will put them on a good path.

 

I've been advising beginners for years, and have seen this story has played out over and over again here.  There are 3 general outcomes.

 

They simply disappear.

 

They get a small refractor, and are amazed to find out they actually CAN do AP.  A lot more common than the third outcome.  I have referenced a couple of cases of this in #3, and have _many_ more.

 

They succeed with the SCT.  It happens, and it's rare.  Moreso than outcomes 1 and 2.

 

If people's goal are to image small DSOs with a SCT, they are virtually guaranteed to reach it faster/better/cheaper if they start with a small scope and big targets.  Those are simply far better things to learn on and with.  They're the right tools for the job.

 

Not distinguishing learning imaging, from doing imaging, is a real problem on CN.

You used to see this a lot with mirror making as well. What's the fastest way to learn how to build a good 10" mirror? First, grind a 6" mirror. Don't start with the 10". It will take you longer to get to that good result than if you started with the 6", finished it, then moved on to a 10". It's important that we not send people down a time consuming, frustrating, unrewarding path. You got it exactly right.


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#15 TelescopeGreg

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Posted 14 April 2021 - 01:28 PM

You used to see this a lot with mirror making as well. What's the fastest way to learn how to build a good 10" mirror? First, grind a 6" mirror. Don't start with the 10". It will take you longer to get to that good result than if you started with the 6", finished it, then moved on to a 10". It's important that we not send people down a time consuming, frustrating, unrewarding path. You got it exactly right.

Another perspective.

 

If someone already has that proverbially inappropriate 8" SCT with a reducer and wants to try some DSO AP with it, we should help them get the most from it.  "The most" will not be an APOD.  It will be constrained in terms of the targets.  But they can get an image, and start getting a feel for what is involved.  Getting some sort of an image can both meet their immediate desires, as well as spur an interest into what they might do to improve.  THAT, in my opinion, is our objective.  It is not our objective to remove all potential stumbling blocks, as that is how we all learn.  If these things "just worked" with the push of a button, we'd learn nothing. 

 

They don't need to have their nose rubbed in the fact that they're a beginner.  They already know that, and being constantly reminded of it does. not. help.  There are lots of things to learn about the hobby, and different bits of hardware will expose them to different things to learn.  There is not a single path to navigate.  Some paths are more direct, some more challenging, and some can lead to unexpected personal discoveries.  If someone already has the kit, they are already standing on a path.  Let's help them understand what lays ahead, and let them make an informed decision as to whether to continue on, or back up and take a different path.  We are travel agents, and it's the journey that counts as much if not more than the destination.

 

If I were told 4 years ago that I should throw out my 8" f/5 Newt and take wide-field Milky Way images first, I doubt I'd be typing this right now.  As gorgeous as those images can be, they don't really interest me into taking them, and I'd be far more likely to find a different hobby.  Learning about polar and star alignments, guiding, Bahtinov Masks, and all the rest has been the interesting part of my journey (so far).  In a back-handed sort of way, that Celestron did a really bad job at describing what to buy did me a favor in forcing me onto what has turned out to be the more interesting path.  That first image of M13 was blurry, noisy, and had little color, but it was an image.  Hook set.

 

This is a hobby.  The worst thing we can do for many is to push them down a curated, university-style catalog of tasks to do, and lab-style equipment to buy.  Those that complete the course work will certainly have a thorough understanding of the field, but I would rather see more folks taking the journey in what appears to be a random walk, than to get them through it on the most expedient path.  Getting to the end with some sort of "degree" is not the objective.  Having fun and learning about the sky and what it takes to image it is.


Edited by TelescopeGreg, 14 April 2021 - 01:29 PM.

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#16 APshooter

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Posted 14 April 2021 - 05:56 PM

You can do some planetary Imaging with that scope as well as lunar photography you can also try short exposure stacking through a program like sharpcap. In none of these situations do you need guiding, and it will give you immediate results.
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#17 AhBok

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Posted 14 April 2021 - 06:51 PM

I think APshooter has the best response and that is to lead newbie astrophotographers in the direction of what is reasonably possible with their current equipment. I personally, would not recommend learning DSO imaging with a C8, though it is obviously possible. I have often recommended starting AP of the moon and planets with a C8.

#18 TelescopeGreg

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Posted 14 April 2021 - 08:28 PM

I think APshooter has the best response and that is to lead newbie astrophotographers in the direction of what is reasonably possible with their current equipment. I personally, would not recommend learning DSO imaging with a C8, though it is obviously possible. I have often recommended starting AP of the moon and planets with a C8.

+1, absolutely.

 

But, note this is the Deep Sky Imaging forum...




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