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Celestar 8 good for DSO astrophotography?

astrophotography SCT
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#26 Cometeer

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Posted 08 August 2020 - 02:54 PM

The OP is talking about integrating multiple short exposures. That's a completely different animal than one 30 second exposure, and is the standard process for modern AP. It's the total integration time that counts, not the length of the individual exposures,

 

Lee

I am well aware of how modern AP is done. My point is that a 30s exposure at f/10 will require a much longer integration time than with a faster system. 
 

I stand by my words, I still would not recommend a SCT on a older fork mount to a beginner for AP. Any sort of dithering or guiding must be done manually. 

 

 


 

#27 Cometeer

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Posted 08 August 2020 - 02:58 PM

The SCT is considered by many the best 'all-around' scope. While other scopes may do specific tasks better, the SCT does them all- moderately well. I've left mine on its fork mount, if the one you're considering is already mounted on one, try it out before going to a GEM. If it's properly polar aligned, exposures of 2 or 3 minutes (like the image I referenced above) should be possible without guiding. Gear error, or 'periodic error', if present, on that scope, occurs at four minute intervals. If the 'error' occurs during some of the exposures, they can simply be discarded prior to stacking.

 

Lee

 Periodic error has to do with the mount, not the scope. You cannot make a general statement that a 2-3 minute exposure can be achieved simply based on the scope. If his particular mount is very accurate, then perhaps 2-3min is possible with or without the reducer. But, for the majority of the Chinese-made gems, I would use guiding for the pixel/arcsec scale that the SCT/camera will be operating at.  


 

#28 Cometeer

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Posted 08 August 2020 - 03:03 PM

OP, from your discord posts, I’m under the impression that you do not own the Celestar C8 yet. If that’s the case, there are better scopes to purchase for imaging. If you do already own it, then go ahead and give it a go for imaging. 


 

#29 Pokitomas

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Posted 08 August 2020 - 03:10 PM

OP, from your discord posts, I’m under the impression that you do not own the Celestar C8 yet. If that’s the case, there are better scopes to purchase for imaging. If you do already own it, then go ahead and give it a go for imaging.


I do not have the C8. I’m not quite educated about good alternatives though, as many of them seem to be perhaps out of my price range.
 

#30 lee14

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Posted 08 August 2020 - 03:27 PM

I think that works for me. Maybe I won’t be able to take those stunning pictures of the dumbbell nebula etc., but I it seems like a solid imaging and visual scope.

M 27 is a well suited target. Also M 57. They're small, so the long focal length is an advantage. The surface brightness of many planetaries is relatively high, so exposures don't require multiple hours. 

 

M 27 comp.jpg

M 27

 

M 57 comp.jpg

M 57

 

These are several minutes at f/10, on high ISO film. A tad grainy and noisy, but that's what you got with high speed color film back in the 90's. Film AP often necessitated multiple trips to the color lab, trying to get the lab tech to fuss around with his auto settings so the image would look better. I'd much rather spend my time at home at the computer with modern software and processing techniques. You'll do fine with the dumbbell as long as the total integration time is there.

 

Lee


Edited by lee14, 08 August 2020 - 03:30 PM.

 

#31 lee14

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Posted 08 August 2020 - 03:36 PM

 Periodic error has to do with the mount, not the scope. 

No kidding. The reference was clearly to the standard fork mount supplied with Celestron's 8 inch SCT's. The 4 minute periodic error is solely dependent on the gear ratios in the mount.

 

Lee


Edited by lee14, 08 August 2020 - 03:39 PM.

 

#32 kathyastro

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Posted 08 August 2020 - 05:27 PM

Man! That’s a pain. Hopefully a reducer would help with that.

Indeed, the reducer will help a lot.
 


 

#33 jprideaux

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Posted 09 August 2020 - 04:21 AM

The EAA forum has lots of people who bought a CST for visual and then later wanted to do some imaging. Then they buy focal reducers to get the F# down quite substantially. There is a .63 reducer but also some options from Starizona to go down to F4 (night owl) or F2 (hyperstar). Some in that forum still use their alt-az Mount with their CST reduced to F2 and do a style of imaging with stacking many short exposures to get something viewable on a monitor after a couple minutes. So there are lots of options. But if you are only interested in imaging the advice is good to get a small light good quality refractor on a GEM and guide.

Edited by jprideaux, 09 August 2020 - 04:22 AM.

 

#34 schmeah

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Posted 09 August 2020 - 05:53 AM

This was taken many years ago with a fork mounted SCT (10”LX200R on wedge) at f/10 shortly after I began imaging. It was unguided short exposures. But the LX200 has a much sturdier fork. 
 

I am one of the biggest proponents here of “give it a shot with what you’ve got”. But you don’t have it yet. So don’t get it. It will be very difficult to get any decent results consistently with that setup. As advised by others, a short refractor on a GEM is a far easier and likely more successful way to start. If you really want to image with an SCT, I would start with one that at least has mirror locks to mitigate shift, and a sturdier mount.

 

Derek

 

12C164D7-E62C-42E1-BECF-EDE792758A43.jpeg

 

 


 

#35 endlessky

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Posted 09 August 2020 - 06:57 AM

I am one of the biggest proponents here of “give it a shot with what you’ve got”. But you don’t have it yet. So don’t get it. 

I was under the impression that the Celestar C8 was something that the OP already owned. If that was the case, I agree with you: if you have it, there's not much you can lose by trying it (one imaging session).

 

But if you haven't spent the money on anything, yet, then - of course - go through the easier, more panoramic hiking route, before you try climbing a mountain bare handed.


 

#36 lee14

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Posted 12 August 2020 - 11:49 AM

Ok...I've been looking over many of the outstanding images posted on CN over the last few days, and the majority of them have been acquired with SCT's. While fast Newtonians and short focus Apo's can certainly produce good results, SCT's are equally capable. The ease of achieving good results may vary, but the most important variable is the skill of the photographer, not the type of instrument they're using.

 

Lee


 

#37 bobzeq25

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Posted 12 August 2020 - 12:17 PM

The SCT is fine for _doing_ astrophotography, in the hands of an experienced imager.

 

A large number of beginners have pretty much found it to be a nightmare for _learning_ astrophotography.  Just makes everything very hard.  A common solution is to ditch it in favor of a smaller scope.  The difference is day and night; going from frustration to enjoyment.  I have a great many of these quotes.

 

"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!"

 

Learning and doing are completely different activities.  Unintuitive, but, as has been demonstrated many times, true.


Edited by bobzeq25, 12 August 2020 - 12:20 PM.

 

#38 lee14

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Posted 12 August 2020 - 12:38 PM

The SCT is fine for _doing_ astrophotography, in the hands of an experienced imager.

 

A large number of beginners have pretty much found it to be a nightmare for _learning_ astrophotography.  Just makes everything very hard.  A common solution is to ditch it in favor of a smaller scope.  The difference is day and night; going from frustration to enjoyment.  I have a great many of these quotes.

 

Yes, and experience is achieved by.....getting experience.

 

This reasoning is what in formal logic is called a 'hasty generalization'. In this case, citing anecdotal evidence over empirical. Retaining the evidence that supports a proposition, while ignoring that which does not. Count up the solar system or deep sky images posted over the last week. The instruments are overwhelmingly SCT's. Perhaps the SCT requires a little more skill or effort, but certainly not the level implied by 'regretting 6 months of effort'.

 

Lee


 

#39 bobzeq25

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Posted 12 August 2020 - 12:49 PM

Yes, and experience is achieved by.....getting experience.

 

This reasoning is what in formal logic is called a 'hasty generalization'. In this case, citing anecdotal evidence over empirical. Retaining the evidence that supports a proposition, while ignoring that which does not. Count up the solar system or deep sky images posted over the last week. The instruments are overwhelmingly SCT's. Perhaps the SCT requires a little more skill or effort, but certainly not the level implied by 'regretting 6 months of effort'.

 

Lee

Here's my point.  People learn better if they're not struggling with a difficult setup.  The data shows clearly that beginners find SCTs _very_ difficult to learn on.  You didn't like "6 months".

 

How about a year?

 

"Of all the recommendations though, if you want to get into imaging then a short imaging refractor is probably the best one (IMHO).  I have a C8 and this was the scope I learned AP on.  It was a long, tough struggle and I have no good pictures to show for it.  I could have easily saved a year by starting with a more image-friendly scope."

 

How about two years?

 

"I'm biased as I wasted two years starting out with a C11. After I sold it and bought a 660mm refractor I was up and running 2nd or 3rd night out."

 

I've got as many of those as you want.  One guy was so interested in steering others away from his mistake (it's a common one, the degree of difficulty involved is just not intuitive) that he took the time to make a YouTube video about it.

 

The SCT is just the wrong tool for the job.  It's like trying to learn to build fine furniture while driving nails with a Crescent wrench.  You may learn a lot about driving nails with a Crescent wrench, but it won't help you learn to build fine furniture.

 

Experienced imagers do fine images with SCTs.  They're horrible to learn on.  Which is my only concern here.


Edited by bobzeq25, 12 August 2020 - 12:58 PM.

 

#40 endlessky

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Posted 12 August 2020 - 01:13 PM

Yes, and experience is achieved by.....getting experience.

As with most things, getting experience is easier if you do it in smaller steps, starting with easier things.

 

Let me explain with some examples. You don't learn math by jumping straight in differential equations, if you can't do the basics (addition, subtraction, multiplication or division). You don't learn car racing going on a Formula 1 car, if you don't do go-karts first. The list can go on and on.

 

Can I learn driving with a Ferrari F430? Probably, if the driving school would even have one to begin with and trust me enough to drive it and learn with it. Is it easier to learn with a small Renault Clio? Obviously yes.

 

Given the choice, I would gladly learn astrophotography with a small, fast refractor, rather than jumping straight into the 2000mm+ focal lengths. And, from my personal journey - having tried even my old C8 - it's not only an easier experience, but also a much more enjoyable one.


 

#41 mackiedlm

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Posted 12 August 2020 - 01:26 PM

Here's my point.  People learn better if they're not struggling with a difficult setup.  The data shows clearly that beginners find SCTs _very_ difficult to learn on.  You didn't like "6 months".

 

How about a year?

 

"Of all the recommendations though, if you want to get into imaging then a short imaging refractor is probably the best one (IMHO).  I have a C8 and this was the scope I learned AP on.  It was a long, tough struggle and I have no good pictures to show for it.  I could have easily saved a year by starting with a more image-friendly scope."

 

How about two years?

 

"I'm biased as I wasted two years starting out with a C11. After I sold it and bought a 660mm refractor I was up and running 2nd or 3rd night out."

 

I've got as many of those as you want.  One guy was so interested in steering others away from his mistake (it's a common one, the degree of difficulty involved is just not intuitive) that he took the time to make a YouTube video about it.

 

The SCT is just the wrong tool for the job.  It's like trying to learn to build fine furniture while driving nails with a Crescent wrench.  You may learn a lot about driving nails with a Crescent wrench, but it won't help you learn to build fine furniture.

 

Experienced imagers do fine images with SCTs.  They're horrible to learn on.  Which is my only concern here.

When trotting out your old selective chestnuts you always seem to miss this one Bob ;

 

"I have spent a year working on getting my LX200 GPS to take some pictures. It was difficult and complicated but I am now getting 3 minute guided exposures that I am happy with. I have recently added a fast short refractor and solid GEM to my kit and its great. Do I regret spending that year with the SCT - Not for a second. I had a blast, learned a ton of stuff which will only help me as I progress further. Do I feel I wasted time or money by not going immediately to a short fast refractor - Not for a second. It was worth every second and every cent to get the pleasure and experience I gained from it.  Will I now be getting rid of or mothballing the LX200 now I have a nice little refractor. No way! In fact on my last clear night the two were out together taking targets suitable for their own specific capabilities"

 

But, as has already been said above - if the OP does not actually have the C8 already there are better options than that.


 

#42 schmeah

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Posted 12 August 2020 - 06:26 PM

Almost any scope can be used to begin astrophotography, even the the C8. However satisfaction for the imager will depend upon his/her expectations. If any recognizable representation of target is satisfactory, then by all means use whatever scope you like. But most imagers will eventually like to get images comparable to those that they see posted here on CN. That requires a system that doesn’t have flaws that will make that desire impossible regardless of the effort put into it. The challenges of a greater FL and image scale can be overcome with effort. Excellent images can be obtained with a fork/wedge setup. There is one “flaw” inherent to SCTs that can’t be overcome even with the effort, namely mirror flop, leading to image and focus shift and poor guided results.So IMO, the minimum requirement for success when imaging with an SCT is a mirror lock and to a lesser degree an off axis guider. The C8 doesn’t have a mirror lock, and the plastic single arm fork is not robust enough to provide a stable imaging platform. So I would never suggest that someone get this system if their interest is in imaging DSOs.
 

But regarding those quotes about all that wasted time trying to image with an 8” Edge (assuming on a robust mount), that I don’t get. I suspect that with more effort or some good guidance it shouldn’t be a problem.

 

Derek


 

#43 bobzeq25

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Posted 13 August 2020 - 05:44 PM

Almost any scope can be used to begin astrophotography, even the the C8. However satisfaction for the imager will depend upon his/her expectations. If any recognizable representation of target is satisfactory, then by all means use whatever scope you like. But most imagers will eventually like to get images comparable to those that they see posted here on CN. That requires a system that doesn’t have flaws that will make that desire impossible regardless of the effort put into it. The challenges of a greater FL and image scale can be overcome with effort. Excellent images can be obtained with a fork/wedge setup. There is one “flaw” inherent to SCTs that can’t be overcome even with the effort, namely mirror flop, leading to image and focus shift and poor guided results.So IMO, the minimum requirement for success when imaging with an SCT is a mirror lock and to a lesser degree an off axis guider. The C8 doesn’t have a mirror lock, and the plastic single arm fork is not robust enough to provide a stable imaging platform. So I would never suggest that someone get this system if their interest is in imaging DSOs.
 

But regarding those quotes about all that wasted time trying to image with an 8” Edge (assuming on a robust mount), that I don’t get. I suspect that with more effort or some good guidance it shouldn’t be a problem.

 

Derek

I understand some don't get it.  But I'm a scientist, well used to evaluating data, and the data on this is unquestionably clear.

 

One can reasonably disagree about the extent of the problem.  But _many_ posts here (and the recommendations of a substantial majority of experts) make it clear that:

 

It's a problem.

 

For a substantial number of people dropping back to a smaller scope solved the problem.  Made them _much_ happier.  That's exactly the experiment that one would design to investigate the phenomenon.  You could not ask for better data than that.

 

I just can't see not letting the average person who wants to image and coming here for advice hear about that _large_ amount of data.  Problems and unhappiness are a major risk.  I'd say clearly the expected outcome.  There are exceptions, but they're exceptions.


Edited by bobzeq25, 13 August 2020 - 05:52 PM.

 

#44 schmeah

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Posted 13 August 2020 - 07:55 PM

I understand some don't get it.  But I'm a scientist...

rolleyes.gif

 

I just can't see not letting the average person who wants to image and coming here for advice hear about that _large_ amount of data.  Problems and unhappiness are a major risk. 

Folks who are passionate about astrophotography are far from average. And many can do stuff with a little effort even as you discourage them. 

 


 

#45 lee14

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Posted 14 August 2020 - 07:15 AM

A compilation of anecdotal evidence supporting a preconceived outcome is not an experiment, it's a confirmation of experimenter bias. An actual valid design would be a double blind longitudinal study including a control group. Or, a straightforward statistical analysis could be applied to images posted on CN within a given period of time, including a sufficient sample size of photographers and instruments to determine the level of significance as a P Value. A subjective measure of 'happiness' might be appropriate as a sociological or psychological experimental metric, but it has little value in determining the outcomes of AP with various types of instruments, particularly when those results can be determined objectively.

 

Lee


 

#46 spereira

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Posted 14 August 2020 - 07:26 AM

Since the OP has not posted since #29, and this topic has (once again) devolved into the same argument that we've seen many times before, I'm going to shut it off.

 

:lock:

 

smp


 


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