Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Celestar 8 good for DSO astrophotography?

astrophotography SCT
  • This topic is locked This topic is locked
45 replies to this topic

#1 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 03:17 AM

I’ve heard that they shouldn’t be used for deep-sky astrophotography because of the narrow FOV. Is it possible, but difficult? Totally impossible? What has your experience been with them? Let me know. I’m new to this site so forgive me for any formatting mistakes. Thanks!

Edited by Pokitomas, 08 August 2020 - 03:17 AM.

 

#2 endlessky

endlessky

    Viking 1

  • -----
  • Posts: 543
  • Joined: 24 May 2020
  • Loc: Padova, Italy

Posted 08 August 2020 - 03:49 AM

I bought a Celestar C8 at the end of the 90s. I used it back then to do some piggy-back, film astrophotography, by mounting a SLR on top of the telescope tube and using an illuminated reticule eyepiece for manually guiding. Back in those days, I even tried mounting the SLR directly on the C8 and use an off-axis guider, with the same eyepiece, to take some photographs of M1, M31 and M42.

 

I recently restarted - digital - astrophotography in January of this year. I bought a used NEQ6 Pro, deforked the C8, put a Losmandy dovetail on it, so I could mount it on the GEM. I mostly use it for visual, as I don't have an auto-guider setup, yet. Mainly, I do astrophotography with a Nikon D5300, mounted on the NEQ6 Pro, and some lenses that I have from daytime, normal photography.

 

I did, however, try to take some pictures with the C8. Results were not completely horrible, but I was really limited to only 30-45 seconds exposures, being unguided and completely having to rely on the tracking of the mount. I think I can definitely go longer, once my auto-guiding setup arrives.

 

The field of view is limited, for some objects (wide nebulae), but it is perfect for galaxies, planetary nebulae, globular clusters, planetary imaging and the Moon. So, it really depends on what you are interested in capturing. Also, wider, shorter focal lengths telescopes or lenses are more forgiving in terms of tracking/guiding and you can do longer exposures without an auto-guider.

 

I haven't tried doing digital imaging with the C8 on the original, forked Celestar mount, as I didn't have the tripod anymore and I sold the fork after I removed the OTA, before buying the NEQ6 Pro.

 

So, it all depends on what you are interested in capturing, what equipment you have and - mostly - your skill set, that will get better and better the more you do this.


 

#3 Cometeer

Cometeer

    Vanguard

  • *****
  • Posts: 2,471
  • Joined: 07 Aug 2013
  • Loc: SF Bay Area, California or Illinois

Posted 08 August 2020 - 03:59 AM

I would not recommend it at all if it’s on the original forks, wedge or not. 

 

If it’s just the OTA, I still would not recommend it for a beginner. The focal length is unforgiving and its a very slow system (f/10). This requires longer exposure times than a faster system. 
 

I think the best scope to start out with for AP is a small (60-80mm) fpl-53 doublet or better. 


 

#4 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 04:09 AM

I bought a Celestar C8 at the end of the 90s. I used it back then to do some piggy-back, film astrophotography, by mounting a SLR on top of the telescope tube and using an illuminated reticule eyepiece for manually guiding. Back in those days, I even tried mounting the SLR directly on the C8 and use an off-axis guider, with the same eyepiece, to take some photographs of M1, M31 and M42.

I recently restarted - digital - astrophotography in January of this year. I bought a used NEQ6 Pro, deforked the C8, put a Losmandy dovetail on it, so I could mount it on the GEM. I mostly use it for visual, as I don't have an auto-guider setup, yet. Mainly, I do astrophotography with a Nikon D5300, mounted on the NEQ6 Pro, and some lenses that I have from daytime, normal photography.

I did, however, try to take some pictures with the C8. Results were not completely horrible, but I was really limited to only 30-45 seconds exposures, being unguided and completely having to rely on the tracking of the mount. I think I can definitely go longer, once my auto-guiding setup arrives.

The field of view is limited, for some objects (wide nebulae), but it is perfect for galaxies, planetary nebulae, globular clusters, planetary imaging and the Moon. So, it really depends on what you are interested in capturing. Also, wider, shorter focal lengths telescopes or lenses are more forgiving in terms of tracking/guiding and you can do longer exposures without an auto-guider.

I haven't tried doing digital imaging with the C8 on the original, forked Celestar mount, as I didn't have the tripod anymore and I sold the fork after I removed the OTA, before buying the NEQ6 Pro.

So, it all depends on what you are interested in capturing, what equipment you have and - mostly - your skill set, that will get better and better the more you do this.


Thank you so much for all the great advice! It’s so nice to hear from somebody with direct experience. You have given me some wonderful insight that will help my final decision, thank you.
 

#5 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 04:11 AM

I would not recommend it at all if it’s on the original forks, wedge or not.

If it’s just the OTA, I still would not recommend it for a beginner. The focal length is unforgiving and its a very slow system (f/10). This requires longer exposure times than a faster system.

I think the best scope to start out with for AP is a small (60-80mm) fpl-53 doublet or better.


Thank you! This helps a lot. About the original fork (assuming it has the wedge) what if I took multiple ~30 second exposures, and then stacked them in top of each other? Would this help?
 

#6 Cometeer

Cometeer

    Vanguard

  • *****
  • Posts: 2,471
  • Joined: 07 Aug 2013
  • Loc: SF Bay Area, California or Illinois

Posted 08 August 2020 - 04:17 AM

Thank you! This helps a lot. About the original fork (assuming it has the wedge) what if I took multiple ~30 second exposures, and then stacked them in top of each other? Would this help?

 At f/10, a 30s exposure would not show much at all. I really wouldn’t recommend  this for AP. 


 

#7 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 04:28 AM

At f/10, a 30s exposure would not show much at all. I really wouldn’t recommend this for AP.


Aw man bummer but good to know! Does that apply to pretty much every DSO?
 

#8 endlessky

endlessky

    Viking 1

  • -----
  • Posts: 543
  • Joined: 24 May 2020
  • Loc: Padova, Italy

Posted 08 August 2020 - 04:30 AM

Thank you so much for all the great advice! It’s so nice to hear from somebody with direct experience. You have given me some wonderful insight that will help my final decision, thank you.

Glad to help! As far as taking multiple 30s exposures, that's what I was doing when I mounted the C8 on the NEQ6 Pro. It takes hundreds of them, before you can actually start seeing some details. F/10 is really slow and 30s is really short, for the frame to be exposed correctly. It can be done - and I have done it as well - but the results I get from my 70-300mm Nikkor lens, despite it being a not ideal lens for astrophotography, are much more enjoyable and easier to collect.

 

Plenty will advice you to start with a good, solid German equatorial mount (HEQ5 Pro and beyond), and with a small, fast refractor (80mm f/6, possibly with a flattener/reducer, to bring it to f4.8). Me included. The zoom kit lens I am using has very bad tilting, aberration and internal flares. After 6 months I got tired of using it, as the results I am getting are not skill-limited but optics-limited and I ordered exactly that: an 80mm f/6 triplet apochromatic refractor and a 0.8x flattener/reducer. There's a whole lot of targets that look perfect in an APS-C sensor and 380mm focal length. It will be a lot easier and a more enjoyable experience starting with this, than going straight into the 2000mm+ focal lengths. These require massive - and expensive - mounts, good guiding (preferrably off-axis guiding, to avoid flexure and mirror flop) and longer exposures. I'll try my C8, sure, once I get my new gear and the auto-guiding setup I ordered, but I can bet I'll do most of my imaging with the refractor.


Edited by endlessky, 08 August 2020 - 04:31 AM.

 

#9 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 06:40 AM

Are modern short FL, fast refractors, on a modern GEM easier for AP than an f/10 fork mounted 8" SCT? Sure. To imply though that SCT's are poorly suited for AP is a rather unrealistic assessment. These instruments were designed with AP in mind. These two images, M13 and M42 were taken at f/10, on a fork mounted Ultima 8. These are old pics, film pics, manually guided single exposures of a few minutes duration. They are noisy and grainy, but those are artifacts of the film, not the fault of the instrument. Modern software and sensors used with the same setup would produce much cleaner results.

 

M 13 comp.jpg

 

M 42 comp.jpg

 

Lee


 

#10 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 06:48 AM

Solar and lunar are a piece cake for an SCT. These were taken with the same Ultima 8 working at f/6.3. Again, they're single exposures, short ones, so no guiding was involved. The Mercury transit is obviously a combined image of multiple exposures. Do not denigrate the venerable 8 inch SCT. Certainly, if that's what you have, don't splurge on a fast APO without experimenting with your Celestar first. 

 

7-24-15 comp.jpg

 

Transit Combined comp.jpg

 

Lee


 

#11 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 06:51 AM

 At f/10, a 30s exposure would not show much at all. I really wouldn’t recommend  this for AP. 

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


Edited by lee14, 08 August 2020 - 07:13 AM.

 

#12 kathyastro

kathyastro

    Vanguard

  • *****
  • Posts: 2,256
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 08 August 2020 - 07:07 AM

The big factor working against you with that scope is the focal ratio. 

 

I image at f/4, and I finally got an image of M101 that I was happy with at 4.5 hours of total integration time.  At f/10, the light-gathering power is (4 / 10) ^ 2 as much, requiring 6.25 times as much exposure time to collect the same number of photons per pixel.  So the same image that I get in 4.5 hours would require 28 hours of integration time at f/10.

 

Or, going the other way, what you get in a single 30 second exposure is what I get in a 4.8 second exposure.  Which ain't much.


 

#13 endlessky

endlessky

    Viking 1

  • -----
  • Posts: 543
  • Joined: 24 May 2020
  • Loc: Padova, Italy

Posted 08 August 2020 - 07:22 AM

Lee, I am not saying that the C8 cannot be used. The single exposure you took of M42 looks pretty much the same as the one I took in the 90s, by manually guiding for 10 minutes, with a film SLR.

Conversely, using a faster 300mm lens, 40 shots taken at 45s each, for a mere total integration time of 30 minutes, which was my first digital photograph taken back in January of this year, looks much better and yields a lot more details and more nebulosity captured.

If you already have the C8, by all means, try it. But the learning curve of digital astrophotography is already pretty steep, why making it even steeper when it doesn't have to be?
 

#14 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 07:27 AM

The big factor working against you with that scope is the focal ratio. 

 

I image at f/4, and I finally got an image of M101 that I was happy with at 4.5 hours of total integration time.  At f/10, the light-gathering power is (4 / 10) ^ 2 as much, requiring 6.25 times as much exposure time to collect the same number of photons per pixel.  So the same image that I get in 4.5 hours would require 28 hours of integration time at f/10.

 

Or, going the other way, what you get in a single 30 second exposure is what I get in a 4.8 second exposure.  Which ain't much.

Certainly true. That's why the f/6.3 reducer/corrector is such a handy item for an f/10 SCT. It's not f/4, but it makes a big difference.

 

Lee


 

#15 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 07:32 AM

Lee, I am not saying that the C8 cannot be used. The single exposure you took of M42 looks pretty much the same as the one I took in the 90s, by manually guiding for 10 minutes, with a film SLR.
 

I know. Your write-up was spot on. My comment was directed to the statement "I would not recommend it at all". 

 

Lee


 

#16 Woody218

Woody218

    Vostok 1

  • *****
  • Posts: 123
  • Joined: 01 Jul 2020
  • Loc: Bismarck, ND

Posted 08 August 2020 - 07:49 AM

The f/6.3 reducer/corrector is something that everyone who owns an SCT should have.


 

#17 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 12:44 PM

Here is an excellent example of what an 8 inch SCT working at f/10 is capable of. Image just posted here: https://www.cloudyni...pelican-nebula/

 

Lee


Edited by lee14, 08 August 2020 - 12:52 PM.

 

#18 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 12:52 PM

The f/6.3 reducer/corrector is something that everyone who owns an SCT should have.


I am really considering purchasing this!
 

#19 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 12:55 PM

Here is an excellent example of what an 8 inch SCT working at f/10 is capable of. Image just posted here: https://www.cloudyni...pelican-nebula/

Lee


That is great. Thank you! I appreciate your other reply on SCTs as well. It seems that a C8 would be good for my purposes, but perhaps I should get an alternative to the fork mount.
 

#20 endlessky

endlessky

    Viking 1

  • -----
  • Posts: 543
  • Joined: 24 May 2020
  • Loc: Padova, Italy

Posted 08 August 2020 - 01:01 PM

I know. Your write-up was spot on. My comment was directed to the statement "I would not recommend it at all". 

 

Lee

Thank you for clearing that up! The C8 can definitely work, even if it will take a little more work. The focal reducer, as you suggested, will certainly help (both in exposure time and in tracking/guiding).


 

#21 Achernar

Achernar

    Voyager 1

  • *****
  • Posts: 11,786
  • Joined: 25 Feb 2006
  • Loc: Mobile, Alabama, USA

Posted 08 August 2020 - 01:24 PM

The OTA certainly can be used for DSO astrophotography, but you'll want to upgrade the mount. Also focal reducers and electronic cameras will enable you to record objects much faster than you can with film. It is not suited to photographing large DSO's such as the North American Nebula in their entirety, but ideal for small DSO's such as the Ring Nebula.

 

Taras


 

#22 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 01:29 PM

That is great. Thank you! I appreciate your other reply on SCTs as well. It seems that a C8 would be good for my purposes, but perhaps I should get an alternative to the fork mount.

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


Edited by lee14, 08 August 2020 - 01:31 PM.

 

#23 lee14

lee14

    Apollo

  • *****
  • Posts: 1,036
  • Joined: 19 Dec 2009
  • Loc: CNY

Posted 08 August 2020 - 01:44 PM

One caveat I've neglected to mention about guiding. The standard 8" Celestron SCT did not include a declination motor. That was an add-on, and it came with a hand control that corrected both axes.

 

Lee


 

#24 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 02:28 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


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.
 

#25 Pokitomas

Pokitomas

    Lift Off

  • *****
  • topic starter
  • Posts: 9
  • Joined: 08 Aug 2020

Posted 08 August 2020 - 02:30 PM

The big factor working against you with that scope is the focal ratio.

I image at f/4, and I finally got an image of M101 that I was happy with at 4.5 hours of total integration time. At f/10, the light-gathering power is (4 / 10) ^ 2 as much, requiring 6.25 times as much exposure time to collect the same number of photons per pixel. So the same image that I get in 4.5 hours would require 28 hours of integration time at f/10.

Or, going the other way, what you get in a single 30 second exposure is what I get in a 4.8 second exposure. Which ain't much.


Man! That’s a pain. Hopefully a reducer would help with that. And perhaps I’ll have a better time with the smaller DSOs as well.
 


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: astrophotography, SCT



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics