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Telescope for capturing galaxies

astrophotography
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#1 Jesus Munoz

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Posted 17 September 2019 - 11:28 PM

Hello,

 

I have been astrophotographying large objects for about 5 years (mainly nebulas) with telescopes from 255-1000 mm of focal lenght.  Now I want to go beyond and hunt some galaxies, but at 1000 mm those objects are shown very small (MN190 + ZWO ASI1600).  What telescope do you recommend for taking for example a close up of the hamburger galaxy in Leo or NGC 2903 also in Leo?

 

My mount is a CEM120EC, permanently installed on a pier. 

 

Thanks in advance

 

Jose


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#2 dhaval

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Posted 17 September 2019 - 11:35 PM

You need the big boys to get up close and personal - Celestron C11 EdgeHD (2800mm FL), GSO RC scopes - at least 10in, 12in is better. At F8, a 12in RC scope will give you around 2400mm FL while the 10in will give you around 2000mm FL. You need that much at least. You want to ditch reducers. RC scopes will need flatteners. The C11 should be fine without flatteners. I should also mention C9.25 EdgeHD. I won't go lower than that.

 

That camera will produce over sampled images - ensure your are guiding appropriately. 

 

CS!



#3 Jesus Munoz

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Posted 17 September 2019 - 11:44 PM

You need the big boys to get up close and personal - Celestron C11 EdgeHD (2800mm FL), GSO RC scopes - at least 10in, 12in is better. At F8, a 12in RC scope will give you around 2400mm FL while the 10in will give you around 2000mm FL. You need that much at least. You want to ditch reducers. RC scopes will need flatteners. The C11 should be fine without flatteners. I should also mention C9.25 EdgeHD. I won't go lower than that.

 

That camera will produce over sampled images - ensure your are guiding appropriately. 

 

CS!

Thanks Dhaval!  Checking the telescopes you own I see you have a C11 EdgeHD and a Meade ACF 10" f/8 (working with a KAF8300 sensor, around the same size of my ZWO ASI1600).  What's your opinion of your telescopes, the performance of the C11 vs M10 ACF?

 

Regards



#4 james7ca

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Posted 18 September 2019 - 12:31 AM

It's image scale that matters when imaging small objects, not just the size or focal length of the telescope. In fact, given the seeing conditions that most have to deal with it probably doesn't do much good to go beyond eight inches in aperture in terms of the detail that you can record with a camera (you may find that a bigger but blurrier image isn't much satisfaction). That said, for any given image scale a larger aperture telescope will generally produce a "faster" system in terms of exposure. But, that also depends upon your camera and its read noise and quantum efficiency.

 

Thus, you should be thinking about BOTH the scope and the camera and for the "best" results you need to match one to the other for any particular image scale and type of DSO. And, of course, once you change image scale you need to consider how well your mount will perform, since poor guiding could negate any change in image scale or aperture.

 

Your signature says that you have access to a 14" Newtonian and a 9.25" SCT and both of those should make a completely satisfactory scope for imaging galaxies.

 

If you just want more image scale then one inexpensive option would be to change your camera to something like Sony's IMX178 or IMX183 (both with 2.4 micron pixels). A change to that camera from your current ASI1600 would give you an image scale boost of 3.8um/2.4um ≈ 1.6X which would be similar to taking your MN190 to a focal length of 1600mm (with an image scale of approximately 0.5 arc seconds per pixel).

 

However, if you are looking for the ultimate galaxy imaging system then you probably want the largest scope that your mount can honestly handle with the largest pixel size camera you can find in a combination that will give you something near to the same 0.5 arc second per pixel scale that you could get by just changing cameras on your current MN190.


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#5 Chucke

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Posted 18 September 2019 - 01:29 AM

Something to consider if you are using a Newtonian is the spot size produced by your coma corrector.  It won't do much good to move from a camera with 5 micron pixels to one with 2 micron pixels if your coma corrector produces a 10 micron spot.  It is not always easy find this spec for coma correctors.


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#6 james7ca

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Posted 18 September 2019 - 02:59 AM

Something to consider if you are using a Newtonian is the spot size produced by your coma corrector.  It won't do much good to move from a camera with 5 micron pixels to one with 2 micron pixels if your coma corrector produces a 10 micron spot.  It is not always easy find this spec for coma correctors.

Yes, the performance of your optical system is a factor. The OP's MN190 has a theoretical Airy disk diameter of 6.6 microns (green light, f/5.3) which would be sampled with 2.8 pixels using a camera like the IMX178/IMX183. That's a decent value and I know that my five inch, f/5.2 refractor which produces a similar sized Airy disk (6.5um) is more often limited by the seeing conditions than my sampling with either of those cameras. Of course, with an aperture of nearly 7.5 inches the MN190 should offer a better angular resolution than I get with my refractor (1.35 arc seconds versus my 2.02). Thus, with really good seeing and assuming good optical performance and guiding that should result in even better results than I see.

 

That said, I don't image galaxies that often given my red/orange zone light pollution and the fact that my seeing is usually not that good. But below is an image of the so-called Black Eye galaxy (M64) that I did last year with a five inch refractor and the ASI178MM that has pretty good resolution (note the detail in the core and the evidence of the double star on the lower right, not often revealed in most images of this galaxy regardless of the size of telescope used for the imaging). This image had only 20 minutes of exposure using a series of 7.5s subs and that resulted in a measured FWHM of just 1.7 arc seconds (luminance only).

Attached Thumbnails

  • Black Eye Galaxy.jpg

Edited by james7ca, 18 September 2019 - 03:03 AM.

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#7 leemr

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Posted 18 September 2019 - 03:15 AM

I'm basically just going to second everything James already said, but especially the point that it's more about image scale than focal length.

 

I shoot mostly galaxies and will probably be almost exclusively galaxies going forward. Everything in my astrobin gallery from 2018 onwards (including 4 IOTD and 3 TP) has been shot at 0.5"/px with an 8" Newtonian running at F5 with a Paracorr and the QHY178m.

 

Again going back to what James said though, a longer focal length and bigger pixels that still get you 0.5"/px may be a better option if you have the wallet for it. It can still be done well at shorter focal lengths though.


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#8 jgraham

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Posted 18 September 2019 - 07:17 AM

My favorite scope for imaging galaxies in an 10" f/4 Schmidt Newtonian; big, fast, with a decent focal length. I'd be curious to see how well a modern imaging Newtonian with a good coma corrector would work as well.

 

The Beast...

 

SN10 ZWO ASI071MC (v1).jpg

 

:)

 



#9 james7ca

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Posted 18 September 2019 - 09:18 AM

I'm basically just going to second everything James already said, but especially the point that it's more about image scale than focal length.

 

I shoot mostly galaxies and will probably be almost exclusively galaxies going forward. Everything in my astrobin gallery from 2018 onwards (including 4 IOTD and 3 TP) has been shot at 0.5"/px with an 8" Newtonian running at F5 with a Paracorr and the QHY178m.

 

Again going back to what James said though, a longer focal length and bigger pixels that still get you 0.5"/px may be a better option if you have the wallet for it. It can still be done well at shorter focal lengths though.

Lee, those are really excellent images of galaxies. Thanks for sharing your work with the IMX178.


Edited by james7ca, 18 September 2019 - 09:19 AM.

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#10 Noobulosity

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Posted 18 September 2019 - 06:31 PM

I'm basically just going to second everything James already said, but especially the point that it's more about image scale than focal length.

 

I shoot mostly galaxies and will probably be almost exclusively galaxies going forward. Everything in my astrobin gallery from 2018 onwards (including 4 IOTD and 3 TP) has been shot at 0.5"/px with an 8" Newtonian running at F5 with a Paracorr and the QHY178m.

 

Again going back to what James said though, a longer focal length and bigger pixels that still get you 0.5"/px may be a better option if you have the wallet for it. It can still be done well at shorter focal lengths though.

I don't really have anything to add here... sorry.  Just chiming in on your Astrobin images...  just, wow!  Absolutely amazing.  Those integration times...  lots and lots of data to capture all that detail, not to mention the processing involved.  Very nice.


Edited by Noobulosity, 18 September 2019 - 06:32 PM.

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#11 Jesus Munoz

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Posted 18 September 2019 - 10:44 PM

Thank you for all of your posts.  I have much more clear the way to go: image scale.  Maybe my MN190 with a ICX183 sensor is a good route.

 

By the way, incredible images James and Lee, really inspiring images.

 

Regards


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#12 leemr

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Posted 20 September 2019 - 12:35 AM

Did you mean the IMX183, Jesus? I think the IMX183 combined with the MN190 would be a great galaxy rig, definitely worth trying considering you already have the scope and the cameras that use that sensor are relatively cheap.

 

And thanks everyone for the kind words about my galaxy images :D



#13 Acer

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Posted 20 September 2019 - 08:30 AM

Thank you for all of your posts.  I have much more clear the way to go: image scale.  Maybe my MN190 with a ICX183 sensor is a good route.

 

By the way, incredible images James and Lee, really inspiring images.

 

Regards

That is what I've been using, a ZWO ASI183MM Pro with a Skywatcher MN190.

 

I have been EXTREMELY pleased with it.

 

Here are a few galaxy examples.  The Triangulum was just imaged and is only around 6.3 hours of integration.  The others are when I first got the scope and was still learning the setup (I am still learning).

 

Triangulum-800px.jpg

 

This one is just over 2 hours total integration

 

M51-128-Minutes-LRGBHa-800.jpg

 

This one is 3 hours integration

 

The-Needle-182-Minutes-Large-800.jpg

 

 

 

If I had more patience, all of these would be better, more detailed.  I am also shooting in Bortle 6/7 skies, so far from a dark sky site.

 

I LOVE this setup, especially in narrow band.


Edited by Acer, 20 September 2019 - 08:56 AM.

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#14 Jesus Munoz

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Posted 20 September 2019 - 09:21 AM

Oh, yes, you're right, its IMX183.   I've been reading articles of cameras with this sensor and sounds great for deep sky and lunar and planetary work.  laugh.gif  Thanks for the reccommendation.  waytogo.gif

 

Regards

 

 

 

Did you mean the IMX183, Jesus? I think the IMX183 combined with the MN190 would be a great galaxy rig, definitely worth trying considering you already have the scope and the cameras that use that sensor are relatively cheap.

 

And thanks everyone for the kind words about my galaxy images laugh.gif



#15 Jesus Munoz

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Posted 20 September 2019 - 09:33 AM

That is what I've been using, a ZWO ASI183MM Pro with a Skywatcher MN190.

 

I have been EXTREMELY pleased with it.

 

Here are a few galaxy examples.  The Triangulum was just imaged and is only around 6.3 hours of integration.  The others are when I first got the scope and was still learning the setup (I am still learning).

 

Triangulum-800px.jpg

 

This one is just over 2 hours total integration

 

M51-128-Minutes-LRGBHa-800.jpg

 

This one is 3 hours integration

 

The-Needle-182-Minutes-Large-800.jpg

 

 

 

If I had more patience, all of these would be better, more detailed.  I am also shooting in Bortle 6/7 skies, so far from a dark sky site.

 

I LOVE this setup, especially in narrow band.

I really liked your astroimages!  Outstanding resolution.  I really like the MN190, not having to deal with flatteners or reducers, just placing the camera and taking the picture. 

 

I've been working with a professional asteroid and comet researcher in a sudamerican university and my MN190 have reached magnitude 19.7 stars in very clear and steady nights.  The camera I use for that purpose is an Atik 414 mono with photometric V filter.  I feel the camera has poor resolution, that's why I started the post, for intending get more resolution.  I never imaged the problem could be resolved more easily with a camera with smaller photosites.

 

Thanks!


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#16 palaback

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Posted 02 May 2020 - 09:14 PM

This has been a really useful thread. Great example of the tradeoff between camera resolution vs getting a bigger telescope with longer focal length to image small galaxies. I have been debating endlessly whether to get a medium sized refractor like 120-130 or the MN190 to get cleaner images than I get from my c9.25, or to get a big RC or SCT. I have an ample mount, so aperature fever is a problem. But I do like idea of smaller and simpler is sometimes better.  This discussion makes me think a MN190 and possibly a higher resolution camera is the way to go. Much  less complex than a big scope (problems with thermal currents, need for large expensive camera, issues with focal reducers, seeing conditions required, super precise guiding and focus). I just got a zwo 1600 based on looking at the great results I saw people were getting with it and to dip my toes into the monochrome world. Maybe if all goes well I will try a 183 as others have suggested to get more reach with the 190. Seems like a great strategy. 



#17 Ron (Lubbock)

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Posted 02 May 2020 - 11:11 PM

Galaxies are my primary area of interest, and I went with a C11 Edge HD after considering basically every scope in the 10-14" aperture range.  The deciding factor for SCT over RC/Newt/DK was that I didn't want an open tube design where dirt and insects could easily get onto the mirror.  I lived in Lubbock, Texas at the time (east of you), which has a very windy, dusty climate.  I am happy with the light-gathering and detail-resolving capabilities of the Edge HD, and I plan to continue using it on galaxies.

 

Here are some insights gained from experience that might be helpful:

 

1) I ended up buying the 0.7x reducer because I had a lot of unforeseen problems running at f/10, and not the obvious one (guiding).   I am still oversampling at f/7, so I did not lose any resolution.  I do not plan to go back to f/10 except maybe to image a small PN at some point.  I think oversampling is the way to go if you want to use deconvolution to sharpen up tiny details in galaxies.  Just my opinion.

 

2)  At higher focal length, you'll find yourself waiting for nights with good seeing.  Keep the shorter focal length 'scopes for the rest of the nights.

 

3) Long subs and large aperture can conspire to produce bloated stars with unpleasant color  distortions.  In order to bring out the faint, outer arms of most galaxies, a very aggressive stretch is needed, which can absolutely ruin the stars.  A large fraction of my processing time is spent "working on" stars, often by combining two versions of the image with different stretch  characteristics.  

 

4) Going for the closed tube design was a good decision, but if you live in a humid climate, dew and frost on the corrector plate of an SCT will rapidly ruin an imaging session.  I think you're OK in El Paso (on most nights) but I lost some good nights to dew problems in Lubbock....

 

5)  People with 14-17"  astrographs will produce images that blow away the best image I can get with the 11" SCT.  However,  I can take my 11"  SCT in the trunk of my car to a dark site.   I am  not a retired guy who lives at his pristine dark site and has an observatory (yet).  Light pollution is bad news for fainter galaxies, and narrowband filters aren't going to save you.




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