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Anyone with experience using a newtonian for astrophotography willing to share knowledge, tips, and recommendations?

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#1 volk317

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Posted 14 February 2020 - 07:32 PM

I have had a z10 on a dobsonian mount for the past 6 years and I have been using it more and more but I find that I am limited when it comes to using it for astrophotography. I have used my dslr to take some nice pictures of the moon but I want to do more. So far I have decided to mount the z10 on a cem60 mount with a tripier, to use an off-axis guiding system, and to use my DSLRs for the photography. 

If anyone has any experience with a setup similar to this and is willing to share their knowledge, tips, and some recommendations, things to look out for and things to remember I will be super grateful. Thanks!

PS: I know that this is already posted in the reflectors section but someone recommended that I post it here instead. I know I'm not supposed to have multiple posts in different sections but it wont let me delete this post from the "reflectors" section. So I apologize for the multiple posts. There is only supposed to be thos one here on this section.

#2 AstroEdge

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Posted 14 February 2020 - 07:53 PM

I would suggest an autocollimator for precise collimation so that the stars are round to the edges. I assume you are getting a coma corrector? though with a coma corrector you would not be able to use a DSLR and OAG because most coma correctors need 55mm of back focus to use them properly. I would say that a coma corrector would be more nescessary for imaging than a OAG because you can guide just fine with a guide scope and guide camera at a normal newtonians focal length. You might need to get a better focuser if the stock one does not reach focus with a DSLR.

 

Hope this helps,

Caleb



#3 Galaxyhunter

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Posted 14 February 2020 - 08:11 PM

My first question to you would be: What kind of  a mirror cell is on the OTA?  I have an 18" reflector on a GEM.  I designed my OTA with an 18 point mirror cell, so I have no problems holding collimation when I move across the sky. If you have a strap style mirror cell, you might have problems with collimation as you change the OTA attitude.

Outside of the mirror cell & possible focus issue with a OAG,. I would say your good to go.


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#4 Couder

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Posted 14 February 2020 - 08:17 PM

I used a 10" F7 Newtonian for several years. First off, like Sputnik said, make sure you are collimated. And polar aligned. I assume you have the adapter you need, or a holder for your cell phone already. The most important thing to know is:.........good photographers are good because they throw away the ones that are not good - you only see the best! With digital, it is as easy as "delete". Take several, then look at the best and the worst and figure out why.  I take plenty notes, such as which eyepiece, was the wind blowing, streetlights on, how long you let the mirrors cool down, temperature, whatever else you can think of that might differ from one picture to another. I don't know what all makes a difference. 



#5 rkinnett

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Posted 14 February 2020 - 08:57 PM

My main rig (pic attached) is a 10" GSO Newt on an EQ6-R.  The GSO is heavy for the EQ6-R, but at f/4, 1000mm focal length, it's very forgiving of small vibrations, and generally a pleasure to work with, although it's a beast to setup.  Your Z10 has only slightly longer focal length, 1250mm, so you might have similar success with that on your bigger mount.

 

Some thoughts..

 

Study and truly understand collimation.  A common mistake with Newts is collimating only the primary mirror and neglecting the secondary.  Also don't forget to collimate your laser collimator!

 

Backfocus is typically an issue with Newts.  This thread discusses challenges with backfocus, using a GSO coma correcton on a Z10.  You might need to change out the focuser.  Another option is to modify your tube to move the primary mirror mount either in or out (beyond the range of the collimation bolts) to get your focal point where you need it to be with a coma corrector and your imaging train.

 

You might find a DSLR to be heavy for this application.

 

You might need a small step ladder if you need to look through an eyepiece.  I've seen some guys mount their tube upside down so the focuser points downward rather than upward like in the attached pic of my own rig.

 

I have not tried using an off-axis guider with my setup.  Again, the system does not leave a lot of backfocus to work with.  Maybe try a thin off-axis guider (TOAG).  I use a 60mm guide scope mounted in the finder scope shoe.  That works well even though it doesn't seem super stable, given the flexibility of my aluminum tube.

 

A green laser pointer works wonders for your alignment routine, although you have to take a minute to co-align the laser with the tube.

 

Lastly, be sure this is really the path you want to go down.  The 10" Dobs are not generally designed for DSO imaging and you may find it to be like fitting a square peg in a round hole.  For the same price as the cem60 and a focuser upgrade, you might be able to put an imaging rig together around a smaller, easier to handle and operate refractor or an astrograph.  My GSO and EQ6-R together cost $1k less than the retail price of a new cem60.  Mounting the Z10 is a bold endeavor but there are cheaper and much easier ways to get into AP.  That said, don't let me discourage you if you've got your mind set on this.

 

This epic moon pic was shot with a similar XT10 on an EQ6-R, by the way.

Attached Thumbnails

  • gso_newt_sunset.jpg

Edited by rkinnett, 14 February 2020 - 08:58 PM.


#6 kathyastro

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Posted 14 February 2020 - 08:59 PM

A 10" Newt is a lot of scope, but the CEM60 should be able to handle it. 

 

Since you say you have taken Moon pictures with your DSLR, so I assume you have worked out any back focus issues.  I would be concerned about adding an OAG, whether it would take too much back focus.  You might want to measure what focuser travel you have left to ensure there is room for it.  If it won't fit, you may have to go with a guide scope.



#7 Alex McConahay

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Posted 14 February 2020 - 10:20 PM

If you are sticking with the Dob mount, you will be limited to very short exposures. Pretty much the moon is what you can get. On the other hand, if you plan to get an equatorial mount lie a German Equatorial, be very careful that the mirror cell holds the mirror securely. GEM's can turn the tube in such a way that an unsecured mirror can fall right out of its cell. This is even worse than getting out of collimation. 

 

The other choice you have is an equatorial platform. But that is a whole 'nother operation. I did not see that you wanted to go that ruote. 

Alex



#8 TOMDEY

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Posted 14 February 2020 - 11:06 PM

Well, I absolutely love Newtonians for astroimaging! For Deep Sky aka something more than snapshots of the moon... that takes on a lot of added difficulty. But the relatively simple optical system of a Newt enjoys a lot of advantages. Here is my old film-based Newt that I enjoyed for many years and many thousands of hours of imagery. As others have mentioned, you need a sturdy, stable, well-aligned OTA with coma corrector. Trying to rebuild and harden a visual-use Dob for imaging may be problematic.    Tom

Attached Thumbnails

  • 157 12.5 inch scope Tom torsion compensator.jpg
  • 158 Toms Old 12.5 Astrola with upgrades 65.jpg


#9 volk317

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Posted 15 February 2020 - 01:12 AM

I would suggest an autocollimator for precise collimation so that the stars are round to the edges. I assume you are getting a coma corrector? though with a coma corrector you would not be able to use a DSLR and OAG because most coma correctors need 55mm of back focus to use them properly. I would say that a coma corrector would be more nescessary for imaging than a OAG because you can guide just fine with a guide scope and guide camera at a normal newtonians focal length. You might need to get a better focuser if the stock one does not reach focus with a DSLR.

Hope this helps,
Caleb


Yes, I do plan on getting a coma corrector, I hear those are a must. Yes this definitely helps, thank you very much.

#10 volk317

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Posted 15 February 2020 - 01:19 AM

My first question to you would be: What kind of a mirror cell is on the OTA? I have an 18" reflector on a GEM. I designed my OTA with an 18 point mirror cell, so I have no problems holding collimation when I move across the sky. If you have a strap style mirror cell, you might have problems with collimation as you change the OTA attitude.
Outside of the mirror cell & possible focus issue with a OAG,. I would say your good to go.


My mirror cell is the one that comes with the zhumell z10 and it has 3 clamp-like devises that have 2 little screws to tighten each one down. I will have to check the colimation while I move it on the mount through different positions. Thanks!

#11 volk317

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Posted 15 February 2020 - 01:21 AM

I used a 10" F7 Newtonian for several years. First off, like Sputnik said, make sure you are collimated. And polar aligned. I assume you have the adapter you need, or a holder for your cell phone already. The most important thing to know is:.........good photographers are good because they throw away the ones that are not good - you only see the best! With digital, it is as easy as "delete". Take several, then look at the best and the worst and figure out why. I take plenty notes, such as which eyepiece, was the wind blowing, streetlights on, how long you let the mirrors cool down, temperature, whatever else you can think of that might differ from one picture to another. I don't know what all makes a difference.


Great advice, thanks! I think I will get a notebook to use as a kind of journal to keep nightly notes.

#12 volk317

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Posted 15 February 2020 - 01:59 AM

My main rig (pic attached) is a 10" GSO Newt on an EQ6-R. The GSO is heavy for the EQ6-R, but at f/4, 1000mm focal length, it's very forgiving of small vibrations, and generally a pleasure to work with, although it's a beast to setup. Your Z10 has only slightly longer focal length, 1250mm, so you might have similar success with that on your bigger mount.

Some thoughts..

Study and truly understand collimation. A common mistake with Newts is collimating only the primary mirror and neglecting the secondary. Also don't forget to collimate your laser collimator!

Backfocus is typically an issue with Newts. This thread discusses challenges with backfocus, using a GSO coma correcton on a Z10. You might need to change out the focuser. Another option is to modify your tube to move the primary mirror mount either in or out (beyond the range of the collimation bolts) to get your focal point where you need it to be with a coma corrector and your imaging train.

You might find a DSLR to be heavy for this application.

You might need a small step ladder if you need to look through an eyepiece. I've seen some guys mount their tube upside down so the focuser points downward rather than upward like in the attached pic of my own rig.

I have not tried using an off-axis guider with my setup. Again, the system does not leave a lot of backfocus to work with. Maybe try a thin off-axis guider (TOAG). I use a 60mm guide scope mounted in the finder scope shoe. That works well even though it doesn't seem super stable, given the flexibility of my aluminum tube.

A green laser pointer works wonders for your alignment routine, although you have to take a minute to co-align the laser with the tube.

Lastly, be sure this is really the path you want to go down. The 10" Dobs are not generally designed for DSO imaging and you may find it to be like fitting a square peg in a round hole. For the same price as the cem60 and a focuser upgrade, you might be able to put an imaging rig together around a smaller, easier to handle and operate refractor or an astrograph. My GSO and EQ6-R together cost $1k less than the retail price of a new cem60. Mounting the Z10 is a bold endeavor but there are cheaper and much easier ways to get into AP. That said, don't let me discourage you if you've got your mind set on this.

This epic moon pic was shot with a similar XT10 on an EQ6-R, by the way.


Thank you very much for sharing your set up and experiences! Super beautiful moon pic and nice pic of your rig with a sunset in the background! I didnt get discouraged, I see what you mean with it being cheaper and a little easier with a smaller refractor setup. I eventually want to get a refractor or two someday too. And that may be better for dslr work. Maybe I could go ccd camera rout to keep it lighter weight for the newt set up. Thanks again!

#13 volk317

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Posted 15 February 2020 - 02:05 AM

A 10" Newt is a lot of scope, but the CEM60 should be able to handle it.

Since you say you have taken Moon pictures with your DSLR, so I assume you have worked out any back focus issues. I would be concerned about adding an OAG, whether it would take too much back focus. You might want to measure what focuser travel you have left to ensure there is room for it. If it won't fit, you may have to go with a guide scope.


I am beginning to think the guidescope is the way to go for my set up. I did use a 2x Barlow piece that my dslr went into for my moon pictures. I do need to include a coma corrector to sharpen up the edges.
I also used the stock focuser. That barlow seemed to solved my focus problem. I'm thinking that maybe with a better focuser upgrade for and a guide scope instead of an oag would be ideal for me. Thanks a bunch for your advice!

#14 volk317

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Posted 15 February 2020 - 02:10 AM

If you are sticking with the Dob mount, you will be limited to very short exposures. Pretty much the moon is what you can get. On the other hand, if you plan to get an equatorial mount lie a German Equatorial, be very careful that the mirror cell holds the mirror securely. GEM's can turn the tube in such a way that an unsecured mirror can fall right out of its cell. This is even worse than getting out of collimation.

The other choice you have is an equatorial platform. But that is a whole 'nother operation. I did not see that you wanted to go that ruote.
Alex


That will be a frightening experience if my mirror cell fell out. I will have to check it to see if it can handle the movement and positions that the ota could be in with it being mounted to a gem. Thanks for the heads up. I'm guessing that the gem is the better rout for photography, I'm not to familiar with an equatorial platform, I may want to check into that.

#15 volk317

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Posted 15 February 2020 - 02:17 AM

Well, I absolutely love Newtonians for astroimaging! For Deep Sky aka something more than snapshots of the moon... that takes on a lot of added difficulty. But the relatively simple optical system of a Newt enjoys a lot of advantages. Here is my old film-based Newt that I enjoyed for many years and many thousands of hours of imagery. As others have mentioned, you need a sturdy, stable, well-aligned OTA with coma corrector. Trying to rebuild and harden a visual-use Dob for imaging may be problematic. Tom


Beautiful set up in your pictures!! I dream of getting my set up going so I can begin imagining again, only this time with a mount that can track. I will have to play around with my z10 ota to see if it is solid enough for imaging on the gem. And if it turns out to be too problematic then I will try a different rout, maybe refractor for now until I can get a more solid reflector ota. That must have been really neat imaging with film! Did you develope the pictures yourself?

#16 TOMDEY

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Posted 15 February 2020 - 04:45 AM

Beautiful set up in your pictures!! I dream of getting my set up going so I can begin imagining again, only this time with a mount that can track. I will have to play around with my z10 ota to see if it is solid enough for imaging on the gem. And if it turns out to be too problematic then I will try a different rout, maybe refractor for now until I can get a more solid reflector ota. That must have been really neat imaging with film! Did you develope the pictures yourself?

Yes, I developed them in the basement. Here's a picture of the Rosette taken with that scope. Because it was film, this is a three hour single exposure, making the tracking challenging. My longest single exposure was five hours!    Tom

Attached Thumbnails

  • 161 65 Film Rosette Meh JPG from film.jpg

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#17 TelescopeGreg

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Posted 15 February 2020 - 01:59 PM

Regarding prime focus with the DSLR and the need for a Barlow to achieve it...  When I added a Paracorr-2 coma corrector to my 8" f/5 Newtonian, the slight 15% Barlow effect that it has also solved the focus problem.  I think other coma correctors may have similar effects on focus.  The alternatives of rebuilding the focuser to move the camera in, or moving the mirror cell up to shorten the distance, both cause the use of conventional eyepieces to have problems - not enough outward distance to get them into focus.  The Paracorr can be used with eyepieces too (it comes with an adjustable adapter for that purpose).  Not cheap, but a high quality product and very much worth the cost in my experience.

 

If at all possible, do get rid of the (presume 2x) Barlow that you are using.  Your images will appreciate the shorter focal length, faster focal ratio, and shorter exposure times.  That's a lot of telescope to be swinging around at the sky, and at a 1,250mm focal length (if I found the right model), you're already pushing it for field of view for many targets. 

 

Besides magnifying the sky, you're also magnifying any tracking / guiding errors.  An OAG would normally be best for this sort of length, but I don't know how you would do that with a coma corrector.  I believe they (or, at least the Paracorr) need to be connected directly in front of the DSLR for the proper backfocus depth.  So, that means a separate guide scope.  Besides attention to rigid mounting, scope focal length and guide camera selection will be interesting to maintain a reasonable guide:image pixel scale ratio.  I went "a bit" overboard in that regard, choosing a massive 80mm x 600mm guide scope for my Newt, and while the pixel ratio was a nice 3:1, the extra weight of the scope did more damage to my guiding than the finer control of the scope offered.  I've since replaced the Newt with a 130mm f/7 (so, 910mm focal length) refractor, and am using a 60mm f/4.6 guide scope from ZWO.  Same camera, an ASI174mm mini.  The pixel ratio is now 5:1, but the lower weight and tighter package (weight closer to the rotation axis) has actually improved both the tracking and guiding performance of the system.


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#18 volk317

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Posted 16 February 2020 - 01:12 AM

Yes, I developed them in the basement. Here's a picture of the Rosette taken with that scope. Because it was film, this is a three hour single exposure, making the tracking challenging. My longest single exposure was five hours! Tom


Very beautiful!! I'm sure that length of time for those exposures helped to develope some long term patience! That's inspiring for sure! I cant wait to spend time under the stars imaging all night.

#19 Alex McConahay

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Posted 16 February 2020 - 08:47 AM

>>>>>> That will be a frightening experience if my mirror cell fell out.

 

The cell does not fall out, the mirror falls out of the cell. 

 

Some Dob reflector cells are designed so that the mirror is held in the back by the front of the cell, and below by a strap that runs along the circumference of the bottom half of the mirror. But there is nothing holding the top or sides, really. Of course nothing is needed because in a Dob mount, one side, the same side of the tube is always pointed down compared to the other. These tubes may have trouble when the tube is near horizontal, and will have lots of trouble when rotated, and even inverted, as they sometimes are in a German Equatorial Mount. Tubes in a GEM go through all sorts of orientations that a Dob mount never exposes them to. 

 

Alex



#20 volk317

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Posted 26 February 2020 - 01:03 AM

Regarding prime focus with the DSLR and the need for a Barlow to achieve it... When I added a Paracorr-2 coma corrector to my 8" f/5 Newtonian, the slight 15% Barlow effect that it has also solved the focus problem. I think other coma correctors may have similar effects on focus. The alternatives of rebuilding the focuser to move the camera in, or moving the mirror cell up to shorten the distance, both cause the use of conventional eyepieces to have problems - not enough outward distance to get them into focus. The Paracorr can be used with eyepieces too (it comes with an adjustable adapter for that purpose). Not cheap, but a high quality product and very much worth the cost in my experience.

If at all possible, do get rid of the (presume 2x) Barlow that you are using. Your images will appreciate the shorter focal length, faster focal ratio, and shorter exposure times. That's a lot of telescope to be swinging around at the sky, and at a 1,250mm focal length (if I found the right model), you're already pushing it for field of view for many targets.

Besides magnifying the sky, you're also magnifying any tracking / guiding errors. An OAG would normally be best for this sort of length, but I don't know how you would do that with a coma corrector. I believe they (or, at least the Paracorr) need to be connected directly in front of the DSLR for the proper backfocus depth. So, that means a separate guide scope. Besides attention to rigid mounting, scope focal length and guide camera selection will be interesting to maintain a reasonable guide:image pixel scale ratio. I went "a bit" overboard in that regard, choosing a massive 80mm x 600mm guide scope for my Newt, and while the pixel ratio was a nice 3:1, the extra weight of the scope did more damage to my guiding than the finer control of the scope offered. I've since replaced the Newt with a 130mm f/7 (so, 910mm focal length) refractor, and am using a 60mm f/4.6 guide scope from ZWO. Same camera, an ASI174mm mini. The pixel ratio is now 5:1, but the lower weight and tighter package (weight closer to the rotation axis) has actually improved both the tracking and guiding performance of the system.


Those are all great things to consider, thank you very much for sharing your set up and experiences!! It is very helpful. I think I am also going to go the refractor rout to get back into imaging quicker. As for my newt I think I will take your advice and ditch the barlow 2x for the paracorr-2 and go with a lighter maybe 50-60mm guidescope set up. And yes, my scope has the 1250mm focal length, Zhumell z10.

#21 Sam Danigelis

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Posted 26 February 2020 - 01:49 AM

I enjoy using my Newt for dso's. Your Newt has great light gathering power which is good for those faint fuzzies. Once you get your camera mount setup properly, it's off to the races. Newts are sensitive to wind above 5mph. You can rig up a windscreen for pretty cheap, which allows you to image more of the time.

#22 RJF-Astro

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Posted 26 February 2020 - 03:00 AM

Coma correctors do not have an universal effect on focal length. Some do not alter it, while other offer slight magnification or reduction. For example the GSO has a magnification factor of 1.1x. The Baader MPCC does not alter the focal length and neither does the SW Quattro. The SW 0.9x does what its name implies. So be sure to check this if you got your eyes on one.


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