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Dobsonian DSO Imaging


Astro_Nic

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Hi everyone

Although I bought my scope for visual use - and will still be using it for visual as I love that side of it, I would like to make a move into DSO imaging with my dobsonian.   Not interested in a new scope at this time.  I'm aware it's not the best type of scope for this, so am not expecting amazing results or for it to be easy, however, it would be great if you experts could at least point me on the right path, so at least I stand some sort of chance!  I now have a dual axis equatorial platform and a ZWO ASI678MC planetary camera which I have been messing around with - but the planets are disappearing now!  The EQ platform has been great to be able to keep an object in the eyepiece!

My set-up is as follows:

 - Orion Optics UK 14" 1/10 PV dobsonian.  1600 FL. 1,860 with the Parracor II;

- TEPP dual axis Equatorial platform with support for guide camera;

- Astro Devices Nexus Pro DSC;

- ZWO ASI678MC;

- Orion ST80 'super finder' with ES24mm eyepiece for 16x mag plus standard 10x50 finder;

- Laptop with the usual imaging software etc;

- Based in the Midlands, UK.  Usual frequent cloud covering.  Bortle 5/6, but the East and South views are darker and look away from the nearby town.

So where I would like some help please is......

- I am planning on upgrading the focuser.  Was thinking of the Feathertouch - Does that sound like a decent choice?  If so, what size should I be looking at?  I know nothing about focusers/drawtube lengths/2" vs 2.5" vs 3" etc.  If that is overkill then could consider Moonlight or Baader steeltrack.  Although only the Baader appears easy to get in the UK;

- Where do I start with camera choice with my scope?  There is very little help out there for dob DSO imaging (I know - for very good reason!) - Colour vs mono - Limited opportunities to get out/Bortly 5/6 / dobsonian etc - are any of these relevant or is it really just a choice of mono - better quality, but more expensive once filters and wheels taken into account vs OSC - simple, cheaper, not as good quality?

- Which camera would pair well with my scope?  Compared to planetary cams, it looks like the more you spend, the better the camera you get - but are they all suitable for all scopes?  I was thinking of something like the ASI2600 - either MM or MC.  I do like the simplicity of the colour and the ability to get an image regardless of length of session.  But not if the quality is significantly lower.  Or with a dob set-up, is the camera really not a limiting factor and either MC or MM is fine.  Do I even need to spend up to the cost of the 2600 with my setup or are other models - 294 / 533 / 071MC / 183 etc good enough?  I was thinking with my large FL, a larger sensor would definitely help to fit targets in.  Then there's even the ZWO ASI2400 MC full size sensor.  No real budget, but don't want to chase the last few percent improvements that aren't cost effective.  But a larger sensor size looks very appealing.  Am I looking at this the right way?

- Assume I will need OAG?  Any suggestions here?

- Are there any risks that things won't reach focus etc?  How do I calculate these things?

- Anything else I have forgotten about?

- Once I have the hardware sorted, then I can think about how to operate it all!

Thank you all for your time and considered opinions and help!

Nic

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14 hours ago, Astro_Nic said:

Where do I start with camera choice with my scope?  There is very little help out there for dob DSO imaging (I know - for very good reason!

First and foremost...a dob is a newtonian after all, so if you have got a tracker sorted you should be good with any advice being provided for a Newt. You will find lots of discussions on pros and cons of MC vs MM. Both have their plus and minus points.

As a starting point, I would personally get it working with the TEPP tracker and camera to see whats the longest exposure that you can get without getting trailing stars BEFORE adding guiding to the mix. Have you tried out the FOV calculator on SGL site https://astronomy.tools/calculators/field_of_view/ to see what kind of DSOs will fit into you sensor size for the 678?

Here is what M13 would look like. You might wish to invest in a focal reducer [removed word] coma corrector.

Good luck and Clear skies. Thats the challenge for a lot of us 🙂

 

image.thumb.png.7c19a2af7d6a9d8af9075e83c969cd5d.png

Edited by AstroMuni
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The 678 is tiny - also to get the required 5x pixel size, I need a 2.5x barlow.  So essentially the Sombrero galaxy which is a tiny galaxy would take up the entire field of view/not quite fit.  Who knows how I would even find it!  It is also not a cooled camera designed for DSOs.  Cheers 

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24 minutes ago, Astro_Nic said:

It is also not a cooled camera designed for DSOs. 

You can image DSOs pretty well without cooling. See my signature link for what I did manage to get with a ASI224mc (also a planetary camera with no cooling)

If you are worried about optimal camera for your FL then you need a camera with larger pixels (or you could do a bin2 with 678 and add a 0.7x reducer)

Edited by AstroMuni
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I'm sceptical about the scheme you propose.  You don't need a large Newtonian for imaging deep-sky objects in general, as imaging time will generally substitute for aperture.  For EAA imaging of deep-sky objects I generally use a 102mm f5 refractor rather than an 8" SCT.  With this scope, many galaxies fit onto the FOV of an ASI224MC planetary camera.

If you have the budget to consider buying a large sensor camera, why not rethink and instead look at getting a small refractor, GoTo mount, and a camera that matches your requirements? I'm sure that you will find a GoTo mount that can work with plate-solve is far less annoying than trying to aim the big Dobsonian.  Most deep-sky imagers start with a guided camera or a small refractor, rather than jumping in at the deep end with a big Newtonian (and even then they'd put it on a proper GoTo equatorial guided mount.)

As a first step, I suggest you try imaging some deep-space object, e.g. a 10th mag planetary nebula or a galaxy, with your existing gear and see how much of a pain it is.

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Thanks.  I know I don’t need a big dob, but it’s what I have and is relatively new, so not wanting to buy another scope quite yet!

wife wants to buy me a DSO camera for my birthday so not going to complain!

will certainly be practicing with the 678 before then.

 

cheers

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16 hours ago, Astro_Nic said:

Thanks.  I know I don’t need a big dob, but it’s what I have and is relatively new, so not wanting to buy another scope quite yet!

wife wants to buy me a DSO camera for my birthday so not going to complain!

Ask her to buy you a focal reducer too 🙂 That would greatly help IMO

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1 hour ago, Astro_Nic said:

Any suggestions on which one?

I personally only use a Coma corrector without any focal reduction, so cant speak from experience. But I am sure others on this forum can help.

EDIT: You would need to double check that there is enough travel left in the focuser tube to compensate for the introduction of the focuser!

Edited by AstroMuni
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Yeah that's what I have no experience of - how to work out focuser in/out travel how much focus travel I need etc......complete mystery!

I use a Paracorr II currently for visual - but not used it for photography as I read it needs dismantling and then you need certain spacing or something.....so haven't bothered yet.  I thought I wouldn't need to worry for planets, but I will for DSOs.

 

A reducer would be great to get some larger FOV..... 

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Pretty sure I'm going to get the 2600MC, unless someone says it's not appropriate.  I would go MM, but I can't see myself investing enough time initially and there are limits with the EQ platform - not like I can set up an EQ mount and leave it for 8 hours.  Pricing up the MM with good filters is also VERY expensive!

 

Will go OAG - is the ZWO suitable?  and pair it with the ASI174 mini for guiding.

 

Any advice on focuser?  Want something decent like a Feathertouch but no idea where to start.  

 

Thanks everyone!

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1 hour ago, Astro_Nic said:

Pretty sure I'm going to get the 2600MC, unless someone says it's not appropriate.  I would go MM, but I can't see myself investing enough time initially and there are limits with the EQ platform - not like I can set up an EQ mount and leave it for 8 hours.  Pricing up the MM with good filters is also VERY expensive!

Before you commit yourself to a MM camera, or a filter wheel, check whether you will have enough focal range to accommodate the extra path length introduced by the filter wheel.  A SCT or refractor can usually accommodate such devices, but a Newtonian maybe will not.

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So not going MM....

What I want to do is go MC2600MC>filter>OAG>Nexus reducer (or not if it doesn't work) - but will need a coma corrector anyway so my parracor II.  How do I calculate if this will work???? eeeek......

Then there is the issue of which new focuser will work.....

Very confused!

Thanks!

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