#1  
Old 03-12-2017, 12:43 PM
jman17
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Join Date: Apr 2017
Posts: 48
Advice on buying new scope and mount

Hi,


Sorry about the long post but I just have some questions about a SkyWatcher Black Diamond reflector (8inch aperture and 1000m focal length) that I am thinking of buying with a HEQ5 GOTO mount, if anyone can help me out. I want it for astrophotography mainly (with a Canon 450D now and maybe CCD in the future) and also visual use of mainly DSOs. I know that observing would not be ideal with a Newtonian on this equatorial mount due to the eyepiece position.


So far all I have used is a DSLR with telephoto lens on a star tracker and I am concerned about the difficulty of using a reflector like this with a 1000mm focal length. I am weighing up between this reflector and a SkyWatcher ED80. How much harder is the tracking of this reflector compared to an SkyWatcher ED80 with 600mm focal length, given that it is quite a bit faster? Would the shorter exposures needed for the same amount of light onto the camera sensor compared to the ED80 reduce this difference in difficulty quite a bit? What I am most interested in filming are DSOs, especially galaxies and nebulae (including the small ones) so I am leaning towards the reflector to get good scale on these targets, just don’t want to increase the difficulty too much as I am pretty inexperienced. How well would the ED80 perform on smaller galaxies and nebulae, would it do a good enough job or would I need more focal length for these targets? I know there are plenty of bigger DSOs, I just find the smaller ones something I really want to have the capacity to shoot too. Would using this reflector give too much magnification for many DSOs that are a little bigger to be imaged effectively?



If I want to use an automatic focuser, coma corrector/field flattener and CCD with filter wheel as well will this all fit without sagging or other problems on these scopes? How much could be put on scopes like these with no problems? Would differential flexure or front or back focus be a problem? I do want to use guiding so when using this reflector would the weight limit of the HEQ5 be an issue (if I balance well) once a guide scope and autoguider etc is attached? I am looking at a SkyWatcher guidescope that is around 2kg for a guide scope and this reflector weighs around 9kg. I know there is lighter ones with shorter focal length but read that I shouldn’t go too short for a longer focal length scope. Also, if I use a coma corrector with a focal reducer does this make the scope harder to collimate, given that fast Newtonians are very hard to collimate accurately?




Thanks for any advice that anyone can give me. I am open to recommendations of other scopes/mounts too.



jman17
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  #2  
Old 03-12-2017, 02:15 PM
Wavytone
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Tracking with the reflector will be far harder - the issues are:
- sheer size - it will act like a sail in the slightest of breezes whereas you could use an ED80 in 15 knots and it wouldn’t budge on that mount;

- its far greater mass and rotational moment of inertia which means once it starts to move the wrong way it’s going to go a lot further than the ED80 will before it stops.

Add to that a newtonian is vulnerable to mechanical misalignment, flexure and thermal expansion which are much harder to deal with than using a refractor.

Start with the ED80 first and aspire to an ed150 next Christmas.
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Old 04-12-2017, 01:17 AM
raymo
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Location: margaret river, western australia
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Wavy is spot on; get the process of imaging and processing up and
running, and graduate to something larger later. No one scope is ideal for
all targets. Even an 8" f/5 Newt will not render a decent size image of many of the smaller objects such as NGC 3918 for example. On the other hand it has too long a focal length to allow full coverage of some of the large objects.
Many members have several scopes in order to overcome this problem.
Incidentally, regarding your statement that Newts get into awkward positions for observing with, you can make a D.I.Y. device for about $5
that allows you to rotate the tube to a comfortable viewing position.
raymo
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Old 23-12-2017, 10:30 AM
jman17
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Posts: 48
Skywatcher ED80 and Star Adventurer equipment questions

Hi,


Thanks for the advice. I plan to go with the ED80, but have some more questions. I plan to get a guiding setup, would the QHY 5L-II with an Orion mini 50mm Guide scope be the best setup for a scope with the focal length of the ED80 or would there be something that could do a better job? I plan to use the guide camera with the Skywatcher Star Adventurer also, probably with a small 30mm guide scope like in the attached photo.

This is what the guy using it said he used for it-
I screwed two vixen dovetails back to back, making a male-male dovetail similar to this: http://www.admaccess...vetail-adapter/
I have this saddle on the star adventurer's declination bracket, which accepts the male-male dovetail: http://www.teleskop-...gth--80-mm.html
I use these ADM clamps to attach my DSLR to the dovetail, and my guide camera to the underside: http://www.admaccess...vetail-adapter/

The orion guide scope is attached to the ADM clamp using this: http://www.teleskop-...ting-Clamp.html (you could also use the guide scope's stock bracket. I lost mine)
The lens is supported by ADM 90mm guide scope ring.
Rings for fine focus: http://www.teleskop-...to-D-105mm.html

Would anyone know if this would be an effective setup for the Star Adventurer in regards to flexure/weight/balance or anything else that could be an issue. I am also thinking of adding a mechanical adjustable XYAZ head like this https://www.astromarket.org/astrofot...ed-xyaz-head-5 to put the camera on if possible.


Also, does anyone have any feedback on Kendrick dew heaters? I am thinking of buying their Digifire dew controller with temperature sensor and some Digifire heater bands and am wondering if anyone can recommend these or another product? I am looking for good quality ones that don’t need too much power and that I can also use on a DSLR lens with the right size band. I’d prefer to buy from an Australian supplier if possible.


Also I am looking for a really sturdy tripod for the Star Adventurer and am wondering if anyone can recommend a Zomei Pro VT666 heavy duty tripod?

Thanks
jman17
Attached Files
File Type: pdf Star Adventurer with guiding.pdf (124.0 KB, 19 views)
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  #5  
Old 23-12-2017, 08:52 PM
ausastronomer (John Bambury)
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Location: Shoalhaven Heads, NSW
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I think you're on the right track going with the ED80 on the HEQ5 first up on the basis that you're primary goal is astrophotography with a secondary use as a visual scope.

As others have said most people have different scopes for different purposes and for very good reason.

An ED80 will be a great starter scope for visual astronomy, However, be realistic in your expectations of it as a visual scope. While the optical quality is good, the aperture is very small. If you limit yourself to the moon, planets, double stars and the brighter DSO's you will have a lot of fun with it.

Down the track if you're still keen on some visual astronomy look to add a 10" or 12" collapsible or truss dob. These have good portability and will outperform all of the smaller aperture scopes for all visual astronomy by quite a margin.

Cheers
John B
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