Replacing Finderscope Question

[mikeyjames]

Hi all,
I am getting one of these (http://www.ozscopes.com.au/skywatcher-black-diamond-250-1200-reflector-telescope-w-neq6.html) but for $500 less from Andrews.

I have been doing a lot of reading and thinking about replacing the stock finderscope with on of these. (http://www.bintel.com.au/Astrophotography/Autoguiding/Orion-ShortTube-80--br-Guide-Scope-OTA/1055/productview.aspx) I have read they are better for guiding.

Just wondering what parts I would need and how complex the work would be?

For example, could I just use Something like this to mount it (http://www.stellarvue.com/80-mm-finder-rings-mounts-to-most-finderscope-dovetail-shoes-r080da/)?

Cheers
Mick

[Merlin66]

Mick,
IMHO the proposed 80mm would not normally replace the finder, but would be an additional guide telescope for the main telescope for astro-photography (you then need all the other jazz like guide cameras etc etc etc)
The bracket you found will, I think, fit the 80mm OTA but based on my experience looks a bit flimsy for the job.
Why do you want to up-grade the 50mm standard finder????

[mikeyjames]

Hi Ken,
Thanks for the information. At the moment, all I am really doing is lots of reading and trying to work it out. I have been following threads here and elsewhere discussing whether a stock 9x50 finderscope with some modding is any good for guiding. Some say yes, some say no, and others recommend entirely different solutions such as the 80mm.

Mostly just curiosity at this stage.

Thanks
Mick

[OzEclipse]

Mikey,
The accessory you linked won't work. The ST80 has a 90mm OD tube and extra attached bits, screw heads that have to be cleared when inserting the tube into the rings. The rings you linked to are only 80mm. You'd need 100mm rings.

If you want to use it as a guide scope and even if you can get one with bigger rings, this arrangement might give problems with flexure and balance. The ST80 OTA weighs 1kg, guide camera etc might add another 500g. You'll also have the camera attached to the scope focuser. That's a lot of weight sitting a long way up the tube. You would be much better off mounting it using a vixen style dovetail mount fixed closer to the tube cradle.

The focusers of these instruments can also flex causing movement of the guide camera. If this occurs, the camera will guide the scope to cancel out the flexure. The camera on the main scope will then show trailing stars. Owners frequently use a third ring to support the focuser tube to stop flexure or better yet replace the focuser. Be warned that a good focuser can cost twice the cost of the scope. The third ring is a cheaper if less effective solution. Of course the lighter the guide camera, the less of a problem this is.

cheers

Joe

[RobF]

Hi Mick

A 10" Newt is not the best way to get into astrophotography if you've never done it before. Likewise you'll find there are much bigger issues to learn and sort out than what type/size of guidescope.

A 50mm guider and sensitive guide cam is quite capable of guiding that scope, however the scope itself is likely to have flex in the tube around the focuser that will be a much bigger issue than than the guidescope, depending what you will be imaging with and how heavy it is too of course.

If you're really fixed on getting a Newt, would suggest don't go over 8" or below F5 focal ratio. Seriously consider getting a 2nd hand ED80 instead.

A newt is however a good compromise for visual and AP starting out as long as you're prepared for significantly more challenges than a shorter length refractor. There are lots of helpful people on IIS that can answer your questions and point out the key issues through your decision making.

I think you're in "the rough" at the moment worrying about an 80mm guidescope however. :)

[mikeyjames]

Thanks for the information. At the moment it's just theoretical anyway. I'm looking around, reading other people's ideas, and then wondering what I would need to do to make it happen.

Appreciate the help
Mick

[mikeyjames]

Hi Rob,
For the astrophotography, I'm just reading lots of stuff and wondering how it all works. As usual, since I've started asking questions here, the answers sometimes scare me. I understand there is an absolutely huge learning curve for me.

I should have mentioned that I am still deciding between 8" and 10" scope after some discussion in a previous thread.

Is there a huge difference between the 8" and 10" as far as system management goes?

Cheers
Mick

[RobF]

Hi Mick

I started with a HEQ5Pro and 8" Skywatcher newt, so can only comment on that directly. Have seen a few people use 10" Newts on EQ6.

Some general thoughts:

* 10" is significantly larger and about twice the weight of 8" - its worth checking both out "in the flesh" if you can at a store or star party - online pics can be deceptive

* You will definitely get some differential flexure in your images (leading to challenging guiding and smeared stars) with a metal tube newt. The 10" is twice as heavy, and I've noted others having to strengthen the focus area with metal plates or go to off axis guiding to allow for tube flex

* A newt is a great visual scope (if you don't mind chasing the focuser around at times :lol:) and very capable for photography, however you need to be extremely patient with balance, focus, guiding compared with a more traditional beginners scope (e.g ED80 refractor). Also have to learn to collimate properly - but again not hard, just requires patience


If you really get the AP bug you'll probably end up buying a more expensive refractor or RC at some point down the road. We all have to start somewhere. Its like boats - there is no perfect single scope, and everytime you buy one its gets you thinking what you'd like in your next one :)

One last thought - the focal length and field of view you have plays a great part in what objects you end up imaging. You can't have great resolution drilling down into small galaxies and also image big wide fields (nebulae, star clouds). CCDcalc is a great freeware tool that is worth downloading and setting up all the scopes, cameras etc you're thinking of using. Have a look at what focal length, f ratio etc do when trying to image say M42, M104 and M45 for a start. Eta Carinae is another large object that gets you thinking what it is you want to achieve - see it all, or drill in for detail?


Many of the pics here were done with an 8" Newt, Canon 450D and inexpensive guidescope. If you press the "i" icon you'll get extra info explaining what scope etc used, if this is any use:
https://photos.google.com/share/AF1QipMdLLH7jmetqQiAZmJQLPfWGs6tQXr gjOjgJfJpb6bKtFf_B4tjRDm2J5zf1m46_A ?key=YjIyc2hxY3hkX0lxX0tlQWVQZDluME tXc0VSYXVR

[thegableguy]

Just to add my own experience...

I started my imaging journey with an ED80 atop a NEQ6. No guiding. It was an excellent place to begin - taught me all about alignment and various other tricky aspects of the game, all quite manageable with the small OTA and relatively simple setup.

I've recently upgraded to an 8" f/5 reflector and am now using the ED80 for guiding... and bugger me if it isn't all waaaaaay more difficult. If I'd started with this setup I doubt I'd have stuck with it. The two scopes together are much, much heavier and more unwieldy; though adding guiding seems like it would make life easier, it really just adds another bunch of factors that can go wrong! The end results will be better (or at least I'm seriously hoping so - haven't had much luck yet) but it's very much worth remembering that the more complex and sophisticated a rig is, the more opportunities for stuff to fail.

My strong advice would be to start simple. There are many excellent reasons why ED80s are such a popular choice for beginner astrophotographers. You could start with an 8" or even a 10" if you insisted, and you may well get good results straight away... but you'd be in a pretty small minority!

Let us know which way you choose to go. Always nice to see the different ways other newcomers (one of which I very much still am) start their adventures.

[mikeyjames]

Hi Rob,
I really appreciate the detailed information you've given me.

I've been playing around with CCDcalc and starting to think the 8" may be a better all-rounder to begin with - a good balance between smaller and lager objects out there.

Thinking I may drop down to 8" and use the money saved - plus a few hundred extra - to get a carbon fibre scope. The advertising promises less issues with flexure (some adverts claim it eliminates the issue).

Any experiences / views on the carbon fibre flexure issue?

Thanks again
Mick

[RobF]

I'm no good comment on carbon fibre sorry. Might be worth reading up on RCs with metal versus CF to see pros/cons. I suspect you'd be better buying an astrograph newt with a quality low profile focuser rather than CF tube, but hopefully reviews from real life will help clarify. I think you'll find threads on CF versus metal on IIS.

One last comment I should have included earlier - it gets a LOT harder doing AP at longer focal lengths, and the 8" is a little shorter FL than 10" for same focal ratio. Above about 750mm things rapidly get unforgiving in terms of mount quality, balance, polar alignment, flexure, focusing and sheer navigation (figuring out what you're pointed at!). Chris made some very good points about why smaller refractors are a good place to learn the essentials.

[mikeyjames]

Hi Chris,
I appreciate the advice and knowledge. There is a really nice bunch of people here. My first question was re polar alignment on a US based astronomy forum. The only response was to tell I had broken some posting guideline - just too old for that kind of thing nowadays so glad I found this place.

Anyway, I do appreciate your advice but have my heart set on a reflector and will go that route, but I am more inclined to go the 8" rather than the 10" after all of the advice in threads on this forum. I'm hoping for a bit of an all-rounder as I'm not sure at this point what type of astrophotography is going to interest me.

I will likely deserve an "I told you so" :) from few people, but I'm sure, from what I have seen from this forum, it won't stop the help and advice will still keep flowing.

I hope by Christmas you will see a few my first attempts in the astrophotography forum.

Cheers
Mick

[mikeyjames]

Hi Rob
Thanks again. There seems to be a lot of debate on the net re the benefits/costs of fibre. Some people swear on them and others think they are simply an exercise in eye candy. I'll do a search on these forums.

Can I just verify what you mean. There is two scopes I am now thinking about - a 200/1000 and a 200/800. Are you saying the F4 would more forgiving than the F5?

Cheers
Mick

[thegableguy]

If it's the same US forum I tried at first, I had a similar experience; when I suggested I wanted to go from an 8" Dobsonian to the exact imaging rig you're suggesting, ie the one I have now, ie 8" f/5, everyone leapt down my throat and told me it's WAY harder than I think and that basically there was absolutely zero chance I would have any success ever. There were a few more friendly & helpful people, but they seemed to be the exception rather than the rule - the opposite of IIS!

Totally get it about wanting an all-rounder. I started with a Dob so knew the small frac would be a big step down, but only a temporary one. If you're patient, know your way around Google and enjoy problem solving, there's no reason you won't have a lot of success fairly quickly.

Re 800mm vs 1000mm, yep - shorter focal length is more forgiving, which is why a 600mm frac is usually where most people start. However you'll be getting considerably more light than an ED80 so it's actually a fantastic place to begin. You may miss the extra focal length, but that's what upgrades are for!!

Be in no doubt - no matter how well you choose your first telescope, it's absolutely 100% guaranteed to not be your last...

[RobF]

Even though guiding will be a bit easier at 800mm, an F4 scope is a bit trickier to collimate than F5, and the critical focus zone smaller. F4 is likely to magnify any issues with scope stability/construction versus F5.

My Newt is F5 and holds collimation very well. I don't have direct experience with F4 - again, probably worth reading around a bit here and elsewhere on the net. Remember you'll need a coma corrector (e.g. MPCC) to get a flat field in a Newt.

This thread talks about newts. More pros and cons to consider :)
http://www.iceinspace.com.au/forum/showthread.php?t=96521

[mikeyjames]

Thanks Chris. Certainly sounds like the same US forum.

I'm now sold on dropping down to an 8". I understand I'm not making it easy but I love a challenge and enjoy problem solving so it should eventually work out.

[mikeyjames]

Thanks Rob. After reading the thread you linked I am now pretty certain I'll got the 8" F5 route, as it seems to good compromise for what I want.

With Coma issues, is it 100% necessary to get this sorted straight away or will I be able to have lots of viewing/learning/beginner photography before I need to worry about that?

Cheers
Mick

[thegableguy]

Just in case...

It doesn't sound like you're keen to save money on anything, but I actually have a spare Skywatcher 8" f/5 Newt lying around doing nothing. It was a fixer-upper, which is now fixed up - just needs either a new focuser or a new bearing for the old focuser and it's good to go. Has finderscope, rings & dovetail so ready to start imaging immediately.

Depending on what brand you want you're looking at $500-$800 for a new one. I'll be selling this one for $300 with old focuser or $400 with a new one. You'd need a coma corrector; I could throw my GSO one in (with appropriate spacing rings) for $120.

PM me if you're interested.

[mikeyjames]

Hi Chris,
Much appreciated. I sent a PM but not sure if it was sent.
Mick

[thegableguy]

Didn't come through (they often don't for some reason); I tried sending my own to you just now....

[mikeyjames]

Yep, got your message and replied. Nothing earth shattering in it so happy to post here if you don't get it this time.