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2nd scope musings

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#1 dx_ron

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Posted 27 January 2021 - 03:29 PM

I'm not in any hurry (and nothing is in stock anyway), but it's cloudy and might as well think about the future. Current scope is a Z61 with a 1x flattener. Camera is dslr now, but likely to change before a 2nd scope is acquired and will deal with those issues separately.

 

My current thinking is that the baseline for comparison is the AT115EDT + 0.8x flattener. So $1550 new, and about 13.5 lbs not counting camera and guide gear. I believe a CEM25p should be able to handle that - if not, then I'll be saving up for a mount upgrade next :).  So any alternative should both cost and weigh no more. The closer the cost (mostly) gets to that level, the more I would want to think about how the results would be preferable to the refractor.

 

Current ideas:

 

6" Newtonian. Cheap, but needs an pricey coma corrector. What level of coma corrector makes for a good experience? Likely to need a focuser upgrade? (and what are we looking at there). Any other hidden costs?

 

6"RC. Everyone says "NO", which is probably the right answer. But *can* they be made into a good instrument? What does it actually take?

 

Edge HD 8. This is a whole different class of beast in many ways. Base cost and weight are similar to the refractor, reducer costs more, longer focal length system. The *idea* of the Nightowl reducer is really appealing, but that might be vaporware anyway. Very scary seeing people talk about a $1000 guide camera and all the issues with getting an OAG to fit in the system. But this is an academic exercise anyway, so if you think this is a viable option I'm happy to listen.

 

Some other SC?

 

Something else entirely?

 

Nothing serious yet, just hoping for some interesting and fun discussion.



#2 rgsalinger

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Posted 27 January 2021 - 04:18 PM

Getting an OAG to work with an Edge 8" SCT is easy. Even after you add in the necessary .7 reducer, it's still easy (IMO) because there is plenty of back focus to work with. Where people get in trouble with setting up an OAG is when they try to shoehorn everything into the limited back focus that comes with some flatteners/reducers made for some refractors.  

 

What's really nice about having an OAG is that once it is working properly, the compactness of the device means that you can (as I do) leave it permanently connected to the flattener on one side and the camera on the other side. Then each night just plug/screw it into the focuser and you're done. 

 

So, for a second scope, the Edge with reducer and OAG would be the best choice give what you already have. It might or might not be a challenge with the CEM25, but you will be amazed at the resolution that you will get once you are sampling at a rate that makes you seeing limited. 

 

Rgrds-Ross



#3 jrcrilly

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Posted 27 January 2021 - 04:25 PM

You will want something with much more focal length than the Z61 to give you a good variety of targets between the two. If you stay with lightweight units, that probably means a compound telescope of some kind. The 6" RC at F/9 is very slow but the 8" at F/8 is more encouraging, and provides even greater focal length.



#4 draakken

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Posted 27 January 2021 - 04:45 PM

if you're going to change cameras, I assume you're going to a cooled/dedicated astro camera. that would mean if you can swing $150 more, you are in RASA 8" territory. It would not give you much more FL than the current scope, but you could get your imaging done faster, much faster. Finish in a night what now takes several.



#5 Phishin_phool

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Posted 27 January 2021 - 05:54 PM

+1 on RASA8 suggestion or else something like a Zenithstar 103 or similar sized refractor.

#6 dx_ron

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Posted 27 January 2021 - 06:50 PM

The RASA would replace, rather than augment the 360mm refractor - of course with the 3+ F Stops being > 8x faster. The bare RASA weighs 17 lbs, though I suppose at 400mm issues with the CEM25p would be minimized. There don't seem to be any examples on astrobin of the RASA on that mount.



#7 draakken

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Posted 28 January 2021 - 10:40 AM

you gave us some ideas for new scopes you were considering, but not really the why behind them.

 

Do you want more speed, longer focal length, flatter field, larger imaging circle etc.? its easier to make suggestions when we know the goals you have.



#8 rgsalinger

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Posted 28 January 2021 - 11:37 AM

Before buying any of the cheap RC telescopes, find someone who has one. Have them show you how much fun it is to collimate one. Ask them how often it needs to be collimated. If you like the answers then it's viable.

 

There's really little advantage that an 8" RC has over an 8" Edge HD other than collecting data a bit faster. Were you to put a reducer on the Edge you still have 1400mm of focal length at F7. The Celestron also has support in the USA if that matters. I'm not sure where a GSO scope has to go if it needs something fixed after the 30 day return period has ended.

 

Rgrds-Ross



#9 dx_ron

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Posted 28 January 2021 - 12:33 PM

you gave us some ideas for new scopes you were considering, but not really the why behind them.

 

Do you want more speed, longer focal length, flatter field, larger imaging circle etc.? its easier to make suggestions when we know the goals you have.

 

Thanks for the feedback. The main goal is to be able to add variety to my reasonable targets, without having an ironclad list of target requirements. I will find a way to have fun with any of the options, as long as they are outfitted in a way that makes them a viable imaging rig.

 

The scopes I listed all have a longer focal length than the 360mm refractor. If I had an exact focal length in mind, that would narrow it down quite a bit, but I am OK for now including a range and having that be one factor in the decision. A 6" Newtonian would be slightly faster than the f/5.9 Z61, but also not so much longer focal length. But I am interested in the specific question of what does one need to spend beyond the basic $400 OTA. What price class of coma corrector is really needed? Focuser upgrade? Anything else?

 

Same type questions with the RC (what add-ons are needed to make one a good imaging scope?), though I start with a healthy dose of skepticism about the RC being a good answer, and I hear Ross's comment (thanks!).

 

The Edge HD 8 pushes the limit of what I would consider, both in terms of focal length (with a reducer) and my current mount, but it is on my list of possibilities. Are other SC designs worth considering?




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