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What is a good telescope for Variable Stars?

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#1 NorthWolf

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Posted 27 December 2012 - 12:14 PM

What would make an amazing telescope for variable star observing? Also, one for astrophotography of variable stars, and one for both? I'm more interested in viewing/imaging variable stars/novae/comets/asteroids than anything else. Thank you. Forgot to mention that I have a budget of let's say the price of a SCT 11"

#2 Ed Wiley

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Posted 27 December 2012 - 12:30 PM

Visual measures of variables can be made with binoculars, it all depends on what kind of variables you wish to observe visually. Imaging of variables can be done with a DSLR and a tripod. Again, it all depends on what kind of variable you what to study. To get into imaging, have a look at

http://www.citizensky.org/

To get into visual, download the AAVSO visual manual.

http://www.aavso.org...bserving-manual

If you are looking at CCD imaging and measuring you are in another circle of observing. For example, I do my variable work with a Meade 8" Schmidt-Newtonian on a Losmandy G-11 with a SBIG 402ME fitted with BVI filter wheel. Total investment in excess of 3K as I bought all used. Minimally you need a mono-CCD camera and a V-filter and a decent mount. With that kind of rig almost any scope will gather useful data, including telephoto lenses.

Hope this helps,
Ed

#3 vsteblina

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Posted 27 December 2012 - 02:44 PM

The standard snide answer is the one that you will use. There are enough variables to match every scope and observing conditions.

HOWEVER, my recommendation is one with good digital setting circles. I found it more interesting to make observations than star hoping to the variable field. Does not matter if it is push to or go to.

My personal favorite scope is a 12.5 f5 with digital setting circles. I can view without a ladder and the scope is large enough to show the more interesting variables under moderately light polluted skies.

#4 MG1962

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Posted 27 December 2012 - 05:15 PM

Yes I would agree some sort of goto would be a major advantage. With mine, and a little planning I can bang out an estimate every two to three minutes

#5 Ed Wiley

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Posted 27 December 2012 - 05:46 PM

I agree that either push-to or go-to is a major advantage, both in urban (finding something) and dark skies (more targets/time) environments. I also agree with others that just about any scope you buy will be good for visual estimates. And you don't need tracking when doing visual measures. BTW, many variables are too bright at maximum for CCDs, which is one reason visual observations are essential and valuable.

Ed

#6 brianb11213

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Posted 28 December 2012 - 02:51 AM

just about any scope you buy will be good for visual estimates.

Agree but beware of vignetting issues with "optimal" diagonals in many Newtonians (you need a larger than standard secondary mirror to get full illumination over a useful field) and, for visual work, anything with a focal ratio faster than about f/6 because of the off axis performance of even the best eyepieces making comparisons difficult. (Not impossible but why make life any harder than it needs to be?)

If you're interested in visual observation of faint variables (dwarf novae, BL LAc objects etc) then you need aperture & realistically the best scope for you will be the biggest you can handle, unless you have the money to build a proper observatory. I found the CPC 1100 was a good choice for me when I got mine three or four years ago but recent health issues means it doesn't get out as often as I'd like to use it. A 12" - 14" Newtonian on a computerised tracking mount, or at least with digital setting circles, would be as good provided you can shround the top of the tube properly (light leaking in to the "tube" end of the focuser tube can wreck the effective light grasp unless you have a moonless, jet black observing site).

Good quality triplet apo or ED doublet refractors with focal ratios around f/7 are ideal in many ways but, unless your pockets are very deep indeed, the relatively small aperture will result in seriously restricted light grasp.

For CCD work there is a great deal of useful work that needs to be done on the brighter variables - often unsuited to visual work because of small range - this probably doesn't need much more than a "standard" lens; I found I needed a neutral density filter to get good measures of epsilon Aurigae with a 50mm focal length lens (working at f/2) on a DSLR, with exposures short enough that a motorized drive wasn't necessary. (5 sec)

#7 nytecam

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Posted 28 December 2012 - 05:16 AM

What would make an amazing telescope for variable star observing? Also, one for astrophotography of variable stars, and one for both? I'm more interested in viewing/imaging variable stars/novae/comets/asteroids than anything else. Thank you. Forgot to mention that I have a budget of let's say the price of a SCT 11"

Your first 'amazing' sentense says a lot but in reality the field is so wide any optics will serve and it's a trade that has to be learnt with results passed by the scrutiny of organisations submitted to - there's no quick fix :grin:

#8 BrooksObs

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Posted 28 December 2012 - 09:49 AM

I cannot say just how many of the foregoing posters are serious variable star observers on any systematic basis. However, I am and have been for some five decades with the AAVSO. So let me offer you my thoughts based on actual experience and personal observation in addressing your question.

Visual and imaging VSO are two distinctly different fields. While they may share a few commonalities in general they tend to draw upon rather different types of "observers". There are those who enjoy actually seeing the sky and then there are others who lean more toward being a sort of technician.

From a visual perspective, my advice concerning an appropriate scope would be to get a modestly large aperture instrument that is very easily set up and operationally smooth and convinient to use (particularly, no step ladders).

Over the years having employed instruments ranging from large binoculars to a 20" reflector, I've found that the most efficient VSO scopes tend to be 10"-14" Dobs. If you know the sky well (as ALL amateurs once did before the advent of GoTo) one can move around the sky quickly and easily while very accurately covering up to 45-50 variables per hour. And a great many of the most visually interesting variables are within the range of such apertures too.

Smaller scopes limit the selection of stars that are trully interesting and worthwhile following. On the other hand, most really large instruments are usually too bulky and slow in operation to provide any advantages. In addition, and if at all possible, in either the case of visual or CCD work, a permanent location with even just a simple housing/shelter for the instrument in relatively close proximity to your residence is an enormous advantage in instrument usage.

CCD imaging has a long, steep, learning curve to truly master and a fully equipped and reliable operation providing valuable, publishable, results will run to something at least equal in cost of purchasing a top-end 14"-16" Celestron, maybe more. A good background in electronics doesn't hurt you here either.

In conclusion, give very careful thought as to which direction you want to go, or at least start out in. If well done, either approach is very rewarding and valuable, but a half-hearted approach is likely to result in nothing more than disappointment and frustration.

BrooksObs

#9 brianb11213

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Posted 28 December 2012 - 12:25 PM

Over the years having employed instruments ranging from large binoculars to a 20" reflector, I've found that the most efficient VSO scopes tend to be 10"-14" Dobs. If you know the sky well (as ALL amateurs once did before the advent of GoTo) one can move around the sky quickly and easily while very accurately covering up to 45-50 variables per hour.

I don't disagree with the sentiment here but I'd respectfully point out that a tracking drive effectively extends the effective light grasp of any scope, partly by allowing a higher magnification to spread out diffuse sky light and partly by making it easier to use averted vision to observe very faint stars that are only visible intermittently. This effect is probably of the order of about a whole magnitude, equivalent to at least a 50% increase in aperture. Maybe even more than that in bright twilight / moonlight or with the sort of semi-urban light pollution that many of us are forced to endure these days.

Most commercial Dobs in the 10" - 14" range have inadequate shielding from light leaking into the open end of the focuser & a focal ratio which is IMHO uncomfortably fast. And the designers often make a "virtue" of restricting the diagonal mirror size; central obstruction is not relevant to VS work but uneven illumination of the field most certainly can be.

#10 NorthWolf

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Posted 28 December 2012 - 07:24 PM

Visual measures of variables can be made with binoculars, it all depends on what kind of variables you wish to observe visually. Imaging of variables can be done with a DSLR and a tripod. Again, it all depends on what kind of variable you what to study. To get into imaging, have a look at

http://www.citizensky.org/

To get into visual, download the AAVSO visual manual.

http://www.aavso.org...bserving-manual

If you are looking at CCD imaging and measuring you are in another circle of observing. For example, I do my variable work with a Meade 8" Schmidt-Newtonian on a Losmandy G-11 with a SBIG 402ME fitted with BVI filter wheel. Total investment in excess of 3K as I bought all used. Minimally you need a mono-CCD camera and a V-filter and a decent mount. With that kind of rig almost any scope will gather useful data, including telephoto lenses.

Hope this helps,
Ed


Thank you, I will check out the visual and imaging areas!

#11 NorthWolf

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Posted 28 December 2012 - 07:29 PM

I agree that either push-to or go-to is a major advantage, both in urban (finding something) and dark skies (more targets/time) environments. I also agree with others that just about any scope you buy will be good for visual estimates. And you don't need tracking when doing visual measures. BTW, many variables are too bright at maximum for CCDs, which is one reason visual observations are essential and valuable.

Ed


As much as I liked to hunt for objects with my first plain 10" dob, I really would prefer to use a go-to tracker this time around. I want to spend almost all my time observing rather than chasing. Good to Great nights are very limited in these parts and I will save specific hunting for other times, maybe for new comets and asteroids, or even novae/supernovae when the time comes.

I love to use stellarium on night mode and chase/hunt for specific objects. I remember finding Uranus and than Neptune my first times out, that was very rewarding.

#12 NorthWolf

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Posted 28 December 2012 - 07:43 PM

If you're interested in visual observation of faint variables (dwarf novae, BL LAc objects etc) then you need aperture & realistically the best scope for you will be the biggest you can handle, unless you have the money to build a proper observatory. I found the CPC 1100 was a good choice for me when I got mine three or four years ago but recent health issues means it doesn't get out as often as I'd like to use it. A 12" - 14" Newtonian on a computerised tracking mount, or at least with digital setting circles, would be as good provided you can shround the top of the tube properly (light leaking in to the "tube" end of the focuser tube can wreck the effective light grasp unless you have a moonless, jet black observing site).


That setup will have to wait for the time being. Maybe when I'm older and more professionally involved. My budget is calling for something in the class of a Nextar 8SE with stock mount.

Good quality triplet apo or ED doublet refractors with focal ratios around f/7 are ideal in many ways but, unless your pockets are very deep indeed, the relatively small aperture will result in seriously restricted light grasp.


Am I better off with an 8" SCT now?

For CCD work there is a great deal of useful work that needs to be done on the brighter variables - often unsuited to visual work because of small range - this probably doesn't need much more than a "standard" lens; I found I needed a neutral density filter to get good measures of epsilon Aurigae with a 50mm focal length lens (working at f/2) on a DSLR, with exposures short enough that a motorized drive wasn't necessary. (5 sec)


Very interesting thank you! I would want to specialize in taking photos of variables and others if possible. I've tried the afocal method with various eyepieces/adapters/camera and it was fun. I hate the fact that it can consume time from the visual experience..

These are some 2010 unprocessed pics of Betelguese and Rigel I had taken, hopefully I'll improve someday.

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#13 MG1962

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Posted 28 December 2012 - 11:27 PM

Well I use a Nextar SE8 for my observing, so of course I am going to agree it is a good scope. I specialize in long period variables, and with my rig I will do 20 to 30 estimates an hour.

What I did was connect my scope to my laptop and using a commercial program have my entire list of stars pre-loaded. So I basically sit there, click the button, make the estimate, click the button again and so on and so forth

#14 BrooksObs

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Posted 29 December 2012 - 08:25 AM

Well I use a Nextar SE8 for my observing, so of course I am going to agree it is a good scope. I specialize in long period variables, and with my rig I will do 20 to 30 estimates an hour.

What I did was connect my scope to my laptop and using a commercial program have my entire list of stars pre-loaded. So I basically sit there, click the button, make the estimate, click the button again and so on and so forth


While admittedly "old school" myself, I can still fully appreciate some of the advantages that GoTo and computer assisted systems offer today's observers. Nevertheless, there is a tremendous advantage to actually being able to find one's away around the sky without mechanical assistance.

For those variable star enthusiasts who are not also otherwise intimately familiar with sky itself, any malfunction, power outage, or glitch in the system, even the inability to use some one elses non GoTo instrument to get a quick look at some stars, can potentially leave them helpless in locating a variable's field on a beautifully clear evening. It is a situation I've seen played out more often than many here might imagine. The moral here being, don't overlook the possibility that often the more basic, or simplistic, approach to one's equipment offers the greater advantage.

BrooksObs

#15 NorthWolf

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Posted 29 December 2012 - 09:31 AM

Well I use a Nextar SE8 for my observing, so of course I am going to agree it is a good scope. I specialize in long period variables, and with my rig I will do 20 to 30 estimates an hour.

What I did was connect my scope to my laptop and using a commercial program have my entire list of stars pre-loaded. So I basically sit there, click the button, make the estimate, click the button again and so on and so forth


Hey there! I am totally confused as to whether to buy a Nexstar SE with it's usual mount setup for 1200$, or save for a C9.25 for around 1500++ with mount im probably looking at 2000$.

Or a late model C8 sct optical tube complete with featherlite focused for 650$? + a mount?$?

Can I enjoy my nights with either scope? Is there enough variables and other objects to be viewed with the 8", or will I regret not buying the 9.25 as an easy grab and go setup from my 2nd floor to backyard and an occasional dark site or camping trip?

I wanted to buy an 8 or 9.25 to last me a while before I can setup an observatory with a 14-18"

Is the 8 more than adequate? For both visual and imaging? How much clearer can variables be seen through a 9.25 over 8"?

Thank you.

I also plan on immediately buying a mount and Hyperion 8-24 mm eyepiece afterwards.

#16 groz

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Posted 29 December 2012 - 12:39 PM

I will pipe up and echo a few of the earlier thoughts. First off, there is a WORLD of difference between chasing variables visually, and doing so photographically. Both require completely different types of kit.

When we first started, our goal was a very specific type of variable, transit of exoplanet. I did my first transit observations with an 8 inch SCT, using an SXV-H9 camera. I got what I felt were VERY good results considering the amount / quality of the gear. Over time, I also learned what is and is not important for the type of observing we wanted to do over time, and started my hunt for what will become the 'retirement telescope'. I recently found it, and purchased an FRC-300 on the used market, 12 inch takahashi corrected ritchie cretien telescope. The things that made me home in on this one, when I first looked at the specs.

- 2300+ mm focal length, allows for decent resolution and well depth when paired with a ccd using appropriate sized pixels.
- 90mm wide flat imaging circle, allows for a huge potential field when hunting for comparison stars of appropriate color etc.
- Tak construction = built like a tank
- This was the largest telescope I could buy, yet still fit it in our camper for travel, before we build a permanent observatory.
- One came available, that fit my budget with only a small stretch.

The last item is actually very important, budget always becomes an overriding factor when choosing things, and it's not just the telescope that drives the budget, dont forget all the anciliary things like camera, filter wheel, and filters. Particularily when you get into larger stuff, filters and wheels add up very fast, and become a large expenditure.

When I got the telescope, it came with an sbig st10mxe camera, so in the short term, that will likely be the camera we use. In the longer term, I plan to replace the camera and get something that will take full advantage of the very large imaging circle available from this telescope.

For the type of variable work we plan to do over the next few years, this telescope works out to be our ideal compromise, but, it's a specialized instrument, and likely the wrong thing for most folks. After we add a large format camera, we will be able to do precision photometry on a field of over 50 arcminutes square (assuming a u16m or equivalent), which is an enormous field compared to what we had with the sxv in the c8, 24x18 arcminutes.

We have done many exoplanet transit measurements with the C8, typically done using the 0.63 reducer with the H9 camera. I can say with certainty, that setup is quite capable of the millimag type measurements required for this application. Mag 14 stars with a 0.02 magnitude dip, worked out good for us, but, getting a smaller dip on a mag 15 star (keppler candidates) turned out to be an exercise in frustration. Mag changes of 0.005 on a mag 15+ star get lost in the noise component of the measurements when using our original equipment.

So where I'm leading with this, is fairly simple and strait forward. When choosing your ideal telescope, first you have to determine what kind of variables you want to measure. If you are intending to monitor stuff in the mag 8 to 12 range at 0.1 mag precision, it's a completely different set of equipment than if you want to do 0.01 mag precision in the mag 15+ range. When we did the upgrade, our goal was to increase the capability on a number of fronts, which brought a very specific set of requirements. Getting a large field, with a long focal length, is a difficult combination to combine, and very few amateur telescopes can offer essentially both, without stepping into 'second mortgage' price ranges. We found one that we think will fit the bill, but, wont know definitively for some time yet, it's going to be another month or two before it sees first light with cameras attached.

#17 RAKing

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Posted 29 December 2012 - 12:41 PM

The short answer is your C8SE will be fine and there isn't a whole lot of work you can do with a C925 that you can't do with a decent 8 inch SCT. We are talking about 0.3 magnitude difference and when you get down to the fainter range of your scope, your estimates are less accurate anyway.

Me? I am quite happy with my TEC 140 refractor and my Mach1 mount. No, I don't do 40+ estimates an hour - it's more like 10 for me. But I enjoy my VSO estimates as much as anyone and I do them in conjunction with observing my double stars, planets, and DSOs.

My answer to your initial question is to use a scope you like and are comfortable with. I think knowing your equipment and how well it functions is more important than any other aspect.

Cheers,

Ron

#18 groz

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Posted 29 December 2012 - 12:52 PM

Good to Great nights are very limited in these parts


The profile says 'Canada', pretty big place. What part of Canada ? We are on Vancouver Island, and at this time of year, good nights are close to non-existant. But, that usually changes by February, and we have had at least one week of good clear nights during Feb for the last few years.

#19 NorthWolf

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Posted 29 December 2012 - 10:01 PM

We have done many exoplanet transit measurements with the C8, typically done using the 0.63 reducer with the H9 camera. I can say with certainty, that setup is quite capable of the millimag type measurements required for this application.


To be able to do that is amazing...especially with a C8??!

So where I'm leading with this, is fairly simple and strait forward. When choosing your ideal telescope, first you have to determine what kind of variables you want to measure. If you are intending to monitor stuff in the mag 8 to 12 range at 0.1 mag precision, it's a completely different set of equipment than if you want to do 0.01 mag precision in the mag 15+ range. When we did the upgrade, our goal was to increase the capability on a number of fronts, which brought a very specific set of requirements. Getting a large field, with a long focal length, is a difficult combination to combine, and very few amateur telescopes can offer essentially both, without stepping into 'second mortgage' price ranges. We found one that we think will fit the bill, but, wont know definitively for some time yet, it's going to be another month or two before it sees first light with cameras attached.


Good luck!

#20 NorthWolf

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Posted 29 December 2012 - 10:07 PM

Good to Great nights are very limited in these parts


The profile says 'Canada', pretty big place. What part of Canada ? We are on Vancouver Island, and at this time of year, good nights are close to non-existant. But, that usually changes by February, and we have had at least one week of good clear nights during Feb for the last few years.


Updated profile, I'm near Montreal! Hope to visit BC sometime, especially the great coast! True, we seem to have a week or 2 of very clear nights in January-February, easy to forget about them.






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