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Reflector Vs. Refractor Vs. SCT

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Ivan H
Ivan H's picture
Reflector Vs. Refractor Vs. SCT

Hello!

I am a proud owner of a small Skywatcher 80mm F5 refractor and have been using it for almost a year now. It's a great low budget scope and I love estimating variable stars from the binocular list. 

However, I am looking for an additional bigger scope, also suitable for visual VS estimation. So far I am thinking of getting the GSO/Revelation 12" F5 dobsonian. I would very much like to hear the opinion of experienced visual observers regarding their favorite aperture and setup. How deep can I go with the 12" reflector? 14-15 mag? I would like to add some CV to my observing list. 

Of course, a 6" refractor is also an alluring option, since I know how good my own refractor is performing. Or maybe an 8" SCT? Is someone using a similar scope? What are advantages and disadvantages of the different scopes regarding VS observing? Is coma a problem with the bigger reflectors? Or CA with the fast F5 6" refractors? 

I would be grateful for any kind of advice or shared experience.  

 

Greetings from cloudy Croatia, EU,

Ivan H.

pox
pox's picture
Hi from the

Hi from the not-quite-so-cloudy UK!

Limiting mag depends on so many variables (sorry!). I use a 14" dob, and the limiting mag relies heavily on sky conditions. I am in a small village with no light pollution, and my faintest mag so far is 16.5, but usually I get to about 14.5-15. I also used to have a 6" refractor and got to about 13.5 with that, so in terms of faintness, go for the dob, despite the ancillary problems like realuminising every 5 years or so. You do need to know the sky very well for this, since you will be finding everything 'manually'. But getting to know the sky is a profound pleasure, not a job, so good luck with that!

Also, certain parts of the sky seem to give better results, probably due to the background. For example, the fields around EM Cyg and TZ Per look much darker (and thus better contrast) than, say, R Leo which is a long way from the galactic plane where the dark nebulae are. Add to that the possibility of background illumination (faint, but 'there' nonetheless) from the highly-plentiful external galaxies in these areas

I'd say that, unless you are doing CCD stuff, anything near 8" aperture is out. Simply not enough light-grasp. I constantly dream of a 20" scope!

Ivan H
Ivan H's picture
Eyepieces...

Hello Michael,

Thank you for the reply and advice. I'm real excited about your input, since it came from such an experienced visual VS observer. 28,637 submitted visual estimations, the first one made in 1971! I wasn't even born back then! I'm just happy to have this opportunity to learn something from you.

It was a great pleasure to read through your website, especially the descriptions of different VS categories and your favorite stars from each category. It's such a great overview! Once I get a bigger scope it will be my starting point in choosing new stars for my observation program.

Furthermore, your garden-shed-observatory is just great! It's something I dream of, but unfortunately I live in a light polluted area. I need to drive to a dark spot, which is not such a problem, since I own a VW Caddy Furgon. It's therefore easy for me to move a 12" dobsonian. The much bigger problem is lack of free time. I'm an owner of a start-up company and working practically 24/7. And when I do have some spare time, like this weekend, it's raining out of buckets! Just frustrating!

I'm wondering what eyepieces do you use. Also, are you fond of some other accessories, like filters, binoviewers, etc?

Thank you and best regards,
Ivan H 

SVD
Hi Ivan, Just a comment about

Hi Ivan,

Just a comment about a 12 inch f5 Dob.  

I own two of them...don't ask. They are by far my favorite scopes to use.  The size is large enough to show objects and fairly faint variable stars.  It is also small enough that you do not need a step ladder. In so many ways, it really is the perfect size for visual observing.

I have digital setting circles on mine and it makes finding variables a breeze once they are programned into the computer.

I use Naglers for visual viewing, but for years I used the standard televue 1 1/4 eyepieces. I have not found a need for a coma corrector at f5.

I would give up all my other scopes before giving up a 12 f5. 

Vladimir

lmk
lmk's picture
Realities

[quote=Ivan H]

It's something I dream of, but unfortunately I live in a light polluted area. I need to drive to a dark spot, which is not such a problem, since I own a VW Caddy Furgon. It's therefore easy for me to move a 12" dobsonian. The much bigger problem is lack of free time. I'm an owner of a start-up company and working practically 24/7. 

[/quote]

Hi Ivan, nice to hear of your interest in starting/moving up to more advanced observing! I bet your situation is common to the vast majority of people in the world today - light pollution at their homes. So, my comments can generally be applied to this ubiquitous situation, rather than living in a spot with good dark skies.

As BRJ says, and it is a well known fact, the best scope is the one which is convenient for you to use most of the time! The process of taking a scope out to remote, dark places sounds appealing, and many people do/try it, however, after a while the time consumption and inconvenience of doing it starts to wear on you. The hours spent round trip driving, setup/teardown of the large scope really detracts from the time you could have been observing at home. Not to mention fuel costs. Plus, you could make the big trip, and its cloudy there!

So, I think the modern trend is to try to do VSO as best you can right at your home location. (Or sign up for remote telescope time!) Unfortunately, visual observing is really handicapped by light pollution. Your eye/visual perception depends on contrast more than absolute light grasp to detect fainter objects. As the background gets brighter, your ability to see stars visually drops dramatically. But, it depends on the severity of your LP. If only moderate, things can be done to compensate - using high power, well shielded from local light sources, LP filters, etc.

So, this means larger telescopes are needed to counteract the LP. But the cost and hassles of large aperture rises rapidly with size. My new 25" f/3 may end up being just too much for convenient use. So, I am starting plans for a 16.5" f/3 as an "optimal" compromise. Pretty powerful, yet I can just pick it up and use it on a moment's notice.

Though this is a visual observing thread, in all due fairness, a 65mm refractor and ST8 CCD with 60 sec exposures will equal the visual views with a 14" aperture, under dark skies. The difference gets even more pronounced under light pollution or moonlight! Just some food for thought ;) No wonder, this is a major reason most newcomers prefer the CCD route under the typical urban/suburban conditions we live in today.

Mike LMK

 

pox
pox's picture
Hi Ivan, Thanks for your nice

Hi Ivan,

Thanks for your nice comments! A few things you might consider:

1)  If you have to drive with your Dobsonian you might experience the optics coming out of collimation through vibration, holes in the road or whatever! My garden shed observatory has now been dismantled for various reasons; there is an elder tree in one corner which blots out the NE sky! Therefore I currenly carry the tube/optics to the mount and like to check the collimation frequently as a result. One of the 'negatives' of open-tube reflectors! Might be a good idea to invest in one of those laser collimators.

2) I don't use any 'add-ons' at all other than a gizmo to stop dew forming on flat/finder. I live in a wetland area of the UK (the Norfolk Broads) and dew is a problem! However my favourite extra is a software app for windows I have written and installed on a laptop used at the scope, which contains a database of variables and their charts. It both displays your chosen chart and fills in various text boxes for the variable such as chart date, observation time and so on. When the session is over, the observations are saved to a text file in the correct AAVSO format and uploaded to webobs.

3) Eyepieces - nothing outstanding. A wide-angle one for bright stars, one that gives a power of 70 (my favourite, just a regular plossl) and a recently-acquired 6mm one. The higher power improves contrast and so shows fainter stars.

potterrb
potterrb's picture
Windows app for the field

Hi Michael,

Would you be interested in sharing out your windows app for viewing charts and recording observations in the field? I have a Surface Pro I take to the scope with me (screen covered in red film). My process is to search a folder structure for the right chart (PDF) and display it, then save my results in an Excel spreadsheet that calculates the star magnitude based on my interpolation between comp stars. Still, at the end of the night I have to manually transcribe the results into WebObs from the spreadsheet. I suppose I could write the results to a file from the XLS but I've not done anythingn with VB for years.

Would love it if you were open to making this available!

Thanks,

Brian

pox
pox's picture
windows app

Hi Brian,

No problem passing the program on to you, but just a few things to be aware of...

I originally wrote this for me, personally, and it comes with an MS-access database of stars that are on my observing list. They may not be on yours. The stars are mainly YSOs and CVs with some Miras. You will need to delete any stars not on your observing list. Also, the JD calculation subroutine uses my time slot (Greenwich) which you may have to change for your observing site.
For the same reason, all the charts and finder charts are for 'my' stars. If there are any stars that you observe and I don't, you will need to:-

1) Download your chart from VSP and resize to half-measure (600 x 750 pixels) with red stars on black so they fit in the app's picture box. Finder chart can theoretically be any size but mine are usually a maximum of 300 x 300 px.
2) Save all the charts in the named folder (called, wait for it... 'charts') and in the following format example, since the search routine uses it:-
t ori.gif for main chart (have to be .gif, 64 colours is OK) / t ori-finder.gif for finder (i.e., same format as main chart but with 'hyphen, finder' added to the star name)

There may be other inconveniences/frustrations I haven't thought of

The first time it runs it creates a file called "cumulative.txt" where ALL observations you make with the app are recorded (it has come in handy more than once!) so at some stage you could download all your obs from AAVSO as a text file and paste them in to this file (in the appropriate format of course)

The access db includes a field that the app picks up in order to format the JD (4 d.p. for erratics, 2 d.p. for 'red stars'). This field is a boolean which uses a checked box for the red stars. I realise now this is a bit counter-intuitive but changing it now would be pointless. Call it a bit of English eccentricity!

If after all this you are still interested, what I can do, rather than send the whole app, is to send the individual VB files (form, db, modules etc) which you can then amend as necessary. All this assumes you have VB on your machine, which it seems you might. Then, when everything is working properly you can package the whole thing as an .exe and then create an app using the package and deployment addin.

Currently - again, since this was intended for me only to use - I manually add charts to the charts subfolder and the matching details in the database. I could create another screen (for the thousands of potential users out there) where one adds the charts and db details via a VB routine. But as I say at the moment you have to do this hard work yourself!

Ivan H
Ivan H's picture
...

...

BRJ
BRJ's picture
Upgrading to a Larger Instrument

Hello Ivan,

I'm pleased to learn that you consider yourself ready to move up in instrumentation in your pursuit of variable star observing. Certainly more visual observers are badly needed these days. I started out more than 50 years ago myself and my interest has never waned one iota. Over the course of those decades I have owned and employed just about every aperture of instrument in my VSO, ranging from wide field 10x50 binoculars to a 20" f/5 Dobsonian. In doing so, I've learned a great deal about what works best for observing convenience as well as VSO productivity.

First off, I think that it might be beneficial to you to point out that the step up from an 80mm refractor to a 12.5" reflector is truly an enormous one. Such a sudden increase in aperture and its resulting magnitude threshold gain can easily prove frustrating when it comes to even locating VS fields that you are familiar with from working with the 80mm. So many fainter new field stars will be included in the view, particularly anywhere near the Milky Way where most of the more interesting variables are located, that you may quickly become utterly lost in the star field while attempting to identify the variable and its comparison stars. This is particularly true if you're away from home observing site happens to enjoy relatively dark skies. A very good knowledge of heavens, one more often available to the traditional observer of long experience, is a virtual necessity to quickly finding your way from field to field with a big scope.

A very important second point to consider is how easily your instrument can be handled. One's ability to cover more than a few variable stars per session is inversely proportional to the aperture of your telescope. When I was heavily engage in observing binocular variables decades ago I had no difficulty estimating 100 different stars with accuracy in the course of just an hour of 2. My very portable 8" RFT Newtonian could still manage nearly 50 estimates per hour, But once I had my 12.5" in a permanent backyard observatory - even with all my charts and sequences memorized - I rarely could cover more than perhaps 35-40 stars in the course of an hour. By the time I up-graded to my 20" Dobsonian, although I could go very faint indeed with it, I had difficulty observing more than a dozen stars during a one hour observing session in spite of have a great familiarity with the fields. In short order I pretty much returned to observing with the old workhorse 12.5".

Now I would also make the point that observing from one's own backyard is far far better than hauling out your scope, stuffing it into the car, driving out to a better site to set up and after the session doing it all in reverse. This inconvenience becomes progressively worse as the size of the telescope increases and eventually leads to one re-considering about doing it on a clear night. I've personally found that, as a young man, an 8" Newtonian is very easy to manage for away from home observing sessions, while a 10" often tends to grow annoying to man-handle on any regular basis. A 12.5", unless it's one of those of modern light weight skeletal designs, is just a bear to manage and its remote used after the initial joy of it wanes quickly goes to making a remote observing session a task rather than enjoyable.

Just some observations from one of today's AAVSO Old Guard. Good luck whatever your ultimate choice may be.

J.Bortle   (BRJ)     

BRJ
BRJ's picture
Upgrading to a Larger Instrument

Hello Ivan,

I'm pleased to learn that you consider yourself ready to move up in instrumentation in your pursuit of variable star observing. Certainly more visual observers are badly needed these days. I started out more than 50 years ago myself and my interest has never waned one iota. Over the course of those decades I have owned and employed just about every aperture of instrument in my VSO, ranging from wide field 10x50 binoculars to a 20" f/5 Dobsonian. In doing so, I've learned a great deal about what works best for observing convenience as well as VSO productivity.

First off, I think that it might be beneficial to you to point out that the step up from an 80mm refractor to a 12.5" reflector is truly an enormous one. Such a sudden increase in aperture and its resulting magnitude threshold gain can easily prove frustrating when it comes to even locating VS fields that you are familiar with from working with the 80mm. So many fainter new field stars will be included in the view, particularly anywhere near the Milky Way where most of the more interesting variables are located, that you may quickly become utterly lost in the star field while attempting to identify the variable and its comparison stars. This is particularly true if you're away from home observing site happens to enjoy relatively dark skies. A very good knowledge of heavens, one more often available to the traditional observer of long experience, is a virtual necessity to quickly finding your way from field to field with a big scope.

A very important second point to consider is how easily your instrument can be handled. One's ability to cover more than a few variable stars per session is inversely proportional to the aperture of your telescope. When I was heavily engage in observing binocular variables decades ago I had no difficulty estimating 100 different stars with accuracy in the course of just an hour of 2. My very portable 8" RFT Newtonian could still manage nearly 50 estimates per hour, But once I had my 12.5" in a permanent backyard observatory - even with all my charts and sequences memorized - I rarely could cover more than perhaps 35-40 stars in the course of an hour. By the time I up-graded to my 20" Dobsonian, although I could go very faint indeed with it, I had difficulty observing more than a dozen stars during a one hour observing session in spite of have a great familiarity with the fields. In short order I pretty much returned to observing with the old workhorse 12.5".

Now I would also make the point that observing from one's own backyard is far far better than hauling out your scope, stuffing it into the car, driving out to a better site to set up and after the session doing it all in reverse. This inconvenience becomes progressively worse as the size of the telescope increases and eventually leads to one re-considering about doing it on a clear night. I've personally found that, as a young man, an 8" Newtonian is very easy to manage for away from home observing sessions, while a 10" often tends to grow annoying to man-handle on any regular basis. A 12.5", unless it's one of those of modern light weight skeletal designs, is just a bear to manage and its remote used after the initial joy of it wanes quickly goes to making a remote observing session a task rather than enjoyable.

Just some observations from one of today's AAVSO Old Guard. Good luck whatever your ultimate choice may be.

J.Bortle   (BRJ)     

WI
I have made many VS estimates

I have made many VS estimates with a wide variety of instruments, from 6x30 binoculars to a 36-inch Cassegrain. Each scope was selected at the time for the star to be observed. Good work can be done with any aperture, as long as you select your target stars appropriately.

John Bortle is absolutely right, productivity is inversely proportional to aperture - the bigger the scope, the fewer stars per hour. Also, portability is another drag on frequency and productivity. I solved that problem by gaining use of two observatories in addition to my convenient home instruments. I can simply drive to either (fairly dark) site, hauling nothing larger or heavier than a key. Then I can go to work with 20x100 mounted binoculars, 7-inch refractor, 12-in Dob, 14-in and 16-in SC, or 36-in Cass (there's also a 28-in Dob, but I have never used it because it is very difficult for one person to start it up and requires a lot of climbing). I have also occasionally taken home two 10-inch Dobs that are loaner scopes from one of the clubs, and other apertures are available. You may not be so fortunate.

At any rate, I would strongly recommend a 12-in Dob over a 6-in refractor. I have reached as faint as 13.6 with a 5-in f/12 refractor, and I have done a lot of PEP with the 7-in refractor, but both are permanently mounted in a roll-off shed and a dome. (The 7-in even has a motorized pier, just push a button and the scope rises or descends to bring the eyepience to a convenient level). Except for very short-focus refractors, larger apertures and heavy, cumbersome to set up, and the eyepiece height to reach a particular field may be anywhere from knee-level to over your head.

My experience with 12-in and 13-in f/5 Dobs has been very satisfactory. The eyepiece may be close to the ground when you are observing down at 10-degree altitudes, but otherwide they are easy to point around the sky and don't require a ladder or step stool near the zenith.  An 8-in Dob is even easier to move and set up, but in my experience it is almost too small - The eyepiece is seldom as high as you waist, so buy a set of knee pads if you choose to acquire an 8-in.

As for limiting magnitude, that's a question of magnification and therefore eyepieces. A high-quality eyepiece is always worth some additional investment. The only problem with very high magnification is the narrow field of view and the Earth's rotation. The narrow field becomes a problem without a clock drive, since you have to constantly nudge the scope along to keep the field in view. Except for special occasions when you are greedy to observe a very faint star, I would plan to use a Dob at low to medium power; even then, there are more variables available than you could ever observe.

 

Lew Cook
Lew Cook's picture
Clint Ford's Advice

Clint Ford once told me that "Your telescope should be located no further than 50 feet (15 meters) from your bed." I'm sure he had one there, too. Of course, he told me this when he was out at his "cabin" in Wrightwood, California - on the west coast of the US when I visited him. Chas. Scovil was also there. They both lived on the east coast of the continent!.

We were there to use his 18 inch telescope he had in a dome about 4 miles out of town. We started with a short, windy night. The next day there was snow - a lot of snow. That kept us from even leaving his house. I had brought a portable 17 inch f/4.5 Newtonian reflector that I set up in his driveway and used for the night. Clint looked thru it and approved. The road never was drivable to his observatory, and the rest of the time, it was cloudy, as best as I recall.

Like you, Ivan, I have significant light pollution. I combat this by building large diameter telescopes. When I was doing visual observing, I'd use higher power eyepieces. Now, I do only CCD observing and get down to 19th magnitude stars with my 74 cm (29 inch) reflector which I have changed to a prime focus instrument.

Lew

BRJ
BRJ's picture
Clint Ford, His Observatory and the 18" Scope

"Clint Ford once told me that "Your telescope should be located no further than 50 feet (15 meters) from your bed." I'm sure he had one there, too. Of course, he told me this when he was out at his "cabin" in Wrightwood, California - on the west coast of the US when I visited him. Chas. Scovil was also there. They both lived on the east coast of the continent!." - Lew Cooke

Yup, Lew, Clint indeed had his roll-off-roof observatory and its 12." Cave Newtonian right in his backyard in Connecticut some 50+/- feet from his backdoor for many years.

Incidentally, the 18" in the observatory outside Wrightwood atop Mount Peltier actually belonged to the late Claude B. Carpenter, an old acquaintance of mine and one of the nicest guys I've ever come across in the hobby. If you made it up to the observatory that first windy night, as your post suggests, you'll recall that the 18" was a real beast, constructed in the classical massive fully f/7 of f/8 Newtonian fashion of big amateur scopes from mid 20th century. As I recall, just reaching the eyepiece required a large rolling stairway-ladder. The story of the observatory's installation atop the mountain, with its associated trials and tribulations, was docuimented in the pages of S&T back in the 1960's sometime.

Cheers - J.Bortle   (BRJ)

lmk
lmk's picture
Dobs

Well, Thanks to my late friend John Dobson, and further improvements to even faster f/ratio, which I am involved with myself, 18" scopes can essentially become "travelscopes" and setup for instantaneous visual use! Using sphere mounts and lightweight materials, moderately large apertures can be made about as convenient as small refractors. Attached is an 8" f/3.7 in a 16" diameter plastic ball which weighs ~12lbs.

Mike

Lew Cook
Lew Cook's picture
Mt. Peltier & Aperture Fever

John, thanks for filling those gaps in my knowledge! I really didn't think there was anything unusual about the "beast" atop Mt. Peltier. My first exposure to a "real telescope" was at LSU. It was an 11.5 inch Alvin Clark & Sons f/15 refractor. I was used to climbing halfway to the stars to observe. The only difference was that with the refractor, you observed stars at the zenith from the floor, and climbed to observe stars low in the sky, while with Carpenter's/Ford's 18 inch the reverse was the case - except that the pier, as I recall, was fairly elevated and you were never on the floor.

My first use of the telescope at LSU was observing a transit of Mercury a L-O-N-G time ago. I followed it thru sunset and ended up about 10 feet (3 meters) above the floor. I had the observatory to myself. Prof. Ray Grenchik demonstrated the controls to me and went downstairs to his office. It was on the weekend, and I was impressed he came in for me.

Back to the topic at hand. Ivan, I only hope "aperture fever" doesn't infect you. 

I suffered from it badly! I started with a 3 inch (7.5 cm) reflector. Then a 3.25 inch (8 cm) refractor. Then I switched back to reflectors - 8 inch (20 cm). Then 17.5 (44 cm). And another 17.5 (the one Clint Ford liked). My current scope is a 29 inch (74 cm) prime focus reflector. I am converting one of the 17.5 inch reflectors to prime focus configuration. I haven't used the other collapsable 17.5 telescope in YEARS - but I do keep the mirror in a crate for use as a replacement for the mirror in my number one 17.5 when it's off for re-aluminizing.

In its early days, the 29 was in a Newtonian configuration on an alt-azmuth mount. I built a platform to observe from. It, just like the Carpenter/Ford instrument, required "climbing to the stars". During the earliest days of having it, I recall looking at M110 (thinking I had M31) and I was disappointed. I thought "M31 doesn't look any different in this big telescope than it did in my 17 inch." Soon, I was overjoyed when I saw my error as I searched about the area!

Good luck and enjoy many clear nights!

 

dedricksond
Use Them All

In the backyard I use a 80mm refractor or 4.5" reflector on a good mount. But nothing is better than putting them all ( including a 12" dob and binoculars) into the back of the 67 El Camino and going out to the woods!

Duane

ggotta
Choose something you're comfortable with

Well, even if I too own a 8 f/5 refractor, it's more for Sun monitoring and my favourite workhorse is a venerable 23 years old binoculars 15 x 70. If you want go deeper than a 80 f/5 refractor, you have to evaluate what is your available storage, what telescope size your observing site allows, what variable stars are your favourite target.

I would drop the SC option. Compact, portable, but expensive and with a mere 0.8 degree field of view, unless you introduce another expensive focal reducer. But it's an excellent, overall general purpose telescope, so if you want have if for observing targets different from variable stars only, that's ok. 12" GSO dobson it's fine to follow Mira full cycle, even their faintest minima, monitor quiescent former or dwarf novae and a good share of cataclismic variables. But it's big and heavy and if you don't have a good dark sky nearby it's not easy to carry around:  a good 200 mm f/6 Dob is a compromise betewen limit magnitude and portability and its shorter 1200 mm focal length gives you a larger and well definied field of view nearly to the edge, compared with 300 mm f/5 Dob: coma correctors and variable star estimations does not work very well along together. Gso, Orion XT8, Skywatcher, it does not matter, I had XT8 and GSO and both of them have good and weak spots, but overall they are all fine. A 6" refractor ? Yes, but why ? Modern acromats do not suffer too much coma and false color troubles, but a humble 150 mm f/5 refractor is in the 5.5 - 6.1 kg range weight, compared with a 9 - 10 kg for a 150 mm refractor and even with a 32 mm / 1.25" eyepiece gets a respectable 2 1/3 field of view, with no false colors and not too much coma. And it costs 1/3 of a 150 mm refractor, asking only a decent alt-azimuth mount or a small equatorial to work. Moreover, GSO has a 150 mm f/6 Newton too ( see European distribution ) with a 2" focuser and a perfectly matched 50 mm obstruction. Eager to swap my used XT6 f/5 for this GSO f/6, as soon it worns out definitively.

Ivan H
Ivan H's picture
Where to engage?

First of all I would like to thank everyone for the time you took and shared on this topic. For me as a mere beginner in VSO this is a great and valuable source of knowledge and enthusiasm. Special thanks to the most senior VS observers John Bortle and Lew Cook for their advice. Over 200,000 reported observations, that is breathtaking, legendary. It got me thinking and reevaluating my goals in VSO. 

To be honest, I did not think about quantity and as John described, productivity drops inversely proportional to the aperture of the telescope. How is it even possible to do approx. 50 estimates per hour with an 8" Dobsonian? That's like one VS per minute. I mean I am a rookie, no doubt, but I can't even theoretically imagine it. Just to look at the next map, point the scope, look through the eyepiece, focus, find the VS, find the comp. stars, make the estimate and write it down, just in 60 seconds?! How? I can imagine that long year practice and memorizing the star fields will do the trick, but still it's super fast. 

Then I had to ask myself, what would be the goal I should set for my observing sessions? Productivity, because there is a lack of VS observers? On the other hand, doesn't the accuracy of the estimates suffer if I push myself to observe more and more VS per hour? Or is there maybe a lack of reported observations for the fainter VS? Then one needs a bigger scope, but the productivity drops. 

So there is naturally my new question. If there is a lack in VS observers, there has to be also a lack of reported observations. Where would you engage new observers if you could decide?  

BRJ
BRJ's picture
Observing Goals

"Then I had to ask myself, what would be the goal I should set for my observing sessions? Productivity, because there is a lack of VS observers? On the other hand, doesn't the accuracy of the estimates suffer if I push myself to observe more and more VS per hour? Or is there maybe a lack of reported observations for the fainter VS? Then one needs a bigger scope, but the productivity drops. 

So there is naturally my new question. If there is a lack in VS observers, there has to be also a lack of reported observations. Where would you engage new observers if you could decide?"  -  Ivan H.  

 

Addressing the questions raised in your latest post, let me offer the following responses.

As to one's accuracy suffering by rapidly covering a host of stars, this really doesn't occur once the observer has gained significant experience. Although I more often than not spend less than 60 seconds in estimating the brightness of a variable, my data's accuracy rarely deviates more than a tenth of a magnitude from any CCD V value obtained very close to the same date and time (given that the v and V sequences and the CCD detector's response are nearly identical with visual, which they aren't always). Shifting between two variable star fields rarely requires more than 10 or 15 seconds and since my program is composed of mainly eruptive stars checked each and every clear night, I've long since committed all the chart sequences to memory simply out of endless repetition. This has been true for most of my long-time colleagues as well.

Concerning areas most in need of better observer coverage, my view would be the following.There was a time years ago when the AAVSO had considerably more dedicated visual observers using fairly large personal telescopes and they covered a huge number of the legacy eruptive stars. These were being very well followed and their lightcurves were virtually unbroken for several decades. In more recent years I've noted that this has become true of only the brightest, most easily located, of this group. Many of the only slightly fainter, more difficult to locate, members now often gain no more than sporadic coverage and for some I find that I am today virtually the lone observer of a surprising number of them. Without question CCD observers are not numerous enough to fill in for the Old Guard visual folks of the past in this area, and most of today's high tech CCD observers are likewise more interested in monitoring the latest, ultra-faint, bizarre objects the AAVSO Alerts so often address. So, from my standpoint, I'd love to see broader coverage of the eruptives to continue their detailed documentation, particularly so since I've seen more than a few dramatically shift their overall behavior patterns - often permanently - over the years.

HOWEVER, any newer observers should consentrate on observing what he/she enjoys most now and do so at whatever pace they feel comfortable with and not worry about other matters. As one gains more and more experience there is always time to modify one's observing program to center around a specific sub-class of variables whose particular type of variations most interest them. Variable star observing often becomes a life-long pursuit, so there is plenty of time to make different personal choices.

J.Bortle   (BRJ)

 

 

hhu
hhu's picture
Which variables?

 

Hello John, maybe it's time to tell which variables you wish that should be observed more. I'm have done now more than 30.000 visual estimations of mostly mirastars. I stopped observing a few years ago but I want to start again. I'm just looking for a scope again and a new program. Maybe you can send me on the right track.

BRJ
BRJ's picture
Just a fw under-observed stars

Hi, HHU. In regard to your question about possible new and interesting vso programs for yourself, if your intent is to acquire a reasonably large new scope, say a 12" or so, than I think that you would find the dwarf novae as a challengining and rewarding field of endeavor. As I indicated in my earlier post, I feel that many of these stars, most with long previous coverage, are wanting for additional data today to maintain some semblance of reasonable coverage. Just a short list among such stars that I feel are decidedly less well covered than they should be and that I have, and in many cases still am, monitoring goes as follows.

AM CAS, FN AND, FO AND, LX AND, BI ORI, CC CNC, CI UMA, EX DRA, FO AQL, VY AQR, VZ AQR, V368 PEG

There are certain to be a host of additional, just as deserving, similar stars on the AAVSO's program others might point out, to say nothing of the even more poorly covered symbiotic and even brighter RCRB stars for whom brightness activities remain largely a mystery. If you do indeed turn to these stars in the future I asure you that you won't be disappointed in what you see revealed with time. I have observed dwarf novae on the AAVSO program suddenly double and triple their outburst interval after decades of exhibiting unending much shorter cycles. Others whose outbursts came so often that I rarely missed even one in a given observing season which suddely ceased to show outbursts all together for years thereafter! There have even been a few stars long classified as UGEM-type for which I've seen obvious standstills and eventually had to be re-classified as actually ZCAM-type stars as a result. There's great fun in the dwarf novae field with much still to uncover.

J.Bortle   (BRJ)

 

hhu
hhu's picture
A new program

Hi John, yes my new scope will be a 12" dobson. I used to have a 16" but that one is sold. A 12" is better for moving around because I attend on regulary base starparty's in my country. 

Thanks for your comment. Ofcourse I have done also some observations of dwarf novae. I was the one who discovered the rare outburst of V1251 Cyg in 2008 ( http://www.theastronomer.org/tacirc/2008/e2492.txt )  That was really fun. But my main goal was to observe mirastars. I probably will get starting again within a month or maybe sooner. Sadly the nights are getting shorter.

Thanks for your reply. I will concentrate my program around the Legacy list of cv's and put also the ROP stars from the BAAVSS in it. If you have any other suggestions feel free to let me know. If you want you can contact me via Hubert.hautecler@gmail.com

thanks and clear nights, Hubert

phxbird
phxbird's picture
CCD defeats some light pollution

I am using a CCD on my 11" SCT. Even with the light pollution from being in the center of a town with 25,000 people I get 17th magnitude stars and can do photometry on stars around 15-16 magnitude. My AR102 does 16th magnitude stars. So to defeat light pollution and to keep from having to keep buying bigger and bigger telescopes you can go to CCD imaging. However, there is something still magical about doing visual estimates and it is much cheaper! 

Ivan H
Ivan H's picture
New 10" GSO f/5 dobson

Greetings from once again rainy Croatia!

I am waiting eagerly to test my newly acquired 10" GSO f/5 dobson and want to use the time to thank you all for the input and advice. It has been a great help and encouragement. Initially I was thinking of buying a 12" dobson, but in the end decided that a 10" would be somewhat better for a new VS observer like myself.  It's much more easier to pack it in the back of the car and haul it to the dark site. Also the shorter focal length (1250 mm) allows for a decent FOV.

Attached are a few pics of the new scope. The only upgrade I've done so far was a new 8x50 right-angled finderscope, so I can still observe VS from the binocular list.  

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