Have you ever looked thru a good 6 inch frac ? they are the best up to a given size ( 8-12 inch Joe blogs reflector , not the multy $1000's hand made babies like you have , nice ) and thats not just the views , cool down , set up/down ease of use and lots of other factors come into it .
Brian.
And I have used them much bigger than 6". Here is a photograph of the 15"/F12 D & G refractor I used for two consecutive nights at Comanche Springs in Texas in 2007. It might not look that big but the little finderscope sitting on top of the main scope is a 6"/F12 D & G refractor. There is a 5"/F12 D & G refractor mounted underneath on the blind side of the scope, which is another finder scope.
There is also a picture of me behind the wheel of this monster.
now thats a refractor , lucky you and merry Christmas .
Brian .
Quote:
Originally Posted by ausastronomer
And I have used them much bigger than 6". Here is a photograph of the 15"/F12 D & G refractor I used for two consecutive nights at Comanche Springs in Texas in 2007. It might not look that big but the little finderscope sitting on top of the main scope is a 6"/F12 D & G refractor. There is a 5"/F12 D & G refractor mounted underneath on the blind side of the scope, which is another finder scope.
There is also a picture of me behind the wheel of this monster.
Best telescope is one you use most, not the biggest!
People who recommend that a beginner should start with a 12 inch telescope are people who usually have little experience with comparing the useability of many different telescopes and optical designs. There are plenty of people who will tell the beginner to get a 10 inch right away, and this may be right for some beginners, but it is surprising how often the "10s" end up being infrequently used.
I have said this a few times before and I will say it again..... the best telescope, however big or small, is one that you are able to use frequently.
This means that it is best not to get a giant "white elephant" that is too big for the beginner to handle or to transport
In general, an 8 inch telescope could satisfy an adult beginner for a long time. An 8 inch Schmidt-Cassegrain or an 8 inch Dobsonian is fairly easy to move around and set up, so this is what I would probably recommend for an adult person starting in astronomy.
(However, I have known some of the smaller ladies who prefer a 6 inch Dob, or even a four inch refractor, on the grounds of its greater ease of use!)
The idea of a 10 inch telescope is very seductive to beginners because of the "large and powerful" image..... BUT the size and especially the weight of a ten inch telescope quite often presents considerable difficulties for someone who is not used to using telescopes and who wishes to cart the telescope to a better viewing site. There are quite a lot of ten inch telescopes sitting unused in people's garages simply because they are substantially bigger and heavier than 8 inch telescopes.... and therefore they are harder to use and to set up and to transport. Furthermore, it is best to learn to use a smaller telescope, before moving on to a bigger one, as smaller is easier to handle.
(Some people seem to take to the "10 inchers" right away, but a large number of beginners find them unwieldy; an 8 inch telescope will get more use by a beginner, simply because it is easier to set up! )
[[ For instance, when I was a beginner, I had a large and long and heavy and impressive looking 10 inch F6 Newtonian with an iron metal tube, that got very little use due to its size and weight.
My solution to this problem was to shorten the tube, and I ground a 10 inch F4 mirror to fit the tube.....the optical compromises of the shorter focus, and my poor optical skills(!!), made no difference to the views of most deep sky objects....and the 10 inch F4 Newt. tube assembly fits on the back seat of a small Japanese car! ]]
[[ A 10 inch Schmidt-Cassegrain is still a Big and rather heavy telescope, despite its compact optical design....for some reason, nearly all 10 inch telescopes seem to qualify as "big". Certainly, an 8 inch S-C is much more easily portable than a 10 inch S-C! ]]
In general, a 12 inch telescope, of whatever optical design and mounting design (and I have used several different designs), is a large and heavy object that is difficult to move around. In general, beginners do find it difficult to handle, and set up, and use, a 12 inch telescope, so I would strongly discourage beginners from starting with a 12 inch. ( an 8 will get a lot more use!!!)
These intuitive observations can be expressed mathematically;
if we scale up an 8 inch telescope to a 10 inch telescope and then to a 12 inch telescope, using precisely the same materials and precisely the same design for both the optical tube assembly and the mount, then:
(1) The 10 inch will be twice as heavy as the 8 inch.
(2) The 12 inch will be more than three times as heavy as the 8 inch
This is why my intuitive observations are correct!!
A 10 inch is always a large object, and 10 inch telescopes are often heavy. (It will, in most cases, be considerably harder to lug it to a dark sky site than an 8 inch telescope.)
A 12 inch is nearly always a conspicuously large and heavy object;
so, despite what you may have heard, a 12 inch telescope, in nearly every case, does considerably exceed the limit of easy portability and set up
( I have set up 12 inch Dobs, 12 inch Schmidt-Cassegrains, and I have even set up 12 inch Newtonians on heavy German Equatorial mounts ).
There are a lot of people around who do get good use out of apertures of 12 inches and above, but these tend to be experienced amateurs!
How many times have we seen a beginner start off with a big telescope, and then end up rarely using it?
cheers, madbadgalaxyman
P.S. A lot of the people who will tell you to "get a 12 inch right away" are young blokes in good physical condition.
(when their initial enthusiasm wears off, will they still feel like lugging a massive heavy object to the viewing site?)
When you are "bobbing on" and you also have a "dicky back" (like me!) , or , god forbid, if you are of the female gender, your perspective as to what is a useable telescope is very different.
Last edited by madbadgalaxyman; 29-12-2012 at 01:09 AM.
Reason: more
How many times have we seen a beginner start off with a big telescope, and then end up rarely using it?
Hi Robert,
Probably less times than you see a beginner start with a telescope smaller than 10" and rarely use it because they are unimpressed with the quality of the visual images, particularly as we are affected by ever increasing urban light pollution.
I agree that a 12" telescope is really way too much for a beginner to handle, particularly if it is a solid tube telescope. I think a 10" scope is handled reasonably easily by an adult particulalry as dobsonians are a lot shorter and lighter than they were 20 years ago. In addition the newer collapsible tube versions make things easier and lighter again. Twenty years ago a 10" telescope was a big telescope, by todays standards it's a small telescope for visual use. When Andrew Murrell got his 20"/F5 in the early 1990's it was the largest amateur telescope in the Southern Hemisphere. By todays' standards it's a baby.
I used to have big refractors years ago, and found the bigger the scope, the less I used it. Big scopes are good if you have an observatory, but if you have to carry them, set them up and take them down again, they are a pain!
Hi Robert,
........you see a beginner start with a telescope smaller than 10" and rarely use it because they are unimpressed with the quality of the visual images, particularly as we are affected by ever increasing urban light pollution.
I agree that a 12" telescope is really way too much for a beginner to handle, particularly if it is a solid tube telescope. I think a 10" scope is handled reasonably easily by an adult particulalry as dobsonians are a lot shorter and lighter than they were 20 years ago.
Cheers,
John B
John,
I think the 8 inch vs 10 inch controversy , as to what would be the best aperture for the beginner to start with, boils down to what kind of person is going to use the telescope. You say start with a 10 and I say start with an 8.......
Oh well, experienced observers have always differed about such things.
For instance, some of the ladies do find even the average 10 inch Dobsonian to be too large to handle. I have even known some beginners who find any Newtonian to be too fiddly! Also, many (but not all) people do find that the views in an 8 inch, while not exactly bright enough to burn out your eyeballs, are interesting enough to sustain their interest in astronomy.
Furthermore, some people seem to find setting up and collimating a telescope to be a real pain, and others don't!
Also, as humans are subjective creatures, the very same view of an astronomical object (in the same telescope) can be either deeply impressive or deeply unimpressive, depending upon the person doing the looking.(as we know from public star parties)
You would probably recommend a 10 inch telescope for a beginner; I do agree with you that the views of deep sky objects are Very Noticeably more impressive in a 10 inch than in an 8 inch, as the 10 inch has about 56 percent more Light Gathering Power than the 8 inch. The jump in LGP is much larger between an 8 inch and a 10 inch than it is between a 10 inch and a 12 inch. Indeed, neglecting light transmission and contrast and suchlike, a 12 inch has only 44 percent more light gathering power than a 10 inch (while being about 70 percent heavier than a 10 inch)
My personal view is that an 8 inch Dobsonian is significantly easier to set up and transport than a 10 inch Dobsonian, and I give the "easier setup & transport" factor a greater weighting than the brighter views attainable in a 10 inch.
My opinion is that an 8 inch is more likely to be used frequently by a beginner than a 10 inch, so that is why I recommend an 8 inch for a beginner instead of a 10 inch......but the needs of the beginner and "type of person" he/she is could sway the decision in favour of a ten inch telescope.
cheers, Robert
Last edited by madbadgalaxyman; 29-12-2012 at 11:53 PM.
Celestron 6se. I started with Skywatcher 8" dob and hated it. I called it it the point and hope scope, I am not the most patient person. Sold it and and bought a 6 SE. Better views through it, half the weight, go-to and track your your objects, not having to constantly nudging your scope. You take pics with it, not faint DSOs, but bright ones like the Pleiades, etc., and lunar and planetary imaging. Bought mine Andrew's Communications $1600 posted down to Tassie. So happy now I have got something useful, and would highly recommended it.
I think your post sums this thread up nicely. 8", 10", 12", reflector, refractor, it really doesn't matter. It's what you'll use that keeps you in astronomy that counts.
I understand your frustration with a point and hope scope and there are certainly nights when I wish I could just 'dial in' a location to find a DSO in the middle of the FOV, but for me half the fun is the challenge of finding stuff for the first time.
Celestron 6se. I started with Skywatcher 8" dob and hated it. Sold it and and bought a 6 SE. Better views through it, half the weight.
Hi Andrew,
If you get better views through your 6" SCT than you did through your 8" newtonian there was clearly a lot wrong with the 8" newtonian.
There are several reasons within the laws of physics as to why an 8" SCT cannot equal the visual performance of an 8" newtonian. All things being equal, a 6" SCT cannot get remotely close to the performance level of an 8" newtonian. Generally in fact, a 6" newtonian will perform to the same level as an 8" SCT.
1) Larger central Obstruction
2) More air to glass surfaces 2 sides of the corrector plate and a star diagonal.
3) Closed tubed design which hinders thermal stabilisation of the telescope.
If you prefer the ergonomics, imaging capability and GOTO capability of the 6" SCT I can totally understand that, but better visual views ? Something seriously not right with that 8" newt !!
There are several reasons within the laws of physics as to why an 8" SCT cannot equal the visual performance of an 8" newtonian. All things being equal, a 6" SCT cannot get remotely close to the performance level of an 8" newtonian.
If you prefer the ergonomics, imaging capability and GOTO capability of the 6" SCT I can totally understand that, but better visual views ? Something seriously not right with that 8" newt !!
Cheers,
John B
(I am going to keep this thread at the level of "recommendations for beginners", so I won't go into extensive optical details)
Today's 8 inch Schmidt-Cassegrains do underperform a good 8 inch Newtonian, but the difference is not - in my view - as great as you say it is. The older Schmidt-Cassegrains developed a really bad reputation amongst observers due to: light losses due to the large number of surfaces in the optical train, and poor optical accuracy, plus the inherent limitations of the large central obstruction causing a lot of light to end up in the diffraction rings around the airy disk (around the "star image", if expressed in popular language).
The "defocusing" effect of the diffraction from the large central obstruction means that the optics of an S-C have to MORE accurate than the normal optical tolerances necessary for sharp planetary views, yet the optics of the old Meade and Celestron Schmidt-Cassegrains were, if anything, pretty bad.
However, some of the new S-Cs do have decent optics, and the light losses in modern Schmidt-Cassegrains are not any worse than in a Newtonian, due to high reflectivity coatings on the mirrors and due to the availability of coated corrector plates and high-reflectivity star diagonals.
I own a well-coated modern Celestron C8 (8 inch Schmidt-Cassegrain) which I use together with a 99 percent reflectivity diagonal; the light gathering power of this telescope is NOT reduced relative to a Newtonian of the same aperture, because of the modern coatings used throughout the light train. This C8 is about as good on Deep Sky objects as an 8 inch Newt., though the planetary detail visible in the C8 still suffers due to the limitations of the Schmidt-Cassegrain optical design.
cheers, Robert
I think that the 8 inch S-Cs are certainly one option that should be considered by beginners, as they are reasonably quick and easy to set up. Most that I have looked through do seem to suffer compared to a Newt., when it comes to planetary views, but at least you don't have to lug a large and heavy object to your observing place!
Has anyone ever lined up a number of very recently manufactured 8 inch-Schmidt Cassegrains and assessed their planetary performance? As I mentioned, the optics of this design have to be accurately made in order to achieve decent performance on the planets, yet commercial telescope optics are traditionally noted for their variability in quality rather than for their consistently high standards!
Last edited by madbadgalaxyman; 05-01-2013 at 11:43 AM.
Reason: more
I think your post sums this thread up nicely. 8", 10", 12", reflector, refractor, it really doesn't matter. It's what you'll use that keeps you in astronomy that counts.
I understand your frustration with a point and hope scope and there are certainly nights when I wish I could just 'dial in' a location to find a DSO in the middle of the FOV, but for me half the fun is the challenge of finding stuff for the first time.
Regards
Vaztr
I am not patient enough for a dob. So much observing time was wasted, just trying to find something to look at.
If you get better views through your 6" SCT than you did through your 8" newtonian there was clearly a lot wrong with the 8" newtonian.
There are several reasons within the laws of physics as to why an 8" SCT cannot equal the visual performance of an 8" newtonian. All things being equal, a 6" SCT cannot get remotely close to the performance level of an 8" newtonian. Generally in fact, a 6" newtonian will perform to the same level as an 8" SCT.
1) Larger central Obstruction
2) More air to glass surfaces 2 sides of the corrector plate and a star diagonal.
3) Closed tubed design which hinders thermal stabilisation of the telescope.
If you prefer the ergonomics, imaging capability and GOTO capability of the 6" SCT I can totally understand that, but better visual views ? Something seriously not right with that 8" newt !!
Cheers,
John B
3 other people, who all spent time with both scopes, agreed with me. The SE outperformed the dob
3 other people, who all spent time with both scopes, agreed with me. The SE outperformed the dob
Dear M110,
If you are comparing a 6 inch Schmidt-Cassegrain with an 8 inch Newtonian, and the 6 inch produces better views, I completely agree with John that there must be something severely wrong with the optics of the 8 inch Newtonian.....
Several possibilities suggest themselves as reasons for the severe underperformance of the 8 inch Newt:
- very poor optics of one or more components of the optical train
and/or
- very poor eyepieces
and/or
- severe miscollimation of the optics
and/or
- severe mechanical strain on one or more of the optical elements.
3 other people, who all spent time with both scopes, agreed with me. The SE outperformed the dob
Hi Andrew,
I am not disputing what you saw. I am trying to get you to understand that if that's what you saw, there was something horribly wrong with the 8" dob, including all the optical issues Robert mentioned, asuming that both telescopes were properly cooled.
Ouch Andrew , thats the whole idea of amaterur astronomy ,, learning whats out there and the feeling of actually finding a galaxy 20million light years away is way better than just looking at it ?? what do ya say ?? , if you want to just look , google it , its all here ( Hubble photos ) , but the hunt is where its at mate .sorry to say .
Brian.
Quote:
Originally Posted by M110
I am not patient enough for a dob. So much observing time was wasted, just trying to find something to look at.
Have you ever looked thru a good 6 inch frac ? they are the best up to a given size ( 8-12 inch Joe blogs reflector , not the multy $1000's hand made babies like you have , nice ) and thats not just the views , cool down , set up/down ease of use and lots of other factors come into it .
Ouch Andrew , thats the whole idea of amaterur astronomy ,, learning whats out there and the feeling of actually finding a galaxy 20million light years away is way better than just looking at it ?? what do ya say ?? , if you want to just look , google it , its all here ( Hubble photos ) , but the hunt is where its at mate .sorry to say .
