I have been following this thread with much interest. Right now, Peter Read, SDM Telescopes is building my 28" f/3.3. Among other factors, it depends on what you observe as to whether a big dob is for you. I observe variables and look forward to getting down to mag 16.5+. Most of the stars I observe are in the South to West quadrant. Because stars move in a westerly direction as the night proceeds, I don't need to look directly overhead. I have a small ladder and may need to go to the second step. But not often.
From what I read above, two of the disadvantages with a big dob are transporting it and the set up time. These are not an issue for me. I have an observatory at my place, about 100 metres up the hill from the house. I won't be moving it around as it will be set up permanently.
One big advantage in getting one made by SDM is that Peter contours it to your specific needs and he is doing just that for me. When it arrives, I will post pictures and give a report.
Stephen Hovell
Pukemaru Observatory
341 Snelgar Road, RD 2
Kaitaia, New Zealand 0482
+173° 20' 07.67" -35° 05' 39.52"
Sounds like an excellent spec scope for your setup. I might have to take a trip to Kaitaia now that we have an international airport here in Canberra.
As for the ladder issue, it really is mostly a non issue. I find that at least half the time I am actually standing on the ground to view my targets, and when on the ladder it is usually only the second step. I watch many people with shorter scopes hunched over their eyepiece, a posture that I would find very tiring very quickly. I prefer to stand upright using the ladder handrail as a leaning post and the tray at the top for my coffee cup, eyepieces and snacks.
At outreach events I tell the guests to keep both hands on the handrail saving errant fingers poking into my Naglers. Your scope at 28x3.3, or 92.4"FL will be quite a lot lower than mine. Should be under 80" focuser height at zenith.
I've owned everything from small refractors through to a 29" newt. The 29 was the best, hands down, and was a killer scope on anything I looked at. I get frustrated on small scopes and am currently building a 22" newt. to complement a 14" SCT. Drama comes from usability and so an observatory is a must. That's what stops most people I suspect.
The discussion on setup times is interesting. Big dobs are often seen as inconvenient and hard to setup, but I know I can put my 20" together in about 20 minutes including collimation and alignment of the Argo(if I am organised and don't muck around).
Having recently been playing around with some imaging gear, I would guess the equivalent time for it is closer to 60 minutes if everything works ok.
I've owned everything from small refractors through to a 29" newt. The 29 was the best, hands down, and was a killer scope on anything I looked at. I get frustrated on small scopes and am currently building a 22" newt. to complement a 14" SCT. Drama comes from usability and so an observatory is a must. That's what stops most people I suspect.
Perhaps a little off topic but what would motivate one to own such a large telescope?
Is this still just a hobby or do you actively participate in global astronomy efforts? Perhaps the near earth object type program or something like that?
Or is this still a personal hobby for the owners of these very large telescopes?
I am not being critical? Quite the contrary, I would love to have something like this if I could afford it and if I had a place for it.
And a 20" newt is an APO. In fact it's better than an APO because every wavelength of light will focus at the same spot, not just three.
And once you get into the 6"-8" APO territory where you have a hope of seeing deep sky objects, albeit quite dimly, you will find that the cost function is parabolic, not linear.
OK, my 8" GSO dobsonian mirror APO cost me about half of my 70mm Vixen APO, both second hand. So yeah I guess the cost function is not linear... still tryin to work out the shape of the parabola though
I'm still tryin' to see any DSOs though it too, but I'm fairly optimistic now I
OK, my 8" GSO dobsonian mirror APO cost me about half of my 70mm Vixen APO, both second hand. So yeah I guess the cost function is not linear... still tryin to work out the shape of the parabola though
I'm still tryin' to see any DSOs though it too, but I'm fairly optimistic now I
Don't get me wrong - one of my favourite pastimes is trying to reproduce O'Meara's observations of the Messier objects with my 4" achro. But from the city this requires every trick I've learnt over 35 years of observing and my eyes are definitely getting worse. Then I look at the same objects through a 25" to give my eyes a treat.
The advantage of aperture is that many of the ESO catalogue galaxies are much more interesting than those in the messier list.
Oh yes - another of the myths about big dobs- they are not more affected by light pollution.
Cheers,
Andrew
Don't get me wrong - one of my favourite pastimes is trying to reproduce O'Meara's observations of the Messier objects with my 4" achro. But from the city this requires every trick I've learnt over 35 years of observing and my eyes are definitely getting worse. Then I look at the same objects through a 25" to give my eyes a treat.
The advantage of aperture is that many of the ESO catalogue galaxies are much more interesting than those in the messier list.
Oh yes - another of the myths about big dobs- they are not more affected by light pollution.
Cheers,
Andrew
All good Andrew
On topic, I agree with others that it's the convenience factor that makes smaller scopes so attractive to many, both physical and temporal in nature. I just love the ability to observe instantly, i.e. less than a minute to get started. Partly thanks to club membership, I now have everything from 2" through to 18" at my disposal (2" increments) and there is a time for each of these. Combination is key perhaps, and I'm fairly certain the OP (Hi Matt!) still feels that way too. My standard setup for out-of town observing is a dob and a small refractor mounted separately.
There also are areas of visual observation that rely less heavily on aperture than deep sky.
Also agree on the LP thing. That one is less a matter of aperture than exit pupil, I think.
Perhaps a little off topic but what would motivate one to own such a large telescope?
Is this still just a hobby or do you actively participate in global astronomy efforts? Perhaps the near earth object type program or something like that?
Or is this still a personal hobby for the owners of these very large telescopes?
I am not being critical? Quite the contrary, I would love to have something like this if I could afford it and if I had a place for it.
So why such large scopes?
I might have a "little dig here".
Why do folks prefer a 22 megapixel camera over a 4 megapixel one????
Having experience with apertures 30mm(1960) to 838mm(2016), I have to say Aperture Does Matter. If it didn't, I would still be happy with 30mm.
My current stable (see signature), includes 4"(102mm), 14"(356mm), 25"(635mm) and 33"(838mm) apertures. I have owned a bunch of 6", 8", and a 12" dobs and newts, and find viewing through anything less than about 12" is like peering into the focuser wearing dark glasses.
Maybe I am an "apertureaholic", (well, yes I must confess I am).But, I make no apology, its a fact. Started with making my own 6-7"mirrors when I was a youngster. After going from 30mm to 76mm(my first reflecting telescope[commercial Japanese]) it was wow! when pointed it into the night sky. Same with my first homebuilt 6" (like doubling the pixels), wow!, and same through each size increase.
Did a "head to head to head" very recently, (14",25",33") dobs (forget the 4" refractor). Subjects Moon, Jupiter, Mars, Saturn. At this point in time neither 25 or 33 have mirror coatings (so tested in "skinny dip form").
The pixel analogy works well as the apertures were compared. The 25" and 33" so far as fine detail on Luna "smoked" the 14" so far as the detail sharpness is concerned. Even when magnifications were matched.
Again take the pixel analogy. When an subject/object/image is captured in a 2 megapixel camera (I had one once), and you blow up the image by a large amount, (take for instance a 2" aperture telescope at 250x), all that happens beyond 25x per inch(where all info that aperture can give you is available,) (50x), beyond that the visual image is just stretched, and when stretched far enough becomes blurred and a pain to look at (empty magnification), BUT, increase the aperture (pixels) and the same 250x in a 25" aperture (10x per inch as compared to the 125x per inch with the 2"aperture). The difference is like "day and night".
I have aperture "as my friend" and like to maintain a large exit pupil and so can avoid the eye floaters that occur for most around the less than 1.5mm. Prefer to keep magnifications in larger scopes at 12x per inch, 2mm exit pupils, to provide, bright sharp images. I feel I don't require to use more than 12x per inch to access full information from a 25" scope. [I am still able at 71 years able to resolve naked eye some of Luna's larger craters when positioned on the terminator, (not difficult when the moon is well placed at sunset or sunrise, before flaring is a problem).]
On the planets, Jupiter (now lowering in my N West [evening]), 25" and 33" showing more than 14", (even as uncoated optics). Didn't get to use 33" on Mars and Saturn due to too much elevation for my current ladder (have to organize a suitable viewing platform, (even though the 33" is f4.1-don't know how folks manage with 36"f5 Obsessions and similar). Again 25 over 14 was"no contest". The smaller scope showed the Martian features, but not as sharply as the 25. (BTW with the 25 being f3.8 I only need a couple of steps on the small ladder to access the zenith). At the time of the 25 v 33 shootout (Jupiter),was watching an upcoming occultation of Io, so was watching this small sphere (easily resolved by both scopes) approach the Jovian limb. It was two steps up the 33 and down over to the other scope (no ladder needed), back and forth until the moment of occultation (happened whilest at the focuser of the 25- was beautiful).
Saturn: even though the 14 easily was able to show Cassini division, planet banding, planet shadow on the bands, the extra aperture of the 25 "aced it" with its superior resolution.
........
On topic, I agree with others that it's the convenience factor that makes smaller scopes so attractive to many, both physical and temporal in nature. I just love the ability to observe instantly, i.e. less than a minute to get started. Partly thanks to club membership, I now have everything from 2" through to 18" at my disposal (2" increments) and there is a time for each of these. Combination is key perhaps, and I'm fairly certain the OP (Hi Matt!) still feels that way too. My standard setup for out-of town observing is a dob and a small refractor mounted separately.
There also are areas of visual observation that rely less heavily on aperture than deep sky.
Also agree on the LP thing. That one is less a matter of aperture than exit pupil, I think.
Absolutely! My TOA130 and Binovues with Tak LE eyepieces or a pair of 14mm Delos are still my weapon of choice for lunar viewing as well as the 3 bright planets.
Why do folks prefer a 22 megapixel camera over a 4 megapixel one????
Having experience with apertures 30mm(1960) to 838mm(2016), I have to say Aperture Does Matter. If it didn't, I would still be happy with 30mm.
My current stable (see signature), includes 4"(102mm), 14"(356mm), 25"(635mm) and 33"(838mm) apertures. I have owned a bunch of 6", 8", and a 12" dobs and newts, and find viewing through anything less than about 12" is like peering into the focuser wearing dark glasses.
Maybe I am an "apertureaholic", (well, yes I must confess I am).But, I make no apology, its a fact. Started with making my own 6-7"mirrors when I was a youngster. After going from 30mm to 76mm(my first reflecting telescope[commercial Japanese]) it was wow! when pointed it into the night sky. Same with my first homebuilt 6" (like doubling the pixels), wow!, and same through each size increase.
Did a "head to head to head" very recently, (14",25",33") dobs (forget the 4" refractor). Subjects Moon, Jupiter, Mars, Saturn. At this point in time neither 25 or 33 have mirror coatings (so tested in "skinny dip form").
The pixel analogy works well as the apertures were compared. The 25" and 33" so far as fine detail on Luna "smoked" the 14" so far as the detail sharpness is concerned. Even when magnifications were matched.
Again take the pixel analogy. When an subject/object/image is captured in a 2 megapixel camera (I had one once), and you blow up the image by a large amount, (take for instance a 2" aperture telescope at 250x), all that happens beyond 25x per inch(where all info that aperture can give you is available,) (50x), beyond that the visual image is just stretched, and when stretched far enough becomes blurred and a pain to look at (empty magnification), BUT, increase the aperture (pixels) and the same 250x in a 25" aperture (10x per inch as compared to the 125x per inch with the 2"aperture). The difference is like "day and night".
I have aperture "as my friend" and like to maintain a large exit pupil and so can avoid the eye floaters that occur for most around the less than 1.5mm. Prefer to keep magnifications in larger scopes at 12x per inch, 2mm exit pupils, to provide, bright sharp images. I feel I don't require to use more than 12x per inch to access full information from a 25" scope. [I am still able at 71 years able to resolve naked eye some of Luna's larger craters when positioned on the terminator, (not difficult when the moon is well placed at sunset or sunrise, before flaring is a problem).]
On the planets, Jupiter (now lowering in my N West [evening]), 25" and 33" showing more than 14", (even as uncoated optics). Didn't get to use 33" on Mars and Saturn due to too much elevation for my current ladder (have to organize a suitable viewing platform, (even though the 33" is f4.1-don't know how folks manage with 36"f5 Obsessions and similar). Again 25 over 14 was"no contest". The smaller scope showed the Martian features, but not as sharply as the 25. (BTW with the 25 being f3.8 I only need a couple of steps on the small ladder to access the zenith). At the time of the 25 v 33 shootout (Jupiter),was watching an upcoming occultation of Io, so was watching this small sphere (easily resolved by both scopes) approach the Jovian limb. It was two steps up the 33 and down over to the other scope (no ladder needed), back and forth until the moment of occultation (happened whilest at the focuser of the 25- was beautiful).
Saturn: even though the 14 easily was able to show Cassini division, planet banding, planet shadow on the bands, the extra aperture of the 25 "aced it" with its superior resolution.
Pic: comparing 3" with 33" (mirror sizes).
Stephen
Thanks for the detailed response.
So, for you this is still a hobby, a pleasurable pass time. You are not involved in any form of scientific research.
BTW, there is one area were your camera pixel analogy breaks down. Whether a 2 MP camera or a 20 MP camera, I don't need a ladder to use it or a truck to move it or a building to house it if I don't want to take it apart after each use.
That's a really good post Stephen, I have always wondered if I would want to go over the 25" mark but so far the biggest telescopes I've looked through is the 18" Guinevere
I had the 29" back in 1984. At that point it was probably the biggest privately owned scope in Oz. I sold it to pay for my first Uni. degree... real hard to part with it!
I have been building up again slowly for a few years now and I scored a set of 22" mirrors a while back at a price I could not refuse. OTA is well on the way to completion, observatory is under construction...
I'd kill for a monster again but the 22" will be kick arsenal as it is.
Perhaps a little off topic but what would motivate one to own such a large telescope?
Is this still just a hobby or do you actively participate in global astronomy efforts? Perhaps the near earth object type program or something like that?
Or is this still a personal hobby for the owners of these very large telescopes?
I am not being critical? Quite the contrary, I would love to have something like this if I could afford it and if I had a place for it.
So why such large scopes?
For visual observing, aperture is king. In the 20"+ range, planetary detail is stark on most targets. DSO's show a lot of detail and many targets are just gob smackingly beautiful.... 47 Tuc and The Tarantula are beyond words, as I am sure others will testify. Some things require a bit of care. Sirius is off limits without filtering, you get retinal burn-in So, detailed visual views= big scope
The scope I am building now will also be a science/education instrument. Lot of work to do yet, but getting there. Accurate tracking with a big scope is harder and consequently more expensive. You don't want to set that over and over again, so you need an observatory. Comes down the all mighty $
Sorry i don't buy the pixel argument. Imagers know the important factor is not how many mega pixels you can cram onto a sensor but the optimal relationship between pixel size and the focal length of the scope, (see info on the Nyquist Criteria), as well as many other factors such as low noise performance, light sensitivity (QE) of the sensor etc.
People can, and do, create all sort of arguments to justify their scope choices, but the hard core aperture chasers ignore the realities of the Seeing conditions and what can be gained, or not, by increasing aperture. Bigger is not always better.
Sorry i don't buy the pixel argument. Imagers know the important factor is not how many mega pixels you can cram onto a sensor but the optimal relationship between pixel size and the focal length of the scope, (see info on the Nyquist Criteria), as well as many other factors such as low noise performance, light sensitivity (QE) of the sensor etc.
People can, and do, create all sort of arguments to justify their scope choices, but the hard core aperture chasers ignore the realities of the Seeing conditions and what can be gained, or not, by increasing aperture. Bigger is not always better.
Seeing is only an issue for planetary, and even then I have never seen a smaller scope provide a better view in the same conditions. And I have had plenty of opportunities to compare them.
My point earlier was that the setup of a small newt on an equatorial mount is far more onerous than setting up a big dob. It's really not that bad, and once you are setting up a truss dob it doesn't matter if it's a 16" or a 30". Same amount of work.
As for justifying the expense, I do supernova searching, although I know I cannot compete with the host of automated search scopes, I do it anyway. I also have a friend who asks me to confirm planetary nebula visually, but ultimately, I bought it because I wanted it, and the 18" mirror I ground cured me of wanting to make anything bigger. The only person whose opinion I'm interested in regarding my purchasing choices is my wife, who is usually just glad it's not another racing motorcycle... And glen, that is not in response to your comment
Cheers
Andrew.
An interesting thread Matt. I have my 16" Skywatcher Dob set up to wheel out .Hadn,t used it for a while so I rolled it out and viewed Omega Centauri I,ll keep it for another year.All my other scopes are converted in some way to image the Sun.
When I first purchased this scope I set it up and showed the kids the moon there reaction was ten fold that when compared to the smaller apertures.
I know as we age eyesight declines but with todays DSLRs the views are fantastic and you can always hook up a video camera when light pollution intervenes. As much as I enjoy all the electronically assisted Astronomy nothing quite beats trying to tease out the detail in a Galaxy as you return to it year after year.
Cheers
now that we have an international airport here in Canberra.
So, detailed visual views= big scope 
