largest convenient//backyard Dob
Posted 10 February 2004 - 06:57 PM
The key points of emphasis are:
(1) this is exclusively a DSO scope (because you've already got a 5" Mak to kill planets in your backyard)
(2) It's a backyard scope. So, it doesn't have to be automobile-portable to your favorite dark site, but it does have to be quick and convenient for carrying outside on an almost nightly basis, and for moving around your yard through the night as objects move behind various trees and roof tops (hence a Dob rather than equatorial scope).
(3) Relatively wide fields would be a plus. Afterall, you've got to find DSOs in a somewhat light-polluted setting, so a fast scope (f5) might be better than slow scope (f6-8).
Ok, then...the question...what's the biggest Dob you'd get for your easy-to-use backyard scope?
10-12" would be COOL, but first, are these too cumbersome to roll outside on a high-frequency basis? Second, a 12" f5 has a 1500mm focal length (not exactly wide field). A 10" f5 is still long at 1250mm.
So, drop down to 8". At f5, this would be great, but it seems that most 8" Dobs are f6 (not f5), and are therefore just as long as a 10" Dob. So now we're down to a 6" Dob, which allegedly just gives aperture envy, and most of these are f8, which are also 1200mm long.
Can you get a big-aperture Dob that's only 1000mm long?
Posted 10 February 2004 - 07:08 PM
I usued to carry my 10" dob outside everytime I had to use it, not an easy or fun task. Since I don't have anywhere to 'roll' it from, I bought a desert storm cover. This cover allows minimal cooldown times and I never have to move the dob!
To recap, many truss telescope companies now offer the wheel barrow handles to make something highly portable, even more easy to move.
Posted 10 February 2004 - 07:24 PM
Dobs take awhile to cool down because the tube holds the warmer air and traps it. My Hardin 8" dob is a great scope and I will be (finally) using it tonight for some serious viewing of our pal Orion. It is very portable with a total weight of 42 pounds (base and OTA). You're a young, big guy...look at the Hardin 10 or 12" scope also. Think about the weight and the awkwardness of carrying it (Seriously, it is awkward).
Then there is the Hardin 6" for under $300...
Let's keep discussing...
Posted 10 February 2004 - 11:23 PM
Personally, I think that about 14-15" is the sweet spot, since you can skip the ladder. They are available in f4-4.5, so you get a reasonably wide FOV (maximum of about 1.4 degrees or so).
Posted 11 February 2004 - 02:45 AM
I'd go for scopes in the F/5 focal ratio, F/4 telescopes suffer from coma a lot and are difficult to align.
Then you have the eyepiece height problem...
I guess you could get a 12 to 14" dob then.
Posted 11 February 2004 - 03:10 AM
is a bit less...
but if you ask me, you should get a 12"
Or, if it's in your budget:
P.S. make sure you leave a tracking platform/motor and/or DSC's in your budget if you want that.
Posted 11 February 2004 - 10:13 AM
Jeff, I think you need to understand field of view and f-ratio a little better (please don't take that wrong). An f/5 scope is pretty fast and gives a wide FOV. My 8" f/6 is an amazing wide-field scope! What is your reflector? Ever consider making a dob base for it???
hey, Tom. no worries...not taking anything the wrong way. Yes, I'm well aware that f5 is fast and gives wide FOV, relative to longer f-ratio of same aperture (e.g., 8" scope at f5 gives wider field than 8" scope at f6). However, we both know that FOV is ultimately determined by focal length, not f-ratio per se. So, a 20" Dob, even though it might only be f4, is still 2000mm long, and therefore gives pretty narrow FOV.
I guess we need to define "wide-field". It's a relative term. For me, I'm thinking of a scope that can give you at least 1.5 degrees...preferrably > 2 degrees TFOV. Tom, your 8", f6, has focal length of 1200mm. With a 32mm Plossl, this gives 1.4 degrees. Not bad. Of course, you can put in a 2" wide-field EP, and get closer to 2 degrees, but I'm trying to avoid the 2" path for now.
My 8" is f5 (1000mm focal length), and I'll get 1.6 degrees with the 32mm Plossl I just bought.
I just found out last night that Discovery makes a 6" f5 Dob. Focal length is 750mm. TFOV is 2.2 degrees with a 32mm Plossl. Now THAT's what I'm talking about. Sure, it's only 6", but for a lightweight, portable, quick-setup with wide FOV and pretty good aperture (especially compared to an 80mm), it's looking really nice.
Jarad...your suggestions are WAY out of my price range!!
In actuality, I'm not REALLY thinking of buying something like this right now. For those of you who aware (like Tom), I just bought my 3rd scope last week, so I'm fine for now. But, I was bored last night, so I was strategizing for the future, and thought I'd solicit some suggestions. I already have an 8" Newtonian, and am planning to upgrade that in the next year or two (probably two) to a 10" (probably Orion Atlas). But, I'm not going to set up an 8" or 10" Newt in backyard everytime there's a break in the clouds.
My 5" Mak (most recent purchase) is a great backyard scope for planets, but FOV is narrow, and therefore limiting for starhopping. So, I'm thinking about supplementing my collection (eventually) with another backyard scope that will be really easy to take outside on short notice, give wide FOV, and still have decent aperture. Hence the questions.
Tom, yes, I've thought about making a Dob mount for my 8", but don't know what's involved. Can the OTA be simultaneously compatible for Dob and EQ mount (i.e., could I leave tube-rings on when Dob-mounted, and leave Dob-contraptions on when EQ-mounted)?
Posted 11 February 2004 - 10:38 AM
FWIW, tend to agree with Jarad on the perfect size for a large dob (although it does not seem like you are really all that interested in a large dob). I feel that 17-20 (especially if it's an f5 or longer) starts getting awful big for one person to handle on a regular basis - not too mention the eyepeice height.
Incidentally if you are planning (dreaming) for long term, why not plan on a premium dob? Especially if you are willing to consider buying used...
I have a 15" f5 starsplitter (swayze) that I keep fully assembled in my garage to be wheeled out at a moments notice (takes me about 5 minutes to be out with it). This is a truss dob, so it's very portable and I can pack it off to other locations without too many issues.
IMO anything over a 10" f6 should be in a truss for weight and portability reasons.
I decided on the 15-16 range after seeing a few larger scopes, including a very nice 18" starmaster. I decided that they were just a little bigger than I wanted to deal with on my own. However I've since seen the obsession design, and I have to say that I would consider an 18" f4.3 or f4.5 obsession as these are only slightly larger than my current scope (and yet significantly smaller than my friends 18" starmaster), and I'd also give very serious thought to a plettstone (www.plettstone.com).
If you are looking for something smaller and lighter you might want to take a gander at these - www.starbuckets.com - (I just ordered an 8") and the UTI from www.infinityscopes.com Course in reality that sounds like it's more than you want to spend.
Heh - If you are going to dream - might was well dream big.
Posted 11 February 2004 - 11:33 AM
there's long-term, and there's long-term. No question...I'd love to have a 14.5" high-end Truss scope one day. But that's probably 5-10 years away. I definitely do not have $3000 to spend now. Hell, I don't even have the couple thousand that I've spend over the past 6 months...that's all on my credit card. ouch.
So, I'm trying to optimize, GIVEN my current constraints. When I say long-term, I'm just talking over the next few years. In this time span, I'm thinking more about putting together a collection of scopes that are *relatively* affordable, and that give me a full range of options in terms of when/where/what I can look at...and a diversity of scope-types to experience. Expensive quality-upgrades that are fine-tuned to my preferences will come much later.
The largest scope I can afford now is a mass-produced 10" Newt. So, that's my ultimate "big-scope" goal over next 2-3 years. I've got an 8" now, so I'm happy for the time being. BUT, my 8" isn't something I can just wheel outside and be viewing in 5 mins with, partly because it's not a Dob (it's an EQ, which requires setup time), and partly because I don't have a garage, or a covered back porch, and I have steps outside my front and back door. So I can't "wheel" ANYTHING outside. Therefore, I wish to supplement my "big" scope with something that I CAN haul out in a matter of minutes, and that will give me a wide FOV with decent aperture. Hence, my interest in the 6" Dob.
I do appreciate all of your feedback though.
Posted 11 February 2004 - 01:27 PM
Posted 11 February 2004 - 02:23 PM
Well, I hope my 40MK shows up tomorrow! I want that spacewalk look if I can get it!
I went to discovery telescopes website to see the 6" f/5 Dob but I couldn't find it. How much is it? For a quick grab and go scope in the backyard, the scope would probably be fine except for the cool down issue (which is probably minimal after 30 minutes). With your 32mm EP, it could be what you're looking for. Have you considered a short fl refractor in the 5" range?
As for making the newt into a dob mounted newt...you would have to design and build the base (you may be able to buy one from AM from someone that has converted to an EQ mount exclusively) and then add the discs needed for it to rotate onto the OTA. After all is said and done, it might not be worth it. The trick will be allowing the OTA to fully rotate in the GEM orientation with the dob discs on the OTA (follow that?).
You might be able to see if Hardin or Discovery (or Orion or Hands-On) has a "second" base that they would sell for cheap. Do they offer your OTA in a Dob mount? They might have the parts you need for it.
Posted 11 February 2004 - 02:37 PM
it's an EQ, which requires setup time
Maybe I'm not doing it right, but it takes me about 15 seconds to pick up my whole setup and point it North. I'm not going to do any astrophotography that way, but giving the dec knob a nudge every ten minutes isn't that big of a deal, IMHO.
YMMV of course, but a 6" f/5 seems to fit a GEM much better than a Dob to me.
Posted 11 February 2004 - 03:49 PM
JeffP...I have a 5" Mak that I leave setup on it's EQ-mount, and sure, I can haul this outside from my living room in one piece and plunk it on the ground in no time. But I can't do this with my 8" Newt. Set up, the whole thing weighs almost 80 lbs, which wouldn't be prohibitive if it was a small dense object (like an 80 lb dumbell), but 80 lbs of clunkiness is not something I can move around in one piece. Apparently you find the 6" much more portable. I would have a thought a 6" f8 would still be kind of a beast to move around (just as long as my 8" Newt, and presumably almost as heavy), but maybe not?
Posted 11 February 2004 - 05:33 PM
Posted 11 February 2004 - 11:17 PM
Posted 14 February 2004 - 09:55 PM
However, you mentioned the Discovery 6" f/5. That's why I'm responding to this thread. I've got one. Do you want it? $200 plus shipping in conUS.
Before answering, consider this:
1. It's so short that the eyepiece height is absolutely ridiculous even when seated. Plan to either sit on the ground and crane your neck, or get used to doing aerobic squatting. Maybe having both legs amputated at the hips would help.
2. It doesn't balance well, and is much like a little Civil War fat mortar waiting to tip when eyepieces are swapped out. This can be remedied by sliding the center of gravity along the bearing channels, but it's a pain.
3. It's so fast, and the mirror so curved that it is the only scope I've got that requires collimation each and every time it's used for best views.
4. It's no more portable than the much easier to use, and far more capable Hardin DSH 8.
5. It's got a cardboard (Sonotube) OTA, rather than a nice metal tube like on the newer Orions and Hardins.
6. It lacks the spring tensioners that keep the OTA in the rocker cradle, since Discovery didn't think that they were necessary, even though they really, really help with the scopes that have them.
7. That means that it's actually harder to pick up and carry as a unit than the larger 8" Hardin DSH. (or Orion XT8)
8. It' s discontinued, and you can forget any help from Discovery with it should you have problems like those mentioned above.
9. It's really not terribly useful for anything in specific, and is not really a good general purpose scope, either. It's lousy on planets, and only so-so on DSOs.
10. It's currently on loan to somebody else, but I doubt if he'd mind if I got it back from him, since he is pretty ambivalent about it, too.
So, with all those great points going for it, where would you like it sent? Eventually, I'll probably put rings on it, and mount it on an EQ, but honestly, I'm not sure this scope is worth the cost of the additional mount. So, I'd love to help out if I could. ;-) ;-) ..... Be careful what you wish for, you just might get it.
Posted 15 February 2004 - 12:49 PM
Posted 15 February 2004 - 01:21 PM
Just to defend two points about the scope though...
(1) as for eyepiece height, I'd probably put in on a raised stand
(2) Yes, I know it's fast, but no faster than my 8" Newt, or any faster than the high-end Dobs mentioned in this thread. I'm used to regular collimation, so no big deal.
As for the rest...hmmm...no thanks.
I should point out, everyone, that if I am actually going to buy a scope to fill the needs of my original inquiry, one of my main objectives is to get the largest amount of portable aperture I can get, and still get a REALLY WIDE FIELD. This latter emphasis seems to be overlooked by most of you....
It seems to me that well-made 6" f5 would be perfect for this. With 650mm focal length, you're talking a good 2.5 degrees of true FOV or so with a 32mm Plossl. You're getting the rich field of a short-fast 80-100mm refractor, but with 6" of aperture. THAT's what I'm looking for here. A 14.5" Truss would be awesome, no doubt, and I would like to have one someday, but you're only going to get 1 - 1.3 degrees with this, so even if I had one of these beautiful big Dobs, I'd still be left wanting for that wide, rich-field scope with decent aperture.
I have a rich-field scope now...but it's 80mm. Sometimes I wish I had the same FOV, but with the brightness of a bigger scope.
Posted 15 February 2004 - 01:30 PM
Orion SkyQuest XT10
At 58#s for the 10" though, that might be pushing the weight limit. I do move my Hardin 8" all over the yard (when it isn't a swamp) and it really is no big deal...it is about 42 pounds or so. I'm still going to try and keep both mount options available on the 8" (the dob is great looking at zenith).
Happy Dob hunting!
Posted 15 February 2004 - 04:42 PM
Besides, I'm convinced that DSO-hunting is a waste of time from my backyard anyway...too much light pollution. So, I'll just stick with my Mak and focus on planets in my backyard. When I get out the country, I'll set up the Newt to hunt down those galaxies.
Posted 15 February 2004 - 07:14 PM
Posted 15 February 2004 - 09:44 PM
Besides, I'm convinced that DSO-hunting is a waste of time from my backyard anyway...too much light pollution.
Don't believe it, Jeff! Go messier hunting with your DSO scope...everyone of them will do! Look for a cheap 8" dob on AM or think about how to convert your newt to a Dob base. Dobs are cool, you know!
Now go add a FAQ to my FAQ question in the O-T forum!!! What's a Newt???
Posted 16 February 2004 - 12:19 PM
It's kind of like a salamander.
Go messier hunting with your DSO scope...everyone of them will do! Look for a cheap 8" dob on AM or think about how to convert your newt to a Dob base. Dobs are cool, you know!
Yes, Tom, Dobs ARE cool. But I'm not convinced one will solve my problems in my light-polluted backyard. Yes, I've set up my *salamander* in my backyard before, and it was great for M42, M31, some bright open clusters, etc...but my Mak will probably do just as well on those bright objects, especially for non-scutinizing viewing sessions. When it comes to finding fainter stuff, though, the street lights just wash it all out. I dunno, Tom, I'll probably be posting "my new 10-inch Dob" soon, but for now, I'm resisting temptation.
Now go add a FAQ to my FAQ question in the O-T forum!!!