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Trying to compensate for something


spaceboy

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At what point would you stop and think ...."maybe I might have over done it this time??"

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I've never had the luxury of looking through anything this big but even if the views are breath taking, mind blowing, astro wonders, I doubt you'd get me up the ladder in the first place. I mean even a rough estimate I'm guessing you near second floor height there and lets be honest a lot of people have died or seriously injured themselves falling from similar heights. I sure wouldn't feel comfortable balancing those ladders on grass even if the fall was going to be softer.

On another note just how practical would a scope like this be? I mean moving it to targets must be a challenge and to keep it on target while you set up ladders and make the climb, not to mention tracking said object.

Is there a point when a scope is so big its impractical for anything other than a proper observatory ? I know many do this but I'd struggle to see where the enjoyment is when your risking life and limb. I can't imagine its the most comfortable of observing positions.

 

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If you think that's a bit "over-the-top," take a look at John Dobson (RIP 1915 - 2014):

 

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To be fair, I don't know if this is actually his 'monster' as I call it. But in answer to your question - I'd call it quits when your telescope requires it's own proprietary trailer to haul it to & from your observing-site, star-party, planet.....

Dave

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If I could go as BIG as that... I might be thinking of
alternative ways of extracting light rays to focus? ;)

https://en.wikipedia.org/wiki/Reflecting_telescope

In all seriousness... Coude (Nasmyth too seemingly!)
focus etc. I just makes rather more sense to me. :) 

It has wryly amused me some 2nd'ary mirrors are
bigger than my (one & only) primary mirror tho! :D

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I thought of that several times. I concluded I would never own a dob that requires a ladder. So my personal limit is a 400mm f/4.5 scope to keep the eyepiece accessible (assuming I get a dob larger than my 300mm someday). That would also keep the f/ratio reasonable, I mean Explore eyepieces could take it, no need to resort to expensive Tele Vue's.

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I've used a 24" dob on a small step ladder with a wide base (standing on rung 3 or 4 and leaning on the top of it) and tracking's not that bad to be honest. You only have to move the ladder once in 15-20mins and panning around is like moving a large circle over a steady background. It takes 7 or 8 mins for an object to move right across the view. It's a quite different experience to using smaller apertures that require constant nudging every 20 seconds or so. The chap I was with was sketching a comet and he had plenty of time to absorb the view and pop down to his desk to record it. :)

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I believe that the gentleman concerned does have a full aperture film solar filter. I can't help but be impressed. It isn't really a one man scope. 

Go big! Or, Go home! (he must never see his family.)

Despite the obvious logistical and safety issues, I would love a gander

Paul

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1 hour ago, Paul73 said:

I believe that the gentleman concerned does have a full aperture film solar filter. I can't help but be impressed. It isn't really a one man scope. 

Here's the detailed story of German amateur Dr. Erhard Hänssgen and his one-person 42" dob (including the picture of the full size solar filter):

http://www.cruxis.com/scope/scope1070.htm

For me, my 18" is the limit; still easy enough to handle, and needs just a two-step ladder. As Kriege/Berry state ("The Dobsonian Telescope", p.40/41): "Due to the geography of the universe, the laws of physics, and the design of the human eye and brain, the visual thrill you get from enormous apertures succumbs to the law of diminishing returns". Always found this true ( and a flimsy excuse for myself, when I'm using more and more my 8kg lightweight  8" f/4 Hofheim Traveldob.....).

Stephan

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Would love a look through it, under a decent sky. The ladder looks pretty stable so no worries there. I would never have one as I would never use one. Like Stephan I reckon an 18" would be as far as I go. Enjoyed my 16" f4.5, very manageable although too wobbly for the dob mob :p 

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Doubling the aperture will give you a visual gain of 1,5 magnitudes, no matter whether you step up from 2" to 4", or from 4" to 8":

     Telescope Limiting Magnitude
 Aperture           Probability of  Detection
 Inches        98%    90%    50%    20%    10%     5%     2%

     1         9.7   10.2   10.7   11.2   11.7   12.4   13.2
     2        11.2   11.7   12.2   12.7   13.2   13.9   14.7
     3        12.1   12.6   13.1   13.6   14.1   14.8   15.6
     4        12.7   13.2   13.7   14.2   14.7   15.4   16.2
     5        13.2   13.7   14.2   14.7   15.2   15.9   16.7
     6        13.6   14.1   14.6   15.1   15.6   16.3   17.1
     7        13.9   14.4   14.9   15.4   15.9   16.6   17.4
     8        14.2   14.7   15.2   15.7   16.2   16.9   17.7
    10        14.7   15.2   15.7   16.2   16.7   17.4   18.2
    12.5      15.2   15.7   16.2   16.7   17.2   19.9   18.7
    14        15.5   16.0   16.5   17.0   17.5   18.2   19.0
    16        15.7   16.2   16.7   17.2   17.7   18.4   19.2
    18        16.0   16.5   17.0   17.5   18.0   18.7   19.5
    20        16.2   16.7   17.2   17.7   18.2   18.9   19.7
    22        16.4   16.9   17.4   17.9   18.4   19.1   19.9
    24        16.6   17.1   17.6   18.1   18.6   19.3   20.1
    30        17.1   17.6   18.1   18.6   19.1   19.8   20.6
    36        17.5   18.0   18.5   19.0   19.5   20.2   21.0

So, if I'd want to go 1,5 mag deeper, I'd end up with a 36" monster.

Stephan

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While I would love to have more than a peak through that monster, one issue I would think would present itself is the focal length. The big show piece objects (M42, M31 etc) just would not fit in the maximum achievable field of view so you would be unable to view familiar friends in a new light, thus forcing one to chase ever smaller, dimmer objects which perhaps negates some of the aperture advantage. However, being able to chase down stuff from the PGC catalogue would still be fun!!

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What a scope!

Yeah I dream of stepping up to a 22" or so, and I used to wonder if I should have gone for an 18". But, I'm pretty happy with my 15" - it is no fuss, fits me, and I almost 100% of the time select it over my grab-n-go 10".  That's hopefully a measure of making a good choice.  I watched a large dob being set up and dismantled recently, and was privileged to get a look through it.

Right now, I'd be very happy to just get out observing more often, and see more of what my 15" can show me: with good weather, around weekends, around the new moon - and getting the freedom to head off!!! Not asking for much, huh? :grin:

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2 hours ago, DirkSteele said:

While I would love to have more than a peak through that monster, one issue I would think would present itself is the focal length. The big show piece objects (M42, M31 etc) just would not fit in the maximum achievable field of view so you would be unable to view familiar friends in a new light, thus forcing one to chase ever smaller, dimmer objects which perhaps negates some of the aperture advantage. However, being able to chase down stuff from the PGC catalogue would still be fun!!

I tend to agree Matthew. I guess that's where the little stubby ones come in to play?

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1 hour ago, Alien 13 said:

Yikes but I do wonder whats the point of it, you must be nudging it every few seconds with the risk of falling off and instant death, It would be far better on an EQ mount with a camera attached..

Alan

Observing in a public area may have another inherent risk.....

A crowd might gather around you on your ladder and begin chanting: "Jump! Jump! Jump!"

But this may be an "Only in America" phenomena.

<getting hat>

Dave

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1 hour ago, Stu said:

I tend to agree Matthew. I guess that's where the little stubby ones come in to play?

 

 

Stubby all the way!  If I were to ever buy a big dob (and I would have to get over my "mirrors are for shaving point of view":icon_biggrin:) I would definitely go short and stubby.  The advent of the very short focal length mirrors in the world of large dobs brings back into play the familiar favourites.

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I still think the the guy is a bloody hero!

Whilst the rest of us dream of 18", 20", 22". This man says, "No!!!! Let's do this properly."

Paul

PS. I defy any red blooded stargazer to look though @mapstar (Damien's) or @swamp thing (Steve's) Dobs and say 16" is enough. It isn't. End of. I have a 16" and it is no way big enough!

 

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20 hours ago, LukeSkywatcher said:

I know of a guy here in Ireland who has a 30 inch Obsession. Ladder does not come included.

Got to look through a 20" Obsession at the SSP ;) Very sound owner - generously sharing the EP with all!

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