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DSO Telescope Viewing Sizes

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#1 bleep

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Posted 07 January 2013 - 01:22 PM

Hi all
I've noticed on different websites that tell what's in the sky for the month say that the object is view able in binoculars or small or large telescopes. I was wondering what size is a small telescope or a large telescope? What size would my Orion XT8 be? or even my 10x32 binoculars? Thanks!

#2 kfiscus

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Posted 07 January 2013 - 01:31 PM

There are a variety of opinions on this question. I know there was a thread about this last fall. For reflectors 4" and under is small, 6"-10" medium, 12" and above large. Others will argue that 8" is the top end of medium and 10" is large.

Other types of scopes and binos will have will have their own unofficial size classes.

#3 kenrenard

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Posted 07 January 2013 - 02:10 PM

What's viewable would be more dependent on sky conditions then size. M31 looks like a smudge in the city in a scope and is naked eye in good skies.

I would say 8 is medium as Ken stated.

#4 csrlice12

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Posted 07 January 2013 - 02:19 PM

If you are using Sky Maps, your 8" should be able to see most anything listed. I belive Skymaps actually does state in some entries that it requires a 12" or larger scope on some objects. I use skymaps regularly to help me plan a night out.

#5 Dave Mitsky

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Posted 07 January 2013 - 05:34 PM

Since there are a number of amateur-owned telescopes nowadays with apertures greater than 30 inches, including ones of 40, 41, and 48 inches and a 70-incher that's under construction, I classify reflectors up to 10 inches as small, from 10 to 20 inches as medium, and over 20 inches as large.

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#6 CosmoSat

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Posted 07 January 2013 - 11:44 PM

I held back from posting earlier because the replies would be varied with everybody having their own opinions and not a single conclusion can be met upon. But guess thats the way it is..

For the newtonian scopes on dob mountings, I like to categorize them with not just their diameter but also their f/ratio. As this is the beginners forum, for the popular sizes available..

f/8 to f/6 - 4.5" to 8" = small
f/5 - 10" to 14" = medium
f/4.5 and faster - 16" or bigger = Large

Clear Skies!

#7 Ed D

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Posted 08 January 2013 - 05:51 AM

In the context of your post, the XT8 can be considered a medium to large size scope, a small scope being a 60mm or 70mm entry level refractor or 3" or 4.5" reflector. You can get a whole range of answers, as you can see, depending who you ask and in what context.

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#8 Tony Flanders

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Posted 08 January 2013 - 06:38 AM

I've noticed on different websites that tell what's in the sky for the month say that the object is view able in binoculars or small or large telescopes. I was wondering what size is a small telescope or a large telescope? What size would my Orion XT8 be? or even my 10x32 binoculars? Thanks!


As a professional astronomy writer, I find myself caught between a rock and a hard place when trying to make these kinds of statements.

I could use specific apertures, and say, for instance, that Pluto is visible in a 12-inch scope -- which I know to be true from personal experience. But on the one hand, a fair number of people have seen Pluto in 4-inch scopes. And on the other hand, a newbie in a bright city probably wouldn't be able to see Pluto with a 20-inch scope, and certainly wouldn't be able to identify it.

Skill counts for a huge amount. Experienced observers like Sue French and Steve O'Meara have seen things in their 4-inch scopes that elude me in my 12-inch. And I routinely see things in my 3-inch refractor that would challenge newbies with 8-inch scopes.

So I often prefer to be vague, and use term like "big" and "small." When I use them, I think of 4 inches and less as being small, and 12 inches and more as being big. Where that leaves 5 to 11 inches is up to you.

As for binoculars, when used without qualification that means normal, hand-holdable binoculars. Your 10x32s definitely qualify.

Tony Flanders
Associate Editor, Sky & Telescope

#9 Jon Isaacs

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Posted 08 January 2013 - 07:32 AM

Skill counts for a huge amount. Experienced observers like Sue French and Steve O'Meara have seen things in their 4-inch scopes that elude me in my 12-inch. And I routinely see things in my 3-inch refractor that would challenge newbies with 8-inch scopes.

So I often prefer to be vague, and use term like "big" and "small." When I use them, I think of 4 inches and less as being small, and 12 inches and more as being big. Where that leaves 5 to 11 inches is up to you.

As for binoculars, when used without qualification that means normal, hand-holdable binoculars. Your 10x32s definitely qualify.



:waytogo:

I agree... small, medium and large are guidelines, there are other factors that are equally important, the skill of the observer as well as the conditions, the darkness of the sky, the steadiness of the sky. These are big factors.

I agree with Tony's rating system but add "very large" to include very large scopes.... :) Where the boundary's lie, it is vague but I know my 25 inch F/5 is a vary large scope because it is very large... Circular logic. And I know my 12.5 inch and 16 inch are large scopes because people looking at them certainly think they are large.

Medium and small are more difficult to define but I think of up to about 4 inches as small, up to about 6 inches as smaller though refractors tend to confuse the rankings.

Jon

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#10 Ed D

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Posted 08 January 2013 - 08:17 AM

Jon, be careful you don't fall off that ladder or you may float out into space. :lol:

Ed D

#11 Dave Mitsky

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Posted 08 January 2013 - 09:22 PM

I agree that the semantics involved are vague.

However, I find it curious that large tends to be qualified into very large in such discussions, but that never seems to happen with small telescopes.

Times have changed. In the 1960s, when most amateurs owned 60mm refractors or 6" reflectors, a 12.5" Newtonian was considered a giant telescope but by today's standards, thanks to Mr. Dobson, it's not very large at all.

Most of the DSOs listed in my monthly calendar can be seen with an 8" aperture from a good dark site by an experienced observer.

http://www.cloudynig...5596155/Main...

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#12 City Kid

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Posted 08 January 2013 - 09:51 PM

Something to think about: a telescope that is "medium" size when viewing through it can suddenly turn into a "large" scope when it comes to transporting and storing it. :grin:

#13 Tony Flanders

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Posted 09 January 2013 - 06:50 AM

I find it curious that large tends to be qualified into very large in such discussions, but that never seems to happen with small telescopes.


Interesting point -- but where would you draw the line?

I think we can safely agree that any telescope with an aperture under 60 mm is very small.

See my blog on Ridiculously Small Optics.

#14 Jon Isaacs

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Posted 09 January 2013 - 07:03 AM

a 12.5" Newtonian was considered a giant telescope but by today's standards, thanks to Mr. Dobson, it's not very large at all.



To you and me, a 12.5 inch Dobsonian may seem relatively small and certainly in comparison to an equatorially mounted 12.5 inch of days of yore, the Dob is much more compact and manageable but it is still a large telescope that requires planning and effort...

(For comparison purposes, my two 12.5 inch telescopes)

Jon

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#15 Jammer53

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Posted 10 January 2013 - 12:01 PM

Wait. What? That big scope is clearly two feet taller than you. How in the world do you use the spotting scope when it's mounted so near the front lens???

#16 newtoskies

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Posted 10 January 2013 - 12:54 PM

Love those two buckets Jon....and the sign too...lol

#17 Jon Isaacs

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Posted 10 January 2013 - 05:05 PM

Wait. What? That big scope is clearly two feet taller than you. How in the world do you use the spotting scope when it's mounted so near the front lens???


The scope is mounted in "rotating rings" so the observer can position the eyepiece and the finder for comfortable viewing. But for most objects, this is definitely a "ladder scope." Before John Dobson, this is what a 12.5 inch Newtonian looked like. In the previous photo, the scope on the right has the same aperture but is much easier to use, it's a Dobsonian. There are advantages to large scopes on equatorial mounts but transporting them is not one of them.

Jon

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#18 Gert K A

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Posted 10 January 2013 - 08:15 PM

That’s a wholesome scope but I would wear slippers :smirk:

#19 Tony Flanders

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Posted 11 January 2013 - 05:02 AM

That’s a wholesome scope but I would wear slippers :smirk:


Slippers on a metal-rung ladder would be a really bad idea. There's a reason they're called slippers, you know!

Bare feet always give the best grip, except on ice and snow.

#20 MawkHawk

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Posted 11 January 2013 - 09:13 AM

Man, I used to drool over those big GEM-mounted reflectors back in the day. Yours is a thing of beauty.
I actually did have an RV-6 and even that was so heavy. I remember thinking then that there must be a better way, and John Dobson showed us that there was....

#21 Gert K A

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Posted 11 January 2013 - 09:17 AM

Slippers on a metal-rung ladder would be a really bad idea. There's a reason they're called slippers, you know!

Bare feet always give the best grip, except on ice and snow.


Point taken about the slippers, although I figured they were called slippers because they are easy to slip on not because they are slippery in use.
However any kind of foot wear that gives support is generally a good idea for lengthy use of ladders no matter the weather
and also as often advertised in here, a comfy observing environment calls for better views.
Anyway it was just a silly side remark, I would wear footwear but to each his own.

I still like the scope though a lot and I wish that I would have a place to house something of this size.

#22 Jon Isaacs

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Posted 11 January 2013 - 09:31 AM

However any kind of foot wear that gives support is generally a good idea for lengthy use of ladders no matter the weather and also as often advertised in here, a comfy observing environment calls for better views.



Gert:

Some good points. The first time I posted that photo I did not realize I was barefoot until someone pointed it out. San Diego is relatively warm in the winter so one can be comfy barefoot, even in the winter.

But I don't recommend it. Several years ago I was out in the backyard, again barefoot. I wanted another eyepiece so I started inside through a sliding glass door. The door itself was open but the screen was closed, I tried to walk through the screen and ended up severely lacerating my big toe, blood all over the place, a rushed trip to hospital, three weeks in bed, it became infected...

You'd think someone 64 years old would be smart enough to wear shoes outside but I still haven't learned my lesson.

Jon

#23 newtoskies

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Posted 11 January 2013 - 09:37 AM

My wife has the habit of going outside bare foot. Me, I always have shoes or slippers on when going out doors. Lesson learned when I was younger and stepped on a piece of glass....sliced my big toe open. Lots of blood and stitches so now I am cautious.

Agree with above comment....I would LOVE to own a big bad scope like that....even if it meant being bare foot while observing..lol

#24 Gert K A

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Posted 11 January 2013 - 09:58 AM

Jon:

I’m a winter "child" living in an urban environment up north, being barefooted is a luxury to me, as is good seeing and big scopes..
just write me down as envious :o

Gert

#25 Dave Mitsky

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Posted 11 January 2013 - 02:39 PM

a 12.5" Newtonian was considered a giant telescope but by today's standards, thanks to Mr. Dobson, it's not very large at all.



To you and me, a 12.5 inch Dobsonian may seem relatively small and certainly in comparison to an equatorially mounted 12.5 inch of days of yore, the Dob is much more compact and manageable but it is still a large telescope that requires planning and effort...

Jon


Relative is the operative word here. I'm looking at the spectrum of apertures that are available to today's amateurs, not ease of use or other factors. At most any major star party, an 18" truss-tube Dob hardly draws any attention any more and with the new ultra-fast mirrors, a 20" doesn't even seem all that big.

http://www.starmaste...es.com/MX20.htm

Dave Mitsky






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