Short Tube vs Long Tube

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Abber

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Hi,

I can't seem to decide between a 4.5" short tube reflector or a long tube reflector. I'm not sure of the disadvantages of either as I've read contradictory reports on both. They are within my limited budget.

Also a local scientific company which supplies scientific equipment here has their own "house brand" of telescopes which they claim come out of the same places in China that Meade, Sky Watcher scopes come out of. The scoped I looked at are identical twins to a few Meade & Celestron models but include better finder scopes and extra Plossol eye pieces for very little more. This place was recommended to me by a friend who is into Astronomy

Any comments would be appreciated
Thanks in Advance
Abber
 
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crazyeddie

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Stay away from the "short tube" reflectors. They are notorious for poor optics.

The only way you can cram a long focal length into a short tube is to use a mirror with a "fast" (or low) focal ratio, then boost it's focal length with some kind of barlow lens. This is problematic for a variety of reasons. The first one is that mirrors with a fast (F/5 and lower) focal ratio are very difficult to manufacture to a good parabolic figure. Mass production does not lend itself to cranking out decent mirrors of this type. Secondly, the short focal ratio of such a mirror necessitates the use of a relatively large secondary mirror, and introducing such a large obstruction to your optical system will cause an excessive amount of image-degrading diffraction, which reduces contrast. That makes these scopes a poor choice for planetary viewing. Lastly, in order to boost the focal length in order to achieve higher magnifications, these short-tube reflectors must employ a barlow lens built into either the secondary mirror assembly or the eyepiece holder, and they are often of inferior quality....I've even heard that some are made of plastic instead of glass, if you can believe it.

Bottom line: "short tube" reflectors are no bargains. They compromise too much for the sake of compactness.
 
A

Abber

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Thanks for the reply. You've convinced me NOT to go short tube. But I'm still leery about the "house brand".

This is what one gets for $355 (Canadian $$) from this local scientific company (which has a good grade from the local Better Business Bureau). I think the "277x with the 2x Barlow lens" is really beyond the scope's practical means.

I'd appreciate a comment on this
Many Thanks
Abb

The reflector telescope uses a curved mirror to gather and focus light. This telescope has an aperture of 114mm (4½") and a focal length of 900mm. 3 Plossol eyepieces are included (6.5mm, 10mm, 25mm), as well as a 2x Barlow lens. Total magnification is 277x with the 2x Barlow lens. Also comes with accessory tray and 2 year warranty.

Accessories:

* Plossol 6.5mm AF 50º eyepieces
* Plossol 10mm AF 43º eyepieces
* Plossol 25mm AF 40º eyepieces
* Equatorial mount with cable controls
* Equatorial mount with cable controls
* Moon and sun filters
* Camera adapter to be used with 35mm CSR
 
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crazyeddie

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Abber":25mis4qm said:
Thanks for the reply. You've convinced me NOT to go short tube. But I'm still leery about the "house brand".

This is what one gets for $355 (Canadian $$) from this local scientific company (which has a good grade from the local Better Business Bureau). I think the "277x with the 2x Barlow lens" is really beyond the scope's practical means.

I'd appreciate a comment on this
Many Thanks
Abb

The reflector telescope uses a curved mirror to gather and focus light. This telescope has an aperture of 114mm (4½") and a focal length of 900mm. 3 Plossol eyepieces are included (6.5mm, 10mm, 25mm), as well as a 2x Barlow lens. Total magnification is 277x with the 2x Barlow lens. Also comes with accessory tray and 2 year warranty.

Accessories:

* Plossol 6.5mm AF 50º eyepieces
* Plossol 10mm AF 43º eyepieces
* Plossol 25mm AF 40º eyepieces
* Equatorial mount with cable controls
* Equatorial mount with cable controls
* Moon and sun filters
* Camera adapter to be used with 35mm CSR

Without knowing more about the specific brand, all I can say is that most inexpensive 114mm reflectors are built in China these days, and most come from a company called Synta, based in Taiwan. All of Celestron's lower-priced telescopes come from this company. I would not worry about the source, however. I would be more concerned with performance. Is the mount sturdy, or wobbly? Does it use cheap plastic parts, or machined metal for such things as the eyepiece holder and focuser? Does it come with clear instructions on how to use it, especially on collimation of the mirrors? Finally, does it give pleasing images with low and medium magnification eyepieces? A scope of this aperture maxes out around 180x or 200x....anything higher isn't very useful. The 6.5 mm eyepiece is probably unnecessary with the barlow, but I'm concerned that the 25mm and 10mm plossl eyepieces have such narrow fields of view. Most modern plossls have at least a 50 degree field, so I suspect that these eyepieces are cheap and may not even be real plossls.......more likely they are modified Ramsdens or Kellners, the least-expensive type. That does not mean they are bad. Such eyepieces were used for generations and can produce very sharp images, but they do produce narrow fields of view compared to more modern designs.

Just make sure that the vendor has a generous return policy, so that if this scope doesn't test out well, you can get your money back or exchange it for something better.
 
A

Abber

Guest
Many thanks for the response, it IS appreciated. Unfortunately, the nearest place really seen a decent selection of telescopes is a 4+ hour drive from here, a place called Khan Scope Centre on Toronto - they don't seem to want to bother with me (I've called twice now) since I'm interested in a starter scope and shipping starts around $45 and up :( This local place was recommended to me by a high school math & physics teacher - the local schools and college & university get a lot of scientific stuff from them, but their selection of scopes is very limited. Other than that, I have seen a few 4.5" Bushnell scopes with 675x magnification (wow hahahaha) for $250 here - thanks, but no thanks!

For what this place is selling the scope I'm interested in and what you get, it is a bit much - the fact that it includes a Barlow to get the magnification up had me concerned since the Bushnell also came with one. However pushing the magnification up to 277x is better than the 675x with the Bushnell. Also, I found out today this place is really a wholesaler but they'll sell to me since my my friend teaches highschool so maybe from a whole aspect, $355 may not be so bad for what you get. I've seen sales around Christmas from Khan where a $500 scope will be on sale for $300. We just moved from an apartment to a house which is why the sudden interest in a telescope. But I will check everything out you mentioned (again many thanks0

Now to throw a wrench into all this - a scope just came up for sale in a local ad today - a Meade DS-2080AT
80mm Altazimuth Refractor Goto with an extra set of Meade lens for "$175 or best offer". The scope itself sells for $300 US from Meade without the extra lenses. A little small than what I want but perhaps a better *safer* way to go :) ????
 
K

kg

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I have a 8 inch Celestron reflector and I believe the way works (please someone correct me if I'm wrong) is the primary mirror is short f/2 or so and is ground spherical to recuce the cost of manufacturing. The secondary mirrior is convex instead of being flat. The secondary corrects for the spherical aberration of the primary and gives the apparent image of a f/11 scope. Here is a much better explanation...
http://en.wikipedia.org/wiki/Schmidt%E2 ... _telescope

I like my Celestron alot, it fits my needs but I think for yourself you need to decide what your own needs are. I've seen refractors with a smaller apature give clearer views of plantets than my scope. If you like looking at star fields and nebulas a big light bucket on a Dobsonian mount might do well for you. Sky and Telecope gives product reviews which might be able to help you out.
http://www.skyandtelescope.com/
You can also look up events and associations on the Sky and Telescope site. It might be helpful to go to a star party and look through a bunch of different scopes and talk to some people who are not sales people.
 
C

crazyeddie

Guest
Abber":13og47hw said:
Many thanks for the response, it IS appreciated. Unfortunately, the nearest place really seen a decent selection of telescopes is a 4+ hour drive from here, a place called Khan Scope Centre on Toronto - they don't seem to want to bother with me (I've called twice now) since I'm interested in a starter scope and shipping starts around $45 and up :( This local place was recommended to me by a high school math & physics teacher - the local schools and college & university get a lot of scientific stuff from them, but their selection of scopes is very limited. Other than that, I have seen a few 4.5" Bushnell scopes with 675x magnification (wow hahahaha) for $250 here - thanks, but no thanks!

For what this place is selling the scope I'm interested in and what you get, it is a bit much - the fact that it includes a Barlow to get the magnification up had me concerned since the Bushnell also came with one. However pushing the magnification up to 277x is better than the 675x with the Bushnell. Also, I found out today this place is really a wholesaler but they'll sell to me since my my friend teaches highschool so maybe from a whole aspect, $355 may not be so bad for what you get. I've seen sales around Christmas from Khan where a $500 scope will be on sale for $300. We just moved from an apartment to a house which is why the sudden interest in a telescope. But I will check everything out you mentioned (again many thanks0

Now to throw a wrench into all this - a scope just came up for sale in a local ad today - a Meade DS-2080AT
80mm Altazimuth Refractor Goto with an extra set of Meade lens for "$175 or best offer". The scope itself sells for $300 US from Meade without the extra lenses. A little small than what I want but perhaps a better *safer* way to go :) ????

In my opinion, beginners need to "keep it simple". A simple, high-quality F/10 or F/11 80mm or 90mm refractor on an easy-to-use alt-azimuth mount. A simple 6"aperture F/8 reflector on a dobsonian mount. Skip the GOTO and other fancy gadgets. It's better to spend your money on good accessories, such as a Telrad finder or a wide-field eyepiece and a few filters for planetary viewing. The Meade scope is probably not a bad choice, but such a scope has limited aperture and is really only good for viewing the moon, planets, star clusters, and the brightest nebula.....all of which are easy to find without GOTO under all but the most light-polluted skies. GOTO mounts are valuable only when you get into higher apertures......I wouldn't bother with it in any scope under 8 inches of aperture. If you decide you like this hobby, you can keep your accessories and trade up to a better telescope.
 
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Abber

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Hi,

I went to the local dealer and looked at it as he just got some in. Apparently they've been in scientific business (especially microscopes) for over 30 years under a wholesale name and the manager said they weren't about to compromise their good name by ordering junk. The name I had been given was their retail name. Also, because they have technicians on site, every microscope/telescope etc is checked out upon delivery. There's nothing I need to do except put it together. And I was told this scope is very popular with them.

The new one was slightly different than the one listed in that it no longer included the 2x Barlow, and they upgraded the mount and tripod to the same heavier ones that's on their 8" Newton - they seemed very sturdy to me with the 8" on it (they had an 8" on display and so I played with it - that 8" was nice!!!) The technicians there assured me that the eye pieces were true Plossols (I asked since you mentioned the possibility that they weren't) . Also the manual is unusually good and thorough - I downloaded a few manuals from various manufactures when I was doing my homework on various scoped and for the most part, they sucked. Yes, the manual tells how to collimate the scope if necessary - something I didn't see with a few other manuals.

They said if I wasn't happy with it I could bring it back within 30 days but they said the long tube scope doesn't come back but occasionally the short tube one does and it's usually upgraded to the long tube one by the customer. And because they have technicians there, fixing anything within the 2 year warranty would be done there - no sending anything out. And the charge card I used gave an extra year warranty thus bringing the warranty period to 3 years.

Now for the kicker - I turned 62 on the July 25th and I told them this was a late birthday present so they gave me an addition $62 off the price :)

And as chance would have it, we have cloudy skies tonight with the possibility of rain.......:)

I apologize if I was a nuisance. Many thanks for all your help and it was truly appreciated
 
A

Abber

Guest
Hi,

Well, I managed to get this thing together. As chance would have it, last night it was very cloudy. The clouds cleared up a bit enough to sneak a peak at the moon for a few minutes just after midnight. This sucker is much sharper than I was actually expecting - even with the highest x eyepiece the moon was still razor sharp!!! And the thing is heavy!!! I won't complain about it's heaviness since that's a good thing because a good friend of mines father got a $250 Bushnell 4.5" long tube scope (675x!) for Christmas and it's light as compared to mine and even the lowest X eyepiece doesn't really produce a very sharp image, and in my opinion, the other eyepieces are useless. However, he's happy with it.

Getting to know how to use the scope will be another matter.......

Remember I said this was a newer model??? Well the book claims it's a 5", not a 4.5" as the box says and the tube seems a bit larger than my friend's father's Bushnell. BTW, I got bit by the bug with my friend's father's Bushnell. But having been into photography as a hobby for most of my life and owned a couple medium format cameras, I know a crappy image when I see one and the Bushnell images were not very good which is why I stayed clear of Bushnell.

Many thanks for all your help - it was GREATLY appreciated :)
 
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