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General Astronomy >> Beginners Forum

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pdxmoon
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Loc: Oregon
Re: Newbie Lunatic Needs Advice new [Re: John Kuraoka]
      #5948883 - 06/30/13 11:28 PM

"The 90mm Mak-Cass packs a lot of magnification into a very compact rig, but be aware that the stock Dobsonian-style mount (the one you get at the $199 price point) doesn't let you take advantage of those higher powers. You'd probably soon want to get something like the Porta II for its added stability and slow-motion controls."

Jon, can you explain why the mount does not permit me to take advantage of the increased magnification?


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star drop
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949512 - 07/01/13 11:48 AM

The motions of the lower end Dobsonian telescopes tend to be problematic. There can be some sticking and then a jerk as one tries to move the telescope but there are some easy fixes that are inexpensive. Some of the mounts use a lazy Susan azimuth bearing that rolls along easily, sometimes too easily. But some people can overcome these problems without tinkering, it just takes practice and a strong arm.

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Paco_Grande
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949517 - 07/01/13 11:49 AM

Quote:

Would this do?
http://www.mrstarguy.com/scripts/prodView.asp?idproduct=351

Also, my tube is bracketed to hold it to the scope. I see no way to attach my tube to these.




No, the mini Porta is not what you want for a long scope like yours. And I did wonder about the mounting setup on that scope. You'd need to attach a "Vixen-style" dovetail to the scope. The Vixen-style dovetail is used by Orion, Celestron, and a bunch of other companies, it's a very common configuration.

The dovetail can be attached using scope rings.



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Jon Isaacs
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949533 - 07/01/13 12:03 PM

Quote:

"The 90mm Mak-Cass packs a lot of magnification into a very compact rig, but be aware that the stock Dobsonian-style mount (the one you get at the $199 price point) doesn't let you take advantage of those higher powers. You'd probably soon want to get something like the Porta II for its added stability and slow-motion controls."

Jon, can you explain why the mount does not permit me to take advantage of the increased magnification?




I have observed with John Kuroaka and enjoyed the views through his 90mm Mak on the mini-Dob mount. As he says, the mount is problematic, it is difficult to use at higher magnifications, it's jerky and very small motions result is large angular changes.

Newtonians on a Dob mount work well because the telescope itself is a long lever arm, this means fine control is possible... With small, short scopes, it is just more difficult, particular with the scope is not smooth.

Geared controls like your scope or the Portamount are a big help.

Jon


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pdxmoon
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Re: Newbie Lunatic Needs Advice new [Re: Jon Isaacs]
      #5949578 - 07/01/13 12:35 PM

So, if the 90mm mak is jerky, what mount would improve it? Can you show me with a link? :-)

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pdxmoon
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949581 - 07/01/13 12:36 PM

Also, back to the Celestron 4SE (which has that goto mount), in your opinion is their a huge difference between the 4SE and the 5SE?

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Jay_Bird
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949765 - 07/01/13 02:08 PM

Hi

Glad you had some better luck with your 80mm f/11 achromat.

It seems to me like you can choose from a few paths:

1) Work on your current scope and mount to see if they get to where you want for a backyard observing system. Almost no cost except adding an eyepiece or two.

2) Remount your current scope, maybe on an alt-az mount with slow motion controls. The one I'm familiar with is the Vixen Porta (now the Porta II) in the $200 to $300 range; it's great for long 80mm and OK for long 100mm refractor or short 130-150mm reflector, and adequate for almost any scope up to about 10-12 pounds. The slow motion gears on both axes are smooth and offer continuous 360° motion.

The mount has a "dovetail" clamp that tighens onto a dovetail bar on any scope you want to use. The dovetail bar attaches to your scope with a set of tube rings, these are a like a split version of the clamshell holding your scope on current mount. Orion brand rings are about as affordable as they get, in the $20-$30 ballpark for a pair of split rings, plus close to that for a dovetail bar (maybe $50 total for pair of rings and dovetail bar); you bolt the dovetail bar to the rings and close the rings to hold your scope; the whole assembly goes in the mount dovetail.

The one caution with the Porta (or simlar) and a longer telescope is to get a longer set of legs, maybe the 130cm legs not the 110cm legs if you go with the Vixen, then you won't be as low to the ground when looking at higher objects.

New eyepieces don't need to be expensive for yout longer focal ratio scope. Some people here like Sterling Plossl's or the Astro-Tech (is it called dual ED?) equivalent from Astronomics. Maybe 10-12mm and 6-7mm range for mid-high power (more than 25mm alone) and close to maximum power for your scope.

3) Or you can get a new scope. Some packages of the Porta II mount include a 95mm or 110mm compact Cassegrain, which is a shorter tube, f/11 or so scope, kind of like a C-90 or C-4 or ETX-90.

Among the SE computerized options, the C-5 optics might be the more versatile at f/10 than the C-4 at f/13 or f/14. I don't know how sturdy the SE mounts and tripods are compared to say the Porta-mouunt.

I've tried out several ideas for "travel scope" and "grab and go" backyard scope:

- 80mm short tube achromat refractor (mine is f/6) works well for both uses. Only difference from yours is f/6 vs. f/11, making for a shorter tube. My old one is heavy, but has a 2-inch focuser and can see up to 5 degrees of sky at lowest 12x to 15x power; if yours has a 1.25-inch focuser you may get down to about 1.5 to 2 degrees of sky in widest view at about 30x. For travel a old, sturdy photo tripod is adequate, for backyard or car camping a Porta-mount works well. This scope has some achromat refractor pros and cons: it's nice on the moon over 100x (I stop at 120x due to eye floaters but it shows more a little more detail at 160x), OK on Saturn and Mars, not so great for Jupiter, with all limits above due to chromatic aberration. It is superb for wide field views under dark skies. I kept this, and it's my most-used scope.

As I finish setting up a 4-inch (102mm)f/10 refractor to use with an old equatorial mount, the 80mm may get more competition for backyard lunar & planet use, but the 80mm will stil be smaller and more one-trip-to-yard 'grab and go'.

- a C-90 90mm f/11 Maksutov. This is OK for daytime spotting (birds across lake at 35x) and was almost what I wanted for a quick look lunar scope. I traveled with this a few times too, it weighs less than 1/2 what my heavy old 80mm short tube does. It sacrifices some field of view for higher power with any given eyepiece compared to the 80mm listed above. It just didn't outperform the 80mm f/6 enough on the moon or planets for me to keep both. I sold it.

- a 130mm f/5 reflector came with my Porta-mount. It took only 1.25 inch eyepieces, and it worked well at the upper range of what the Porta could hold steady, but also didn't do enough better than the 80mm f/6 for me to keep the Newtonian 130mm f/5 too.

Now, a 6-inch reflector is a noticeable jump up from 130mm and might better complement an 80mm. Almost all reflectors are likely require more frequent internal alignment ('collimation', you can learn how easily) than refractors, which may never require collimation.

Good luck, keep asking questions about tweaking or tuning you current scope.


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pdxmoon
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Re: Newbie Lunatic Needs Advice new [Re: Jay_Bird]
      #5949798 - 07/01/13 02:29 PM

Hi jay:

I'll probably do both--continue to tweak what I have and look for a new scope.

When you say 130mm, do you mean something like this:
http://www.telescope.com/Telescopes/Reflector-Telescopes/Reflector-Telescopes...


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Jay_Bird
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949840 - 07/01/13 02:53 PM

Hi, yes on telescope tube, maybe not on mount.

Based on small local sample, the least expensive 'go-to' mounts may not be the most durable, solid/stable, or reliable.

That's why the Porta-mount is OK for quick looks at the moon, IMHO, since it has smooth manual tracking for use at high power, is sturdy; and for longevity, it has no circuit boards or batteries, even though it's not go-to.

Now, the Celestron Nextstar (4 or 5 you asked about) may be better (I haven't used one) in that the 4 & 5 SE's may be a grade or level up from the lowest-cost go-to scopes I've seen people asking for help with at outreach, and not refect a compromise in the mount hardware to meet a target price.

I just relayed my experience with a few scopes like you're looking at. For me the smaller aperture had other attributes (widest range of power to low/wide field) that made me pick it to keep. Others might have picked the 90 Maksutov or the 130 Newtonian.


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Tony Flanders
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Re: Newbie Lunatic Needs Advice new [Re: pdxmoon]
      #5949854 - 07/01/13 02:59 PM

Quote:

So, if the 90mm mak is jerky, what mount would improve it? Can you show me with a link? :-)




How about strapping a long dowel to the tube to give it a longer moment arm? Seems like it might work.


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John Kuraoka
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Re: Newbie Lunatic Needs Advice new [Re: Tony Flanders]
      #5949973 - 07/01/13 04:06 PM

Yeah, what Tony said!

I use the Porta II mount with my 90mm Mak-Cass, and it helped a lot at higher magnifications.

It wasn't horrible with the stock mount, especially at lower magnifications where it really worked just fine. But, for example, the 10mm that comes with the $199 kit gives something like 125x. With the simple friction bearings and manual grab-the-tube-and-rock movement, it was difficult (but not impossible - my kids had no problem) to move the telescope around in order to manually track objects as they drifted across the view with the Earth's rotation.

Adding a longer lever might help make those fine adjustments. But, before Tony had that wonderful brainstorm, I'd already gone out and bought a demo Porta II from Mr. Star Guy. It'd be really neat if someone could try it out and report back to us!

Anyway, this may all be moot since it sounds like you're doing great with your refractor!


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pdxmoon
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Re: Newbie Lunatic Needs Advice new [Re: John Kuraoka]
      #5950002 - 07/01/13 04:26 PM

My continued thanks to all for taking the time to offer your opinions to this newbie.

I'm also thinking, since the refractor I own has given me great service, stick with what I know: maybe The C80ED or this https://www.astronomics.com/astro-tech-at72ed-72mm-refractor-telescope-white-...
..as a grab and go lunar/planetary observer.

My reading is telling me that certain smaller tube refractors (is that what the ED means?) have no chromatic problems and so might make great grab and go lunar scopes. Heck even this:
http://www.telescope.com/catalog/product.jsp?productId=102007
..was rated by S&T as a good scope for lunar viewing, although it's not a refractor.

So what I'm leaning towards is this: sticking with my 80mm scope and getting a port II mount, and then getting a set up for portable use. Perhaps with the port II mount I can also use the small scopes listed above. Thoughts?

Edited by barnum54 (07/01/13 04:28 PM)


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pdxmoon
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The best Possible Outcome new [Re: pdxmoon]
      #5950354 - 07/01/13 09:06 PM

Well friends, my 28 year old son informed me that he would love to have the scope he remembers using as a kid, and thats the Celestron 80 that started this whole thread! Hahaha!

He'll pick it up in a few weeks, which gives me time to buy a new scope.

And you know what? I really like the refractor. I'm not ready for a dob, or anything that I have to worry about aligning. I'm a sit in the chair, not on the ground, traditionalist :-). Someday on the dob, when I branch off past lunar viewing. But I've got a lot to learn looking at the moon. So..

I like the moon views with the 80mm. What I don't like is the EQ mount. So the porta II looks really good to me.

I'm going to start a thread in the refractor section asking for advice there. I appreciate all your help, and if you have more to tell me, come on over!


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