71 replies to this topic

[Protheus]

The primary-mirror of that one is reportedly spherical(per Celestron itself), instead of parabolic as it should be, at f/5.  One tell-tale sign is that the primary-mirror is not center-spotted.

 

This sounds like superstition to me, or at least dangerously simplistic.  Parabolic mirrors of course don't have to have a center spot, and spherical ones always could.  Many which have been through the hands of an experienced astronomer likely do, even if it's just a paper ring.  It may be less likely for a spherical mirror to come from the factory with a center spot right now, but I'm not sure I'd rely on that as an indication of the mirror figure.  What you probably can rely on is that if a manufacturer doesn't advertise that their cheap Newtonian uses a parabolic mirror, it's probably spherical.

 

Chris

[Sky Muse]

 What you probably can rely on is that if a manufacturer doesn't advertise that their cheap Newtonian uses a parabolic mirror, it's probably spherical.

I've gone by that as well.

[tturtle]

Just buy this

 

https://www.cloudyni...onto-telescope/

[Protheus]

I've gone by that as well.

Of course, by that metric, the low end market is disturbingly devoid of parabolic mirrors, especially considering how saturated it is with short tubes.

 

Chris

[JetLinkin]

I think the Orion ShortTube 80 (or one of its Celestron or Meade clones) would be a good first instrument for anyone. A new one along with a sturdy camera tripod would be well within your budget. If you really want something American, as others have suggested, you could look at used older C90, ETX, or perhaps a C5. The newer Bushnell 90mm Maksutov (which I think is basically a C90 clone made by the same company) seems like a decent budget scope as well. These have been discontinued, but I see them used on the auction sites periodically.

 

Cheers, Mario

Edited by JetLinkin, 19 December 2022 - 09:53 PM.

[radiofm74]

There are many excellent "first scopes" for visual out there…

- A short refractor on a light alt-az

- a 6" Newt on a manual GEM

- a 6-8" Dob

- a lovely little SCT or Mak, ideally on a GoTo mount

- even binoculars, ideally on a parallelogram mount.

 

As for which is best, much depends on intended use and context. OP, give us more info ;D

[aeajr]

This article might be helpful.

 

How Much Does a First Telescope Cost?
https://telescopicwa...telescope-cost/

 

In general I recommend one of the Celestron StarSense Explorer Scopes.  102 mm or larger.

https://www.astronom...ope_series=1039

 

 

Where will you store it?

Where will you use it?

How will you move it?

[RobertMaples]

Yes that Orion 130 ST is a good one too !

 

https://www.amazon.c...e/dp/B00D05BKOW

 

https://www.telescop...roductId=137399

 

I believe Celestron and Orion telescopes optics are made by the same company, Synta.

 

Nevertheless the above Celestron was good enough for me to take the picture of Mars shown below with a $140 Newtonian scope and a $30 Logitech webcam, a few years ago.

 

Btw, well known facts are clearly stated here:

 

The question arises: if parabolic mirrors are more efficient than spherical mirrors, why even make spherical ones?

For optical applications, like Newtonian telescopes, the illustrations here are greatly exaggerated. Telescope mirrors are much less curved, almost flat. And parabolic telescope mirrors look spherical and very nearly are spherical, deviating from the sphere by perhaps only millionths of an inch. In reality, all optics suffer from diffraction. If the spherical aberration causes less image degradation than diffraction, then little or nothing is gained by using a parabola, which is harder to make. If a spherical mirror is a small enough section of a sphere of large enough radius, then it can still be diffraction limited. Small Newtonian telescopes, commonly around 114 mm diameter and 900 mm focal length, usually have spherical mirrors and are diffraction limited or nearly so.

.

The statement about spherical vs. parabolic mirrors is true, and for the example 114/900 Newtonian a spherical mirror works fine, but for a 130/650, a spherical mirror definitely is not diffraction limited (the larger the aperture, the higher the focal ratio has to be for a spherical mirror to be diffraction limited).  I'm certainly no expert on the subject, but from looking at your picture of Mars I think your Celestron does have a parabolic mirror. From what I have gathered, apparently some of the AstroMaster 130s have parabolic mirrors and some have spherical.  I don't know why that is, but since Celestron doesn't specifically say that it has a parabolic mirror (and their customer support sometimes says yes and sometimes says no), and there have been people to claim that they have one with a spherical mirror,  I wouldn't recommend somebody buy one.

[RobertMaples]

Don’t buy a newtonian on an EQ mount as a first scope for visual use. Get something on a Dobsonian “altitude-azimuth” base. You gain nothing from a polar alignment if you’re not imaging DSO, which isn’t in your budget...

You gain "nothing"?  How about extreme ease of tracking?  Not only that, but when talking about telescopes in the $300-400 price range with an alt/az mount you're not likely going to get slow motion controls on both axes.  When working at high magnifications the dual axis slow motion controls of the EQ mount makes it much easier to get the target in view in the first place.

[RobertMaples]

Fair, I've just seen far too many newbies come around our astro club with little idea how to use their $200 manual EQ mounts, completely frustrated with them and about to quit or sell us the scope for pennies on the dollar.

 

The worst cases I've seen, they are constantly adjusting their mount's latitude bolt and trying to use it in an Alt-Az fashion, despite me telling them, "listen, unless you move, lock that thing in at 40ºN because it's not changing unless you're driving 1+ hour away from here north/south.

 

GEMs need specific knowledge to even roughly polar align, and a newbie unfamiliar with Polaris (or unable to see it) is in for a very confusing first time.

Actually, most EQ mounts work just fine as an alt/az mount when adjusted for 90° latitude.  In fact, when talking about low end mounts, If I wanted alt/az controls I'd still generally rather use an EQ mount as an alt/az mount over a regular alt/az mount.  The EQ mount gives you dual axis slow motion controls that most low end alt/az mounts don't, making it much easier to center and track objects.

 

The only specific knowledge needed to roughly polar align an EQ mount is "waht's my latitude" and "which way is north"?

 

I do wonder how many of those newbies would get just as frustrated trying to center an object in a cheap alt/az mount.

[Herb_H]

... looking at your picture of Mars I think your Celestron does have a parabolic mirror. ....

No it does not, read the description.

[Herb_H]

Saturn with the $130 Celestron Powerseeker EQ 114mm Newtonian.

 

Pretty much "Out of the Amazon Box", 2x Omni Barlow and Logitec C310 webcam, picture from a few years ago (2014).

 

The mirror optical quality is excellent for the price, yes it is spherical.

 

https://www.amazon.c...e/dp/B0000Y8C2Y

 

Btw that also disproves the claim that German Equatorial Mounts (EQ) are expensive ... not sure where that patently incorrect blanket statement came from.

 

Polar alignment on the above mount takes less than a minute, if you know where Polaris is (that always helps).

 

I also used this inexpensive Celestron battery operated 9V Equatorial Mount clock drive motor, to keep Saturn centered.

 

https://www.amazon.c...e/dp/B00039R23G

 

So that you don't waste precious time constantly chasing objects in the sky ...

 

Just to show one more time that you don't need overly expensive, gadget loaded equipment to get good views of the major planets.

 

The limitations could be in your equipment, or more simply sometimes in your ability of using what you have, properly ...

 

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Edited by Herb_H, 20 December 2022 - 02:07 PM.

[Hexley]

Actually, most EQ mounts work just fine as an alt/az mount when adjusted for 90° latitude.  In fact, when talking about low end mounts, If I wanted alt/az controls I'd still generally rather use an EQ mount as an alt/az mount over a regular alt/az mount.  The EQ mount gives you dual axis slow motion controls that most low end alt/az mounts don't, making it much easier to center and track objects.

 

The only specific knowledge needed to roughly polar align an EQ mount is "waht's my latitude" and "which way is north"?

 

I do wonder how many of those newbies would get just as frustrated trying to center an object in a cheap alt/az mount.

You and I have been around. I know my latitude and where north is wherever I am with my compass app. This does not occur to a newbie who can't be bothered to watch a 5-10 minute video on polar aligning. I understand the benefits EQ mounts provide, but I don't think they outweigh the sheer convenience of AltAz mounts when you're talking about newbies doing visual astronomy. I put Orion Starblasts in the hands of 11 year olds with a red dot finder (and a Celestron zoom) and they point it right at the moon or Jupiter. That simplicity cannot be duplicated by any EQ mount.

Edited by Hexley, 20 December 2022 - 01:23 PM.

[UnityLover]

You and I have been around. I know my latitude and where north is wherever I am with my compass app. This does not occur to a newbie who can't be bothered to watch a 5-10 minute video on polar aligning. I understand the benefits EQ mounts provide, but I don't think they outweigh the sheer convenience of AltAz mounts when you're talking about newbies doing visual astronomy. I put Orion Starblasts in the hands of 11 year olds with a red dot finder (and a Celestron zoom) and they point it right at the moon or Jupiter. That simplicity cannot be duplicated by any EQ mount.

Any newbie that comes onto cloudy nights should get an EQ mount then, since you can teach them how to polar align! 11 year olds can learn plenty if they have a real interest in something.

[Hexley]

By the same token, their cost for the class is $40, which mostly goes into their Celestron 7x50 Cometrons. We're getting off topic though. I'll let you know when one of them buys an EQ mount.

[Napp]

Actually, most EQ mounts work just fine as an alt/az mount when adjusted for 90° latitude. In fact, when talking about low end mounts, If I wanted alt/az controls I'd still generally rather use an EQ mount as an alt/az mount over a regular alt/az mount. The EQ mount gives you dual axis slow motion controls that most low end alt/az mounts don't, making it much easier to center and track objects.

The only specific knowledge needed to roughly polar align an EQ mount is "waht's my latitude" and "which way is north"?

I do wonder how many of those newbies would get just as frustrated trying to center an object in a cheap alt/az mount.

You and I have been around. I know my latitude and where north is wherever I am with my compass app. This does not occur to a newbie who can't be bothered to watch a 5-10 minute video on polar aligning. I understand the benefits EQ mounts provide, but I don't think they outweigh the sheer convenience of AltAz mounts when you're talking about newbies doing visual astronomy. I put Orion Starblasts in the hands of 11 year olds with a red dot finder (and a Celestron zoom) and they point it right at the moon or Jupiter. That simplicity cannot be duplicated by any EQ mount.

Most first time telescope buyers know almost nothing about mounts and don't even consider them. Look at the most asked questions by a newbie - "What's the best telescope?" or "What telescope should I buy?" Nothing about mounts - "That's just the tripod holding up the scope, right?" I agree that with proper instruction an eq mount is not hard to use. I have a CGX and a Losmandy G8/11. I have a simple non-motorized eq, too. However, almost anyone can operate an alt-az mount with little to no instruction. An eq mount involves some more complicated concepts. Complicated is too strong a word. Most everyone agrees the earth is round and rotates. Most are aware of the North Star and maybe understand the earth's axis points toward it. However, they have never tried to put that knowledge to practical use with a piece of machinery. Most do not have an easy time learning how to use an eq mount unless they have a knowlegable person to help them. And the idea that an eq could be used as an alt-az would not occur to them because they don't even know what alt-az means - let alone the differences between eq and alt-az. As to centering an object in the scope for the first time an alt-az is simpler. It moves up/down and left/right which people are used to. Telescopes on eq mounts don't move directly up/down and left/right. We are entering the season when a lot of newbies get new scopes. A lot of them will appear at club outings and meetings looking for help. One of my clubs advertizes and devotes its January club meeting to helping folks with new scopes and mounts. And I'm quite sure we will be helping a fair number understand "how do you operate this equatorial mount?"

[vtornado]

One of my clubs advertizes and devotes its January club meeting to helping folks with new scopes and mounts.

 

what a great idea!  I will put it on our agenda.

[RobertMaples]

Saturn with the $130 Celestron Powerseeker EQ 114mm Newtonian.

 

Pretty much "Out of the Amazon Box", 2x Omni Barlow and Logitec C310 webcam, picture from a few years ago (2014).

 

The mirror optical quality is excellent for the price, yes it is spherical.

 

https://www.amazon.c...e/dp/B0000Y8C2Y

 

...

Ahh, that makes more sense.  The telescope you linked to previously was the AstroMaster 130EQ, a 130mm f5 (650mm focal length) telescope, which would not be diffraction limited with a spherical mirror.  As I mentioned before, spherical is fine with with a 114/900 telescope like yours.

[daveb2022]

I use my refractors on an alt/az tripod with digital setting circles the most. A nice small scope will always be of use to me and the simple alt/az mount is often my choice over any of my GEM's or computerized mounts I own. My simple non-powered alt/az mounts are easy to haul & I can put a variety of small scopes on them. They're easy to set up and align plus I find a refractor is comfortable to use (IMO). Having no tracking abilities does not bother me at all. In fact when finding a target it's much quicker than waiting for a go-to scope to slew to an object. Probably out of the price range the OP wants for the tripod, encoders and pointing computer though.

 

I have practically no experience with packages costing less than 500 bucks except the ETX 90 spotting scope and a 150 dollar Celestron 80mm refractor I own. But both of those scopes become an accurate pointing device on one of my alt/az tripods using DSC's. The Celestron Star Sense pointing software is very interesting to me. If it works as advertised, it could make the difference how long one stays interested in the hobby. 

 

I'm one to believe a person new to astronomy should try to actually try to find someone to help them that has a good background in the hobby. But I did it on my own in the late 90's and if it wasn't for a few good books and a cheap little go-to scope helping me actually find targets, I'd have a lot more money in my bank account today. Look at how my life would be different today if I would have strayed away due to frustration in trying to navigate the night sky. I hate to see someone spend a substantial amount of money if the reason for leaving the hobby is because of a poor purchase and/or a lack of personal guidance. Go to an astronomy club event if you can.

 

Lastly, I feel a small spotting scope or refractor that can be used for astronomical or terrestrial viewing can still be of value if astronomy isn't in a persons blood. JMO

[radiofm74]

It's getting a little too contentious. I think we can all agree that an alt/az is more intuitive to operate and more portable (if in the same payload class), and that an EQ mount has a bit of a learning and set-up curve but makes tracking objects easier. From there, everyone has their preferences… 

 

In any case, should the OP make contact again, we've given him or her a powerful lot to ponder ;D 

[JorgeRG]

I’ve read a lot of these posts , and seen multiple points of view, being obviously an absolute noob. Given that, I feel kinda satisfied about our choice haha, even without using it for the first time (it is still in the garage hidden, we suppose it’ll be too obvious in the tree haha). A small refractor is easy for a kid to set up and will show a decent amount of things to our son, enough to keep him (us) interested. If it catches the hobby, voilá, he will grew his scope out and we'll get something else. He’s already having fun with my binos so, next week we’ll chase dark skies and try the little one.

Edited by JorgeRG, 21 December 2022 - 11:21 AM.

[HeavyJohnny]

My advice is save your $300 for a decent refractor. Reflectors require collimation which requires a learning curve and patience, be prepared for many lost nights and lots of frustration and tinkering. If you can hold out for something like a doublet refractor, its point and shoot. Also, if you decide to get into astrophotography its something that will grow with you. They pair perfectly with mono cameras.