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Should I buy the Celestron Astromaster 70?

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13 replies to this topic

#1 stargazer193857

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Posted 18 August 2019 - 04:42 AM

I found it used locally for $40. I'm tempted to see how much it can resolve on Jupiter with the 70mm aperture. It is f12.9, 900mm fl. It is $130 new, so I bet I can get my $40 back. Will I be disappointed? I'm used to a 6" newt that may have collimation or cooling issues.

Edited by stargazer193857, 18 August 2019 - 05:02 AM.


#2 sg6

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Posted 18 August 2019 - 06:43 AM

70/900 will do a reasonable job on Jupiter. An 8mm eyepiece should do well in it, although 12mm will be sensible also.

 

I have viewed Jupiter at around 30x and seen clear banding on a 70mm f/5. You should surpass that but Jupiter has moved away and so is smaller then when I looked, also lower.

 

Good scope for outreach. simple. easy, right shape, 2 or 3 eyepieces and all set. Maybe look on it as a project scope and see what you can make better on it with a bit of tindering. Actually at outreach the tinkering and improvement will be as big a conversation point as the scope and how it performs. I find I spend more time explaning what and how they work then anything else. ETX #494 handsets need a fair bit.



#3 junomike

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Posted 18 August 2019 - 06:48 AM

Disappointed, probably.  Poor investment, probably not. 

Maybe use it for a quick peek or times when you don't feel like hauling out the 6"er.



#4 stargazer193857

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Posted 18 August 2019 - 02:54 PM

Probably not as disappointed as with a Bird Jones. For only $40, I guess I'll go get a learning experience.

#5 stargazer193857

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Posted 18 August 2019 - 05:16 PM

I have the astromaster 70x900 az with me now. I'm very pleased for $40.

It is light weight, easily grab n go, and folds up nicely under my arm, with a leg as a handle. I'm carrying it with one arm on my bicycle.

It seems precision made, or at least with good tolerances. No looseness. Just slews smoothly with hand pushing any direction. Simple. The focuser seems very good tolerances too. No noticeable recoil or overshooting at 45x.

The focuser has two baffles and is flat black inside. I'll add another baffles mid tube. The objective needs some flocking an inch before and after.

The diagonal is a 90 degree amici prism that is great for reading signs. But it has an uncoated aperture of only 19mm. Interesting I did not notice a reduction in the 20mm 66 deg eyepiece afov.

There is enough back focus for up close bird watching. Leaf veins look sharp at 45x.

The objective appears to have good coatings on it and is easily accessible.

I'll test it on Jupiter later at 160x, but this scope seems like a keeper so far. I'll also test the finder. The previous owners killed the batteries.

Edited by stargazer193857, 18 August 2019 - 05:51 PM.

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#6 aeajr

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Posted 18 August 2019 - 05:32 PM

I am all for buying something on the cheap, just to play with it.  If you get bored with it you can always give it to a friend to help them get started. 


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#7 MalVeauX

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Posted 18 August 2019 - 05:48 PM

I found it used locally for $40. I'm tempted to see how much it can resolve on Jupiter with the 70mm aperture. It is f12.9, 900mm fl. It is $130 new, so I bet I can get my $40 back. Will I be disappointed? I'm used to a 6" newt that may have collimation or cooling issues.

You will be disappointed, compared to a 6" view.

 

But it will be fun and $40 it nothing. Will re-gift nicely. Also a fun challenge scope.

 

Very best,


Edited by MalVeauX, 18 August 2019 - 05:49 PM.


#8 KerryR

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Posted 18 August 2019 - 06:35 PM

I've been having a lot of fun with small achros lately, even though I have a range of other apertures from 80mm up to 406mm at nearly every standard increment.

I've been very pleased with what I've been able to see with my Meade 70mm f13 ota ($50 shipped at Telescope Warehouse), which probably has identical optics and tube to the Celestron 70mm f13's.

 

It's a different 'style' of observing, and as long as you recognize that, there's no disappointment. While it can't compete with larger apertures (assuming decent optics), it's capable of very aesthetic views, and a surprising amount of detail on Jupiter.

 

Interestingly, the 70mm made me want to try even smaller apertures (known as "reverse aperture fever"). I now have a 50mm f10, and a 60mm f8, and enjoy those scopes immensely. For teeny apertures, though, I consider 70mm a sort of sweet-spot-- small enough to qualify as teeny, yet large enough to split most of the commonly observed doubles easily, and reel in pleasing views of most of the brighter DSO's, something that's considerably more difficult with sub-70mm scopes (though still a lot of fun!).


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#9 stargazer193857

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Posted 19 August 2019 - 12:16 AM

I used 160x on Jupiter and Saturn. I was lucky to get Saturn centered and was rewarded with a higher contrast more detailed view than I recall from my former 114mm f8 newt ever having on several nights. Much less washed out. The Cassini was not as banging as the best view I've seen in the 6" or 8", though I've only seen such quality views once in those scopes.


I was not so lucky getting Jupiter in view. The slew was either too stiff or settled down out of view after letting go no matter how high I let go from. I was using an 82 deg eyepiece. Side to side slewing had issues too.

The scope was very grab n go. Also the f13 focus was very easy, though shaky till I let go.

Edited by stargazer193857, 19 August 2019 - 12:23 AM.


#10 stargazer193857

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Posted 19 August 2019 - 12:31 AM

I'll try soap bar lube, optimal tightness position, and counterweight, after I clean up some other stuff.

#11 GOLGO13

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Posted 19 August 2019 - 12:25 PM

With some work I bet that will be a great scope. I bought an Orion observer 70 for my parents. When I was there a few weeks ago I didn't bring a scope (only my night vision unit). I cleaned up the scope and used it on Jupiter, Saturn, the Moon and Alberio. Turns out, it performed quite well. I thought it was especially good on the moon.

 

At low power with the 25mm kellner it was really good. Couldn't even tell really it was an achromat. But when I used a 7mm TMB planetary I could tell it was an achromat and you could see the chromatic aberration a bit. Still, the image was fine and quite serviceable.

 

All that being said, my Vixen 81s does blow it away at higher powers and in general.

 

Usually the biggest issues with these scopes are the mount and not the optics. And that's no different than the Observer 70. The mount is pretty light duty (which is a good thing also). With some work, it can at least be used. But it can be a bit frustrating. The slow motion on the observer 70 works well. But getting objects to stay in the view when first finding them is not as easy.

 

Absolutely nothing wrong with that scope and at $40 it's well worth it. If for no other reason grab and go and something you could take anywhere and not worry about it.


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#12 vertex2100

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Posted 20 August 2019 - 02:09 PM

Yes, with upgraded diagonals and eyepieces, you can get fine view with these 70 mm scopes. You have the long focal ratio one so should have even better color corrected high power views than the f10 ones.

#13 vertex2100

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Posted 20 August 2019 - 02:22 PM

I used 160x on Jupiter and Saturn. I was lucky to get Saturn centered and was rewarded with a higher contrast more detailed view than I recall from my former 114mm f8 newt ever having on several nights. Much less washed out. The Cassini was not as banging as the best view I've seen in the 6" or 8", though I've only seen such quality views once in those scopes.


I was not so lucky getting Jupiter in view. The slew was either too stiff or settled down out of view after letting go no matter how high I let go from. I was using an 82 deg eyepiece. Side to side slewing had issues too.

The scope was very grab n go. Also the f13 focus was very easy, though shaky till I let go.

sounds like you have the alt az mount. I take the play out of the altitude slow motion bar by using Teflon tape in the loose areas. I put Teflon spray on the bar itself. Check your altitude motion to see where the play comes from. Take apart each loose part and wrap with the tape. Work on everything until it has minimal play to it. Also, round over the sharp ends of the two knob headed screws used to tighten the altitude and azimuth axies. The problem with the azimuth axis is that the screw tightens directly onto the plastic shaft and gouges it. You can remove that shaft by loosening the large hex screw from the bottom, clean the heavy, sticky grease off re grease with lighter grease, then, cut a thin piece of aluminum from a soda can to size so it will fit around the azimuth shaft and put it back together . Now, the rounded head tightening screw will tighten onto the aluminum and protect the plastic shaft from damage. It also takes the play out of that axis. With some care and tuning, you can get these mounts to work much better than new from the box. I do it all the time and before I give these to any kids so they will get the most out of them. Hang a heavy weight like a gallon of water from your tripod, too, to help stabilize it.

Edited by vertex2100, 20 August 2019 - 02:35 PM.


#14 stargazer193857

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Posted 21 August 2019 - 11:41 AM

The Orion Expanse 6mm would go great with this scope. The Vite 23mm would be good enough for wide views.

I don't plan to give this away for a while. The contrast is wonderful, and the scope is delightfully grab and go. I'll compare it to my 6" f5 for a while.

I'm definitely modifying it.


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