Eurolux Loc: NYC

Dear Fellow UHH members,

You've always been great with standard camera issues. Hoping a few may assist pointing me in the right direction for acquiring my first telescope.

I have two particular models in sight, but am hoping for someone here to enlighten me further. Figure I can start with something in the $400 range and upgrade myself whenever it seems right.

Here are those two models:

Celestron 22094 COSMOS 90GT Wi-Fi Telescope

Celestron Nexstar 102 SLT Computerized Telescope

This is my first post here. Thanks you for your help.

Mitch

JimH123 Loc: Morgan Hill, CA

Hi Mitch,

I looked at the specs on both scopes. Of the two, I would say that the Nexstar 102 is slightly better. They are both beginner scopes. The mounts are not real robust, and I suspect they would not work real good for Astrophotography, mainly due to the need to track the target as accurately as possible.

The Nexstar 102 does have a 2" focuser, although comes with 1.25" eyepieces. Its rated max power is listed as 200x and for a 4" scope, this power will not be real useable. Realistically, perhaps 1/2 half that power will be nice and clear. There is a rule of thumb with scopes that the max usable power is 50x per inch of objective or mirror, and 200x is right at that limit. Usually, that limit is not obtainable and a somewhat lower limit is more pleasing to use. When you exceed the usable power, you get what is know as empty magnification which means that as you increase power the image quality degrades with that added power such that it is actually resolving less then the optimum magnification.

I searched around and did see some images taken with the 102 that looked nice. It wasn't mentioned if the stock mount was used or if they had mounted it on a better mount. I was concerned if a camera could focus using this scope, but since I saw images, it must be capable, but doesn't seem to be advertised. Depending on the accuracy of this mount, perhaps it can track a 30 sec exposure? I don't expect much better than this.

It should perform very good as a GoTo scope meaning that if you want to see star XYZ, it will go to that star and you should be able to see it. I did read that you should be able to see stars to the 12th magnitude. With a camera, that number should be exceeded by a couple magnitudes.

As it is a 4" scope, many of the deep sky objects will be very faint or dim. You might see a bit of fuzz where it points out a galaxy should be.

It would also be possible to mount your camera in place of the scope and open up the world of wider angle astrophotography. You can get some stunning exposures using a wide angle, or medium focal length or even a telephoto lens this way. Be aware that doing this may expose the flaws of the lens if it is not the highest quality lens. Mostly what you see with cheaper lenses is clear in the center and stretched radially as you move outwards (called coma distortion). The better quality lenses have very little, and the less expensive may have more.

Since it is a Altazimuth mount, it can be used for terrestrial viewing. It is a 660mm lens. I don't know if it will suffer from chromatic aberations or not. This is a distortion that leaves purple fringes around high contrast targets. More expensive lenses use doublets or triplets of a special type of glass to reduce this effect. But this is too expensive for the cheaper scopes. Much of the CA can be removed in post processing, but the results are not perfect.

But as far as starting out with something cheap to see if you like it, this is a good choice. Be aware that it is a battery eater. For my Celestron CG5 equatorial mount, I use a car battery. But it is a much heavier duty mount and I mount a 22 pound scope plus equal counter weights.

Have fun!

Eurolux Loc: NYC

Hi Jim. Thank you very much for your well considered reply.

I suppose it will be better to spend just a little more and get something that will meet a minimum level of capable performance. I checked a little further and found this model:

Orion 8945 SkyQuest XT8 Classic Dobsonian Telescope

It is still just under $400 and seems nice. I suppose I could spend a little more if I could get a good steer.

Again, I sincerely thank you.

Mitch

JimH123 Loc: Morgan Hill, CA

Now the issue with this is that it doesn't do the pointing for you, nor does it track. It is a larger 8" reflector, and that is good. But that means you have to find the target on your own. You can use a finder scope, but the finder scope can see the dimmer targets.

So which will serve you better? To have a smaller scope that finds the objects. Or to have a bigger scope in which you are left to find the objects on your own?

As a help in this, suppose you want to look at M108 tonight? See if you can figure out from star charts and going outside and looking up where to point a scope. Remember you won't see M108 in any binoculars.

I pick this one because I was experimenting with my 300mm F2.8 lens last night. Using a crop sensor camera, that made it 450, and using a 2.0x teleconverter, that made it 900mm. The 300mm lens is sort of like a 4" scope. The GoTo capability took me right to M108. I snapped a 30sec shot and I could see it, just a fuzzy patch. Took a 2 min shot, and it was more distinct, but still not what I would call useable.

Perhaps I will look tonight with the bigger scope at M108.

dlmorris Loc: Loma Linda, Ca

If you want to do visual,astronomy, and don't mind learning the sky (and you should anyway, that is art of the fun), then the best bang for the buck would be a dobsonian design, and minim size of 8". But the only photography you could do would be the moon, and maybe a planet. If you are interested in long exposure deep.space photography, you MUST have some sort of equatorial tracking mount of pretty good quality. You can get some tracking mounts designed for holding a camera for aroumd $300.00 that will allow up to two or three minute exposures.

Oknoder Loc: Western North Dakota

With the criteria you mention and your proposed budget, I would forgo the telescope altogether and use your budget on a GEM mount. Now while 400 will not get you a new mount you can probably pick up a used CG-5 which is a decent beginner mount.

You also do not discuss what it is you would like to image, DSO or Planetary. So my suggestions here would be for mostly DSO and widefield imaging. You can use your existing camera and lenses mounted to a GEM to gain very acceptable images. This route will also help you become familiar with the night sky and the processes involved with imaging and processing of your images to gain the look and feel you are wanting out of this hobby, all the while helping you in deciding if this is a hobby you wish to proceed with or give up on.

After a bit of time you will be able to better access the type of imaging you want to do, which will help you in deciding the best scope for you to accomplish your goals. Hopefully you stick around and read what many of the great posters here have to share, there are some great photographers and there are some of us, myself included, who are striving to learn all we can to improve our images.

Clear Skies,
Matthew

JimH123 Loc: Morgan Hill, CA

As Matthew was saying, there is a lot of Astrophotography that can be done with just a camera mounted on a good drive. This example was just on a tripod. Went to a dark sky location and used a 50mm f1.7 lens on a crop sensor type camera, so this was effectively 75mm. I shot RAW and then processed out the noise (yes there will be noise at ISO 3200) and then processed to darken the sky.

What you can see from this is just how many stars the camera can see. This is a shot of Orion. At 50mm, the nebula is just a blob, but I am just in amazement as to the shear number of stars.

50mm f1.7, 6 sec at ISO 3200

(Download)

Albuqshutterbug Loc: Albuquerque NM

I started off using a standard tripod and a Canon 7D with a 300mm prime lens. It was the largest lens I had and I was after the moons of Jupiter. I shot a lot of constellation shots with my kit lenses to learn what I was doing and how long to expose. I would recommend that you do that before jumping in with both feet to see if this is really what you want to do. The Milky Way is a wonderful thing to capture with just a tripod and a camera. You will benefit a lot from doing that.

http://www.uglyhedgehog.com/t-234344-1.html

This was shot with a standard tripod and wide angle lens.
I like the stars reflected in the boat surface in the very front of the shot along with the Milky Way in the background.

CraigFair Loc: Santa Maria, CA.

Hello Mitch welcome to the Astro Forum.
I still have the Celestron NexStar 102 SLT Computerized Telescope and recommend it. Good starter Scope.
It served me well for a few years. It's a huge fulcrum so don't expect to put a DSLR on it. To much vibration.
You can put a P&S camera on it and get some decent pics.
Good luck, Craig

SonnyE Loc: Communist California, USA

Hi Mitch, and Welcome to the stardust section.
I'm also brand new to this, but the more I looked, the more I needed to invest to get to where I wanted to be.
I figured I could only pull this trigger once, so I got the bells and whistles lined up first wish "Wish Lists". Those I groomed as I continued to look at where I wanted to be.
Finally, I decided to pull that trigger. And not am I disappointed.
I have a ton to learn, but some great stuff I won't need to replace anytime soon.
Look harder at what you want to do in the end, then build your own "Wish List" to get you there.
BTW, I'm now waiting on an all important adapter to arrive tomorrow... seems like it never ends. :lol:

CraigFair Loc: Santa Maria, CA.

Sonny what adapter are you getting now??? I just got a Crayford Focuser
Craig

SonnyE Loc: Communist California, USA

An all important 2" Crayford to 42mm.
First I ordered what sounded like the best Off-Axis Guider. An Atik.
Nice unit! But it ONLY fits on an Atik electronic filter. :hunf: The ad is totally misleading (see the link). You must buy a $575 filter it mounts on.
No response from the vendor (apparently they don't want it either), Amazon took care of me to return it, and then refunded the costs and shipping.

Still in need of an Off-Axis Guider, :roll: I ordered a Celestron because it sounded like the better unit. And it is...
It's built like a tank. But in spite of 47 dozen ways to hang it on a telescope, for my ED80T CF, I need that leetle missing link.
Seems that Celestron missed my scope when they engine-eared it around mine. They state in the booklet that you might need an adapter for other telescopes. Oh Joy, Oh Rapture!
So... when the adaptikator to hang the tank on my 2" Crayford focuser, I'll hopefully mount the beast on my tube.

(I would preferred to have these assemblies threaded together, But when the 2" clamp is removed there are 54mm threads on the Crayford that I guess even Orion is unaware of, and nobody makes an adaptikator for that little piggy. :?
So... this 2" X 42mm dealie should screw into one of Celestron's options and clamp into the tank to mount it in the scope.

If that turns to sh... frusterization, I'll ship it all back an settle on an Orion Off-Axis Guider.
And if that doesn't work, well, I guess I'll just shoot myself in the foot. :lol:

I'm no stranger to figuring things out and getting things to work. Something that made me valuable to my employers. ;)

W7MEV

If you are going to do any astrophotography there are a couple things you will HAVE TO HAVE in your telescope. First off, you will need an equatorial mount. A scope with an altitude/azimuth mount will not work. The scope will need to automatically track the target star. If you are going to shoot anything that requires more than about 30 second exposures you will have to have an auto guider. This will consist of a small secondary telescope coupled with your main scope. The main scope will be equipped with the camera. The guide scope will either need to be equipped with an autoguider camera connected to a computer with software such as PHD auto guider or you will have to observe the star in the secondary scope and constantly issue corrections to the scope tracking for however long the exposure is. Without guiding the scope will not track accurately enough to get long exposures. The stars will be oblong smears instead of round stars.

If you want to start with an inexpensive scope and then step up, start with a good motorized "go to" equatorial mount and then almost any scope, say a 4" or larger Newtonian or a 80 m/m or larger refractor. You can always step up to a better scope as you get the $$$ to do so. But, if you are going to do photos, the most important item is the good, stable, equatorial mount.

Feel free to contact me anytime with questions. Some I can answer, others... maybe not!

CraigFair Loc: Santa Maria, CA.

Hey Mitch, welcome to the HHG Astro Forum and I have the Nexstar 102 and it was a great starter scope.
Craig

SkyKing Loc: Thompson Ridge, NY

...what do people think of the ORION 80MM (3.15") ED APO REFRACTOR TELESCOPE OTA...?