What scope to get?

[danielpiasecki]

Hello everyone,

 

I am new to telescopes and wondered which one I should get. I m baically interested in seeing crates in the moon, rings of saturn, cloud bands in jupiter and some other galaxies, I read good things about 4 scopes: celestron advanced vx 8" schmidt cassegrain, nexstar 8 se computerized, skywatcher 12" collapsable dobsonian, and proed 120 mm doublet apo refractor.

 

I really want to go ahead and get a all around good telescope right off the bat instead of starting with a beginners one. I m just not very familiar with which one would work the best for me. My budget would be between 1 - 2 K.

 

Thanks 

[Olli]

Don’t know that much about the other scopes but if you want a good scope that does everything then can’t really go wrong with a dob

Edited March 7, 2018 by Dinoco

[Cosmic Geoff]

I suggest that you not spend the £2K right away, but acquire a small and easy to manage instrument first.  Otherwise you may conclude after a while that you have spent £2K of an instrument that you don't much like and which is a pain to use.  The instruments you cite all have their merits and you won't know which is best for you without trying them (or a smaller and cheaper variant). 

Things to consider:  How portable do you want it to be? Are you interested in deep-space photography (in which case scrap that list and start again)?

What mount? For visual, there is a case for having an alt-azimuth GoTo.  But if you want to do planetary astrophotography, an equatorial GoTo might be better (ask the experts). 

If I was spending £2K, I'd probably get a 8" Celestron SCT on one of the more expensive alt-azimuth GoTo mounts.   

[Handy_Andy]

I recommend seeing them in person if you can, I've got the vx 8 and it's a formidable beast for a first scope. But if you know what you're getting into it's a great telescope, just know that your expenditure won't stop with just the telescope and mount. There are a multitude of extras and aids to consider as well as a wide array of eyepieces. First will be a decent power supply, mains if your close to your house or a power tank if you plan on going out and about

[danielpiasecki]

Thanks for the quick responses?

 

I was aware that dobsonians are not good for astrophotography, but i thought the skywatcher refractor pro ed would be. Is that right?

how about the celestron vx 8"?

I don t think i m that worried about portability. I m basically gonna set it up on my yard. As far as the mount, i guess a go to would be very handy, but it is not my priority. 

 

thanks again

[Cosmic Geoff]

43 minutes ago, danielpiasecki said:

I was aware that dobsonians are not good for astrophotography, but i thought the skywatcher refractor pro ed would be. Is that right?

It might be, but the experts will tell you that a smaller apo refractor on a massive mount would be better.

The Celestron vx8 (I assume this a C8 on a AVX equatorial mount) would be good for planetary photography but the field of view will be on the small side for some other objects. 

Calling GoTo 'very handy' is an understatement. Without it, you could find locating fainter objects represents either an evening's entertainment to locate one or two, or too much like hard work, depending on your tastes. I saw Venus and Mercury this afternoon. Try doing that without a GoTo.

[danielpiasecki]

I guess a go to is a must then!!

Would you elaborate why the mount is so important?

 

Also, will i be able to see  saturn ring, moon craters, and nebulea with any telescope of 6 inch aperture ? or the focal lenght, mount, magnification, lenses have something to do it too?

[danielpiasecki]

one more thing. 

I m looking at this 10" go to collapsable skywatcher. I know the mount is not ideal ( or far less than ideal. It will also be very heavy i presume?). However, it seems like it has the go to capability and a 10 inch aperture. Will I be able to see planets, moon crater on it?

It is price at $1100 SKY-WATCHER GOTO COLLAPSIBLE DOBSONIdsadad10″ (254

[Cosmic Geoff]

21 minutes ago, danielpiasecki said:

Would you elaborate why the mount is so important?

 

Also, will i be able to see  saturn ring, moon craters, and nebulea with any telescope of 6 inch aperture ? or the focal lenght, mount, magnification, lenses have something to do it too?

Mounts are what make the telescope pleasant to use or even usable. Especially for deep space astrophotography, where it has to be rigid and track perfectly.

I can see all the above mentioned objects with my 127mm Maksutov.  Any smallish telescope will suffice. The brighter planets and Moon are easy targets for anything that claims to be an astronomical telescope.

Somewhere on this Forum you should find a "What can I see with..."

[danielpiasecki]

thanks for your help again

[Ben the Ignorant]

Hi, Daniel.

Since you seem to insist on planets, the apo refractor gives the steadier views that are required when you examine planets. It's always done at high magnifications because planets and Moon detail have small angular size. That makes steadiness important, and the apo refractor is the most contrasty and least disturbed by turbulence among all scope designs. 

[danielpiasecki]

thanks for the info.

But do you think a 100mm apo would do a better job than a 10 inch dob? they would both be skywatcher .

[Ben the Ignorant]

No, I was thinking of the 120ED you mentioned in your first post. The best planetary views I've ever had were through a friend's 130mm Vixen doublet. Calmest, sharpest views ever, no large reflector could compete, except the club's 400mm but it's a monster, not comparable, and steady images through the 400 are rare. We stop it down to 150mm for quieter views, an aperture close to the superb Vixen apo's aperture.

On the other hand, a ten-inch mirror deep-sky scope can be stopped down to an obstruction-free 100mm planetary scope, that would make a fine two-in-one instrument.

[danielpiasecki]

What do you mean by stop it down?

I was reading some post and learned that fast focal ratios like dob (f/4 and f/5) will have a very wide range of view right? is that a good thng or bad? I was almost sold on the 9.25" cst celestron, but it has very slow focal ratio f/10. Those posts were saying that it is sort of like looking at a stamp in space, so narrow your view is.

 

You are very helpful my freiend. It sounds like you are very knowledgeable.

 

Thanks again

[Ben the Ignorant]

43 minutes ago, danielpiasecki said:

What do you mean by stop it down?

Put a cap on the scope with an off-center hole, so the light enters the scope through a smaller aperture without hitting the secondary mirror or its spider. It's called an off-axis mask, and tames turbulence very well. Less powerful than the full-aperture scope but much steadier views. It's so cheaply made every large reflector should be sold with one.

This is the one I made for my 300mm dob, the reduced aperture is 115mm, the space between the large mirror's edge and the small mirror's edge:

[Ben the Ignorant]

48 minutes ago, danielpiasecki said:

I was reading some post and learned that fast focal ratios like dob (f/4 and f/5) will have a very wide range of view right? is that a good thng or bad?

The field width does not depend on f/ratio, it depends on focal length. Faster f/ratios make for a wider field for a given aperture, but change the scope's diameter and the focal length changes, too. A 100mm diameter f/7 scope has a 700mm focal length but a 300mm diameter f/5 scope has a 1.500mm focal length, about twice the length, so about twice less field width, despite the faster f/ratio.

Then again a larger focuser allows eyepieces with larger front lenses that will accept a broader image. Focal length and focuser size determine the field, you need to compare these when you shop around.

[danielpiasecki]

thanks for the info.

Ok, so if my intention is to look at moon, saturn rings and some galaxies, would i be better off with a long focal length or shorter one?

a bigger aperture will always be better than a smaller one or not necessarily?

[Cosmic Geoff]

39 minutes ago, danielpiasecki said:

Ok, so if my intention is to look at moon, saturn rings and some galaxies, would i be better off with a long focal length or shorter one?

a bigger aperture will always be better than a smaller one or not necessarily?

Again, my advice is to try this sort of thing for yourself, without committing to a £2K outlay.  The whole moon will just fit in the field of view of my C8 with the minimum magnification.  Saturn is small and a long focal length scope will likely be better.  Galaxies - it all depends. Some actually cover a lot of sky, but visually all you can usually see is the brighter core, so a narrow field scope will work fine. And the vast majority of galaxies are rather small.

A bigger aperture is a big advantage for deep-sky objects.  For planets, rather less so, as if the conditions are poor a larger aperture is more severely affected.  But I'm told the most impressive views of the planets are obtained with big scopes under perfect conditions.  I have never gone in for 'stopping down' and found that on the whole my C8 is the most effective instrument of my collection for looking at planets. 

[danielpiasecki]

OK.

I guess a celestron CST 8" with 2000 mm focal length will be a good chouce then? 

This one already comes with a mount. Specs say it is a rigid and sturdy mount. What would be a very good mount if i want to buy a new one? They can get as expensive as the scopes itself right? Also, if i buy a skywatcher mount will i be able to mount other telescope brands on it?

 

thanks

[Cosmic Geoff]

Lots of people here use the Celestron C8 and it is well regarded. There is a choice of mounts if you are buying a package. The AVX seems good , but for pure visual may be heavier and more fiddly to set up than you want.  The SE GoTo mount is one of the cheapest, and just about adequate for visual only use. It has the advantage (shared with some of the other mounts) that you can pick up the whole OTA/mount/tripod outfit and carry it outside. 

Mostly, the OTA is held to the mount by a standard dovetail so that you can mix and match between brands of scope and mount.  But changing the mount on a C8 is going to be expensive, so I'd advise you to be sure of which of the several alternatives you want before investing.

[danielpiasecki]

I ll go with the advance vx 8" then.

 

Just a technical question. What would be the difference of a 100mm scope with a 700mm focal length (f/7), and the same telescope with the same aperture but a focal length of 1000 (f/10). Will they both have the same performance or the one with a bigger focal length will have a larger magnification capability?

 

Thanks

[Stu]

9 minutes ago, danielpiasecki said:

I ll go with the advance vx 8" then.

 

Just a technical question. What would be the difference of a 100mm scope with a 700mm focal length (f/7), and the same telescope with the same aperture but a focal length of 1000 (f/10). Will they both have the same performance or the one with a bigger focal length will have a larger magnification capability?

 

Thanks

The simple answer is.... 'it depends'  

Basics here, Magnification = Focal length of Scope/Focal Length of Eyepiece.

Fundamentally a 100mm scope will have a certain resolution so will cope with a certain level of magnification, let's say x200 ish.

The focal length will define which eyepiece will give you max magnification. In many cases, the shorter the focal length of the eyepiece, the shorter the eye relief which means it is less comfortable to observe. In this case, the longer f/l scope let's you use longer f/l eyepieces to achieve the same mag, so therefore more comfortable.

Exceptions to this are more expensive eyepiece designs which have consistent eye relief across the range.

Coming back to different focal lengths scopes, depending on the type of scope, a faster focal ratio ( focal ratio = focal length of scope/aperture or scope) can result in certain abberations becoming more visible. In an achromatic refractor, you will see more chromatic abberations (false colour) and most likely more Spherical abberation which makes things softer at higher powers. That means that the f10 scope 'may' produce better higher power images than the f7.

ED doublets and triplet apo objectives are used to over come these issues in faster scopes.

With a Newt, coma becomes more and more pronounced as you get to faster focal ratios, say below f5 or so. This is the effect where stars appear to become little comets towards the edge of the eyepiece with their tails pointing away from the centre, rather than being points of light.

[danielpiasecki]

I m starting to learn that there is a lot to study about telescopes. I guess the best thing ti to buy my first scope which will be a cst 8" celestron and sort of learn trying out different eyepieces and such.

 

thanks

[Cleetus]

On 08/03/2018 at 20:02, danielpiasecki said:

I m starting to learn that there is a lot to study about telescopes. I guess the best thing ti to buy my first scope which will be a cst 8" celestron and sort of learn trying out different eyepieces and such.

 

thanks

Indeed there is, and that is why I would forget about astro photography until you have more experience, or knowledge, about the pros and cons of the telescopes already mentioned. Astro photography is a whole new ball game and it brings with it more equipment and more expense. So my advice would be to cocentrate on familiarising yourself with using a telescope and all that it entails and learning about how the sky works. Probably get a few books. 

Edited March 9, 2018 by Cleetus

[TareqPhoto]

Get a Mak like i did, i bought Skymax 180mm, it has 2700mm regardless its F15, give it a try or a think.