small SCT vs big Dob - Paradox?

[BigJ]

Hi,

I'm new to this group and considering my first real 'scope (my 30 year old 600mm Tasco with table-top- tripod doesn't count!).

I have been doing a lot of reading, and seem to have come to the conclusion that for general planetary, lunar and DSO work, an 8" Dob is ideal, especially considering the price. I'm considering a Celestron 8" Star Hopper. But some Celestron Schmidt-Cassegrains caught my eye

Now, here's what I don't quite understand: I have seen a lot of smaller Schmidt-Cassegrain's for sale, which are quite small (eg Celestron Nexstar 4 or 5), but inordinately expensive compared to the Dobs. Granted, some of the expense is because they tend to have fancy go-to mounts. Bus aside from that, if you were so into astronomy that you were prepared to spend $1,500 on a scope, why would you choose a 4" or 5" SCT over the light gathering power that an 8" Dob would give you?

Surely, optically speaking (and also since aperture wins), the view of distant nebulae, galaxies and star clusters would be inferior...?

[BigJ]

... for that matter, even a 6" SCT would have far less light gathering ability, and would cosr more than twice as much...

[jase (Jason)]

BigJ,

To help everyone out;

What is your interest in astronomy? Visual solar system, visual deepsky objects? Will you dabble into a bit of astrophotography?

Is portability a concern?

[casstony]

Hi BigJ, if you're considering an 8" sct, there is an 8"LX90 in the for sale section - I'd describe the LX90 as a most convenient all rounder.

[robagar]

With $1,500 in my pocket, I would be wandering over to the even bigger dobs

[Greenswale (Wren)]

I have just been down this path, and purchased a Celestron Nexstar 6SE. The decision was made by determining my real needs and then making a cost effective decision.

In my case, portability, a degree of ruggedness, dust resistance and the ability to stay on 'target' to enable sustained observation are the real needs. I was dubious about a 5" (there's that aperture thing again!), the 8" was bulky and too expensive, so the 6" was the winner.

Am I pleased with the scope? Absolutely!! It has kicked all the goals, and I'm even starting to learn about the sky.

And guess what? When I learn more stuff and actually stay at home a while, there is always room for something with heaps of appeture, perhaps requiring a ladder to reach the eyepiece?!

[ving (David)]

since you are talking about doing some photography you may very well have to aviod the dobs as track will be important. its a shame cause you will loose so much aperture in doing so, but its about priorities i guess.

[duncan]

Well i'm extremely happy with my 12" Dob. I can even put it in my little Ford Laser (no room for anyone else though,LOL). And you can use a cam on it to do astrophotography, it's just that you are a bit limited for long exposure stuff. Time over again i'd still get the 12". Nothing under $1500 compares to it.

[csb (Craig)]

Portability. Think about it.

I have a 6" newt on EQ mount. But it was annoying trying to manouvre it outside, through 3 doors and up to 2 sets of steps. So got a 6" sct - very easy to handle.

Portability doesn't always mean for travelling away from the house. I didn't use the newt as much as I was using the sct.

Do you understand about how aperture size affects what you see?

[BigJ]

OK but why would anyone spend so much more cash on a 4" or 5" SCT?

Also (and completely off the topic) does anyone know how to set preferences to sort posts in a thread in chronological order (first post first and last post last)???

[merlin8r]

A big dob has more light gathering power for sure. If you are interested in photography though, this is less of a concern. Loosely speaking, with photography you can compensate for aperture with longer exposures. With the modern computerized GOTO telescopes, you can add autoguiding functionality, which makes astrophotography that much easier.
Basically it comes down to this: For X amount of dollars you can have a big dumb scope, or a small smart scope.
The last consideration is your personal preference. Do you want to spend your time finding objects (get the dob) or looking at them (get the goto)

Clear skies,
Shane

[Kal (Andrew)]

Originally Posted by BigJ

OK but why would anyone spend so much more cash on a 4" or 5" SCT?

Also (and completely off the topic) does anyone know how to set preferences to sort posts in a thread in chronological order (first post first and last post last)???

Sometimes they might want it simply for portability and ease of travel with that smaller scope!

Regarding the forum thread sorting posts newest to oldest first, go to:

User CP > Edit Options > Thread display options > Linear (newest First)

[csb (Craig)]

I am not a serious amateur and I find a 6" is perfect in regard to seeing & portability. As I showed above, I need something that is compact otherwise I won't use it so much.

Other reasons for sct :

Collimation - SCT's stay collimated better than reflectors. How often do people have to recollimate their sct? Most types of scopes beat newt's in this.

Size - they are shorter more compact = more easily moved in & out of house. After having the 6" newt I really found this important for me so I got the sct.

Viewing Position - although with a newt (on a GEM) you do tend to be standing in a good upright position, you can be turning the scope in it's tuberings to reposition the focuser (does this apply to a dob?). With the sct, the position may be slightly crouched (still comfortable though) and add a diagonal to help with your stance. If repositioning of eyepiece is required, just rotate ep/diagonal combination in focuser.

This link is to a site started buy a guy who was thinking of getting a 6", but couldn't find info about what he would be able to see. So he started this site. Many, many detailed reports by people with 6" scopes (sct, newt, etc) and what objects they looked at including what detail they could see.

http://www.geocities.com/the_150mm_reflector/

The site's home page is titled "Observing With a 150mm Reflector". I found it very useful.

[Stephen65]

I have been doing a lot of reading, and seem to have come to the conclusion that for general planetary, lunar and DSO work, an 8" Dob is ideal, especially considering the price. I'm considering a Celestron 8" Star Hopper. But some Celestron Schmidt-Cassegrains caught my eye

For all those reasons I would buy a 10" Dob. Its only a little more expensive (eg $679 v $549 at Bintel) and you get 56% more lightgathering power and better resolution. It's still very portable, only slightly heavier and you'll never regret having more aperature. Also, a 10" Dob can be fitted with tube rings and mounted on the more common GEMs like the EQ-6 if you ever want to go that way in the future for tracking or photography.

I do think the difference in price to the mass market SCTs is largely because of the mount and people pay that extra because they want GOTO and tracking even though that is at the cost of aperature. The SCT OTAs are probably a little more expensive to make due to the cost of the corrector lens.

[csb (Craig)]

You know what is missing?

There aren't any images of what you actually see when looking through a scope.

Most if not all images are looong/multiple exposures to bring out detail & colour, and images are manipulated for enhancement.

So what about a page or section (at iis would be perfect) that allows those people considering what telescope to get, to quickly/easily see what can be seen through various apertures and types of telescopes and magnifications.

Images would be b&w and only manipulated to represent what would be seen by the eye.

Would something like this help,BigJ?

If anyone cares to comment on this idea then click the link to go to a post that requsets this feature http://www.iceinspace.com.au/forum/s...ad.php?t=20289

Thanks

[BigJ]

So what about a page or section (at iis would be perfect) that allows those people considering what telescope to get, to quickly/easily see what can be seen through various apertures and types of telescopes and magnifications.

Images would be b&w and only manipulated to represent what would be seen by the eye.

Would something like this help,BigJ?

CSB, EXACTLY! You have hit the nail on the head.

For the record, I am planning to head out with a club or two. I know I should, but with a pair of 3 year old twins I don't get a lot of spare time right now. It's just not realistic. So in the meantime, YES! Some images that show what a user can expect to see - as realistically as possible - through various scopes would be brilliant.

I reckon at least 50% of all the newbie questions I have seen on various websites could be answered by such a page.

[dhumpie]

Good points everyone In my opinion you need more than one scope...hahaha (tell that to my wife). They all serve different purposes. There are the big guns for deep sky work (the dobbie's) and then there are the portable "grab and go" "on the spur of the moment" scopes. I have been through my fair share of scopes and current have three, a 6" f/5 EQ newt, a 80mm f/5 ST refractor on a photo tripod and my big dobbie a 10" f/5. However if I were to have to choose just one scope, I would definately be keeping the 6" (And maybe mount it on a dob mount of some sort. I agree that the EQ is a pain). Its offers the best balance in my opinion between seeing deep enough (like seeing detail on planets and resolving globs) and being grab and go portable.

Darren

[BigJ]

Jase said:

What is your interest in astronomy: Visual solar system? visual deepsky objects? Will you dabble into a bit of astrophotography?

Answers: Yes, yes and yes. There are no areas up there that I wouldn't like to give myself the option of looking at! My goal is not necessarily restricvted to astrophotography, but if I can find a way to end up with a 'scope that is (or will be later, after addition of motor drives & CCD or camera mount) suitable for astrophotography, then that's a bonus.

Is portability a concern?

Hey, all things being equal, sure I'd prefer a unit that is smaller and more portable. Wouldn't everyone? Can I manage with a large Dob? I guess...

Maybe the whole equation comes down to money. If I can spend up to around $800 I guess that means a decent sized Dob. If I can manage to scrape up closer to $1500 I guess that means a possibly second hand 4" or 5" SCT or a 6" LXD75 Newtonian reflector with an EQ tracking mount.

I guess it depends on exactly how much can be seen with those, which comes back to CSB's previous post.

[KG8]

If I wanted a nice scope and had $1500, I would keep my eye on the trading post and ask around. An 8" celestron SCT with mount and accessories went for $1500 here in Brisbane just a month ago through the Tpost and a guy at my local astro club picked up a meade 8" fork mount SCT with tripod and hand controller for the same price of a member. They are older ones but they are usually just as good, or better "mechanically" than a new one of the showroom floor.

[BigJ]

Thanks everyone for your comments.

I went to Bintel earlier today to have a chat with the guy there. After discussing some options, the more we spoke the more I got to realise that you can't treat astrophotography as an afterhtought. You need to (1) really know what you want to do and how, and then (2) invest a significant amount of money if you want to do it properly. I am not in a position to do either of these! So... I'm probably going to go for a Bintel 10" (GSO) Dob.

One question though: does anyone know about the eyepieces this comes with, in terms of quality?