Schmidt-Cassegrain/Schmidt-Newtonian

astro_set · #1 10-01-2006, 10:58 PM

Hi,

I was wondering if someone could tell me the difference between a
Schmidt Cassegrain and a Schmidt Newtonian. I'm new to astronomy,
haven't even bought my telescope yet.

Thanks

janoskiss (Steve H) · #2 10-01-2006, 11:01 PM

Welcome!
In reply to your query, pls check out:
http://en.wikipedia.org/wiki/Reflecting_telescope

janoskiss (Steve H) · #3 10-01-2006, 11:09 PM

Having just read the wikipedia page I linked above, maybe that is not the best place to get an answer to your question. As far as I know the Schmidt-Newt is like a normal Newtonian, but it has a corrector plate like the SCT which allows the use of a spherical instead of a paraboloidal primary mirror. As opposed to the SCT, in the S-Newt, the secondary does not reflect the light back towards the primary but out the side of the tube like in a normal Newt, and it is not used to increase the effective focal length of the scope, so it is not oversized = more contrast... but half of what I'm saying here is a guess...

gaa_ian (Ian) · #4 10-01-2006, 11:09 PM

Good link Steve !

ballaratdragons (Ken) · #5 10-01-2006, 11:18 PM

When I wanted an answer to this about a year ago, I googled for hours and no-one really explained the difference properly.

The best I could find were reviews which said that Newtonians are far superior than Schmidt/Newtonians!

asimov (John) · #6 10-01-2006, 11:26 PM

http://www.quadibloc.com/science/opt02.htm Try this one.

#7 11-01-2006, 10:35 AM

The Schmidt Newtonian is a very fast scope and as such I have found because of its quite large central obstruction not very suitable for planetary obs. It is a light bucket though and when collimated correctly is very good at deep sky stuff. Now collimation on this scope, mine is an F4 is critical and can be a pain in the bum. It also, obviously is a very short focal length for the aperture, my sn10 FL is 1000mm so image scale is quite small compared to the 2.5m focal length of the equivalent LX200 10" sct. They also tend to be a little unwieldy and you have problems with corrector plate dewing up, hence a dew shield and or dew zapper is important.

astro_set · #8 11-01-2006, 10:04 PM

Thanks for all the info. I'll be busy reading for a while.

ballaratdragons (Ken) · #9 11-01-2006, 10:07 PM

Astro-set,

What do you want to use your scope for?

You might be better of with a large refractor or a Reflector! Or even a Dob!!!

astro_set · #10 12-01-2006, 09:51 AM

I would like to get a telescope that I can use for astrophotography later
on. I'm a pretty small person so I need something I can manage in terms
of size and weight.

#11 12-01-2006, 10:01 AM

In that case, I would not recommend the SN10 it is quite heavy, not sure about the 8" or lower versions, but you want good aperture. Having seen Paul's (Rumples Riot) C9.25, I would say it is a much more manageable option and a damn site better scope, IMO.

astro_set · #12 12-01-2006, 07:23 PM

After looking at a lot of the advice for beginner's telescopes I am seriously
re-thinking the whole astrophotography thing. Everyone seems to love
dobsonians so maybe I'd be better off with one of those. They seem to
cost a lot less and weigh less.

Are dobsonians easier to set up and do you need a power source? Are
you able to move the reflector from a dobsonian mount to an equatorial
mount?

Thanks for the help.

astro_set · #13 12-01-2006, 11:29 PM

I just found the answer to the mount upgrade question on another thread.
With regard to the power source, I guess you would need one if the
telescope had a cooling fan.

iceman (Mike) · #14 13-01-2006, 05:45 AM

Dobsonians don't need any power, you push the scope around with your hand.

Power is only needed for a cooling fan, but that usually runs off a 12V battery (not 240v power). Not all dobs come with cooling fans, and it's not an essential bit of gear right off the bat. It's something you can upgrade to later on.

If you're looking to get into astrophotography, set your budget at $3k to $5k. If you're not sure yet, then spend significantly less (under $1k) and get a good dobsonian (8, 10 or 12") with a crayford focuser and a few middle-of-the-range eyepieces.

If you really get into it, the money will start flowing on extra accessories after that

h0ughy (David) · #15 13-01-2006, 07:29 AM

Quote:

Originally Posted by iceman

Dobsonians don't need any power, you push the scope around with your hand.

Power is only needed for a cooling fan, but that usually runs off a 12V battery (not 240v power)............

Oh now thats a slap in the face, just 'cause my 12" SCT needs a 10GW power station for a nights viewing!!! Older SCT suck the juice of a battery very quickly as they convert from 12V to 18V and the motors are very heavy on the amps!! The new ones are no as bad. An eq6 is even less and a good platform to build a photography platform from. Put virtually anuy scope you like up to a 10" newt or a 12" SCT on it, or like me several scopes 8" sct, a 5" MC and a 80mm refractor. Get a EQ6 and a 80ED if you want to start and do some photography and view the skies, easy to handle and set up and all you need is a 17AH power jump starter pack. then you can choose your next weapon, whether its an 8" Newt or SCT or the 9.25" SCT or a 10" SCT.

astro_set · #16 14-01-2006, 11:49 PM

Thanks for all the help. I've decided to give the SCT and the EQ mount
a miss and go for the biggest dobsonian I can carry (which probably
won't be that big, but anyway). I'll check out a few observing nights
first so I know what to expect.

mickoking · #17 15-01-2006, 12:03 AM

Quote:

Originally Posted by astro_set

Thanks for all the help. I've decided to give the SCT and the EQ mount
a miss and go for the biggest dobsonian I can carry (which probably
won't be that big, but anyway). I'll check out a few observing nights
first so I know what to expect.

Very wise

RAJAH235 · #18 15-01-2006, 12:41 AM

Susan, see >http://www.bintel.com.au/
They can/will/should, give you the contacts to all the local Societies in your area. They put out a monthly 'Night Sky' info flyer. If you go there, buy a 'Chandler' large version, planishere ($22.00?), & red LED torch & they'll prob throw in the flyer.
Good choice re; the dob. Min 8" to start, imho. Not too big or heavy.

HTH.

L.