who has what REFRACTOR, REFLECTOR OR BOTH

[John]

Stupid question..... is a SCT considered a slow reflector then ? From what I gather to achieve this in the standard reflector design would require too long an OTA to be practical.

The overall focal ratio of the optical system is usually around F/10 but the primary mirrors are about F/2 I believe. Overall though they are considered "slow" reflectors. A conventional 8" F/10 newtonian would need a tube around 6 and a half feet long.

[spaceboy]

Excuse my ignorance but is a SCT the same as a Maksutov-Cassegrain?

I'm new to all this and am just trying work out all the jargon.

Same light train but maks correct with objective lens and SCT with mirror.

[spaceboy]

The overall focal ratio of the optical system is usually around F/10 but the primary mirrors are about F/2 I believe. Overall though they are considered "slow" reflectors. A conventional 8" F/10 newtonian would need a tube around 6 and a half feet long.

Thanks John that's some thing new I have learnt I had a TAL 200k and I guess the same principle applied to this but I found after getting used to using an F/5 I much prefer the view over a F/10.

[GazOC]

Same light train but maks correct with objective lens and SCT with mirror.

The SCT also corrects with the front plate like a Mak.

[spaceboy]

The SCT also corrects with the front plate like a Mak.

I stand corrected then!!

what's the collimation of the secondary necessary for then? I thought this is why MAKs don't tend to require collimation. The objective corrects the image on to the primary which returns it to the already corrected aluminized secondary. I thought the SCT objective glass was purely to hold the secondary. My bad

[GazOC]

I stand corrected then!!

what's the collimation of the secondary necessary for then? I thought this is why MAKs don't tend to require collimation. The objective corrects the image on to the primary which returns it to the already corrected aluminized secondary. I thought the SCT objective glass was purely to hold the secondary. My bad

The front plate on the SCT is a thin correcting plate.

The collimateable secondary is due to the fact that most cheaper Maks are f12, f15 or even f20 which allows a fixed aluminzed secondary to be used on that design of scope. There are Maks that are f10 and they tend to have collimateable secondaries like SCTs.

The 2 different Mak designs are called Rumak and Gregorian. The Gregorian tends to be cheaper because it has a fixed secondary but they also tend to be slower than f12. The Rumak has the SCT like movable secondary which increases cost but that enables a faster, relatively speaking, scope.

[brianb]

is a SCT the same as a Maksutov-Cassegrain?

No. The SCT has a thin corrector plate with a complex curve but which appears to be flat; the Mak has a thick corrector plate with strong spherical curvature. Mak-Cas scopes also tend to have a much longer focal ratio, f/15 is typical whereas Schmidt-Cassegrains are typically f/10.

[Talitha]

All of my scopes are in my signature.

[JonH]

At the moment a MN190 and hoping to add a refractor plus ALT-AZ mount very soon!

[Ant]

I have several scopes.

1 x Celectron C925

1 x SW 6" F5 Newt

1 x Revalation ED80

1 x SW Skymax 127

The picture below is a line I did a few years ago - got me into a fair amount of trouble as no-one had seen them all in one place before

If you replace the Skymax 180 for the C925 (and also the TAL mount was given to Hugh at SGL5) you pretty much see what I have...

Cheers

Ant

[ollypenrice]

Refractors from 66 to 140mm, SCT of 250mm and 500mm Newt. They all do different things. For me, the most beautiful, but not the deepest, views are in the refractors. The best telescope I ever looked through was Ralf Ottow's 12.5 inch watercooled Newt described a while back in AN. But it was also collimated by Ralf and he is a professional optician. Refractor sharpness, Newtonian depth, not for sale...

Olly

[CGolder]

ok just took some pics for you.

I might put them in the gallery later

[Whippy]

(and also the TAL mount was given to Hugh at SGL5)

Your memory is terrible mate...

I have a bit of a mix too although that's kind of dictated by what sort of stargazing I'm doing. I've currently got 3 refractors for imaging and a 4.5" newtonian for observing. I did get a new arrival this week in the shape of a 6" Rithchey Chretein astrograph which should prove interesting as previous attempts at imaging with anything other than a 'frac has been unproductive.

Tony..

[brantuk]

Didn't mean to put a damper on it Spaceboy - sorry for that - but having read your reply I think I see what you're trying to achieve.

Perhaps a better reply would be that it all depends on what you want to do and what your budget is.

If you just want quick and easy viewing of everything with max possible detail on dso's, then pick a large aperture dob.

If you want to image dso's, then a wide field fast appo on highly accurate EQ tracking mount would be the tool of choice. You may additionally choose a guiding setup so two refractors/cameras would be needed.

If you want to image planets then a slow Mak or Sct would be appropriate - either EQ or Alt/Az tracking mounts are fine.

Those are the reasons for my setup - although I didn't really know it as I collected them lol - which kinda proves your point about confusion over the best scope to choose for a newbie.

When starting out, I'd say choose a proper instrument (not high st shop toys), but keep it cheap while you learn what you want to do with the hobby. Scopes hold value well and can be sold for around 60-70% of new price within the first 18mths.

You can't beat a 5 or 6 inch newt on a manual or driven eq mount for a great intro to astronomy at reasonable cost. From there onwards you're only limited by the extent of your own imagination

Pics of my gear here: http://stargazerslounge.com/members/brantuk-albums-telescopes.html

[spaceboy]

All of my scopes are in my signature.

Are ST refractors ??

[CGolder]

I presume its a skywatcher 120 star travel

[spaceboy]

I presume its a skywatcher 120 star travel

Ahhh Thanks CG

Didn't mean to put a damper on it Spaceboy - sorry for that - but having read your reply I think I see what you're trying to achieve.

Perhaps a better reply would be that it all depends on what you want to do and what your budget is.

Pics of my gear here: Stargazers Lounge - brantuk's Album: Telescopes

Nice set up Brantuk. But even with out doing the numbers it's looking like SCT are the favorite over both fraks & fleks. Unfortunately SCT's are out of my budget and my previous experience of slow scopes didn't give me the wow factor a faster scope did. Why are there slow scope designs ? I can understand the need for fast scopes regards imaging exposure etc but what I gather is a slow scope is for higher magnification. I get confused by this as 9/10 in the UK you can't get above 200X magnification anyway.

One thing has been proven and that it appears there is no way of getting away with just one scope design. (which I kind of knew) All members posting have such a wealth of astronomical knowledge and from what I see, some have very deep pockets also but none seem to have reached a happy medium and settled for one scope. This is why I keep coming back to thinking I need a refractor to get the whole experience so to speak. But I think TBH this thread has already answered my question which was no so obvious before. SCT's seem to be the clear favorite despite having obstructed objectives and dew problems.

Thanks everyone for all your help.

I will take the time to total up all the choices at the end in the hope it may help beginners as it has helped this novice.

[JAO]

Spaceboy

My telescopes have been built up over many years of trial, experiment and error, all have specific functions and purposes. I am lucky enough to live under dark skies with the nearest street light being neraly three miles away. My scope choice reflects my location. Also I am solely a visual observer, again this has dictated my choice of instrument.

Two Dobsonians: 12"f4.5 (soon to be sold) and 18"f4.5

Two Maksutov Cassegrains: 7"f10 Rumak (soon to be sold) and 10" f12.5 Rumak

Three Refractors 70mm F6.8, 100mmf10 and 101mm f5.4

Picture of my observatory scopes: 10" MCT and 100mm f10 the main portable scope the 18" f4.5 (the scope in the forground).

[spaceboy]

SCORES ON THE DOORS

REFRACTOR...................34

SCT.............................13

MAK.............................7

REFLECTOR....................16

MAK-NEWT....................2

RC................................1

I hope you can now see there was method in my madness.

Clearly the classic design still has it's followers despite my original thinking.

There may be the odd one I got wrong as some have referred to their signatures and I have no idea what some of the numbers resemble

[Moonshane]

main portable scope the 18" f4.5 (the scope in the forground).

I have said it to you before Adrian but this sort of truss dob scope is for me the most beautiful scope you can buy/make. I hope I can do anywhere near as good a job when I can afford the mirrors!

Got my router now so will be starting work this spring in theory (although the body once built will be empty for a while! )

[JAO]

Thanks Shane, judging by the progress on your Equatorial Platform I am sure your truss dob will be a stunner.

Looking at Speceboys 'scores on the doors' the newtonian reflector fraternity are some way behind the Refractor community in numbers, your 18" will buoy that up a bit!

[brianb]

Add the apertures to get a fairer "score" ... most of the fracs are small ...

[brantuk]

Interesting totals - not quite what I expected. Of course - anyone imaging dso's will likely be guiding and have two refractors. So the apparent results may be skewing a bit

[CGolder]

Add the apertures to get a fairer "score" ... most of the fracs are small ...

I think this is ultimately the reason that the other designs are more common for primary visual instruments than fracs, i would like a 10" apo refractor , but that's not going to happen any time soon so the SCT is the next best thing.

Its all to do with cost

[spaceboy]

Add the apertures to get a fairer "score" ... most of the fracs are small ...

I think this is a good representation as it also makes the point that portability of a scope is also a strong consideration to most even though the views may not be as deep as a larger aperture reflector. Besides from what I have been advised unless you have bottomless pockets for a large apo you are best advised to stick to the smaller aperture achro. I also think that it proves that regards portability the frak still wins over the compact MAK. I assume this is due to MAK's long cool down times compared to fraks ??

The portability was another consideration for me as said earlier in the thread. UK skies are a drag and a refractor may offer me the opportunity to get more observing in over my reflector. I really do feel this has helped me make my mind up. Looks like I need to get saving those pennies again!