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Refractor vs SCT


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Depends ...

If we are talking about tripled or ED doublet refractor with good figure vs SCT with good figure - refractor wins in almost all areas. With achromatic refractor - it will depend on F/ratio of the scope.

Problem is that it is hard to find refractors with matching aperture to that of commonly available SCTs. C5 is smallest SCT, and next is C6. You can find apo refractors in that range that don't cost an arm and a leg. They will still cost more (even twice or three times more in 6" range) than SCT. In 8" and above - apo refractors will be seriously expensive.

For same aperture - they will provide more light gathering. SCT has two mirrors, central obstruction and corrector plate. Mirrors have lower reflectivity than losses in the lens (with modern coatings). Good lens will also have better sharpness than SCT telescope, and better correction (SCTs have some spherical aberration depending on focus position due to moving primary mirror - only one distance between mirrors has best correction - but you move mirror to focus). No central obstruction with refractor will provide better low contrast (better detail) performance.

SCT will be easier to mount due to shorter tube and lighter for same aperture.

 

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well the sct biggest plus is its size per weight compared to any other size.

whats funny I just did this comparision last weekend iam posting it tonight or sat on my u tube channel

I used a 6" sct compared to a 6'f/5 reflector then compared my my 6"f/8 SW evostar refractor apo.

all are 6" wide but sct is about 13" and only 6 lbs

 reflector is about 30" long cant remnember weight

refractor is about 54" long and 22 lbs

the 6"sct u can add FD if u want wider fov u can even use a 2: sct diagonal to it and a 28"mm 2 inch ep ( yes I know the 6 has a slighty smaller holle than the 8" sct but it does work) its more like a 1.75" rear opening. and you can even use the 6SE on a eq2 as its only 6lbs and the mount can handle 10 lbs. it wont be rock solid but its light and it can do it for visual.

the 6"f/5 reflector will need a eq3-2 or the cg4 mount, this will be twice as big and 2x the weight as the first option.

last is the refractor will need a eq5 minumium which used to sell like this since 1999. Back then it had the alum legs where now its the steel legs. Even so this is at the limit of the mount it can work for visual but with vibrations. A slighty better set-up could be on the AVX or LXD85 mount bit better then EQ5, however best bet is on HEQ5 or EQ6 if u want it rock solid.

If you live in an apt or condo type (which stats says is one of the most built type building for over 25 years ) the first 2 option can be done 3rd cant be done.

joejaguar

 

Edited by joe aguiar
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if the admin lets (I aready email an admin they said its ok to put a link once and awhile but not too often, this would be my first time) once I post my video maybe I should do it tonight rather then Sat, then u can see theres a huge differences between the 3 scopes even tho they are same size. yes one give u wider views, the  other give u shaper more contrast view but to me size and weight are  go hand in hand. if u always go by biggest aperture it doesn't get used often, or at all many times.

joejaguar

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1 hour ago, piff said:

Millimetre for millimetre, is it considered that you get clearer images or greater magnification or both  from a refractor, or from a Schmidt-Cassegrain of equal aperture?

In my opinion, for visual use and everything else being equal...

An apochromatic refractor will outperform any other scope of the same aperture on pretty much any target.

An achromatic refractor will outperform pretty much any other scope of the same aperture on DSO targets, not so much on planets or lunar due to chromatic aberration.

This is due to the lack of central obstruction ad better light throughput as mentioned by Vlaiv.

Of course everything else is rarely equal.  Cost, size, ease of mounting etc... all play their part too.

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I think depends on what you enjoy viewing the most.

If like me, you live in a small flat/apartment and space is limited, then a Maksutov or SCT. They do not take up much storage space when not in use; (also easy to slew if you have a balcony [I do not] assuming it does not induce vibrations through the tripod/pedestal/mount to the OTA.

A good quality achromatic refractor will be a better viewing experience, assuming it is the same aperture. It can also be stored 'out of sight' ...and depending on the size/aperture/case and also used on a balcony if you have the space to slew it. 

There are some amatuer astronomers that have conquered the downsides of living in a flat/apartment and have been able view the night sky from the confines of a balcony.

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A good newt is hard to beat and I would think that you either have to splash out on an expensive SCT or get a "good" one to compete with the newt.

2 hours ago, piff said:

Millimetre for millimetre, is it considered that you get clearer images or greater magnification or both  from a refractor, or from a Schmidt-Cassegrain of equal aperture?

Which refractor? which SCT? generalizing is not the best option IMHO.

A top refactor offers such purity to the view.... and will take high mag, at a large price. However a top SCT type scope can deliver stunning views, @dweller25 might (does) have a good opinion.

Then there is the 200mm f6 newts out there that can make so many high end scope owners cringe under good seeing...

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SCTs are great all purpose Relatively compact scopes. Not the best at any one thing but able to perform well at most things. Had a C11 that was put performed on planetary by an OO 200m f8 newt.

The 8” Classical Cassegrain is an outstanding planetary performer and initial impressions are it is better on lunar / planetary than my 10” dob. Not as good an all rounder as a  C8 but on planetary in a different league.. 

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well as u can see i have all 3 so sizes is not everything ( wait did i say that? LOL thats for a different subjet that doesnt belong here) ok they each are good so if you can buy all 3 lol

joejaguar

Edited by joe aguiar
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I picked up a 4 inch doublet semi-apo recently and compared it with my 8" SCT. The SCT will always have the edge due to the aperture but for sharpness and nice wide field views the refractor is lovely. If I was on a fixed budget and had to decide between SCT, refractor and a reflector this would be a tougher choice. For the same price you could get say a 4 or 5" doublet apo, an basic 8" SCT ota or a good 12" dobsonian. The dob will blow the other instruments away on practically everything except for the portability. I could never decide what I wanted so I got all three!!😀

 

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