Refractor vs SCT

[F15Rules]

Hi Mark,

As ever with this forum, loads of answers to a single question..and that's why we all love it on here so much.

As a self confessed long focus refractor nut (F15 Rules kind of a giveaway?), I can totally see why you'd like a long fl scope for planets and lunar. Trouble is, in a refractor, they get very BIG at longer FL, I know, I had an F12 6" last year which was 82" long from tip to toe:eek:. And then I found I had a double hernia (I kid you not, although it wasn't the fault of the scope:rolleyes:).

So I had to let the big beast go and for ease of handling and more portability I turned to a Mak. I was fortunate enough to find a Lomo 6" Mak, which is Russian built and optically superb - not far behind a refractor in sharpness. In fact, with the possible exception of very long fl reflectors like Shane's, and Mak-Newts like John's (Jahmanson), I think Maks offer probably the most refractor like images you can get.

The other night I had a very quick peek at Delta Cygni with my Mak, a notoriously tough double to get a really clean split on, due to the big difference in brightness of the two components, and the Lomo split them very clearly and easily - at over x300 mag. And that's one of the great things about a good Mak...they will take very high magnification, and on a good night I reckon the limiting factor on how high you can go is more the quality of your eyepiece than the mirror/corrector. I've had x500+ on my Lomo more than once on exceptional nights, and the Moon at such a mag is something else!

But back to your dilemma..FWIW, I'd advise to stick with the 80mm frac for now, try to view through a few Maks/Mak-Newts, SCT's at 5"-7" and see what grabs you.

I confess I'm not an SCT fan, I just find them too high maintenance in terms of collimation and the images in the ones I've looked through seem very soft to me compared to a refractor, but I am sure there are really good ones out there - before I get lynched by the pro SCT Fan Club:p.

The Maks are factory sealed sytems normally, so no collimation issues, although cooldown can still be an issue. If you can get one with high end glass, such as Zerodur or Astro-Sital (which the Lomo has), then cooldown is almost as fast as a frac.

The tubes are very portable and easy to manouevre, a joy to use..my lomo weighs 6kg and has a built in carry handle which is a Godsend. And image shift isn't a major issue on a good Mak..my lomo has none.

I think we all know that no one scope, however good, can suit every observing need, that's why so many of us have several. But I'd say a good shorter focus refractor with a wide FOV and a decent Mak with F12 or longer would between them cover most bases.

And if you could stretch to a Skywatcher 180 Mak (but still manageable for one person), you are then getting into some proper DSO light grasp as well.

Sorry for the rambling on, hope all these opinions give you some food for thought:).

If you haven't seen it already, these pics will give you an idea of the very compact size of a 6" F14 Mak tube, pictured here on a CG-5...very portable and ideal for a decent altaz mount/tripod for dark site use.

Good luck!

Dave

[MjrTom]

Thanks again Shane,

I was looking at Johninderby thread here which got me thinking in the first place.

http://stargazerslounge.com/equipment-discussion/138200-skytee-2-alt-az-mount-photo-tripod.html

He is using a Manfrotto 475 photo tripod which is rated to 12kg load capacity.

I currently use an Induro Aluminium alloy tripod rated to 44lbs or 20kg load capacity.

I dont think it will struggle under these circumstances.

I find it really stable when using my ED80 at 167x magnification mounted to this tripod.

If your interested info is here: INDURO | Products | Tripods | Alloy AT Series 8M Tripods | AT413 – Cat. 472-413

[Moonshane]

ha ha fair enough Mark - I agree - unlikely to be any tripod issues!

[MjrTom]

Sorry cross posed with you F15rules

Many thanks for all the info, I really love the simplicity of refractors and the pinsharp views these provide I am a huge fan of them

I am trying match this in a longer focal length but compact package.

That 180mm Mak looks like a beautiful OTA, probably on the limits of what I would want size wise but its great to see one in the flesh

The lack of collimation issues is very tempting. One thing I like about refractors in general.

Big thanks to you all for your help and patience during my rambling and uncertainty.

I love this forum

[MjrTom]

ha ha fair enough Mark - I agree - unlikely to be any tripod issues!

Its a beast! it weights more than my telescope lol

[MjrTom]

What would your thoughts be regarding a Celestron C9.25 SCT?

Is that too much scope for a sky-tee 2?

It would make a good all round scope I would think with a large aperture and long focal length.

[Moonshane]

I know that johninderby is buying a 925 for his so I am sure it's hefty enough. maybe send him a pm - he's always glad to help.

[MjrTom]

I know that johninderby is buying a 925 for his so I am sure it's hefty enough. maybe send him a pm - he's always glad to help.

Thanks Shane

I think a bit of aperture fever is setting in, gone from considering a 6 inch to an 8 now to a 9.25...

Will drop John a PM.

Thanks

[F15Rules]

Just to be clear Mark, my Lomo is 6", not the 180mm (7")..the SW 180mm is significantly beefier I think...

but a good 6" will show plenty. I had an 8" Celestron SCT for a short time and couldn't see anything in that that I couldn't see in the Lomo - and the Mak was much sharper..

Dave

[MjrTom]

urrh decisions decisions... My head hurts

[Mr Spock]

You can see what I have (below) and I can't recommend the combination highly enough.

I have two hernias and a slipped disc and can transport this set up from house to patio (mount, tube and weights all separate) easily enough.

[MjrTom]

Thanks Mr Spock although you are not making my decision any easier lol.

I just cant decide between a large SCT (9.25 inch) and a large mak (6 inch).

Seeing conditions really mean that the best of the optics cannot be utilised anyway so I should be looking at light grasp for a given price range.

9.25 inches of aperture is always going to trump a smaller 6 inch scope for faint DSOs.

Planetary and lunar I dont think I would notice the difference I suspect.

I have had so many ideas kicking around my head that I still have made no firm decision. However the temptation just to go oh what the hell and get the big SCT is really tempting..... Its a more Jack of all trades scope in the long run I suspect.

[John]

9.25 inches of aperture is always going to trump a smaller 6 inch scope for faint DSOs.

Larger aperture improves the view of the brighter DSO's as well - with my 10" newtonian the globular clusters M13 and M92 were looking like their photographs last night. My 4" and 6" scopes show them nicely but the 10 really gets in deep

On nights of good seeing the larger aperture will deliver more on the planets and the moon too.

Sorry if this is not helping the decision but there's no getting away from the benefits of aperture

[MjrTom]

Larger aperture improves the view of the brighter DSO's as well - with my 10" newtonian the globular clusters M13 and M92 were looking like their photographs last night. My 4" and 6" scopes show them nicely but the 10 really gets in deep

On nights of good seeing the larger aperture will deliver more on the planets and the moon too.

Sorry if this is not helping the decision but there's no getting away from the benefits of aperture

Thanks that was what I was looking for to be honest, I just needed someone to confirm these thoughts

I am a big globular cluster fan so for these targets the extra aperture is going to trump.

I am looking for a scope which can cope with most things well but might not excel in any given field. I suspect a scope of this calibre I shall not be disappointed.

I am willing to sacrifice a bit of performance for a more convenient scope. A jack of all trade scope so to speak.

[MjrTom]

Hmm still going round in circles and its starting to hurt my head...

I think I have narrowed the current list down the the following:

A Celestron C8 SCT First Light Optics - Celestron C8 XLT Optical Tube Assembly on a SkyTee 2 First Light Optics - Skywatcher SkyTee-2 Alt-azimuth mount

or

An 8 inch f/4 Newtonian on the skytee 2 mount. Cant decide between the SW Quattro or the Altair Astro equivalent.

First Light Optics - Skywatcher Quattro f4 Imaging Newtonian

Altair 8" Imaging Newtonian telescope.

I appreciate there is not a universal scope but really struggling to juggle the differing attributes to come up with the right balance and therefore my final decision.

I just love refractors so much that I feel a little apprehensive about any other types until I have had a good play with them to appreciate their complexities.

FYI my budget is in the region of £1000-£1200 (for scope and any accessories) if anyone fancies making any other suggestions

[John]

An F/4 newtonian might be good for imaging but collimation will have to be spot on (challenging with such a fast scope) and it will be very tough on low / medium cost eyepieces.

[MjrTom]

An F/4 newtonian might be good for imaging but collimation will have to be spot on (challenging with such a fast scope) and it will be very tough on low / medium cost eyepieces.

Thanks

Yeah that is my concern the f/4 Newt will need to be spot on the there is the issue of field limited coma present with such a fast scope. If I go for a slower one like an f/5 the tube length starts getting a bit long.

This is where the SCT steps upto the plate with its catdioptic, folded light path keeps the tube small.

I doubt I will have any issues when it comes to eyepieces, I bought these in the knowledge that they will be top performers irrespective of the scope used.

[John]

I doubt I will have any issues when it comes to eyepieces, I bought these in the knowledge that they will be top performers irrespective of the scope used.

The Tele Vue's are tested down to F/4 so should be OK although coma will be an issue unless you plan to use a coma corrector. The Hyperion 31 and zoom will probably show some astigmatism in the outer parts of the field of view in such a fast scope.

[Moonshane]

not quite on topic but certainly relevant. I have just had first light with my 16" f4. collimation was really no harder than with any other scope (I generally make sure it is as close to spot on as my eyes tell me) and coma whilst there was not as awful as expected without my paracorr coma corrector. I could certainly live without the paracorr if I did not have one / could not afford one.

[MjrTom]

Completely relevant info Shane thanks for the info. Glad to hear your project is nearing completion, bet it is an awesome view!

I had my concerns regarding collimation and coma, I intend upon getting a Parracor as well if I was going down that route.

I suspect that the size of the secondary does not affect contrast too much when used visually? This is another concern that I have...

John, Yes I suspect those EP's will suffer but then I plan on sticking to my TV Ep's for a scope of this type

Thanks all for entertaining my my thoughts and decisions.

It really is not easy!

[MjrTom]

My head hurts, gotta stop looking at FLO and all the other stockists.....

SCT or Newtonian... that is the question!

[Moonshane]

I suspect that the size of the secondary does not affect contrast too much when used visually? This is another concern that I have...

my secondary is 82mm so 20% by diameter (4% by area) of the primary. I have only used it once briefly and cannot really say but what I can say is that a 20% obstruction (which is why I chose it) is around the best size in terms of compromise from what I read, when it comes to DSOs and general visual observing.

this scope is definitely a light gathering tool although it will be good at higher mags too I think.

my 6" f11 has a 16% obstruction (2.5% by area) and thus is more refractor like in performance.

[MjrTom]

Thanks Shane

Urrh had enough gonna go for an eight inch f/6 Dob and be done with it

A cheap one has come up on the forum for sale and it's in my local town so gonna give it a shot

I will have to make space for it in the shed and hopefully the other half won't be too annoyed

[Moonshane]

I knew you'd go for that one! you'll not regret it mate.

[cgarry]

Thanks Shane

Urrh had enough gonna go for an eight inch f/6 Dob and be done with it

A cheap one has come up on the forum for sale and it's in my local town so gonna give it a shot

I will have to make space for it in the shed and hopefully the other half won't be too annoyed

I was going to suggest that you make a short list and buy the first one on it to come up for sale second hand but you beat me to it! It saves making the decision yourself and you can always sell it on and try out different scopes at a later date.

Cheers,

Chris