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EDs APOs and all that jazz...!

davekermito

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davekermito

davekermito

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Hi there

I currently own a C6 SCT which for the price I got it for, is a lovely scope - decent enough aperture, nice and portable etc.

I upgraded from a 4" achromatic which was a great start up scope but the vivid colour fringing was too much and was off loaded to the old man!

But recently I've seen a number of semi APO / ED refractors coming into my price range - but I know next to nothing about them, so a little advice please!

1. For visual use how much difference is there between a ED budget scope (like the Celestron C100ED) and a far more expensive 'real' APO?

2. Would a C100ED be comparable to my 6" SCT in terms of views? I understand it would suffer from less aperture, but would the optics and the lack of a central obstruction counteract this?

3. Am I being sensible looking at changing a 6" scope I'm happy with for a 4" (or smaller if truly APO) scope I know chuff all about? Bearing in mind I'm a 90% visual 10% imaging type of person!

Thanks in advance...

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Ben Ritchie

Ben Ritchie

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1. For visual use how much difference is there between a ED budget scope (like the Celestron C100ED) and a far more expensive 'real' APO?

If you mean the 100mm, f/9 (same optics as the SkyWatcher 100ED I think) then the differences are pretty subtle, the entry level far-east Apochromats are very strong performers for the money. If anything, the difference is in the fit and finish of the 'scope, rather than the optics.

My SkyWatcher 80ED (price a touch over £200 new) is one of my favourite ever 'scopes for visual use, cracking value for money and no false colour unless you really go searching.

3. Am I being sensible looking at changing a 6" scope I'm happy with for a 4" (or smaller if truly APO) scope I know chuff all about? Bearing in mind I'm a 90% visual 10% imaging type of person!

Yes. No collimation, quicker cooldown (pretty much zero really) and sharp, constrasty views - even if you don't see deeper, i'd say it was an upgrade over the C6

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brianb

brianb

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3. Am I being sensible looking at changing a 6" scope I'm happy with for a 4" (or smaller if truly APO) scope I know chuff all about?

Aperture, aperture, aperture .... even if the 4" was perfect and the 6" was OK the 6" will show more detail visually (though the contrast may be slightly lower & the images may appear a bit less tidy). For imaging, more light means shorter exposures means sharper images even in poor / bad seeing.

The SW 100ED f/9 certainly is a good one but I'd far, far rather have a C6 OTA - which is also easier to mount; because of the shorter tube length, the vibrations die own faster. The only real issue with the C6 OTA is the coarse, stiff stock focuser, which can be "worked round" with a SCT threaded Crayford or, better but more expensively, the Feathertouch replacement focuser.

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MartinB

MartinB

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Dave, you are going to get a lot of conflicting advice with your question! The reason is that it isn't clear cut and often the differences with be subtle as Ben has said. People often exagerate the difference between scopes which is unhelpful.

You have a nice scope which is a very good all round performer. It has enough aperture to give good views of DSOs. You will also get good solar system performance. It may be best just to stick with the scope you have rather than fretting about kit, you scope is plenty good enough for where you are now.

SCTs are compact and newer scopes tend to hold their collimation well. Cool down time can be slow although this is probably less of a problem with a 6" than larger SCTs.

The optical disadvantage cited for SCTs is chiefly the central obstruction. This has the effect of reducing contrast. This is noticeable when looking the moon, saturn and jupiter if viewing side by side with a decent apo but I have always found the differeces to be nothing like as marked as people often suggest.

Aperture is obviously a factor, esp visually. This is most noticeable viewing fainter DSOs but it does improve resolution on the moon and bright planets but you need good seeing to get the benefit of this.

Good refractors are great for splitting double stars!

If you spend a lot of money on a small apo you will be making an emotional as well as a financial investment. This will affect what you see down the eyepiece more than the optics!!! High quality small refractors are wonderful short focal length imaging instruments and great for those wanting ultimate portability, otherwise in terms of your return of pounds spent, for visual use, stick with your 6"SCT.

Blue touch paper well and truly lit, I'll get my coat...

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brianb

brianb

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Who was it said the best scope is the one you use the most... cant remember who ....

Anyone with any sense.

Fact of the matter is, I have a CPC1100 and a WO FLT 110 - there's no doubt that the FLT deliveres cleaner images but the C11 outperforms it by a huge margin in terms of detail as well as light grasp. The FLT110 gets used for rich field work where the relatively short focal length (770 mm vs 2800 mm) is a huge advantage. But I'm still thinking of getting rid of the FLT 110 in favour of a C6 as a "grab 'n' go" scope mounted on a simple undriven altaz mount.

Impeccable optics cannot outperform significant extra aperture, irrespective of central obstruction. Even for close bright double stars, a 1/4 wave 6" SCT is going to outperform a 1/40 wave 4" APO, though (as I admitted above) the APO image may appear neater.

BTW my FLT 110 is heavy & takes well over an hour to cool near enough to ambient to perform well - I'd expect a C6 to cool in less than 30 minutes, with its thin walled, lightweight tube construction.

Small/medium short focus apo refractors are terrific for deep sky imaging. For everything else, the equation to be balanced is aperture vs cost vs convenience; depending on your requirements, it's either a Newtonian (cheap) or an SCT (convenient) in the largest aperture you can afford & handle.

Sure, for pure planetary work, the ideal scope would be a 12"+ (preferable 20"+) f/30 apochromatic refractor, but unless you're a star footballer or win the lottery jackpot several times....

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GazOC

GazOC

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Who was it said the best scope is the one you use the most... cant remember who ....

Peter...

I know what you mean Peter, I see that line at least once a month on astro forums but it still gets passed on like its some little known and obsure titbit of information known only to hardcore telescope gurus...:)

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Psychobilly

Psychobilly

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Martin I am about 0.005% visual and I am working on a method to get rid of the last little bit... Probably using the DMK.... as I am running the obs from the house these days... long term need to motorise the dome... might have a word with Heath the weekend see what he suggests over a glass or two of lemon barley...

As far as the one you use the most quote goes... I suppose when your starting out then you have to go with other peoples "opinions"... and we all have our favourite scopes and our "aspirational" scopes....

Peter...

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RobH

RobH

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Who was it said the best scope is the one you use the most... cant remember who ....

Peter...

It was Sir Patrick, many years ago.

He also said that, due to central obstruction etc, a 3 inch refractor was the equivalent of a 6 inch reflector.

I looked at Jupiter visually through my rather good 6 inch refractor the other night, and it significantly outperformed my well collimated 14 inch SCT.

Where the bigger scope won out was on faint targets, but in terms of detail, due to the seeing we tend to get over here, they are very close.

Personally, I'm with Martin B....stick to your C6 for the moment, unless you can run to a Skywtcher 120, which will knock spots off it :)

Cheers

Rob

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davekermito

davekermito

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Oh well regardless of the good advice, I saw a ZS80II on ABS. And couldn't resist it at the very very good price! So I picked it up yesterday and parted with a wallet friendly amount of cash.

So now I've got a grab n go to use on my old SLT mount, and for imaging use when I get bitten by the bug, as well as my trust old 6" SCT (with piggy back camera mount for wide field shenanigans).

So apologies for the clouds in advance...

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