Maksutov vs achromatic refractor

[bobson]

For visual observation of the planets, which telescope would give better results?
Price wise they come close, for example at Andrews:

150 x 1200 refractor OTA!
Inc. dovetail bar, tube rings, diagonal, 8x50 finderscope and two eyepieces!
$799.00 AUD

PROMAK150 OTA 150mm x 1800mm Maksutov-Cassegrain OTA has a 1.25" visual back and is gold in colour.
$699.00

Or maybe I should put PROMAK180 OTA 180mm x 2700mm Maksutov-Cassegrain OTA $999.00
'cos of secondary mirror obstraction against 150x1200 refractor?

Big difference in F ratio too 1200 against 1800 or even 2700?

So which one is better for viewing planets?


cheers

bob

[dannat]

the refractor will probably have some false color being f8 but i would still personally prefer it - it will be a lot heavier also - its fov will better than the long f/l mak

[bobson]

Hey Daniel,

Yes, I prefer refractor too, much simpler and less moving parts as well. Promak is more portable in the other hand.

What do you think which one would give wider field of view and how does this huge difference in F ratio translate in size and quality of viewing?

cheers

bob

[renormalised]

The refractor is going to give a larger FoV than the Promak, a much crisper image showing better detail (to a point) and a better corrected FoV. However, being an achromatic, you'll will get some blue/violet fringing on very bright objects...though you probably won't notice it visually. You can get filters which will reduce this effect. One thing to remember though, the larger the FoV, the smaller the image scale for any given magnification...all things else being equal (i.e. lens/mirror size etc). You'll notice this more obviously if and when you decide to take piccies through the scope. However, you can get around this as well (to a certain extent) using a barlow lens or powermate to effectively increase the focal length of the scope. Given the Promak 150 and the SW150/1200 are the same size, I'd go for the SW OTA. In a comparison of the SW and the bigger Promak, I'd still go for the SW as the promaks of this size (being close to the size of the SW) don't offer enough advantage over the SW to warrant their purchase...except that the Promak 180 wil have somewhat better light garthering capacity and hence see a bit deeper....not enough, though, to really worry you.

The only advantage of the promaks is their portability.

[Mike21]

I jumped at the Promak 180 from Andrew's and then found that IIS member Ian Fry, selling one for $800, I think he still is. For about $170 more I put this together. I haven't fully tested it yet (weather) but first indicators are very exciting. It certainly made Jupiter an eyefull. It even takes my 2" 30mm, 80deg EP. Brilliant!

[renormalised]

For viewing planets, it's a trade off between focal length/FoV and sharpness of image in this case. The longer FL's of the promaks will give you somewhat larger images, for the reasons I stated in my last post. But the SW will give you crisper views as there's no central obstruction, hence no light loss. The apparent resolution of the SW will look about the same as the larger promak, even though the actual Dawes Limit for the 6" SW will be less than the promak. That's due to the crispness of the image, so it's a subjective quality.

Both, in reality, are good scopes for planetary viewing, but if you want that "zing" to what you're seeing, the SW will trump the Promak.

Actually, Bob, if I were you and had the money to get both, I would (SW and larger Promak). Then you'd have the best of both worlds:D

[Peter Ward]

The refractor will be a colour machine (I'm being polite).

A no brainer. The Mak is the way to go.

[bobson]

:rofl: Wouldn't that be nice?

The problem is I never had a chance to look through this scopes side by side. I had 102mm SW refractor before, and my 12" Bintel dob, but that was not fair comparision. But 150mm would be nice to compare and according to Duncan who receantly bought it, it is much better for planets and Moon than 12" Dob.

I read somewhere on the web that refractor should never win against reflector and it usualy does for planets 'cos reflectors mirrors are not of higher quality. Premium mirrors would always win according to this mirror maker.

http://www.rfroyce.com/reflectr.htm

bob

[bobson]

Peter,

Thanks mate, I respect your input, but just to make sure, this is for visual observations. Do you still think The mak is the way to go?
The local telescope shop owner told me the same.

cheers

bob

[Merlin66]

I recently aquired a SW SkyMax pro 150 Mak, a very nice piece of equipment!
The ronchi shows clean straight bands, and the star images seem very crisp, with diffraction rings showing.
However.....
The small baffle diameter of about 25mm will severely limit any thoughts of a wide FOV. It will take all the usual SCT 1.25" fitting etc, but the baffle will still limit the field.
Other than that its a nice piece of work; sits well on the HEQ5pro.

[renormalised]

Pffft!!!:P:)....little bit of chro-ab' showing some slight blue/violet fringing!!!!. It's not going to be that bad you can't do anything with it, and I've seen results from the same scope posted here (piccies of the Moon (http://www.iceinspace.com.au/forum/showthread.php?t=48460)...now you'd expect a veritable rainbow from that!!!), and there was hardly any fringing at all in the pic. I doubt, unless you looked for it, you'd even bother to notice it in the visual. I suppose if you don't like that sort of annoyance then you'd notice it. And, yes, it ain't in the Mak....which is a bonus. And the Mak is cheaper.

In any case, they both have strengths and weaknesses.

[Nightskystargaz]

I have a Meade ETX125 and I like it.

Don't have enouh "Green Back" to get an APO.

Thanks,

Tom

[gbeal]

I don't have a ProMak, but do have a very nice Mak/Cass, 7" and would never look at a 6" achro in favour of it. The Mak's have an excellent view and for the original requirement, planetary, would beat the achro refractor hands down in my opinion.
Gary

[jjjnettie]

It would be ideal if you could set both scopes up for a side by side comparison.
The astro shop should let you do this. (doesn't really matter if it's daytime)
Aim them both at the same objects, corner of a building, a power pole, what ever. And you'll soon see how much of a difference there is between the two. Keep in mind that the higher the magnification you use, the more CA there'll be with the refractor.

[renormalised]

That's really the only way you could compare them. Although a more objective one would be a star test. And, that's the only worry....more mag' = more CA. Unless the optics were of very high quality the problem would get quite a bit worse at higher mag's. It'd be nice if he could get a 6" apo (a better comparison, really) but that'd mean mortgaging the house!!!:P:D

If he could get one, I'd be looking at an achro with a longer FL....that way the CA would be reduced.

[Miaplacidus]

CA isn't just a nuisance. When you are looking at planets, it is costing you detail. The mak is the obvious choice in this situation. (It just isn't fair to a shorter focal length achro to even compare it to a mak on planets and the moon. They're really very different scopes which suit very different purposes.)

[Terry B]

From a visual point of view the mak would be easier to use also because it is much shorter.
It won't be as affected by wind, bumping etc as the long refractor.

[Satchmo]

I would definately go for the Mak for all around use.

I own two of those 6" F8 Achros. tube assembly ( stalled binocular project.

The CA colour renders them useless in my opinion at about a 12mm eyepiece . ( 96X ) At that power white stars have a blurry yellowish tinge and things are not looking crisp. My favorite EP is an 18mm Radian and 24mm Panoptic . Jupiter , at a useful magnification is bathed in out of focus color, and lunar craters have a strong pruple fringe. Saturn is about the only thing that looks great at high power because it is so monochromatic ( yellow ) allready.

I think they are of novlty value only , in the sense that they give nice looking view at low power only.

The rack and pionion focusser units are _really_ bad, loads of play. I look forward to the time I can replace at least one with a suitable Crayford ( about $250 ) .

They served the purpose for me to get over the boy hood fantasy of owning a large refractor...I got off cheaply :)

[Peter Ward]

Ditto.

[DavidU]

I'm trying a few techniques with my 6" refractor. I don't think people have bothered to nail achro photography.
Sure I would like a TOA130 however I do not have the funds.
I got the Celestron 6" f8 for $350 and used the kids 6mp camera.

[g__day]

My two cents. MAKs require a 10:1 fine focuser - there sweet spot is hard to reach and the normal supplied focuser doesn't cut it. A Feathertouch microfocuser or an adapter to allow a BinTel 10:1 fine focuser is a must have.

I have a 80mm WO SD - its views are tack sharp, but the blue fringe irrates me now - even for visual. The more you kick into the hobby the tighter your demands with seeing and colour fidelity I guess.

If you can - go to an astroparty and see both scopes in action on the targets you want to view.

Matt

[renormalised]

Matt, get a -V filter or a chromacorr, that should help:D

[g__day]

lol - I have a minus V filter on Vixen LWV eyepieces - still hate the blue fringe!

[renormalised]

How much fringe does it get rid of??...remember...there are filters, and then there are filters...so to speak:D

[marki]

Go the mak, there is no other choice in this senario.

Mark

[bobson]

Here in Perth, we have a lot of rain lately, too much I dare to say. I hope this weather will get better soon so I can go out to Golden Grove and compare those scopes.

bob