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Vixen scopes


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Hi Rick,

they are of the VMC type - "Vixen Maksutov Cassegrain" - however the Maksutov corrector is not at the front but in the secondary mirror cell. So you have an open system that cools off quickly and does not dew up so much. At least the 110mm version comes with curved vanes, suppressing spikes when imaging.

A friend in Germany had a 110mm version but he was not happy as the craftmanship was not up to standard. However, this was 2-3 years ago and is maybe not representative for all of them.

The large VMCs (200, 260, 330) have the same systems, as the TAL Klevtsovs have and the Orion OMC 250/300/350 had. I currently have an OMC 250 - a stunner for high resolution work like planetary watching, but rather moderate in the field as on my DSLR chip I get coma on the edges. So I would not recommend it as a telephoto system for DSLRs but as a travel or guide scope the small VMCs may be useful.

It all depends on what you want to do with them.

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Hi Astrogeordie,

Thank you for your detailed reply.

I currently own a 4" achromat refractor for imaging and DSO work, but because it is a fast scope it is not that great of lunar or planetary viewing, which is a pitty. I want something to do this and have been looking around for a mak cass for quite a while; someone was selling a 4" one last night, but someone got it even though I was first inline for it, but that's another story. lol

I know other SGL members rave on about dobs and reflectors saying aperture is king, but I do not have the storage space for one of those at the moment, I was thinking a medium sized mak cass would do the job nicely.

Would one of the vixens be alright for looking at the moon and planets or would you recommend something else entirely?

Thank you,

Rick.

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Hi Rick,

having a 4" refractor already I do not think another 4"-ish reflector makes sense. You get rid of the chromatic aberration but get loss of contrast by the central obscuration.

There is a rule of thumb made up by Zmek (an optics guy I think from the US) who introduced the "effective contrast diameter" of a reflector as being the primary diameter minus the secondary diameter.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3808386/page/8/view/collapsed/sb/7/o/all/fpart/1

According to this and assuming about 30% obscuration, you would need at least a 6" reflector to gain significantly over your 4" refractor unless your chromatic aberration is really bad. I take it yours is an f/10.

What mount do you have ? Mabye a Newtonian would suit you as the secondary can be relatively small if you opt for something like f/8. Skywatcher has a 150/1200mm Newtonian on sale that would suit this. I had a 6" f/8 myself (was an old Dynascope from the 1970s) and it was the first time I could see clearly the shadows of Jupiter's moons on the planet.

However, it depends on your mount as well. Skywatcher sells their 150/1200 on an EQ3 and I am sure that is not a good choice due to the leverage of the long tube.

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I only have a very simple EQ1 mount, which my 4" refractor sits on. I know it's not brilliant, but as I am new to astronomy it serves my purpose for the time being.

My scope is an f/5, which is good on DSO's as I said, but not so on the moon and planets.

I don't have enough storage space for a large reflector at the moment, and the wife would not be happy either if I bought one! Surely, a 4-5 inch mak would be better on the moon/planets than my f/5 refractor, no?!

Regards,

Rick.

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Hi Rick,

sounds like you got a Helios Startravel 102/500 or another Skywatcher equivalent. I had one of those - nice porable setup, and my optics were quite good but of course colourful. It is a nice rich field scope but rather limited on the planets due to the colour fringing. In this case, a 110mm should provide higher contrast.

However, the EQ1 mount is not a good option as especially with higher magnification everything wobbles. Maybe it is more worthwhile to look out for a cheap 2nd hand mount like an EQ3 or EQ5 before getting another scope ?

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Hi Astrogeordie,

Yes, I have one of the Skywatcher 102's and it does suffer from pretty bad CA. I was looking into getting a new mount, but there is no way I can afford a HEQ5 or 6 mount. I was looking at either a CG4 Omni EQ mount or a EQ5 as you say, they are not that expensive I think.

Just wish I had pocket-fulls of money to spend of astro gear. :-(

Regards,

Rick.

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Hi Rick,

taking your "funding situation" into account, what's about a Dobsonian ? You get a cheap stable mount, nearly all money is invested in good optics but the price to pay is you have to track by hand in both axes.

As an astrophotographer I could not be without an EQ mount but if you do visual - there are loads of "Dobsonauts" around who like nothing more than this way of observing. To stay with Skywatcher, they have a 150/1200mm Dobsonian for example selling for around 200 quid.

And you can always "equatorialise" it later. Going from 100/500 achromatic to 150/1200 Newtonian should be a revelation when it comes to low contrast objects like the planets.

EDIT: STUUUPID ME ! Just found all your equipment is mentioned in your signature - lots of redundant questions made.

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