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Boneheaded mount question

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#1 dudeyes62

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Posted 01 March 2021 - 08:58 PM

Just recently rejoined CN/astronomy after loooong absence (15+ years). I bought a Stellarvue 80mm Nighthawk achromat that came with an M4 eq mount way back in 2005, I think, and have been using it 3-4 times/week  since last December (weather has been cooperating here in NorCal). So far it's been great- pretty much grab and go availability/convenience, and I'm getting reacquainted with the constellations, planets, various DSO's and even saw the conjunction of Jupiter and Saturn. Woohoo! That really rekindled my interest in skywatching, and having my son actually show some interest in astronomy too (he's a recent college grad) really sealed the deal. I hope this is something we could both grow into. I've added a few eyepieces and some filters, which has improved observing a lot, so it's getting addictive....

 

Anyway, I have a question regarding a possible telescope upgrade/addition. A friend told me he has a Vixen R200 f/4 reflector he wants to get rid of and wants to know if I'd buy it- so of course I said yes. It would be nice to have some extra aperture to zoom in on the faint fuzzies, so it sounded like a good opportunity.  However, he has no mount - he already sold it. So I'm wondering if that telescope could fit the mount I currently have, and if so, what other parts would be necessary.

 

Also, he didn't get the coma corrector, which I've read could help with preventing stars from appearing like comets near the edge of the field, but I'm wondering if I even need it for now. Is it important for a visual observer, or is it primarily a concern for astrophotography?

 

Any help is really appreciated.

 

Clear skies all



#2 cookjaiii

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Posted 01 March 2021 - 09:28 PM

F/5 seems to be the tipping point below which many people consider a coma corrector to be necessary. 

 

Such a short focal ratio suggests it might be an astrograph, so check it with some eyepieces to make sure it reaches focus if you want to use it for visual.

 

Good luck with it.


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#3 rhart426

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Posted 01 March 2021 - 09:32 PM

Most mounts have a saddle, which come in Vixen or Losmandy flavors.  You attach your telescope to the compatible rail, then clamp it in to the saddle and you're good to go.  I'm not familiar with the M4EQ so I can't say what it has.  Weight is the other concern; if you can't balance the scope with the available counterweights, using it is dangerous to both you and the equipment.  Even if you can balance it, too much scope and not enough mount makes for a poor observing experience.


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#4 Gazpacho

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Posted 01 March 2021 - 09:34 PM

I have experience with neither scope nor mount but . . .

 

Only info on the Stellarvue M4 GEM that I could find listed a 20 pound load capacity.

Vixen lists the R200 at 11.7 pounds.

 

You should be good to go, provided you don't bolt 10 pounds of whatever to the scope.

 

Try the scope sans the corrector and see how it's image appeals to you.


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#5 SeattleScott

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Posted 01 March 2021 - 09:55 PM

I use my R200 visually on an AZ4, which is rated for 18 lbs and has 1.75” tubular steel tripod. I don’t know what an M4 equatorial mount is. If it has a Vixen saddle and is rated for 15-20lbs, it could work, although it will be inconvenient compared to my Alt az.

You really do want the coma corrector or else it is going to be pretty brutal on eyepieces. It will be anyway. Of course that adds $250 to the cost of your scope. More if you need a different mount. And it won’t tolerate cheap wide field eyepieces well. If you do get it I could give you some advice there. But still expect to pay around $100 an eyepiece for budget options that perform well, and probably considerably more for the 2”.

I like my R200. 8” aperture and can frame the Pleiades. At 35 lbs it is light enough to pick up and tree dodge. It holds collimation well, although it takes a little getting used to the push/pull thing. It has good optical quality. I got mine used with coma corrector and dual speed focuser.

BUT...
The thick spider veins, significant CO and internal reflections off the coma corrector make it less than ideal for lunar planetary observing. Also the back is kind of closed off so it takes awhile to cool. From what I understand, once the mirror coatings fail, you can’t really recoat it so they have a limited life. Probably last 20-30 years, but a limited life nonetheless.

AND...
I already had a suitable mount, a $200 laser collimator and premium eyepieces to go with it.

I like mine. Light, ergonomically friendly (on my Alt Az anyway), powerful, with good wide field capabilities for easy starhopping and learning the sky. But if you have to buy the coma corrector, and possibly a different mount, and more expensive eyepieces, at a certain point an 8” F6 Dob might make more sense.

Scott

Edited by SeattleScott, 01 March 2021 - 09:59 PM.

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#6 SeattleScott

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Posted 01 March 2021 - 10:05 PM

I have experience with neither scope nor mount but . . .

Only info on the Stellarvue M4 GEM that I could find listed a 20 pound load capacity.
Vixen lists the R200 at 11.7 pounds.

You should be good to go, provided you don't bolt 10 pounds of whatever to the scope.

Try the scope sans the corrector and see how it's image appeals to you.

That is the bare tube weight. With tube rings, dovetail, extension tube for 2” eyepiece, 7x50 Finderscope and coma corrector, I figure it is around 17lbs. Quite light for an 8” reflector and probably suitable for the mount unless the weight rating is considerably exaggerated.

From what I can tell of the mount, it doesn’t look like it has a saddle so that will probably require some investment to be able to attach the scope to the mount. And apparently the tripod isn’t very stable and might need to be upgraded,

Scott

Edited by SeattleScott, 01 March 2021 - 10:09 PM.


#7 dudeyes62

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Posted 02 March 2021 - 03:45 AM

Thanks to all for the replies, this has really helped clarify several things.

 

It sounds like a coma corrector might be on the shopping list, which leads to the next question -

Vixen makes their own coma corrector, but from their website it looks like its 649.00.

However, I also saw Televue has their own coma correcting device - the Paracorr , for ~ 490.00

I already have a 2x Barlow, a 9 mm Delite and a 32 mm Plossl from TV and am really happy with their performance so far, so I don't think I could go wrong using the TV. Plus its 150.00 less than the Vixen. But then again, Vixen has their own solution to their product, so it might be a better fit for the scope I'm getting. Any suggestions?

 

 

As for the mount problem, I got an email from Stellarvue right after I posted here, and they discontinued those mounts and all the parts associated with them in 2009! So it looks like there might be a problem finding a saddle to mount the tube rings for the OTA. I was afraid of this, but I'll keep looking. I've seen several stores mention universal mounting plates or saddles - would this be a possible solution?

If not I might be in the market for a new mount too.

 

 It seems like every answer to a question just leads to more questions...

 

Thanks again everyone,

 

Clear skies



#8 spereira

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Posted 02 March 2021 - 08:17 AM

Moving to Mounts.

 

smp



#9 SeattleScott

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Posted 02 March 2021 - 12:27 PM

Vixen makes two coma correctors for it, a high end one for serious Astrophotography or a lower end one for visual or less perfectionist imagers. The high end one normally costs $500 but probably higher due to pandemic. The cheaper one is normally $250 but might be out of stock due to pandemic. Ideally you want the Vixen one because it screws right into the focuser so it reduces the fuss of using a coma corrector, although I suppose a P2 would also work.

Scott

Edited by SeattleScott, 02 March 2021 - 12:27 PM.

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#10 dudeyes62

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Posted 02 March 2021 - 02:12 PM

@SeattleScott

 

I didn't know they had two coma correctors, so that's good to know. It does seem the Vixen cc is more specific to the kind of scope I'll be getting, so I'll look for that one.

Thanks again


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