Mewlon 210 or a pimped up vixen VMC260ML?

[DJT]

A question i never thought I would ask...
I want to image PN's and Galaxies. Am covered with wide field and mid with a couple of fracs but Sagittarius is wandering off and am keen to image more the just the poster boys, but I can't go the 6" frac route just now so dipping toes in this space.

The challenge is that the specs in the vixen appeal and with a reducer it appears to be flexible but I keep reading about the upgrades needed, (focuser, visual back, etc) but the mewlon on ccd calc is comparable but a slower scope with not much in the way of upgrades via reducers available.

Am in very light polluted burbs, I image with a 60da (no plans to change just yet) and use Ha a lot as a blend to get detail. Über fast scopes for rgb therefore are pretty pointless.

Mount is not an issue (ap900)..

The obvious alternative might be Unipols cn210...?

Guidance? Thoughts ?

Interested in experiences.

[LewisM]

The Vixen focuser receives a bad rap, usually by people that haven't properly tried it to appreciate it'smerits as opposed to it's weaknesses.

The standard Vixen focuser holds a LOT of weight without shift - the same cannot be said for a LOT of Crayfords out there, especially most of the Chinese ones (mainland China or Taiwan). The Moonlites require a special locking mechanism (extra) if you don't really want slip.

Fit a Vixen dual speed knob to the standard focuser, and the world opens up - I use one continually. I swapped out the focuser (Moonlite) that came on my FL102S for the factory original, as I found it a LOT better.

My William Optics refractor focuser starts to slip with my SBIG camera with filter wheel. The Vixen does not even remotely.

The only downside to the VMC's is collimation - a real chore, but once you understand it and get it, it stays there.

Personally, I'd go the ZVixen due to the cheaper and more sensible adapters etc,compared to the buzzillion adaptors (at exorbitant prices) for the Taks.

[Logieberra]

M210. Mirror flop. No fixed mirror. Some focus shift. It's primarily a visual scope. I found it tough to image with, even using the matching Mewlon Tak reducer/flattener.

VMC260L. Mirror flop. No fixed mirror. Likely some focus shift. But some amazing photos out there taken with these on Flickr, and US forums mainly.

VC200L. Fixed mirror. Tailored for imaging. Shame Vixen don't make a VC260L! :(

[DJT]

Great, wondered about the 200. So as an inexperienced frac boy, what's the pain points between fixed and not fixed mirror..slow optics would be a concern as well here.


Was hoping you would pipe up. Thanks for the update. Focuser and back plate is of big interest so experiences are valuable.

[gregbradley]

That's a tough one, PNs and Galaxies in light pollution. You should be able to get the brighter ones.

As far as scope goes, you will need 1500mm focal length or thereabouts, a smaller chipped camera like the 8300 or the new Sony 694 chipped cameras. 8 to 10 inch scope should get you there.

Not sure the comment about fast would be no good because of light pollution. Why would a fast scope be more effect of light pollution? (perhaps it is, I am just unaware of an optical reason for that).
I know DSLRs get limited by sky glow faster than astro CCDs.Is it more the camera and less the scope?

The solution to light pollution is usually a light pollution filter and shorter exposures. Also excellent gradient processing (there are several techniques).

Greg.

[DJT]

Hi Greg
Thanks for the pointers.

As you point out, it's a camera issue not an optics one. I find I can get around 6 minute subs using a canon with an LP filter and an f7.7 scope before it all goes pear shaped.

So the concern is that getting a very fast scope won't really be a great advantage, just pulling in Sky glow faster unless I am using a ha filter?


Objective is really trying to get a good range of focal lengths for imaging but based on DSLR ahead of going the ccd route. Currently referencing the kit used by Ian cooper on the " imaging the southern sky's" book as I try to figure this out.

[Logieberra]

' ... what's the pain points between fixed and not fixed mirror ... '.

I spent time centering the object on the chip, you focus the scope and think great, I'm all set to get a series of exposures. Then over the next 30min-1hr, as the scope tracks in RA, the mirror moves! Your object may still be centered on the chip, thanks to guiding, but your focus is now out big time.

Also, I focus on something towards the East, then slew to the west and that object is out of focus and definitely not centered. Don't get me wrong, for visual uses the 210 is superb. But clearly there is a reason why the larger and more expensive Mewlons - 250, 300 etc all have fixed primaries and electric motors on the secondaries to reach focus.

In theory, a cheaper Newtonian would exhibit some of the same issues as it flops in the mirror cell, but look at what people can do with those! For me, also as a refractor guy, I just don't have the patience for it, and like to see things fixed and secure :)

[gregbradley]

Yes I think that is the case that a DSLR is more affected by light pollution than a CCD I think its because of ISO on DSLRs. When you hit a certain level of ISO in a DSLR you are above 1:1 amplification whereas CCD the amplification gain as far as I know is very mild and around 1 I think. So if you are above about ISO800 amplification is multiplying everything including the light pollution so it fills up the smaller pixel wells faster than a slower deeper CCD image without that amped up affect. I think it can be demonstrated mathematically as well.

I imaged with a Tak BRC250 from an earlier house that was quite light polluted. It actually did pretty good with an Apogee U16M. I was surprised. That was HaLRGB imaging of things like the Tarantula Neb.

That BRC 250 in hindsight was a beautiful scope. Its F5.

Greg.

[LewisM]

The VC200L is a brilliant scope. I have had 3 now, and only ever sold them to get another refractor. Now I find the lust for a 200L AGAIN! Nil mirror shift, superb optics, and a real galaxy slayer. Downside - HUGE diffraction spikes thanks to the VERY thick spider vanes (at least the secondary doesn't move!!!), but those can be milled down to reduce them, and, like all these kind of scopes, collimation is a chore if WAY out (but simple if only a touch out). Several techniques exist to fix this issue.

I live in a HEAVILY light polluted area, since I can rarely escape to the Dark Site (cue Darth Vader music), and found the VC200L was superb. THe R200SS f/4 Newts I had (2 of) were nightmares to deal with light pollution, as they seemed to suck in every photon of light around, making washed out images in under 3 minutes!!!

YMMV, but I love the Vixens, and now have every adaptor imaginable, just in case :)

[Logieberra]

Also, have you considered the GSO line of RCs?

[DJT]

Hi Lewis. I looked around at some great images from the Vixen but the defraction spikes are going to be an issue for me I think. They look loke great scopes though.


aaah...theres one on astromart..hmmmmm. Its fast enough and the FOV looks great. Reasonable fit for both the DSLR and a sony chipped camera by the looks of things at least for the targets I am interested in.tempting but need to do some more research first. The obvious question would be why you moved yours on?



Thanks. I have been looking at the BAZ thread and will keep looking at that.

[rmuhlack]

I really like my VC200L. Mine has the secondary vanes reduced in thickness. I find it to be a lovely scope for imaging (http://www.astrobin.com/search/?q=rmuhlack%20vc200l&search_type=0&camera_type=any&camera_type=0&camera_type=1&camera_type=2&camera_type=3&camera_type=4&camera_type=5&telescope_type=any&telescope_type=0&telescope_type=1&telescope_type=2&telescope_type=3&telescope_type=4&telescope_type=5&telescope_type=6&telescope_type=7&telescope_type=8&telescope_type=9&telescope_type=10&telescope_type=11&telescope_type=12&telescope_type=13&telescope_type=14&telescope_type=15&telescope_type=16&telescope_type=17&telescope_type=18&telescope_type=19&telescope_type=20&telescope_type=21&telescope_type=22&license=0&license=1&license=2&license=3&license=4&license=5&license=6&sort=-uploaded). Visually I find it to be great as well (despite my cheap GSO eyepieces).

(Note that the VC200L and VMC200L are not the same scope). For imaging the VC200L is certainly the preferred model. Not sure if the application is purely for visual use.

[DJT]

Hi Richard
I saw quite a few of your images on Astrobin. Nice. The intent is for imaging. Where did you go to to thin the vanes or do Vixen themselves offer it?

[LewisM]

You'll need a machinist to do the vane mod. Vixen does sell the vanes seperately, and you can then have it done. Richard's came that way, as Guy (who did it) is a machinist and also truss modded the scope.

[Andy01]

Pardon the hack gents, :) but Greg what LP filter would you recommend? I'm in the Melbourne 'burbs, using an SBIG 8300 OSC on an ED120. As to shorter exposures, would you recommend 5 or 10min subs under these conditions?
Cheers
Andy

[JohnH]

Sorry I cannot agree with the other posts re the Vixen VC200L. It will give you an image scale of 0.49" per pixel by my reckoning, that seems a bit excessive to me given you are in suburban skies (2-3" seeing?) so you will need to use the FR all the time. This will in turn, in my experience, reduce the sharpness and flatness of your field. It also means you cannot replace the focuser except with (iirc) a very expensive unit from Starlight. Then there are the square stars from the fat spider - sure mill down the vanes - replace or at least motorise the focuser (the stock unit is crap for imaging - and locking it causes tilt) - use a FR, maybe change the tube and dovetail (both are light duty if you are going to use a guidescope, oh and if not you cannot use the Vixen OAG with the FR in place....)

Or get a scope that better matches your camera.

[rmuhlack]

I should have mentioned that I do all of my deep sky imaging now with the VC200L using both a Canon 1000D (with 5.7micron pixels) and the Vixen f6.4 reducer. This gives me an image scale of ~0.91 arcsecs per pixel - probably still a little over sampled, but still workable.

I must admit that I missed the mention of the 60Da in the original post. I agree that a 60Da is not a good match with a VC200L at the native focal length (in fact the 60Da is not a good match to any of the long FL scopes that have been mentioned in this thread). I have found the VC200L with focal reducer to be a good setup for imaging, but agree that you need to have the right camera to suit.

[DJT]

Hi Richard and John
Good comments coming out here, am learning which is always a good thing. I looked at quite a few images and yup, the spikes really are going to get to me so looks like the vixen will be a pass. (thats just a personal preference thing)

On the imaging scale though I will need to do more reading up as I am not knowledgable in this area so thanks for the heads up, both of you. theres a lot to consider and knowing all the constraints (environment, equipment, etc) is really important so I dont stuff up my next purchase.

Theres no rush :)

Thanks for all the input

[LewisM]

David,

The diffraction spikes are what ALWAYS keeps me away from reflectors, regardless of thick or thin spikes. I dislike artificial artifacts in images.

As much as I loved the VC200L's, the spikes kill it for me. Same with the R200SS.

[DJT]

We do like the tintaweb..:D

Found this article with a great diagram and now I think I get it. Will want to read up a lot more on this but I see John H's point.

http://www.skyandtelescope.com/howto/astrophotography/3304356.html?page=2&c=y


So given my imaging kit, assuming the 60Da still has a well depth of 6.4, and my local seeing (based on being in Sydney and best available weather on the night) will be at best 2, more likely 3, its short focal length refractors for me?

Am I reading this right? If so this thread may have just saved me a pile of cash...

cheers

[gregbradley]

Yes you are. Most DSLRs have relatively small pixels so I don't think you are really going to see any difference unless you are imaging beyond 1500mm.

Other considerations limit DSLRs before pixel size is much of an issue. Colour Noise, well depth, low QE, they pick up light pollution more easily than CCD. It sounds like I am bagging DSLRs - I'm not as they are a lot of fun. But they do have their limitations for imaging deep sky.

The main gain of CCD over DSLR is the fact that the mono chip has every pixel count and usually at about double the QE of a DSLR unless you have one of the few high QE DSLRs (Nikon D800, Nikon D5200, some Canon 1D series).

Mono converted DSLRs seem exciting but they will need filters but Jim Chung is selling converted Nikon D90 and D5100 (that would be the one to get that uses the awesome Sony Exmor 16mp sensor).
They are under $700.

Greg.

Greg.