SW MN190 Advice please

[MartinB]

I am thinking about getting the SW MakNewt and a medium focal length scope to fill the gap between my FSQ and 10"LX200R.

I know when it came out it seemed to tick all the boxes and got rave review - spot on optics with high contrast, fast speed and a flat field.

I know it's quite heavy. The EM200 should be able to handle that ok esp given that I have a dome observatory. I could use it with the built in OAG of my QSI 532 but I might want to use it with my QHY8 and would probably opt for side by side guiding.

Are the rings very substantial and does it come with the option of a losmandy dovetail?

How good is the focuser, I'm not too worried about silky smooth but will it cope with moderately heavy imaging gear?

Is collimation straight forward?

Are their any gremlins in the optics department.

I am considering getting a large format camera e.g. SX H36, does anyone know whether the it can handle that size of chip?

Does it have suffiecient back focus to cope with filter wheels OAGs and the like.

I would be very grateful for any feedback.

[ollypenrice]

Did you mean this to go in the imaging section, Martin?

Olly

[MartinB]

Eek, thanks Olly. This is now where I meant to put it!!

[Deneb]

I am thinking about getting the SW MakNewt and a medium focal length scope to fill the gap between my FSQ and 10"LX200R.

I know when it came out it seemed to tick all the boxes and got rave review - spot on optics with high contrast, fast speed and a flat field.

I know it's quite heavy. The EM200 should be able to handle that ok esp given that I have a dome observatory. I could use it with the built in OAG of my QSI 532 but I might want to use it with my QHY8 and would probably opt for side by side guiding.

Are the rings very substantial and does it come with the option of a losmandy dovetail?

How good is the focuser, I'm not too worried about silky smooth but will it cope with moderately heavy imaging gear?

Is collimation straight forward?

Are their any gremlins in the optics department.

I am considering getting a large format camera e.g. SX H36, does anyone know whether the it can handle that size of chip?

Does it have suffiecient back focus to cope with filter wheels OAGs and the like.

I would be very grateful for any feedback.

The MN190 weighs about 10kg, the tube rings & dovetail are the stock skywatcher ones, but i like others have replaced the dovetail with a more sturdy/stronger ADM universal 14" dovetail.

The focuser is very good, it's dual speed now, it's got a 50mm extension tube which can slide out when needed. From what I hear SteveL is still using the stock focuser on his with filter wheels as well with other bits & pieces - but not sure if thats with the earlier version of the focuser which was the single crayford focuser. Adamsp123 has also got some substantial stuff used on the focuser which is being handled quite well.

Collimation is straight forward, im currently working with Bob @ Bobs Knobs to create collimation thumbscrews for the MN190, I have the prototype primary collimation & locking thumbscrews, tried & tested (if needed I can post up the images of the prototypes fitted), were currently working on the secondary collimation screws now. My report will be posted up once I have recieved & fitted the secondaries as well. The standard screws are philips type for primary & secondary & allen key screws for locking the primary..

Regarding gremlins in the optics department - never heard of any !

Im currently imaging with a 450D & I know like TJ, he uses a ccd with large sized ccd chip, he seems to be happy, i think the optics of the MN190 seems to handle large chipped cameras quite well. HTH..

Nadeem..

[ollypenrice]

Confirmed refractor nut that I am, I had a good look at a fullsized M13 from SteveL taken at f10 via Powermate and it shows utterly astounding resolution. It has thrown my entire optical religion into confusion!! I can hear Nadeem chuckling...

Olly

[Whippy]

I think the only issue you might have Martin would be your plan to use the QHY8/MN190 in a side by side arrangement, achieving balance might be a bit tricky. If I had one (and the thought has crossed my mind a few times!) and a OAG isn't on the agenda, I'd look into piggybacking rather than SBS.

Big chips shouldn't be an issue, the secondary in these is larger than normal newts to fully illuminate these.

Tony..

[MartinB]

Thanks for the very helpful replies. The ADM universal dovetail sounds like a good idea. Is it possible to get sturdier rings for this scope? Unfortunately 190mm makes it a bit bespoke, I guess the tube diameter is a bit smaller than a typical 200mm newt.

Side by side balance shouldn't be a problem although I will have to move my side by side plate well over, but I do think flexure is on the cards with those flimsy SW rings.

Thinking about OAG, is the focuser rotatable?

[Deneb]

You could always put another dovetail on top of the tube rings to give it more rigidity, it does help.. The telescope focuser is not rotatable if you mean something like rotatable WO focuser.

Nadeem.

[MartinB]

Thanks Nadeem

[SteveL]

There are a few issues with the 190MN that you need to be aware of before you get to use the awesome optics on this thing, some of which have been mentioned here. My 190MN is a pre-retail press-review model, so its black with black rings, and may have a non-standard focuser base.

- The skywatcher dovetail is made of soft chocolate, and flexes even if you look at it too hard. Replaced mine with a ADM dovetail, which helped with flex (but didnt eliminate it)

- Even with the replacement dovetail, I still needed to go the OAG route to get anything longer than about 6-8 minutes without differential flex showing up. I think its due to the weight and the leverage created at the rings/dovetail which is causing the movement.

- Its a heavy beast, and with a ADM side by Side bar, with an ED80 pro on the other side, I had to slide the SBS *RIGHT* over to get it near balance, and really needed my DSLR/QHY8 combo piggybacked on the top of the ED80 to really get it balanced.

- It is a long OTA, and will pick up any breeze.

- I was going to upgrade the single speed focuser to a dual speed version, but once I used the Bahtinov mask, I decided it really wasnt worth the upgrade.

It only comes with a Vixen dovetail option, collimation is dead simple, unsure how big the illuminated field is (i.e for a H35/H36 CCD).

Back focus is the bit that nearly caught me out. I needed to go OAG, but also needed to keep my Gerd Neumann filter drawer in-line. For the first light, I also had a Televuew 2" 2x powermate (for my M13), and the imaging part of the kit looked like the image below. I did add some spacers to get everything parfocal, so will need to measure the exact distances when I get home, but with the below setup, I had somewhere in the region of 7-8mm of spare back focus

[MartinB]

Brilliant, thanks Steve. Yes, I think the OAG route is the one to go down. My QSI has a built in OAG but I will need to get something for the QHY8. I have the same filter drawer but wont be using a power mate!

I remember you getting a very flat field with the QHY8 so guess it will give a reasonable performance on a full format chip.

Which OAG are you using?

[SteveL]

Its the Teleskop Services 9mm OAG, as anything else would be too thick for me to get to focus.

[adamsp123]

What I have found so far!

Stock single speed focuser seems absolutely fine.

Dovetail needs to be chunky, I would also add one to the topside of the rings.

Tube rings - once they are locked down tight I can't see them being a problem but..... the tube might flex with the weight at each end flexing the tube, ideally I would like to be able to have 3 rings, one close to each end and one in the middle on a rock solid dovetail.

It is heavy so I stuck with my 50 finderguider which I got 15 min subs with nice round stars in SII.

I agree with Olly, refractors are nice but the extra aperture and faster optics make this a real winner for me.

[ollypenrice]

Sounds like it deserves some high end, accurate rings and a long Losmandy plate for generous spacing thereof. A good carbon tubed version would be welcome too, it the stiffness of my new carbon road bike is anything to go by...

Olly

[Whippy]

Sounds like it deserves some high end, accurate rings and a long Losmandy plate for generous spacing thereof. A good carbon tubed version would be welcome too, it the stiffness of my new carbon road bike is anything to go by...

Olly

To be honest Olly, the type of tubing used on the MN is noticeably thicker than the ususal SW newts (probably to keep the corrector in place) so in that respect it's more like an Intes Micro and those OTA's just don't flex at all, although if the carbon kept it's shape well enough it'd certainly reduce the weight somewhat (IIRC Teton Telescopes in the US use carbon fibre on their MN OTA's that use Intes Mirco optics).

If one drifted into my hands, I was thinking along the lines of using ADM dovetails top and bottom and bolting my ZS66 as a guidescope to the top. If that caused issues then it'd be an OAG.

Tony..

[MartinB]

So losmandy dovetail, another bar across the top. Anyone got any recommendations for high quality rings, I guess the diameter of the OTA wont be right for 200mm newtonian rings. Although the option of side by side would be quite nice I'm an old hand with OAG through using AO.

One advantage of a dome obsy is that I'm very sheltered. The EM200 should be up to the task.

[barkis]

Perhaps radiused blocks for the rings, or radiused platform with a machined in dovetail, surmounted with a clamshell instead of seperate rings, would ensure total stability.

(Is there such a thing?)

Probably would have to be a one off project for a machinist, unless a few orders by several owners would bring the probable high cost down a little .

A prototype for stringent testing is the way to go.

Anyone know if Arthur's busy? .

Ron.

[Andrew*]

Martin, from what I've heard I think the OD is actually the same as the Skywatcher 200P newt tube but I'd wait for confirmation on that.

Andrew

[barkis]

As Tony said, the tube wall is thicker than in the normal OTA's. I think the thicknes is 3mm, or just under 1/8th inch. Should be pretty rigid really.

Ron.

[Steve25]

Andrew,

I have just measured the Circumference of the tube on the MN190 and its 29.5", so my calculations make it 9.3" in diameter (or there abouts).

Steve

[MartinB]

Thanks Steve

[opticalpath]

Hi. I'm seriously considering the SW MN190 too. A lot of useful info in the posts here, but can anyone tell me more precisely what the maximum back focus is? I.e. with the focuser drawtube racked fully in, how far is the image plane from the end of the drawtube?

Thanks

Adrian

[fatwoul]

My thoughts based on a few months of use of my MN190/EQ6:

I'm using a Nikon D3 with mine, the full-frame sensor of which is able to discern a vignette at the extremities. So far I've had mixed results in combatting this with flat frames. However, the vignette is...sudden; it doesn't build up gradually, but instead just cuts through the corners of the frame fairly sharply, which is advantageous. The D3, for those unaware, is a full-frame DSLR, so that might give some indication of the field these scopes seem to be capable of.

The weight can be a little tiresome for me, but that's partly because I have to carry it up and down stairs every time I set up. I've heard some reports recently that the EQ6 is struggling with heavier scopes (I would include the MN190 in the category of "heavy"!), but so far my mount has proved capable, provided it is set up correctly. Be warned, that the MN190 does max the EQ6 out, with its two provided counterweights set to their greatest extension. With a camera attached aswell, I have to use a third counterweight, but so far this hasn't presented any obvious load problems.

Cooling time seems to be quite short with the door removed.

Collimation was a bit of a headache for me when I first attempted it, but this was my first reflector, and I foolishly attempted it with a laser collimator before realising the collimator itself wasn't collimated! Since obtaining a Cheshire collimator the process has become much easier.

The only irritation I suffer with my Mak-Newt is one that isn't specific to the scope, but to all Newtonians; the eyepiece being on the side is taking some getting used to for two main reasons. First, because I am short, and don't like climbing stepladders in the dark, I am forced to use the EQ6 tripod at its lowest height, in order to be able to comfortably reach the focusser in any orientation (I'm also not comfortable putting the scope onto the EQ6 at its highest setting, as it involves me reaching awkwardly with a heavy, expensive object!). Second, I find the addition of a camera to the side of the tube presents some balancing complexities that took some fiddling to tune out. I now orient the eyepiece and finderscope so they are on the side of the scope nearest the mount. Not only does this allow me access to the focusser wherever the scope is pointing, but it also minimises the torque introduced by quite a heavy camera.

Once my scope is set up permanently in a dome (within 12 months, is the dream), the height issue should no longer matter, and the balance can be resolved permanently.

I have an SW80ED, which I find complements the MN190 beautifully, as a wider field scope, either for imaging, guiding or just enjoying the view (depending what my mission for the evening is)

Hope some of that helps.

[MartinB]

Thanks for that Fatwoul, very helpful.

[Catanonia]

All very interesting and definately a candidate to go alongside the ED120 pro I have via SBS ADM bars. Should help balance it all out.