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Skywatcher 190MN - Help please.

Komet

By Komet
in Discussions - Cameras

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ollypenrice

ollypenrice

Posted
Posted
A while ago I was getting similar issues with mine. I collimated it till I was blue in the face.

My problem was a out of square focuser, resulting in the removal of the focuser and corector plate to realign.

My 190MN also responds better to a Cheshire collimation rather than a laser.

HTH

I do think orthogonality in the focuser is critical in fast systems.

It seems to me that the 190 is great value and would be even better value if it cost about half as much again with the bugs ironed out by better mechanical construction.

At one time (looking at SteveL's M13!!) I thought about losing the TEC in favour of the 190. But that is not going to happen.

Olly

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Komet

Komet

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A while ago I was getting similar issues with mine. I collimated it till I was blue in the face.

My problem was a out of square focuser, resulting in the removal of the focuser and corector plate to realign.

My 190MN also responds better to a Cheshire collimation rather than a laser.

HTH

Hmm ....

I have been using a Cheshire of late as its easier to see what the secondary is doing than using the laser.

I will have to have a play.

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Komet

Komet

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OK - some positive news.

Firstly, feedback from OVL reports that there have only been issues with this scope regarding the single speed focuser and not at all on optics. They suggested it was a secondary/focuser issue. I don't disagree with that at all although perhaps it could be reclassified as an "original setup problem" with "total lack of any documentation" issue.

As a few people have contacted me with similar tales of misshapen stars then perhaps they too can go some way to solving their problems.

Comments from a few reagrding the focuser - I thank you.

Anyway .... yesterday, after removing the primary cell to check it I decided to strip the whole thing down just to check that it was all as I felt it should be. I found nothing visually wrong at all. I reassembled it, collimated it - with a Cheshire - and then faffed around with one of those artificial star torches from Hong Kong (Ebay). I could get focus at 60ft with a 2" extender on the camera. As the torch is stationary everything I did was with the mount stationary - no tracking issues to muddy the waters,

Firstly I had the same airy disk as I previously posted with the "nibbles" as Nadeem put it ;) and the softer edge. I then tried to screw it all up on the premise that if I could understand where it was all wrong I could then try and make it all right. For this I had the OTA virtually level with the camera pointing down vertically with the view that that would give the flattest camera plane. I moved the focuser, I shimmed the focuser I played with the secondary until I felt that the artificial star was showing more symmetry. I was also rotating the torch through 180 degrees when checking to see if the image altered. It never did which showed how symmetrical the light from the thing was.

When I was happy-ish I recollimated (just the primary) and waited for darkness.

Once again off the the M27 region (loads of stars there). The camera was back in its usual position under the OTA.

This is a crop of a 20 second exposure .....

komet_mn1902.jpg

A definite improvement although not perfect yet. RA is left to right (not quite level but rising as it goes right. The stars show some bias that way and could well be tracking)

I believe the camera is tilted slightly as the field is not totally flat - I would much prefer a direct connection, the single screw compression fitting on the the focuser is just not up to the job especially as the scope is marketed as an astrograph. Suggestions?

Also I think the secondary needs aligning (rotating) - does anyone know how that is done with accuracy on this scope?

Anyway I feel I have made some progress. Life doesn't look so gloomy now.

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steppenwolf

steppenwolf

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This looks much more promising so well done for persevering with it. You mentioned shimming the focuser, did you end up leaving the shims in place? Any chance of a link to your artificial star supplier?

It is still disappointing that this instrument appears to have required more than just collimation (which we all have to accept as a fact of life with any reflector) but having seen the fantastic results that this telescope is capable of achieving (at one time it was my 'dream' telescope) I have no doubt that your patience and work will be amply rewarded.

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Freff

Freff

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Although my focuser sat square on the OTA, it was not centre. The only way I could check this was by removing the corrector plate. I then used my Hotech laser to shine a dot on the the opposite side of the OTA. (pre measured) As a result it was out by 3mm.

Once this was sorted, collimating the secondary involved a slight rotation to bring it back. Surprisingly, collimation was almost smack on after re-assemlbling.

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Komet

Komet

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This looks much more promising so well done for persevering with it. You mentioned shimming the focuser, did you end up leaving the shims in place? Any chance of a link to your artificial star supplier?

It is still disappointing that this instrument appears to have required more than just collimation (which we all have to accept as a fact of life with any reflector) but having seen the fantastic results that this telescope is capable of achieving (at one time it was my 'dream' telescope) I have no doubt that your patience and work will be amply rewarded.

The shims I ended up removing as they were not needed in the end.

The artificial star = Ebay ref: 200613562889

Runs on 3 AAA batteries (not supplied). Also useful for focusing both main camera and an OAG I should think. Can be used in daylight!

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  • 7 months later...
Explorer 190 MN

Explorer 190 MN

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I realise this is an old thread, how did you get on with your problem? I have noticed if you dont pull the draw tube focuser all the way out collimation can be off also be careful tightening up the focuser locking screw as it also knocks collimation out you need to look at the star whilst tightening up the locking screw. It maybe flex in the draw tube!!

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Tim

Tim

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If you use a Bahtinov mask when focusing, then you can immediately see the effect of tightening the locking screw in real time. Usually that pushes the image off to one side or another a little.

Armed with that information, when you collimate, carefully adjust the locking screw to the same degree as you will when imaging, and then you'll be working at around the same configuration with the collimator as the camera.

Its a compromise. Ideally, a decent focuser which doesn't tilt when locked is the way to go. I find that at either extreme of adjustment the standard Skywatcher focusers exhibit more movement, so try to use them in the middle of their range.

As with any Newt, getting the focuser square to the secondary is important. You can use the marking on the MN190's mirror for this. With a self-centring laser you can adjust the focuser mounting until the laser lands squarely on the secondary mirror marking. (This assumes the secondary is set properly, which you can still do with the focuser being off square)

HTH

Tim

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  • 4 weeks later...
Explorer 190 MN

Explorer 190 MN

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Posted

Thanks for the tips on the focuser...... Now I have autoguiding sorted amongst all the other hurdles I have had to climb over with the celestron mount and now it looks like I got the three star issue...

Was it the retaining clamps?

Out of line focuser?

Out of line secondary?

All of the above?

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