Skywatcher 190MN / fitting of a Moonlite focuser

[Gunnar]

Finally the last step was to remove the primary mirror cell again and loosen a bit more on the mirror clips to ensure that there were gaps so that a typing-paper may be inserted between clips and mirror. This to be sure not to clamp the mirror.

Then a new collimation, now using the secondarymirror centre-circle as reference on the cheshire crosshair

[Gunnar]

Test shooting agin!

Air currents in the upper edge of the telescope tube forms the airy disc asymmetrical patterns on my Canon EOS 500D, shows that the telescope is still not cooled sufficiently. Skywatcher 190MN takes very long time to cool down to ambient temperature. I've actually been thinking about mounting a cooling fan.

The next two pictures are the bright stars Capella and Betelgeuse again. A marked improvement. It looks like the telescope has become much better after this fix.

Perhaps the primary mirror was pinched after all? But it can not be excluded that there has been a combination of several errors, pinched corrector lens? This is however a major step toward fixing the errors but there is certainly a little more fine tuning to do.

Thank you for reading this thread!

[Gunnar]

Hi,

For comparison, unfortunately, slightly rotated.

Capella before and after! What do you think?

Thanks

Gunnar

[Tiddles]

Good job and well explained. Thank you for sharing.

[Auntystatic]

Brilliant thread, well done great reference material.

[Explorer 190 MN]

Hej Gunnar tack för ett mycket bra inlägg.

I have the same problem with my 190MN except maybe worse at lower temperatures -15 I get triangular shaped stars. So my question is how did you adjust the nylon corrector lens screws? I take it these screws align the optical axes with the mirror system?

Is the moonlight focuser shorter in profil than the original focuser?

Last but not least I live just south of Stockholm and was wondering if you had the time to show me how you adjusted these nylon screws? I can take my OTA to you.

Aaron

[Gunnar]

Hej Gunnar tack för ett mycket bra inlägg.

I have the same problem with my 190MN except maybe worse at lower temperatures -15 I get triangular shaped stars. So my question is how did you adjust the nylon corrector lens screws? I take it these screws align the optical axes with the mirror system?

Is the moonlight focuser shorter in profil than the original focuser?

Last but not least I live just south of Stockholm and was wondering if you had the time to show me how you adjusted these nylon screws? I can take my OTA to you.

Aaron

Hi, Aaron

I found that the 190MN-front corrector-lens is not so critical in the optical axis, I have tried to adjust my lens in all directions with not much difference. The screws were set to NOT make any pressure to the lens, about 0.10 mm gap!

My advice is to check..

1. secondary mirror adjustment screws so they are not to tight. If this is OK.. go to nr2.

2. The primary mirror. Make sure the mirror holders doesnt make any pressure to the mirror surface, also the same 0.10mm gap for the radial support screws for the primary mirror.

-15 temperatures = long cooling time, I plan to mount a coolingfan to my scope for this winter.

Gunnar.

[Gunnar]

User manual 190MN

http://www.telescope...29370_07-09.pdf

[Xplode]

Thanks for the user manual.

I have newly bought MN190 myself and and i need to adjust the tilt of the secondary, but the ring i need to loosen is very tight, any tips?

[Freff]

Mine was ridiculously tight. I had to resort to using a pair of pipe grips like these, but with tape on the jaws.

I first cut a snug fitting piece of thick card the same size as the corrector lens as a protector. Good luck.

[Xplode]

I'll try the same, thank you!

[Blind Io]

Nice write up. Good advice. It has given me the confidence to check my 190mn out

BI

[perfrej]

Brilliant, Gunnar!

I decided to buy myself one of these little naughty boys and got it in the mail today. I discovered first hand that the center screw of the secondary is way too short, luckily with the tube horisontal! It is now replaced with a much longer one.

I will definitely tune this scope and fit a moonlite to it. The standard focuser doesn't even hold a 2" eyepiece properly...

All the best,

Per

[alan potts]

An absolutely excellent piece of reference work, it makes me want to go and take mine apart now. I will have to give mine a try with the Canon 40D Mod that I have bought, even thought the HEQ5 Pro is a bit small, well balanced and with no wind I may get away with it for 2-3 minute exposures.

It is a solid as a rock for visual the only movement I get is if I knock it.

Alan

[AndyH]

Superb thread, worthy of my click for 5 stars.

Don't have this scope, but never the less, quite wonderful resource material in here.

Andy

[Explorer 190 MN]

Hi, Aaron

I found that the 190MN-front corrector-lens is not so critical in the optical axis, I have tried to adjust my lens in all directions with not much difference. The screws were set to NOT make any pressure to the lens, about 0.10 mm gap!

My advice is to check..

1. secondary mirror adjustment screws so they are not to tight. If this is OK.. go to nr2.

2. The primary mirror. Make sure the mirror holders doesnt make any pressure to the mirror surface, also the same 0.10mm gap for the radial support screws for the primary mirror.

-15 temperatures = long cooling time, I plan to mount a coolingfan to my scope for this winter.

Gunnar.

Hi, Aaron

I found that the 190MN-front corrector-lens is not so critical in the optical axis, I have tried to adjust my lens in all directions with not much difference. The screws were set to NOT make any pressure to the lens, about 0.10 mm gap!

My advice is to check..

1. secondary mirror adjustment screws so they are not to tight. If this is OK.. go to nr2.

2. The primary mirror. Make sure the mirror holders doesnt make any pressure to the mirror surface, also the same 0.10mm gap for the radial support screws for the primary mirror.

-15 temperatures = long cooling time, I plan to mount a coolingfan to my scope for this winter.

Gunnar.

Hej Gunnar tack för att du har tog tid till att svara på mina frågor jag be ursäkt att det dröjt så länge innan ni fick svar, haft tok mycket att göra med firman.

I think in the case of my 190 its mostly the focuser that is at fault. I noticed a lot of image tilt in my pictures causing weird star shapes there is a walk around You need to wiggle the drawtube whilst over tightening the set screws lol, its a new focuser that required where did you get yours from outside of Sweden i guess? Can I get a moonlight focuser inside of the EU?

[perfrej]

Teleskop-service sells Moonlite. I have one on the way in from them, should be here Thursday. It's about SEK 3500,- incl VAT. Call Hans at 0301-42972 and tell him you want the same as I (Per Frejvall).

/per

[Gunnar]

Hi Aaron!

And FLO sells them. it`s about £248.

http://www.firstligh...newtonians.html

Gunnar

[Gunnar]

Hi.

Here comes part two!

More collimation and modification of Skywatcher 190MN.

I have continued to work with some adjustment on my Skywatcher MN190. The reasons are,

1. I recently discovered that the mirror cell can be in an off-centered position in the tube, which I completely missed earlier!

2. I still get weird spikes around stars.

3. I suspect that the mirror clips could cause some disruptions / reflections in the image.

I wanted to improve my MN190 on these points!

I even found an interesting article by Paul LeFevre

which was very interesting!

http://lefevre.darkh.../clipectomy.htm

The pictures he shows before and after a modification from his Schmidt-Newtonian telescope are very similar to one of the errors as I get on my images. A Schmidt-Newtonian telescope also has a corrector lens in front of the primary mirror, just like the Mak-Newt has.

Centering of the primary mirror cell.

Is this important in a Makstov-Newton telescope? Maybe not in a normal Newton telescope.

What distinguishes these two types of telescope then?

As Adrian (opticalpath here on SGL!) who also have an 190MN told me, in a Newton the aperture stop is at the MIRROR. In a Mak-Newt, it is at the CORRECTOR!

This means that it must be very important to get the primary mirror completely centered in the tube on a Mak-Newt to match the optical train!

Last time when I worked with some adjustment of the mirror clips, my mirror was sitting completely centered in the cell and I was confirmed that the mirror was not pinched and everything was ok.

Now, when I worked with the modification of the mirror attachment, I discovered that there was a problem with an error in the centering of the mirror holder / cell. The mirror cell proved to be slipping sideways a few mm when undoing all collimation screws completely. I completely missed this error earlier because the screws were tightened at the occasion.

I decided to go with this idea I found in the article, to remove the mirror clips and glue the primary mirror in the cell! And I had to fix the centering error.

1. Centering error! This error was corrected with soft spacers between the mirror cell and the wall.

3. I removed the mirror clips, and also the cork/supports under the mirror was removed. The mirror was then glued at the rear with 3 silicone blobs. 3mm spacers was used to not compress the silicone too much. This was allowed to dry for a week.

Meanwhile I manufactured three new very low mirror brackets from aluminum to replace the regular rubber-mirror clips. These new brackets have a hole from the side. I then injected the proper dose of silicone thru the hole to make a silicone blob between the bracket and the mirror!

Results,

I now have a Skywatcher 190MN with glued primary mirror and low mirror holder that does not protrude over the surface of the mirror! Am I the first to do a modification like this on a Skywatcher 190MN? This is of course a bit of an experiment and I can always restore to original configuration if there will be problems with this silicone-glued primary mirror.

After this work, it's all been cloudy for more than a month. With curiosity, I waited for an opportunity to try out the telescope to see some result, poor or good! So this week, it became clear but windy. I mounted the tube on my NEQ6 and tried to take some images but the guiding was terrible in the wind and there were no images that could be evaluated. The next night was clear, too, but now there was no wind, but it was full moon and much haze in the air. I did not see so many stars but I tok some pictures.

Here is one of the starry images taken in full moon and hazy sky! No flats or darks and focus not perfect.

Gunnar.

[Gunnar]

Some pictures on the mirror after the modification!

[perfrej]

Gunnar!

Thanks for the report! I discovered the "sliding mirror" when I was loosening my clamps a bit in order to fit the office paper in there as per your suggestion. My idea was to solve it by adding a small foam pad between the edge and the clamp (outer edge, not surface). Your method, of course, is more sophisticated!

I wonder how much the small clamp obstruction really matters, though, but having weather as we do you might as well fiddle with the stuff

I'm still waiting for the Moonlite base plate and won't do anything until I have it in my hand.

All the best, and let's see what our 190's can do!

Per

[Gunnar]

Hello Per!

I hope you will recieve your Moonlite baseplate quickly, because the weather going to be better soon!

It is not the mirror itself who is sliding on mine. The silicone blobs you can see at the picture on the outher edge of the mirror here is only for glueing the mirror to not fall out from the cell! I was afraid that this can happen if the mirror only is siliconed with 3 blobs of silicone at the rear.

The mirror is not moving inside it`s cell. The problem is that the whole mirror cell is sliding a few mm off centre when losening the collimation screws. So I also put 3 soft foam spacers on the outside of the big mirror holder/cell, they are not visible on the pictures here!

Gunnar.

[opticalpath]

Looking forward to seeing test images taken under better conditions, Gunnar. First result looks very promising .... I'm watching with interest!

Adrian

[Gunnar]

Test image in post nr #44 found in better resolution here! Klick on the link and scroll down to IMG_4719.jpg and IMG_4719.2.jpg

http://www.astronet....p?t=6895#p26684

[Freff]

Hi Gunner. I agonised with this the last time my 190mn was dismantled. I was getting the same effects as you.

I was keen to get my scope back together and try out my new focuser. Fearing that if I didn't think it out properly the mirror may fall about with just a silicon type fix.

So in my haste I simply put some self adhesive chrome tape on the clips giving them a mirror effect. Eureka. it worked, to a fashion. It's not perfect but very near.