Mini Observing Report and test after 200p Collimation

[Johnnyaardvark]

Hi all,

No imaging yet this month so to speak but did manage to sneak a few hours visual in Saturday night before the clouds and the rain set in.

Main reason for the visual was that I have finally got around to fitting a smooth flat metal disc between the secondary mirror and the collimation screws (Thanks Zidder!). Not glued it in or anything just relying on pressure and does not appear to slip?! Collimation seems a lot smoother with the metal disc in place (thanks for the disc dad!) and collimation felt pretty successful even though I was not entirely sure how good my technique and process was!! Hence I needed to get out and try it.

Set up quite late (10 ish) and I could already see some cloud low on the southern horizon... heading my way... so I knew I had limited time. My plan was to quickly get set up, polar align and run a 3 star alignment... I can get this done pretty quick and brought the 200P out into the garage early to start it cooling down.

Polar alignment done I got the scope and counter weights on and set about running the alignment routine... bugger... I occasionally have problems with power disconnecting and this happened a couple of times while I was loosening clutches to move through the axis... At one point a panicked a little as the handset crashed and had strange horizontal moving lights on the display. Rebooted and took more care what I was knocking while loosening clutches and the rest of the evening was uneventful in terms of power supply!

Polar alignment done with the help of Stellarium so I knew what usable stars to select I proceeded to look at Arcturus - main reason was to defocus on some bright stars and see the airy disc (?) around them and to check out my collimation. Things seemed a bit off centre at first but looked fine when the star was more centralised in the eyepiece. I did make some fine adjustments to the secondary but mostly I think its seemed pretty good. Any advice here in terms of how to tell if its out and by how far would be greatly appreciated.

I also wanted to check a few favourites and see how I felt it was performing. A little easy and cheating maybe having goto but I was away.

1st off had a look at M57 Ring Nebula. One of my favourites and had not seen it yet this year with the 200p (usually I have the Ed80 set up as its easier to move around and ready for imaging) looking good in my 31 mm but of course very small. Upped the magnification and tried the 13mm and Barlow. Still looking nice and clearly a ring when using averted vision. Not at it's best though as the night sky was still light. While high up moved to Bodes Nebula and then a little nudge on the controlled for M81 and 82 to add the cigar into the same ep (dropped to lower mag now 18mm and/or 31mm again.) Very faint against the bright sky but both visible. Cigar showing a little more shape but I may have missed them if I did not know what I was looking for. Swung around for the double cluster... looking quite stunning as ever. Very nice in the 18mm as well as my 31mm. At F4 though the 31 is a bit soft around the edges.

Some cloud had cleared a little to the south so took the opportunity to have a look at Saturn and the nearby waning 1st quarter (ish) moon. Quite a lot of turbulence low down but able to make out the Cassini division in moments of good seeing and possibly Titan a distance away to the right (in my fov) tried various magnifications and was looking fairly good in all through the murk! While looking in that direction scanned along the moons terminator possibly a part glimpse of the lunar x (more of a lunar >) still something I have not seen. Many craters looking nice and crisp even if there was some discolouration (redish colouration... Collimation? I think more due to how low the moon was as it was across the whole surface!?)

Since I was looking south I thought I would check out a few objects in Sagittarius... especially as I had enjoyed scanning the area so much with binoculars last your from slightly further south. Found that most were too low... either cloud moving in, poor skies or my garage in the way!!! Looked on Stellarium what was a little higher and decided on M11 wild duck cluster partly as I had remembered seeing it on the sky tour on the handset earlier. It turned out to be a highlight of the evening. Even though very small and faint it was quite beautiful and so many stars... quite incredible... almost more like a globular than open cluster.

Finally back to a few bright stars to look at them out of focus to check collimation and had a quick look at a hard to see M13 through cloud... looking a little grim decided it was time to pack away.

A nice evening, good to get out and scope looks to be back up and running. Still could do with a little help with collimating... trying to do it with just a Cheshire... but think its about right.

Best wishes

Steve

Edited July 27, 2015 by Johnnyaardvark

[Doc]

Way back in 2009 when I bought my 16" dob I done a modification which I called "The dimple Mod" it was basically a flat steel washer with three little indentations drilled into it at 120° apart. 

 

This was place under the secondary mirror housing. The three collimation screws were then sharpened to points. Then the collimation screws were inserted and tightened until the points were inside the indentations.

 

This stopped the slipping motion you had with flat bottom screws. It improved collimation and felt very positive when collimating.

 

Nice report Steve it made great reading.

[Tweedledee]

Nice report Steve, glad you had a good session

 

M11 is even better when you give it some magnification.

[BAZ]

A nice read there Steve, not a bad night considering the incoming weather front.

[tuckstar]

Sou ds like you had fun matey, if your coming to ww on the 8th I'll have my hotec with me if you want a play.

[Daz Type-R]

Could I suggest, if you don't have a Hotec Steve, use conventional methods (Cheshire, laser ETC) and only use Andy's Hotec to see how close you are, otherwise, you will never perfect your collimation with the tools you have.

[Johnnyaardvark]

Thanks all. Hope to come over to Wymeswold but moving house shortly after so will have to see hie much I have to do. Don't normally travel with the 200p but should be able to squeeze it in.

Thanks for offers of help. Fair advice Daz and Andy that would be great to see how close I got/am.

Mick. My secondary has some dimples in the back of it as it is but they are a bit rough and I felt they were preventing me from positioning the secondary quite how I wanted it... trying with smoothed off collimation bolts and a flat washer for now. Will be interesting to see how quickly it slips out but if I can quickly and accurately improve collimation especially outside I can live with some movement. Will see!

Thanks for the kind words. Glad you enjoyed the read... a few typos to sort out though!

S