New silicone job on my GSO F4 Newt

[blinky]

It’s seems that I rather overdid the silicone on the mirror last time I did this and it may have been contributing to triangular stars due to the mirror being a little pinched in the cell. I’m not 100% convinced but the general opinion was that all is needed is 3 pads of silicone for the mirror to sit on – not, as I had previously, the whole cell being covered in silicone!

Anyway, tonight I set about removing the old stuff and replacing it was said ‘blobs’……. Getting the stuff off was not too bad, got a craft knife set for £1 (from Poundland, of course!) and it worked a treat, I sliced throught the old stuff, removed the mirror, then used a flat edged blade and it just came right off the mirror when slid under the remaining silicone – All in all it took about an hour to get it back to ‘normal’

Next was to work out how to create a little space between the cell and mirror so that when placing it on the silicone pads it would not just squash them and sit back on the mirror cell itself. After pondering for quite a while about what to use to create this spacer I glanced uppon the rubber mirror clips – these are like a little L shaped piece of rubber, so now there is 3 little spacers and the mirror sitting drying on to the 3 blobs of clear silicone. When it’s dry in 24hrs time, I will remove the spacers and stick them back on the mirror (I had actually done away with them when I had previously siliconed the mirror to the cell but think that as I now only have 3 blobs of silicone, it’s best to have them back in for safety!). The only (slight) concern is that the mirror is now sitting higher in the cell than it was before and does not have as much lateral support, I have slid 3 cardboard spacers in beside the cork spacers to tighten then up but am wondering whether to place a further 3 blobs of silicone to give more lateral support to the mirror????

A couple of other potential areas for problems were also addressed as part of tonights re-silicone….

First up, the lenght of the collimation screws

The collimation screws supplied are just a bit too long and if tightened right up will actually touch the mirror surface, pushing the mirror forwards in the cell and further up against the mirror clips. Too tight mirror clips cause triangular stars, thats bad enough but having a metal screw touching my glass mirror, somthing had to be done! I bought a pack of washers and added 4 to each screw, now when in as tight as they go, they still dont touch the mirror – Job done! (BTW, the springs supplied with this scope are inadequite, I have already replaced them with stronger ones from ‘Bob’s Knobs’)

Finally, the centre spot – I have heard from a few people that the centre spot was not erm… centre! I found a cacke tin exactly the same size as the mirror, drew round it on to a sheet of A4 paper and cut it out, folder it in half, then half again and cut a littl from the centre to make a circle. I placed this on top of the mirror and it seems that my spot is, spot on!

So… Now I just need to wait on it drying and then re-collimate and hopfully I will have some nice round stars!

Check out my blog for the full story with images!

[blinky]

How do these stars look? 100% crop from the left side of the image (what appeared to be the worst area in my M42 image)

[Stephen]

Tiny distortion towards the centre of the field I think?

[Tim]

Craig, you'll always get some distortion near the field edge with a newt, unless you use a very small chip camera.

How do they look in the central third?

[blinky]

Here is pretty much centre of frame...

[blinky]

I just started taking some sky flats today and noticed this appearing on the stretch..... Does it mean maybe my secondary is tilted?

[Peter Drew]

Something is!

[blinky]

yeah but what?

[DIYASTRO]

I would be tempted to try adjusting secondary, perhaps marking the position its in first to set it back if no improvement. It's not the focus / crayford out of alignment is it?

Boyd

[blinky]

Well, I dont know where that flat came from! I applied it to my image from last night and it came out with the flat plainly obvious, so I dont know what went wrong. Still..... I re-did my collimation in case and this is the result - 10s, 100% crop of Aldebaran.

Still not 100% round but I think it's about as good as I'm gonna get!

[Euan]

This is why I bought a refractor, collimation drives me nuts

You got crappy fog and / or high cloud tonight Craig? Central Scotland is not looking good on radar

[blinky]

I Dunno, looks OK to me? In saying that I have not checked my first 15min sub yet.....

[Euan]

I Dunno, looks OK to me? In saying that I have not checked my first 15min sub yet.....

I might just be getting all the har from the Forth

The red sky temperature value would be totally flat if it was clear, but it's bobbing all over the place