Collimation Cap Hole size

[Bizibilder]

Hi all - I'm just turning up a collimation cap for my SW 200P on the lathe (Far too posh to use a 35mm film canister !!!) and I was wondering - What size should the hole in the cap be?

Searching the forum and other sites usually comes up with "small" but how big is "small"?

Thanks in anticipation.

[Merlin66]

1.5 to 2mm would be ideal.... just to keep your eye on the optical axis

Ken

[Bizibilder]

Thanks Ken - Astro Baby's site ( and other's) show pics that "guesstimate" to this size - I just wanted to be sure.

[Bizibilder]

This is what I ended up with - POSH or what??

[orionhunter]

er? mines not so posh.

2mm hole though.

[yeti monster]

Mine's even less posher, a cap from a hydraulic fitting at work. All my EP caps are of the same source.............

[LukeSkywatcher]

Mine's even less posher, a cap from a hydraulic fitting at work. All my EP caps are of the same source.............

MINE is about as cheap as it gets. I used a dust cap from the star diagonal off of my 90EQ scope and drilled a hole in it using a corkscrew. I dont even know if the hole is 2mm......(its pretty close)...........but it seems to work pretty well. When i look into the hole on the cap....................everything that should be centred IS centered.Its not 100% but is about 95% accurate.

[Astro_Baby]

Thats a posh collicap. You could almost put a mirrored surface on the back side of it and have it as an autocollimator

[Rusty Strings]

Very posh, a bit cold to the eye of a frosty day though.

[Bizibilder]

I'm POSH - I always get the butler to do the collimation!

[Coco]

I took a tip from me new great mate Dave Gibbons

I drilled a hole in the focus tube dust cap on me Dob and pushed some silver foil in the other side to reflect back.

Works perfectly

£0.00 Priceless....

[Rob]

Heres a thing. I'd been looking for one then found on my AE ali dust plugs that they are part drilled on the reverse in the dead center. Got the drill out and finished the hole off all the way through (I of course removed the AE badge)

Got myself a nice collicap now!

[nigelwr]

I think you could sell those Bizibilder!!!!!

[Glider]

Shimples.

[albedo0.39]

Very pretty - like the engineering !

[brantuk]

Mines a plastic barlow cap with a drilled 2mm hole slightly off center to compensate for the fact that I was using an electric drill and holding it on the kitchen chopping board with fingers lol

[brantuk]

It slipped a bit lol

[Bizibilder]

I've added a picture of the underside of my collimation cap - You should be able to see that the flat annulus is polished (if very slightly scratched!). This helps in aligning things. I copied the idea from a commercial cap design that I found on the web.

[TopHouse]

Nothing worse than a scratched annulus!

[Bizibilder]

:D:D

[great_bear]

found on my AE ali dust plugs that they are part drilled on the reverse in the dead center.

Now your secret's out I bet they all get snapped up off Astroboot!

[yeti monster]

Nothing worse than a scratched annulus!

You should see my annular, it's totally wrecked!!!

[AndyH]

You should see my annular, it's totally wrecked!!!

So that'll make it an annulus Horibilis..............

Andy.

[yeti monster]

No, an annular horriblis! I'm busy rebuilding it the noo, new seals, heaps of epoxy filler and a new packing element. Also awaiting the arrival of the slotted body sleeve, which has had to undergo serious reconstruction, due to "them" attempting to force their tool through MY annular, using in excess of 20,000 lbs! They really should know better........ but they don't.

[acey]

Standard thing used to be a 35mm film cannister with a hole punched in the end (which is what I used before getting a cheshire). But film cannisters aren't as common now as they once were.