Help - collimation with a film container cap?

[Astrosurf]

I've heard you can collimate with a simple old film container cap (pics attached). I have one, but:

1. It's a bit loose, so how do I tighten it?

2. How do I drill the hole

3. How big should the hole be?

I'm not at work today so it would be nice to have a go rather than wait for a delivery of something dedicated to the task!

The reason why I want to collimate today is because I had a spot of bovver with an out-of-shape Mars last night and gave up. I know it was low and turbulence was bad but it looked odd (plus atmospheric refraction). Plus stars weren't round. See below. I know I had a little star trailing but you can see the distortion. It was most noticeable when the image was out-of-focus while I was focusing it.

Is this a collimation issue? My scope's not been knocked or anything. I hope it's not more serious!

Can I use the cap?

Alexxx

[Kedvenc]

To make a hole I used a red hot needle and made it about 2mm in diameter. Seems to be ok. I'm not sure about the tightness but need to make sure the hole is in the centre of the focusing tube when its attached.

[Thirdway]

You also need a Cheshire and sighting tube or laser. The cap only works to get the base setup right, you cannot really get the primary aligned without a Cheshire and sight tube.

[MikeD]

Use the can not the lid and a pin hole should be fine.

You can collimate with just this cap if you have a centre spot on the primary.

Mike.

[Astrosurf]

Thanks guys. I put a bit of tape at the end of the can, where the hole will be, so the thing won't fall into the OTA! How do you heat up a needle? Will a drill do?

[Merlin66]

Yes, go for the canister not the lid, a 1.5 to 2mm hole. It should slide nicely into the focuser. Not as sexy as the Cheshire but will do 99% of the job.

[Merlin66]

Yes you can use a small drill bit.

(BTW You can heat the needle in a gas flame - watch your fingers!)

[Astrosurf]

Excellent, thanks. So I can do the full job, secondary and primary, accurately with this?

Also, this looked an OK guide:

CosmicOne - Ultra Cheap Collimation Eyepiece

[dag123]

Another vote for using the canister, not the lid!

I saw many posts saying that using an old film canister would not do the job and so for a birthday present I requested a standard chesire from FLO. I am glad I did it this way as I have not really used the chesire since. Perhaps I did not give it a proper chance but it seems to take me much longer, mucking about with the chesire, then the canister.

I know a lot of others might disagree with this, but in my view if you just want to check the primary, get as close as you can with the film canister and then finish off with a star test.

dag123

[Merlin66]

On all my dobbie's 10" through to 18" the simple colli cap was all I used for fifteen years!

[Merlin]

I use an old, high-power, eyepiece with the lenses taken out. I find this better than a canister.

[Astrosurf]

Thanks guys. This is the view through the tube. Obviously without the collimation cap! I've aligned the camera as centrally as poss. Does it look like the primary is off?

[Merlin]

It looks off-centre to me. It's too far to the left and also pointing down.

[Astrosurf]

I've got the primary's collimation ring in the centre of the collimation cap, but I don't know how to move the mirror over to the right to get everything centred!

[Astrosurf]

It's OK. Astro-Baby's collimation guide said that fast scopes, like my F5, are offset, so this is aligned OK. Thanks Astro-Baby, you're brilliant!

Now I've done my first collimation and I'm well chuffed!

[Hypernova]

Looks near enough dead on, only thing is that you can't see the whole of the primary mirror which may just be the camera being slightly off-centre.

I've never use a simple colli-cap like this only ever using a Cheshire sight tube with crosshairs. I suppose it works in the same way by centring the doughnut with the pinhole's reflection, the crosshairs seem to be of little use as they are scewed to one side with the brass compression ring.

[DoctorD]

Hi

Just to go against te general view - I made my collimation cap by drilling a hole in the canister lid and then cutting the bottom off the canister.

This has the advantage of not dropping down the focuser tube.

HTH

Paul

[Quatermass]

Once upon a time I was going to get a lazer and a chesire then I read astrobabys webpage on colmination and just got an old film canister. heated up the end of a compass over the gas oven burner and used that to put the hole in. I have never used anything but that old film cap to colminate my scope does a great job.

[Tim]

Sounds like you are getting there Alex

[Astrosurf]

I did wonder about the mirror. How can I move it while it's still in the centre of the collimation cap??

[SeedyF]

Hi

Just to go against te general view - I made my collimation cap by drilling a hole in the canister lid and then cutting the bottom off the canister.

This has the advantage of not dropping down the focuser tube.

HTH

Paul

That's exactly what I did, it behaves just like an eyepiece in the tube. I drilled it with a 2mm drill bit. And it works like a dream

[kernowstargazer]

I found this the other day when i was looking into a cap to use for collimating 150p dob hope this helps Collimation Cap