Collimating in the dark

[spaceboy]

Hi All

How do members go about collimating in the dark. I find it hard enough to collimate in the day light despite being confident in the whole collimating process. I have to use paper behind the secondary and inside the ota to ensure good collimation as my eye gets so distracted by the primary reflection. My thinking is that light has to be shone down the objective but surely even the dullest of red torches is going to blow your night vision once it hits a parabolic mirror??

[nightfisher]

Im by no means an expert on collimation......................in fact far from it!

However it seems that once a secondary (little) mirror is well set, it is unlikely to shift and the primary is a simple 20 sec job, i would be happy to shine a light in prior to starting a session

[Owmuchonomy]

I have just got a Dob. I'm happy the secondary is aligned. My intention is to fine tune the primary in the dark using the de-focussed star technique and aligning the airey disk. I'm happy to be told otherwise by those much more experienced in the dark arts.

[cotterless45]

Simple, get a laser collimator, ensure that it's collimated. Insert it into a Barlow and ensure that your focuser is wound in. If collimated you should see the outline of your primary centre circle ( marker) on the collimator screen. Minor adjustments with the primary adjusters will make this dead reflection centre.

This is most useful in the dark, particularly with truss Dobs liable to flex. Apart from very high magnification of planets, most targets look good with collimation carried out before observing.

I took a 200Dob 160 miles down to the New Forest and it was only out by about 2mm. Unless you seriously drop or knock your ota, it should hold collimation. If tweaks are needed then it's just to the primary. This may be helped by fitting stronger primary springs, than those supplied ,especially with larger mirrors.

Night collimation by this method only takes a few seconds and is a good and quick check,

Nick.

[Moonshane]

It is a bit tricky to do the secondary but this is unlikely to be out and even then has hardly any effect. I do my primary with cheshire and dim torch.

[spaceboy]

Thanks guys.

[wookie1965]

As Moonshane as alluded use a Cheshire and shine a dim torch on the reflective surface of said Cheshire and collimation is a doddle.

[RikM]

As Moonshane as alluded use a Cheshire and shine a dim torch on the reflective surface of said Cheshire and collimation is a doddle.

I do the same.

[Paul73]

+1 for the "forget the secondary and shine your red light into the side of a Cheshire".

Paul