Collimation using collimation cap or star test?

[ian0138]

Hi,

Seeking opinion on collimating a 5" Maksutov scope.

I have been getting different result when checking collimation with collimation cap and by doing a star test.

I tried doing collimation with a collimation cap, but the star test would fail badly.

And if I collimate using a star test, then looking back into the collimation cap. It will be very off center.

Any idea why this would happen? and which is a better way to collimate the scope?

Thanks all

Cheers
IAN

[VinSnr]

Hi,

Seeking opinion on collimating a 5" Maksutov scope.

I have been getting different result when checking collimation with collimation cap and by doing a star test.

I tried doing collimation with a collimation cap, but the star test would fail badly.

And if I collimate using a star test, then looking back into the collimation cap. It will be very off center.

Any idea why this would happen? and which is a better way to collimate the scope?

Thanks all

Cheers
IAN

Use star test. You cannot use collimation cap with SCT and Mak. But refractors is ok.

[kayheem]

Vin is right. Use the star test for MCTs and SCTs.

Kay Heem

[VinSnr]

Hi,

Seeking opinion on collimating a 5" Maksutov scope.

I have been getting different result when checking collimation with collimation cap and by doing a star test.

I tried doing collimation with a collimation cap, but the star test would fail badly.

And if I collimate using a star test, then looking back into the collimation cap. It will be very off center.

Any idea why this would happen? and which is a better way to collimate the scope?

Thanks all

Cheers
IAN

Use star test. You cannot use collimation cap with SCT and Mak. But refractors is ok.

actually I want to correct my statement. You can't use collimation cap with refractors either. But you can use a cheshire tube with a cross hair at its end. Orion called that a Collimation eyepiece.

Collimation caps are used only for reflectors. You use it to check that the secondary is squared with the focuser.

[ian0138]

Thanks, then the orion instruction is very misleading, it even teaches how to make a collimation cap with a film cannister. No wonder both does not sync

Will use star test to check the collimation again but got to wait for clear sky.

Cheers.
IAN

[Canopus Lim]

Yup.. I tried using the orion collimation eyepiece to collimate my SCT but the star test shows that it is way off. The reason I think is because collimating SCT involve only adjusting the tilt of the secondary. Due to manufacturing, the primary mirror is probably off centred and tilted a bit. Hence by just using the geometric centre (by placing a small hole at the centre of the focuser tube, like in the cheshire eyepiece) will not give an accurate collimation. However, for the Newtonian, the secondary and primary mirrors can be adjusted so that the optical axis and geometric axis can be in line. The best collimation for all cases should be the star test.

[weixing]

Hi,
The below link got a description on how to do collimation of MCT in daylight: http://www.mira.org/ascc/pages/lectures/collim.htm

By the way, my own experience is that you need to put the star right at the center of the FoV when doing star test... The star test will show that the scope is out of collimation even if the star is slightly off center.

Have a nice day.

[ariefm71]

The below link got a description on how to do collimation of MCT in daylight: http://www.mira.org/ascc/pages/lectures/collim.htm

I thought chinese and meade maksutovs use aluminized spot on the back of the corrector lens for the secondary mirror? hence uncollimatable?

This is different from russion maksutovs (intes, intes micro, stf, etc) where both secondary and primary mirrors are collimatable.

[weixing]

Hi,

I thought chinese and meade maksutovs use aluminized spot on the back of the corrector lens for the secondary mirror? hence uncollimatable?

Most MCTs are "uncollimatable", but the primary mirror of the Sky-Watcher/Orion MCT can be collimated by adjusting the 3 sets of push-pull screw behind the MCT.

Have a nice day.

[kayheem]

The below link got a description on how to do collimation of MCT in daylight: http://www.mira.org/ascc/pages/lectures/collim.htm

I thought chinese and meade maksutovs use aluminized spot on the back of the corrector lens for the secondary mirror? hence uncollimatable?

This is different from russion maksutovs (intes, intes micro, stf, etc) where both secondary and primary mirrors are collimatable.

For those with SCTs and MCTs contemplating to use this daytime collimation method, my advise is *don't do it!*

Theoretically, this works if the primary and secondary mirrors are 'square' with each other and the optical axes are in line. Practically, it is not so simple. There have been many cases where the correction plate of SCTs are made a bit small and are not centred exactly. Doing the daytime method actually mis-collimates it. Do read the end of the article where the writer notes that the scope looks good on star test but appears off during the day time collimation method.

Also, don't use a laser collimator for SCTs and MCTs. Same reason as above.

Kay Heem