which collimator for st80

[iwols]

hi all following a previous thread about my st80 guide scope which i need to collimate,just wondering which collimator would be best suited to the st80,bearing in mind i have an ed80 and sct8 edge as well thanks

https://www.firstlightoptics.com/other-collimation-tools/premium-cheshire-collimating-eyepiece.html  or

https://www.firstlightoptics.com/other-collimation-tools/baader-laser-collimator.html

i understand that the st80 has no form of adjustment really but you can in other ways

[Knighty2112]

Never had the need to collimate any of my ‘fracs. Not sure how you would do it on the ST80 lens cell end as you say there is no adjustment available, as I think the main problem would most likely be at the focuser end anyway unless you scope has been badly dropped and damaged the front end lens cell. 

[Stu]

I think @Ben the Ignorant may have done this?

[johninderby]

I have used a laser collimator in the focuser and a paper disc over the objective with the centre marked. That way you can see the red dot of the laser on the paper and adjust accordingly. Although as mentioned in this case adjustment will have to be made at the focuser. 

It will get collimation very close but should be fine tuned with a star test.

[happy-kat]

There is a youtube by Dion on the ST80 and checking collimation and how it might be adjusted if out.

[Adam J]

2 hours ago, iwols said:

hi all following a previous thread about my st80 guide scope which i need to collimate,just wondering which collimator would be best suited to the st80,bearing in mind i have an ed80 and sct8 edge as well thanks

https://www.firstlightoptics.com/other-collimation-tools/premium-cheshire-collimating-eyepiece.html  or

https://www.firstlightoptics.com/other-collimation-tools/baader-laser-collimator.html

i understand that the st80 has no form of adjustment really but you can in other ways

generally speaking refactors do not need colimation, is there something that makes you think that it is out of colimation? Is the main lens cell on the ST80 even adjustable?

[Ben the Ignorant]

After you have adjusted your focuser you can center the lenses as explained above. The method is a little crude but so is the ST80 ?.

Or you can take advantage of the ribs in the cell to install centering screws, as I did on my 80mm f/7.5 achro:

Only one lens needs screws, the other is kept motionless by shims. Since the front (convex) lens has a much narrower rim there is a risk the screw holes won't be exactly aligned with it, so it's prudent to simply shim it, and put the centering screws on the much broader concave lens' rim. Plastic is readily drilled and tapped.

After a while I modded the mod so the adjustment can be made from the outside, through the dewshield, thanks to 6mm knobs/screws I recovered from finders:

The only pic I had is this one with the solar filter attached. To collimate the lens, use very high power, at least 120x, and defocus to the point you see two or three rings around the central dot. Orient the scope so the screws are in an X pattern, and loosen the two top screws. Center the dot using the two bottom screws, and tighten the top screws gently. If the retainer ring or the lens spacers are not too tight the weight of the lens will provide the downward push while you have to take care of upward motion only.

But in case the lenses are tight, work on opposite screws simultaneously, tighten one while you loosen the opposite, or vice-versa. You still have only one axis to work on at a time, it's not more complicated, and it prevents slack. This is the optical collimation.

About the mechanical collimation, no need to buy a tool; I've seen they cost as much as an eyepiece! Draw a thick cross on white paper, and make a hole at the center. Arrange it like so, light the paper, and place your eye where the second flashlight is:

 

Looking through the hole you will see reflections of the cross:

Here the bigger cross is bloated because the camera was a little too close but pulling a few centimeters back makes it sharp. The reflections are much easier to see than to photograph.

[John]

I generally use a well collimated laser to check that the focuser optical axis is aligned with the objective optical axis (this is the 1st step). Once I am comfortable that the focuser does not need adjustment, I use a simple cheshire eyepiece to check the objective tilt. So two tools:

[Ben the Ignorant]

5 hours ago, Stu said:

I think @Ben the Ignorant may have done this?

Yup, you have good memory.

[iwols]

thanks guys for all the great answers appreciated?