I have tried collimating my telescope , a fast 8" Newtonian with a Cheshire eyepiece and find it fairly easy and accurate. However I find the cross hair at the end of the cheshires tube difficult to focus on and to obscure my view of the mirrors centre spot. This could be overcome to some extent if the crosshairs had a circular centre that you could look through.To try to solve the problem I took an old eyepiece , removed the lens and replaced the retaining ring to leave a small opening. This gave me a similar tool to a film canister collimator. I then painted the area inside the eyepiece around the hole and its supporting structures with luminous paint as shown by the first 3 pictures . This when exposed to a strong light provided a glowing cross with a centre circle and black dot ,see 3rd picture. When placed in the eyepiece the glowing cross and primary centre spot can be seen reflected in the mirror , see the 4th picture where the primary is just out of collimation. When the primary is adjusted the centre spot can be made to coincide with the centre of the glowing cross to achieve collimation , see the 5th picture. I have used this to collimate the primary mirror and get exactly the same result as with a conventional long tube cheshire , except its much easier to see collimation with my luminous tool. You can also check collimation in the dark after charging the luminous paint with a flashlight.
regards philip
ps The last 2 pictures were taken through the peephole
Last edited by 5ash; 19-01-2015 at 10:30 PM.
Reason: addition
Hi Michael ,
Glad you liked the concept its so "simple" and easily made from an old eyepiece. Bought the luminous paint on eBay from an Australian supplier , it's acrylic based so dries quickly. It stays glowing for quite a while depending on how long it's exposed to light. Have used it on a round tray attachéd to my observatory pier. Looks a bit like the controls of the " Tardis" when you first turn the lights off.
Regards philip
I have tried collimating my telescope , a fast 8" Newtonian with a Cheshire eyepiece and find it fairly easy and accurate. However I find the cross hair at the end of the cheshires tube difficult to focus on and to obscure my view of the mirrors centre spot. This could be overcome to some extent if the crosshairs had a circular centre that you could look through.
Hello Philip,
The cross-hairs of a typical sight-tube is meant to align the focuser axis with the primary mirror. That is why the secondary mirror is adjusted to align the cross-hairs with the primary center. In your case, the cross-hairs marked on the back of the eyepiece do not serve the same purpose.
Jason
Hi Jason,
My sight tube is aligning the optical axis of the primary mirror and the focusser. Alignment is achieved when the sight hole is aligned with the centre spot of the primary. The secondary has previously been aligned using a sight tube to ensure the mirror clips can be seen equally and the secondary looks circular.i have also used a web cam and Al's collimating aid to do the same. Whether I use a long tube Cheshire or the device being discussed I achieve the same collimation result.
Regards philip
Hi Jason,
The secondary has previously been aligned using a sight tube to ensure the mirror clips can be seen equally and the secondary looks circular
It sounds we are in agreement. I got the impression from your first post that the cross shape reference placed at the back of your eyepiece was meant to function as the cross-hairs of a sight-tube.
