Hi all,
Firstly, I would like to thank everyone who talked me out of getting a 10" scope as my first. I got the 8" and couldn't be happier and I'm quite glad I am not having to set up a scope which is about 6kg heavier (getting up near the weight of the NEQ6 mount head).
Now for my collimation question. How often do people normally have to collimate their Newtonian scopes? I am using a laser collimator and finding it's out every day, with the laser dot on the mirror 2-3cm out from the centre donut. I fix it as per instructions and next day the same thing.
I am very careful when setting up and packing up. The scope is stored overnight in the house upright with mirror facing down. To set up means carefully carrying a whole 10m to the backyard and mouthing it.
Is it normal to need collimation daily with such limited physical movement of the scope? If not, what could be wrong.
I check mine (same scope as yours) every time I go to use it, and its always the secondary that needs adjusting but only about 1mm (from the inner edge of the white ring to the centre).
If yours is moving 2 -3 cm make sure the secondary screws are tight and also check that the spider vanes are tight as well.
Also rotate the laser in the focuser draw in case it is causing the wide discrepancy, this is probably the main cause of your problem. The lasers do need collimating by sitting them in a V block and pointing at a wall and minimise the circle it draws while rotating the laser.
Adding to what Bill mentioned. Wind the focuser right in. Insert the laser and hold it flush against the focuser. Spin it around by hand slowly - does the beam stay centre or move around the primary in a circle? If it stays centre, tighten the fastening screw - does the beam move when you do this? Often, these lasers have quite a bit of play in the focuser.
For reasons above, a cheshire is often a better way of checking and setting alignment, unless you have a really good quality laser and already have your alignment close.
I got these instructions for laser collimation off CN but I can't remember his name, sorry.
Once you have the laser in a static position where it can only rotate, and not slide back and forth in any way then you can rotate it through 360 degrees . Number the laser collimation screws 1, 2 and 3 with a pencil (as this can write on the black tube) and then as you rotate mark the position of the spot on the wall when screw 1 is up, then 2 , then 3. Numbering the dots will help you work out which to adjust and which to slacken.
Next join the dots to form a triangle and then put a spot in the middle of this. Now adjust the screws to move the laser spot onto this. Once again rotate the laser to make the triangle, draw another centre spot and readjust again.
By doing this I managed to get a single spot when rotated within about 10 min’s and three "triangle" cycles.
Hands down the cheshire collimator is the way to go. You would be surprised how out collimation can be with a laser, well the cheaper ones anyway. I collimate my newton 8 inch f5 maybe every second use, they stay fairly in tune if treated with love.
I check mine (same scope as yours) every time I go to use it, and its always the secondary that needs adjusting but only about 1mm (from the inner edge of the white ring to the centre).
If yours is moving 2 -3 cm make sure the secondary screws are tight and also check that the spider vanes are tight as well.
Also rotate the laser in the focuser draw in case it is causing the wide discrepancy, this is probably the main cause of your problem. The lasers do need collimating by sitting them in a V block and pointing at a wall and minimise the circle it draws while rotating the laser.
Bill
Hi Bill,
My secondary is a bit loose and can be easily moved with minimum force. I was too scared tighten it up in case I broke something. So I can tighten the Philips head screw until the secondary can't be moved??
Thank you
Quote:
Originally Posted by Robh
Hi Mick,
Adding to what Bill mentioned. Wind the focuser right in. Insert the laser and hold it flush against the focuser. Spin it around by hand slowly - does the beam stay centre or move around the primary in a circle? If it stays centre, tighten the fastening screw - does the beam move when you do this? Often, these lasers have quite a bit of play in the focuser.
Regards, Rob
Thanks Rob, it does seem it moves a bit when spun around so I guess my laser needs collimating as well.
I was actually reading an article earlier today where the author believes newbies should not use laser collimators because much of the time it actually results in de-collimating a scope that was fine in the first place.
Thank you
Quote:
Originally Posted by RobF
For reasons above, a cheshire is often a better way of checking and setting alignment, unless you have a really good quality laser and already have your alignment close.
Sound like a plan. Thank you Rob.
Quote:
Originally Posted by billdan
I got these instructions for laser collimation off CN but I can't remember his name, sorry.
Once you have the laser in a static position where it can only rotate, and not slide back and forth in any way then you can rotate it through 360 degrees . Number the laser collimation screws 1, 2 and 3 with a pencil (as this can write on the black tube) and then as you rotate mark the position of the spot on the wall when screw 1 is up, then 2 , then 3. Numbering the dots will help you work out which to adjust and which to slacken.
Next join the dots to form a triangle and then put a spot in the middle of this. Now adjust the screws to move the laser spot onto this. Once again rotate the laser to make the triangle, draw another centre spot and readjust again.
By doing this I managed to get a single spot when rotated within about 10 min’s and three "triangle" cycles.
Thanks Bill, I will definitely have a go at this.
Quote:
Originally Posted by Cosmic
Hands down the cheshire collimator is the way to go. You would be surprised how out collimation can be with a laser, well the cheaper ones anyway. I collimate my newton 8 inch f5 maybe every second use, they stay fairly in tune if treated with love.
Thank you Daniel. I have a GSO collimator and not sure where it stands for quality. I think I will take the advice here and get a cheshire.
To everyone, I very much appreciate the help and advice
Cheers
Mick
There is usually a bit of give in Skywatcher focusers, so you're really just aiming to get it close in the "wobble position" your focuser would normally be in use. Whatever tool you use, its probably a worthwhile exercise man-handling the focuser assembly a little to see how far it affects things.
Arguably you could say any focuser wobble will magnify the difficulty of getting colimated well with a laser more so than a cheshire.
Most of this really didn't dawn on my until collimating using cateye tools. Realised pretty quickly my focuser was way down the quality scale compared to the catseye.
At F5 you've got a bit of give anyway. Very capable scopes 8" Skywatcher
There is usually a bit of give in Skywatcher focusers, so you're really just aiming to get it close in the "wobble position" your focuser would normally be in use. Whatever tool you use, its probably a worthwhile exercise man-handling the focuser assembly a little to see how far it affects things.
Arguably you could say any focuser wobble will magnify the difficulty of getting colimated well with a laser more so than a cheshire.
Most of this really didn't dawn on my until collimating using cateye tools. Realised pretty quickly my focuser was way down the quality scale compared to the catseye.
At F5 you've got a bit of give anyway. Very capable scopes 8" Skywatcher
Hi Rob,
Yes, my focuser has quite a bit of give in it when I checked after reading your post. The bit that is screwed on to the focuser tube (is it called nosepiece holder??)wasn't tight so tightening that helped a bit, but still some give.
I did the star test last night and my airy disk looked pretty good.
If you know the strengths and weaknesses of your gear you're 90% of the way there. If your airy disk inside and outside focus is good you must be pretty damned close.
I found my (8") Newt rarely needed collimating, even after long trips padded in blankets in the boot. Always a good idea to check, and experience over time with that process gives you and idea how far out you have to be before it affects viewing (or photography). Will depend too on tension on your secondary screws, springs/locking bolts on your primary, as well as focuser movement we talked about above.
If you know the strengths and weaknesses of your gear you're 90% of the way there. If your airy disk inside and outside focus is good you must be pretty damned close.
I found my (8") Newt rarely needed collimating, even after long trips padded in blankets in the boot. Always a good idea to check, and experience over time with that process gives you and idea how far out you have to be before it affects viewing (or photography). Will depend too on tension on your secondary screws, springs/locking bolts on your primary, as well as focuser movement we talked about above.
