Hi all,
I've had my little scope (76mm) for almost 6 months now... and I have never collimate it! Yeah I know I know ... but I didn't want to ruin it!
I'm now thinking it's time to make the big step (I have attached an image of how I see the 2 mirrors, so as you guys can tell me if it's time to collimate it - I think I already know the answer ).
So, just waiting for your advices in this important moment of my life lol. What do you think?
Cheers, Luis.
Last edited by DarkRevenge; 02-12-2010 at 11:57 AM.
You need to defocus a star and look at the patterns it displays. You should see a large white circle with a smaller black circle in the middle, with nice concentric rings going out from the edge of the black circle to the edge of the white circle.
Have a look at this picture for an example, the image on the left is a telescope that is well collimated, the picture on the right is a telescope with poor collimation.
Yes Luis, be a devil and throw caution to the wind! Have a go at adjusting the collimation! If it gets worse one way, you wind it back and go the other way - simple as that.
Che, viejo, mis hijos usan el mismo telescopio que tu.
There are two things you can do:
1, leave things as they are
2, make the most of a modest instrument to suck as much out of it as possible.
I would prefer No. 2. And it is not expensive.
You probably may have an old photo film canister with its lid. The Kodak ones fit perfectly into the 1.25" focuser. You can use this little canister to help collimate. Make a little hole (3 or 4mm) in both ends (bottom & lid) right in the centre. Insert the canister into the focuser and you will be able to gauge two things, how well centred the secondary mirror is (up and down and side to side), & if it is pointed in the right direction (rotation). Get the secondary right first, and the primary is even easier to work on. You can use the pictures Kal posted in his link to help fine tune even more. Total cost: $0.
I use one of these film canisters with my 17.5" scope! Nothing fancy and it works. I'm happy.
There are many threads here in IIS on collimation, and on the net. It is not hard and you will end up learning more, & be able to make the most of the gear you have too. If you would like more help, just ask, .
Yep, the film cannister does it for me too. It's all I ever used on my 10"dob. And when I got a mate to double check it with his laser collimator, it was spot on.
If the reflection of your eye doesn't sit dead center. Its time to adjust.
Adjust the screws on the main mirror first, then adjust the secondary. Repeat if necessary.
Thanks everyone for your replies!
First of all, I would like to apologize: I realized too late that I had made some terrible mistakes while writing. I wrote "now" instead of "know" (sounds similar in spanish).
Quote:
Originally Posted by multiweb
Hard to tell by looking at the shot. Have you stuck a cheshire or laser in it? There are various way of checking this if you search those forums.
Hi Marc. Unfortunately I don't have any of these tools. I looked for a laser in a shop near my home and it's a bit expensive (in fact it was almost the price of my scope ). So I think I should wait until I owned a better scope to buy it.
Quote:
Originally Posted by Kal
You can't tell by taking a photo of the mirrors.
You need to defocus a star and look at the patterns it displays. You should see a large white circle with a smaller black circle in the middle, with nice concentric rings going out from the edge of the black circle to the edge of the white circle.
Have a look at this picture for an example, the image on the left is a telescope that is well collimated, the picture on the right is a telescope with poor collimation.
Hi Andrew. I've heard about that method you mention there, I'll try it as soon as I can take the scope out.
Thanks for the info
Quote:
Originally Posted by erick
Yes Luis, be a devil and throw caution to the wind! Have a go at adjusting the collimation! If it gets worse one way, you wind it back and go the other way - simple as that.
Thanks for that words Eric I have always been a very cautious person (something good or bad?) so it'll be difficult to do what you say! But of course I'll try
Quote:
Originally Posted by mental4astro
Che, viejo, mis hijos usan el mismo telescopio que tu.
There are two things you can do:
1, leave things as they are
2, make the most of a modest instrument to suck as much out of it as possible.
I would prefer No. 2. And it is not expensive.
You probably may have an old photo film canister with its lid. The Kodak ones fit perfectly into the 1.25" focuser. You can use this little canister to help collimate. Make a little hole (3 or 4mm) in both ends (bottom & lid) right in the centre. Insert the canister into the focuser and you will be able to gauge two things, how well centred the secondary mirror is (up and down and side to side), & if it is pointed in the right direction (rotation). Get the secondary right first, and the primary is even easier to work on. You can use the pictures Kal posted in his link to help fine tune even more. Total cost: $0.
I use one of these film canisters with my 17.5" scope! Nothing fancy and it works. I'm happy.
There are many threads here in IIS on collimation, and on the net. It is not hard and you will end up learning more, & be able to make the most of the gear you have too. If you would like more help, just ask, .
Hi Alex. I must say I really enjoyed reading your post (love that final sentence lol).
I choose the second option of course
It's a really good idea what you mention there. I'll definetely try it (as soon as I find a photo film canister - I used to have two or three but I don't remember where I put them).
Thanks a lot for that
Quote:
Originally Posted by jjjnettie
Yep, the film cannister does it for me too. It's all I ever used on my 10"dob. And when I got a mate to double check it with his laser collimator, it was spot on.
If the reflection of your eye doesn't sit dead center. Its time to adjust.
Adjust the screws on the main mirror first, then adjust the secondary. Repeat if necessary.
Hi Jjj. Thanks for sharing that. If it works with a 17.5" and a 10" dob, it must work with mine too It's nice to know that!
Well, I think the answer is yes! If you have something like the Celestron 76mm, 700mm focal length Powerseeker reflector, it is an f9.2 (focal ratio). The 'sweet spot' for an f9.2 is somewhere around 15mm (haven't got the exact figure to hand). This means that as long as your collimation is somewhere within a 15mm diameter of the centre then your viewing will be the same as if it was perfectly collimated.
If your f ratio is less, then collimation becomes much more important - for instance an f4 reflector (of any size) has a tiny sweet spot of just 1.4mm diameter!
So do it once for peace of mind, and you'll probably never have to worry about it again!
I have a 76mm reflector that I collimated just the other day.
The Primary, it was jammed tight in place so I had to loosen the screws first and pushed the mirror up a little bit with my fingers. Then I tightened to screws to suit. The secondary was easier to adjust.
Hi all,
Thanks a lot for all your responses!
Here's what I've decided to do: Next month I'm buying a new scope (130/900) for which I've been saving money for some months. If I have the 130mm at my house, I'll feel free to try to collimate the 76mm scope - without fear! lol. I can even try to disassemble it and then reassemble it again (as Geoff has said). It'll be like a training. What do you think guys?
Thanks again for taking the time to answer.
Cheers, Luis.
Last edited by DarkRevenge; 13-12-2010 at 04:04 AM.
... but I didn't want to ruin it! 
). 
.
). So I think I should wait until I owned a better scope to buy it.
I have always been a very cautious person (something good or bad?) so it'll be difficult to do what you say! But of course I'll try 
