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Jonny

New 8" Skywatcher Dobsonian

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The dot should really be in the centre of the primary ring, if the hole in the canister its just a tint pinprick, try making it a little larger so its easier to see. Have you tried adjusting the primary yet?

I'm leaving the primary mirror alone until I have a vague idea of what to do. The online guides just dont seem to explain when/why I need to adjust the primary mirror. The thing is, the day I bought the scope I adjusted the secondary into position using alan keys, which means the secondary is aligned with the primary.... now the thing I don't understand is how tilting the primary mirror using the adjustment screws will have any effect on centralising the hole in the canister.

Anywho, I'll do some more reading and once it becomes clear i'll be able to have a go at it.

Another thing.... hen I do a star test, I don't see any rings around the star, just a fuzzy, stretched appearance, and it doesn't seem to focus into one point but does seem to focus into several points within itself.

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I'm leaving the primary mirror alone until I have a vague idea of what to do. The online guides just dont seem to explain when/why I need to adjust the primary mirror. The thing is, the day I bought the scope I adjusted the secondary into position using alan keys, which means the secondary is aligned with the primary.... now the thing I don't understand is how tilting the primary mirror using the adjustment screws will have any effect on centralising the hole in the canister.

Anywho, I'll do some more reading and once it becomes clear i'll be able to have a go at it.

Another thing.... hen I do a star test, I don't see any rings around the star, just a fuzzy, stretched appearance, and it doesn't seem to focus into one point but does seem to focus into several points within itself.

Hey Jonny,

I understand your fear of messing up the scope by trying collimation. I got a 8" Skywatcher Newt at Christmas and had never collimated a scope in my life. Its really really simple. All you do is slacken off the locking screws at the back and then adjust the other screws so the dot is centralised. It changes the tilt of the mirror. Its easier to look yourself and have someone else adjust it, I can reach two of the screws myself but not the third, so running back and forth is needed otherwise.

Dependinding on "f" aperture of your scope depends on how often you have to collimate it. (The lower the number the faster the scope and the more sensitive it is)

If I'm saying anything wrong here, the pro's will correct me, but I've collimated my scope 3 times since Dec25th(I travel to meet friends some nights) and the difference each time is noticable.

Go ahead and get your feet wet. You'll soon be doing it without thinking :D

Best of luck

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Hey Jonny,

I understand your fear of messing up the scope by trying collimation. I got a 8" Skywatcher Newt at Christmas and had never collimated a scope in my life. Its really really simple. All you do is slacken off the locking screws at the back and then adjust the other screws so the dot is centralised. It changes the tilt of the mirror. Its easier to look yourself and have someone else adjust it, I can reach two of the screws myself but not the third, so running back and forth is needed otherwise.

Dependinding on "f" aperture of your scope depends on how often you have to collimate it. (The lower the number the faster the scope and the more sensitive it is)

If I'm saying anything wrong here, the pro's will correct me, but I've collimated my scope 3 times since Dec25th(I travel to meet friends some nights) and the difference each time is noticable.

Go ahead and get your feet wet. You'll soon be doing it without thinking :D

Best of luck

Thanks,

The first thing I need to do, however, is fix this old film canister so that I can see the hole where my eye looks through in the reflection. At the moment, since my eye is there, there's no light hitting the hole and I therefore can't see it :/

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Thanks,

The first thing I need to do, however, is fix this old film canister so that I can see the hole where my eye looks through in the reflection. At the moment, since my eye is there, there's no light hitting the hole and I therefore can't see it :/

Yeah, that's a pain, I have to shine my mobile phone flash light up the focuser, just play around til you can see the peep hole.

I actually just collimated my scope, took less than 5 minutes. It's just getting used to which screw to adjust.

Don't hesitate to contact me if you're having issues.

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Hi Jonny, I know how you feel. I am completely new to this and collimating my scope scared the life out of me to be honest.

I don't know anyone into astronomy in my area who could help me out if I messed it up and it put me off for a while.

Mine was second hand and the views I was getting were great of the moon etc, but Jupiter etc were a bit fuzzy. I bought a Cheshire from FLO and collimated mine yesterday. I have to say the secondary was a real nightmare but once that was done the primary was really easy. I did a star test last night and was really pleased with the results. It does seem to be alot sharper now.

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Yeah, that's a pain, I have to shine my mobile phone flash light up the focuser, just play around til you can see the peep hole.

I actually just collimated my scope, took less than 5 minutes. It's just getting used to which screw to adjust.

Don't hesitate to contact me if you're having issues.

I just read somewhere on another forum to try and stick a metal washer underneath the eye-hole.... I've just done this and it worked a treat. I can now see how 'off' the eye-hole is from the centre of the mirror.

Here is a drawing of what it looks like....

http://img832.imageshack.us/img832/4113/telescopecoll.png

the size of the centre ring and the washer is a little exagerated.

You can see it's off slightly to the right.... not sure if this enough to create some of the images that I'm seeing, e.g stars that won't focus to a pinpoint, Planets being blurry and with a lot of red/blue on either side.

I will have a go at doing the primary mirror now.... on another note.. what happens when I fully unscrew the adjustment screws? will the mirror fall out of place?

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Primary Mirror now appears to be fully collimated. I unscrewed the 3 adjustment screws, wondering whether the mirror would fall out of its position or not. I then screwed them all in bit-by-bit until the centre of the mirror was in the centre of the metal washer.

It's cloudy now so I'll have to wait until tommorow to see if it has improved, and if it hasn't then I'll assume it's something to do with the optical quality of the mirror.

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Does everything now look centred through the cap you made? I noticed on you're last drawing that both the cap reflection and the primary centre ring were both over to the left, and yet your secondary looks to be in a good position. One thing to check is the cap you made, if you rotate it, does the eyepiece hole stay in the same position, if not, then the hole isn't in the centre of the canister. I am confident the optics will be fine and after spring the collimation issues you will be good to go.

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Just a quick question but where can you get hold of a film cannister these days?

Sent from my GT-I9100 using Tapatalk

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Not sure tbh, you can always make a small hole in the centre of the cap that comes with the 1.25 eyepiece holder, then just cover it with black insulation tape when you are not using it.

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Does everything now look centred through the cap you made? I noticed on you're last drawing that both the cap reflection and the primary centre ring were both over to the left, and yet your secondary looks to be in a good position. One thing to check is the cap you made, if you rotate it, does the eyepiece hole stay in the same position, if not, then the hole isn't in the centre of the canister. I am confident the optics will be fine and after spring the collimation issues you will be good to go.

Last night when I did it, everything looked perfectly centred, even when i swivelled the cap around. I've just checked it now and it appears to be off again. Which means I'll have to have another bash at it. I can't understand why it's gone like that, since it hasn't been knocked. The only 'knock' that it does get is when I take the cap off the scope.

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One thing to consider, if, like mine, your canister is plastic, then tightening the 2 screws can have an effect on the position of the cap, if you overtighten, then the cap will become a bit crushed, I am presuming you have the scope horizontal, just tighten the 2 screws just enough as to hold the cap. The other method of a little hole in the 1.25 holder also works a treat. your secondary looks about right, it is just figuring out why the little peep hole in the cap seems to be to the left of the view.

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The last drawing you did, you put in a little red arrow pointing to the washer, at the point underneath the point of the arrow, this is where the reflection of the peep hole should be roughly, then when you adjust the primary, the engraved ring should start to nerve towards the peep hole in the middle. I had mine in bits this afternoon trying to replicate your problem, but no matter what I do I cannot get the hole to the left without squishing the cap.

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The last drawing you did, you put in a little red arrow pointing to the washer, at the point underneath the point of the arrow, this is where the reflection of the peep hole should be roughly, then when you adjust the primary, the engraved ring should start to nerve towards the peep hole in the middle. I had mine in bits this afternoon trying to replicate your problem, but no matter what I do I cannot get the hole to the left without squishing the cap.

I sort of mis-drew itin that picture. I've done a more details picture of what I'm seeing.

http://img29.imageshack.us/img29/7931/telescopecol2.png

As you can see, the reflection of the secondary on the primary is slightly off.... not sure whether this is normal or not.

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Given that a hole made in a film canister is never going to be accurate like a Cheshire would be, your last drawing doesn't look half bad. I would wait for some clear sky now and try it again, if it looks a lot better then you can manage with this method until your funds allure for a Cheshire. now that you are familiar with adjusting the primary, when you do get it under the stars, see if you can centre polaris, this star will hardly move, if at all, get it centred and do some focusing/de-focusing, you can always tweak the primary while you are doing this star test. Look forward to hearing how you get on.

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Jonny, in the first post you mentioned that the main problem arose when you were using a 6mm EP with the scope. My 8" Skyliner didn't come with a 6mm, so can I ask what EP this is? Is it from your 3" scope?

(With my 8" dob I can see the GRS on Jupiter, Andromeda nebula clearly, Crab nebula faintly, and I'm looking through city centre LP with, ahem, 'lazy' collimation...

As already said, the 10mm is defintely worse quality than the 25mm, but still not awful.)

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Jonny, in the first post you mentioned that the main problem arose when you were using a 6mm EP with the scope. My 8" Skyliner didn't come with a 6mm, so can I ask what EP this is? Is it from your 3" scope?

(With my 8" dob I can see the GRS on Jupiter, Andromeda nebula clearly, Crab nebula faintly, and I'm looking through city centre LP with, ahem, 'lazy' collimation...

As already said, the 10mm is defintely worse quality than the 25mm, but still not awful.)

Yep. Not sure what make it is, but I kept it from my 3" scope.

It's not just the 6mm lense where the problem arises though. On the 25mm and 10mm lense it is sometimes hard to get a decent focus, and when you do it has red/blue on either side of the object you're looking at.

I haven't so far seen anything of Jupiter that I'd deem as brilliant, but I've seen more than I would from my 3" scope, as on the 3" scope I could barely make out any brown bands... whereas on this scope I can make out the brown bands, they're just too small/blurry to make out any proper detail.

Mars through the 25mm lense is very small but I can make out a tiny white patch that I assume is the polar cap. Higher zooms are blurry.

Jupiter looks something like this \/ using the 6mm lense.

http://img41.imageshack.us/img41/5429/telescopejup.png

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Mars through the 25mm lense is very small but I can make out a tiny white patch that I assume is the polar cap. Higher zooms are blurry.

I can get no detail from Mars at all - using either lens. You are doing better than me on that.

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I can get no detail from Mars at all - using either lens. You are doing better than me on that.

Video's like this:

leave me wondering if im doing the right thing. That video was taken through an 8 inch scope and yet it has 10x more detail than through mine. :/

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