davidpretorius
16-11-2005, 04:41 PM
Part III is a short one due to the fact that it has already been bought up.
One night at star camp, i asked the crowd "what is the next biggest step in getting the imaging process right" You could see bird's brain ticking over and i thought he was about to say "seeing, camera, processing". Bird basically said "controlling the temperature is one of the biggest single improvements he has made in his imaging"
Rewinding back a few days and we were starting to collimate our scopes "properly" for the first time. At the end of the day, it comes down to this.
Be confident but take precautions as you must be able to take your primary mirror out of the base and centre spot it with a binder ring. A black spot is fine like mine, but it is harder to see, so I would always recommend a binder ring. Think it all through. There would be nothing worse than adjusting your secondary and having it drop down onto the primary!!!!
Having centre spotted your primary, then the next step is to tighten up the clips holding the primary so that they are only just finger tight and then get your secondary set up. A sight tube is the best and really the only way. You want a nice long tube so that when you are looking at the secondary mirror, you want to make sure that your eye can't move side to side and thus adjust where you think the secondary mirror is centred. I have a $29 cheshire, but i cannot be more than 75% certain that my secondary is centred properly.
Once the secondary has been adjusted, then it is time to adjust the primary. I believe that this is a two step process:
In daylight, you adjust the primary so that the centre spot is lined up with your cheshire. Here you can have differences. My $29 cheshire was out, when compared to the more expensive cheshires and thus i have to allow an offset.
At night with a star test, or in daylight with a laser, you fine tune the collimation. My biggest mistake here was to try and get the diffraction rings so commonly shown in collimation articles. Firstly choose a brightish star near the zenith and take out of focus. You must do your star test when the star is in the middle of the field of view. You then adjust the primary. This is always done best with two people. Now to my mistake: unless the seeing conditions are very very good, then you won't see diffraction rings.
This is the basic collimation process, now how does temperature affect it. We are all told "cool your scope". Yes, cool your scope and larger eyepieces so that everything is the same temperature. Then there should be no air currents formed by temperature differences to affect your viewing. The biggest thing I found out was that if the temperature drops during the night quite quickly, then you are back to square one!!!! Wait another 1/2 hour!!!!
Do not collimate or think your scope may be out of collimation unless the temperature has been steady for at least 1/2 hour. Come back and have another look and see if the viewing has picked up due to steady temperatures. Most of the guys comment that early morning is the best time to view and that is because the temperature during the night is as low as it will get and thus steady!!!
Birds elaborate temperature controlling systme is not for the fun of it and I may have secretly giggled initially, but as he said "It is one of the most important factors" and "He is spot on"
A quick example:- Here is me one night at star camp with a newly collimated scope and my $150 ultrawide 82 degree 30mm looking at orion. Along comes john with his 32mm Televue ultra wide (version before the panoptic). "Look at this view mate" says John. I am shaking with anticipation and so grateful that John is sharing his very expensive eyepiece in my scope. Earlier in the night I was so happy with how sharp the stars were once i had got properly collimated. John puts the eyepiece in and I would have to say, that the view was no different!!!!
John then has a look and says the same. Hmmmm, it must be out of collimation.......so we start the process of collimation......"hang on" yells bird, "the temp has fallen 1 degree in the last few minutes".
A very expensive eyepiece has been made to look bad, mistakenly taken for out of collimation by a falling temp!!!!.
By the way, the expensive eyepieces did look good thru my scope, but that is a later part.
Next: Observing Summary.
One night at star camp, i asked the crowd "what is the next biggest step in getting the imaging process right" You could see bird's brain ticking over and i thought he was about to say "seeing, camera, processing". Bird basically said "controlling the temperature is one of the biggest single improvements he has made in his imaging"
Rewinding back a few days and we were starting to collimate our scopes "properly" for the first time. At the end of the day, it comes down to this.
Be confident but take precautions as you must be able to take your primary mirror out of the base and centre spot it with a binder ring. A black spot is fine like mine, but it is harder to see, so I would always recommend a binder ring. Think it all through. There would be nothing worse than adjusting your secondary and having it drop down onto the primary!!!!
Having centre spotted your primary, then the next step is to tighten up the clips holding the primary so that they are only just finger tight and then get your secondary set up. A sight tube is the best and really the only way. You want a nice long tube so that when you are looking at the secondary mirror, you want to make sure that your eye can't move side to side and thus adjust where you think the secondary mirror is centred. I have a $29 cheshire, but i cannot be more than 75% certain that my secondary is centred properly.
Once the secondary has been adjusted, then it is time to adjust the primary. I believe that this is a two step process:
In daylight, you adjust the primary so that the centre spot is lined up with your cheshire. Here you can have differences. My $29 cheshire was out, when compared to the more expensive cheshires and thus i have to allow an offset.
At night with a star test, or in daylight with a laser, you fine tune the collimation. My biggest mistake here was to try and get the diffraction rings so commonly shown in collimation articles. Firstly choose a brightish star near the zenith and take out of focus. You must do your star test when the star is in the middle of the field of view. You then adjust the primary. This is always done best with two people. Now to my mistake: unless the seeing conditions are very very good, then you won't see diffraction rings.
This is the basic collimation process, now how does temperature affect it. We are all told "cool your scope". Yes, cool your scope and larger eyepieces so that everything is the same temperature. Then there should be no air currents formed by temperature differences to affect your viewing. The biggest thing I found out was that if the temperature drops during the night quite quickly, then you are back to square one!!!! Wait another 1/2 hour!!!!
Do not collimate or think your scope may be out of collimation unless the temperature has been steady for at least 1/2 hour. Come back and have another look and see if the viewing has picked up due to steady temperatures. Most of the guys comment that early morning is the best time to view and that is because the temperature during the night is as low as it will get and thus steady!!!
Birds elaborate temperature controlling systme is not for the fun of it and I may have secretly giggled initially, but as he said "It is one of the most important factors" and "He is spot on"
A quick example:- Here is me one night at star camp with a newly collimated scope and my $150 ultrawide 82 degree 30mm looking at orion. Along comes john with his 32mm Televue ultra wide (version before the panoptic). "Look at this view mate" says John. I am shaking with anticipation and so grateful that John is sharing his very expensive eyepiece in my scope. Earlier in the night I was so happy with how sharp the stars were once i had got properly collimated. John puts the eyepiece in and I would have to say, that the view was no different!!!!
John then has a look and says the same. Hmmmm, it must be out of collimation.......so we start the process of collimation......"hang on" yells bird, "the temp has fallen 1 degree in the last few minutes".
A very expensive eyepiece has been made to look bad, mistakenly taken for out of collimation by a falling temp!!!!.
By the way, the expensive eyepieces did look good thru my scope, but that is a later part.
Next: Observing Summary.