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Had an idea for easy field collimation for Dobs

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#1 SpaceRooster

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Posted 11 January 2013 - 06:16 PM

I was thinking to myself earlier about the difficulty of collimating dobs in the field without nuking everyone elses night vision, when I had a bit of a revelation. Has anyone tried coating the inside of their telescope caps with illuminescent material? All you would have to do to collimate would be to shine light onto the inside of the cap till it is bright enough to see in the mirror, and then pop the cap back on the end of the tube and viola, you have a bright surface almost the exact size of your mirror shining just enough light to collimate without having to use any flashlights that bother other astronomers nearby. This also turns your dust cap into a multipurpose collimation tool. Good idea, bad idea?

#2 Jon Isaacs

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Posted 11 January 2013 - 07:35 PM

Good idea, bad idea?



I don't know.. I can't imagine it would be bright enough, it would be worth a try.

I use a laser...

Jon

#3 Jason D

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Posted 11 January 2013 - 08:33 PM

... and viola


:question:

What about the primary mirror center spot?
What you have described will allow you to see the reflection of the bottom of the collimation cap. What are you going to align it against?
Jason

#4 SpaceRooster

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Posted 11 January 2013 - 08:44 PM

... and viola


:question:

What about the primary mirror center spot?
What you have described will allow you to see the reflection of the bottom of the collimation cap. What are you going to align it against?
Jason


Not sure I follow your question. If you have light coming in that covers the entire aperture of the tube, it is the same as looking at a lit white wall. The center dot would show up just the same.

#5 Jason D

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Posted 11 January 2013 - 09:29 PM

If you have light coming in that covers the entire aperture of the tube

I thought you were only going to illuminate the bottom of the collimation cap before starting the collimation procedure without any addition light source. Did I misunderstand?

#6 CosmoSat

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Posted 12 January 2013 - 03:23 AM

If you have light coming in that covers the entire aperture of the tube

I thought you were only going to illuminate the bottom of the collimation cap before starting the collimation procedure without any addition light source. Did I misunderstand?


Guess he meant illuminate the inside of the telescope tubes front aperture cover.

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#7 Jason D

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Posted 12 January 2013 - 03:46 AM

Oh, now I understand what the OP was trying to say. I do not believe the idea will work.

#8 Ty Williams

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Posted 12 January 2013 - 04:10 AM

Oh, now I understand what the OP was trying to say. I do not believe the idea will work.

Why not? Isn't it substantively similar to pointing the scope at a white wall during the day?

#9 Jon Isaacs

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Posted 12 January 2013 - 06:58 AM

Oh, now I understand what the OP was trying to say. I do not believe the idea will work.

Why not? Isn't it substantively similar to pointing the scope at a white wall during the day?


What tools are you using?

My intuition is that it will not be bright enough but you should try it and see how it works. The center dot is in the shadow of the secondary but I think that will only be a minor problem.

Jon

#10 Jason D

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Posted 12 January 2013 - 10:59 AM

Why not? Isn't it substantively similar to pointing the scope at a white wall during the day?


I do not believe there will be enough brightness as Jon mentioned.
But why not use a laser or a red LED clip-on? Both if used properly will not produce enough brightness to bother the user or others.
Besides, wouldn't someone need to apply a very bright light at the bottom of the cover first? I believe that bright light might cause more harm to night vision to the user and others.
The OP asked a question whether it is a good or bad idea. My opinion is that it is not a practical idea but this is my opinion. Anyone can try it and present results. If the results look encouraging I will be the first to admit I was wrong.

Jason

#11 howard929

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Posted 12 January 2013 - 11:02 AM

Wouldn't any of the various methods available for a barlowed laser collimation eliminate those concerns and be more accurate?

#12 Pharquart

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Posted 12 January 2013 - 11:43 AM

Isn't it substantively similar to pointing the scope at a white wall during the day?


Maybe I missed this lesson, but how do you collimate by pointing at a white wall during the day? Is this just to get enough illumination to use a Cheshire or collimation cap?

Brian

#13 Ty Williams

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Posted 12 January 2013 - 03:24 PM

Maybe I missed this lesson, but how do you collimate by pointing at a white wall during the day? Is this just to get enough illumination to use a Cheshire or collimation cap?

Correct, it's just for a nice big illumination source to use with other tools.

I do not believe there will be enough brightness as Jon mentioned.

From the OP's post, I got the impression that he wanted to line the inside of the aperture plug with electroluminescent material. EL sheets can vary from quite dim to quite bright. By placing the cap onto the scope first, then flipping the switch, there's no danger of "flashing" other observers. By filling the entire cap, you should have no problem with the secondary shadowing the center mark.

Unfortunately, a 12" diameter sheet of EL material plus the igniter to run it is priced out of "shot in the dark experiment" range for me.

But why not use a laser or a red LED clip-on? Both if used properly will not produce enough brightness to bother the user or others.

They're certainly functional, I just find clip on lights fussy. It always annoys me to try to find a position for them that illuminates the stuff that needs illumination without blinding myself with the light at the same time.

#14 Bill Weir

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Posted 12 January 2013 - 03:27 PM

So if I read this correctly the OP is wanting to coat the tube end cover with a phosphorescent material to create a glow within the tube so he/she can then collimate in the field by putting the end cap on. That way he/she (although I'm now guessing he's a he because of the word "Rooster") won't have to bother others with light. I have just one question to this idea. How are you going to activate this phosphorescent material? Whenever I've dealt with glow in the dark toys light is required in the first place.

To me this seems like trying to reinvent the wheel. I bought a good barlowed laser system and never bother anyone. In fact I'm the one who is bothered (not really) when others want to borrow my laser.

Bill

#15 SpaceRooster

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Posted 14 January 2013 - 09:34 AM

You guys have the right idea. Coat the tube cap, then apply light to get it bright enough to collimate. From what I have read, many are not so fond of laser collimaters as they must be collimated themselves. I figured this would be a decent alternative if it works.

As for the light required to get it bright enough, yes you have to apply light to it to work, but it is light that you can conceal. It can also be a very brief, bright flash, such as a camera flash. If you have the cap under something opaque such as a blanket or something of the sort, you could flash it and get to collimating very quickly without disturbing anyone.

As for what tools are required, just your tube cab and collimation cap as normal.






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