I received the laser collimator and the Cheshire collimator a couple of days ago. Both were in excellent shape and well worth the money I paid for them.
Now - the bad news...
I used the laser collimator to check the initial alignment of the Primary and Secondary mirrors and found out the eye piece focuser assembly is not aligned properly with the optical path within the telescope tube. Seems time, heat and humidity have conspired to change the cardboard tube of the telescope to offset the focuser towards one side of the scope tube - now I have to figure out how to correct this offset with the current focuser (which is not the best in the world) or purchase a better focuser for the beast! I may opt for the later. It appears the focuser is not perpendicular to the secondary mirror any longer - about 2-3 degrees off which is more than enough to cause alignment issues! For you to get the best images from a telescope you MUST have the optical path aligned pretty much DNO (dead nuts on).
A second observation - it looks like the primary mirror is "shifted" to towards one side of the telescope tube. The interesting part is the mirror is mounted to a particleboard plate using RTV which does not normal do such things so I must have offset mounted the mirror when the mirror was re-coated. DUH - this will play havac with not only the optical alignment but also the visual observations through the telescope in terms of secondary mirror refraction (not centered will cause side-ghosts - duplicate images that can not be focused to a single image, which is what I am observing in the scope now).
Not only did the laser collimator "show" these problems the Cheshire collimator confirmed the problems as I can not get the alignment correct without being "offset" in the secondary mirror images to get the Cheshire images "close" to where they should be - and I observe one "side" of the telescope tube where I would normally not see the tube side (primary mirror offset is causing this).
Before I can align this beast I have to fix the above listed issues...
Now I have to decide if I want to continue using the current Dobsonian-style mount or construct a different one - decisions, decisions!
More to follow - stay tuned!
Thursday, November 13, 2008
Sunday, November 2, 2008
Telescope Mirror Alignment
Alignment of the telescope's optics...
All Newtonian telescopes require alignment of the Primary and Secondary mirrors to the optical path for the best resolution of the image. Wow - that is sure a "simplistic" sentence which contains all sorts of implications! There are over six (6) variables I can identify which affect the alignment of the telescopes optics. This means there are six different adjustments, some of which interplay with each other, that directly affect the alignment of the optical path within the telescope.
Most of the instructions I have found to perform the alignment mention one of two popular methods. Several of the instructions actually mention using both methods to insure a proper alignment of the optics within the telescope. These methods are Laser collimation and Cheshire collimation. As it's name implies the Laser collimation method utilizes a laser beam to align the optics within the telescope. You place the laser collimator device in the eyepiece holder on the telescope then adjust the secondary mirror so the laser beam is striking directly in the center of the primarey mirror - then you adjust the primary mirror so the laser beam is reflected back to the eyepiece holder by way of the secondary mirror with the reflected laser beam striking the laster beam source. Sounds easy enough - you just have to "have" a laser collimator.
Building a laser collimator - or - Efforts in Total Frustration!
One would think building a laser collimator would be a simple thing to do - get a laser pointer and mount it in something to hold it within the eyepiece mount then align the telescope mirror....
Well....
Not so simple after all!
I have three laser pointers, two are the type used for presentations and one is built into a LED flashlight. After playing with all three I have determined NONE of them are aligned with the housing containing the laser diode! Normally, you would not notice such a discrepancy since you are using the pointer to point to something and you adjust for the "error" visually while highlighting whatever it is you are highlighting. This is NOT the case when you are using the laser pointer as a reference itself.
Compounding the issue is the pointer casing is much smaller in diameter than the telescope's 1.25-inch optics mount tube so you have to come up with "something" to not only mount the laser pointer in, but also make it adjustable to "correct" for the mis-alignment of the laser diode's mounting within the pointer housing itself. After checking hardware stores I have determined there is really nothing available for use as a mounting tube of the correct diameter. The closest I came was a piece of PVC tubing for 1-inch coupling - it is about 2 or 3 millimeters larger than the optics tube on the telescope but I do not have anything to turn the diameter down and maintain the parallelism of the tube so that is not a choice either. I can hear others saying "use a drill press and sandpaper"! That may or may not work! You really NEED to maintain the critical diameter so the laser collimator tube fits correctly within the optics mounting tube or you will introduce an error and you will not get the optical path collimated correctly - this manifests itself as a "smeared" image that will not focus correctly! I learned that the hard way!
My final solution? I ordered a laser collimator from a website on the web (grin) so as to remove all the headaches associated with attempts to fabricate one! Money well spent since I will need to collimate the telescope each time I move it around, which is every time I use it, and I have a second six (6) inch Newtonian telescope that will need the same collimation as well.
Cheshire Collimation Tool...
Well - after a couple of days attempting to build a Telescope Optics Alignment Tool and using it to align the primary and secondary mirrors I have come to the conclusion I do not have the required tooling to build such a device. On the surface it appears to be a very easy-to-construct device, cross-hair in one end, a hole in the side with a 45-deg reflector piece (that also has a hole in the center) and an end-cap with a hole in the center. I am afraid a hand drill just is not stable enough to drill the required holes and I have not been able to find anything that is 1.25-inches in diameter to fit correctly within the telescopes optics tube (the same problem as described earlier)!
Again - my "solution" was simple - Throw some money at the problem! I went on E-Bay and found a Cheshire collimator there for a very reasonable price and have placed a bid on it. Hopefully I will Win the bid and get the collimator, and if not, I will order one from the same location I purchased the laser collimator (grin).
Now I wait for the collimator hardware to arrive!!!
More to follow...
gm...
All Newtonian telescopes require alignment of the Primary and Secondary mirrors to the optical path for the best resolution of the image. Wow - that is sure a "simplistic" sentence which contains all sorts of implications! There are over six (6) variables I can identify which affect the alignment of the telescopes optics. This means there are six different adjustments, some of which interplay with each other, that directly affect the alignment of the optical path within the telescope.
Most of the instructions I have found to perform the alignment mention one of two popular methods. Several of the instructions actually mention using both methods to insure a proper alignment of the optics within the telescope. These methods are Laser collimation and Cheshire collimation. As it's name implies the Laser collimation method utilizes a laser beam to align the optics within the telescope. You place the laser collimator device in the eyepiece holder on the telescope then adjust the secondary mirror so the laser beam is striking directly in the center of the primarey mirror - then you adjust the primary mirror so the laser beam is reflected back to the eyepiece holder by way of the secondary mirror with the reflected laser beam striking the laster beam source. Sounds easy enough - you just have to "have" a laser collimator.
Building a laser collimator - or - Efforts in Total Frustration!
One would think building a laser collimator would be a simple thing to do - get a laser pointer and mount it in something to hold it within the eyepiece mount then align the telescope mirror....
Well....
Not so simple after all!
I have three laser pointers, two are the type used for presentations and one is built into a LED flashlight. After playing with all three I have determined NONE of them are aligned with the housing containing the laser diode! Normally, you would not notice such a discrepancy since you are using the pointer to point to something and you adjust for the "error" visually while highlighting whatever it is you are highlighting. This is NOT the case when you are using the laser pointer as a reference itself.
Compounding the issue is the pointer casing is much smaller in diameter than the telescope's 1.25-inch optics mount tube so you have to come up with "something" to not only mount the laser pointer in, but also make it adjustable to "correct" for the mis-alignment of the laser diode's mounting within the pointer housing itself. After checking hardware stores I have determined there is really nothing available for use as a mounting tube of the correct diameter. The closest I came was a piece of PVC tubing for 1-inch coupling - it is about 2 or 3 millimeters larger than the optics tube on the telescope but I do not have anything to turn the diameter down and maintain the parallelism of the tube so that is not a choice either. I can hear others saying "use a drill press and sandpaper"! That may or may not work! You really NEED to maintain the critical diameter so the laser collimator tube fits correctly within the optics mounting tube or you will introduce an error and you will not get the optical path collimated correctly - this manifests itself as a "smeared" image that will not focus correctly! I learned that the hard way!
My final solution? I ordered a laser collimator from a website on the web (grin) so as to remove all the headaches associated with attempts to fabricate one! Money well spent since I will need to collimate the telescope each time I move it around, which is every time I use it, and I have a second six (6) inch Newtonian telescope that will need the same collimation as well.
Cheshire Collimation Tool...
Well - after a couple of days attempting to build a Telescope Optics Alignment Tool and using it to align the primary and secondary mirrors I have come to the conclusion I do not have the required tooling to build such a device. On the surface it appears to be a very easy-to-construct device, cross-hair in one end, a hole in the side with a 45-deg reflector piece (that also has a hole in the center) and an end-cap with a hole in the center. I am afraid a hand drill just is not stable enough to drill the required holes and I have not been able to find anything that is 1.25-inches in diameter to fit correctly within the telescopes optics tube (the same problem as described earlier)!
Again - my "solution" was simple - Throw some money at the problem! I went on E-Bay and found a Cheshire collimator there for a very reasonable price and have placed a bid on it. Hopefully I will Win the bid and get the collimator, and if not, I will order one from the same location I purchased the laser collimator (grin).
Now I wait for the collimator hardware to arrive!!!
More to follow...
gm...
Friday, October 31, 2008
Cleaning the Mirrors...
Both the Primary and Secondary mirrors on the telescope were not in the best of shape.
The telescope tube was stored in an outside metal shed for several years and even though I thought the tube openings were closed off both spiders and roaches found their way to the inside of the telescope! Seems both of these bugs have no problems finding ways into perfectly sealed enclosures.
The spiders had a field day creating all sorts of webs across the primary mirror surface and the secondary mirror was a great place for them to attach their webs - too bad for them other bugs did not find their way into the telescope tube so the spiders simply starved to death - too bad!
The roaches, on the other hand made a bigger mess - they too did not find much in the way of food so promptly just died on the primary mirror surface. Of course, since the telescope tube was stored in the vertical position as there are rubber feet on the primary mirror back-plate at the end of the telescope tube put there for just this purpose, the roaches had not problem staying on the primary mirror surface after they died. This is where they decomposed!
As you can imagine - there was a pretty good "mess" on the primary mirror surface. Thankfully, about nine (9) years ago, I had the primary and secondary mirror surfaces re-surfaced by a local shop (http://www.spectrum-coatings.com) who did an excellent job of putting a new enhanced aluminum surface coat and a silicon dioxide (Quartz) surface coat on the mirrors! This re-coating actually protected the surface of the mirrors since the quartz coating acted to protect the enhanced aluminum surface coat and I only had to do a cleaning on the mirrors to restore them to a clean condition.
NOTE: If you need mirrors re-coated I would HIGHLY recommend Spectrum Coatings for the task! They have developed a very good method of recoating mirrors and the added step of depositing a quartz coating on top of the enhanced aluminum coating really does an excellent job of protecting the reflective surface with very very little loss in efficiency or reflection! Check out their site as they have some information and test data on the process they use! They can handle Primary mirrors up to 32-inches in size and their coating technique is the best in the business, and their prices are very very reasonable too! Tell Paul I sent ya - it won't get me anything but I am sure Paul would like to know where you found out (grin).
The technique I used to clean the mirrors was really very simple. There are a good number of ways to clean telescope mirrors but the technique I use is a little different from most. I use a combination of Windex (yep - good ole fashion window cleaner) and HDTV Screen cleaner. The only place I have found (to date) for the cleaning spray is in a Kit for HDTVs -Buy.com carries the kit (http://www.buy.com/prod/belkin-hdtv-essentials-kit-includes-hdmi-cable-surge-protector/q/loc/111/204871868.html) but it contains not only the cleaning spray but also an HDMI cable, surge protection power strip along with the cleaning cloth that comes with the cleaner. I have not located a place to just get the cleaning spray and cloth but since I do have an HDTV it was not an issue for me (grin). Be sure to get the cleaning cloth as it is specially designed to be lintless and not scratch! Very important, especially the "not scratch" part!
First I wet the mirror surface with the Windex and let it stand for at least five (5) minutes to loosen any surface dust, dirt, lint, bugs or what-not... DO NOT rub the surface to remove anything and do not allow the Windex to dry on the surface of the mirror. Rubbing on the mirror at this point would be a great way to scratch the mirror surface from the foreign matter on the surface! Let the Windex do all the work and if there is still something sticking to the surface just apply a second coat of Windex after draining off the first coat.
I usually drain the Windex off the surface and wet the surface again with Windex to make sure most all of the foreign surface contamination has been cleaned off the surface of the mirror.
After the second cleaning I drain off the Windex then wash the surface off with water (best to use distilled so as not to add any dissolved contaminates to the surface of the mirror). After this step I use the HDTV screen cleaner with the lintless cloth to VERY LIGHTLY clean the mirror surface - this step should be performed with care so as not to scratch the mirror surface.
Once I am happy with the screen cleaner step I wash the mirror off with distilled water (again) then use 99% Isopropol alcohol (available at hardware stores as lacquer thinner, I believe) to rinse the mirror surface (this removes any water film left) and drain the alcohol off one end of the mirror - you can remove any droplets left with a SOFT lintless cloth - blot, do not rub!!!
Performing the above cleaning on the Primary and Secondary mirrors of the telescope restored the mirrors back to a VERY clean state - that is a GOOD THING (tm) for the purposes of obtaining the best possible images through the telescope.
Of course all of the above steps required removing the mirrors from the telescope tube - and completely destroys any previous alignment of the telescope's optics. The next step will be to install the mirrors back into the telescope tube then perform an optical alignment of the mirrors.
First - I have to make a collamating tool to use during the alignment process - one tool I need to make and the other was ordered on the Internet ...
More to follow...
gm...
The telescope tube was stored in an outside metal shed for several years and even though I thought the tube openings were closed off both spiders and roaches found their way to the inside of the telescope! Seems both of these bugs have no problems finding ways into perfectly sealed enclosures.
The spiders had a field day creating all sorts of webs across the primary mirror surface and the secondary mirror was a great place for them to attach their webs - too bad for them other bugs did not find their way into the telescope tube so the spiders simply starved to death - too bad!
The roaches, on the other hand made a bigger mess - they too did not find much in the way of food so promptly just died on the primary mirror surface. Of course, since the telescope tube was stored in the vertical position as there are rubber feet on the primary mirror back-plate at the end of the telescope tube put there for just this purpose, the roaches had not problem staying on the primary mirror surface after they died. This is where they decomposed!
As you can imagine - there was a pretty good "mess" on the primary mirror surface. Thankfully, about nine (9) years ago, I had the primary and secondary mirror surfaces re-surfaced by a local shop (http://www.spectrum-coatings.com) who did an excellent job of putting a new enhanced aluminum surface coat and a silicon dioxide (Quartz) surface coat on the mirrors! This re-coating actually protected the surface of the mirrors since the quartz coating acted to protect the enhanced aluminum surface coat and I only had to do a cleaning on the mirrors to restore them to a clean condition.
NOTE: If you need mirrors re-coated I would HIGHLY recommend Spectrum Coatings for the task! They have developed a very good method of recoating mirrors and the added step of depositing a quartz coating on top of the enhanced aluminum coating really does an excellent job of protecting the reflective surface with very very little loss in efficiency or reflection! Check out their site as they have some information and test data on the process they use! They can handle Primary mirrors up to 32-inches in size and their coating technique is the best in the business, and their prices are very very reasonable too! Tell Paul I sent ya - it won't get me anything but I am sure Paul would like to know where you found out (grin).
The technique I used to clean the mirrors was really very simple. There are a good number of ways to clean telescope mirrors but the technique I use is a little different from most. I use a combination of Windex (yep - good ole fashion window cleaner) and HDTV Screen cleaner. The only place I have found (to date) for the cleaning spray is in a Kit for HDTVs -Buy.com carries the kit (http://www.buy.com/prod/belkin-hdtv-essentials-kit-includes-hdmi-cable-surge-protector/q/loc/111/204871868.html) but it contains not only the cleaning spray but also an HDMI cable, surge protection power strip along with the cleaning cloth that comes with the cleaner. I have not located a place to just get the cleaning spray and cloth but since I do have an HDTV it was not an issue for me (grin). Be sure to get the cleaning cloth as it is specially designed to be lintless and not scratch! Very important, especially the "not scratch" part!
First I wet the mirror surface with the Windex and let it stand for at least five (5) minutes to loosen any surface dust, dirt, lint, bugs or what-not... DO NOT rub the surface to remove anything and do not allow the Windex to dry on the surface of the mirror. Rubbing on the mirror at this point would be a great way to scratch the mirror surface from the foreign matter on the surface! Let the Windex do all the work and if there is still something sticking to the surface just apply a second coat of Windex after draining off the first coat.
I usually drain the Windex off the surface and wet the surface again with Windex to make sure most all of the foreign surface contamination has been cleaned off the surface of the mirror.
After the second cleaning I drain off the Windex then wash the surface off with water (best to use distilled so as not to add any dissolved contaminates to the surface of the mirror). After this step I use the HDTV screen cleaner with the lintless cloth to VERY LIGHTLY clean the mirror surface - this step should be performed with care so as not to scratch the mirror surface.
Once I am happy with the screen cleaner step I wash the mirror off with distilled water (again) then use 99% Isopropol alcohol (available at hardware stores as lacquer thinner, I believe) to rinse the mirror surface (this removes any water film left) and drain the alcohol off one end of the mirror - you can remove any droplets left with a SOFT lintless cloth - blot, do not rub!!!
Performing the above cleaning on the Primary and Secondary mirrors of the telescope restored the mirrors back to a VERY clean state - that is a GOOD THING (tm) for the purposes of obtaining the best possible images through the telescope.
Of course all of the above steps required removing the mirrors from the telescope tube - and completely destroys any previous alignment of the telescope's optics. The next step will be to install the mirrors back into the telescope tube then perform an optical alignment of the mirrors.
First - I have to make a collamating tool to use during the alignment process - one tool I need to make and the other was ordered on the Internet ...
More to follow...
gm...
Dragging out the 13" Dob.
Well - the subject of this blog is "Telescope Fun" and that pretty well describes what I am enbarking on here. I have a Coulter Optics 13.1-inch (33.27 cm) diameter I had purchased in 1986. Coulter Optical no longer produces this telescope nor the primary mirror - the largest they have listed on their website (http://www.e-scopes.cc/) is a 12-inch primary mirror and secondary for around $600.00 (just the mirrors) I purchased the 'scope to view different objects in space along with watching the comet fragments collide with Jupiter in 1994 (and it could be seen through this 'scope as it was big enough to catch the action!). These telescopes were the largest you could purchase for a very inexpensive price (I paid around $700 for mine) and still have some excellent views of the night sky. Given the size of the telescope it is no wonder they are called "light-buckets".
Here is an image of what the telescope looks like - some people actually thought I had a cannon in my garage! (grin).
The telescope was stored away for some years due to infrequent use and the need for the space within the garage for other projects. It was "weatherized" and stored away in an outside shed (metal shed on raised floor) but in Florida that is not saying all that much! Sometimes the temperatures within the shed would reach over 120-deg. F or as cold as around freezing (depending on the time of year of course) and since Florida in not known for low humidity you can guess what that could be like!
All in all the telescope faired out pretty well give the environment it was stored in. The optics (primary and secondary mirrors) were covered in a layer of dust, bugs and only God knows what else so a good cleaning was in order to determine the actual shape of the mirror. Luckily I had stored all of the primary objective eye-pieces inside my air conditioned home so they faired a great deal better than the telescope (hind-sight being what it is I should have stored the whole telescope inside, dumb me!).
My next entry will be on the disassymbly and cleaning of the telescope optics - stay tuned!
Here is an image of what the telescope looks like - some people actually thought I had a cannon in my garage! (grin).The telescope was stored away for some years due to infrequent use and the need for the space within the garage for other projects. It was "weatherized" and stored away in an outside shed (metal shed on raised floor) but in Florida that is not saying all that much! Sometimes the temperatures within the shed would reach over 120-deg. F or as cold as around freezing (depending on the time of year of course) and since Florida in not known for low humidity you can guess what that could be like!
All in all the telescope faired out pretty well give the environment it was stored in. The optics (primary and secondary mirrors) were covered in a layer of dust, bugs and only God knows what else so a good cleaning was in order to determine the actual shape of the mirror. Luckily I had stored all of the primary objective eye-pieces inside my air conditioned home so they faired a great deal better than the telescope (hind-sight being what it is I should have stored the whole telescope inside, dumb me!).
My next entry will be on the disassymbly and cleaning of the telescope optics - stay tuned!
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