mldee
09-05-2010, 03:34 PM
In a recent thread I have been passing on my learner experiences with putting scopes on mounts. That's a bit like airline 'bums on seats' but the opposite; less is better. Anyway, I exchanged the C8 for the 8" Newt the other afternoon and got it all set up, including quick laser collimation check, for a night's testing.
Well, surprise, surprise, every star I tried to look at was in the midst of going supernova! After deciding that probably was not the case, I looked closer at the scope (using CCD and laptop) and found that even when quite tightly focussed, the stars were still smearing and exploding. Hmm, must be collimation. As it was a beautiful cloudless night, I turned off the obs and went inside to study up on laser collimations again:sadeyes: I suppose I could have swapped back the C8, etc, etc, but I had lost the mood. All I wanted to do was a good collimation check on the Newt when the sun came out.
My studies of all the great info on IIS and CN gave me the confidence to attempt a Barlowed laser collimation when I got the chance.
Today was that day! Better half went out, leaving me alone on a pleasantly warm sunny day to play around in the obs. So here's my experiences at doing a Barlowed laser collimation of my Newt.
Remove spider & secondary for check and clean. Don't worry, it's easy to put back ;). Remove primary for access to rear of scope. Flock the complete OTA. Done. Looks good and it's very dark in there! Only took about 10 minutes. Replace the primary.
On to the collimation. A summary of the previous night's studies showed the following steps would be needed:
1 - Study the spider and secondary mirror setup so you are comfortable with what all the bits do. Note the flocking! (Pic 1). Eg, is the mirror offset on the support? Mine was, (SW BD 8" 1000mm Newt), also had previously shortened tube for DSLR work. Overall length now about 800mm too, and mirror assy uses 6 screws to attach to OTA, dunno if that was original, but good idea anyway.
2 -It is very important to centre the spider assembly in the OTA. (The secondary mirror may be offset from that, but the spider must be centered.) I just measured the spider arm lengths, took a look at the screw fastening system and decided that a trusty tape measure would be OK to ensure centering within 1mm. Loosely reinstall the spider (4 screws held it to the OTA wall in my case. (A front aluminum ring prevents the OTA from deforming as you later tighten the screws to make the spider firm.) Using the tape measure, precisely measure the distance from the centre of the mirror support phillips screw to a defined point at the OTA fastening end of the spider. I measured from the screw to the inside of the OTA front aluminium ring as it was easiest to do repeatedly. (Pic 2) I finished up with all four spiders being 108mm. Use the spider tightening screws to adjust. Don't fully tighten them yet.
2 - Now it's time to take a look at the secondary mirror reflection from the front of the OTA , to ensure the oval surface is "square" to the spider that leads to the focusser hole. Loosen the phillips support screw slightly and get the mirror aligned. Using the focuser tube with a collimation tool is also handy. Lots of IIS and Google info on how to do this correctly. The final check is a nice round mirror when you look into the focusser. the piece of white paper below the mirror works well too, to remove extraneous primary mirror reflections. Firmly finger-tighten the spider nuts.
3 - Laser collimator alignment check. Make sure your laser is well collimated. Spend a weekend learning how to do this sometime. Then insert the laser into the focuser. BE CAREFUL OF THE LASER WHEN LOOKING INTO THE OTA! You have been warned. I dunno if it's dangerous, but it sure is bright when you get things lined up! (Pic 4). You should see the laser spot on the secondary mirror and down on the primary. Align the secondary so you have a nice spot bang in the centre of the primary donut. (Pic 4) Now's a good time to carefully rotate the laser a bit to check it's collimation. You need to get this step reasonably OK, but not agonisingly so, as the later Barlow bit will take care of that :) Make sure all the secondary screws are just firmly tightened.
4 - The Biggie! Primary initial alignment;). Check if you can see a return bright red dot in the laser reflector panel. (Pic 5 & 6). If not, don't worry, just means the primary is way off collimation. Leave the laser on and take a look in the front of the OTA, you should see the spot on the secondary and primary, nothing else. Carefully put your finger (or something) in front of the focuser tube. You should see a red dot coming from the laser on the focuser side, and a red dot on the finger inner side, which is the reflection from the main mirror. You can also look down the OTA to try and find where the hell the reflection is shining on it's return path. Mine was initially missing the secondary completely, and was shining onto my forehead when I took a look. I could see it on my face reflection in the primary mirror.
The object here is to adjust the primary mirror collimation screws to get that dot shining back into the focuser as close as you can to the outcoming dot. You should also see it hitting the secondary on it's return path. It might take 10 or 15 minutes to do it, but it will happen. You need to see that bright red dot on the laser panel. Not just a blur, a real dot! (Pic 6). Adjust the primary collimation screws to put the dot in the laser hole on the panel. More primary adjustment to come, so don't tighten the lock screws yet.
5 - Primary Barlowed laser finetune. OK, we've got the optics sorta lined up. Now we want to do the icing on the cake and get it spot on. I presume you've read up on barlowed laser collimation and know what we're about to do: Insert the laser in the barlow ( I used an Orion 2x shorty barlow) then securely insert it into the focusser. (Pic 7). Take a look in the OTA front and ensure you have a blurry red mark somewhere on the centre of the secondary, and the primary donut is covered in red light. (Pic 3). It may also spread beyond the donut. Doesn't matter, your previous studies will have explained it, won't they? This little procedure is so forgiving. Very cool.
Now, remembering where we had the nice red dot on the laser panel in step 4, (pic 6) you should now have a softer red illumination on the panel, with a big (~15mm) donut-shaped shadow as well. (Pic 8). Ta Da! Notice that if you wiggle the laser, the red might move, but the donut stays still. Adjust the primary collimation screws again to centre the donut hole on the laser hole in the panel.
As needed, repeat from step 1 to step 5 until happy with your abilities and the end result.
Strongly recommend this method for it's simplicity and repeatability.
It's cloudy again here, so still haven't been able to confirm it all works with stars, but that big donut shadow in step 5 sort of says it all. Some pics follow. Hope this post may give some other less experienced imagers the impetus to tune up their own setups.
Well, surprise, surprise, every star I tried to look at was in the midst of going supernova! After deciding that probably was not the case, I looked closer at the scope (using CCD and laptop) and found that even when quite tightly focussed, the stars were still smearing and exploding. Hmm, must be collimation. As it was a beautiful cloudless night, I turned off the obs and went inside to study up on laser collimations again:sadeyes: I suppose I could have swapped back the C8, etc, etc, but I had lost the mood. All I wanted to do was a good collimation check on the Newt when the sun came out.
My studies of all the great info on IIS and CN gave me the confidence to attempt a Barlowed laser collimation when I got the chance.
Today was that day! Better half went out, leaving me alone on a pleasantly warm sunny day to play around in the obs. So here's my experiences at doing a Barlowed laser collimation of my Newt.
Remove spider & secondary for check and clean. Don't worry, it's easy to put back ;). Remove primary for access to rear of scope. Flock the complete OTA. Done. Looks good and it's very dark in there! Only took about 10 minutes. Replace the primary.
On to the collimation. A summary of the previous night's studies showed the following steps would be needed:
1 - Study the spider and secondary mirror setup so you are comfortable with what all the bits do. Note the flocking! (Pic 1). Eg, is the mirror offset on the support? Mine was, (SW BD 8" 1000mm Newt), also had previously shortened tube for DSLR work. Overall length now about 800mm too, and mirror assy uses 6 screws to attach to OTA, dunno if that was original, but good idea anyway.
2 -It is very important to centre the spider assembly in the OTA. (The secondary mirror may be offset from that, but the spider must be centered.) I just measured the spider arm lengths, took a look at the screw fastening system and decided that a trusty tape measure would be OK to ensure centering within 1mm. Loosely reinstall the spider (4 screws held it to the OTA wall in my case. (A front aluminum ring prevents the OTA from deforming as you later tighten the screws to make the spider firm.) Using the tape measure, precisely measure the distance from the centre of the mirror support phillips screw to a defined point at the OTA fastening end of the spider. I measured from the screw to the inside of the OTA front aluminium ring as it was easiest to do repeatedly. (Pic 2) I finished up with all four spiders being 108mm. Use the spider tightening screws to adjust. Don't fully tighten them yet.
2 - Now it's time to take a look at the secondary mirror reflection from the front of the OTA , to ensure the oval surface is "square" to the spider that leads to the focusser hole. Loosen the phillips support screw slightly and get the mirror aligned. Using the focuser tube with a collimation tool is also handy. Lots of IIS and Google info on how to do this correctly. The final check is a nice round mirror when you look into the focusser. the piece of white paper below the mirror works well too, to remove extraneous primary mirror reflections. Firmly finger-tighten the spider nuts.
3 - Laser collimator alignment check. Make sure your laser is well collimated. Spend a weekend learning how to do this sometime. Then insert the laser into the focuser. BE CAREFUL OF THE LASER WHEN LOOKING INTO THE OTA! You have been warned. I dunno if it's dangerous, but it sure is bright when you get things lined up! (Pic 4). You should see the laser spot on the secondary mirror and down on the primary. Align the secondary so you have a nice spot bang in the centre of the primary donut. (Pic 4) Now's a good time to carefully rotate the laser a bit to check it's collimation. You need to get this step reasonably OK, but not agonisingly so, as the later Barlow bit will take care of that :) Make sure all the secondary screws are just firmly tightened.
4 - The Biggie! Primary initial alignment;). Check if you can see a return bright red dot in the laser reflector panel. (Pic 5 & 6). If not, don't worry, just means the primary is way off collimation. Leave the laser on and take a look in the front of the OTA, you should see the spot on the secondary and primary, nothing else. Carefully put your finger (or something) in front of the focuser tube. You should see a red dot coming from the laser on the focuser side, and a red dot on the finger inner side, which is the reflection from the main mirror. You can also look down the OTA to try and find where the hell the reflection is shining on it's return path. Mine was initially missing the secondary completely, and was shining onto my forehead when I took a look. I could see it on my face reflection in the primary mirror.
The object here is to adjust the primary mirror collimation screws to get that dot shining back into the focuser as close as you can to the outcoming dot. You should also see it hitting the secondary on it's return path. It might take 10 or 15 minutes to do it, but it will happen. You need to see that bright red dot on the laser panel. Not just a blur, a real dot! (Pic 6). Adjust the primary collimation screws to put the dot in the laser hole on the panel. More primary adjustment to come, so don't tighten the lock screws yet.
5 - Primary Barlowed laser finetune. OK, we've got the optics sorta lined up. Now we want to do the icing on the cake and get it spot on. I presume you've read up on barlowed laser collimation and know what we're about to do: Insert the laser in the barlow ( I used an Orion 2x shorty barlow) then securely insert it into the focusser. (Pic 7). Take a look in the OTA front and ensure you have a blurry red mark somewhere on the centre of the secondary, and the primary donut is covered in red light. (Pic 3). It may also spread beyond the donut. Doesn't matter, your previous studies will have explained it, won't they? This little procedure is so forgiving. Very cool.
Now, remembering where we had the nice red dot on the laser panel in step 4, (pic 6) you should now have a softer red illumination on the panel, with a big (~15mm) donut-shaped shadow as well. (Pic 8). Ta Da! Notice that if you wiggle the laser, the red might move, but the donut stays still. Adjust the primary collimation screws again to centre the donut hole on the laser hole in the panel.
As needed, repeat from step 1 to step 5 until happy with your abilities and the end result.
Strongly recommend this method for it's simplicity and repeatability.
It's cloudy again here, so still haven't been able to confirm it all works with stars, but that big donut shadow in step 5 sort of says it all. Some pics follow. Hope this post may give some other less experienced imagers the impetus to tune up their own setups.