Collimating the Polaris EQ 130
Posted 26 July 2016 - 05:51 AM
OK, it's been a couple of months and I ordered and received a laser and cheshire. After a bit of a learning curve, I believe I have this scope dialed in about as close as I can get it. The laser and cheshire agree and the star test looks good as well. I'm getting the impression that once we get below about 9mm with the eye pieces, the definition starts to go away. The 6mm that came with it must be pushing the limits. Saturn looks pretty clear down to the 9mm.. (my old eyes might have something to do with it as well.).
Can you see the Cassini ring for example?
I can make out the color bands on Jupiter and 4 moons but not the red "dot".
Posted 26 July 2016 - 05:40 PM
I have not been able to make out the red spot with even an eight inch f/5 reflector. I have seen the Cassini Division with long refractors and high end scopes. With a small wide field reflector, you can see the A and B ring sort of butt up to each other and sometimes get a hint of a thin darker strip in between. I believe a higher observing elevation and lower light pollution might help.
Planets are tricky when looking for fine detail. With the Moon, you can get a lot more.
Exactly what a person can see does depend on that individual's eyes. Part of the issue is the size of the image going through the eye. With a 9 mm eyepiece and 650 mm focal length, the magnification of the Polaris 130 is about 72x. Divide the 130 mm diameter by 72 and you get something around 1.8 mm. I have heard some people say they thought the optimum size for the image going through their pupil was around 2 mm, which is pretty close to what you are seeing with your 9 mm eyepiece. I have had other people, normally ones with really good eyes say they thought the optimum for them was closer to a 1 mm exit pupil, but they were normally using some pretty high end scopes. A six mm eyepiece will give you an exit pupil getting close to, but still larger than 1 mm.
Probably what you are seeing is about what to expect.
Some objects are naturally harder to see than others. Practice over several days can help. This has to do with a form of eye/brain mapping that improves as you look at a particular object or area over several sessions if they are close together. With a 60 mm refractor (Meade NG 60) I set out a few years ago to see a supernova in M-82, a lenticular galaxy. The supernova was magnitude 10 at the time. The first night, I found M-81, another galaxy in the area fairly easily and finally made out M-82. The second night, I found M-82 easier and could make out two brighter spots on the axis of M-82. Looking at pictures in books, I could see that these spots were normal. On the third night, every now and then, I could see another tiny pin prick of light show up and then go away. Researching images on line, I found that the supernova was right where I was seeing the pin prick winking in and out. On a fourth night, I took out my DS 2102 optical tube to look at the supernova.....piece of cake! I looked through the 60 mm and there was the little spot, winking in and out again. I think finding the great red spot might work something like that over time.
Hope this helps,
Posted 27 July 2016 - 06:00 AM
Posted 29 July 2016 - 06:07 AM
One thing I decided to do when using the Cheshire and Laser. I don't bottom out the focus assembly. I find that if it is at either stop, it doesn't remain centered so I position the focuser about mid way. Once it's off the bottom or top, everything seems to center up nicely. I guess this is what you get with an entry level scope.
Posted 29 July 2016 - 08:52 AM
That is quite true with entry level scopes. They are less expensive for a reason. With the Polaris 130, I found the mirror is quite good, with a standard aluminum coating (no exotic layers) plus a protective layer if silicon dioxide, which is the newest type for top notch protection. The focuser is adequate, but does have its limitations.
One point with what you are doing is that somewhere in the middle of the focus range is where you should normally be when viewing, rather than at an extreme.
Posted 05 August 2016 - 12:03 AM
After about 3 weeks of haze, clouds and storms, last night was a very good sky. After setting up, I decided to check in with Saturn. I believe I now have the 130 dialed in as close as it can be. Of course I'm now going to start exploring other areas of the night sky but had to battle mosquitos last night so ended early. Thanks for all of your advice.
BTW, I really haven't yet seen much difference between the original 9mm and the 9.6mm 4000 plossl. Maybe in a more advanced scope.
Posted 05 August 2016 - 05:03 PM
The main difference between the two eyepieces, in my opinion, is the field of view or how wide the field is in the eyepiece. The MA eyepieces that come with the scope have an apparent field of view of 45 degrees while the 4000 series Plossles are 52 degrees, except for the 32 mm (about 50 degrees) and the 40 mm (44 degrees). The longer focal length eyepieces are simply limited by how much sky can be pulled into a 1.25 inch eyepiece. When more width is required, that is when two inch eyepieces come into the picture, which the Polaris 130 is not set up to use.
The Plossles have four lenses inside, rather than the MA's three, which help provide a better image around the outer edges than the MAs. They also have multi-coatings on the critical surfaces which knocks out some extraneous light that the standard anti-reflection coatings of the MA eyepieces. Depending on the situation, the 4000 series are worth it, with others, there really is not much difference. Much of the time, it takes an experienced eye to see the difference, other than field width.
Incidentally, I think the MA eyepieces that came with my Polaris 130 were very well made. They are not fancy, by modern standards, but can certainly get the job done for most things that you would be using that scope for. The most likely reason to get a better eyepiece has to do with wanting to get a wider piece of the sky into the view and still have the size of it small enough to fit through the pupil of your eye. Another situation is when you want to get that last tiny bit of resolution when doing something like splitting tight double stars.
Hope this helps!
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