Bird - Jones collimation note (AstroMaster 114)

[mplanet62]

Today had to collimate my AstroMaster 114 Bird-Jones from Celestron. Good job collimating it was done last year by local astronomy shop. Now I found it off and did it myself. Two notes on that:
1 Center dot on primary is a must. Center donut (paper hole reinforcement ring) even better. Visual collimation is almost useless without it.
2 Telescope must be collimated WITH the lens in focuser tube. Otherwise it looks exactly like you are collimating classic Newton (DOB) mid- tube.
Adjusted the primary without the lens, then had to refine it (a lot) with lens in. Easier to do it with telescope complete. This sort of collimation is extremely quirky - the view is quite different from that of a classic Newton, but the principle is the same. Cheshire tube is of a great help, laser collimator won't work because of the focuser lens. As an extra, blackened the edge of focuser lens. Matte nail polish did it OK. Now the nice edge blackened lens sits in the focuser very tight.
Attachment 8836
Clear skies,
Michael

[Kris me]

Thanks for posting this information. Just a couple weeks ago I bought on e_bay telescope simply because of very solid and sturdy EQ (I have seen it last year in Hong Kong). The OTA looks like a cheap copy of Astromaster 114EQ.
I could see something ... but it needed collimation. I thought that it is reflector with Ross corrector.
Just yesterday ask catadrioptic forum about it. I posted the pictures from telescope analysis I did with MODAS. Guys told me that it is Bird-Jones design and way of collimating it - same way as you described. So happy like a baby I did collimation again tonight.
Just an hour ago I had look at the sky - lucky first day in a week no rain, is clear + Moon.
Yep, it is collimated very well. What I see - quite visible coma effect. Now it is difficult to say why ? We have very intense sky pollution from volcano in Chile, planes hardly fly. When looking at the Moon naked eye, it has a "cap" - I never seen such a interesting phenomena. Looks like Moon is surround by wide diffraction rings. If you have a chance have a look - it is quite intriguing.
Now - the coma of the telescope tonight, is it problem with scope or is it because the of volcanic dust in the atmosphere?
You have same type of telescope for a while so you would have some observational experience. Would mind sharing them please.

with kind regards ...... Kris

[JamesandmyOpinion]

The astromaster is a very nice beginners scope, and I have no real big issue with it at all. That being said, culmination is different, though not necessarily harder.

A laser scope is handy for aligning the secondary mirror, but leave the Bird-Jones lens in place. Look down the front of the tube, and the laser spot will be faintly visible on the inevitable dust particles collected on the primary. If it's hitting the center of the primary, you're there.

If you don't have a laser, you won't be as accurate, but look down the focus tube (without a lens). Ignoring everything else, you should be able to see all three primary mirror clips. If you can't, adjust the secondary mirror until you can.

Now put a culmination cap on the focus tube. (a pinhole in the protector cap works fine). You will see a "donut" of light, with a darkspot and crosshairs. These are the silhouettes of the secondary mirror and supports. Using the adjustment screws on the primary mirror, center the "crosshairs" in the middle of the "donut".

Check your work at night, using a moderate star, and a 10mm lens. Unfocussed in either direction, you will again see that "donut". As you focus, if you are absolutely dead on culminated (ha!) the "donut" will collapse evenly on all sides until it becomes the star. Chances are more than good though that it will become "fat" on one edge, and it will turn into a "comma". Turn it back out of focus, and it should be just a slight adjustment to put the "hole" in the center of the "donut". Hope this helps.

[shawnsmooth]

Thanks very much James, I been trying to figure out how exactly to collimate these bird Jones scopes!!! I have a 127eq celestron ...

[Bob327]

I gave up keeping the corrector lens in the focus tube when I needed to collimate my old Celestron 114 GT ..I just removed it then collimated the darn thing...which actually was pretty darn close when I went out at night and star tested the scope...only took a 30 or so seconds to tweak the collimation screws a hair this way or that way to have the scope star test great.... BTW I used a 4 mm eyepiece BARLOWED (yep 500x) to see the airy disc to tweak the collimation...

If you have to do it day time...then use an artificial star , a glass insulator on a telephone pole or an old Christmas tree bulb illuminated from the side with a flashlight etc to tweak the final collimation... The only thing that matters s the star test itself...

Bob G

[bradford]

Oh! That explains what I just found. I've been working on a 114mm Celestron reflector GOTO scope for an elementary school astronomy club, and I happened to notice that the focal length said 1000mm, but the scope was very short. I kind of scratched my head for a minute and then started to explore the scope. I found a small lens at the bottom of the draw tube on the focuser and reasoned that it was responsible for the long focal length on such a short tube. After reading this thread, I did some research on these scopes and figured out what was going on. Interesting concept. Spherical primaries are a lot easier to make, so I can see why it would be more attractive to manufacturer. Thanks for the post.

[Kris me]

Hi guys.
I got one JB last year. Thanks for advice to those who told me how to collimate the thing.
The way to collimate it with laser - it is possible. Make a circle at the centre of main mirror, same like you see these days in some of the telescopes. Place the laser collimator as usual, turn up intensity and you will see your circle on the collimator screen. ( usual alignment must be done before hand ) Adjust the mirror cell screws so picture of the circle you see lines up with circles on collimator screen. Tweak during start test and it is done.

I found a lot of very negative and plain stupid comments about JBs. I guess some never used one nor see one in reality.
I found it quite well performing machine, compared with two other reflectors I have. JB ( 114/F8) is very handy as "grab & go", small just under 50 cm long, very light ( without eye piece ) 2.1 kg. Actually I am impressed with performance, it has a little bit of astigmatism (apparently this is the feature of JBs) but it can be corrected with selection of glass types in correcting lens (in tubus) some manufacturers actually did it.
I can say from personal experience that is as good as full size 114/F8 Newton, at times I have impression that is brighter.
Could you please, owners of JBs, share your seeing experience so we have honest and unbiased opinion.

I wish you clear skies ........... Kris.

[James897]

"Could you please, owners of JBs, share your seeing experience so we have honest and unbiased opinion."Yeah,they're junk and hobby killers,there are many good scopes available for the same price of a JB telescope that are easy to collimate,provides excellent views at the eyepiece,and will not end up sitting in the closet collecting dust.I want beginners to enjoy their first telescope,not get frustrated and quit.

[Joe Lalumia]

Bob is correct-- take the lens out and collimate it.

[jproffitt1]

Owning a Newtonian with a Bird-Jones lens assembly requires the owner to learn the mechanics of the design as well as the proper procedure to collimate it. That is the case when going from any design to another, gaining knowledge of the fundamentals of how the scope transfers images to the eyepiece and learning what procedures will make it transfer those images better. There is nothing wrong with owning a B-J Newt other than not taking the time to understand the design and how to maintain it.