So I've been helping someone with their telescope because I have the exact same one. It's a Jones Bird 130 1000, and I've written here about my struggles to get it aligned. So the guy obtained one, but it turns out it's missing the eyepiece adapter on the end of the focuser draw tube! I tried to find one for him, but it's a dead end search, so I built a really cool one which fits an eyepiece perfectly so that it pressure-seats, no need for a thumb screw. I'm giving him the original piece because I don't use this scope much. I'm still going to build a Dobsonian mount for it sometime for the children.
Anyway, I was testing if I could get the telescope to focus without issue because my adapter is a bit longer than the original, and I decided to give the scope a test while I was at it (now that I've obtained years of experience since I last used it). I had a look at Orion nebula, the jewel box, then omega Centauri, and then the moon. Man, I was impressed! It shows colour on the jewel box easier than my 5" Mak, and the moon was crystal clear and razor sharp. Stars come to a pin-point sharpness too. I actually think contrast and sharpness on the moon are better than my Mak.
The massive, glaring flaw was the limit of maximum magnification - I don't see much use going past 100x. There is also the other major issue that the edge of field can't come to focus. And it's not just 10% or something, it's a lot of the edge.
Accepting the flaws and taking cost into consideration, are these really that bad? I think I've personally knocked the design, probably because of how much I struggled to collimate mine, but I'm not so sure. I would be more than happy to use it along side my Mak, until I can afford a large aperture Newtonian, perhaps.
I also found that it's extremely comfortable to use on the EQ mount, so I've put a fast Newtonian onto my shortlist for my upgrade.
I also have a technical question. Would the Jones Bird telescope be better if I used a long tube and no corrector in the focuser? It's about f/8, so I'm hoping it's slow enough that spherical aberration isn't a problem.
Hi to everybody.
My humble answer to this question is simply ... NO
I purchased back in 1985 a Comet Catcher Jr (Cometron). The instrument, as you may know, is a TRUE ONE Bird-Jones 125mm diameter and 1000mm equivalent focal length.
I had noticed early on that the trouble with this OTA depended on a huge collimation difficulty, NOT because bad optics!
Its mechanical arrangement has been designed in a very rough way :
a cylindric 'mug' housed the small elliptical secondary. It also supported the corrector at its end, and what's more, the entire block was precariously supported by only three rods attached to the tube. In addition, the primary mirror apparently had no possibility of being collimated.
However, the instrument by some stroke of ... luck (!) could occasionally give me planetary images of better quality than a classic very good Newtonian, having the same optical-geometric characteristics (5" f/8).
I noticed that on the primary cell edge, there were three threaded holes (M3). It was evident they were used to collimate the mirror ONCE FOR ALL, before the scope being placed on the market (only tightening thoroughly the three screws that secure the cell to the tube). Once the cell was removed - or even accidentally moved, it was impossible to reposition it properly.
At that point I set to work to make its collimation more precise and stable possible.
This was my intervention:
1) I fastened three short M4 hook screws 120° apart on the inside edge of the cell. I then put three more screws from the outside of the tube - secured on the inside with nuts, about 90mm from the end of the tube and in line with the screws on the cell.
Once I extracted the mirror (it slides out from the outside, after removed the round plate that holds it in place, I then applied three coil springs of appropriate strength between each of the two pairs of screws.
I put the mirror back in and reposition the plate in its place.
I buy short M3 knobs to screw them into the 3 threaded holes of the cell.
Now the primary mirror coluld be easily and precisely collimated!
2) A well trusted glazier drilled a hole of 35 mm exactly in the center of the glass plate. The precision was pinpoint and the work was perfect.
With the lathe I make a round plaque + an extension ring - both aluminum, that I will use to secure at the glass plate the cylindrical block housing the corrector + the secondary.
The extension ring has adequate length to ensure the original distance corrector/primary mirror.
In this way, the block cannot longer move by itself.
I replaced the original secondary pivot with a piece of M4 bar, I put a coil spring on it and I placed three adjustment knobs - which were not originally designed to be there (!).
Knobs of course go through the central round plaque.
Now, the secondary position could thus be either adjusted along the optical axis, or tilted from it, and it was fairly locked in a suitable position with two nuts screwed on its the axial bar.
Here you can also very well collimate the secondary mirror, too!
I'll stop here for now. I will soon tell how to go about collimating this telescope. See you later!
Edited by benzomobile, 05 September 2021 - 02:52 PM.