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Jones Bird - is it really that bad?

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#1 Mrcloc

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Posted 27 April 2021 - 03:57 PM

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.
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#2 petert913

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Posted 27 April 2021 - 04:25 PM

I believe it's called a Bird-Jones.  And they are claimed to be pretty bad.  Both optically and mechanically.


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#3 mashirts

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Posted 27 April 2021 - 04:26 PM

Yeah, something positive said about Jones Bird!  On axis they perform great has been my experience.


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#4 ButterFly

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Posted 27 April 2021 - 04:37 PM

As implemented and sold, yes.  The original design had the corrector before the secondary.  Most commercial iterations have the corrector in the drawtube, and it's not much more than a single element plastic barlow.  The cost cutting is applied everywhere until the whole thing becomes rather unpleasant to use.  Mine would get knocked out of collimation by starlight.  It got me very good at collimating and into the habit of checking often.  But my money would have been better spent on a dob.

 

A well made version with proper functioning elements is ... well made.  The point of the design was to overcome the small fields of SCTs and Maks.

 

F/8 is pretty slow for the primaries used on these.  Are you sure that's not f/8 with the corrector?  Assuming a 2x "corrector", the primary comes out to around f/4.


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#5 mashirts

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Posted 27 April 2021 - 04:56 PM

Here is a pic I grabbed off the internet of the Celestron G-8N.  The 8 inch bird jones they came out with where the corrector is located just before the secondary mirror.

 

A very attractive telescope.

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  • Screenshot_20210427-164914_(1)_711873_crop_4820_SP-9812.jpg

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#6 mashirts

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Posted 27 April 2021 - 05:10 PM

I have always assumed all spherical optical design is typically easier and cheaper to produce.  And the shortening of the OTA decreased cost a well.  Unless you devoted to ATM or follow a monk's devotion like John Dobson telescope production is all about making profit.



#7 Jon Isaacs

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Posted 27 April 2021 - 05:43 PM

A well made version with proper functioning elements is ... well made.  The point of the design was to overcome the small fields of SCTs and Maks.

 

 

I think it's more about spherical optics, inexpensive. A standard Newtonian overcomes the narrow field of the Mak and SCT.

 

I had a Vixen made 125 mm F/8 Jones-bird. It was very disappointing. 

 

The only really well made Jones-Bird I know was built by Rik ter Horst who is an ATM as well as an optical guru for the Dutch space agency.. he likes a challenge.

 

Jon


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#8 maroubra_boy

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Posted 27 April 2021 - 05:49 PM

There are two parts to this:

 

1, the TRUE Bird-Jones design is a specific telescope design, just like the SCT and Maksutov.  We do not confuse an SCT with a Mak, nor a Mak with an RC, so we shouldn't with the Bird-Jones.

 

The Bird-Jones is a Newtonian variant that uses a good quality spherical mirror and has a purpose designed corrector lens assembly between the Primary and Secondary mirrors.  This corrector lens is to correct for spherical aberration.  The design was used by some telescope manufacturers as a way around the THEN difficulties of mass producing good quality parabolic mirrors.  Once the mass manufacturing of parabolic mirrors was sorted, the Bird-Jones design became obsolete.  The most well known TRUE Bird-Jones telescope is the Tasco 8V.  Celestron also made one, the G-8N that mashirt posted, but it was a very short lived model as it came out just as mass produced parabolic mirrors started.

 

The Bird-Jones design was never a cheap instrument to manufacture because it required a GOOD quality spherical mirror and a GOOD quality purpose designed corrector lens assembly.

 

The true BIRD-JONES telescope design:

Jones_bird%20layout%20%28Large%29.jpg?he

 

2,  NO BIRD-JONES TELESCOPES ARE MANUFACTURED TODAY!

 

What is produced today is only a BARLOWED NEWTONIAN that sees a barlow lens shoved down the focus tube.  The are NOT Bird-Jones telescopes.

 

These all use cheap components, cheap spherical mirrors and cheap barlow lenses.  And NONE of these produce a quality of image comparable to the 8V as an example.  These Barlowed Newtonians do not correct for spherical aberration, and will only exacerbate the aberrations that a poorly figured spherical mirror has.

 

The BARLOWED NEWTONIAN

csm_fig62_e08b8f63c9.jpg

 

These Barlowed Newtonians are the reason for the bad rap that the Bird-Jones design gets.  True Bird-Jones Newts were not perfect either, but to make one required matching the optics to suit.  The Bird-Jones is not a cheap optical system to manufacture, and Tasco offered the 8V with an amazing mount and tripod, unlike the other Barlowed Newts it also offered like the 132T.  Celestron also splashed out in kitting out their G-8N with a decent focuser, mount and tripod.  Please do not confuse the Bird-Jones with the rubbish Barlowed Newts that are offered today.  They are not the same telescope designs.

 

Alex.


Edited by maroubra_boy, 28 April 2021 - 12:18 AM.

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#9 John Rose

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Posted 27 April 2021 - 07:03 PM

I had one of the Tasco's. It did not take much magnification before getting soft. It is to date the only reflector I have looked through with chromatic aberration.

 

John


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#10 jgraham

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Posted 27 April 2021 - 07:09 PM

I was surprised that I was able to find a Bird-Jones that actually worked fairly well...

 

Tasco 132T (11-13-2020)-1c.jpg

 

This is a Tasco 132T and I bought it thinking that it might be a tiny Schmidt-Newtonian, but nope, its a Bird-Jones. I was encouraged with I saw that the corrector was a cemented doublet and not a single element plano concave. The trick is that in order to work well it has to be precisely collimated and while the secondary of the 132T can be adjusted, the primary cannot. I modified the mirror cell on this one, and once adjusted it worked very well, about what you'd expect for a 75mm telescope with a large central obstruction. It has blossomed into a fine little star hopper.

 

Sooo, a well designed and executed Bird-Jones can work quite well, but most inexpensive modern variants don't seem to check these boxes.

 

 


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#11 Stricnine

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Posted 27 April 2021 - 10:31 PM

My Dad bought a Jason Comet Chaser (480mm) when Haley's comet made a pass through the inner solar system way back in 1986.  I was recovering from a broken leg (femur, from running in front of a car in an alley), and have vivid memories of driving out to a dark site (local astronomical society) and seeing the comet (small as it was).  I remember later using it to view Moon and Sun.  Was it perfect, no, the finder scope could never quiet be aligned with the telescope's optics.  I enjoyed it regardless, not knowing anything better existed at the time, and it helped sustain my interest in space/science/engineering as a boy way back in 'the day'.

 

David


Edited by Stricnine, 27 April 2021 - 10:31 PM.

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#12 PJBilotta

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Posted 28 April 2021 - 01:41 AM

I briefly owned a Celestron 6" Bird-Jones briefly sold by them about 20 years ago - very similar to the G-8N shown above. Compact, handsome looking, and absolutely dreadful optically. Sold it in about a month and replaced it with a standard 6" f/5 Newt I still own. Bad, bad memories of that one.
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#13 Mrcloc

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Posted 28 April 2021 - 05:27 AM

F/8 is pretty slow for the primaries used on these. Are you sure that's not f/8 with the corrector? Assuming a 2x "corrector", the primary comes out to around f/4.


Yes, of course. I don't think the corrector is a 2x, but I should experiment again. It's likely to be near 2x though, rendering the primary too fast to be useful without a corrector.

The sad thing is that the primary mirror is actually really good. It's a fun scope to use, giving excellent performance in the centre of field. Maybe I'll find a way to properly correct it and get sharp views to the edge.

Thanks for the replies. I'll need to read it all again, it's all very interesting.

#14 Cotts

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Posted 28 April 2021 - 11:26 AM

Any off-the-shelf, bog-standard 6-inch f/6 or f/8 Dob-mounted Newtonian from SkyWAtcher/Orion/Celestron/Meade/ExploreSci etc. would be a huge improvement over a Bird-Jones (barlow in the eyepiece drawtube).  Hands down.... 

 

Dave


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#15 Jon Isaacs

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Posted 28 April 2021 - 12:31 PM

A little more about the Opticon Jones-Bird scopes. 

 

https://www.cloudyni...-2#entry6753943

 

https://www.cloudyni...l/#entry8420475

 

Jon


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#16 ButterFly

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Posted 28 April 2021 - 12:39 PM

I think it's more about spherical optics, inexpensive. A standard Newtonian overcomes the narrow field of the Mak and SCT.

 

And both of those are really about avoiding hyperbolic optics.  The Bird-Jones corrector does for a spherical primary what a coma corrector does for parabolic optics - avoids the need to grind hyperbolas.  Spherical is easier to figure than parabolas, and sub-aperture correctors are obviously cheaper to make than whole aperture correctors.  The race to bottom began.

 

The other advantage over newts is the much shorter tube.  These were made with imaging in mind.  Even though the camera is dangling way up there, instead of at the bottom like with an SCT, it's still shorter than a newt of the same focal length.  Everything has to be more rigid than with an SCT.  There is the camera as well as sub-aperture corrector to support, without the benefit of the side walls of a whole aperture corrector.  As soon as hyperbolas became feasible, it replaced all of these designs in practice for research imaging.



#17 Paul Sweeney

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Posted 28 April 2021 - 01:43 PM

I have a 114/500. A friend of mine bought it for her son, but they couldn't get it to work. I just happened to have a 114/900 laying around, so I traded with her.

I've tried to collimate it, but it never produces a usable image. Someday I will dissect it, and maybe make a standard Newt out of it. This is the type of scope that really kills this hobby for newbies.
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#18 jgraham

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Posted 28 April 2021 - 02:16 PM

I had the original long tube and the later short tube (Bird-Jones) versions of the Meade DS-2130. The long tube version had excellent optics, I really couldn't get the Bird-Jones version to work. I still have the Bird-Jones in storage and I might look at it again to see if tweaking the colimation helps, but I doubt it. It's too bad; they can work well if properly executed, but that doesn't seem to be the case with many of the bargain versions.

I'll never forget how Gavin (Nytecam) converted a Bird-Jones into a cute and functional lensless Schmidt camera. :)
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#19 Jon Isaacs

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Posted 28 April 2021 - 04:08 PM

And both of those are really about avoiding hyperbolic optics.  The Bird-Jones corrector does for a spherical primary what a coma corrector does for parabolic optics - avoids the need to grind hyperbolas.  Spherical is easier to figure than parabolas, and sub-aperture correctors are obviously cheaper to make than whole aperture correctors.  The race to bottom began.

 

The other advantage over newts is the much shorter tube.  These were made with imaging in mind.  Even though the camera is dangling way up there, instead of at the bottom like with an SCT, it's still shorter than a newt of the same focal length.  Everything has to be more rigid than with an SCT.  There is the camera as well as sub-aperture corrector to support, without the benefit of the side walls of a whole aperture corrector.  As soon as hyperbolas became feasible, it replaced all of these designs in practice for research imaging.

 

Whatever the theoretical advantages might be, the Opticon's seem to be the only decent quality Jones-Birds scopes every built. 

 

Jon



#20 sickfish

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Posted 28 April 2021 - 04:28 PM

There are no members on this site with the name Bird Jones.

 

Think about it.


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#21 ButterFly

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Posted 28 April 2021 - 05:25 PM

Whatever the theoretical advantages might be, the Opticon's seem to be the only decent quality Jones-Birds scopes every built. 

 

Jon

They were first built by Bird and Jones for a specific purpose and obviously built well.  The mass produced ones deviate from the design enough that Trash-Garbage is a more apt name than Bird-Jones.  Capable amateur hands that stay true to the design can do much better.  You get a short tube dob that uses a Bird-Jones corrector instead of a coma corrector.  I have no issues with using a sub-aperture corrector for my fast parabolic mirror.  I did it so I wouldn't have to pay for hyperbolic optics that are much more difficult to collimate.  If I were to use a junky corrector at the wrong place, I wouldn't be surprised that it didn't work well.

 

The current Trash-Garbage offerings aren't much different than selling a fast parabolic mirror with a cheap barlow attached to the focuser instead of a coma corrector, then calling it corrected.  Calling these things Bird-Jones is false advertising just like improperly alluded to RC optics.  People just happened to be shopping around for expensive RCs enough to complain and get the company to cut it out.


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#22 teashea

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Posted 28 April 2021 - 09:16 PM

There are two parts to this:

 

1, the TRUE Bird-Jones design is a specific telescope design, just like the SCT and Maksutov.  We do not confuse an SCT with a Mak, nor a Mak with an RC, so we shouldn't with the Bird-Jones.

 

The Bird-Jones is a Newtonian variant that uses a good quality spherical mirror and has a purpose designed corrector lens assembly between the Primary and Secondary mirrors.  This corrector lens is to correct for spherical aberration.  The design was used by some telescope manufacturers as a way around the THEN difficulties of mass producing good quality parabolic mirrors.  Once the mass manufacturing of parabolic mirrors was sorted, the Bird-Jones design became obsolete.  The most well known TRUE Bird-Jones telescope is the Tasco 8V.  Celestron also made one, the G-8N that mashirt posted, but it was a very short lived model as it came out just as mass produced parabolic mirrors started.

 

The Bird-Jones design was never a cheap instrument to manufacture because it required a GOOD quality spherical mirror and a GOOD quality purpose designed corrector lens assembly.

 

The true BIRD-JONES telescope design:

Jones_bird%20layout%20%28Large%29.jpg?he

 

2,  NO BIRD-JONES TELESCOPES ARE MANUFACTURED TODAY!

 

What is produced today is only a BARLOWED NEWTONIAN that sees a barlow lens shoved down the focus tube.  The are NOT Bird-Jones telescopes.

 

These all use cheap components, cheap spherical mirrors and cheap barlow lenses.  And NONE of these produce a quality of image comparable to the 8V as an example.  These Barlowed Newtonians do not correct for spherical aberration, and will only exacerbate the aberrations that a poorly figured spherical mirror has.

 

The BARLOWED NEWTONIAN

csm_fig62_e08b8f63c9.jpg

 

These Barlowed Newtonians are the reason for the bad rap that the Bird-Jones design gets.  True Bird-Jones Newts were not perfect either, but to make one required matching the optics to suit.  The Bird-Jones is not a cheap optical system to manufacture, and Tasco offered the 8V with an amazing mount and tripod, unlike the other Barlowed Newts it also offered like the 132T.  Celestron also splashed out in kitting out their G-8N with a decent focuser, mount and tripod.  Please do not confuse the Bird-Jones with the rubbish Barlowed Newts that are offered today.  They are not the same telescope designs.

 

Alex.

More great information - thanks



#23 davidc135

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Posted 29 April 2021 - 03:09 AM

If the OP's spherical primary is a 5'' F4 then it would be under-corrected by 13/4 waves. The performance up to x100 magnification suggests that the Barlow corrects at least some of that. Star test results would show if there is still massive under-correction.

 

The image surface is very strongly curved as, I think, the true Bird-Jones is also. Hence the poor outer part of the field.

 

If the scope gets elbowed out by the larger Newt the F/4 mirror, if good, could be repurposed into an RFT with a bit of ATM work. It's not for everyone but the mirror could be parabolised or the window, if suitable, could be figured, or a classy astrograph with near perfect star images across a flat 2 or 3 degree field achieved with the help of a couple of lenses made from cheap glass.

 

David



#24 Mrcloc

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Posted 29 April 2021 - 06:45 AM

This has been interesting to read. The Bird-Jones I have is my first telescope I bought about 17 years ago. It's always hung around, so I'm repurposing it for my children. A fast spherical mirror is not ideal at all.

 

What I can't quite understand is that the "corrector" moves with the focuser. I would have thought it would be better for the corrector to stay put, no? Perhaps there is an ideal distance from the primary that the corrector could be fixed, and that might improve performance a little.

 

It's really a shame. The tube, mirror, and accessories are actually really decent (mirror glass thickness and reflectivity, at least). The corrector is a glass doublet too. The only plastic is in the focuser. My 5" Mak isn't nearly as bright as the 5" J-B thing.

 

How fast are Maksutov mirrors? Couldn't the mirror be repurposed using a Maksutov corrector meniscus? I would guess it needs at least a 6" meniscus. Still it's not something I would spend too much on.



#25 luxo II

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Posted 29 April 2021 - 07:06 AM

How fast are Maksutov mirrors? Couldn't the mirror be repurposed using a Maksutov corrector meniscus? I would guess it needs at least a 6" meniscus. Still it's not something I would spend too much on.

Maksutov-cassegrain primaries vary but most appear to be in the range f2.5…f/3. Maksutov-Newtonians have been made commercially f/4 .. f/8. In all cases however the corrector is carefully designed to match the primary.

Edited by luxo II, 29 April 2021 - 07:08 AM.

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