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Jones Bird - is it really that bad?

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#26 Mrcloc

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Posted 29 April 2021 - 07:09 AM

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; it isn’t feasible to just slap any mak corrector in front of your mirror in the hope it will be close enough to be ok.

What I don’t understand is why anyone built small Bird-Jones scopes in the first place.

Definitely. The corrector would certainly need to be matched to the mirror, but for a given FL and f-ratio, I'm sure it might be possible to find a meniscus that fits. I mean, it's wishful thinking, but I wouldn't mind the DIY.



#27 luxo II

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Posted 29 April 2021 - 07:11 AM

If you’re thinking of cannibalising a mak corrector, forget it; the original mak will outperform your combination.

Simpler to buy a decent mak and sell your mirror.

Besides I’ve never heard of a finished mak corrector being sold without the rest of the optical set.

NB the tolerances for the corrector and mirror to be a match are quite tight, there’s no way you can match a corrector to a mirror at random and expect good results.

Edited by luxo II, 29 April 2021 - 07:15 AM.

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#28 Mrcloc

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Posted 29 April 2021 - 07:51 AM

If you’re thinking of cannibalising a mak corrector, forget it; the original mak will outperform your combination.

Simpler to buy a decent mak and sell your mirror.

Besides I’ve never heard of a finished mak corrector being sold without the rest of the optical set.

NB the tolerances for the corrector and mirror to be a match are quite tight, there’s no way you can match a corrector to a mirror at random and expect good results.

It certainly appears so. I'd probably have more luck grinding my own Schmidt corrector, but even so, it's far more than I'm willing to do. I see it's possible to buy these, but they're for a specific optical system, and are way too expensive. Perhaps I should try modifying the corrector that's in the focuser. That might be possible and a bit easier.

 

I'm not looking for much. This telescope actually delivers very good performance for the center, and most definitely good enough for outreach or the children.

 

I have another thread asking about modifying it (long ago, I think), and I always seem to get carried away to that topic.



#29 Angeles

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Posted 01 May 2021 - 12:18 PM

its not bad as long you know the images will be softer or not as sharp as a real parabolic reflector scope. BUT then again the parabolic scope cost more. So for a first scope it can be ok so you if you want to stay in hobby after then if you stay in hobby you sell that and get a bigger scope with the better mirror

Angeles



#30 Jon Isaacs

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Posted 01 May 2021 - 12:36 PM

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.

 

Some random comments:

 

-It's not clear that today's scopes are not Jones-Birds despite the different location of the corrector.

 

- The Vixen/Celestron version I owned had the corrector mounted to the secondary.  It was disappointing, I was never able to resolve Castor (3" at the time). A 5 inch should have an easy time of a 3" double.

 

- The only comment about the optics the link you provided were that the planetary views seemed soft.

 

- I don't know how much you read about the Opticon Jones-Birds but they did seem to be of very high quality.  Apparently the optics were designed by Harrie Rutten, coauthor of the book Telescope Optics and built by Rik her Horst. 

 

Jon


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#31 maroubra_boy

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Posted 02 May 2021 - 04:06 AM

For the price that these cheap barlowed Newts are offered at, along with the poor mounts, eyepieces and wobbletron tripods, no, these do not come with any form of corrector lens. They are also sold with poor barlow lenses that do no favours to the image, often exceeding the practical limit of the aperture of the primary with the supplied eyepieces.

These Barlowed Newts are made entirely on a price basis, not for any other reason. The components are all what is currently and cheaply available. There is nothing special or unique in their construction.

If these scopes were anything other than a cheap variant of a Newtonian then larger apertures of the same optical design would be offered, and certainly offered with superior mounts and accessories than they are. There are none.

Don't kid yourself that they are anything else.

If these are the only large aperture scope you can afford, I wholeheartedly encourage you to enjoy your scope. I honestly believe that the best telescope is thes one that is used. But I also believe that in a forum such as this one that the truth of what is marketed needs to be called for what it is. You do not confuse an SCT for a Mak, nor a Mak for a Newtonian. The Bird-Jones is a specific design, not a barlowed Newt.

Edited by maroubra_boy, 02 May 2021 - 04:06 AM.

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#32 Jon Isaacs

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Posted 02 May 2021 - 06:27 AM

For the price that these cheap barlowed Newts are offered at, along with the poor mounts, eyepieces and wobbletron tripods, no, these do not come with any form of corrector lens. They are also sold with poor barlow lenses that do no favours to the image, often exceeding the practical limit of the aperture of the primary with the supplied eyepieces.

 

 

Have you actually verified that?  It is my understanding that the Jones-BIrd design just uses an achromatic doublet that is similar to a Barlow.  It seems to me, one would have measure the radii and glass types to verify that the doublet in the focuser is actually a Barlow and not a corrector of some sort.

 

There is probably no one on this forum who has said more about avoiding the inexpensive "Jones-Bird" Newtonians than I have, I get it.

 

Jon



#33 Mrcloc

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Posted 02 May 2021 - 09:29 AM

For the price that these cheap barlowed Newts are offered at, along with the poor mounts, eyepieces and wobbletron tripods, no, these do not come with any form of corrector lens. They are also sold with poor barlow lenses that do no favours to the image, often exceeding the practical limit of the aperture of the primary with the supplied eyepieces.


Ok, so mine I bought years ago came with a 4mm, 10mm, 20mm, 2x Barlow, 1.5x erecting eyepiece, finder, and equatorial mount. I use the mount to this day. It's been through a little touching up, but it's solid. I've put it on a better tripod though. The 20mm is actually a really good eyepiece. The marketing wasn't the aperture, it was the focal length and magnification, and obviously the accessories. Had it been a 500mm focal length parabolic with the mount and 20mm, it would have been a much better buy, but unfortunately not as marketable to beginners. I've noticed with beginners, it's all about magnification.

 

I experimented with the corrector and put it in a tube to make a Barlow. It didn't quite work as a Barlow, although it did add magnification.



#34 davidc135

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Posted 02 May 2021 - 11:51 AM

Mrcloc, If the prime focus is accessible can the scope's performance with and without the 'corrector' be compared? At a reasonable magnification, say x 100.

Or compare views with the 'corrector' and with a known Barlow. I'd expect an ordinary Barlow to add a little positive correction in a fast, F/4 system.

On the other hand traditional eps like Kellners or Plossls in an uncorrected, F/4 cone would add a slight under-correction making it a touch worse.

 

Does your model have a window which supports the diagonal? If so, it could be just a selected, unworked piece of float glass with errors that limit the scope regardless of how good the 'corrector' is. Or is there a spider?

 

David


Edited by davidc135, 02 May 2021 - 11:55 AM.

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#35 Mrcloc

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Posted 03 May 2021 - 02:41 AM

David, I did try long ago, but I can't remember if the EP needs to be closer or further from the primary. There is only a corrector at the bottom of the focuser draw tube. I have what can be called "extension tubes" which I'll try. I've actually been wanting to do this properly, but I suspect the EP needs to be closer to the primary, which makes it a lot more difficult to use without the corrector, and may be the reason I put it in again.


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#36 Mrcloc

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Posted 03 May 2021 - 03:36 AM

Ok, I did some tests now. I thought I would do some terrestrial testing. I think I'll just leave it from now on. I managed to chip the edge of the corrector while taking it out. Again. It's so fragile! Anyway, I tried with the corrector, without, with a 2x barlow, and with a 9mm (Expanse clone, so has a built-in barlow from what I understand), and then again with the corrector.

 

With the corrector, it absolutely snaps into perfect focus. The focal point from center to edge isn't the same, and only just a little out. Perhaps a field-flattener will sort it out. Without the corrector, it just doesn't achieve good focus, even with the barlow. I mean, I watched a tiny black ant from about 70 ft, and with the corrector and at 50x, I could watch its legs.

 

To get focus without the corrector, I needed to drop the eyepiece into the focuser draw tube. This is possible without the eyepiece adapter attached. The rubber of the eyepiece holds it in place. This is about 5 cm of forward-focus in addition to having the focuser almost all the way in.

 

Did the chip mar the view? Thankfully not that I could see. I know when looking at the moon I'll see a shadow, but thankfully it hasn't affected viewing that I could detect otherwise.


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#37 benzomobile

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Posted 05 September 2021 - 02:21 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.

Hi to everybody.

 

My humble answer to this question is simply ... NO wink.gif

 

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 frown.gif  :
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!

 

Beppe


Edited by benzomobile, 05 September 2021 - 02:52 PM.

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#38 rhaskins

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Posted 06 September 2021 - 10:01 AM

I have seen these articles about Bird-Jones over the years, always interesting reading. I just googled Bird Jones and got this link:

 

https://skyandtelesc...pes-not-to-buy/

 

Bird-Jones gets mentioned by name, not in a good way.

 

My first scope was a 6" F10 newt that was just amazing. I spent my time viewing with it not fixing it. Sharp image from edge to edge.

 

Rick


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#39 benzomobile

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Posted 06 September 2021 - 10:33 AM

I have seen these articles about Bird-Jones over the years, always interesting reading. I just googled Bird Jones and got this link:

 

https://skyandtelesc...pes-not-to-buy/

 

Bird-Jones gets mentioned by name, not in a good way.

 

My first scope was a 6" F10 newt that was just amazing. I spent my time viewing with it not fixing it. Sharp image from edge to edge.

 

Rick

 

Bird Jones scope three advantages are:

 

1) their size is compact, so they are lighter;

2) their primary mirrors have spherical shape (very easy to figure out);

2) they show neither axial nor extra-axial distorsions as Newt ones do, having same aperture ratio.

 

BTW, I've just stressed the concept  B-J scopes aren't  necessarily bad ones.

In addiction, I explained how the Cometron is really a very good telescope - not a definetely bad one, if you only modify it. 

That's all.

 

Your Newtonian (F10) is definetely a very good scope - no doubt about that, but, a Newt 6" F8 is just another thing. In this case the image doesn't appair so sharp edge to edge.

 

Beppe


Edited by benzomobile, 06 September 2021 - 11:05 AM.


#40 benzomobile

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Posted 06 September 2021 - 12:01 PM

Your Newtonian (F10) is definetely a very good scope - no doubt about that, but, a Newt 6" F8 is just another thing. In this case the image doesn't appair so sharp edge to edge.

 

Beppe

https://skyandtelescope.org/author/joltion/:

 

" The corrector lens is supposed to make everything all right again, but it never does. The view through every Bird-Jones scope I’ve ever looked through has been uniformly awful. There might be a decent Bird-Jones telescope somewhere out there, but if there is, I’ve never seen nor even heard of it."

 

If Mr. Jerry Oltion wrote this, then I feel sorry for him: he was unlucky! 

Surely Mr. Oltion will have stumbled upon 'so-called' B-J telescopes (i.e. simply barlowed Newtonian).

The true Bird Jones design is something else, entirely.

The old Celestron Comet Cacther Junior, also marketed by Tasco named it "8V",  (old style one) is optically a true Bird Jones, with an unfortunate mechanical solution, but ... once fine-tuned, it becomes a formidable scope: pinpoint and crisp stars (no spikes!) and well defined planetary images.

In addition, since its tube is closed, image does not affected by the turbulence that plagues Newtonian instruments.

 

I think I'm going to have to post some images taken by my Cometron....

 

Beppe


Edited by benzomobile, 06 September 2021 - 02:39 PM.


#41 rhaskins

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Posted 06 September 2021 - 03:06 PM

In an ideal world I would get up at dusk and tell the scope to go outside and get aligned and then call me. I'd walk out with the EPs and tell the scope what I want to see, fit the EP and watch the cosmos. Once in a while I will ask the scope for suggestions (kinda like Alexa). But the focus so to speak would be observing not fiddling.

 

Do not get me wrong, I get a lot of satisfaction from putting new equipment and ideas into astro reality, but a lot of the time I just want to see and relax.

 

So bye-bye birdie(jones), goodbye.

 

Rick



#42 benzomobile

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Posted 06 September 2021 - 03:21 PM

In an ideal world I would get up at dusk and tell the scope to go outside and get aligned and then call me. I'd walk out with the EPs and tell the scope what I want to see, fit the EP and watch the cosmos. Once in a while I will ask the scope for suggestions (kinda like Alexa). But the focus so to speak would be observing not fiddling.

 

Do not get me wrong, I get a lot of satisfaction from putting new equipment and ideas into astro reality, but a lot of the time I just want to see and relax.

 

So bye-bye birdie(jones), goodbye.

 

Rick

Rick,

 

I agree with you smile.gif, but ...there are several ways to understand the hobby of amateur astronomy, and they all have equal dignity waytogo.gif

 

Mr. Oltion says that B-J scopes are not worth anything ... seriously?  Please, read what Dave writes on 2018:

 

https://www.cloudyni...ctor/?p=8837160

 

So long cool.gif

 

Beppe

 

BTW, I hate Alexa lol.gif


Edited by benzomobile, 06 September 2021 - 03:32 PM.

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#43 rhaskins

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Posted 07 September 2021 - 07:02 AM

I believe the crux of the issue is there are so many poorly made/executed examples being sold to people that just want a scope for the kids to see the moon and planets. They just want to see the moon and planets not have a poor scope view that changes each time they set it up and take it down. A newt would been/is more rugged. My person suggestion would be a small refractor like a short tube 80. 

 

It is kinda like watching some of the auto auctions for vehicles. You always see a group of people that fully restore some old AMC model, spending $150K in funds and get $15k in bids. While the rebuilder may get a lot of satisfaction in the work, it is just a loss over-all. Instead of spending $75 for a cheap scope that is temperamental, spend $250 for a scope that is more of a workhorse.

 

I have looked around because of the discussion and really cannot find anyone that recommends a bird-jones design for beginners or others. Yes they can be fixed but only after sitting in the closet unused for a number of years. The best beginner scope is one that is used.

 

Rick


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#44 Jon Isaacs

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Posted 07 September 2021 - 07:44 AM

I had a Cometron 125 Junior. I even built a cell for it so the primary mirror could be collimated. It wasn't that good. I'd take a decent 5 inch F/8 any day..

 

5973206-monkulus at scope.jpg
 
Jon

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#45 benzomobile

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Posted 07 September 2021 - 02:04 PM

 

I had a Cometron 125 Junior. I even built a cell for it so the primary mirror could be collimated. It wasn't that good. I'd take a decent 5 inch F/8 any day..

 

Jon

 

Of course Jon, the corrector/elliptical mirror assembly cannot be collimate in any way. This is why. 

The position of the secondary determines the centering of the corrector optical axis. If the optical cone is not perfectly centered on the corrector, the image is rubbish.

Please, give me three days and I'll post here pictures of mods I made on my scope and possibly some astroimages taken with my RisingCam imx178m.

I haven't used my Cometron for a long time frown.gif

 

Beppe


Edited by benzomobile, 07 September 2021 - 02:21 PM.


#46 benzomobile

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Posted 09 September 2021 - 11:55 AM

I believe the crux of the issue is there are so many poorly made/executed examples being sold to people that just want a scope for the kids to see the moon and planets. They just want to see the moon and planets not have a poor scope view that changes each time they set it up and take it down. A newt would been/is more rugged. My person suggestion would be a small refractor like a short tube 80. 

 

 

Rick

Ciao Rick,

 

I agree with you, but ...

I don't  like to be  a  calm  Amateur Astronomer at all ... smile.gif

I like to perform diy challenging  works  in this area, and in other ones wink.gif

I enjoy it.

What I'm trying to tell you is that I don't buy new astronomical equipments because I can't afford them, nor do I buy used ones just to save money.

 

Beppe


Edited by benzomobile, 09 September 2021 - 12:05 PM.


#47 vtornado

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Posted 09 September 2021 - 05:50 PM

I believe our rock-star member Augustus has taken one apart and has found that even the mirror is really bad.

 

"To make matters worse, the PowerSeeker 127EQ’s primary mirror isn’t even a precisely manufactured sphere; it’s a random shape that came straight out of the polishing machine. The 127EQ primaries I’ve tested have had rough surfaces and all sorts of microscopic holes and hills which damage the image, and many other complicated flaws.  ... The primary mirror also appears to be secured to its support with solid gobs of epoxy, which warp and distort the mirror due to the stress they induce on the glass. This further hinders  the already-low capabilities of the telescope."


Edited by vtornado, 09 September 2021 - 05:53 PM.



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