Corrective lens for Celestron 127 eq

[Rhino1969]

Hello all I hope y'all are doing well.  I have a question about the corrective lens on the 127 eq.  I just started viewing the sky recently and bought this telescope.  I kept noticing a blur to everything I looked at Moon, Star, Venus etc.  I cleaned everything from mirrors to corrective lens and noticed a tiny scratch on the corrective lens.  I am figuring that this has been causing the issue with the blur.  It is dead center on the lens.  Can anyone tell me if this is the issue for the blur that I noticed?  If so, where can i purchase either a new lens or a new housing where the lens is located?  I have looked online for corrective lens to no avail.  thank you in advance for answers.  Have a good day all.

[johninderby]

Hi 

If it is dead centre on the corrector that would mean it is over the silver spot in the centre and would have no effect. Even if on another part of the corrector would have very little effect if any.

I expect the blur problem is actually caused by not being in focus. Try focusing on a star. It should go from a donut shape down to a point and then back to a donut as you turn the focus knob. I’m assuming you are using the diagonal?

Edited May 9, 2020 by johninderby

[John]

I agree with the above,

Blemishes or dirt on the corrector will have little or no effect on image quality.

Did you take the scope apart to clean the mirrors and the corrector ?

 

[Rhino1969]

Yes i have cleaned the primary mirror using distilled water.  Inspected was clean and re-installed.  Should I also clean the secondary was nervous about taking that one off.  Also the corrective lens was cleaned that is when I noticed tghe scratch

Edited May 9, 2020 by Rhino1969

[johninderby]

Is this the scope?

[Rhino1969]

No sorry it isn't.

 

[johninderby]

Ah so it is a Newtonian scope. In that case it’s probably simply needs collimating. A newtonian doesn’t have a correctot plate.

Edited May 9, 2020 by johninderby

[John]

Did you remove the main mirror from the scope to clean it ?

If you did, you will probably need to re-collimate the scope, that is to ensure that the alignment of the primary and secondary mirrors is accurate. 

I think that design of scope also uses a correcting lens at the bottom of the eyepiece drawtube ?. If so it is a bird-jones design scope.

 

[Rhino1969]

I have collimated  it 3 times.  I did have to put a center on it as it didn't come with one.  Used diagram overlay and watched video on how to.  I have measured to ensure center on mirror.  Should I take off the secondary mirror and clean it?  I am leary with that mirror so if I should any pointers with it and placing back right would be appreciated.  thank y'all for all the help so far.  I used a laser collimater 

Edited May 9, 2020 by Rhino1969

[Rhino1969]

Yes sir it is a byrd-jones design.

[johninderby]

Bit more info.

 

The 127mm Bird-Jones Optical Tube

The PowerSeeker 127EQ is a 127 mm 5ʺ f/7.87 (focal ratio) Newtonian with a focal length of 1,000 mm.

If you do some basic math, you’ll immediately notice something odd. The 127EQ’s tube is only twenty inches long – 500mm. How does one fit a Newtonian optical system (not a Cassegrain, which folds the light path into a smaller physical package) into that small of a tube?

The answer is that the 127EQ not a Newtonian. It’s a Bird-Jones. Bird and Jones were two amateurs in the 1950s who sought to create a simple telescope with a spherical instead of parabolic primary mirror, with a corrector lens/Barlow in front of the secondary mirror. This design in theory can work well, and some properly executed Bird-Joneses do in fact work quite well. But the 127EQ is anything but properly executed.

Unlike the classical Bird-Jones style, which puts the corrector lens just in front of the secondary mirror, the 127EQ’s “corrector” is mounted in the focuser. This means that it will move whenever you dial in the focus, thus assuring the correction is basically never spot-on. 

Even if the corrector being mounted in the focuser was not an issue, the 127EQ’s corrector is just a Barlow lens inserted into the focuser drawtube – not a proper corrector lens. It doesn’t fix the spherical aberration inherent in the roughly f/3.5 spherical primary mirror. It makes the light cone a little steeper, which in theory would correct the system to maybe half a wave – bad at half the tolerance required for a good telescope, but somewhat usable. But due to the positioning of the corrector, this isn’t possible.

To make matters worse, the PowerSeeker 127EQ’s primary mirror isn’t even a precise sphere, it’s a random shape that came straight out of the polishing machine.

[Rhino1969]

So may not even focus correct with no blur?  Hahaha seems right for my first telescope

[Rhino1969]

So what is a good telescope maker to buy from?

[johninderby]

The design of your scope can be very tricky to colimate and many have given up in frustration.

What sort of budget. 

And does it have to be an EQ or would an Alt-Az mount be suitable.

[Louis D]

5 minutes ago, Rhino1969 said:

So what is a good telescope maker to buy from?

It's not so much maker as type.  Celestron markets some really good scopes at the higher end of the price scale, but besmirches their good name by selling these J-B scopes at the entry level end.

I would shop for a Sky-Watcher Heritage-130p Flextube, a Sky-Watcher Explorer 130PS AZ GTi, a Sky-Watcher Skyliner 150P Dobsonian, or a Sky-Watcher Skyliner 200P Dobsonian for a massive improvement, depending on your budget.

Lest you think Sky-Watcher is a much better brand than Celestron at the low end based on my recommendations, just remember that both are owned by Chinese optics manufacturer Synta.

[johninderby]

All the major brands do some low end department store tyoe scopes. As mentioned Celestron and Skywatcher make equivalent quality scopes and some really goid scopes.

Some good beginners scopes.

https://www.firstlightoptics.com/beginner-telescopes.html

[Rhino1969]

Decent price ranges on these scopes.  Is the Sky-watcher a UK company? Or is it Flo that is?

[johninderby]

Skywatcher and Celestron are ownded by Synta a Chinese company. FLO is a UK dealer.

Edited May 10, 2020 by johninderby

[Louis D]

Celestron is formerly a US telescope designer and manufacturer of telescopes.  I don't know if any design and manufacturing takes place in the US after being bought by Synta.

I have no knowledge of the history of Skywatcher.  I'm guessing it's the European house brand of Synta.

[johninderby]

Skywatcher is a world wide brand and is big everywhere but the US where Synta sells the Orion brand. 

Orion branded scopes are pretty expensive in Europe as they are first imported into the US and then exported again to Europe so a lot if extra expenses whereas Skywatcher is shipped directly from the far east. 

Edited May 10, 2020 by johninderby

[Cornelius Varley]

9 hours ago, johninderby said:

Ah so it is a Newtonian scope. In that case it’s probably simply needs collimating. A newtonian doesn’t have a correctot plate.

But that particular telescope, a Jones-Bird, does have a corrector lens built into the focuser.

[Rhino1969]

Thank y'all for all your help

[johninderby]

Best to just cut your losses with the 127 and not waste any money on trying to fix it. 🙁

If you find a scope or two that look intersting just give us the details and we can help with advise on if  it’s a good buy or not. 👍🏻

Edited May 10, 2020 by johninderby

[RT65CB-SWL]

17 hours ago, Rhino1969 said:

I have collimated  it 3 times.  I did have to put a center on it as it didn't come with one.  Used diagram overlay and watched video on how to.  I have measured to ensure center on mirror.  Should I take off the secondary mirror and clean it?  I am leary with that mirror so if I should any pointers with it and placing back right would be appreciated.  thank y'all for all the help so far.  I used a laser collimater 

Have you collimated your laser? ...if 'yes' they need to be collimated too! ...especially the cheaper branded ones.

https://www.youtube.com/watch?v=bE09_X43UUQ

Also cheap 'Bird-Jones' type of 'scopes can be 'hit or miss' to collimate.  

Edited May 10, 2020 by Philip R

[Cornelius Varley]

16 hours ago, Rhino1969 said:

I have collimated  it 3 times.  I did have to put a center on it as it didn't come with one.  Used diagram overlay and watched video on how to.  I have measured to ensure center on mirror.  Should I take off the secondary mirror and clean it?  I am leary with that mirror so if I should any pointers with it and placing back right would be appreciated.  thank y'all for all the help so far.  I used a laser collimater 

Unfortunately this type of telescope cant be collimated using a laser.