Binoviewer on LB 16" - success !

[jarbi]

Hi Everyone,

Yesterday I was finally coming to a good end of my adventures with the 16" Lightbridge. After mounting a Tri-knob Moonlite focuser ( thanks again Steve ) and receiving a new non-astigmatic secondary mirror, I could test the Baader binoviewer on the scope. It was a bit cloudy already in the evening, but I could see the Moon, and I could get it in focus with it ! It was equipped with the 2" Baader coma corrector ( see first foto ), and I had not more than 4-5mm backfocus left after ( second foto ), but who cares . So, whenever you think about it, you can certainly do it !

By the way, I tried the same with an 18" Obsession this week at our astroclub - no way ! It is impossible even with the low-profile Obsession focuser.

cheers,

janos

[Sam]

That's very interesting Janos, glad you got it all working. Why did you have to change the secondary mirror?

Sam

[jarbi]

That's very interesting Janos, glad you got it all working. Why did you have to change the secondary mirror?

Sam

Sam, I was a bit unfortunate to receive my LB with an astigmatic secondary . I have requested a warranty replacement from Meade and it took almost a month, but now it's done ! The new secondary is perfect, and I am looking forward to test it on a nice dark site.

cheers,

Janos

[Astronut]

What led you to believe the secondary was astigmatic and how did you test it? The reason I ask is I'd like to check the secondary on my skywatcher dob but I have no clue how to test it. I have a ronchi grating from Orion UK and the diffraction pattern seems fine. This tool is for testing the primary but because it's placed in the focuser as an eyepiece it's using the secondary for testing the primary.

[jarbi]

What led you to believe the secondary was astigmatic and how did you test it? The reason I ask is I'd like to check the secondary on my skywatcher dob but I have no clue how to test it. I have a ronchi grating from Orion UK and the diffraction pattern seems fine. This tool is for testing the primary but because it's placed in the focuser as an eyepiece it's using the secondary for testing the primary.

Hi Astronut,

I was not sure at the first instance that the secondary was bad. So I did a star test with 60 degrees rotated mirror cell, and the direction of the astigmatic image didn't change. With a bad primary I could have seen a 60 deg. rotation of the elongated star images as well. But - to be 110 % sure - I have done the following evening test:

- placed the secondary cage on a garden table, having the focuser in horizontal position. In the direction where normally the primary is I put an artificial star in about 20m distance.

- I have pointed my ED80 directly to the artificial star and it was a perfect star image. Then I looked at the artificial star through the focuser opening with the ED80 ( using the reflected image from the LB secondary ). I saw exactly the same elongated star images ( perpendicular elongations on the two sides of the focus ). Than I was sure: my LB secondary is defected.

Of course the astroshop double-checked it in their labo, they gave me right.

So I think you can do exaclty the same: just remove your mirror cell and do the steps I described, I hope I was clear enough.

Cheers,

Janos

[Astronut]

So basically you used a refractor known to show a near-perfect diffraction pattern with an artificial star and then looked again at the same artificial star reflected by the suspect secondary. Trouble is I don't have access to a refractor or an artificial star gizmo.

Thanks for the info.

[calibos]

Nice to know that Meade will replace the secondary without sending the whole scope back. Haven't tested my LB16 secondary yet, heck I've only looked through the scope once but should I subsequently find the secondary is astigmatic (much more common than a bad Primary on these GSO scopes) I won't be stuck between a rock and a hardplace with Meade wanting the whole scope back and me after installing a multitude of mods and customisations to the scope.

Good to know!

[calibos]

I don't have access to an Atrificial star either but I am sure I have an artificial Fiber optic Xmas tree in the attic that I could ....'adapt' .

More troublesome would be finding a large enough area to perform the test!!

I am also without a 'Refractor' though I will soon have a Stellarvue F80M2 80mm F4 Finderscope. I wonder could I use this?

[calibos]

BTW, can't wait for the proper First Light Report Janos!! ie What things look like through the BV's etc.

Our 16in LB's have the apeture to really make the light loss of BVing a non issue. ie apparently the effective light loss is equivelent to a 3in reduction in apeture. Thats a big 'ol loss to incur when your 8in is reduced to a 5 or your 12in is reduced to a 8 or 9. Not such a problem going from 16in and effectively reducing apeture to 13in.

[jarbi]

BTW, can't wait for the proper First Light Report Janos!! ie What things look like through the BV's etc.

Our 16in LB's have the apeture to really make the light loss of BVing a non issue. ie apparently the effective light loss is equivelent to a 3in reduction in apeture. Thats a big 'ol loss to incur when your 8in is reduced to a 5 or your 12in is reduced to a 8 or 9. Not such a problem going from 16in and effectively reducing apeture to 13in.

Calibos,

I will certainly come back after a proper First Light with this configuration !

Answering your question about the Stellarview finder, I think this one has a good enough optic and you can drop in an eyepiece to have at least 50-100x mgnification for astigmatism test.

Janos

[calibos]

Cool, thanks for that info Janos. Another reason why I felt it was worthwhile to invest in a premium finder. Its a mini quality refractor in its own right! I hadn't even thought of the EP magnification issue, I was just thinking in terms of the lense quality but of course you are right and its a bit of a 'Doh!' moment for me reading your post. The finderscope optics could be the best in the world and it would still be useless for this test when one couldn't use enough magnification.

This finderscope will be my finder, my widefield refractor, my video astronomy scope and my mirror tester

(re. Video astronomy) With the removable diagonal one can insert 2" EP's in straight through mode. Also has the benefit that webcams can now come to focus. So at outreach I'll have the webcam inserted in the F80M feeding the image of the moon say, to the laptop screen which will be something for those in the queue at my scope to look at before they get to the top of the line and can look at the lovely sharp highres real view through the scope EP. Someday I might even take the Laptop feed and plug it into one of those new mobile phone size pico video projectors and project the image onto a plasma size 50in roll up screen behind the scope!!