Focuser tube : Adapter 57mm > 51mm?

[FrenchyArnaud]

Hi all! I am a bit miffed and could do with some support here. 

I am transforming a newtonian (Celestron C8N, 8", 1000mm, F5) into photographic. All went well but I just realised that the opening of the focuser (where tge ring with the little thumbscrews to lock the EP or camera) has a diameter of 57mm while obviously, my coma corrector, that slides in it, has a diameter of 51mm. So I can't use my dslr+CC as it stands! Even with the thumbscrews all the way in, they are unable to lock the coma corrector, not even to reach it (and if they were, the camera would be totally off center anyway)

 

Anybody has any clue how to sort this?? 

[Mandy D]

12 minutes ago, FrenchyArnaud said:

Hi all! I am a bit miffed and could do with some support here. 

I am transforming a newtonian (Celestron C8N, 8", 1000mm, F5) into photographic. All went well but I just realised that the opening of the focuser (where tge ring with the little thumbscrews to lock the EP or camera) has a diameter of 57mm while obviously, my coma corrector, that slides in it, has a diameter of 51mm. So I can't use my dslr+CC as it stands! Even with the thumbscrews all the way in, they are unable to lock the coma corrector, not even to reach it (and if they were, the camera would be totally off center anyway)

 

Anybody has any clue how to sort this?? 

57 x 3.2 Aluminium tube. Cut it to length to make a sleeve. You might have to slit it down the length, but it should work.

https://www.1stchoicemetals.co.uk/product/2-14-x-10swg-57-15mm-x-3-26mm/

[globular]

Presumably the 57mm opening is threaded?
And you want to insert a 2" nosepiece that is on your coma corrector?

You probably want something like this...

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4695_Borg-2--Adapter---7504---Adapter-from-M57-to-2--Receptacle.html

or this...

https://astrohutech.store/product/m57-to-2-compression-ring/

[FrenchyArnaud]

8 minutes ago, Mandy D said:

57 x 3.2 Aluminium tube. Cut it to length to make a sleeve. You might have to slit it down the length, but it should work.

https://www.1stchoicemetals.co.uk/product/2-14-x-10swg-57-15mm-x-3-26mm/

I actually considered that with pvc! But Globular's proposition is more elegant 👍

[FrenchyArnaud]

8 minutes ago, globular said:

Presumably the 57mm opening is threaded?
And you want to insert a 2" nosepiece that is on your coma corrector?

You probably want something like this...

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4695_Borg-2--Adapter---7504---Adapter-from-M57-to-2--Receptacle.html

or this...

https://astrohutech.store/product/m57-to-2-compression-ring/

Yeps, that's exactly what I need! The prices however 😱😱😱 $55 for that, it's daylight robbery!

 

However now that I know what to look for, I will try and find a good deal... somewhere! 

[FrenchyArnaud]

I contacted Astrohutech and their pretty much instant response (great com skills!) is, they supply FLO so if I contact FLO I should be able to get the part faster, cheaper. FLO is closed until monday for inventory but I am confident they will be able to sort sthg out for me, these guys have always been brilliant service-wise. 

[FrenchyArnaud]

Aaaand... I realise I ****ed up good and proper! The inside of the ring is 57mm but the thread itself is 60mm 😆😐

So I am afraid I need to consider manufacturing a compression ring as @Mandy D was suggesting 🤔

[globular]

Result.

I do recommend you double check the measurements before ordering.

The 51mm you mention is almost certainly really 50.8mm (2") and while there is a 57mm astronomy thread (M57) there are also M56 in both 1mm and 0.75mm pitches. You have to get the right one or they won't screw on correctly.

If in doubt - tell FLO what you are trying to couple together and they'll sort you out.

[globular]

posts crossed.... I had a funny feeling... lol

If it M60 then this will work....

https://www.firstlightoptics.com/adapters/baader-clicklock-m60a-for-vixen.html

but it's not cheap and adds a fair bit to the light path.

[FrenchyArnaud]

3 minutes ago, globular said:

posts crossed.... I had a funny feeling... lol

If it M60 then this will work....

https://www.firstlightoptics.com/adapters/baader-clicklock-m60a-for-vixen.html

but it's not cheap and adds a fair bit to the light path.

The light path is not the issue because part of the convertion was to push the mirror up 70mm (i can now put it anywhere i choose to, between +15 and +70mm using the collimation screws and I calculated it should be around +35mm with dslr+CC in, so plenty of margin)

However at that price, I have a better time buying a crayford. (£129)

I guess diy compression ring it is...

[FrenchyArnaud]

SOLVED! 

Thanks FB, someone pointed out that my focuser was missing a piece. I dug in my astro boxes and what do you know, I found the original adapter that has indeed a 50.8mm bore 🤭🍾🤩

It's basically a plastic sleeve with a couple of thumb screws, 56.5mm OD, 50.5mm ID. I must have taken it off at the time, when i was using it for visual with a 1.25 eyepiece holder. When I began AP, I switched to the 130PDS and forgot about it. Years passed, I decided to recommission the 8" and here we are!  Lesson learned : never throw anything away... I'm sure glad I did not. 

Problem solved!