Spacer for ZWO120

[Datalord]

I'm trying to get my ZWO120 to focus on the OAG for a G3-16200 and I've read that I need 61.5mm backfocus distance. So I need a spacer/extension for the ZWO, which I assume is 1.25".

I'm too stupid to find something this simple. Seems to me I need something that is unthreaded in both ends, one male and one female and extensible somehow. What do I need to search for to find this thingimajig?

[AKB]

If you unscrew the nose-piece, the you have a female T2 (42mm) thread.

Try one of the Baader variable adapters perhaps (assuming money no object!) ...

https://www.firstlightoptics.com/adapters/baader-varilock-29-lockable-t-2-extension-tube.html

[Datalord]

But the noise piece is about 30mm long, and this is maximum 29mm. I need something which can extend further than that. 

[Davey-T]

17 minutes ago, Datalord said:

But the noise piece is about 30mm long, and this is maximum 29mm. I need something which can extend further than that. 

https://www.firstlightoptics.com/adapters/baader-varilock-46-lockable-t-2-extension-tube.html

Dave

[Datalord]

I just can't wrap my head around how I would make those Baaders fit with the OAG. I can see there is threading that might go into the camera, but which part would go into the OAG?

[skybadger]

If you unscrew the eyepiece mount on your oag, you can directly thread the t2 spacers in, for the right separation. Alternatively, put a spacer between the oag and the eyepiece holder, that will provide the extension you need and allow you to use the existing 1.25" adapter on the camera for a bit of easy in and out movement. 

[Datalord]

 

40 minutes ago, skybadger said:

If you unscrew the eyepiece mount on your oag, you can directly thread the t2 spacers in, for the right separation. Alternatively, put a spacer between the oag and the eyepiece holder, that will provide the extension you need and allow you to use the existing 1.25" adapter on the camera for a bit of easy in and out movement. 

Hmm, that doesn't sound right. This thread is much smaller than the one on both ZWO and on the linked Baaders. ?

[skybadger]

Hmm, yes I see. Both of mine by different vendors use t2 barrels. OK, you'll have to do it the other way- extend your t2 to eyepiece barrel.

 

[Datalord]

6 hours ago, skybadger said:

Hmm, yes I see. Both of mine by different vendors use t2 barrels. OK, you'll have to do it the other way- extend your t2 to eyepiece barrel.

 

Yes, that's what I was trying to find, but I just don't know what to search for.

[skybadger]

Sounds like a straight 30 mm t2 spacer between the camera and the eyepiece adapter. Back to that recommended baader piece. 

[Datalord]

4 hours ago, skybadger said:

Sounds like a straight 30 mm t2 spacer between the camera and the eyepiece adapter. Back to that recommended baader piece. 

OK, I'm lost. How would that baader piece fit on the eye piece holder? Everything in it is threaded, while none of my pieces are. 

[almcl]

Would something like this work?

https://www.ebay.co.uk/itm/173396626603

[Martin Farmer]

Hi,

I had the same issue with the camera and ended up making a new holder to hold the guide camera.  Yes it’s a lodestar in the picture but I have used a ZWO 120 and had to make custom adaptors. The supplied part did not work in my installation at all.

The thread is  M18 x 0.75 pitch

[Stub Mandrel]

Don't you need a T2 female to T2 male plain extender to put between the supplied ZWO 1/.25" nosepiece and the camera?

[Datalord]

2 hours ago, almcl said:

Would something like this work?

https://www.ebay.co.uk/itm/173396626603

Possibly. And it's cheap enough that I just made an order for it.

2 hours ago, Martin Farmer said:

Hi,

I had the same issue with the camera and ended up making a new holder to hold the guide camera.  Yes it’s a lodestar in the picture but I have used a ZWO 120 and had to make custom adaptors. The supplied part did not work in my installation at all.

The thread is  M18 x 0.75 pitch

That looks amazing. How did you make it?

[skybadger]

7 hours ago, Datalord said:

OK, I'm lost. How would that baader piece fit on the eye piece holder? Everything in it is threaded, while none of my pieces are. 

Sorry. 

The eyepiece adapter on the camera is threaded for t2. 

So put a t2 threaded extension tube between the 11/4" eyepiece adapter and camera and you have the extension you need.

That is all you need.

[skybadger]

That extension will also do, just not as securely as a threaded connection.

[Datalord]

3 hours ago, skybadger said:

Sorry. 

The eyepiece adapter on the camera is threaded for t2. 

So put a t2 threaded extension tube between the 11/4" eyepiece adapter and camera and you have the extension you need.

That is all you need.

God, the penny dropped. I was focusing on the wrong side instead of at the side where the camera is threaded. Thank you! Ordered a kit with a few different extenders so I can mess around.

[skybadger]

Good. Glad to help. Making a custom 18mm was the next step but should not be necessary. 

[Datalord]

Well, got my mount back this week and set it all up. I just spent 2 hours messing around with a big pile of extenders to no avail.

Then I place an eyepiece on it, with little result. For whatever reason, I took off as much of the eyepiece I could, until only the lens was there. I placed this up to the holder on the OAG and lo and behold, it's full of stars. So the 61.5mm quoted in the manual turns out to be absolute nonsense, it's more like 5mm. Which gives me the problem of finding a T2 threaded piece that is ultra short.

[skybadger]

Can you unscrew or otherwise detach the eyepiece holder from the 18mm thread on the oag?

There may be a t2 thread lurking in there to thread into the camera directly.

Failing that, you're going to have to cut that eyepiece stub on the camera down. But I would check that you still have clearance between your large camera, focuser and guide camera if you do this. 

 

[Datalord]

well, I found this: https://www.365astronomy.com/zwo-low-profile-cover-for-all-zwo-asi-cameras-except-the-cooled.html?gclid=CjwKCAjwlejcBRAdEiwAAbj6KROw7qZvBiJgWZBe224ipz_eqcLcFCWmVTHGYCTmOX_CQT41DKg6BxoClCEQAvD_BwE

5mm. Made an order.

[Datalord]

Nope, no workie. Next step is to saw off the tip to the minimum the eyepiece holder will still attach to. outside of that, I'm completely lost by now.

[Stub Mandrel]

Can you move the main camera out?

That will make you to move the OAG in, allowing you to have the ASI120 further out.

 

[Datalord]

46 minutes ago, Stub Mandrel said:

Can you move the main camera out?

That will make you to move the OAG in, allowing you to have the ASI120 further out.

 

There is an extra 10mm spacer for the main camera I can put in, but how will this make the 120 go further out? I still don't know how this backfocus stuff works.