Baader zoom

[HaiXing]

I just purchased a baader 8-24 zoom eyepiece and using it on a skywatcher 200 dob.   With 1.25  I can see fine but I go and try to use 2" the image is not focusing even at 24mm. I mostly see a white circle with a cross.  Any suggestions what I am doing wrong, this the first time I've used my scope with a 2" eyepiece.

[Franklin]

You might need a 2" extension holder between the visual back and the eyepiece in 2" mode. There's not a lot of difference between the stop point on the BHZ in either mode but you must be taking out the 2" to 1.25" adaptor to use in 2" mode and that will account for some extension. Try loosening the eyepiece holder in 2" and pull the whole zoom out until you get focus. That will be the size of extension you will need.

[Spile]

With the BHZ and 200P, I used the 2” adapter and the regular extender. With the matching Barlow I would need to withdraw the eyepiece about 5mm to get focus. I now have a shorter extender which is used without the Barlow and both extenders when with it. 
https://astro.catshill.com/the-zoom-eyepiece/

[Dave scutt]

I had the same problem but other way round when I was using a 2" eyepiece 28mm I could focus but when I switched to a 1.25" 9mm I couldn't focus.  I had both adapters in at the same time.

[John]

You will need to use the 2 inch eyepiece adapter in the focuser drawtube. It looks like this:

This will put the focal plane of the eyepiece at the correct position so that you can reach focus within the range of travel of the focuser.

 

[HaiXing]

Unfortunately I left my 2"  attachment at home and purchased the bhz while I was heading to the cottage for the weekend oh well I guess there's always next time thx for replies. 

Edited August 29, 2021 by HaiXing
Edit

[John]

If you use the eyepiece in 1.25 inch mode you get the same results. The 2 inch barrel facility is a convenience - it does not turn the eyepiece into a 2 inch one.

[Spile]

19 hours ago, John said:

If you use the eyepiece in 1.25 inch mode you get the same results. The 2 inch barrel facility is a convenience - it does not turn the eyepiece into a 2 inch one.

True but you need 2” mode if you are going to easily use the matching Barlow. The BHZ is far more compliant in 2” mode as far as I am concerned.

[John]

18 minutes ago, Spile said:

True but you need 2” mode if you are going to easily use the matching Barlow. The BHZ is far more compliant in 2” mode as far as I am concerned.

I don't think the OP has the BHZ barlow

 

Edited August 30, 2021 by John

[Louis D]

Does anyone know why Synta hasn't switched over to a GSO style focuser that actually makes sense when switching between 2" and 1.25" mode?  It would prevent a multitude of problems for users of their Dobs.

[johninderby]

Seems strange that SW hasn’t updated their dobs to compete with the other brands available. Are they getting left behind? 🤔