ASI224MC with 0.5x focal reducer

[Forge]

Hi all,

I've got an f/5 Dob (Skywatcher 12" Collapsible GoTo) with which I've used the ZWO ASI224MC quite a few times without many problems. To capture a wider-view (especially for the Moon) I bought a GSO 0.5x focal reducer.

However with the reducer attached to the camera, I'm completely unable to focus! Am I doing something wrong?

Thanks in advance.

[Gavin1234]

I’m no expert but it sounds like your image train is now too long with the reducer added in I.e your sensor is now too far back from your focuser. Do you have spacers between your camera and your scopes/focuser? If so, you could try removing one or all of those

To be sure you could look up how far back your cameras sensor is supposed to be from your scopes focuser and then add or remove spacers as necessary. This is a pic of a 21mm spacer on mine to help explain what I’m talking about.

[ChrisV (Chris)]

+1. As distance between camera & reducer increases so does the focal reduction. Unfortunately, so does the amount you have to wind the focuser inwards. Too much focal reduction and you eventually run out of in-focus.

So where is the focuser set without the reducer. How much room does it have to moves inwards? With the 224MC I always put the reducer on the noise piece (T to 1.25" adaptor) and attached this to the camera. For this I used GSO and antares 0.5 reducers (I much preferred the Antares). The GSO was about 0.4 reduction with this spacing - too much reduction & in-focus!!

So I eventually opted to use a bunch of T-spacers (between camera & reducer) of different lengths to get different amounts of reduction. But then I needed a special short T-1.25" adaptor for the reducer.

Sorry for the long winded answer.

[Forge]

Thank you for the replies guys, based on your info I did some research and found out that the camera has this spec:
Back Focus Distance 12.5mm

And the GSO focal reducer page says 'In our tests, when screwed into an eyepiece, this focal reducer required approximately 8mm of additional in-focus travel so please make sure that your focuser can accommodate this travel requirement.
Focal length (estimated) = 101 - 103mm (3.98 - 4.06")
Total item length (excluding external thread) = 10mm'

I don't believe I have any spacers (I didn't even what that was, sorry - very new to this!). So based on the above, what calcs do I need to do figure what kind of spacers I need? Should I just go with 8mm and try that?