C9.25 Focuser Travel

[Johnboy2011]

I have just hooked up my 1000d for the first time and I don't have enought focuser travel to bring objects into focus.

I am using a 6.3FR, T adaptor and EOS adaptor to my camera, the scope has a feather touch micro focuser installed.

Using live view on APT I can see I was getting close but I have run out of adjustment.

What are my options, I'm stuck!!

Thanks,

John

[Peter Drew]

Hello John.

I think the combination of FR, adaptors and the extra focuser will have exhausted the focus range of the system. The FR is a positive component optically and works in opposite sense to a Barlow and produces less inward travel. The options would appear to be narrower adaptors, a more compact focuser or removal of the secondary focuser and revert to the standard coarse focus knob.

[Merlin66]

John,

I use the C9.25 with a x0.63 reducer and a spectroscope ( similar backfocus as a DSLR -55mm) with no issues.

The distance from the reducer to the sensor must be 110mm. - If the focuser is too big, this can be an issue.

(I use the feathertouch 10:1 micro focuser...)

[Johnboy2011]

I've attached two photos to show how the DSLR is connected. Am I understanding correctly that I need to reduce the distance to the chip to acheive focus? I suppose the only way to do this would be with a shorter T adaptor. I need to be carefull though as the camera body still needs to clear the micro focuser which extends further than a standard focus knob.

Does anyone know if there is a T adaptor out there that would do this or am I barking up the wrong tree?!

Thanks,

John

[rwg]

Your SCT-T adaptor looks very long (I'm assuming that's what the black tube between the camera and the reducer is). There are much shorter ones available - for instance Antares SCT - T Thread Short Adaptor | Telescope Accessories | Rother Valley Optics.

You can also get T thread extension tubes in various lengths (10mm, 15mm etc) if you find the tube you get is too short and you need more distance to clear the focus knob (although maybe rotating the camera would do the trick instead, the left hand side doesn't look to stick out nearly as far as the handgrip on the right).

Robin

[Johnboy2011]

Hi Robin,

Thanks for that, that looks like just what I need! As you say I could rotate the camera to avoid the hand grip and if I measure the projection of the focuser and aim to just clear it I guess that should do it!!

Thanks,

John

[Merlin66]

Hmmm

Check the distance from the camera body to the reducer - this needs to be close to 55mm....you may need a shorter SCT to T adaptor.

[Johnboy2011]

A further thought, ideally I would be using an OAG for guided imaging. Is there a suitable OAG out there that would'nt add too much length to the light path?

[Johnboy2011]

I checked the length of the Meade OAG which is 55mm, do you think this would do the trick?

BS Astro Off Axis Guider | Telescope Accessories | Rother Valley Optics

Looks to be shorter which would hopefully give me enough focus?

[Merlin66]

55mm plus the camera body should bring you very close to the "design" distance of 110mm.

Using an OAG guider can be a bit daunting at first....but certainly does work.

[Johnboy2011]

Sorry Merlin, just re-read my post again which isn't clear, the Meade T adaptor I was using which does'nt allow me to acheive focus is 55mm. I'm thinking the Brightstar OAG in the link looks shorter than the 55mm Meade which would hopefully give me focus?

John

[Merlin66]

Hmm

If the total distance from the sensor to the reducer is around the 110mm mark (adaptor + camera body) then that's not the problem......

The C9.25 should certainly allow you to focus with that set-up.

I use an identical arrangement and can focus OK.

Is there something else which may be causing the problem?

Can you focus on a distant landmark during the day??