Confused by 'visual backs'?

[TheThing]

I have a recently acquired OMC140 Mak with a 1.25" visual back (I think that is right!)

The 1.25" visual back seems to just be an adapter fitted into a 2" focuser and held in with 2 grub screws.

What makes it a visual back then and not just a 2"/1.23" focuser? Can I put a 2" diagonal and EPs straight in the focuser instead (with extension tube as necessary)?

Yours,

Very Confused of Epsom

[Peter Drew]

A visual back is exactly what it says, it is an adaptor which accepts the accessories normally used for visual operation. This is distinct from a photographic back which would usually be threaded for coupling to a camera.

[Merlin66]

The term is usually used for 1.25" adaptors which are screwed onto the rear cell of an SCT using the standard SCT thread...

Does the Mak have a threaded rear cell? If so, then I would have assumed, that the "visual back" would have screwed directed to that. Do you have a focuser fitted to the rear cell? If so then you could be correct and the 1.25" is just an insert into a 2" eyepiece holder....

[TheThing]

Ah, no screw threads so more likely a Focuser than a visual back.

TheThing

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[johninderby]

What age is your scope? Is it a purple, white or carbon fibre tube? The real cells do vary depending on the age of your scope but originally came with a screw on 1.25"visual back, but a 2" visual back could be fitted.

BTW the only focuser that has a small enough diameter body that will fit the OMC140 is the FeatherTouch with the small SCT adaptor. There's only about 1mm clearance between the focuser knob and the FeatherTouch.

John

[TheThing]

Hi John,

It's a very attractive creamy colour, so I suspect it was originally white and has aged a bit.

[johninderby]

So your visual back looks like this one then?

John

[TheThing]

Yes, that's the one.

TheThing

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[johninderby]

Ok then it's a standard type 2" visual back with a 1.25" adaptor so yes you can remove the 1.25" adaptor and use a regular 2" diag with it then.

John

[TheThing]

Thanks John, much appreciated.