Focal Reducers \ Focal Planes & spacings

[AlistairW]

Hello,

Hoping someone can explain this to me. A lot of Flattener\Reducer combinations are tailored to the scope. For example I have a WO refractor and a WO FR/FF. The FR/FF connects to a DSLR via a T-ring. My question is how inportant is the 'spacing' between the FR/FF and the focal plane. I think i read somewhere that in my case I need it to be 55mm. But what if I had a wide T-ring and the distance was 56mm, - what would happen ? - Would it be difficult to obtain focus, would there be fringing ?

Thanks

Alistair.

[ollypenrice]

There's a website somewhere, and an old thread on here, demonstrating the distortions which being too close and too far bring about. How critical the spacing is depends on the particular optics and the chip size, the bigger the chip the more accurate the spacing needs to be. You can focus on axis pretty well with the wrong spacing. In some cases a 5mm error won't matter but in others you need to be sub millimetre.

Olly

[whizzbang]

this might help.....a little

[Dave In Vermont]

You may find this useful if you're playing with focal-reducers:

http://www.mallincam.net/uploads/2/6/9/1/26913006/focal_reduction_for_dummies.pdf

Written around the MallinCam, the principles remain constant.

Dave

[AlistairW]

Thanks for the replies

[BlueAstra]

I've picked up some information over time:

TeleVue TRF-2008, quoted at x0.8 at 56mm +/- 4mm

Celestron x0.63, quoted at x0.63 @ 105mm, x0.7 @ 50mm, x0.5 @ 225mm

Meade x0.63, quoted at x0.63 @ 105mm