f6.3/f3.3 focal reducer for visual use?

[Paul-F]

I have a 17mm Ethos with the 12" LX90 which gives a magnification of 179x and a fov of .56 degree - will using the meade f6.3 reducer make the fov a wider .87 degree and still be suitable for visual use?

Likewise for the f3.3/f5 reducer for visual use?

[michael.h.f.wilkinson]

The F/3.3 reducer is only useful for small-chip CCD cameras. The F/6.3 reducer can be sed for visual use, but only for 1.25" EPs. As the ethos 17 is a 2" EP, severe vignetting will result. The reason for this is that the reducer cannot access a larger image plane than a 2" EP at the widest possible field stop. The widest FOV I get visually with my C8 is with the 40mm TMB Paragon (50x, 1.34 deg true FOV, field stop diameter 45.7mm, close to maximum), closely followed by the Nagler 31T5 (65x and 1.25 deg TFOV). The Paragon is now sold as a clone by Teleskop Service, and I understand the Skywatcher Aero 40mm is the same design. On your 12" you should get 0.893 deg true FOV at 75x with these EPs. The 31 Nagler would give 0.833 deg true FOV at 97.5x.

[Paul-F]

Ok, thanks, I get it - no real use to me then unless imaging!

I have an adler 2" 38mm 70 deg afov ep which is good for .87 tfov but that makes the sky background fairly bright unless its real dark. I was mostly curoius about stepping the ethos down a bit to benefit from its quality and contrast.

I think what I am probably after the widest tfov possible in my scope balanced with a wide afov for contrast ... a 40mm naglar would do well me thinks! I'll start another thread about that.

[michael.h.f.wilkinson]

Naglers go up to 31mm. The 31T5 is a brilliant piece of kit. I do not use the 40 mm very much, except on those rare occasions I need more than 1.25 deg FOV.