Cheap compromise for a 35mm Panoptic

[Piet Le Roux]

I have been toying with the idea of getting a Tele Vue 35mm Panoptic but the Rand is very weak so the $390 plus shipping and tax is going to cost me a bundel. On paper the 35mm Panoptic looks like a perfect fit for both my 8” F10 ACF Meade and my 15” Obsession which has a focal ratio of F5.1 with the Paracorr II. It has a 38.7mm field stop which I think is very close to my SCT’s maximum field stop and on the Obsession it has a exit pupil diameter of just under 7mm. I do have a OPT 2” 0.5 focal reducer but for it to work with my 27mm Panoptic it must be positioned to give a 0.7 deduction ratio. Anything smaller would be too much and lead to vignetting. So today I set my 8” LX90 up facing a electric pylon about 500 meters away and inserted my 27mm panoptic with the 0.5 reducer screwed on directly to it. It focused and had only slight vignetting on the one side. I used the Audiostar controller to measure its TFOV by placing a insulator halfway in view on the left side, zeroing the Az counter and moving it till halfway view on the right hand side. The average results were 71” or 1.18 degrees with the reducer this calculates to about 0.72 reduction. With the 27mm by itself I measured a TFOV of about 0.85 degrees which is very close to what I got using the given field stop of 30.5mm : (30.5\2000) X 57.3 = 0.87 degrees.
So the OPT/GSO 2” 0.5 reducer is a near perfect match for the 27mm Panoptic! But it does seem to lose some of the Panoptic’s crispy sharp focus. I will try to test it tonight on some big deep sky objects and see how the combination does. For now this would have to do for my wide view eyepiece.