I just got a new 2" Siebert Power Mag Wheel today. I'm going to be socked in with bad weather through the weekend, so no use to try it on the fast Newt. I pulled out my 80mm f/6 Nighthawk II and did a preliminary test for terrestrial use.
The input side is a 1.25" tube about 2" long. The body is the standard 3-mag body that Siebert makes. This model is Telecentric in operation, so the output side is much bigger than the input side and and has about 38mm output lens and a 2" eyepiece holder barrel. Included was a 1.25" eyepiece adapter made of Delrin. The output lens is what I would call a T-2 size. It will not illuminate the field stop of the longest 2" EP's. Still, it works rather well. It is a 2X, 3X and 4X mag model.
With a 38mm Siebert Observatory, there is some reduction in AFOV due to slightly small output lens, but the field edge was still fairly sharp. At all mags the view was sharp to the edge, and no refocusing was necessary when going from center to edge. Harry said this model should eliminate the need for a Para-Corr in a fast Newt. When going from 2X to 3X to 4X, you must refocus a bit. The biggest jump is between 2X and 4X and amounts to less than 1/2" in my NH II. The 38mm Observatory is an EP that maximizes the AFOV in a 2" barrel. It vignettes a bit when placed in many 2" diagonals due to the nosepiece of the diagonal cutting off the light cone a bit. Still, a full 2" output lens would solve that problem in the PMW. Your 41mm Pan or 31mm Nagler will have the same issues.
With a 26mm 2" E-Lux Kellner, an EP that gives horrible results when used alone in the NH II, the view was very useable at 2X, and got better from 3X to 4X. At 2X it was a bit soft on edge, but no refocusing was necessary to get the best sharpness. Edge sharpness improved noticeably at 3X and was about the same at 4X. The entire AFOV was preserved in the 26mm E-Lux and the field stop was razor sharp. It would seem to indicate that the PMW flattens the field appreciably in the NH II.
The last EP I tried was a 15mm Axiom in order to get an idea of the performance with a 1.25" EP. It performed well at all mags and had a flat field that needed no refocusing when scanning from center to edge.
The weather was rainy so I could not ascertain how it handled a high glare situation. Antireflection coatings reflect yellow, pink, purple and blue colors. I noticed no problems with backlighting from the sky when looking up at dark pine leaves and cones in a tree across the street.
The magnifications seem close to what Harry said they would be. One oversight was that the input was not threaded for 1.25" filters. That is no problem in my case as my focuser is threaded for 2" filters. The smooth input barrel allows me to move the PMW up or down at least an inch and lock it in place with my Baader Click-Lock holder on my f/4 Newt. When used in a prime focus mode with a camera, the f ratio will be f/8, f/12 and f/16.
The optical performance seems promising so far, and when you consider that it can eliminate the need for a Para-Corr and allow you to use really long focal lengths like a 55mm Plossl with my f/4 Newt, then I believe this could be a useful accessory. It costs a bit more than a 2" Powermate, but it does have 3 times the mag settings available at the push of your thumb and a quick refocus. What I like is the way it makes cheap EP's perfrom in a fast focal ratio scope. There is no need to go down to short focal length EP's with squinty little eye lenses. Harry said I got the first one he made like this, so if there is an interest I will report how it works in the f/4 Newt after the weather clears. I already know I will be using it in the refractor for terrestrial viewing.
If you want to use big, comfortable and cheap 2" EP's in a fast focal ratio scope and need a mag changer for your camera, consider getting a Power Mag Wheel.
Phil
The input side is a 1.25" tube about 2" long. The body is the standard 3-mag body that Siebert makes. This model is Telecentric in operation, so the output side is much bigger than the input side and and has about 38mm output lens and a 2" eyepiece holder barrel. Included was a 1.25" eyepiece adapter made of Delrin. The output lens is what I would call a T-2 size. It will not illuminate the field stop of the longest 2" EP's. Still, it works rather well. It is a 2X, 3X and 4X mag model.
With a 38mm Siebert Observatory, there is some reduction in AFOV due to slightly small output lens, but the field edge was still fairly sharp. At all mags the view was sharp to the edge, and no refocusing was necessary when going from center to edge. Harry said this model should eliminate the need for a Para-Corr in a fast Newt. When going from 2X to 3X to 4X, you must refocus a bit. The biggest jump is between 2X and 4X and amounts to less than 1/2" in my NH II. The 38mm Observatory is an EP that maximizes the AFOV in a 2" barrel. It vignettes a bit when placed in many 2" diagonals due to the nosepiece of the diagonal cutting off the light cone a bit. Still, a full 2" output lens would solve that problem in the PMW. Your 41mm Pan or 31mm Nagler will have the same issues.
With a 26mm 2" E-Lux Kellner, an EP that gives horrible results when used alone in the NH II, the view was very useable at 2X, and got better from 3X to 4X. At 2X it was a bit soft on edge, but no refocusing was necessary to get the best sharpness. Edge sharpness improved noticeably at 3X and was about the same at 4X. The entire AFOV was preserved in the 26mm E-Lux and the field stop was razor sharp. It would seem to indicate that the PMW flattens the field appreciably in the NH II.
The last EP I tried was a 15mm Axiom in order to get an idea of the performance with a 1.25" EP. It performed well at all mags and had a flat field that needed no refocusing when scanning from center to edge.
The weather was rainy so I could not ascertain how it handled a high glare situation. Antireflection coatings reflect yellow, pink, purple and blue colors. I noticed no problems with backlighting from the sky when looking up at dark pine leaves and cones in a tree across the street.
The magnifications seem close to what Harry said they would be. One oversight was that the input was not threaded for 1.25" filters. That is no problem in my case as my focuser is threaded for 2" filters. The smooth input barrel allows me to move the PMW up or down at least an inch and lock it in place with my Baader Click-Lock holder on my f/4 Newt. When used in a prime focus mode with a camera, the f ratio will be f/8, f/12 and f/16.
The optical performance seems promising so far, and when you consider that it can eliminate the need for a Para-Corr and allow you to use really long focal lengths like a 55mm Plossl with my f/4 Newt, then I believe this could be a useful accessory. It costs a bit more than a 2" Powermate, but it does have 3 times the mag settings available at the push of your thumb and a quick refocus. What I like is the way it makes cheap EP's perfrom in a fast focal ratio scope. There is no need to go down to short focal length EP's with squinty little eye lenses. Harry said I got the first one he made like this, so if there is an interest I will report how it works in the f/4 Newt after the weather clears. I already know I will be using it in the refractor for terrestrial viewing.
If you want to use big, comfortable and cheap 2" EP's in a fast focal ratio scope and need a mag changer for your camera, consider getting a Power Mag Wheel.
Phil
