I have an interest in viewing bugs and spiders with two eyes in high magnification at a distance of around 6-10 feet. I already have some equipment in order to view with 2 eyes at low power at this distance (binoculars) and at high power with one eye (Questar 3.5 but at above 15 feet). I could pick up a relatively inexpensive 60mm spotting scope that can focus down to 11 feet at its lowest power (15x) but that would be for just one eye.
In another posting I received some caution that binoviewers may not work with refractor-like spotting scopes with the way the focusing works in the spotting scope and an astronomical refractor may prove to give more flexibility to do unorthodox things.
One combination I am looking at for high-magnification 2-eye close-focus work is the following equipment line-up:
- Orion ED66 CF refractor (focal-length of 400 mm)
- includes Orion Deluxe 45-degree Correct-Image Prism Diagonal, 1.25" which has 27mm clear aperture
- includes 14 mm Wide-field 65-degree eyepiece, 1.25"
- Williams Optics binoviewer
- includes optional barlow and two 20 mm eyepieces
- consumes optical distance of about 100 mm without barlow
I am assuming that the telescope can reach focus at infinity with using the 45-degree Correct-Image prism diagonal with the provided eyepiece
The thin lens equation calculator when plugging in 400 mm focal length and 6.6 feet object distance has the image distance at almost exactly 500 mm (100 mm more than at infinity. Right where the binoviewer would put the image).
Is it correct to reason that the system with binoviewer (without using the barlow) would be able to focus at around 6.6 feet +/- some value dependent on the telescope focus travel distance?
I'm thinking that this might be a good way for me to get a two-eye, high-power, close-focus system.
I could just try a binoviewer with my existing 3.5" Questar but I'm finding that the Questar is producing magnification that is really too high for this particular application. With one-eye, I was looking at just the head of a dragon-fly the other day with the Questar at about 17 feet way.
I could also just buy the Swarovsky BTX with the 30x65 objective which is supposed to focus down to 7.2 feet but this system would cost around $4800. The Orion ED66 + Williams Optics binoviewer combo would just cost $650 + $270 = $920. One-fifth the cost.
Any words of wisdom would be appreciated.