Thanks David,
I couldn't persuade Google to take me beyond page 90, but I have seen illustrations like that before. I've tried using one of my astronomical refractors as a collimating lens with a backlit USAF glass slide placed at the end of the focusing tube. It works fine with the binocular under test (focused at infinity) easily reaching focus on the chart at less than a meter from the telescope objective. Of course, it's still necessary to use an examination scope behind the binocular eyepiece to see the full resolution. Problem is I don't know how to derive arc second resolution from the resolvable LPs/mm on the chart when it's used that way, so I haven't pursued it. I'm sure you are right that they must be using a set-up with a collimating lens and presumably an auxiliary scope.
Henry
Hi Henry, been awhile.
The math for the distance for using a collimating lens is the same as for regular distance to a paper target but using the focal length of the collimating lens. The atan (reciprocal of the lines per mm divided by the distance in meters).
I have attached the ISO page for a resolution collimator and a picture of the one I built that has a 400 mm objective.
I have used a five inch +/- 450 mm lens but it is in the open and not lighted per spec and does not yield good results. You might try a good backlight with a frosted glass diffuser in a dark room and see how close you get.
Lighting is very critical. My home built collimator has a frosted glass diffuser and I use a collimated light source as the ISO diagram shows and get very good results but I can take the glass diffuser out and use an integrating sphere, which gives an almost perfect diffuse light source (also expensive) and get a measurable improvement in my readings. Don’t recommend spending the money for the sphere, all you really want is reproducible results.
Setting the USAF target at the focal point of the collimating lens is critical to accuracy, in your case I would recommend using the K&E double collimator since, unless way out of adjustment, both sides are infinity focus, you can verify that by looking at distant objects outside and comparing one side to the other. Also the grid at the focal point has a 5 minute apparent angle, a rough check against your USAF target.
I have attached a spreadsheet for simple conversion for you. Change the focal length or distance to target in column B, change the resolved group in column C. As a check column G should be the same lines per mm as your standard USAF target.
Let me know of any other questions.
Ron