Whoops, newbie-type mistake .. I don't understand how my previous message got out without a subject line...
I've finally gotten the last components that I need to get the scope to first light, so I'll be trying to figure out BFL soon. I'd definitely like to have the design (and the OSLO LT version). Thanks, Dave.
Not that I'm quite ready yet, but does anyone know of any fabricators for this?
Dave Rowe already responded...
>Here's the design of the 14.5" f/7.65 RC:
>
>Primary: D=14.5" RoC=77.43" SC=-1.11
>Secondary: Spacing=25.625" RoC=40.1" SC=-5.46
>
>BFL=12"
>
>Field Curvature: RoC=14.4"
>
>If you don't use a field flattener and have a flat film surface, at
>1.5" off-axis the RMS spot diameter is about 165 microns and the
>vignetting is 23% due mostly to the primary baffle.
>
>If you use a well designed field flattener that also cancels some of
>the astigmatism, the RMS spot diameter becomes about 35 microns at the
>same off-axis distance as above. The vignetting in this configuration is
>about 20%. The distance from the rear lens to the focal plane is about
>3.5" in this design, but could be increased if you require it to be so.
>The EFL of the corrected design is about 118", i.e., has an f/ratio of
>f/8.13.
>
>The lenses are 3" in diam!
eter and the curves, and tolerances on the
>curves and lens thicknesses, are easily achieved.
>
>Do you need it? Well, that's entirely up to you. But I will say that
>this well corrected RC for medium format film photography would be
>quite an instrument.
>
>If you would like the design, I can type it out or send it in OSLO LT
>format.
I wrote:
Dave, Roland, Bert and Chuck, thanks for responding. Your comments have been helpful so far. The scope is actually a 14.5" f7.65 system. I think that the corrector will be similar to the 12" system, but will have some differences based on the specific application. The focuser is one of the AP 2.7" focusers, and I'll be using one of the Lumicon refracor easy guiders. I don't have the dimensions of that device handy. Here are the specs for the scope that I have in hand:
Focal length: 2875mm
Primary: 14.5" f/2.67
Secondary: 5.5" 2.86x amplification
Mirror spacing = 25.625" = 650.9 mm
Back focus: 12" from front of the primary; 9.0" from back of scope.
Baffles: Primary - 3.5" I.D., 13.5" projection from primary; Secondary - 6.0" O.D., 2.375" projection from secondary.
As Dave Rowe pointed out, I'm sure that the AP field flatteners aren't going to deal with this all that well. I had not considered that there would be correction for coma in a refractor corrector, but any coma correction would, of course, introduce "negative" coma into the images. Also included in the optical test report is a set of Seidel Aberration Coefficients, which I am not proficient enough in optical theory to read/interpret correctly. There is mention of astigmatism, but again, I'm unable to correctly interpret the chart.
I do not yet know the amount of Back Focal Length I need, though I suspect that the 9" should be enough. It is my understanding that since the system RoC will be upwards, the basic correction will increase BFL.
Is what I'm trying to do a lost cause, or would it be worth the effort?
-- Gil
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