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oops again, further correction: at C-14 FL (391 cm): 1u at FP = 0.05" at FP 1u of axis error = 0.0045" at FP (0.05" / f-11) thus FWHM bloat for 132u axis error (264u DOF) = 0.6" Not acceptable for

Oops! I forgot that C14 is F/11 (I've been using C-11 at f/10 lately) mathematical revisions: at C-14 FL (391 cm): 1u at FP = 0.05" Focus error is arithmetically additive (not quadratic) so 1u of axis

"In ideal seeing conditions, with this telescope in the f/10 configuration, we have a depth of focus of 263 microns ... just under 1/3 of a turn of the focus knob" The rings very untrue. With good

With any thread the travel of the nut on a screw is equal to the reciprocal of the (TPI) threads per inch. So on a shaft that has a thread pitch of 32 you would divide 32 into 1. You would then get

Standard Focusing Mechanism <http://kelly.flanagan.io/wp-content/uploads/2018/04/original-focuser.jpg> The focusing mechanism that comes standard with the Celestron CPC 1100is illustrated to the

Well what was the measurement?

Nevermind....took care of this myself.

I am curious about how far the mirror moves per rotation of the focus knob? Or more practically, how far per 10 turns? In characterizing my autofocuser, I need to know the travel per step of the

Maybe. But it seems "common sense" that moving the corrector forward should cause over-correction. The spot diagram clearly shows that effect on-axis but it is presumably a non-diffraction

I would agree with Christian. The ultimate on-axis spot diagram can always be reached by the combination of wavelength and back-focus... sphero-chromatism is really the limiting factor in SCT's --

Hello Stan As a matter of fact, the spot diagrams are a bit deceptive. On the optical axis, the Strelh ratio are about the same with / without moving the plate. I would say that the main benefit of

The spot diagrams show that the on-axis spot is much smaller for the normal plate distance than the extended placement. So this trick would be destructive for narrow FOV such as planetary. As for wide

Hi Charles, The coma is much lower with the plate moved forward by 400 mm. Here are the spot diagrams over a 0.25° field and the classic design. We can see a nice coma:

Christian - how do coma and field curvature change as the corrector is moved forward.?Charles

Hi Charles, Can you post some images of your tube ? I only have two 80 mm holes at the back of the mirror, each of them with a 90 mm fan. This is much better than nothing, but I can see you push it

It would be nice to have a look at some images of your tubeless C14 when your are back home. Christian

Very interesting. I have found that moving the plate 200 mm forward increases the diffraction limited flat field from 2.2 arcmin (nominal design) to 4.1 arcmin (in green light). With 200 mm, you will

Wow 40 degrees- here the total temp variation from 2 PM to 6 AM is rarely more than 20 degrees but much less during the night! Typically only about 6-8 degrees from twilight to midnight and a slower

I do have 3 fans on the back, but the temperature change in California during the evening is pretty steep... often a change of 40 degrees F. I have typically found that even if I had the fan running

I eliminated tube currents in mine by first putting two 4" fans on the back and 4 holes in the tube under the corrector. With about a 10 degree temp difference it comes to thermal eq in about 30