It has been way too cloudy for way too long so might as well do some testing of the old scope :-)
Presented below are images at varying distances from the artificial star to the scope.
This was done to show the magnitude of the introduced spherical aberration by the 'star' to scope distance.
Generic rule of thumb found on the web is either 'negligible' or 1/8 wave at 20X the focal length.
Harold Suiter's book, "star Testing Astronomical Telescopes" provides a formula that, for a 10inch F10 scope, shows 1/4'th wave induced SA at 28 feet, 1/8'ht at 56 feet.
Click on any of the next 6 images to get a slightly less JPG compressed version.
Closest focus I could get was 45 feet
And finally adding a 2X barlow at 125 feet without tube turbulence.
The following are the out of focus (intra/extra) images from my 10inch F10 lx200
Image one is at the F10 SCT focus and second image is with a 2X barlow.
The simulation output from Aberrator is the top row (w/0.05 turbulence applied)
PV: 0.102 RMS: 0.035 without Tube or Turbulence
PV: 0.216 RMS: 0.073 without Tube or Turbulence
The following composite image was done with:
lx200 10inch @ F31.5, raw scaled 2X
etx90 @ F42, raw scaled 4.3X
Target: artifical stars @ 124 feet, 'star' seperation 0.225 inches
Created by piercing aluminum foil with needle, mounting in a box then backlighting.
Note: 'Star' on left slightly larger than star on right, pinhole size wise.
"Seeing" not the best and windy.
Shot from Greenbox Observatory
across the lawn with this rig:
Rig used for images, last image on page
Imaged with ToUCam Pro SC1.5 5.6x5.6um pixel sizes
Captured in Astrovideo to AVI
Registered in Registax, approx 30frames out of 150 used for each
Scaled via pixel duplication in IRIS
Composite performed in PP6
Simulation done in Aberrator by scaling size to lx200 'star' then varying only aperture and central obstruction
for the etx90.
Images before composite:
The image below shows three "stars".
The center 'star' is the simulation output of Aberrator for: 250mm/ F20 with 37% central obstruction
The left and right 'stars' are two different size 'pinhole' stars
at a distance of 125 feet from the corrector of a Meade 10inch lx200 F10 @ F20 via barlow.
Imaging done with ToUCam Pro SC1.5 webcam, captured in Astrovideo in an 190 frame AVI.
Pixel size on the ToUCam is 5.6um yielding about 0.23arcsec/pixel.
The best 4 frames were manually selected and aligned in Registax.
Using image scale of approx 0.23 arcsec/pixel and the pixelation visible is
courtesy 4X duplication blowup in IRIS, so each 'pixel' is 0.23arcsec.
I measured approx 0.86 arcsec for the 'bright' star and 0.69arcsec for the 'dim'
star central disk in IRIS on the original stack.
Final mosaic done in PP6
Original frame ouput from Registax:
Pinhole images and text copyright 2003 Gene Chimahusky