AstroBKK
New Imaging train with flip mirror diagonal
​
Who ever struggled to find a tiny object like a planet on a small CCD chip at F20 or even more? After several nights loosing time groping on the hand controller to track this evanescent halo (defocusing bright planets is quite helpful to increase chances to locate them), I wanted a more robust method to find planets.
​
I build a three steps approach to ensure a progressive FOV increase by one order of magnitude to find and keep the object well centered till the camera's CCD. See the summary scheme below (Astronomy.tools):
.png)
FOV: 5º
9x
FOV: 0.45º
120x
C11 / Aiming arm of flip mirror diagonal
FOV: 0.05º
0.12"/pix
C11 / Imaging arm of flip mirror diagonal
​
I thus modified my setup as follow:
​
​
Replacement of the C11 OTA stock 9x50 finderscope by the 9x50 Right Angle Correct Image (RACI) Finderscope. The generous 5º FOV is ideal to locate objects when Go-To is not aligned. It's double crosshair is very practical to center objects, and it's prism makes it's use very comfortable. Under my light polluted skies and at the 9x magnification, illumination of crosshair proved unnecessary.
​
​
Replacement of the previous imaging train, to include a flip mirror diagonal with an illuminated reticle eyepiece. Key points for the design of this new train are:
- Selection of a reticle eyepiece with a 23mm focal and relatively wide field 55º, enabling a good intermediate FOV between the finderscope and the imaging camera. Note that crosshair illumination is mandatory for accurate aiming, as there's much less photons at the 122x magnification.
- Parfocalization of the imaging and the aiming arms of the train. This proved very important for dimmer objects, as a slight defocus makes them difficult to spot then flipping the mirror to allow light beam reaching the camera.
- Full screw design (no draw tubes) to ensure optimal alignment and rigidity.
- Leave enough space between the flip mirror diagonal and the scope's bottom plate to have the eye well centered when looking into the reticle eyepiece, parallax error will otherwise prevent good centering.
- Easy introduction of an optional ADC.
