Televue 60mm ApoTelescope and
Canon 800D/EOS Rebel T7i (US) with 1.61 Crop factor (APS-C ).
What is the extension tube length that I should be using ?
(I tried with 30mm extension but still cannot get anything on the camera sensor; Been trying out at focal length of 8-24mm on the eyepieces but still nothing. ) . Am not using any star diagonal in between. Any advice?
The focus position with the camera should be quite close to that of the eyepiece, when you look at it with your eye. If you can't reach focus for visual observations without the star diagonal, then you should use it also for photography (or some extension tubes between focuser and eyepiece).
Our MFT-T-ring provides both: The standard distance of 55mm, or a shorter adaptation when you remove the extension.
For an APS-C, you should have approximately 55+30=85mm between the T-thread at the eyepiece and the camera sensor, otherwise there will be distortions or vignetting. This is not an exact distance, but a rule of thumb. With a wide-angle eyepiece, you get get closer to the sensor than e.g. with a Plössl or Ortho.
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|Optical length (mm)||15|
|T-2 Part #||25A|
|Usage||for eyepiece projection with sliding focuser|
|Inner Diameter / Clear Aperture (mm)||38|
|Inner Connection (lens sided)||Thread, T-2 (M42 x 0,75)|
|Outer Connection (eyepiece/-camera-sided)||Thread, T-2 (M42 x 0,75)|
|Compatible Brands||Astro T-2, Baader Planetarium|
|Type of Adapter||Extension|