Real focal lenght in RC10 Ritchey Chretien telescopes GSO Family · Jose Carballada · ... · 2 · 218 · 0

I found so many documents with 2000 mm (f 7. 8 ) and others with 2032 mm (f 8.0), even mixing both on the same page.

Do you have any idea what is correct?

I try to set the better space between primary and secondary to avoid curvature and I prefer start with the right numbers and save some tests.

Originally my trust telescope come with 1999.6 mm solved in astrometry.net without any flattener or anything.
After some collimation and iterations now is 2009.9 mm at same conditions than before.
Move 1 mm the secondary means to correct 10 mm on the focal length, I want to correct it but... to 2032 or 2000?

Also, I'm running out of backfocus to add a rotator, if our scope is designed for 2032 mm, add 3 cm of backfocus could be great to me.......
Another point is about the light entering in to the sensor because the baffle is smaller than required, maybe with 2032 this is improved too. (see this post)
At the end the curvature field will tell me what is correct, but as I said, I prefer not to do to many test and imaging after this horrible winter 
any ideas will welcome

Hi Jose,I'm wondering if you ever found an answer to your question?  I have a 10" TPO Truss RC and I would love to figure out the optimal spacing.  I unfortunately don't have a record of the exact focal length when it was brand new. It arrived out of collimation and my efforts to collimate it changed the distance.

Thanks,

Bruce

Bruce Braunstein
[email protected]

Hi Bruce, the distance never was mesure using 'physical' tools, I mean that it was obtained using plate solve on a picture.
Distance = f.ratio x aperture
You know the aperture and you could know the f.ratio using this formula f.ratio = (pixel size camera * 206.3) / (platesolve resolution in arc/px * aperture)

I hope this help you !