[Doomsayer]

I would concur with comments around this and similar threads on RCs about the critical importance of optical alignment and collimation. I've been getting some personal experience with such RC issues having built two mostly DIY 12.5" ritchey chretien CF truss 'scopes. Not an expert yet...

I've found that in practise there are some significant differences when collimating and aligning RC optics as opposed to newtonians, cassegrains or SCTs. In particular, having had long experience with newtonian/sct/cassegrain collimation, you tend to have visual assumptions. With a newtonian for example, coma can be an aid to diagnosing misalignment, giving a visual clue that you need to re-align components in the ota. With an RC, coma and spherical aberration are pretty much absent. So apart from the concentricity of the out of focus star image, the visual clues are more subtle. As said in an earlier post, decentering or improper spacing gives a general blurring effect. The other thing is that these blurring effects due to minor centering and spacing are pretty much even across the field (ignoring inherent astigmatism/edge curvature)'

There are some interesting academic papers on some early professional US Ritcheys which describe these empirical challenges (more recent pro RCs have had the benefit of CAD opto mechanical design and manufacture). Add seeing effects and optimum collimation can be elusive for amateur level RCs.

So apart from accuracy & smoothness of the RC mirror figure, optical placement and mechanical design are significant challenges. Lately though I'm finding the coincidence between my free time and clear sky to be the biggest challenge to optical alignment perfection.

As another comparison, I have recently rebuilt a Vixen VC200L using a carbon fibre truss configuration and existing Vixen parts - this seemed easier to get properly collimated than the RCs I have built. Commercial RCs such as RCOS and OGS would likely not have so many challenges to colllimation/alignment for the owner as I have had with an ATM project.

cheers
guy