I used my 130mm Zhumell dobsonian with a 10mm eyepiece and my Canon RP attached, just playing around, a little while ago. I'm not sure what the focal length is, but I was amazed I could get this close with that set up. Not the sharpest, or the most detailed picture I have taken. Thanks for looking 
Jim
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© jgoetz4 [SHARE LINK] THIS IS A LOW QUALITY PREVIEW. Please log in to see the good quality stuff. R6, 6D, Canon 10-22 (modified for full frame) 28-135 IS, RF 35 1.8 Macro, RF 50 1.8, RF 85 2.0, RF 24-105, RF 100-400, Tamron 70-200 2.8 VC & 100-400 VC, Voigtlander 40 2.0 II, Fuji X-E3, 7Artisans 25 1.8 Fuji X, Meike 35 1.7 Fuji X, and a bunch of FD/FL glass.
Skywatcher 90mm Mak