Hi everyone,
I have been using a QHY183M and QHYFCW3-M-US for a while and I am now trying to connect it to a Samyang 135mm F2. I say "trying to connect it".. it is actually connected and seems to be spaced out correctly - the Samyang is a Canon EF version, so should need 44mm of back focus.
I have bolted the QHY183M (10mm) directly to the filter wheel (17mm) using a 020063 (1mm) QHY183 to M54 adapter, and used 6mm of spacers before attaching to the QHY M54 Canon adapter (10mm) for a grand total of 44mm. The filter wheel contains 7 Baader 36mm unmounted filters, the usual LRGBHOS suspects, and the whole set up is held in place by an Astrokraken 3-ring setup on a dovetail.
In theory, as far as I can figure, this should all work fine.
I have a windmill that I normally use to test focus, Chesterton, 2.5km away that I can see from my kitchen, and the set up above focuses on the windmill at approximately 9m on the Samyangs focus scale... nowhere near infinity. If I move the lens onto my Canon 6DMk2, i have to rotate the lens to infinity to get focus on the windmill...
I have yet to use the Samyang135/QHY183M at night... everything seems to be fine but that focusing discrepancy seems weird. Everyone else I have seen who has one, where focusing discussions are had, talk about the focus being at or beyond infinity. A little I could understand, but to go from infinity being infocus on an object 2.5km away on one camera to 9m being infocus on the QHy183M seems bizarre!
What am I missing? Why does the focus seem to change so much for the same back focus on 2 different cameras?
Regards, Simon