Large format focus testing

Feb 3 2022

Last night was a real butt kicker of an evening.

Shot 4 test sheets and one hour long portra.

Here's what I tried to do:

Arrived at MBOSP just before sunset. First task was to set up the camera and point it at the distant trees - at least 5 miles away - where the contrast was high and I could get a sharp focus. Using the loupe on the ground glass on the 300mm at F5.6 I got a sharp edge, then put the SX Lodestar X2 on the camera in the place of the ground glass. It was off... again. Nudge nudge, and I thought that I had it right.
By the time it was finished, the sun had gone below the hills.  

In order to get the daytime image, I used the Starlight Live software and ran the shortest exposure that the camera supported. Still needed to stop down the lens to F22. This is probably why the focus was found to be off when doing the star test.

Later in the evening, once polar aligned, I tried the same exercise with the bahtinov mask. Focused on a star image with the loupe, then used the bahtinov mask to check it with the mounted SX. Again, focus was off. This was probably due to stopping down the lens from before.
As a visual reference, this is the "lodestar focusing device."   It's a Copal 0 lens board where I've placed a Lodestar autoguider into a parfocal ring that's been glued to the lens board.  The ring allows adjustments to the guider position.  I've made several attempts to properly set the position of the CCD, finally settling on taking a picture of a ruler with film, developing, then setting the position of the Lodestar to match the film image.  

Two test shots done, then another check. Found that the focus was off again when comparing the loupe view. Wasn't sure what was up, so I spent the time to really check it. With fully dark adapted eyes looking at a decent star field, the faint stars will pop into visibility when using the loupe. I use this as my visual confirmation of focus. The amount of rotation of the focus knob is just enough to overcome stiction - but not much more - maybe a 10th of a turn?

Two more test shots and then the color sheet.

Yes, I would have liked to keep going, but it was late.

To do this evening in the back yard:
Pop on the 400mm lens
Do the loupe focus.
Put the bahtinov mask in place.
Set up the macro lens on the dslr and then shoot long exposure or live view to see if the spikes can be seen.