Since encountering the 'focusing problem' with the factory installed 'fresnel + ground glass' with Arca 6x9, I have learned sevral lessons.
I am using P45 with H1 adapter from Arca-Swiss, and do not use any sliding back. I have Schneider 35, 47, 90 and 210 mm Digitar lenses. Because I had an unfortunate P45 failure (a component in power supply) 5 weeks after I got my unit, I have had two P45s to test the focusing issues. I had a loaner from Phase One for 2 weeks.
1. Arca-Swiss (Martin Vogt) sent me an email to 'inform you that the Fresnel lens does change the focal plane by approx. 4/10. Nevertheless this is compensated on our ground glass.'
2. Arca-Swiss has focus error of .4 mm with fresnel lens installed in front of GG. The GG does not provide the compensation as Mr. Vogt indicates since the unit will focus perfect when fresnel lens is removed. However, the image is difficult to see without a fresnel lens. I have to use fresnel on opposit side for composing.
3. I tried Intense Screen from Beattie, and it is a $280 joke. It is a combination of 'fresnel and clear glass.' Image focuses on fresnel and the clear glass is for its protection. Fresnel sits on the same position as Arca's fresnel and the clear glass sit on the position where Arca's GG sits. First of all, the dimension of both fresnel and glass are wrong. Fresnel is way short and the clear glass requires rounding of all four corners to fit into Arca's GG frame. I had to add a shim (just shy of 1 mm to raise the fresnel lens to focus properly). It is very grainy and the image is not evenly lit.
4. I contacted Boss Screen both in Holland and the US. As far as I can acertain, Boss screen is not in business. I have not received any reply from Holland. The US rep indicated same and he is contemplating producing the screen by himself sometime soon.
5. I ordered Satin Snow Ground Glass on June 20 and haven't received it yet. Mr. Parker of SSGG sent me an email that it will ship within a week on July 28 but I haven't got it yet. I am not screming because it was only $12 and I found the perfect solution, see below.
6. I ordered a focusing screen from Maxwell Precision Optics. It is a combination of 'fresnel/focusing matte screen and a clear protective glass. Both sit on the position where Arca's GG sit. The matte side faces the lens. IT FOCUSES TACK SHARP WITHOUT ANY FUSSES, NO SHIM, NOTHING. AND THE SCREEN IS VERY BRIGHT. It costs $225, and it includes the scoring of parallel lines for P45 image masking.
The focusing screen from Maxwell Precision Optics is made with a slight convex warp on which a clear ptotective glass pushes down in order to maintain a perfect flatness in long tern exposure to different environmental conditions. Its micro prism frenel illuminates entire image so bright, even with 35 mm, I don't need to use a dark cloth to focus. The difference of brightness between the original Arca (if it focuses properly) and Maxwell is at least an order of a magnitude (obviously I don't know the exact difference since I do not have an instrument to measure).
I just returned from a two weeks trip to Peru, and have used all four lenses (35, 37, 90, 210) with perfect results. I did not have any problem with focusing and composing with Maxwell Precision Optics's focusing screen. By the way, the screen was ordered on June 29 and it was delievered on July 14.
Needless to say, Arca-Swiss 6x9 is a superb view camera. I don't know why the factory installed focusing screen does not function properly. But I can list several circumstantial evidences for anyone to make his/her own conclusion,
1. I used two separate P45s with identical results.
2. Arca's system will focus properly if I underfocus by 0.4 mm.
3. H1 adapter functions properly with Arca's GG only and Maxwell Precision Optics's screen.
4. All focusing tests were done by tethering the P45 to a PC and at 100% magnification.
Now, I am a happy owner of Arca Swiss 6x9 with Maxwell Precision Optics's focusing screen, Schnider Digitar lenses, and P45 DB.