Paul said his only focussed infinity. Which would imply the film plane difference changes with focus.
I have a DaYi 617 back. It has no light leaks and seems aligned properly with the film plane. I sometimes leave the darkslide out for a long time waiting for the wind to die and it's still without leaks. Perhaps I was just lucky and got a good one. I had a problem with one side of the negs being out of focus, but discovered that the two levers for tilt and rise on the back standard of my Linhof TK were keeping the film back from seating properly. I filed two grooves in the back and now it's fine. I had a Shen Hoa 4X5 that had the same problem - one side out of focus. I finally discovered that I couldn't reliably lock the back standard swing/shift control and it would drift off. I sent it back to Badger Graphic and they worked on it, but it still drifted. Chinese cameras and roll film backs are inexpensive, but I suspect they lack quality control and the old saw about having to buy a cheap tool twice may apply.
I also have (a relatively new - 4months old) DaYi 612 back. With all those rolls I shot, there is no light leak detected, the focus seems very good. I am very content with it and would recommend it to anyone (and it was very cheap, I paid £125 incl. shipping from China )
It seems we could well be referring to different roll film holders from China.
I have only examined the SH 612 as detailed in my report.
Thanks to those who have contributed to this thread in an effort to highlight possible problems with roll film holders from the far east.
'Determine on some course more than a wild exposure to each chance'
Today, Chinese manufacturing companies are capable of producing even the most complex mechanical and electronic items to virtually any degree of precision, as long as the buyer is willing to pay for it. Thus, you need to be very careful when buying products that seem to be the same. Quite frequently, they are not. Products manufactured by and for Shen-Hao are generally quite good bu tthey are manufactured to meet a particular need at a specific price point so don't expect the same precision or quality you get from Horseman or Linhof. OTOH, some companies who use Chinese manufacturing facilities and closely monitor products seem to get much better quality than you would expect; Fotoman is a shining example.
Stan, yes we are talking about different models - at least the label is different, but visually the Shen Hao SH612 and the DaYi 612 models seem very close to be similar. I also think that the chinese are continually changing their designs and manufacturing, so what was written some months ago could be very different today (to the better or the worse).
Your website is impressive and your description of your approach to photgraphy in revisiting and getting ahead of chance is superb. I hope the sales pay off your careful and dedicated approach of doing everything to the final print yourself.
1. Didn't find a lot of 6x12 swhots. I wonder why you don't find more pano format shots to take as this device would seem to be very easy to use. Maybe you just don't show them or I missed them. Landscape seem to len themselves to wide shots and 6x12 matches more closely our vision whereas 4x5 is simply a derivative of how a taditional large standard piece of paper can be cut up without wasting.
2. For me this 6x12 holder it would allow bracketing instead of a ND filter to combine shots. Can you do this with masking in the darkroom?
3. How long do you have to let a film settle to get rid of the curves from the roll and taking the picture?