Hi LFPF,

This is my first post so I hope everyone is well in this strange period of time.

I own a tailboard camera and have been hitting the wet plate process hard since we have been in lockdown in the UK. My camera can shoot 14" x 14" but I mainly shoot whole plate for ease and cost. I recently purchased a FRANKE & HEIDECKE Heidosmat 1:3/ 250 as I wanted to experiment with a faster lens for portraits as my flash wasn't powerful enough with my other lens.

So my question is why would there be a discrepancy between the focus on the ground glass and the image plate?

My work flow has been:

Focus the ground glass so the eyes are tack sharp (I use a mannequin head for practising as it doesn't move). I remove the ground glass and replace with the darkslide and shoot the plate. After development and fixing the plate the image is out of focus on the eyes.
I have worked out that the focus at this point is 5mm forward (part of the neck is in focus), so it seems that I need to pull the focus back by 5mm after I have focused on the eyes to get a sharp plate.

I have tested that distance between the front of the camera to the ground glass and them the distance to the plate and they are the same.

I know that Wet Plate sees light differently so could it be this? Or is it the lens? I can't work out why the image is sharp when focusing and out of focus when shooting.

If anyone can help me understand what's going that would be great..

Thanks in advance

Paul