[photoptimist]

Looks like half plate size is rather variable. I had been going with 4.75 x 6.5 which is the size of some I have here.
Plus using 8 1/2 inch lens as a wide angle can be out to 6 1/2 x 8 1/2 as per a 1900s advert. Of course that depends on the individual lens capability which is too hard to work out without
actually pre-constructing a body.
So I have gone with 6 x 8 as a primary target.
If I go too small I will start to lose the overall large format effect.
If I have gone too big (Target) then I can always lengthen my digital lens focal length to perhaps 35 mm.
I think my maths is coming out similar to yours - I worked my digital lens distance from fov to get 200mm (8 inch).
One thing that may be insurmountable is getting enough shift with a very limited amount of extension available to me.
But I am unsure of my maths - need a formula!
According to my calculations with a target 200mm from lens centre I need only 3.6 mm extension from infinity. (28mm)
It is going to be hard to keep a shift adapter that small.
At least the K30 has some composition adjust to help.
Here is a screenshot of what I am envisioning. In both cases back of lens is about at outer edge of lens board. obviously digital on top.
The old lens would be mounted inside a K mount bellows extension attached to the lens board. This should give me some focus adjustment before vignetting.

Hmmm... to view a 6x8 target with a K-30 sensor (15.6mm x 23.7mm), the magnification is 0.102X (assuming you want the entire 6x8 image to be captured uncropped). That puts the lens center at about 302mm from the target, much farther than the front standard. You might need a wider-angle lens on the digital camera if you are using a wide angle lens on the view camera.


As for the amount of shift, it's just the magnification ratio multiplied by the total view-camera-center-to-digital-camera-center offset.

Note: you might benefit from testing the focus, field of view, and distances for both your view camera lens and your proposed K-30 setup. A table or stool next to a window can become an ersatz optical bench and some bits of cardboard, graph paper, and a ruler can help you find the plane of focus for the view camera lens and check its image circle size to see how big a view you can get. You can check the K-30 + lens with your proposed 6"x8" target by setting them on a table, too.

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Last edited by photoptimist; 07-17-2022 at 08:27 AM. Reason: Added note

[GUB]

Hmmm... to view a 6x8 target with a K-30 sensor (15.6mm x 23.7mm), the magnification is 0.102X (assuming you want the entire 6x8 image to be captured uncropped). That puts the lens center at about 302mm from the target, much farther than the front standard. You might need a wider-angle lens on the digital camera if you are using a wide angle lens on the view camera.

Were you meaning the 28mm = 302mm from target?
Hmm I calculated with fov (apschorizontal) of 28mm = 46 degrees. > 100 / tan23 = 230mm. This seems close in practise. Can you clarify if I have stuffed this up coz it breaks the plans. !
I was intending the front of the lens at the lens board with optical centre perhaps 20mm back. Giving me not quite my 230mm.

As for the amount of shift, it's just the magnification ratio multiplied by the total view-camera-center-to-digital-camera-center offset.

Yes I was thinking about that much - which is quite a lot to achieve within that 3mm of extension.

By handholding a piece of paper with the old lens I am fairly sure it's coverage gets close to 200mm but how much of that was intended to being good enough to use is another question.

[photoptimist]

Were you meaning the 28mm = 302mm from target?
Hmm I calculated with fov (apschorizontal) of 28mm = 46 degrees. > 100 / tan23 = 230mm. This seems close in practise. Can you clarify if I have stuffed this up coz it breaks the plans. !
I was intending the front of the lens at the lens board with optical centre perhaps 20mm back. Giving me not quite my 230mm.

Your calculations are correct for capturing the width of the 6 x 8 frame. But the 3:2 aspect ratio of APS-C means the digital camera will crop the view camera to about 5.33" x 8"

I was assuming you wanted the camera to capture all of the 6 x 8 frame of the view camera which means setting the digital camera for the 31° vertical FOV of a 28mm on APS-C. 75 / tan15.5 = 270 at infinity focus setting.

When the lens is extended to focus on the view camera frame, the lens center is a little further from the sensor which make the FOV a little narrower which means the lens and camera need to back up a bit. That's how it gets to be 302mm from the view camera focal plane to the lens center with all of the frame in view.

If you want to capture a 5.33" x 8" image of the view camera focal plane, you'll want a magnification of .117 which puts the lens center 267mm from the view camera focal plane.

[GUB]

Your calculations are correct for capturing the width of the 6 x 8 frame. But the 3:2 aspect ratio of APS-C means the digital camera will crop the view camera to about 5.33" x 8"

I was assuming you wanted the camera to capture all of the 6 x 8 frame of the view camera which means setting the digital camera for the 31° vertical FOV of a 28mm on APS-C. 75 / tan15.5 = 270 at infinity focus setting.

When the lens is extended to focus on the view camera frame, the lens center is a little further from the sensor which make the FOV a little narrower which means the lens and camera need to back up a bit. That's how it gets to be 302mm from the view camera focal plane to the lens center with all of the frame in view.

If you want to capture a 5.33" x 8" image of the view camera focal plane, you'll want a magnification of .117 which puts the lens center 267mm from the view camera focal plane.

Dang - I never thought to check the vertical aspect!
The trouble with going out to 302mm is the lens extension gets even less making it all but impossible to create shift.
I think it is best to stay with the current design and accept it is not going to quite cover the image. It is a simple construction by keeping a common lensboard.
And even if I can't get enough "shift" I should get enough of a look at the digital result to decide if it is worth persevering with this approach.
I may be able to get the space between the two lenses down by 5 -10 mm in practise and that should help things in that the shift won't have to be so severe.