Looooong as usual.........
You should probably read through a book on focusing a view camera, and understand what happens to the plane of focus when you tilt. You could also go here.
http://www.trenholm.org/hmmerk/
What you are trying to do is very difficult. Probably best to start out with something simple, like a flat landscape with nothing in the foreground. I dont know how far your subject is away from the lens but it sounds very close. About 2 years ago I was trying to do a semi macro (way less than 1:1) of items on a flat table. If you can imagine about 2-3 feet wide from side to side on the width of a 4x5 frame.
I wanted a 12" dof, angled slightly above the top almost like photographing a macro landscape. I finally got it but I could not do it with a 150. I ended up with a WA 90, used front and back tilt, and stopped down. It was right at the edge of what was doable. I was also limited by the image circle.
Next I will say that LF tilt is blown way out of proportion IMO. Using tilt, any objects close the camera that frame the shot high, like trees, will be OOF. I had a problem with that here not too long ago, and I got one very good explanation about what happens to dof when tilting.
That tiny bit of understanding comes from what happens to the dof range and plane of focus when you tilt and once you understand it, you will know the limitations of using tilt better. When to use it. When not to use it and what happens when you under tilt or over tilt. If you really dissect it, it can get complicated.
Also contrary to what a lot of people think, including me 2 years ago, using tilt does not guarantee and infinite focus everywhere. It obeys the rules on the above site. Look at the movies on that site.
A landscape example.......
In very very general terms, just talking about tilt. When the standards are parallel, just like when you shoot a 35mm camera, the DOF is parallel to the film plane at some distance out. Lets just say you are stopped down and you have a total of 30' of DOF. 15' in front and 15' in back of the subject. I am sure you have stopped down a 35mm camera to get some dof, or shot WO for less dof.
As you tilt the lens down on a view camera, the plane of focus starts to tilt also. It moves along a hinge line and might end up at an angle from your feet going through some point at or above the ground far off. That is the tilted plane of focus and everything along that plane will be in focus.
Now what threw me and the reason it can get so difficult to use the Scheimpflug effect is that that 30' total of dof is not parallel anymore. It would be nice if it was but it is not. What happens is at your feet, it might be only a few inches deep, perpendicular to the plane of focus. As you go out at some point you would hit your 30' and beyond that it might be infinite, but still depth wise perpendicular to the plane of focus.
Generally what you end up with is a wedge going from your feet to the horizon with the small end at your feet.
I am sure your are getting my drift on your cactus shot and I think in your case possibly when tilting you are throwing the sharp plane of focus under or over the cactus. Using tilt takes a lot of getting used to and its easy to over tilt at first. ref below. Also when you are that close the dof is only inches if not fractions deep.
If you are stopped down more the dof wedge along the plane of focus should be wider. WO and it should be narrow.
So to wrap up this long winded explanation (sorry), just talking in generalities, the plane of focus should align with the plane you want in focus. for a simple landscape with tall trees 100 yds off, you would want the plane of focus to go from your feet to the middle of the trees and hopefully have enough dof at the trees to cover it. If not stop down more, but tilting more wont necessarily help.
Same if you had the trees as above, but also a 3' fence about 20 feet away. The plane of focus would need to go from your feet, through the fence and through the trees, with enough dof at each intersection that the tall elements were in focus.
Ie if the dof was shallow at the fence and you had the plane of focus parallel with the ground (too much tilt, a case of overtilting for that situation) the top of fence would be OOF but the bottom would be in focus. If you did not use enough tilt, like the plane of focus went from your feet to the top of the trees, the bottom of the fence could be OOF. In both situations if there was enough dof at the trees due to the wedge shaped dof they could actually be in focus in both examples, but different parts of the fence could be OOF.
If the fence was 8 feet tall, It might not work at all.
Thats why I mentioned above that tilt is over rated. There are just a lot of situations were it does not work, and if you do not understand how it works you can blow a lot of shots. Dont get me wrong, as I think it is a good tool, but you can really screw up a good shot sometimes when you would have been better off just stopping down. That usually happens to me when I am not paying attention and not checking the corners.
The sinar is probably the easiest to setup tilt on. It uses a method of focusing and has a readout dial that tells you the appropriate tilt for a shot. Its really easy. Also 90% of my landscape shots with 4x5 are around 5-8 degrees of tilt.
For your subject really what you need is a WA lens with a huge image circle, that you can stop way down. In my case as I mentioned above my first trial was with 150mm lens and I think at the distance I was at from the subject I had 3" of DOF max stopping down, which meant I had to get the rest with tilt and it just was not doable. I think now I might have a better shot at it, but if I did it again I would use a wider lens and 6x7 MF for more dof.
Also go here for a start. Enter your lens at 1.5' and F64 and see what sort of dof you get. You get about 3"
A 90mm lens at 1.5' and F64 would buy you .95' but you would have to crop. thats what i ended up doing, but I shot at a less F and tilted some to end up with about 14"
http://www.dofmaster.com/dofjs.html
Hope this makes some sense.
If anybody see a mistake in my ramblings please speak up. A LF camera is a steep learning curve.
What's the optical principle of those things I observe? Is it just the angle of ground glass, so it loses right "teeth" in its surface to catch light? How does one properly focus a view camera with plenty of movements applied?
