Chamonix focus wheel disc to calculate focus spread

[GoodOldNorm]

Has anyone made something similar to this for a Chamonix 4x5

https://remorseblog.blogspot.com/202...5-mk4.html?m=1

[Doremus Scudder]

I've got simple paper rulers in mm taped to the beds of my wooden folders. I simply check them with a reference point that's either there already or I make a mark myself. If I'm not mistaken, the Chamonix models I've seen have a mm scale on the bed from the factory. You can just use that to determine the focus spread. If not, something like this: http://www.vendian.org/mncharity/dir...arrow_20cm.pdf would work.

Doremus

[Alan Klein]

Doremus, What changes to the aperture setting table do you used if you use tilts?

[ic-racer]

I did put a marker on the knob and I eyeball 1, 1/2 and 1/4 turn on my Shen Hao. That approximates f64, 32 and 22.

[Doremus Scudder]

Doremus, What changes to the aperture setting table do you used if you use tilts?

Alan,

There's no need to make changes to the optimum aperture setting when using camera movements. The trick, after applying the movements, is to correctly choose focus points on either side of the plane of sharp focus (PoSF) to use to determine the focus spread. For example, when using lots of tilt, the PoSF can be almost horizontal in the scene, so you then have to look for focus points that are above and below the PoSF instead of points in front of and behind. In other words, depending on the movements applied, "near and far" can become "above and below" or, with swings, "right and left." Still, focus spread is focus spread and, if you correctly choose focus points and then an optimum aperture based on that, you'll have optimum depth of field.

Best,

Doremus

[Tin Can]

Sinar has a built in system printed on knobs

Horseman too

[Alan Klein]

Alan,

There's no need to make changes to the optimum aperture setting when using camera movements. The trick, after applying the movements, is to correctly choose focus points on either side of the plane of sharp focus (PoSF) to use to determine the focus spread. For example, when using lots of tilt, the PoSF can be almost horizontal in the scene, so you then have to look for focus points that are above and below the PoSF instead of points in front of and behind. In other words, depending on the movements applied, "near and far" can become "above and below" or, with swings, "right and left." Still, focus spread is focus spread and, if you correctly choose focus points and then an optimum aperture based on that, you'll have optimum depth of field.

Best,

Doremus

You lost me. Sorry.

1. After doing tilts, do I apply the same aperture setting based on the mm distance between the near and far focus points as I would do without tilts? __________? If not, what do you do? ____?

2. What do you mean above and below the PoSF? Let's say I'm focus far on a house. Do I then check mm focus change from let's say clouds above the house that are further away when I calculate the mm distance? _________________?

[Doremus Scudder]

You lost me. Sorry.

1. After doing tilts, do I apply the same aperture setting based on the mm distance between the near and far focus points as I would do without tilts? __________? YES!

Just choose the correct near and far points to determine focus spread (see below).

2. What do you mean above and below the PoSF? Let's say I'm focus far on a house. Do I then check mm focus change from let's say clouds above the house that are further away when I calculate the mm distance?

Alan, you really need to understand better what happens with the PoSF when you tilt! And you need to understand that what we're really doing when determining focus spread is finding the two most distant points on either side of the PoSF that we want to have rendered sharp in the print.

First, though, what the PoSF does when you tilt:

If you set up the camera and have all the tilt controls in "zero" positions so that the lens plane and film plane are parallel, the PoSF is out front of the camera and is also parallel to the lens and film plane. If you've set up your camera level and plumb, then the PoSF is also 100% vertical (i.e., plumb, in line with the pull of gravity).

Now, as you tilt the back back (or the front forward), the PoSF moves from vertical. If you tilt far enough, you can make the PoSF completely horizontal. Usually we choose a position for the PoSF somewhere in between, in order to get a near foreground object in the plane together with a more distant object.

Now, back to placing the PoSF and finding focus points:

Let's start with your camera in "zero" position, level and plumb and the PoSF in vertical position. It's easy to see that either side of the PoSF equates to "near" and "far" in terms of distance from the camera. So you simply choose the nearest and a farthest objects from the PoSF that you want to be the extremes of your depth of field for your focus points to determine focus spread.

Now let's imagine a scene in which tilt would be useful. How about furrows in a plowed field with a barn and trees in the distance and a picket fence in the foreground.

Before you start worrying about focus spread, you must choose points for applying the tilt, i.e., positioning the PoSF. If we laid the PoSF down 100% horizontally, parallel with the ground and focused on the ground, then you can see that there would be nothing below it to focus on (the camera can't see underground!), but lots of things above it like fence posts in the foreground and roofs and treetops in the distance. If you've done this, you haven't placed the PoSF optimally (a common rookie mistake). Better is to choose a points that the PoSF will pass through that are in the middle of the highest foreground and background objects.

So we rethink and choose to tilt so that the PoSF intersects the near fence post at the halfway point and the tallest thing in the distance, a tree let's say, at the halfway point. (This is when you line up your axis line with the halfway point on the distant tree and tilt till the middle of the fence post is sharp. Note: this is not finding focus spread!).

Now the PoSF is not 100% horizontal anymore, rather at some oblique angle. Still, though, we need to choose focus points that are on either side of the PoSF for our focus spread. But, you can see now, that these points are no longer "near/far" in terms of actual distance from the camera, rather "above/below" the plane of sharp focus. Obvious candidates for our focus points are the top and bottom of the near fence post and the top and bottom of the distant tree.

Now it gets a bit more complicated, but stick with me: It is entirely possible that the most distant points from the PoSF in terms of focus spread, out of the four we've chosen to look at, are the top and bottom of the near fence post. That is, two "near to the camera position" points, but which are 1) on either side of the PoSF and 2) "farthest apart" in terms of focus spread. This may seem counter-intuitive at first, but remember that DoF is shallowest closest to the camera position and gets deeper with distance.

In this case (which is not all that uncommon), we've chosen focus points that are the same distance from the actual camera position, but which are, nevertheless, the farthest from the PoSF in terms of focus spread. Often, though, as in a scene with distant mountains, one of the focus points will be the top of something high in the foreground and the base of the distant mountain. The only way to know for sure is to try several likely candidates for focus points and see which ones actually yield the greatest focus spread. Once you've found that, use that distance in mm to reference your table (or whatever) to find the optimal f-stop.

Hope this helps, and apologies to all for our hijacking of the thread

Doremus