Optics Involved in Forward Tilt and Front Rise

[Howard Slavitt]

I've read in several places that when you perform a front forward tilt (say to increase depth of field), you should then also use a front rise. Why? As a com positional device, I have observed the obvious, that the forward tilt in effect lowers the composition. I can correct this in two ways: (1) tilt the entire cam era upward slightly, or (2) use front rise. I understand that tilting it upward will not only change what subject is included in the composition but will affec t the perspective. In my experience, however, this effect on perspective, given the small amounts of forward tilt I use, is negligible. Does using front rise (as opposed to tilting the entire camera upward slightly) also recenter the lens optically so that you are using the "sweetest" part of the lens? Are there oth er optical effects at issue here that I'm missing?

[Ron Shaw]

Using forward tilt would require using fall if you want to keep the optical axis of the lens centered on the film plane (the sweet spot).

[Sal Santamaura]

Doesn't this depend on where one's particular camera locates its front tilt axis relative to the lens' nodal point?

[Alan Gibson]

Tilting the lens, or the back, doesn't change the depth of field as such. Instead, it tilts the plane of sharpest focus. Where did you read that you should also use front rise? Seems very strange to me.

[Masayoshi Hayashi]

Sal, I recall if the pivot of tilt is the same as the rear nodal point of the lens, then the composition is not affected from my past reading of Basic Photographic Materials and Processes (now new edition!). Usually, composition is done at the rear and swing and tilt are done at front if you do not want to distort the image and if the camera meets this requirement. Tilt front downward and raise the rear to get back to where you were and to the sweetest part of the lens. Maybe I'm missing something??

[Pete Andrews]

It helps to understand what's going on when you apply camera movements by imagining a line running through the middle of the lens, at right angles to the lens board. If you tilt the lens down, on any axis of rotation, then where that line intersects the film plane will move up from the centre of the film. To keep the lens axis centred on the film, either the lens board must be dropped, or the film back raised.

Tilting the rear standard backwards will achieve the same effect only if the whole camera is tilted forward to keep the back vertical. Then, if you think about it, you've ended up with the back and the lens in the same relative position in both cases. There're more ways than one to skin a cat, or to get a given lens/film plane geometry.

[Leonard Evens]

It is a bit late to resurrect this discussion, but I came on it because of the forum's excellent linking system.

First let me address the original question. Assume that the two principal points are close together both close to the lensboard, and the pupil magnification is close to one. This is usually the case, and I'd rather not get into complications which might arise otherwise. If you use an axial tilt, there is no displacement downward of the point of view. If you pick the point where you focused originally properly, there should also be no horizontal displacement of the point of view. If you use a base tilt, for a typical 4 x 5 camera, with a typical moderate tilt, I can't believe the vertical displacement of the point of view will be more than a mm or two. A small rise of the front standard should easily adjust for that and put the point of view at the same height as when you started. Or you could use a drop of the rear standard to reframe slightly. The point of view would be vertically displaced slightly, but that should make little difference. There would also typically be a horizontal shift forward of about 10 mm or so, which could also be corrected by moving the front standard back and refocusing using the rear standard.. But unless you are doing extreme close-up photography, the horizontal shift shouldn't really make any difference.

I checked all this both theoretically and in practice with my camera. My Toho FC-45X has the additional feature that the tilt axis moves with the lensboard so you don't have to worry about the effect of a rise done before or after the tilt. But even for cameras where that isn't the case, my estimates should hold.

The orignal questioner asked if it wouldn't be better to tilt the camera up slightly to correct for the drop. You could certainly do that. For example, to correct for a 2 mm drop, with a 150 mm lens, you would have to tilt the camera up less than a degree. That probably wouldn't make much visible difference in a landscape. But in architectural photography, it could easily create some noticeble convergence of verticals unless you tilted the back to the vertical. Of course, tilting the camera up and restoring the back to vertical is equivalent to a rise, so that would appear to be pointless when a slight rise of either front or rear standard would do the job without any significant effect.

Pete's comment about the lens axis introduces an extraneous issue. The lens axis does change as he describes, but that has no effect on what is contained in the frame. That is only affected by the change in the point of view and where the film (rear standard) lies. And as I noted, those things change only very slightly in typical situations as the result of a tilt. It is true that the image circle moves up a significant amount when you tilt, and that can affect the quality of the image, but that is another matter. Generally as long as you stay within the angle covered by the lens, you will be fine, but certainly a very large tilt could put the negative outside that. A typical modest tilt shouldn't. Other people also raised this same issue of preserving a 'sweet spot' of the lens, but usually that is a minor consideration. The first consideration is always to choose the point of view, and the second is to select what is in the frame. Sweet spots, I've found, are almost never relevant.

[Julio Fernandez]

For LF camera operation a website that is outstanding, highly recommended and must be visited is Merklinger's. This can be found at http://fox.nstn.ca/~hmmerk/HMArtls.html Merklinger also has several publications available online which deal with depth of field, camera movements, etc. The video illustrations are specially useful. Even if you do not remember all that Merklinger teaches you will have gained a great deal of understanding about how it all works.

[Sal Santamaura]

Masayoshi, I don't think you're missing anything. Key in your post was "..if the camera meets this requirement." I assume Howard is discussing his Horseman VH, and was considering checking out this situation on my own VH, but realized there are too many variables to reach a useful conclusion. I don't know where Howard's lenses' nodal points are. Also, I recall Howard has at least one lens on a recessed board, which would negate any attempts Horseman might have made to precisely locate the VH's front standard pivot point.

[John H. Henderson]

Sounds like what you read is for cameras with the tilt axis at the bottom of the standard rather that through the lens. If that is the case, then tilting the lens forward is going to lower it a bit, too, though you'd have to tilt an awful lot to make a lot of difference.

I say just look at your composition on the ground glass. If you need to use rise to get want you want, then use rise.