Newbie Question re Tilt and Focus

[G Benaim]

Hi, All

I'm just getting started using a view camera, a Gowland monorail, and have read the articles on how to focus and how to choose the f stop from the main page at LFPhoto.info. I also have Steve Simmons' book on the way, but in the mean time I though I could at least figure out the most common movement. But I'm having a hard time understanding what the end point is. I thought I had to find a tilt position where the near and far focus points are both in focus at the same time (i.e. in the same focus position). When I follow the iterative sequence described in the article, however, I just keep tilting more and more and refocussing on the far point until I run out of coverage, and the tilt angle is beyond 45deg.
So I'm thinking that maybe the endpoint isn't what I thought, but then I don't know what it is. This is reinforced by the procedure for choosing the f-stop, which requires measuring the Distance between focus points, after making movements. So if there's a distance, they're not both focused at the same time at the sam3 place (i.e. D isn't 0). So then, what are you aiming at with the iterative procedure, either the one measuring the distance and adjusting tilt or the one without measuring?
Alternately, just tell me how you do it in the simplest most practical terms. We're talking near-far, no-frills landscape tilt. Thank you.

[Jack Flesher]

This is an over-simplification, but might get you pointed in the right direction ;)

With base tilt, as you tilt either the rear standard back or the front standard forward (both of which will bring the foreground -- the top of the gg -- into focus), you need to SHORTEN the distance between the standards to regain the far subject focus (bottom of gg). As a rule of thumb in a landscape, unless you are focusing on a really close object, you should not ever need more than 10 degrees of tilt -- and often only a few degrees with a short focal.

[David A. Goldfarb]

On the Gowland, you've got axis tilts on the front (you may or may not have axis or base tilts on the rear, depending on what version of the camera you have). So when you use front tilt, the focus will stay pretty close to constant around the axis in the center of the frame (pretty close, because the tilt axis is close to but not exactly at the nodal point of the lens usually). So what I tend to do with the Gowland is to focus in the center along the focal plane and tilt for the near and far points (a little different from what is often recommended--focus near, tilt far, etc.), adjusting focus and tilt until it's right. With some practice this can be done fairly quickly.

[Ralph Barker]

In simple terms, I think the "end point" is best described as getting what you want in focus. The problem is, that's not always an easy decision in landscape work, because other 3-D factors sneak in and complicate matters.

Starting with the camera "zeroed" (composed, standards plumb, and focussed on the far point), I imagine a clear sheet of glass extending from the near object I want in focus (a nearby rock, let's say) to the far point (the tops of the distant trees, for example). Then, tilt (slightly forward) until the rock is sharp. Because that action extends the lens-to-GG distance, the bellows extension needs to be adjusted a touch to get the far point in focus again. That, in turn, requires an even more minor adjustment in tilt. A couple of iterations, and the two points are on the same plane of sharp focus (the imaginary glass sheet).

Remember, the area where DOF comes into play will essentially be a wedge, narrow near the camera and wide in the distance. If there are objects near the camera that extend vertically beyond that wedge, they will not be sharp. Thus, the decision of whether to use tilt depends on the actual geometry of the scene.

[Slade Zumhofe]

Welcome to the world of LF:)

The others have answered your question about as good as can be explained. When you said you got to about 45 degrees--I would have to make the assumption that you may have missed the correct tilt right away. I know you didn't start at 45 degrees but you probably started at 10 or 12 maybe. The "average" tilt is around 6 degrees--not very much. Try it again and this time make your first tilt very minor--say 3 degrees and see if that helps.

Good luck

[G Benaim]

Hi, all

I tried it a couple more times starting w the near in focus and it worked much more easily. My camera has front and rear axis tilt only, so my next step is to try David's suggestion. I'm not yet sure how to choose an fstop if D=0 IF you want objects other than those two points in focus. How do most of you decide on an fstop?

[Brian Ellis]

It would be nice if through using tilt the near and far could always be placed in focus simultaneously but that isn't always possible. When the near and far are suffciently far apart you can't get both in focus at the same time no matter how much you tilt (in fact too much tilt will only make things worse). The idea then is to get one in focus and get the other as close as possible, then stop down to gain enough depth of field to make the other appear sharp. And apart from that, hopefully you understand (or will after you read the Simmons book) that there are many situations in which tilts aren't used because moving the plane of focus around won't accomplish anything (in other words, you don't use tilt with every photograph you make).

Here's a useful tip for knowing when you've tilted too much and are only doing more harm than good. As I'm sure you know, normally things in the distance are brought into focus by moving the lens back towards you (i.e. away from the object in the distance on which you're trying to focus) and things close up are brought into focus by moving the lens away from you (i.e. closer to the object on which you're focusing). If when using tilts things start working backwards (i.e. when you move the lens away from you things in the distance appear sharper and when you move the lens back towards you things closer to you appear sharper) then you know you've tilted too much and you need to back off the tilt until the camera starts working normally again.

[David A. Goldfarb]

I usually tilt and swing wide open and stop down until what I want to be sharp is sharp, maybe with a little extra for good measure, paying attention to other factors like--what I want not to be in focus, diffraction, resulting exposure time, etc.

You also want to think about what will be above and what will be below the plane of focus in the range of the DOF wedge. If you're doing a near/far composition with mountains in the distance, for instance, and you want the horizon to be in focus, you might imagine the plane of focus to intersect the mountain about 2/3 of the way up rather than at the horizon, so that when you stop down the lens, the horizon will be sharp and you will be less likely to lose the middle ground.

[steve simmons]

A tilt of 45 degrees is probably way too much. Unless you are right on top of something a tilt of less than 10 degrees should suffice..

steve simmo0ns
www.viewcamera.com

[Ron Marshall]

Here is an article on this site about determining which f-stop to use:

http://www.largeformatphotography.info/fstop.

[bruce terry]

A tilt of 45 degrees is probably way too much. Unless you are right on top of something a tilt of less than 10 degrees should suffice..

steve simmo0ns
www.viewcamera.com

With all the obsessive paranoia (sic) over VCM Typos, Steve's sign-off here is a most-excellently-delivered intentional Zinger!

If it wasn't premeditated, all the Zingy-er!!

[Leonard Evens]

I think others have pretty much covered it, but let me review the procedure adding one wrinkle which may not have been mentioned.

First, suppose you know what you want the plane of exact focus to be. That would be the case if there isn't any signficant vertical variation about that plane which you want in focus. Choose a near point and a far point. Choose a moderate tilt of about 10 degrees to start. Usually that is the right order of magnitude. Then follow the following rule for refining the tilt. Focus on the far point, and notice the positions on the rail where the standards are. Then refocus on the near point and do the same. If you had to increase the distance between the standards to get the near point in focus, your tilt undercorrected and you need to increase the tilt. If you had to decrease the distance between the standards to get the near point in focus, that means you overcorrected, and you need to decrease the tilt. Using this method, you will always be correcting the tilt in the right direction, and you are unlikely to find yourself making things worse. The worse that could happen is that you find yourself oscillating between overcorrecting and undercorrecting, and in that case, you would just split the distance in the tilt angle.

Most situations, however, do involve some vertical extent above and below the plane of exact focus. To understand how to deal with that, you need to understand the nature of the DOF region when tilting. It is a wedge shaped region bounded above and below by planes extending from the so-called hinge line which lies (usually) below the lens. You can estimate the position of the hinge line if you look to see where you think the plane of exact focus should go. In choosing your near and far points, you should place them so the prospective plane of exact focus will lie somewhere in what you envision the DOF region to be. Usually this will be such that the section of a vertical plane intersected by the wedge will be bisected by the plane of exact focus. Usually the near point will be close enough to the lens that there won't be too much possible vertical variation in its position, so it is best concentrating on the far point in this regard.

Once you have fixed the tilt, the whole wedge swinges about the hinge line as you move the standards. If you got the plane of exact focus exactly right, centered vertically as above, nothing more should be required, but often you find that further adjustments in focus can improve the situation. To help with this, locate high and low points above and below the plane of exact focus that should be in focus. (They need not be at the same distance from the lens.) Focus so that each is in focus, note the position on the rail of each, and set the standard half way in between. You can then use the methods decribed in the LF Photography web page for determining f-stop in terms of this focus spread. (The original spread between near and far points is not relevant for this.) In some cases, you may want to favor the top or the bottom so you may decide to place standard close to one of the two vertical extension points.

[G Benaim]

Leonard,

If I move the focus from the point where the original near/far points are both in focus, and do this in order to get the verticals in focus, don't I then change the degree to which those earlier points will be in focus? How do I take into account both near/far and vertical focus points in order to a) decide what f-stop to use and b) where to place the focus?

[Robert Oliver]

for beginners... focus far - tilt near. Then add depth of field to increase sharpness everywhere else seems to be a simple way to figure it out.