Easy-Bake Scheimpflug Recipe

[sharktooth]

Thanks, I have just done this calculation for two theoretical objects, one at top of ground glass 60cm away and other at bottom of ground glass 600cm away with a 15cm lens.
Focal Difference = 14.62cm (Classical formula gives V = 20 and V = 15.38 for these U values and F = 15)
GGVD = 8cm
61 degrees which is slightly more tilt than available

Try again for first object at 300cm and second at 600cm (classical formula gives V = 15.78 and V = 15.38)
FD = 0.4
GGVD = 8
21.8 degrees which is possible.

Would this still work for a telephoto lens where the FD will be less than for a simple lens?

I don't get some of your calculations. In the first example you say V1=20 and V2 =15.38. To me this would make the difference in focal positions 20-15.38=4.62. I don't know how you got the focal difference to be 14.62
.
if you use 4.62 as your FD and 8 as your GGVD, then the tilt angle will be 30 degrees.

In the second example, arctan(.4/8) gives 2.86 degrees (not 21.8 degrees)

It's an interesting exercise to look at the lens calculations in this way, but that wasn't my original intent. I was considering just measuring the actual distance between the two positions along the monorail.

If you want to use the lens calculation for a telephoto lens, then the nodal point of the lens lies somewhere out in space, and not within the lens. U and V will be with respect to this nodal point, so you need to be careful how those are measured for the calculation. If you just measure the actual distance between the two focused positions on the monorail, it doesn't matter what type of lens you use.

[Alan Klein]

.... a little background.

This came out of a discussion about the Sinar f2 over at Photrio. The poster was asking about one of the scaled knobs on the left side of the camera at the back. He was asking what it was for.
I didn't know either, so I looked it up. It turns out it's a tilt angle scale for focus adjustment, but I had no idea how this could work on a Sinar f2. The Sinar f2 has basic base tilts, and not the fancy in-frame asymmetrical tilt of the P series. It didn't seem to me that it would be possible to determine tilt angle on an f2.

I found a description for use of the tilt angle knob for the f2 (also f1, but not f), also on Photrio. When I read through the description it became immediately clear how it worked, and that the basic principle could also be useful for other cameras. With the Sinar f2, there are horizontal marked lines on the ground glass 35mm above and below the center line. There are also vertical marked lines 35mm to the left and right of the vertical center line. On the P series, these lines represent the asymmetrical tilt or swing axis (depending on orientation). These same lines can be used on the f series using completely different methodology to determine tilt or swing angle.

The Sinar lads were very smart, so they deserve all the credit for this. By focusing the back at two different points on the upper and lower marked lines, they could create a right angled triangle with the focus displacement as one leg, and the vertical ground glass displacement as the other leg. The angle of the resulting hypotenuse is the required back tilt angle. It's just simple high school trigonometry.
Since the vertical displacement on the ground glass is already fixed at 70mm, the only unknown is the focus displacement. Since the focus displacement is proportional to the rotation of the focusing knob, they only needed to put angle scale markings on a secondary knob that rotates with the focus knob. There is no need for a separate calculation.

The big downside of the Sinar system is that your two focus points have to reside on the marked lines. That's probably not going to be practical for many shots, since there may not be convenient points to focus on along those marked lines.

Nonetheless, it is indeed ingenious for Sinar to come up with this system, since it was an easy add to the f series, and would make use of the marked lines already on the ground glass for the Sinar P.

The method I'm using here is just an adaptation of this Sinar approach, but can be used with any camera with any two points on the ground glass. You're not limited to points along a marked line, but you will need a calculator to compute the tilt angle.

Couldn't you just rise or fall the standard until the line overlaps the distant object. Then focus the bellows. Then return the standard to its original position that you framed the picture. Make sure it stays parallel to the film plane.

[sharktooth]

Couldn't you just rise or fall the standard until the line overlaps the distant object. Then focus the bellows. Then return the standard to its original position that you framed the picture. Make sure it stays parallel to the film plane.

That works on the P series with asymmetrical rear tilt, but it doesn't work with the f1 and f2 that have standard base tilts. Sinar figured out a way to utilize the marked lines on the ground glass for the P series, to make them useful for the f series, but using entirely different methodology. That's what I'm trying to point out here. The same basic principle that Sinar uses for the f series can be modified to be used on other view cameras with any tilting design. It's just a novel approach that others my find interesting, but it isn't better than other methods, just different.

You seem to be misunderstanding the purpose of the asymmetrical rear tilt. It was designed to be a convenience in some shooting situations, primarily in commercial tabletop work, where time is money. If you read through the Sinar instructions for the asymmetrical rear tilt, it says to transfer the tilt angle at the back to the front standard, so that you don't disturb the image perspective. It's a bad habit to be using the rear asymmetrical tilt to adjust the focusing plane for every shot. Yes, it can be used this way in some situations without causing problems, but using this for every shot and not understanding it's limitations is poor practise.

There's a pretty good explanation of view camera use and setup here on this site by QT Luong. https://www.largeformatphotography.i...o-operate.html I'd suggest reviewing that, especially regarding the subsections on perspective and focusing.

[Sandokan]

sorry - 14.62 should have been 4.62 and 30 degrees
No idea how I got 21.8 ... unless I did arctan of 0.4. Doh!
Anyway, I did it to try to understand how this Sinar calculation works, which I do now - even if I wont actually use it.

[Alan Klein]

That works on the P series with asymmetrical rear tilt, but it doesn't work with the f1 and f2 that have standard base tilts. Sinar figured out a way to utilize the marked lines on the ground glass for the P series, to make them useful for the f series, but using entirely different methodology. That's what I'm trying to point out here. The same basic principle that Sinar uses for the f series can be modified to be used on other view cameras with any tilting design. It's just a novel approach that others my find interesting, but it isn't better than other methods, just different.

You seem to be misunderstanding the purpose of the asymmetrical rear tilt. It was designed to be a convenience in some shooting situations, primarily in commercial tabletop work, where time is money. If you read through the Sinar instructions for the asymmetrical rear tilt, it says to transfer the tilt angle at the back to the front standard, so that you don't disturb the image perspective. It's a bad habit to be using the rear asymmetrical tilt to adjust the focusing plane for every shot. Yes, it can be used this way in some situations without causing problems, but using this for every shot and not understanding it's limitations is poor practise.

There's a pretty good explanation of view camera use and setup here on this site by QT Luong. https://www.largeformatphotography.i...o-operate.html I'd suggest reviewing that, especially regarding the subsections on perspective and focusing.

I don't really shoot architecture only landscapes. So I haven't noticed the distortion., But your point is well taken. It probably would be easier for me to just use multiple iterations of the front standard than have to also add rise and fall procedures when using rear asymmetrical method. It is handy though when the axis line on the GG lines up with the far object and I only have to tilt the rear back a little.

[sharktooth]

I don't really shoot architecture only landscapes. So I haven't noticed the distortion., But your point is well taken. It probably would be easier for me to just use multiple iterations of the front standard than have to also add rise and fall procedures when using rear asymmetrical method. It is handy though when the axis line on the GG lines up with the far object and I only have to tilt the rear back a little.

With landscape work, where your subject is relatively far from the camera, and tilts/swings will only be a few degrees, then using the rear asymmetrical tilt for focusing is a fast and convenient method. I'd do that too. It's not a matter of right or wrong, it's simply a matter of understanding all the implications, and using a method that makes sense for your own equipment and working habits.

I should add that it's not just architectural work that is a concern. When your subject gets closer to the camera, the focus displacement between your near and far subjects get larger, and this means the tilt or swing angles get larger too. If you have people in your image, then they can end up with swollen, or shrunken heads when using large back tilts/swings. The same applies to subjects that have well known shapes and sizes, such as balls, flowers, cans, boxes, etc. They can end up looking strangely distorted with larger back tilts and swings.

[sharktooth]

After looking at Sandokan's results using lens calculations, I thought it would be interesting to plot some curves to see how lens tilt changes with subject distance from the lens. I know that you need more tilt as the nearest object gets closer, but I didn't know how dramatic the tilt would need to be.

For this example I considered a typical landscape situation where you have some far objects near infinity (trees, mountains, etc.), and closer objects near ground level that you'd also like in focus. I used a 150mm lens, since that's a normal lens for 4x5. Sandokan used an 80mm height difference on the ground glass, meaning the far object and the close object are 80mm apart (vertically or horizontally), when measured on the ground glass. This seems reasonable for a 4x5 imaged viewed horizontally. An 80mm difference would put one point near the top of the frame, and the other near the bottom of the frame. I also looked at a 40mm height difference, which puts the near and far points closer together on the ground glass.

Here are the resulting curves:



For those that are metrically challenged, here is the same graph, but with the distance scale marked in feet.



When your near and far objects are further apart on the ground glass, the tilt needed is less than when the two objects are close to each other. The tilt angle to maintain both objects in focus remains fairly small (less than 10 degrees) when the near object is greater than about 3.5 meters (11.5 feet) from your lens. Once your near object gets closer than that, the tilt required starts to increase at a much faster rate. When the tilt angle gets greater than about 10 degrees, you'll need to be careful about changes in perspective (if tilting on the back). For lens tilts, you need to be aware of the image circle, since with large tilts your image may not cover the entire film area, causing vignetting.

[Alan Klein]

Do tilts effect exposure falloff when using a center filter? Are there these differences if you're doing the tilt from the front vs the rear standard?

Ditto if no center filter is used?

[sharktooth]

I don't know how center filters affect swings or tilts. Maybe someone else can chime in on this.

Without a center filter, you are using the outer areas of the image circle of the lens when you swing or tilt the lens. If your lens has falloff in this outer image circle, then it could become noticeable. It all depends on the lens. With back tilts or swings, you're actually using a smaller area of the image circle, so it shouldn't make any significant difference.

[Doremus Scudder]

Alan,

Your center filter just balances the illumination over the entire image circle, thus preventing the falloff. The tradeoff being having to give extra exposure, of course. It does not affect the size of the IC, nor distort anything. Tilts and swings (and rise and fall) work exactly the same with and without a center filter.

But, as sharktooth points out, if you don't use a center filter and are using a lens with lots of falloff and have a lot of the outside edges of the image circle in one part of the image, the falloff there will be noticeable. Using back tilt and swing does not move the image circle around, so the image stays in the center of the image circle. When you use front tilt or swing, you displace the image circle on the ground glass/film, so the center of the IC is displaced from the center of the image and one side/corner of the image will be closer to the edge of the IC than the rest of it. If falloff is an issue, use the center filter or plan on compensating with burning or whatever during printing.

If you use the center filter when tilting/swinging the front, there should be little apparent falloff.

Doremus