Question about lens tilt on 4x5

[Halide]

Hi,

I have been shooting B&W film for 30 years and converted from 2 1/4" to 4x5, 4 years ago. Most of my images are landscapes - and I rarely have to tilt my front lens to control focus for near and far field focus. I have done this successfully for a number of images, but this last summer I made 4 images at the base of Mt Williamson in the eastern Sierra Nevada. In the attached image the near field and infinity are focused - BUT there is a 3/4" wide band across the entire middle of the image that is slightly out of focus. Does anyone have any ideas what may have caused this? I may have not closed the lens down enough.... I remember using f22 . But at the time of making the image I concerned about using a fast enough shutter speed - the clouds were moving fast. I have successfully made images for the same scene in the past using the same technique of lens tilting and using a greater f stop. I am pretty sure it is not my film holders - because it was defect across 4 images. Thanks in advance for any advice or answers to my problem.

Regards,
Len

[cowanw]

I am thinking you have focused on the top of the foreground rocks and the top of the mountain, with tilt and the plane is insufficiently flat.

[Dan Fromm]

I am thinking you have focused on the top of the foreground rocks and the top of the mountain, with tilt and the plane is insufficiently flat.

The region of adequate sharpness isn't a plane, it expands from near to far.

Len, what did you mean by "greater f stop"? Larger aperture (f/ number smaller than 22) or smaller aperture (f/ number greater than 22)? A smaller aperture would have sharpened the mountains feet at, perphaps, the cost of clouds blurred by motion. Sometimes you just can't win.

[dave_whatever]

Looks like the plane of focus is too high. Having set the tilt angle you might have needed to focus the camera to position the plane of focus lower, otherwise a lot of the depth of field you're gaining by stoping down is wasted in thin air.

[Taija71A]

The region of adequate sharpness isn't a plane...

Very sorry... But this statement is incorrect or perhaps? somewhat 'misleading' (*At the very best)...


Subject Plane:

http://www.trenholm.org/hmmerk/HMbooks3.html#SRpic


The region of adequate sharpness can be thought of... As a 'Plane' (*Much moreso than a cone) -- Depending on the chosen Aperture of course.

... it expands from near to far.

Yes. Most certainly!

I am thinking you have focused on the top of the foreground rocks and the top of the mountain, with tilt and the plane is insufficiently flat.

Looks like the plane of focus is too high. Having set the tilt angle you might have needed to focus the camera to position the plane of focus lower, otherwise a lot of the depth of field you're gaining by stopping down is wasted in thin air.

Agreed!

The focus appears to be 'off' and f/22 was not enough D.O.F... To carry the shot.
Perhaps f/45 would of sufficed?
--
Best regards,

-Tim.
_________

[richardman]

To simplify: when you use tilt to achieve sharpness at both near and far, the "region of sharpness" is sort of cone shape. So the previous advice is correct: lower the cone and you can probably make the in-between rocks sharp too, plus using a smaller aperture opening.

[Lenny Eiger]

Len,

Personally, I would never consider using f22 with a large format camera (except for special situations). I am always shooting at f45 or f64. There are people who like the sharpness falloff, it seems all the rage these days, and they are welcome to it. I am old-school, a lover of craft, and I like depth of field. The rule about 2 stops down from wide open is totally bogus for these types of lenses. This business of diffraction has been debunked with respect to large format. (Or let's just say the effect is minimal enough to be ignored, at least to f45.) There appears to be general agreement on this here, I'd estimate about 85% or so.

When looking at sharpness of an image, you have to analyze the whole system, from film & developer choice, lens and tripod, all the way thru to the print. For example, you can shoot sharp all you want but if you use an Epson scanner the sharpness of the lens and its aperture won't matter at all. Best thing to do is to make sure you set up somewhere without wind and do a test. Shoot at f22 all the way to as far down as your lens will go, upping the time, of course. In 4x5 this won't be too many sheets and won't cost you hardly anything… You will have the answer you want, for your equipment and process, and won't have to take my word for it.

I can't imagine that scene would all be in focus at anything less than f45… that's quite a range from near to far. I'm not even sure 45 would be enough. And yes, for the others who would wish to remind me of things LF, I do know how to tilt the lens as well. Going on 52 years doing photography… but I'd say 30 years is pretty good!

Best of luck,

Lenny

[Halide]

Hi Guys,

Thank you all for the input and information - the next time I tilt the lens I will center my focus just beyond the foreground, then adjust tilt and focus as necessary to bring everything into focus with adequate f stop. When I made this image the center of my focus were the boulders in the foreground and I shifted the tilt and readjusted focus.

Thanks again -
Len

When I go out to this location again I will give it another try - and re post my results on this thread.

[Taija71A]

... For example, you can shoot sharp all you want but if you use an Epson scanner the sharpness of the lens and its aperture ... Won't matter at all.

? ? ? ? ?

Lenny, please don't tell this to all of the Epson V750 Owners... Here on the Forum -- Okay?

Otherwise, they all might as well... Just be using 'Quaker Oats' Pinhole Cameras.
--

-Tim.
________

[Doremus Scudder]

Hi Guys,

Thank you all for the input and information - the next time I tilt the lens I will center my focus just beyond the foreground, then adjust tilt and focus as necessary to bring everything into focus with adequate f stop. When I made this image the center of my focus were the boulders in the foreground and I shifted the tilt and readjusted focus.

Thanks again -
Len

When I go out to this location again I will give it another try - and re post my results on this thread.

Len,

You have made a common mistake.

When you try again, here are a couple of things to keep in mind:

First the plane of focus is indeed a two-dimensional plane; however, the zone of acceptable focus, aka depth-of-field extends to either side of the focus plane.

When the back and lensboard are parallel, the plane of focus is also parallel to these two and the depth of field extends from in front of the focus plane to in back of the focus plane, and is also roughly parallel to the plane,

When you tilt the plane of sharp focus, however, things act very differently. When you tilt the lens forward (or tilt the back backward), the plane of sharp focus extends from a lower line close to the camera position to a higher line at a distant object or infinity. The depth-of-field around this plane results in a zone of acceptable sharpness, i.e., depth-of-field, that is wedge shaped with the narrow end close to the camera.

A common mistake in situations like yours is to choose focus points that are too high, e.g., the top foreground rock and a distant mountain top, which ends up not using the upper half of the zone of acceptable sharpness; basically wasting half the depth-of-field. In your case, you missed getting the base of the mountains sharp enough, likely by position the plane of focus too high. A smaller aperture may have helped increase the depth-of-field, but better is to place the focus plane more precisely and allow an aperture closer to optimum (f/22 for most LF lenses).

Try focusing on a lower focus point at both ends; e.g., the middle of the largest foreground rock and the middle of the mountain range. Then, keeping in mind that the focus plane is relatively flat, check the important areas you want in focus above and below the plane of focus (the mountain tops and the base as well as the foreground objects) and note the distances. Find your nearest and farthest focus points on the camera rail or bed and then position the standard you are focusing with exactly in the middle.

How large the focus spread is should determine your aperture. See here http://www.largeformatphotography.info/fstop.html for info about what aperture to use. See here http://www.largeformatphotography.in...-to-focus.html for info about focusing in general.

Best of luck,

Doremus