Please Help and give me some advise

[rdenney]

Remember that only a loupe on the ground glass tells the truth. Levels on camera bodies do not--they provide a reasonable starting point.

1. The oblong nature of some of the round shapes is caused by rectilinear distortion, which is visible with this close camera position. More distance would reduce this effect, and that's why a longer lens might help.

2. I saw many photos that were not level with the edges of the frame. The closer you are to the subject, the more critical such things become. So, we may tilt the back so that it is vertical using the level, but then we have to check the subject carefully, with a loupe and with measurements (or an accurate grid) on the ground glass, to be sure there is no convergence or slanting horizontals.

3. When you tilt the lens with respect to the film to a given angle, the focus plane tilts by twice that angle. Depth of field surrounds that focus plane. But depth of field is always less when closer to the camera and greater when more distant, so the depth of field space around a tilted focus plane is generally wedge-shaped, with the narrow part of the wedge being closest to the camera. If you chose a focus plane to make it possible to bring in your three-dimensional subjects and keep the table-top in focus, you would have needed a compromise focus-plane position that would allow depth of field to accommodate the subject material not in that plane, and more tightly at the bottom of the photo where that material is closer. With three-dimensional subjects, this is tricky and you have to check your result using a loupe, with the lens stopped down. That's not always easy but that's the gig.

4. Squaring a camera to the subject may not be as easy as it seems. When at the limits of the depth of field, even small errors will yield visible results. Again, the proof of the pudding is in the tasting, not the recipe: Evaluate your positioning and movements on the ground glass.

Rick "noting that you also have to view the whole ground glass for subtle cockeyedness that might not be visible with a loupe" Denney

[megapickle1]

Hallo Rick! Thank you for your remarks.
I realise that there is a lot to lern for me regarding LF-Photography and I have to admit to be a horrible impatient guy. You are right, some of the pictures are not in level but some of them only looks like because the rear endge of the table is not properly aligned. The table itself is in leven though the surface is not very plain.

I use a loupe on my Sinar P2, it is this binocular mirrored gadget. The distance between the lens and the objects was mostly about 2-3 feet. I have not seen these strange "leanings" or OOF-areas on the GG before the shot. But what can an old mans eye see there at f32.

I have just posted some of the critical pictures at my flickr account plus a scetch of the setup. I hope this can clear my mistake better. Please look on the colored marking lines an areas. These are my problems. I am not sure, but I think it is my camera setup per se. Tilting the whole system by 20 - 25 deg. and upright standards. But only with a tilt of the front standard (lens board) I`ll get not the "birds view" intended. So I hope you can give me a hint.

Here is the filckr-site:
http://www.flickr.com/photos/megapic...57628076745078

BTW what is your opinion at a 360mm lens for this kind of work with the standard bellows (400 mm). I think the bellows are too short for this lens, it would need about 500mm or more extension.

Best regards
George

[rdenney]

Your first setup will provide more of a downward view--you'll be able to see the tops of your subjects rather than just the sides. But you will not have vertical convergence, in principle. It may take some micro-adjustment to weed every bit of that out, though. The focus plane will be vertical.

In the second setup, the focus plane will be more tilted than the lens board. How much really depends on bellows draw. The lens board will intersect the film plane on a line, and the focus plane will intersect along that same line. You'll have just a bit less depth of field on the table surface than at the top of the bottle, but probably not by all that much.

The distortion is a function of camera distance. Circles become elliptical when viewed at a shallow angle. When they are viewed straight on, the foci of that ellipse are horizontal to each other. The closer to the line between the lens rear nodal point and the center of the film that circle is, the smaller the minor axis of the ellipse becomes. On that, the ellipse is viewed edge-on and becomes a line.

A circle looks most natural when it looks like a normal ellipse. With a rectilinear lens, the elliptical view of our circle will be magnified as it approaches the corner. So, if the circle is in the lower left of the image, the ellipse will become pregnant in its lower-left corner. That will pull the left focus of the ellipse down and to the left, and you see this with your construction lines. This magnification is built into the design of the lens, and it's what makes the projection rectilinear.

The closer you are to the subject with respect to that offset from the center of the image, the more pronounced the rectilinear effect will be. The steeper the downward angle of the line between the center of the film and the lens, the more the perspective convergence correction effect will be. Using a longer lens reduces the lateral offset of the bottle with respect to the distance of the film to the subject, and so reduces the rectilinear effect.

(The foreground edge of the circle is bigger with respect to the background edge, too, because it's closer and there is perspective convergence in that plane. A longer lens would change the relative distance of the front and back edge of the circle with respect to the camera distance, and would reduce that convergence.)

You could reduce the distortion on that black pedestal (in the picture with the stone egg) by moving the camera to the left and applying a lateral shift to restore the view. That would magnify stuff more going to the right of the picture, which might add a bit of pregnancy to the right side of your pedestal and restore its shape a bit. One of our product photo experts, like Brian K, would know better--that's not usually a correction I'm trying to make. But it's an easy experiment, if your lens has the coverage.

Now, to more practical matters. I use a 12" lens on my Sinar F2 and I think I'd be able to focus it on your subject. You are getting something like a 1:4 magnification. Thus, your 8" (~210mm) lens needs 10" of bellows draw. A 12" lens would need 15" of bellows draw. I would need an extension to my basic rail, of course, but I think a single 6" extension would be adequate. And I think the standard 22" bellows would do fine.

If the magnification is greater, say 1:2, as with your stone eggs, then your 8" lens would need 12" of extension, and a 12" lens would need 18" of extension. You'd probably need a 12" extension or two 6" extensions of your P2 rail.

With a 14" lens (~360mm), you'd need 17.5" of extension for 1:4 and 21" of extension for 1:2. I think that will stretch your bellows pretty tight in the latter case.

Rick "not sure if all this made sense" Denney

[Armin Seeholzer]

The 360mm will be to long for the normal Sinar Bellows, I would not go longer the 240mm or maybe 300mm is already critical for the normal Sinar bellows for your small set ups!

Cheers Armin

[megapickle1]

Thank you Rick!

Your explanations are clear and I can understand what you mean. O.K. I have to apply this in the next shots.

You and Armin gave me the needed advise regarding the possible lens-lenght. Thank you both.

Now I have to find a nice 300mm lens with f5,6 starting aperture for little money - yes they are big and heavy and need a #3 shutter, I will use it for portraits too.
But first I have to learn the proper use of the camera movements with my small tabletop items and waste more material.

Thank you all for looking at my crappy pictures and your kind advise.

George

[polyglot]

If you want the bottle to look perfectly straight, the film plane must be parallel to the bottle.

Think of taking a photo of a building with a camera pointing upwards; the top of the building becomes narrowed. To get parallel sides, you use a vertical film plane (for a vertical building) and shift the lens upwards to get the desired framing without having half your frame be pavement. Same issue with the bottle.

In the case of your images, that will require a lot of front fall (rear rise) to get the effect of looking down on the bottle yet keeping the sides parallel. A normal (no shifts/tilts) photo looking down on a bottle obliquely would have the top of the bottle looking a little larger than the bottom.

Anyway, you should be able to see the tapering on the ground-glass and adjust to suit. A grid on the glass will help. I know that I have a habit of not noticing until it's too late though

Perhaps next time you do a similar setup, take a digital snapshot of the relationship between bottle and both standards of your camera from the side and inspect it for how parallel everything is.

Edit: or, what Rick said.

[r.e.]

George, I think that this is a question of technique, composition and expectations about/understanding of perspective rather than a question of using a 210mm lens. At the magnifications you are using, that lens is in my view capable of superb results. I do not believe that buying a 300mm lens is going to help, and it will result in more compression, which you may or may not want.

I'd like to suggest that you look at the 4x5 photographs of Christopher Broadbent on this site, and elsewhere on the Internet, and read his posts on lens focal length.

[megapickle1]

@ r.e.
Hallo! I know Mr. Broadbent well and so I can say, his studio is approximatly 10 times larger than my spot. I can not walk around my setup because there is no room for. You are right I have to do my math with perspective control.

@polyglot

The film plane (rear standard) was absolutely vertical and the front standard and the bottle were vertical too. I think I have to apply a little bit of front tilt (down) and the lines would straighten up because the top of the bottle would be nearer to the front standard. I do not want to bee a smart ass but I have to do my own math with perspective control. Unfortunately a) I have not enough time for playing around and b) I am pathological impatient. So I have to brutally force myself to learn these principles.

Thank you for your nice answers and your time!

George

[Tom J McDonald]

George, as far as I understand, tilting the front standard will not change your image shape.

[ic-racer]

The easiest way to ensure your subject and film plane are parallel is to use gravity. If the subject is perpendicular to the pull of gravity (measured with carpenter's level) then by making the film plane plumb, you can easily eliminate all tilting, falling, leaning objects in the picture.

In terms of lens plane and depth of field, when the lens and film are parallel you get the most bang for your buck in terms of depth of field. When you start tilting or swinging the lens you narrow the depth of field. Tilts and swings work best when your subject area of interest falls on a plane. Otherwise lens tilts and swings can be a detriment to out-of-the-focal-plane objects.

Distortion in most modern LF lenses is pretty minimal and can probably be totally ignored unless you are doing some exacting flat-field copywork. For example the Schneider 210 APO-Symmar at infinity has about 0.01% distortion.