Vignetting in one camera but not the other.

[leo_grillo]

This is wild ... I can't figure what fundamental issue I am missing. Let's take the Rodenstock 135mm

lens. It has a 7.5 inch circle of coverage and I'm shooting 4x5. On my trusy old Sinar F2 (monorail), no

problem. Wonderful lens and more tilt than anyone could need.

But for the helluvit, I pulled out my old Linkhof Master Technika and mounted the same lens. Other

than square on, any amount of tilt caused vignetting. We're talking 3-5 degrees!

I measured the film plane to lens board and they are the same on both cameras ... as well they should

be. But the Linhoff vignettes badly and the monorail doesn't. I am stumped. Your thoughts?

[ellis_vener_photography]

bellows getting in the way?

[sattler123]

I had the exact same thought as Ellis- the bellows in the Technika might sag a little bit and that might be in the light path of your lens. Look carefully after you've done all the movements and see if that might be the issue.

[jim_norman2]

Has to be the bellows. I doubt the rules of optics are defied by the Linhof MT. Is it possible the camera is not zeroed out, such that front rise or the extension back is way out? I agree with Ellis and Juergen.

[leo_grillo]

Thanks guys. I took your suggestions, but it's not the bellows as far as I can see. I played

with it without a lens board attached ... and aimed it at a light. The circle of light changed

shape perfectly according to forward or backward front tilt. I DID realize a difference

between the cameras though, that I had forgotten about ... the Sinar has an assymetrical

tilt and the MT has an axis tilt. I can see where the axis tilt is more radical to the image

circle. Perhaps this is all it is ... though I have trouble buying that when I see how much I

can tilt the Sinar and not be able to even GET a vignette with this lens.

[michael_briggs2]

Try looking to see if you can figure out what is blocking the light path. Maybe mount a lensboard without lens, then look back through the hole with the bellows extended for a 135 mm lens -- can you see all of the ground glass? If not, what clips the light path?

[leo_grillo]

Thanks Michael, nothing is in the way. Without tilts the lens is fine. With 3 degrees or so it

is fine. Real landscape tilts, 5-10+ degrees: vignetting. I am going to send this camera for

service and ask them what is going on. Now, when they say everything is working

perfectly, I still have this riddle. One thing I noticed in watching the circle's shape without

a lensboard attached: that circle sure narrows down fast with Axis tilting, looking more

like a flying saucer as the tilt grows. Maybe that is the difference with the Sinar's

assymetrical tilt.

[bob_salomon]

Are you shooting at 1:1 or near 1:1?

 

There is an issue where the round track that the back revolves on can sometimes be seen at

close range when shooting macro. Usually this occurs outside the useable negative area of a

45 negative and usually with 210 and longer lenses. It would appear to be a rounding off of

the image in the corners. On the Kardan and Technikardan cameras that do not have

revolving backs they have cut out the track in the corners to eliminate this effect. But if you

cut the corners on the Technika then the back would not revolve.

[leo_grillo]

No Bob, just regular landscape. If you have a 135mm lens and polaroid back I can send

you the camera. (I'm using mine on the Sinar.) It needs servicing anyway -- getting pretty

stiff from sitting. I'm in Los Angeles if you have a local service center.

[bob_salomon]

For service it should go to Marflex and not to us. As we would have to forward it to Marflex

it would take longer to service. Samy or most other dealers in LA can also send it to Marflex

if you rather they take responsibility for the shipping. But they may charge for that.

[kelly_flanigan1]

A tilt is a rotation. In mechansims design the point the object rotates about *is the instant center*. One camera can be rotating the lens about a different point than another; so there really IS some shift going on too. <BR><BR>Imagine sitting in a car. It might be rotated if on say ice about you; the front bumper; the rear bumper. If the car is rotated about the rear bumper 10 degrees you are rotated and also translated with respect to a fixed point on the ice too.<BR><BR>The lens's optical characteristics do change with the camera. The lens and a wax piece of paper will show the image circle. If its vigneting more then something is blocking the image.

[kelly_flanigan1]

Whats intereting is Ansel Adams called the Technika a press camera; the really old ones actually were.

[kelly_flanigan1]

One should not send the camera in without the lens and ask them about a vignetting problem. You might drive them nuts with nothing really to test.

[bob_salomon]

The only Technika camera that was a press camera was the Technika Standard Press made

from 1950 to 54. All other models had front and rear shifts and technically were not a

'press" camera.

[leo_grillo]

"A tilt is a rotation. In mechansims design the point the object rotates about *is the instant

center*. One camera can be rotating the lens about a different point than another; so there

really IS some shift going on too."

 

This is all I can think of -- different axes. The lens has an almost 8-inch circle at f22; but

with the center axis, the circle flattens out quickly and the 5-inch film width has damaged

corners.

[keith_lubow]

I think you are seeing the difference between base and axis tilts. When you use a front forward tilt, your lens is also doing a negative vertical shift (or "fall"). With axis tilts, you see the effect of this NOT happening right on the ground glass: You tilt forward, and the composition shifts up on the ground glass (actually down in proper orientation, but up on the glass), and has be be compensated for, usually with a positive rear vertical shift (or "rise").

 

Also: Where are you seeing the vignetting? On the ground glass, or on the processed film? It could be a difference in how the vignetting shows up on the two different ground glass screens.

 

Keith

[keith_lubow]

second sentence, I am talking about a base tilt camera

[leo_grillo]

Thanks Keith -- this is the direction I was going, and your explanation makes perfect

sense. The vignetting is seen first on the polaroid, hardly visible on the GG.

 

I have a project that demands setup speed in the field (too close to highways and fast

cars), so I timed my setting up the Sinar F2 (monorail) camera and then the MT. MT was

50% faster ... but the vignetting dropped the confidence level and I am sticking with the

F2.

[keith_lubow]

Have you dropped the bed on your Linhof? Not necessary to clear the angle of view at that focal length, but it will give you some more fall on the front. Drop the bed from the beginning, and square up the standard as close as possible to its "straight on position. Then you can rough compose, and give the shot the amount of front forward tilt that you want. Because you will have had to shift your front standard upward in the beginning, you will now have extra downward shift available to compensate for the tilt. If it helps even a little, I think it is worth it, because the Linhof is a much more durable and easy to pack camera in the field. I actually find field cameras slower to get the movements right, since you don't have the full range at your command. However, they pack and unpack into a compact "cube" relatively quickly and without too much fear of damage. I have hauled a monorail out and about. It's not the weight, but the shape of the darned thing, plus the ease of damage, that makes me want to use my Speed most of the time out in nature or for urban shots that don't need significant movements. If I need movements that are not available on the Speed, I will fake the up and down convergence correction as best as I can in camera (by skewing the back and correcting the front back to level), and then do the left to right convergence correction in the enlarger.

[paul_hoyt]

Ther are two different lens boards for Linhof's. Some have a center hole and some are off set to the bottom of the board. My "true" Linhof lens boards are off set and one of my generic lens boards has the centered hole. I am assuming a front tilt with the centered hole lens board is not an "on axis" tilt, since the center of the lens is not projecting on the center of the GG. Can you compensate for the vignetting by raising or lowering the lens?

 

Paul

[leo_grillo]

Ahhhh ... now THAT's an interesting thing ... I have noticed that some lensboards are

offset and the generic are centered. This one is centered. Nowhere in the manual does it

discuss this. Bob S. any comment? That might be a compensation for this center tilt

problem.

 

"I am assuming a front tilt with the centered hole lens board is not an "on axis" tilt, since

the center of the lens is not projecting on the center of the GG." I thought the center of the

lens is projecting on the center of the GG with the centered lens hole. In fact, I wondered

why Linhof allowed the lens NOT to be centered with the offset board.

 

"Can you compensate for the vignetting by raising or lowering the lens?" I played with this,

and yes you can, the way Keith describes. But it takes longer on my clock and makes the

monorail more appealing.

 

Bob Salomon and the offset lensboard hole ... any notes? thx all.

[michael_briggs2]

Genuine Linhof lensboards have the hole off center, this centers the lens on a Linhof camera when the controls are at neutral. Some other camera manufacturers who have chosen to make their cameras use boards with the dimensions of a Linhof Technika board have not copied the off-center position of the lens hole. Some generic Technika-style lensboards from other manufactures thus have centered holes.

 

"I thought the center of the lens is projecting on the center of the GG with the centered lens hole." The Linhof parts, camera and board, are designed to be compatible.

[leo_grillo]

Thanks Michael ... so the generic lensboard is actually causing a rise in the lens and so I

am vignetting. ok. I knew it was something fundamental. This is the last piece of the

puzzle.

 

To explain this point to future surfers ... on my monorail, extended to the 135 focal

length, and the lens being centered, the bottom of the front standard is raised so that the

lens is centered on the GG ... but on the Linhof the botom of the front standard is on the

same plane as the bottom of the GG, so the lens would actually be raised to the GG and

not

centered. Linhoff engineers therefore lowered the lens hole in the lensboard to drop the

lens back to center position. My vignetting is caused by the rise built into lensboards that

are not made by Linhoff and do not have this compensating lower lens hole. Thanks

everyone. This is not descibed anywhere or even in the Linhoff manual.

[kelly_flanigan1]

In optical-mechanical engineering design this problem is studied by doing a moveable layout. One draws the lens fixed on paper or CAD; then rotates and translates the camera box to see what light ray bundles are clipped. This forces one to see what point the box is rotated about; and the tranlation too. In mechanisms one might consider the fixed lens as being a chair for an observer; ie the "little man". In his world the lens is his reference; and the lens body then is seen rotating and translating; and the exiting rays of the lens clipped. Assuming the rotation point without investigating what is going one will give one the wrong model. This exercise works with paper and tracing paper/bumwad or a cad model. Mistakes about the rotation points are sometimes in canned optical modeling programs; getting down to the brass tacks on waht really is happening will clearly show where the clipping of rays occurs.

[kelly_flanigan1]

In several times in optics I have seen mistakes made by assumptions about where an optical device is rotated; and wonky/different results created. These errors can many times "drop out" with small angles of rotation; and give a error that grows with angle; and is huge at larger angles.