Uneven light fall-out on transparencies

[qtluong]

On two of my recent trips, I've noticed that some 5x7 transparencies

have a kind on light fall-out on the edge. The area which is

affected is always the right edge, and the light fall-out takes the

form of a darker band which is approximatively vertical and

about 0.5 inch (1.5cm) thick, between 1 and 2 stops. The left

edge is OK, and no swing was used.

The problem occurs only when using a Schneider 110XL with exposures of a fraction of a second in strong daylight (longer exposures seem OK).

No lens shade was used, and

I have checked for vignetting through the corners of the ground

glass. Film was processed professionally. Because I have not

observed the problem with longer exposures and other lenses, I

suspect the shutter (prontor professional) but I don't know how to test this idea as it appears OK.

Thanks for any suggestions.

[sorin]

I suspect you stepped down when you took those shots. That means the

shutter must malfunction significatly to create that kind of effect.

You should be able to see it with the naked eye.

[cesar_barreto]

Mr. Luong,

Maybe, you could trigger this lens on a flash and photograph the

shutter right open, checking if there's something on the way.

Good luck!

[dmin-99]

I cannot imagine a defect that might occur with a leaf shutter that

would manifest itself in a linear band. Since the image is reversed

on the film it would help to know which "right edge" you are speaking

about.

[dan_smith]

Before checking the shutter, check the bellows when using this lens.

You might have a bellows pleat blocking part of the tranparency when

shooting. I don't know how a malfunctioning shutter would make a line

of underexposure, though that doesn't mean it isn't possible. You

might also have one of the pleats or the back, just in front of the

film holder, reflecting back some light from the edge.

 

<p>

 

Set up the lens in the same configuration as you had when the problem

occured & look through with a strong flashlight & see if there is any

kind of interference in the light path.

[wilhelm]

Damn, Q. I have the same trouble with 35mm trannies, and thought it

was from an uneven focal plane shutter. Could it be from Polarized

light?

[matt_oulman]

Q.-Tuan,

 

<p>

 

Where do you get your 5x7 films. I am having a hard time finding any

lately.

[n_dhananjay3]

Don't know if this is the same thing but I experienced something

similar to what you mention. I was shooting B&W and would get

negatives with lower density along one of the 4" edges of the film.

This seems to correspond to what you are describing i.e., darker edge

with transparency film. My first notion was light leak but then I

realized fogging would increase density, not reduce it. It took a

long time to figure it out. It was a light leak which was coming out

the side of the bellows close to the film plane. The frame blocked

this fogging light from hitting the 4" edge closest to the hole but

the light sort of sprayed across the rest of te neg, increasing

density theree. Of course, when I viewed the neg, it looked the

correctly exposed part (i.e., the bit that was not hit by the light

leak) was underexposed compared to the rest of the film that was.

Proof that perceptual illusions and bugaboos afflict us way after the

picture is taken...

 

<p>

 

You mention that you only get this with one lens, which seems to rule

against a bellows leak (althought it might be worth checking for that

too - pinholes reveal themselves and hide themselves in the field

depending on the focal length used since you rack the bellows out or

fold them in etc). Since this is a shorth focal length, is it

possible that there is a light leak in the bellows near the lensboard

which doesn't affect the film much when the bellows is racked out

with a longer focal length but is visible to the film with shorter

lenses?

 

<p>

 

Good luck. Hope you isolate the gremlin and toss it into outer

darkness where it belongs... Cheers, DJ.

[n_dhananjay3]

Sorry, forgot to add - the strong daylight also makes me suspect

pinhole i.e., it may be the beginning of a pinhole and it take strong

light to get through in sufficient amounts to affect the film.

Although I'm lost as to why longer exposures are unaffected. Cheers,

DJ.

[glenn_kroeger]

Since nothing in the plane of the shutter/iris can be imaged in the

film, I cannot see how that could be the source.

 

<p>

 

With the problem restricted to one lens, it would seem like the

problem involves either the lensboard, or the relative postion of the

front and rear standards causing a light leak.

[john5]

Check your lens board to see if it sits properly. I had the same

problem with a warped board. Maybe try switching lens boards.

[qtluong]

Wayne, that's the right edge on the transparency, so this would

be the left edge in the camera. Matt, for several years I've

been cutting down 8x10 film. I'll soon have an article on the

5x7 format.

[dmin-99]

The reason I asked about the orientation of the film is because I too

suspected a light leak that was fogging the majority of the film

except for the underexposed band. But I suspect that you would have

noticed exposure anomalies on the order of 1+ f/stops. I would have

suspected a poorly-fitting lensboard, since I've come across a few

Linhof-type lensboards that don't seat properly (are you using the

adapter on your Canham?). Maybe the processing? Have you changed

processors? If you can rotate your back maybe you want to load from

the left for a few frames to eliminate somr of the possibilities.

[andrea_milano]

Hi Q-Tuan!

I've very much the same problem with a device which I myself put

together for pinhole photography.

I mountes a metal plate in which there was a pinhole on a self made

lens board and all my negatiwes had Two! bads on two sides (one on each

side) couldn't find any explaination and only now I understand from all

these comments that my self styled lens board must have been allowing

for leakage, I guess that yours does the same and I will mount the lens

on another board believing that the problem is solved!

Take care and thanks for your work on this site.

[qtluong]

Thanks for all the suggestions.

I have some new data. I got back a new batch of film from the

last trip.

<p>

First, this was processed by another lab, so this would

eliminate the possibility of a post-exposure problem.

<p>

Second,

there was one scene where I used 90,110,150, and 300 lenses to

get various croppings of the same basic shot. The 90 and 110

images both suffer from the problem. On the 150 image, it's present,

but extremely subtle, and totally absent on the 300 image. This

eliminates the possibility that the problem would be linked to the

110.

<p>

To be more precise about the dark band, it is more like a horizontal

gradient, the darker side being along the right edge. The rest of

the image appears correctly exposed, and there is noticeable

underexposure in the band.

<p>

Dan's explanation was what I first had in mind, but after

setting up the camera, I could not find obstructions in the light

path, and besides, everything looked symetrical.

[david_goldfarb]

When I've had a bellows obstruction with a wide lens, the result has

been a solid band, not a partial obstruction, but who knows? I

couldn't really see the obstruction when composing the image either on

the groundglass (because of the falloff of the wide lens) or

externally. To fix it, I added some loops and cords described in <a

href="http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=003c

Ag">this thread</a>, for gathering the bellows toward the front

standard, and I haven't had a problem since. It also makes the camera

a bit more stable in the wind.