Square Filters Marking Film

R

rfinlay

Messages
4
Edit My Images
No
I've recently bought a Lee Filter system with a 0.6ND & 0.6ND Grad filter. I can use them successfully with my SLR however when I use them with my 6x17 panoramic camera I'm getting 2 horizontal lines going across the top of each exposure when I use the filters! To me it looks like light is somehow getting in around them and causing this but do not understand why it affects the 120 film when it doesn't affect the 135.

I'm using a Grandagon Rodenstock 90mm F6.8 lens on the Large format camera.

Has anyone else ever experienced something similar with their film or digital systems? If so, what is the cause & cure.

Thanks,

Rod.
 
small apertures?
with small filters
 
You don't say what orientation the back positions the film, so I can't figure out where the lines are running, horizontal in portrait or landscape ?

It doesn't matter really, I think its got to be something to do with image circle, 135 will be easily covered because its a smaller format, but the 120 at 17 full width on that 6x17 could mean the lens has the filter frame in its image circle....but only at the sides or top depending on orientation..^^^:)
 
Welcome to TP :)

I'm not quite understanding the problem but Joxby is thinking along the same lines as me. Angle of view, vingetting, that sort of thing?
 
If the lines are at the top of the frame in portrait format, try sliding the filter DOWN, and see if the lines disappear or move to the bottom of the image.
If this happens, it is due to the filter not being long enough to cover the image area.
 
Sorry for the lack of feedback on my part - I was away all day yesterday.

Thanks for your feedback though. I was thinking the problem had something to do with the size of the filter / edge of the filter.

To answer your question joxby - the camera is in Landscape so the horizon is in line with the 17cm plane.

The lines are appearing towards the top of the images in this format, the filter fully covers the front of the lens in its holder.

I don't think I can pull the filter up as then the bottom won't be covered which would lead to the bottom of the image being 2 stops overexposed with a hard line where the filter starts.
 
Doesn't sound like image circle then.,
Aren't you able to see the image circle on the ground glass of this LF camera ?

Whatever, a picture is worth a thousand words, doesn't matter if you can't scan the full 6x17, a portion with the lines on would be helpful....or a slide copy or something.
 
I've been reviewing the images and thinking about what was happening when I was taking them. I've come to the conclusion that the problem is not the filters at all. The problem is that of late I've been trying to take images at more interesting angles with the Large camera - more interesting as in not perfectly level. In fact the camera has been angled up or down quite sharply. I've been using a high aperature for most shots (F32) and the effect is more pronounced in these pictures probably due to longer periods of exposure.

Anyway, I have come to the conclusion that the problem is to do with the angle that the light is hitting the film at the back of the camera at these non-level angles. I think that the lip at the back of the camera body's bottom edge is getting hit by light and somehow reflecting (or otherwise causing this effect as it's painted black) onto the film causing these ghost lines! It's the only constant as I discovered from my notes that in some affected images where this happened only my screw-on CPol was attached to the lens (and I remember that the camera was angled up / down). Also, the lines also resemble the shape of the edge at the back of the camera body. I also now have evidence to prove that the LEE filters are not causing this problem as I've two slides that I know were taken completely level using the filter system and no lines appear!

The camera has a 20mm Shift ability. I don't fully understand it as it appears to only move the image up / down on the ground glass. I realise it's for correcting parallels. I was wondering if this ability might be used to rectify my problem if I want to continue experimenting with angles other than dead flat...

BTW, the image circle of the lens is 22cm so the edges aren't being thrown onto the ground glass or the resultant images. I can't currently scan the images, I'm saving up to buy a decent scanner now...

If you have any ideas on what I can do to mitigate this effect on the images then I'd really appreciate it.

Thanks.
 
If I'm understanding you right, that sounds quite likely.

With a big image circle like that you've obviously got loads of light flying around all over the film chamber rather than the tighly contained cone in a normal camera.

All interior surfaces must be absolutely matt black, coated in flocking or something. Maybe you could apply some of that, black velvet or felt - that kind of thing. Or just crop it out, or avoid bright areas near the edge, that kind of thing?
 
Ok, thanks for the feedback. Seems like I need to keep the camera on the level and maybe try to use shift to move it up / down a bit. At least I can keep it in mind for the future and maybe gauge for it when taking pictures at an angle and like you say, simply crop the images.

Thanks!

Rod.
 
You must log in or register to reply here.
Back
Top