Does FP4+ base density depend on format?

I have been noticing a "strange" thing one year ago, when I switched to 120. My negatives have become so clear, with an almost transparent base! Instead, in 35mm, I always got a grey base and a rather low contrast image, under the same development condition. I was happy with that so I didn't really care and moved on, but I still have to answer that question; so I started testing again.

At first I thought I might have some light leak into the 135 cartridge, but I have tried loading and unloading film in complete darkness and I still experience this, so I ruled out this cause.

Ilford documents that FP4+ in 135 has a slightly thicker base than the 120: maybe this is the cause for increased base density?

If nobody else has experienced this difference, I must conclude that it depends on a metering system defect or inaccuracy: I manually meter and set my 120 camera accordingly, while I let the auto exposure on the 135 camera do the job on spot mode. (but that is not going to explain the base density, also present in the unexposed frames, is it?).

The film is not expired and has not been through x-rays or the like.

Last thing it comes to my mind is that it might be an issue with agitation, due to the presence of sprocket holes which are absent in 120.

Any input is appreciated.

Have a nice day!

[edit: maybe a lens issue? In the 135 camera I have cheap lens, could be that it somehow `diffuses` the light on the film.. who knows!]

Sure sounds like fog. Does your camera leak? What about your 35mm tank?

I thought the 35mm film had a tint to the base instead of an anti-halation dye.


Steve.

MikeSeb: Uhm, I use the same tank for all my films.

Steve Smith: so I think that is the answer. The gray halo is so uniform, this is certainly the solution. But sadly that makes me hate this film in 35mm and like it in 120! I guess I will have to live with it.

Do you happen to know if all other B&W films act the same?

Thanks.

FP4+ is a great film in all formats. A tint to the base material will not lower contrast, it will just require a little bit more exposure at the printing stage.

And I think most 35mm monochrome films are treated this way.


Steve.

Steve Smith: then I must conclude that it is the camera integrated lightmeter's fault, which is underexposing my FP4, hence the low contrast.

Thank you all for your answers.