Strange marks on film

[richyd]

Yes, it's one of those threads. I came back from a trip to Southwest USA in June with around 10 rolls of E6 shot on a Fuji GA645Zi. On about 6 rolls a couple of frames show darkened areas all with the same pattern in the same area, most noticeable where that coincides with sky. It shows on anything from one to 4 or 5 sequential frames sometimes near the start of the roll some at the end. Most of the film is 100G, two rolls of Fuji 100f and shows on rolls I processed and a lab processed so it is not film or processing.

My thoughts lead to moisture, possibly humidity but it is exactly the same pattern and position in the affected rolls and cannot think of anything that the camera might be responsible for. Any ideas?
Thanks
Samples (Ignore the moire type pattern I think that from cropping and compressing the samples, it is the long sausage shape and large dots)

 

[AgX]

If I understand you correctly, these marks never show up in mid-film?

 

[Michael W]

My guess is specks of dirt or dust on the back of the lens, which is uncovered when you have the camera back open to load or unload film. Similar look to digital cameras when they get dust on the sensor. If that is what is causing it, the lens needs to be cleaned & you should take care when loading or unloading in future.

 

[AgX]

Specks on the rear lens element would not give an image (specks) on the film.

 

[RauschenOderKorn]

Can you show us a full frame with the marks? On which frames of the film do the marks occur?

It is difficult to determine whether this is influenced by handling of the film, the camera, handling of the positives or post-processing (like your scanner).

 

[hashtagquack]

Could be a scanner issue as in it may need to be cleaned

 

[Michael W]

Specks on the rear lens element would not give an image (specks) on the film.

Why not?
I owned this exact model camera, and had this exact problem from that cause.

 

[AgX]

Similar as on the front lens element where rays from one object-point will enter at the whole suface area, they will leave the rear lens element on various points, thus only will be partially covered by a speck. In addition are specks on the rear lens element out of focus.
But I shall try to replicate what you experienced.

 

[richyd]

Thanks for the replies. To clarify further:

The marks are visible on the transparencies.
They are usually mid roll and affect a few frames with diminishing effect. So if 4 are affecting the last number is lighter than the first. On one roll the last frame does show it faintly.
If it was dust on the lens I would expect all frames to show it.
Maybe it was condensation on the lens but always the same pattern? Although perhaps moisture might form in the same areas due dust particles or dirt? I was going back and forth from hot outside environment to a cooler, or cooling car interior.

 

[Gerald C Koch]

My guess is specks of dirt or dust on the back of the lens, which is uncovered when you have the camera back open to load or unload film. Similar look to digital cameras when they get dust on the sensor. If that is what is causing it, the lens needs to be cleaned & you should take care when loading or unloading in future.

This idea pops up from time to time. It certainly is an appealing one. Why there are dust specks on the lens which must account for spots on the negative. The problem is that anything on the surface of a lens cannot be imaged by the lens. Sorry but one of the rules of optics forbids it. Even bubbles in the lens itself will not be imaged. A large amount of crud would be experienced as lower contrast or as flare. But individual particles will not be seen on the negative. Even a cracked lens will still work well. A bit of black paint over the crack to eliminate flare and all is well. BTW with digital cameras dust on the sensor is a very different problem from dust on the lens. You cannot equate the two.

 

[Kirks518]

The problem is that anything on the surface of a lens cannot be imaged by the lens. Sorry but one of the rules of optics forbids it.

Gerald, I subscribed to this belief as well until I saw an image on another forum (POTN), where a fingerprint on a fisheye lens was clearly visible in the final image. I do agree with you that 'normally', anomalies on the surfaces of a lens is not captured on the image, but there are occasions where it can. It's just one of those 'Never say never' things.

With that said, I also don't think this is a case of something on an element (front or rear), and IMO looks more like a processing concern.

PS - Here's the link for the above referenced image

 

[Gerald C Koch]

Sorry I can't see the finger print in the scan. But the laws of optics are strict. All portions of a lens image all portions of the negative. You cannot identify a point A on a lens and say that only it is responsible for point A' in the image. If it were true then photographers would spend all their time retouching prints to remove artifacts caused by dust spots on the lens.

 

[MattKing]

A retro focus fisheye lens is a special case, because the depth of field is such that the surface of the lens is within the zone of acceptable focus.

I would check for some loose flocking or debris in the camera.

Is there any correlation between the affected frames and the zoom setting used?