Developed film has dark/bright wavy line spanning across entire film

Question

Developed two rolls of C-41 for the first time at home. One roll was shot with a LOMO Smena Symbol (have shot with before and developed at shop) and the other with a Zenit ET (first time using). The Symbol roll came out just fine but the Zenit roll has a weird wavy sort of pattern that repeats spanning the entire film.

The scan of the film shows one dark wave that repeats. What could be the cause for this? Some ideas I have:

• The camera has a light leak. (but the constant repeating wave doesn't make sense then)
• During development (when the film was rolled up) a light leak happened in the dark room. This would explain why the pattern repeats (only a sector of the film got exposed).
• Bad film. (unlikely)
• Camera has a bad mirror. This would explain why half of the film is cut off anyway (as can be seen in the scan) but doesn't explain the wavy pattern.

Films were developed separately. Normal printer scanner was used to show the effect hence weird colours.

Answer 1

My presumption is that you developed this film yourself.

The dark (on the negatives) area and slightly wavy edge are due to the film being incompletely submerged in the chemicals. Either you didn't have enough solution to cover the film (250-290 ml, depending on the tank type, for 35mm) or you developed a single roll in a larger tank and the reel wasn't fully seated to the bottom of the tank.

In Paterson type tanks, one thing to watch out for is that a single reel can slide up the column, so that even if you've poured more than the (for this tank type) 290 ml solution required to cover a single 35mm reel, the reel may not be covered. The recommendation is that if you're processing a single roll in the "2-reel" tank (will hold 2x35mm or 1x120), put an empty reel on top of it.

The other thing that can happen is that even if you did this, if the empty reel was on the bottom by mistake, your 500 ml (per comments) of developer would only about half cover the film in the upper reel.

The third thing is that you might have loaded two rolls, but didn't actually measure enough developer to cover two -- my 2-reel Paterson won't hold a full liter, that takes a 3-reel tank (which is prone to the same problems I mention above), so if you had two rolls in a 2-reel tank, you surely did not pour twice 500 ml.

However it happened, that roll of film was only about half covered. The dark swatches in the half of the strip without half-images on it is unfixed emulsion (that section should almost completely clear if you return the film to bleach and fixer or blix steps).