Light leak

I was out today taking the first outdoor images with my Sinar F. I exposed three images, and all three have light leaks along the edge next to the dark slide entrance. I would guess the light seals are gone in the holders, but I find it a little suspicious that it occurred with three separate holders. They are each the same type; fidelity elite. If that the issue, how can I repair them? If its more likely to be something else, what could it be?

Was the light low to the horizon and coming from the same side as the opening? I've had that happen in the circumstance described and changed my work habits by flipping the back to have the opening away from the direct light, then shading the opening with one hand while reinserting the dark slide just far enough to hang. That totally blocks the light and has the side benefit of being a breeze detector so I can watch until the slide is still and then make the exposure without fear of wind motion on the camera or vegetation in the image. Haven't experienced a light leak in years due to this method.

To determine if the seals are bad, put a piece of film in the holders and set them in the sun for a few minutes. Development will tell. Are you inserting the slide straight in? Inserting it at an angle, to get it started, will make it leak. Some cameras are very picky about how you remove and replace the slide. You can raise the holder just enough to let light in without realizing it. My best suggestion is to cover the back of th camera with the dark cloth while manipulting the things. Also, check the bellows where it attaches to the back.

If the seals are bad, can they be repaired? Or do I just toss the holders?

Put the holder in place, remove the lens board, then go into a dark room and shine a bright light into the camera through the front standard. You should see if there is a light leak. If there is, then you know where and can fix it.

Pull the holder out till the film area is fully exposed and the slide is still in the holder. Take a whitout pen and make a line on the dark slide that is out of the holder at the point where the withdrawn slide meets the holder. In the future pull the slide out to that point and then shoot. Do not remove the slide completely from suspect holders.

I went into the darkroom this evening with a flashlight and worked out the issue. The bellows were not connected correctly to the rear standard. I've fixed that and will try with a paper negative tomorrow! Thanks for the advice everyone.