HomeRepairsOld & NewTechnical stuffRessourcesCamera collector blog


Hasselblad backs - light leaks
Changing 1960-'80 35mm camera light seals

Hasselblad 500 C/M
One of the most common problems encoutered with the Hasselblad V series cameras concerns light leaks in the removable film backs:
In order to avoid stray light entering the back while it is removed from the camera body, a metal slide is inserted in a slit seated behind the front plate of the back. During taking pictures, this slide is removed and the slit is closed by a light trap which blocks any undesired light from entering the film back.
This trap consists in a v-shaped mylar foil seated in a recess near the opening for the slide and which is pressed firmly against the front plate of the back by means of a self-adhesive foam strip which itself is affixed on a thin metal plate acting like a spring. The front is equipped with a narrow strip of velvet fabric at the contact point with the mylar light seal.

But as time goes by, the foam becomes less reactive and the velvet on the front plate wears, which causes light leaks on the film as can be seen in the following sample picture:
fuite lumière
Fortunately, this is a rather minor issue that can be resolved by most users by means of a replacement kit for the worn out parts. One only needs a flathead screwdriver of adaquate dimensions and an orderly working method while changing the light seal to avoid any damage to this precision made machinery.
The kits are available directly from Hasselblad but often one has to cope with a minimum order value of about 50,00€ which means acquiring about 4-5 kits (way too much for the common non porfessional user) and furthermore retailers can be hard to find in some countries.

EBay and a few other websites regularly offer a variety of kits, some of which are good quality, others rather dissappointing.
Most of those kits lack the narrow velvet strip for the front plate and even if this part of the light trap is less prone to wear, it has to be replaced also once in a while. The foam included with some kits is very thick and apply too much pressure on the mylar strip which can lead to cracks in the latter when inserting the metal slide. And finally, I have yet to find a kit other than the official ones that include the metal spring strip located fits under the foam: This part has a very particular shape and is certainly difficult to make without specific machinery.

With the following method, you should be able to repair your back without much trouble.
First step: get all the neccessary materials and tools ready; the film back, the kit the screwdriver and a small container for the screws you have to remove which is better than crawling on all four searching for them if they fall of your working surface! A small pait of tweezers come in handy to manipulate the small screws.
Remove the 9 small screws maintaining the front plate (the one with the serial number).
You reaaly must use a very good screwdriver with a blade that matches the screw head perfectly and  maintain a firm even pressure while loosening the screws as otherwise you might skid and damage the screw head or the front plate.
Here the front plate and used seal parts have been removed.
Make shure that the 3 moving parts shown with the red arrows remain seated in their respective recesses: at te bottom you see the lever that prevents accidental use of the shuttter while the metal slide is inserted and the spring that keeps it in unlocked position. At the top you will find the sliding bar that attzches the film back on the camera body. If thos parts would disengage during operations this would be of no major concern as they can be put back in the right place whithout any risk of errors thanks to the pins and notched provided to keep them where they belong. Keep the film back in the shown position and this issue will be unlikely to occur.
One can see that the old foam is worn and compressed, becoming unfit for correct operation.
Note that in this case the velvet fabric strip sittind the front plate opposite the light trap of the back itself is also in bad shape: it has to be replaced too.
We'll start removing the old fabric strip with a small screwdriver or (better) a small wood or bamboo stick. Remove as much of the old adhesive as possible and if it does not come off readily, a few drops of methanol will make is easier for you. Don't put too much pressure on your tool in order to avoid wharping the front plate.
Some more methanol on a cotton swab will get rid of the remaining adhesive.
The new velvet strip is put in the recess. Make shure that the edge is perfectly seated against that of the deepest part of the recess (away from the rectangular film frame). If the work is done properly, the top of the velvet strip will sit on the same height as the metal edge on this side of the recess: this is important because the metal slide could get caught in the fabric when inserting it if the fabric is seated too high.
At film frame side os the strip, the fabric will overlap the shallower part of the recess and protrude a fraction of a millimeter above the surrounding metal. This will ensure adequate pressure on the metal slide and the light seal beneath it.
As we present the light trap in it's recess we can see that the supplied foam is really thick: 6 mm is a lot even if it is low density material. As explained at the beginning of this report, this can cause problems at the square cut upper half of the mylar foil when we need to fold it back over the foam. It will also be diffiult to keep the foam in perfect position while folding the foil and this could ruin all the work.
I have decided not to use this part of the kit but to replace it with a self-adhesive, 2 mm thick foam. This means that I need to recover the original metal spring strip.
Let's get rid of the old foam: more methanol, cotton pads and a thin screwdriver tip will do the trick! As always, work carefully and try to distort the thin metal strip as little as possible as it is difficult to find a replacement due to it's particular shape.
A last sweep with methanol on a cotton swab and the strip is ready for a new foam layer.
The strip is pressed evenly on the adhesive foam and cut to the right dimensions.

We present the spring-foam sandwich on the mylar light trap once again. One can see that it fits much better than the one supplied with the kit.
Now we need to fold the square-cut part of the mylar strip over the foam, making shure that the slanted half of the strip and the foam remains perfectly seated in the recess. Sorry: no picture of this operation: I only have two hands...
After folding the mylar foil back over the foam I put the metal slide on top of it while I put the front cover back in place. That way everything will nicely stay where it belongs.
The front plate is positioned on top of the metal slide.
All tha tremains to is fixing the 9 screws. Make shure they are tightened well but without too much pressure.
After an ultimate check to make shure that everyting works smoothly and that there is firm but not excessive pressure on the slide while in is inserted, the film back is ready once more for long and loyal service!

Just one more tip: Remove the slide from the film back when you don't use it: thus you will put less pressure on the light seal and it will last longer.
Here is a sample picture taken in full sun with the same film back as the one shown at the top of this page: fit for service!