PETRI 7 - INTERIOR SHUTTER

The shutter is the part that lets the light beams reach the film, for only a fraction of a second. So normally the shutter is always closed, only when you trigger it (press the button to take a picture) will the shutter open, and then quickly close again.

Just as with the diaphragm iris, we see three small blades inside the shutter mechanism. These are also connected with a solid part and a rotating ring.

So the principle is the same, if we turn the ring, the shutter will open. But in order to have a working shutter, the blades need to block the light again. So the ring has to rotate forward and back, all in a blink of an eye.

the rotating ring on the other side

the rotating ring on the other side

How exactly? Well, earlier we saw that we need to wind the film before we can take a picture. By winding the film, you are also cocking the shutter mechanism. You remember the part that of the film winding mechanism that was connected with the shutter? Here we see it again.

here you can see how the mechanism is blocked, and the spring is pulled

When the trigger is pulled, the mechanism will unblock, and begin rotating. Now you can see the shutter opening and closing. To see things more clearly, I removed one of the blades.

the shutter is cocked -> the shutter is closed

the mechanism is unblocked -> the shutter opens

the mechanism is fully rotated -> the shutter is closed again

Now here's' the tricky part. There are two small L-shaped parts that are each under tension by a small piece of curved ironwire. Between these two parts, is a small cylinder sticking out of the rotating ring where the blades are connected on.

the two L-shaped parts

Then there's the large part that is connected with the winding of the film, and the large spring. This part begins rotating, and hit's the two small parts in a certain order.

The first small part will make sure the blades open by rotating the ring on the other side. The second small part makes sure the rotating ring is turned back, meaning the blades will close again.

here you can see the rotating ring hitting one of the small L-shaped parts

each L-shaped part is able to rotate, each in a opposite direction

PETRI 7 - INTERIOR LENS

After disassembling the lens, it becomes clear how the diaphragm iris exactly works. You can see these three small blades, wich are connected to a solid part and a rotating ring in the middle. 

diaphragm iris blades

The solid part is the black cover seen in the second picture.

The rotating ring is in the middle, where a small piece sticks out. This piece is connected to the ring of the exterior of the lens. So if you want to change your aperture, you simply need to turn the ring on the exterior of you lens.

ring for adjusting the aperture (exterior of the lens)

To prevent the blades from moving after you have set the right aperture, there's a small piece of curved iron wire that works as a spring.

PETRI 7 - EXTERIOR SHUTTER

An earlier post showed that you had to wind the film before taking a picture. By turning the scroll wheel, you are not only setting the film in motion, but are also triggering the shutter. 

scroll wheel

the scroll wheel triggers the shutter

The shutter is now triggered and there's an empty frame behind the lens opening. The next step is setting everything in motion. The way to do this is, is by pressing the main button.

button for 'taking' a picture

the button above moves the part below 

the part pushes a small lever

this lever will open and close the shutter, in only a fraction of a second 

PETRI 7 - EXTERIOR LENS

how to adjust the aperture (diaphragm)

diaphragm iris on the inside

diaphragm iris on the outside

PETRI 7 - WINDING MECHANISM

After taking a picture you need to wind the film before you can take a new picutre. So you need to place an empty frame behind the lens opening.

You can do this by turning the scroll wheel on the bottom side of the body. An arrow shows the way you have to turn.

the scroll wheel

the mechanism inside

The scroll wheel is connected with some gear wheels, springs and many other small components. This mechanism will make sure that;

• the scroll wheel returns to its original position after turning it
• the scroll wheel is blocked during the time that an empty frame is behind the lens opening
• to unblock the lever after pressing the trigger

turning the scroll wheel

the gear wheel will also turn

a spring return the scroll wheel to its original position

this part blocks the gear wheel

the scroll wheel is connected with this gear wheel on the axis of the film

The mechanism is also connected with the axis of the film. The indicator is connected with the same axis. So the amount of turns on the scroll wheel is the same as the amount of frames you have used.

axis of the film is connected with the indicator

The scroll wheel is blocked during the time that the camera is triggered. After pressing the button on the top of the camera, the shutter will open and light will reach the film. By pressing this button, a serie of mechanical events occur to unblock the scroll wheel.

the lens and scroll wheel mechanism connection

close up

The camera is now ready for the next shot.

PETRI 7 - INDICATOR

A film has a certain amount of frames. Each frame can be filled with one image. Basicly, one frame is equal to one push on the trigger. 

To figure out how many frames you have left, there is an indicator on the body. By removing the top of the body you can see the indicator circle. This part is connected with a small gear wheel, some springs and other mechanical components.

PETRI 7 - FILM REWINDING

When there are no empty frames left on the film, you need to remove the film so you can develop the pictures. But first, you need to rewind the film into his casing. The casing serves as a black box.

Because when opening the body, the film can be exposed to light. This will ruin your pictures. Therefore, it's essential you roll the film into his casing. This is possibly by turning a small lever.