SX-70 Sonar Exposure problems

Sceptic · Jan 2, 2017

Hello All!

I have two SX-70's, however both are over-exposing the images.

I removed the front panel on both units and cleaned the exposure cell, still the same issue.

One of the cameras is over-exposing slightly less, but still too much.

I was hoping someone may have better advice. Maybe I just need to remove the front panel and try to re-clean them again.

I filed down a driver so I can open those annoying screws in case I need to explore further.

Open to all suggestions! Thank you!

Theo Sulphate · Jan 2, 2017

Are you able to use the exposure compensation dial? Usually I set it to the first index to darken the exposure, especially with a scene having a bright sky.

The dial provides a considerable amount of control, either with real Polaroid SX-70 film or Impossible film.

Sceptic · Jan 2, 2017

Due to the over-exposure concern I turned and left the dial on the darkest setting.

I have been using Impossible film

Theo Sulphate · Jan 2, 2017

Hmmm...

I suspect the photocell is telling the camera that there's less light available than is actually there, so the camera is compensating by overexposing.

Odd that would be the case with two cameras though.

If there were a way to affix a neutral density filter to the lens (not the photocell) that would work - but you'd have to fabricate that.

hashtagquack · Jan 2, 2017

Not sure if it's the first time using it but before I used mine I had read that one always needed to use the dial to "underexpose" slightly with impossible films. Just saying as I would suspect its not a camera issue. Ive always had to do this with my own sx70

Chan Tran · Jan 2, 2017

The original SX-70 was designed for film speed of 80 I believe. If the impossible film is rated at 600 thus overexposure will happen.

hashtagquack · Jan 2, 2017

Impossible have both the 600 version and the lower ISO version needed for sx70

zanxion72 · Jan 3, 2017

Can you verify that the shutter speed varies with light? Do you have a "test" pack to do this? Try bright light and then almost darkness and see if the shutter sounds accordingly.

Sceptic · Jan 3, 2017

Thank you everyone for the replies.

I am using the lower ISO SX-70 Impossible film with my cameras.
I have been keeping the exposure dial on the underexposure setting.

If I recall correctly, shining a light at the sensor creates an even longer exposure, so it seems to be reading the light, just having a difficult time?

I guess affixing an ND filter to the lens could work. It would just require some testing for accurate exposure time. HOWEVER, even then the exposure times could be longer than I would prefer for handheld shooting.

I have a few empty packs so I will plug them in tonight and verify how the light effects the exposure time

Theo Sulphate · Jan 3, 2017

Sceptic said:
...
If I recall correctly, shining a light at the sensor creates an even longer exposure, so it seems to be reading the light, just having a difficult time?
...

Just the opposite I would think - when you point the sensor at a bright light source, the camera's logic will deduce you're looking at a bright scene and the shutter will open for a shorter amount of time than if the sensor were pointed at a dark area. In fact, pointing the sensor at a dark area should result in long exposures such as 1/4 or 1/2 second (my SX-70 will).

For simplicity in your experiments, keep the exposure compensation dial centered at the white/black halves of the dial (on mine, just unfolding the camera automatically centers it).

Fixcinater · Jan 3, 2017

Can you look into the lens and verify that the shutter/aperture blades are stopping down as they should, and that they are not sluggish to move? I've had to clean them of oil, which rectified the problem.

Sceptic · Jan 4, 2017

Oops. That's what I meant Theo.

I brought out a flashlight on the sensor and there is immediate ejection with the flashlight. Without, it seems it's taking the full 10+ second exposure.

It's hard to see the aperture blades. On one camera it appears half of a black triangle does not move and covers/blocks half the lens. Is this the aperture blade? On the second camera I don't see it appear at all.

Theo Sulphate · Jan 5, 2017

I put an empty pack in my SX-70 (it just had the battery - no film) and experimented with it.

Pointing it at a bright chandelier-type light, the shutter tripped immediately (instant sound of trying to eject film). I couldn't see the shutter or aperture because it was so fast & because of reflections off the lens.

Pointing it at a darker part of the room, the "exposure" was about five seconds before the attempt to eject film. Even then, I couldn't see the shutter or aperture clearly.

However, the camera is behaving properly. It sounds as if yours is also working this way. In daylight, does it seem to eject immediately? If so, perhaps the film you have is the cause of the overexposure?

Sceptic · Jan 6, 2017

I believe this was my second pack of test film. My first assumption was that the pack was bad.

One of the cameras still had a few shots left in it (might still have a shot left). So on one shot I quickly covered the lens, and an image became apparent, although still slightly overexposed and blurry, but I could definitely make out the picture (my dog).

I will have to take out both in the daylight and play around to see what happens in natural light (my room is somewhat dark and I work late).

One of the cameras definitely needs to be opened again as there is a thin black object protruding from the right hand side and covering half of the lens.

I'll get to the actual testing this weekend, and will post an image of the lens on the one camera

Sceptic · Jan 8, 2017

It will probably be easier if I call them Camera 1 and Camera 2

What I've learned:

Camera 1:
I took a picture in daylight, didn't touch the exposure compensation knob. The release/ejection was fairly quick/instant. The picture is overexposed but I can still make out the picture. I will have to pick up a new pack and give another test, maybe I just had two bad batches.

Camera 2:
The aperture blade on the right had somehow disconnected from the one on the right. I was able to reconnect it so they move simultaneously. HOWEVER, the aperture blades seem to have lost their spring all together. *EDIT HERE. I found that a green arm that connects to spring is no longer resetting or controlling the aperture blades, it has somehow lost the grip. Does anyone know how I can remove the focus knob that blocks my way to this area?

Thank you for your help and suggestions everyone!

Fixcinater · Jan 8, 2017

How old is the film you were using? The earlier Impossible releases did not age well at all and get more and more overexposed as they age.

As for the disassembly, I found a walk through on Flickr. I'll try to dig it up.

Sceptic · Jan 9, 2017

Thanks Fix!

For Camera 1, I do not recall the age of film, although it was probably around a year old, and had been stored in my refrigerator.

For Camera 2:
It was fairly easy to remove the focus wheel. From there it became a bit difficult, but I managed to reconnect the aperture blade mechanism. This meant re-attaching the right aperture blade to the mechanism, and the arm of the mechanism to the spring.

My next issue is one I believe I may not be able to overcome entirely, or at least not easily. The spring that keeps the blades in open position appeared stuck. After playing with it a bit and became much looser. and springer again. However, something appears to be preventing the right aperture blade from reaching the fully open position. Even if I find a way to resolve the open position issue I wonder whether the spring/shutter for the blades will behave accurately.

SX-70 Sonar Exposure problems

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