Bronica SQ-a problems at high shutter speed

[vmodam]

Hi guys, after some prints from my last roll I realized that all negatives has a underexposed slice at the top. This happened by using a delta 3200 at midday (first time I was using the 1/500th speed). I guess this has to do with the mirror, so the shutter opens before mirror is completely flap. Does anyone experience something similar?

But, shutter is open mechanically and the exposure is then determined electronically... so I dont see how the speed would matter in this mirror hypothesis.... unless it is always happening!! And, only with the highest speeds, the relative underexposure is noticeable?

Cheers,

Victor

 

[DWThomas]

SQ-A owner here -- this gear is easily 25 or more years old, it might be time for a cleaning, etc The mirror mechanism may be hanging up a bit. But the image on the film is upside down, I would think it more likely a sluggish mirror would underexpose the bottom (as seen in normal viewing). I am assuming you mean there is a lighter, clearer section across the negative. As I think about it light leaks in the back sometimes appear as a fairly sharp edged "slice," but they would be darker on the negative (and generally extend outside the borders of the frame), showing lighter on the positive print.

I raise the light leak question because I would say that is the most common problem with the SQ series backs. It also tends to be variable from frame to frame depending on ambient light intensity and angle, etc.

Perhaps a photo or scan of an example negative that shows the full width of the film un-inverted might help a discussion here.

 

[wiltw]

Hi guys, after some prints from my last roll I realized that all negatives has a underexposed slice at the top. This happened by using a delta 3200 at midday (first time I was using the 1/500th speed). I guess this has to do with the mirror, so the shutter opens before mirror is completely flap. Does anyone experience something similar?

But, shutter is open mechanically and the exposure is then determined electronically... so I dont see how the speed would matter in this mirror hypothesis.... unless it is always happening!! And, only with the highest speeds, the relative underexposure is noticeable?

Cheers,

Victor

Two points to puzzle about...

1. The shutter is a LEAF SHUTTER in the lens, and not a travelling curtain focal plane shutter!
2. And, (at least true of my ETRSi) the shutter cannot normally be opened before the mirror has fully travelled upward.

...so how might the reflex mirror get in the way of light striking the film plane, if it is all the way up?!

I know point 2 is true of the ETRSi...I had a new body and a used back which would intermittently NOT FIRE the shutter, and it was not lens dependent. Sent camera and back to Bronica distributor for repair, and they fixed the back to shorten the film-advanced interlock pin which was sometimes preventing the mirror from going all the way up so the shutter could then open.

 

[DWThomas]

Two points to puzzle about...

1. The shutter is a LEAF SHUTTER in the lens, and not a travelling curtain focal plane shutter!
2. And, (at least true of my ETRSi) the shutter cannot normally be opened before the mirror has fully travelled upward.

...so how might the reflex mirror get in the way of light striking the film plane, if it is all the way up?!

I know point 2 is true of the ETRSi...I had a new body and a used back which would intermittently NOT FIRE the shutter, and it was not lens dependent. Sent camera and back to Bronica distributor for repair, and they fixed the back to shorten the film-advanced interlock pin which was sometimes preventing the mirror from going all the way up so the shutter could then open.

Agreed! I would feel a lot better speculating on this if I could see an unadulterated picture of a negative, including the surrounding border areas. The (leaf) shutter is a wild hybrid of mechanical power and actuation timed by electronics, and there seems to be darn little solid information out on the web about all the mysterious interlocks and such in the Bronica ET/SQ series. I also admit that about 99% of my SQ-A shooting is of inanimate objects, working from a tripod. Doing that I normally flip the mirror lock-up, then release the shutter; if there was a weird problem related to that shutter/mirror interaction, I might not even know it! I believe in addition to the mirror, there is a separate internal flap to cover the film gate behind the mirror. The two are linked but somewhat independent. If either were not fully open, I would expect the blocked area to be at the bottom of the picture due to the inverted image on the film plane. Hopefully we'll soon learn more to flesh out a rather skeletal Bronica knowledge base!

 

[wiltw]

I believe in addition to the mirror, there is a separate internal flap to cover the film gate behind the mirror. The two are linked but somewhat independent. If either were not fully open, I would expect the blocked area to be at the bottom of the picture due to the inverted image on the film plane. Hopefully we'll soon learn more to flesh out a rather skeletal Bronica knowledge base!

 

[vmodam]

I dont have the negatives with me, but I can show you one of the print. Even though the strip is clearly seen in all the negatives as well.
Thomas, the slice on print is darker, the slice in negative brighter, so Im more for the mirror argument more than light leakage.
I will send a negative pic as soon as i can.

 

[Vw1302]

The problem is with the lens, not the body.. I have got the same issue with my PS80mm, all times are OK, only 1/500 doesnt work properly.. I have more lenses, which are OK, so I am pretty sure about that... you can try it manually with the mechanism on the lens.. than you will see that the problem is not in your body... I am going to send it for cleaning..

 

[vmodam]

Indeed, I have the 50mm and the 80mm...and think that happens with both. It could be the way the little small rod in the body, that triggers the lens (the one marked in green) and opens a bit earlier?

 

[vmodam]

Vw1302, I dont see your point sorry...you say it only failed to you at one 500th, and that it is on the lens and not in the body, and that you can checkit manually on the lens. How do you check the lens shutter at 500th without the lens? So you mean that you take the lens in your hands, and click the small side button and move the mechanism by yourself? In that case, I dont see how te sutter speed will affect. My problem is a "very low dense strip on the bottom part of the negative, corresponding to the upside part of the picture". Most probably it is the mirror (mirror mechanism, either the mirror either the back cover). When it flaps, it is shadowing the upper part of the lens, close to the lens flange, so do affecting the lower part of the negative.
I tried with my two lenses (50mm and 80mm), doing a digital video of 1/15 secod exposures. The video rate is very low, just 60 fps, and each frame is 1/4000 speed, at 6400 iso. In this situation, one would expect 4 video-frames fully open in average. If the mechanism were perfect though, the shutter would be fully open by the time the mirror is completely up. So, I presume two hypothesis: 1) The star-like shape of the shutter leafs shouldnt be seen in any video frame. 2) The white circle (shutter fully open) shouldnt be never cut by the mirror.
Here I put strips frame-by-frame for both lenses (first 50mm second 80mm):
Already in the first example on the 50mm, you see the mirror blocking. In the 4th and 5th example you see the leafs.
In the 80mm series... well... sorry I thick I took the same video...
More thoughts later.

 

[Dan Fromm]

Leaf shutters don't open or close instantaneously. And they're not fully open for 1/shutter speed either.

 

[choiliefan]

Probably a good idea to have the body serviced by a qualified tech. Clean parts and fresh lubricants will no doubt work wonders.

 

[DWThomas]

Thinking out loud here ... I'm still having a problem with synchronizing the cause and effects here (I could plead old age, but ...).
The underexposed strip appears to be at the top of the picture.
In camera, the image will be upside down.
The mirror not fully lifted would block light to the upper part of the film -- the bottom of the image.
(The above all assumes the camera was held focus screen/viewfinder up.)

Were you using mirror lock-up?
If not, it could be instructive to try some shots at different shutter speeds using MLU. That would/should mean the mirror is out of the way long before the shutter opens and tend to eliminate the effects of sluggish motion or messed up synchronization.

Do you have another back?
One of the positives about these rather complex "system" cameras is that having a bunch of the various components to swap in and out can sometimes assist in isolating a defective component.

I am still seriously mystified by the combination of symptoms.
The normal sequence should be:
1: Shutter release pushed
2: Mirror and light baffle flip up
3: Lens aperture closes down to set value
(not totally certain; 2 & 3 might be reversed or even simultaneous)
4. Shutter opens mechanically
5. Electronic timer times out
6. Shutter closes
Everything lays there until you wind the crank for the next exposure

Now admittedly one thing is different about 1/500. That is the fastest the shutter can go, and in fact, is not timed electronically (that's why the camera shoots at 1/500 without a battery). Apparently for slower shutter speeds a little electro-magnetic dojigger intercepts the shutter mechanics and holds it open until the timer times out.

As brought up earlier, it is a leaf shutter; essentially a round opening, with a star-shaped effect as the leaves are in mid-travel. Nothing in the shutter operation should produce an even, straight line.

Since the strip is apparently under exposure, something long and straight is "doing something" but yet not totally blocking, as might happen with a stray piece of film sticky label or the like.

Assuming the camera was held viewfinder up, the stripe is across the narrow width of the film. If it were parallel to the long edge, one might suspect an under filled developing tank and insufficient agitation.

(OK, I'll have another coffee and move on to installing TurboTax .... )

 

[vmodam]

Hi all...thats right, the mirror movement should leave a underexposed negative just in the down side (floor).....

 

[wiltw]

The underexposed strip appears to be at the top of the picture.
In camera, the image will be upside down.
The mirror not fully lifted would block light to the upper part of the film -- the bottom of the image.
(The above all assumes the camera was held focus screen/viewfinder up.)

In agreement with the analysis...the top of the image is at the bottom of the camera focal plane area, yet a malfunctioning mirror flipping out of the way and bouncing back (to affect the shot) is at the top of the camera where the bottom of the image would be!

1. It should be possible to remove the lens and get the mirror to flip up with the mirror lockup control of the SQA, so you can peer thru the camera body and see the film back opening obscured by its metal darkslide plate, with nothing interfering between the opening (the removed lens...your eye) and the film back.

2. Also, with the SQA film back removed from the body, you should be able to remove the darkslide and see the pressure plate fully, with nothing obscuring the lower part of the opening (where the top of the image would be cast).