different frames different exposures?

[zenza]

Over the past couple months I've started to notice my Bronica exposing different frames differently. It isn't like it's exposed by a third of a stop or anything, it's either the proper exposure or full on over exposed. It only happens with my fisheye too. Suggestions?

Here is an example. Top frame is properly exposed and bottom frame is the messed up one. These were straight out of the scanner so excuse the colours, dust, etc.

I'm rather frustrated and about ready to toss this and get a hasselblad setup...sheesh.

 

[markbarendt]

It looks like a strobe is in use, true?

Are you in manual?

Had a CLA lately?

 

[keithwms]

That's nice, it's like auto-bracketing

Sorry.

Does it only happen when the frames are shot in rapid succession?

 

[zenza]

It looks like a strobe is in use, true?

Are you in manual?

Had a CLA lately?

yes, I'm using strobes. yes, the camera is manual. what is a CLA?


keithwms - it varies, to be honest. for that certain shot, the first one I shot exposed properly and the other two did not. on another occasion(not pictured above) the first shot was over, the second wasnt, the third and fourth were over and the fifth one wasn't.

 

[keithwms]

cla= clean, lube, adjust...

 

[markbarendt]

A CLA may help if the shutter is sticky.

In looking at the examples again I'm going to rule out the strobes.

 

[Nicholas Lindan]

If it is a focal plane camera then the automatic diaphragm is sticky. The usual cause is thick oil from the focusing helical getting on the blades or in the mechanism. If the shutter is in the lens then the shutter can also be suspect, but shutters tend to be consistently in error rather than erratic.

 

[removed account4]

does your camera have lenses that when they are stopped down
the little metal thingamabob on the bottom of the lens
keeps the lens wide open until the shutter trips ?
sorry for my technical-speak .. but sometimes the little
metal thingy that sticks out, gets stuck and this sort of thing happens.
a repair person if/when they clean the lens can make sure
the whatchamacallit operates smoothly

do you have any pix with your friend doing a handplant?

good luck!

john

 

[zenza]

I'm not sure what metal "thingamabob" you're talking about...the DOF preview button?

I just had this lens cleaned and lubed last year so it may very well be the body since the shutter is in the body.

It definitely isn't the strobes causing the flex in exposure, they're on specific power levels that don't change.

 

[Nick Zentena]

It definitely isn't the strobes causing the flex in exposure, they're on specific power levels that don't change.

Have you metered them? Which strobes are they?

 

[Q.G.]

It definitely isn't the strobes causing the flex in exposure, they're on specific power levels that don't change.

Doesn't mean that they definitely aren't causing this.
Why would a camera or lens be able to have a fault producing the effect, but flash units not?

Are shutterspeed and aperture set manually? (And if so, they too are on specific levels that don't change, right? )
Or is there something automatically adjusting things?

 

[markbarendt]

With regard to the strobes guys, look at the houses in the back ground. The exposure changed there too and that's way outside the range of the strobes.

 

[removed account4]

I'm not sure what metal "thingamabob" you're talking about...the DOF preview button?

I just had this lens cleaned and lubed last year so it may very well be the body since the shutter is in the body.

It definitely isn't the strobes causing the flex in exposure, they're on specific power levels that don't change.

i think it is the DOF preview i am talking about.
it holds the diaphragm open while you focus and releases
it to to the set fstop when the shutter is tripped.
sometimes they get sticky ... and like with sticky aperture blades
exposures vary because the diaphragm stays open.
exactly like what it seems is happening to you ...
if the preview (lever) sticks out of the mount of your lens
stop your lens down and move the lever to see if it sticks.
if you have a repair person that gives free estimates,
it might be worth the trip to take the lens ( and body ) there and have them look at it.

 

[Nicholas Lindan]

look at the houses in the back ground.

Good point - the problem is definitely in the auto-aperture mechanism. If it were the shutter it would only have brightened the background but had no effect on the flash portion of the exposure.

 

[David A. Goldfarb]

I agree that it's the auto-aperture mechanism. This can either be stickiness in the lens (usually oil on the diaphragm blades) or with the lever in the camera body. Try actuating and releasing the DOF preview button, and see how quickly it reacts with this lens and with other lenses, and that should tell you something. Also remove the lens and see what it's doing inside the camera. Which Bronica are you using?

The usual strobe issue would be a recycling speed problem, but I don't think that's likely, given how long it takes to advance the film manually on a medium format camera, and anyway, if it were a problem, you would be getting frames that were too dark rather than too bright, and it's not that for the reason that Mark Barendt points out.

 

[Anscojohn]

I'm not sure what metal "thingamabob" you're talking about...the DOF preview button?

I just had this lens cleaned and lubed last year so it may very well be the body since the shutter is in the body.

It definitely isn't the strobes causing the flex in exposure, they're on specific power levels that don't change.

*****
I do not know this camera; so do not know if it is a leaf or a focal plane shutter. If a leaf; then it could be a slow shutter because of the cold weather. Or it could be the diaphram; perhaps even both.

If a focal plane, then it definitely is the diaphram not stopping down quickly enough due to the cold and oil on the blades.

 

[polka]

I had exactly this kind of situation with a 24x36 SLR, and indeed it was because the diaphragm was not closing to the preset aperture fast enough : to ascertain this, you may fire the camera looking through the film window from the back and see if while the shutter is open the diaphragm is closed to correct preset or if it is still open (or on its way closing) ; do this test at all the fastest shutter speeds, and with any aperture preset.

Paul

Edit : I just read the post about the houses in the background and it indeed exclude the strobes, but there is also another proof pointing to a slow diaphragm : the DOF in the foreground seems shorter in the overexposed picture, signaling a more open aperture ?

 

[markbarendt]

Good point - the problem is definitely in the auto-aperture mechanism. If it were the shutter it would only have brightened the background but had no effect on the flash portion of the exposure.

Oh man I should have caught that, you go Nicholas!

 

[Q.G.]

One very apparent difference (which i only just noticed ) between the two images is that the branches of the tree obscure in one image what appears as a very bright spot (the sun?) in the other.

There will be nothing wrong with your camera at all.
It's just the changing amount of light it is metering.

On the other hand, it probably is just a reflection in the lens...

 

[Sirius Glass]

I think that either Q. G. in on to it or the shutter is sticky. But I am betting on Q. G.

Shoot off a test roll before looking to send it out. If you send it out, include the prints.

Steve

 

[zenza]

I actually had the same lens repaired less than a year ago for the exact same problem. Maybe my lens in is just prone to this? Also, do you think it would help if in between each shot I simply flicked the DOF preview button to make sure it would stick when I'm actually shooting?

 

[Sirius Glass]

I actually had the same lens repaired less than a year ago for the exact same problem. Maybe my lens in is just prone to this? Also, do you think it would help if in between each shot I simply flicked the DOF preview button to make sure it would stick when I'm actually shooting?

Naah, just sell it on eBay as "minty", "rare", and "I do not know much about these things" and you will be fine. Then take the money and buy a replacement from KEH and use the surplus money from the eBay sale and have a few brews.

Steve