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70200G Over exposure


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Hi all,

I´m new to this forum. (I just found it)

 

Having a bit of a problem with my A77M2 and a SAL70200G. (Gen1)

 

If i have the camera in fully manual mode and set the exposure as camera tells me to, I get over exposed pictures.

(if i follow the small arrows that shows exposure in view finder)

 

If i adjust settings to under exposed as much as 2.0, I get correct exposure.

Is there something wrong with the lens? (Bought it second hand)

Or is there any settings for light reading that i have missed?

 

Have tried to shot in fully automatic mode and it seems OK sometimes i get slightly over exposed pictures there too.

 

See attached pics.

 

​The over exposure one is when camera says its OK 0.0 in viewfinder. (200mm, F8, 1/160 sec, ISO400 )

The other, correct exposured one has -2.0 in viewfinder (200mm F8, 1/250, ISO 100)

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Guest Jaf-Photo

It looks like the black cat was spot-meterd in the top foto. That will bring exposure up by quite a bit, as the camera thinks the cat should be gray.

 

What is the reason for shooting manual exposure on reflective metering anyway? You'll get different readings everytime you move the lens slightly.

 

I don't know what's causing your problem but it seems unnessary. Either use autoexposure with the appropriate metering area, and adjust it to your preference in post - or take an incident light reading (or take a reflective reading on a grey card) for manual exposure.

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Guest Jaf-Photo

I've never had aperture blades cleaned by a Sony workshop, but I can't imagine it would be cheap. Perhaps start by havaing a word with the seller?

 

Also, I don't understand the point of shooting manual but copying the exposure reading of the camera. You'll get the same result in P A S without the hassle.

 

So, if you get correct exposure in those modes, it might be better to keep shooting to see if the blades ease up. They may have become stiff from a lack of use?

 

I just remembered that I've bought a few Minolta AF lenses with sticky or itregular irises. I put them on a cycle of a few hundred exposures and that fixed the problem.

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No, i think your right! it will not be cheap.

I´m waiting for a cost estimate from workshop.

 

You´re right about P A S, I used manual setting to be able to step down shutter speed and see how much under exposure it needed to get correct exposure with the sticky blades.

Maybe they will ease up, but it´s a pain in the ass to verify every picture for overexposure, and i guess if a perfect, split second foto opportunity shows i will definitely get a overexposured foto.

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Guest Jaf-Photo

Shutter speed will be the relevant factor to allow the sticky iris to catch up. Although, it will probably vary, as mechanical lag is rarely consistent.

 

When I had my sticky Minolta lenses, I stuck them on an old body and hammered away a couple of hundred exposures. That cleared them, so that could be a thing to try.

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  • 3 weeks later...

Lens is back from service, still the same!

They want to charge me $1000 for a service that is no good!!

 

I don't know that much about lenses, i mean, how they work inside.

Really need some tech guy to help.

 

Been doing som serious test shooting and this is how in looks:

 

Shooting the same objekt in Aperture priority, pics are ok at 1/400 f/2.8, when stepping down aperture and shutterspeed they gradually overexpose 

Uploading some files to show the problem.

 

I came to the conclusion that if shutter speed is under 1/80 the picture is heavily overexposed.

 

Can it be that when shutter speed is low then the aperture does not close fast enough,  then too much light enters the sensor?

Seems like a shutter speed lower the 1/80 - 1/100 is the break point for overexposing to be visible.

All shots in Aperture priority.

 

1/400-f2.8 

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1/160 f4.5 

1/100 f5.6 

1/60 f7.1 

1/20 f13 

1/4 f29 

 

Did the whole serie from f2.8 to f32 but can not upload all files here.

 

Any tech guy out there who can explain this to me??

 

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Adding a screen capture from lightroom with all images.

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And another image when shot with another lens. (SAL1650 SSM)

As it should look.

 

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Guest Jaf-Photo

I do feel for you. It strikes me that your shutter speeds are faster on the 70-200, and still the images are over-exposed. The over-exposure also seems to increase steadily as you stop down. Maybe there's a difference with electronic first shutter on or off?

 

In any case, you should agree with the service shop to return it for further repairs. $1000 is a lot of money, which basically could have bought you a second used copy,

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I tried to shot with electronic "first curtain" off. but there is no difference.

Your absolutely right about the repair cost matches the price of a second hand lens.

 

There is a 3 month function warranty on the repair so i will call them tomorrow (Monday) to arrange a return.

I guess it will not get any cheaper this time to get it fixed!

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As to why ... maybe why ... auto modes are close to

correct exposure, I haven't a full picture of how Sony

sequences the events leading up to image capture,

but I suspect they use a system that has been on a

few other cameras all the way back to film days.

  

The sequence I'm thinking of actually reads the final

check for light level after all mechanisms have done

theeir pre-exposure events. That means the iris has

closed,as best it can, even if defective, i.e. lagging. 

 

That sequence will fairly well compensate for a slow

iris by a last-moment tweak of the shutter time. That

means it compensatess only in P and A mode where

AE modes govern the shutter. It cannot compensate

in S or M mode where the use governs the shutter. 

 

Your extreme problem in M mode suggests that the

probelm is as above. But modern gear is too smart.

I don't know if S mode has, or has not, an override of

the user-set speed when the user makes an "unwise"

choice. Very likely it has this, and equaally likely it can

be toggled in or out of the sequence thru the menus. 

  

As best I can follow the progress of the thread I have

not seen that you set M mode and ran a test spread

of equivalent exposures across the f/stop stop range,

manually resetting the shutter speed for every f/stop

to maintain constant exposure.  

 

You do the above without any metering help from the

camera [avoiding a variable]. For a lagging iris this is

expected to show a gradual trend from normal to over

exposure.Normal should occur at the wide open f/stop

where lag cannot influence results.

  

There will be a second variable in the above exposure

run,and that is shutter time, cuz longer times may allow

a lagging iris to get reasonably close to where it needs

to be, the iris still closing further during the shutter run. 

 

You can use a constant 3-digit shutter speed and vary

ISO instead of the shutter. This can avoid the effect

describes just above. But doing it both ways and then

comparing theresulting exposure series is worth doing

as that may also be informative.

 

There's another variable lurking in your "too smart"

gear. In some modes, for some reasons, Sony's will 

not be operating at full-open aperture while viewing

and other preliminary activities occur. This will give a

lagging iris a head start, so that it may successfully

stop down to approx the correct size even tho it's not 

operating as fast as it should. 

  

Keeping ALL of the above in mind, run new tests. I'm

expecting you will diagnose a lagging, sluggish iris.

Read it all twice or more, write a script to follow for all

your test exposure runs, reread your script, compare

it to all of the above, then get busy.

  

If the iris is lagging get an independent nonSony repair

repair. There is some roll of the dice in choosing which

repair service to use, but it can't be worse than Sony so

best of luck to ya ;-)   

  

P.S. 

 

I don't know your familiarity with the mechanisms here,

so I don't know how well the above made sense to you.

But in case it's helpful, know this: Altho a shutter has a

speed, it is a fixed speed. It never varies. It's just the

speed at which the blades travel. We don't know that

speed and we don't care. As photographers we never

deal with shutter speed ... a factor not under our control.

 

The control we exercise over the shutter is not speed

but DURATION ... meaning the length of time that the

shutter remains open and exposing the sensor [or film].

"Speed" has no length, "duration" has length. It tell of a

span of time in which various events can occur. "Time

was invented so that everything doesn't happen all at

once". I don't remember who said that, but it explains

almost everything :)

  

So, to get a grasp on how "shutter speed" [sic] interacts

with a sluggish or lagging iris, always think of "duration"

and not "shutter speed". It will help you visualize how all

the above stuff makes sense.

   

DURATION ! Say it LOUD ;-) 

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That was something to chew on! :) Like it a lot!

Will get to it tomorrow, its getting late here!

 

Think i have to read it a few times more.........

 

Don't know if you read it earlier in the thread, if i manually open the iris with the lens in my hand looking through it i can clearly see that the blades closes really slow, almost as they are working in oil.

My guess is that it takes almost half a second to close from wide open.

This was the reason i brought it in for service. I told them this when i left it there.

They claim to have replaced the whole aperture unit (Cost $150)

But it is exactly the same as before they got it.

 

Thanks for a very High-Tech answer, exactly what i was looking for!

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Guest Jaf-Photo

No way should they charge you for the second service. Rectifying the first failed service should be free of charge.

 

Clearly, this behaviour is not normal, so you shouldn't need a workaround, you need a fix.

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Contacted service center today, they claim the lens was working when shipped out. (I doubt it)

They want me to sent it in again for another look.

Got contact with actual service technician, he also claims everything in the back part of the lens is replaced (Aperture unit) and cleaned from leaked oil and tested.

Will send it in today and then I`ll just have to wait .......again!

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Looks like even if the entire aperture mechanism was

replaced, nothing was ever done to find and eliminate

the source of oil that migrates to the iris blades. They

definitely owe you a re-do of their so-called repair. But

they may tell you that eliminating the source of the oil

means dismantling additional areas of the lens, maybe 

the zoom cams and sleaves. That would be legitimate

on their part and extra expense on your part :-(

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Finally the lens is back from service, in working order! :) 

The technician told me exactly as You "Golem" was mentioning, he had to dismantle the zoom mechanism to get rid of all the grease that was leaked out to the aperture.

Will make a marathon shootout during the weekend to see if it stays ok.

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Got the bill today, same price as the pre quota. 7023.64 SEK ($820).

About as much as you can pay, anything more , it is cheaper to buy a second hand lens.

On the other hand, you don't know what you get when buying second hand!

Got the lens back in working order, i´m pretty happy with that!

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