Corner Issue on 35/2 Summicron

[jaapv]

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How was your exposure on these? Very nice shot btw. This kind of subject is very easy to underexpose. Not dramatic in the digital age, but pulling up exposure is bound to enhance the natural vignetting (more than 2.5 stops according to Erwin Puts for the IV) out of proportion.

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[adli]

Update:

 

After some searching, I found one other picture which also shows signs of vignetting. More interesting, it has something in common with the previous one, they are both shot wide open at 1/4000.

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[jaapv]

In this image I measure less than two stops vignetting in the sky. It should be nearly three on the Summicron IV.That means the M9 is applying a conservative correction. That tallies with the words of Mr. Daniel who said Leica has chosen to be careful with such corrections. I can only say: absolutely normal for this lens.

[adli]

But how do you explain that the vignetting only show up on pictures shot wide open at high speed?

 

Attached is two test pictures I took (for an other purpose), one wide open and one at f/16. Only visible vignetting in one of them:

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[lars_bergquist]

Vignetting comes in two flavours: Natural and mechanical. Natural vignetting is caused by the 'cosine rule': just as the sunlight is weaker when the sun is low, oblique rays in the corners fall on a larger area than an equivalent bundle of rays in center, hitting at a right angle (this of course is a very simplified explanation, but essentially correct.)

 

Mechanical vignetting comes from the fact that the lens mount has depth. Look at the world through the center cardboard spool of a roll of toilet paper. Seen straight on, the area you see is round and larger than when you look at an angle. Angle the roll enough, and you see nothing. Now do the same experiment with a camera lens. You get the toilet roll effect with the lens too -- as long as the aperture is wide open.

 

But stop the aperture down, and the 'hole' in center does not look much different when you angle the lens. So, mechanical vignetting IS APERTURE DEPENDENT. Take the v.4 35mm Summicron for an example. At f:2, light transmission in the extreme corners is less than 20% of what it is on center. When stopped down to 5.6, transmission is 50%. Stopping down beyond f:8 does not increase corner transmission; now only natural vignetting remains.

 

Now, if you shoot a scene at f:2, your shutter speed (given the same scene and same ISO) will be 32 times faster than if you had stopped down to 16. Check your EXIF data. High shutter speeds do not cause vignetting. The vignetting and the high shutter speed are both parallel effects of the same cause, the wide open aperture.

 

And of course Leica had to go easy on correction. As I said above, vignetting is aperture dependent, and the camera does not 'know' for certain what the actual aperture is. Full or even nearly full correction of vignetting at full aperture would result in 'negative vignetting' when stopped down: Corners brighter than the center! That would look ugly indeed.

 

The old man from the Age of Hypo (not 'hype')

[adli]

Lars,

 

Thanks for your explanation

 

However, I am still a bit puzzled that I don't see this vignetting on all my wide open shots?

[lars_bergquist]

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You are welcome. In the old days you could read all about these things in books. Most manufacturers nowadays think they will scare potential customers away if they explain things. There is a very comprehensive, though not up-to-date (it's pre-digital) book by Gunther Osterloh, 'Leica M'. I don't know if it is available in English; maybe only Germans want to know the basics. Does anybody else have any good tip about reading?

 

The old man from the Age of Basic Facts and Acid Hypo

[jaapv]

Yep - " Leica M- Advanced Photo School" is the English title. A similar book is : Johnathan Eastland, Leica M compendium.

[jaapv]

Lars,

 

Thanks for your explanation

 

However, I am still a bit puzzled that I don't see this vignetting on all my wide open shots?

As soon as you overexpose a bit the vignetting is less apparent to the eye.Pull the exposure slider down in Photoshop and you will see it.

[adli]

There is a very comprehensive, though not up-to-date (it's pre-digital) book by Gunther Osterloh, 'Leica M'. I don't know if it is available in English; maybe only Germans want to know the basics.

 

Hm, I actually have that book somewhere in the bookshelf. have to re-read it

[xrogers]

But how do you explain that the vignetting only show up on pictures shot wide open at high speed?

 

Attached is two test pictures I took (for an other purpose), one wide open and one at f/16. Only visible vignetting in one of them:

 

It would be interesting to look at the exif makernotes for each of these photos and see what the estimated aperture was.

 

This is just the sort of scene I'd expect to result in a poor estimated aperture (you shoot at 1.4, but it decides you were at 5.6), which could result in a poor in-camera correction and dark corners.

 

Until later,

 

Clyde

[adli]

The exif for both pictures are spot on. One shot at f/2 and exif says f/2, the other shot at f/16 and the exif says f/16.

 

Seems as it is correct as earlier mentioned in this thread that the software is very conservative in applying in-camera correction for vignetting.