APO Summicron 50/2 ASPH: Central veiling flare / fogging

[Rick]

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Huh?

[thighslapper]

I may be a bit dim...... and I am no expert in optics ...... but I find it curious that this occurs with very small apertures ...... when the great majority of aberrations and other problems are much worse at large apertures.......

 

Could it possibly be due to light from the diaphragm blades being reflected back from the lens elements in front of them ????. They are never completely matt black from what I can see...... and possibly some are more reflective than others..... or aligned in a slightly different way..... there may be no single factor but a combination of several.

[Rick]

I may be a bit dim...... and I am no expert in optics ...... but I find it curious that this occurs with very small apertures ...... when the great majority of aberrations and other problems are much worse at large apertures.......

 

Could it possibly be due to light from the diaphragm blades being reflected back from the lens elements in front of them ????. They are never completely matt black from what I can see...... and possibly some are more reflective than others..... or aligned in a slightly different way..... there may be no single factor but a combination of several.

 

No, it is clearly flare. The effect can be completely illuminated by shading the from element from light with your hand.

 

After much trial with this lens this morning, it seems to me this is just the flare characteristic to this particular lens. All lenses seem to flare differently. This one just produces a central flare spot when lighting conditions are such that the front element has light falling on it and the central field has something dark'ish to better highlight this particular flare pattern.

 

The pattern size doesn't change size with change of aperture. But, opening up the aperture does have the effect of making the central flare harder to detect. But, if you look closely it doesn't completely eliminate it and it doesn't change size.

 

Opening up the lens just reduces contrast across the whole field by introducing more of the common type of flare, from the effect of opening the lens aperture up. This effect just makes the relative central flare harder to detect. It is still there.

 

I suspect my lens is not defective in the sense that it behaves differently than other's lenses. I would suspect that every lens produces this effect if, one knows how to elicit it. My hope is that this is coating problem or a lens interface problem or something that has been fixed in newer copies because, this is otherwise a fantastic little lens.

 

The good news is that when testing the APO 50 for flare against my 50/1.4 FLE, the later was much, much more well behaved when it came to flare resistance. The 50 FLE is still a darn good lens.

 

I'm off to the Leica dealer to return my lens.

[01af]

... I find it curious that this occurs with very small apertures—when the great majority of aberrations and other problems are much worse at large apertures ...

The Central Veiling Flare phenomenon is fundamentally different from optical aberrations which usually are at their worst at full aperture.

 

At wide apertures, the exit pupil's diameter is wide and the exit pupil's brightness is dim—in relation to the shutter speed which at a wide aperture is fast. At small apertures, the exit pupil's diameter is narrow and the exit pupil's brightness is high—in relation to the shutter speed which at a narrow aperture is slow. The smaller and—relatively spoken—brighter aperture will emphasise the mirroring between the glossy sensor and the rea element's surface. The Central Veiling Flare basically is a mirror image of the exit pupil, and it's more clearly visible when it's smaller and—relatively spoken—brighter ... in other words, sharper focused.

[thighslapper]

The Central Veiling Flare phenomenon is fundamentally different from optical aberrations which usually are at their worst at full aperture.

 

At wide apertures, the exit pupil's diameter is wide and the exit pupil's brightness is dim—in relation to the shutter speed which at a wide aperture is fast. At small apertures, the exit pupil's diameter is narrow and the exit pupil's brightness is high—in relation to the shutter speed which at a narrow aperture is slow. The smaller and—relatively spoken—brighter aperture will emphasise the mirroring between the glossy sensor and the rea element's surface. The Central Veiling Flare basically is a mirror image of the exit pupil, and it's more clearly visible when it's smaller and—relatively spoken—brighter ... in other words, sharper focused.

 

.... so it's related to reflected light from the sensor interacting with the rear lens elements ..... ???. Is it absent in film cameras as a result ??

 

.... sounds like a real challenge to avoid or eliminate ....

[melantye]

I am sad to report that my copy has similar flare issue at f/8-f/16. Here is an example.

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[01af]

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Is it absent in film cameras as a result?

Not really absent—but muuuch weaker due to the matte, non-glossy surface of a film's emulsion side, so it's basically invisible on film.

 

 

... sounds like a real challenge to avoid or eliminate ...

Well—some lenses have it, and others don't.

[Jeff S]

Disappointing to see and read about all of this, although no lens is perfect. But the 50 Summilux asph is plenty good enough for my needs and print sizes, with no bothersome CVF, an extra stop...and a lot more money in my bank account.

 

Happy to confirm, too, that focusing on my new M is spot-on based on tripod test using LV versus RF (wonderful benefit of LV).

 

Jeff

[helged]

240 with (in order): APO 50 Summicron - 50 Summilux (latest version) - 50 Summicron (latest version). Focus on infinity. On tripod. No post-processing. First f2.

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[helged]

Then f5.6.

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[helged]

And finally f16.

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[k-hawinkler]

Thanks.

 

I would put the black sheet a little higher in the middle of the window so that it shows up in the middle of your image.

 

To me it seems the non-AA Summicron at f/16 shows more CVF than the other two lenses. What's your conclusion?

 

Thanks again.

[helged]

Similar to the above examples, but for f16 and with focus at 1.5 m.

 

In conclusion: The APO 50 Summicron shows some loss of central contrast but, in general, with weaker loss than seen by the 50 Summilux.

 

As has been mentioned and demonstrated earlier in this thread, clearest sign of central contrast issue is found at f16. But again, the copy of APO-50 that I have behaves, in general, better than the 50 Summilux, indicating differences between the copies.

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[Rick]

I am sad to report that my copy has similar flare issue at f/8-f/16. Here is an example.

 

Yes, your lens exhibits central flare as well. I'm afraid this is a design flaw in the lens. I am certain now that they all exhibit this flare. It is the signature-flare of the APO 50. Sorry, I would return it. I just returned from returning mine. I'm afraid Karabe laid an egg.

 

Also, The exit pupil explanation doesn't take into account why when the light is removed from the front element by shading it, the flare disappears. That changes nothing about the exit pupil. The exit pupil may be responsible for the shape of the flare or something, but the exit pupil is not the cause.

 

This effect is just flare from the front element. Every lens has this problem if the light falling on the front element is strong enough compared to the darkness of the central portion of the field. The APO 50 just happens to be worse than any lens I've used. Sorry.

[MarkP]

You must be somewhat disappointed Rick. Now you can have a really good holiday instead with the money you saved and perhaps take some photos with your old crappy 50s

[lct]

Design flaw or fixable problem? As long as Leica will stay mute i will have the feeling that it is a design flaw personally.

[Rick]

You must be somewhat disappointed Rick. Now you can have a really good holiday instead with the money you saved and perhaps take some photos with your old crappy 50s

 

Yes, I am both disappointed and a little relieved to see the eight-large back on my credit card right before we leave for Europe.

 

I also appreciate now the 50 Lux is not only a venerable adversary, but also the better lens.

[k-hawinkler]

Well, I wonder whether there is any connection to the M sensor design with elongated micro-lenses?

I think somebody else already expressed that thought here on the forum.

Has the AA50/2 been linked to the CVF when used on an M9?

[Rick]

Well, I wonder whether there is any connection to the M sensor design with elongated micro-lenses?

I think somebody else already expressed that thought here on the forum.

Has the AA50/2 been linked to the CVF when used on an M9?

 

Flare is a lens phenomenon not a sensor characteristic.

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Hallo,

Look here: Leica M

[k-hawinkler]

Thanks. Yes, if it is just a flare.