Minolta 58/1.2 with extreme "flare" problem, fixab

[Ivan Lee]

Hey guys... I have this lens on sale now, but discovered that this lens suffers from extreme flare. What causes this? the coatings look ok. Maybe something with the convertion to M42? I even tried my Sony 70-300G hood! it didn't help

Here are the samples:

Minolta 58/1.2 at f/4, look how the contrast is low, specially on the lower left part of the heart.



Minolta 50/1.2 at f/4, contrast is just perfect.



Minolta 58/1.2 at f/2.8 (look the giant "blob")



Minolta 58/1.2 at f/4 (now it's obvious)



Industar 50/3.5 at f/5.6 (look how the old and cheap tiny Industar performs, without hood)



Those were tested on my GH1, I'd like to try on my NEX, but I don't have a M42-NEX adapter yet...

what do you think about this? thanks!

[kds315*]

a typical "hotspot" effect.

[Orio]

It's a so called "ghost" image that is produced by internal reflections inside the lens,
basically, the glasses make the highlights "bounce" between glass surfaces, and when
there is a strong light point inside the frame, this highlight takes the shape of the iris aperture.
Wide open, of course, it just looks like a big roundish blob.

[Arkku]

With digital, this may also be caused by reflection from the sensor (which is more reflective than film) reflecting back yet again from the lens elements. The large rear element surfaces of the Rokkor may exacerbate the problem, and pre-digital era lenses may not be coated as well on the rear side of elements (I believe the marketing term “digital coatings” refers to better coatings on the rear side of elements to address sensor reflections, although I admit I do not know how commonly these coatings were neglected before digital).

[Ivan Lee]

yeah, I just don't know why this is happening, if it's common with all 58mm 1.2 Rokkors, or it's something with the GH1 sensor.... or maybe because of the conversion... I don't know if i will be able to make a DIY back conversion to the original MD mount. But I think I'm going to try it...

Do you know if I can just swap the mounts? I have some MD lenses that I could remove the mount...

[Arkku]

I don't know how yours is converted, but the mount is just a passive piece of metal, it should have no effect.

For what it's worth, I also haven't noticed hotspots this bad with mine. It's the oldest version, MC Rokkor-PG, nice and radioactive.

[scsambrook]

I'm sure there's nothing "wrong" with this lens - it's simply the way it works and Orio has given a concise explanation of it.

That may not be good news, but we should remember that when this lens was designed there was always a price to be paid for achieving very wide apertures. In essence, the "speed giants" traded image quality for wide apertures, while the Industar and its cousins provided [relatively] higher image quality at the price of a much smaller maximum aperture.

Back in the 1960s nobody ever expected an f2/f1.4/f1.2 lens to be used in bright daylight at its widest aperture, even with films rated at ISO 25. Ivan's night shot with the bright street lights shows the lens at its worst, or rather provides a particularly severe test for it. The accepted doctrine was always to use the smallest aperture possible in the prevailing light conditions to maximise image quality. We (I was around then!) accepted as "characteristics" what are now often seen as "deficiencies". And that included internal reflections and flare. That Ivan describes his lens as having "extreme flair" shows how far subjective assessments have changed over time - I'm pretty sure a lot of other people would hold similar opinions to his.

Although my digital experience is limited to only two makes, I do think that flare, in particular, seems to be somewhat more noticeable than on film, although "ghosts" and other reflections seem to be about the same.

[Lightshow]

My MC PG handles flare better than this, it's possible an element is seated incorrectly.

[F16SUNSHINE]

I think arkku has it right. This is from reflection off the sensor.
I noticed this with a Tomioka 1.2/50mm as well. No problems with flare on film but nasty on my 5D.
It's m42 right? Shoot a roll of film before going to crazy about what is "wrong" with the lens.
I have a 1.2/58 and it i a bit lower contrast to be sure but I like that way. It renders beautifully and low contrast is an asset with digital work flow.

[Ivan Lee]

The true is that my lens is not performing as it should, or as it many samples I've seen online...

Lightshow, maybe you're right, but I don't have the time, or knowledge to verify this...

F16SUNSHINE, I don't have a M42 film camera with me...but what explain my other fast lenses not perform like this?

I've seen 2 Minolta 58 1.2 for sale on my country, I think I'm giving a try on other samples...

[dnas]

Have a look a the rear lens element....

I have an older Tamron 90mm F2.5 Macro, and the back element is perfectly flat. I think this flat rear surface makes it more prone to the reflection off the sensor. You can see here the effect of that:

F11 (just the faintest of ghosts)


F16 (more obvious)


F32 (very obvious)



At apertures larger than F11, it's hard to see any spot, as it's larger (because the aperture blade circle is larger), but I'd say larger than F8, the "circle" takes up the while shot, so the result is decreased contrast across the whole frame.

I tend to avoid older lenses with dead flat rear elements these days......