Strange behavior with the 58mm f/1.2 Rokkor

[Ivan Lee]

hey fellow lens lovers...

something very strange with my 58mm MC Rokkor 1.2 is bothering me. At f/1.2 and f/2 apertures, the image is the same! and I am absoluttely sure that the aperture closes at f/2. I mean, the bokeh is identical...

And comparing with my other f/1.2 lens (MD Rokkor 50mm) the behavior is different.

I set my camera at 0 EV, pointed at a white blank surface and closed the aperture from 1.2 to f/2 and then f/2.8... (full stops)
With my 50mm MD Rokkor, I closed from 1.2 to f/2 and the meter showed -1 EV, from f/2 to f/2.8 (-2 EV) and from f/2.8 to f/4 (-3 EV)

This is how it should be... 1.2 --> 2 --> 2.8 (full stops)

Now with the 58mm MC Rokkor:

1.2 --> 2 ( -2/3)
2 --> 2.8 (-2 EV)

Now some samples with the MD Rokkor, the brightness should look the same because the exposure is the same (obvious)

f/1.2 - 1/200



f/2 - 1/100



f/2.8 - 1/50



Now with the MC 58mm Rokkor

f/1.2 - 1/200



f/2 - 1/100



f/2.8 - 1/50




Look how strange is that... with the 58mm Rokkor the f/1.2 and f/2 photos looks identical except that the f/2 photo is brighter...

wow, I´m confused...

All I can think is that the f/2 setting is not f/2 for real...is something like f/1.4... but the aperture closes at f/2!! look how uniform the MD 50mm lens performs...

any ideas?
thanks!

[francotirador]

I promise I'll give it a try with mine. But for me there is little difference in the bokeh

[Pancolart]

Hula, that really looks the same. Maybe area outside sensor differs more. Can you show a photo of lens aperture at F1.2 and F2.0? Did you check if your adapter interferes with aperture pin?

[8310]

I suppose you checked that the aperture really does close down to a circle of roundabout a bit less than half the diameter than at 1.2, right?


What camera are you using? Depending on the angle of the light rays hitting the sensor at 1.2, it might have to do something with that sort of thing:
http://www.luminous-landscape.com/essays/an_open_letter_to_the_major_camera_manufacturers.shtml

I have to admit that I have not yet really thought through that whole story and all the consequences that come with it, but on a first glimpse, it looks like it could be your sensors fault.

[Orio]

It is not identical! I see a clearly visible difference.

[fatdeeman]

I can see a difference, to me it seems noticeably smoother at f/2

[Ivan Lee]

Hey guys...some new discoverings today

First, the picture of both lenses at f/2, the MD 50 and the MC 58



My 58mm Rokkor is converted to M42 and I use it with a M42-m4/3s adapter in my GH1.

And today I shot some different pictures and indeed the f/2 picture has a different bokeh. BUT, I was right about the 2/3 of stop difference...

Actually, is exactly like this: from wide open to f/2 (2/3s of stop) and from f/2 to f/2.8 is 1 1/3s of stop! then from f/2.8 to f/4 is 1 stop difference...

1/2500s to 1/1600s (2/3 stop) then from 1/1600s to 1/640s (1 1/3 stop)

look at the photos from today:

f/1.2 - 1/2500s



f/2 - 1/1600s



f/2.8 - 1/640s



So I'm sure that the f/2 setting is not f/2 for real... maybe a problem with the aperture?

And the MD 50mm looks sharper at f/2 than the MC 58mm at f/2... but the 58mm is absoluttely sharper at f/1.2 than the MD... interesting...

[Ivan Lee]

[Ivan Lee]

[ZoneV]

We had this microlens problem here before:
http://forum.mflenses.com/fast-lenses-and-microlenses-t33709.html

In your 4/3 camera it could be, that the microlenses are optimized for telecentric lenses - and thet the exposture and depth of field difference between f/2.0 and f/1.4 for example is smaller than expected.
But on the other hand the bokeh rendering could be a bit smoother because of this.

[Ivan Lee]

[AhamB]

[francotirador]

The F2 in your 58 is not real, I have compared with mine. Has the same difference as your 50mm.