F0.95 ???

[Roland Karlsson]

The Voigtländer 25 mm Nokton for u43 is F0.95. That is cool, sort of. A great potential for shallow DOF, or ... ?

I thought, correct me if I am wrong, that the photo sensor, with micro lenses, Bayer filters, etc, etc, cannot see more than F1.5 or so. Everything else is wasted.

Have I got it right?

In that case, nothing will happen when opening the lens from F1.4 to F1.0.

 

[Great Bustard]

The Voigtländer 25 mm Nokton for u43 is F0.95. That is cool, sort of. A great potential for shallow DOF, or ... ?

I thought, correct me if I am wrong, that the photo sensor, with micro lenses, Bayer filters, etc, etc, cannot see more than F1.5 or so. Everything else is wasted.

Have I got it right?

In that case, nothing will happen when opening the lens from F1.4 to F1.0.

It depends on the microlens efficiency of the sensor, but, if I had to guess, I'd say an f/0.95 lens on an mFT sensor would be effectively f/1.2 or so. But f/1.5 would be too much of a light loss, I should think.

 

[xpatUSA]

Indeed. Falk Lumo says:

"the equivalent [to a full frame 50mm f/1.4] crop-2 camera would be a FourThirds (25mm, f/0.7, ISO 25) camera. Even though the Voigtlander Nokton 25mm f/0.95 Micro FourThirds (µFT) lens exists, it is very expensive (about 4x) and no µFT camera sports less than ISO 160 [Feb 2012 paper] while we would need ISO 25 for equivalence."

http://www.falklumo.com/lumolabs/articles/equivalence/index.html

--
Cheers,
Ted

 

[RussellInCincinnati]

Roland Karlsson wrote: The Voigtländer 25 mm Nokton for u43 is F0.95. That is cool, sort of. A great potential for shallow DOF, or ... ? I thought, correct me if I am wrong, that the photo sensor, with micro lenses, Bayer filters, etc, etc, cannot see more than F1.5 or so. Everything else is wasted.

Agreed that when a light ray starts going through lots of glass at ever more extreme angles, at super wide apertures, hitting sensors at ever more extreme angles, that one cannot strictly predict the "T-stop" from the F-stop. Heck just look at the max T-stop measurements on the DxOmark lens measurements, they are rarely exactly the same as the nominal widest F-stop/aperture.

But it feels a bit pessimistic to predict that the Voigtlander 25mm Nokton with a geometric aperture of F/0.95 is going to have a T-stop rating of F/1.5 or higher. After all, the Canon 50 and 85mm F/1.2's get a T-stop rating of F/1.4. I suppose that is on full frame cameras, that might well make more efficient use of oblique light than the ultra dense pixel setup of a micro Four thirds camera. But it's not like getting below T/1.4 is harder than breaking the sound barrier.

 

[Leonard Migliore]

Indeed. Falk Lumo says:

"the equivalent [to a full frame 50mm f/1.4] crop-2 camera would be a FourThirds (25mm, f/0.7, ISO 25) camera. Even though the Voigtlander Nokton 25mm f/0.95 Micro FourThirds (µFT) lens exists, it is very expensive (about 4x) and no µFT camera sports less than ISO 160 [Feb 2012 paper] while we would need ISO 25 for equivalence."

Equivalance relates to invariants between different formats. The O.P.'s question was, how much of f/0.95 gets to the sensor, which is a different thing entirely.

 

[Leonard Migliore]

Roland Karlsson wrote: The Voigtländer 25 mm Nokton for u43 is F0.95. That is cool, sort of. A great potential for shallow DOF, or ... ? I thought, correct me if I am wrong, that the photo sensor, with micro lenses, Bayer filters, etc, etc, cannot see more than F1.5 or so. Everything else is wasted.

Agreed that when a light ray starts going through lots of glass at ever more extreme angles, at super wide apertures, hitting sensors at ever more extreme angles, that one cannot strictly predict the "T-stop" from the F-stop. Heck just look at the max T-stop measurements on the DxOmark lens measurements, they are rarely exactly the same as the nominal widest F-stop/aperture.

But it feels a bit pessimistic to predict that the Voigtlander 25mm Nokton with a geometric aperture of F/0.95 is going to have a T-stop rating of F/1.5 or higher. After all, the Canon 50 and 85mm F/1.2's get a T-stop rating of F/1.4. I suppose that is on full frame cameras, that might well make more efficient use of oblique light than the ultra dense pixel setup of a micro Four thirds camera. But it's not like getting below T/1.4 is harder than breaking the sound barrier.

Is T-stop measured with a given sensor? Because otherwise, it's going to change a lot depending on the sensor geometry.

 

[bobn2]

Roland Karlsson wrote: The Voigtländer 25 mm Nokton for u43 is F0.95. That is cool, sort of. A great potential for shallow DOF, or ... ? I thought, correct me if I am wrong, that the photo sensor, with micro lenses, Bayer filters, etc, etc, cannot see more than F1.5 or so. Everything else is wasted.

Agreed that when a light ray starts going through lots of glass at ever more extreme angles, at super wide apertures, hitting sensors at ever more extreme angles, that one cannot strictly predict the "T-stop" from the F-stop. Heck just look at the max T-stop measurements on the DxOmark lens measurements, they are rarely exactly the same as the nominal widest F-stop/aperture.

But it feels a bit pessimistic to predict that the Voigtlander 25mm Nokton with a geometric aperture of F/0.95 is going to have a T-stop rating of F/1.5 or higher. After all, the Canon 50 and 85mm F/1.2's get a T-stop rating of F/1.4. I suppose that is on full frame cameras, that might well make more efficient use of oblique light than the ultra dense pixel setup of a micro Four thirds camera. But it's not like getting below T/1.4 is harder than breaking the sound barrier.

This isn't a T-stop issue, it's to do with the f-number of the microlens on the sensor. Essentially, the microlens has to be faster than the taking lens, otherwise it can't couple all the light from the exit pupil of the lens onto the photoreceptor. Mostly, they seem to be giving out at f/2-f/1.8, though the old style Panasonic 'Maicovicon' sensors were faster. I don't know about the newer CMOS ones - but I'd hazard a guess they're much like all the other CMOS.

 

[dosdan]

There's a fair bit of detail and useful links in the 2010 "Microlenses, f-numbers and vignetting (ultra techy thread)"

http://www.dpreview.com/forums/post/36025858

Dan

 

[Roland Karlsson]

There's a fair bit of detail and useful links in the 2010 "Microlenses, f-numbers and vignetting (ultra techy thread)"

http://www.dpreview.com/forums/post/36025858

Thanks.

As usual, it is a thread full of speculations and also errors. I have not read it all yet. There is an interesting comparison between taking an image at F1.4 and F2.0. At a first glance, I cannot see any DOF differences. Which is striking, if true. And puts a big question mark for lenses with F0.95 for those sensors.

 

[bobn2]

There's a fair bit of detail and useful links in the 2010 "Microlenses, f-numbers and vignetting (ultra techy thread)"

http://www.dpreview.com/forums/post/36025858

Thanks.

As usual, it is a thread full of speculations and also errors. I have not read it all yet.

As always in open discussion, some people are wrong, others right - but there is some good stuff there ;-)

 

[Joe Pineapples]

Thanks.

As usual, it is a thread full of speculations and also errors. I have not read it all yet. There is an interesting comparison between taking an image at F1.4 and F2.0. At a first glance, I cannot see any DOF differences. Which is striking, if true. And puts a big question mark for lenses with F0.95 for those sensors.

 

[Roland Karlsson]

Joe Pineapples wrote:
There was a (possibly) related thread a couple of months ago comparing DoF for a 25mm f/1.4 lens on a m4/3 camera with a 50mm f/2.8 lens on a FF camera, but the potentially interesting discussion got a bit lost amongst all the other posts:

That is another discussion really. It is about the behaviour of F values depending on sensor size.

Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

 

[Joe Pineapples]

Joe Pineapples wrote:
There was a (possibly) related thread a couple of months ago comparing DoF for a 25mm f/1.4 lens on a m4/3 camera with a 50mm f/2.8 lens on a FF camera, but the potentially interesting discussion got a bit lost amongst all the other posts:

That is another discussion really. It is about the behaviour of F values depending on sensor size.

Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

Not at all - I suspect that both posts relate to the same phenomenon: the so-called "f-stop blues". Here is a link to a DxOMark article about it:

http://www.dxomark.com/Reviews/F-stop-blues http://www.dxomark.com/Reviews/F-stop-blues


J.

 

[xpatUSA]

[]
Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

Not at all - I suspect that both posts relate to the same phenomenon: the so-called "f-stop blues". Here is a link to a DxOMark article about it:

http://www.dxomark.com/Reviews/F-stop-blues

J.

Interesting link - thanks.

Prompts me to use LO res on my Sigma DSLR when the 30mm f/1.4 is attached. 18.24um effective pixel pitch, not much loss there . . .

 

[bobn2]

[]

Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

Not at all - I suspect that both posts relate to the same phenomenon: the so-called "f-stop blues". Here is a link to a DxOMark article about it:

http://www.dxomark.com/Reviews/F-stop-blues

J.

Interesting link - thanks.

Prompts me to use LO res on my Sigma DSLR when the 30mm f/1.4 is attached. 18.24um effective pixel pitch, not much loss there . . .

Binning pixels doesn't help, because it is the f-number of each microlens that matters. On the other hand, some Sigma DSLRs didn't have microlenses, so you might be OK anyway.

 

[xpatUSA]

[]

Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

Not at all - I suspect that both posts relate to the same phenomenon: the so-called "f-stop blues". Here is a link to a DxOMark article about it:

http://www.dxomark.com/Reviews/F-stop-blues

J.

Interesting link - thanks.

Prompts me to use LO res on my Sigma DSLR when the 30mm f/1.4 is attached. 18.24um effective pixel pitch, not much loss there . . .

Binning pixels doesn't help, because it is the f-number of each microlens that matters. On the other hand, some Sigma DSLRs didn't have microlenses, so you might be OK anyway.

Correct - my SD9 has no micro-lenses, so I guess I'm OK.

With a 54% fill factor, it needs all the light it can get!

--
Cheers,
Ted

 

[Sasha B]

F-number is a geometrical lens property of and does not directly corresponds to light gathering ability (see T-stops). So F0.95 is F0.95.

 

[Roland Karlsson]

F-number is a geometrical lens property of and does not directly corresponds to light gathering ability (see T-stops). So F0.95 is F0.95.

Ah ... but there is, as far as I know, two reasons for losing light.

1. Light get generally attenuated in the lens (and sensor) due to lots of glass and loss in surfaces. This one just makes the image darker, and maybe also colored and vignetted.
2. There is a limited acceptance angle. This can be due to the aperture of the micro lens. It can also be due to oblique rays hitting the sensor is reflected away. It might also be an optical behaviour of the lens. peripheral rays might be attenuated more.

It is the effect 2 above that affects the useful F stop and therefore also affecting the thinnest DOF you can get.

 

[Great Bustard]

Joe Pineapples wrote:
There was a (possibly) related thread a couple of months ago comparing DoF for a 25mm f/1.4 lens on a m4/3 camera with a 50mm f/2.8 lens on a FF camera, but the potentially interesting discussion got a bit lost amongst all the other posts:

That is another discussion really. It is about the behaviour of F values depending on sensor size.

Hmmm ... maybe there is some conclusions regarding this fact not being true because of limits in max useful aperture.

Not at all - I suspect that both posts relate to the same phenomenon: the so-called "f-stop blues". Here is a link to a DxOMark article about it:

http://www.dxomark.com/Reviews/F-stop-blues

Indeed, that could be the issue here, which directly addresses the OP's concern. On the other hand, even a small difference in subject-aperture distance can have a huge effect on background blur.

For example, in the thread you linked:

http://www.dpreview.com/forums/post/53127833

the person may have gone to great pains to make sure the camera was at the same distance from the subject. But what "same distance"? From the subject to the front element? From the subject to the sensor? From the subject to the aperture? For small distances to the subject, even a small difference like 1-2 cm can have a large effect.

 

[Roland Karlsson]

It is very easy to test

Just focus the lens to infinity.

Then take an image of a nearby point source, i.e. a small hole in a black cardboard, or even better a pin hole if you have one.

Take images with different apertures and see the size of the circle go up when opening the aperture.

At some aperture, it might stop being larger. Then - that is the limit.

You probably even can see this on the LCD directly.