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Should 4/3 lenses be half the size of full frame lenses?

 
 
nospam
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      06-16-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> >> If instead you concentrate them all on the
> >> quarter-size sensor, then you've gained two full stops of exposure.
> >> So how on earth do you make that "equivalent" to the different
> >> f-stop.

> >
> > If you actually did that as described above, it would be an actual
> > f/1.4, or equivalent f/2.8.

>
> An "actual f/1.4" lens is one with a maximum effective aperture 1/1.4 of the
> focal length, eh? Does "f/1.4" have any other meaning than that? I don't
> understand what "equivalent f/2.8" even means in this connection.


equivalent image, including dof & noise. you don't get to pick and
choose which ones qualify as equivalent.
 
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David Dyer-Bennet
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      06-16-2011
On Jun 16, 1:52*pm, Wolfgang Weisselberg <(E-Mail Removed)>
wrote:
> David Dyer-Bennet <(E-Mail Removed)> wrote:
> > A 6MP E-PL2 would be a lot more valuable to me than the
> > 12MP one they actually make! *But apparently I'm not normal
> > (I've kind of gotten used to that over the years).

>
> Is there *so* much difference between a 6MP camera and a 12MP
> camera downsampled to 4.3MP, and then optionally upsampled back
> to 6MP?


Yeah, not really so bad. I have a personal problem with
a workflow that involves deliberately throwing away information,
though, which ends up meaning I see the junk when I'm
working on the photo.

> 100% crops aren't good to compare anything but per-pixel noise ---
> which is only valuable on identical pixel counts. *(Noone looks
> at *photos* at 100%, because they cannot see the image then.)


I work at 100% a lot while retouching. Or 200%.

 
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J. Clarke
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      06-16-2011
In article <160620111642293671%(E-Mail Removed)>,
http://www.velocityreviews.com/forums/(E-Mail Removed)d says...
>
> In article <(E-Mail Removed)>, Neil
> Harrington <(E-Mail Removed)> wrote:
>
> > Sure, you're correct of course, but I'm afraid it's a waste of time with
> > Nospam. As you mentioned in one post, he skips from one thing to another,
> > from exposure value to noise to DOF, as if all of those could somehow be
> > equivalent at the same time for different formats.

>
> i've been completely consistent. if you think i skip around, then you
> don't understand it.
>
> > The argument really should begin and end with: the same f-number means the
> > same exposure regardless of format, all else being equal. Noise, etc., are
> > separate issues and while important in themselves, should not be brought in
> > to this.

>
> all else is *not* equal if you ignore noise and depth of field.
>
> > The notion that f/2.8 in full frame is "equivalent" to f/1.4 in Four Thirds
> > is simply bizarre.

>
> however, it's correct.


Fine, take a 4/3 and a full frame and shoot the same scene at the same
ISO and shutter speed with both, with the full frame at f/2.8 and the
4/3 at f/1.4 and show us your results.


 
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nospam
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      06-16-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> >> ISO is ISO, just as f-number is f-number. If f/2.8 at 1/250 is
> >> correct at ISO 100 on a full-frame camera, f/2.8 at 1/250 will still
> >> be correct at ISO 100 on a 4/3 camera.

> >
> > that will get you the same exposure, but *not* the same noise or depth
> > of field.

>
> Of course.


that means the images are not equivalent, they just have the proper
exposure.

> >> Again, you can't just put an f/1.4 lens on the 4/3
> >> camera to collect otherwise missing photons and leave everything
> >> else the same.

> >
> > which is why you raise the iso of the larger format to use 2 stops

>
> Which changes something else entirely.


right, it matches the noise of the smaller sensor and lets you use a
smaller f/stop so you can match depth of field. that way you get an
equivalent image.

> >>> we know that simply isn't true. Smaller sensors work less well at
> >>> high ISOs.
> >>
> >> Of course.

> >
> > which is why you have to normalize it for equivalency.

>
> No, the ISO remains the same. What "you have to" do to achieve some other
> purpose, however appropriate and useful that might be, does not change the
> ISO.


if the iso remains the same you have less noise on the larger sensor,
so it's not equivalent.

it's really quite simple.
 
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nospam
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      06-16-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> >> An "actual f/1.4" lens is one with a maximum effective aperture
> >> 1/1.4 of the focal length, eh? Does "f/1.4" have any other meaning
> >> than that? I don't understand what "equivalent f/2.8" even means in
> >> this connection.

> >
> > equivalent image, including dof & noise. you don't get to pick and
> > choose which ones qualify as equivalent.

>
> There's nothing to "pick and choose." The f-number means: the focal length
> divided by the physical size of the aperture. That's why it's written that
> way, and that's all it means.


an f/number by itself is independent of any sensor size. once you put
it on a camera, you *must* take into account the size of the sensor.

you're also ignoring other characteristics of the image.

if the noise and depth of field are different, the image is *not*
equivalent. you do not get to pick only one thing.
 
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nospam
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      06-16-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> >> The notion that f/2.8 in full frame is "equivalent" to f/1.4 in Four
> >> Thirds is simply bizarre.

> >
> > however, it's correct.

>
> No. You apparently have some sort of "equivalence" in mind that does not and
> cannot actually exist.


it exists.

> When you change sensor size you change several
> characteristics, such as those you've mentioned, which have nothing to do
> with equivalence in exposure.


there you go again, picking only one item.
 
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tony cooper
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      06-17-2011
On Thu, 16 Jun 2011 18:24:42 -0400, "Neil Harrington" <(E-Mail Removed)>
wrote:

>David J Taylor wrote:
>> "Neil Harrington" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed) ...
>> []
>>> In "its common-day usage," a half frame is half a frame, whether
>>> "specifically photographic" or not. Take a 36x24 frame and cut it
>>> exactly in half, and what do you have? An 18x24 piece, a half frame.
>>> This applies to any sort of rectangle I can think of.

>>
>> The topic is "4/3 lenses compared to full-frame lenses". 4/3 has
>> approximately half the linear dimensions of full-frame, and it is
>> that to which I was referring, as I have clarified several times.
>>
>> A half-pint glass doesn't have half the linear dimensions of a
>> full-pint glass, otherwise it would be a one-eighth pint glass! <G>

>
>But if you gave that pint glass to someone with a suitable glass cutter and
>told him to cut it in half, which would reduce only the height dimension, it
>would be a half-pint glass.


Only if the pint glass has perpendicular sides, and I've never seen
one like that. Beer glasses are either tapered, bowed out, or
schooner-shaped so cutting the height in half would result in a
container that would hold significantly less than a half-pint.


--
Tony Cooper - Orlando, Florida
 
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David J Taylor
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      06-17-2011
"Neil Harrington" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
[]
> But if you gave that pint glass to someone with a suitable glass cutter
> and told him to cut it in half, which would reduce only the height
> dimension, it would be a half-pint glass.


Indeed!

> Of course if he cut it in half lengthwise it wouldn't hold anything at
> all, which would be a shame.


... and the hole falls out of the argument. <G>

David

 
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Bruce
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      06-17-2011
"Neil Harrington" <(E-Mail Removed)> wrote:
>
>But if you gave that pint glass to someone with a suitable glass cutter and
>told him to cut it in half, which would reduce only the height dimension, it
>would be a half-pint glass.



Pity the guy who got the top half ...

.... a no-pint glass.

 
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nospam
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      06-17-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> >>>> An "actual f/1.4" lens is one with a maximum effective aperture
> >>>> 1/1.4 of the focal length, eh? Does "f/1.4" have any other meaning
> >>>> than that? I don't understand what "equivalent f/2.8" even means in
> >>>> this connection.
> >>>
> >>> equivalent image, including dof & noise. you don't get to pick and
> >>> choose which ones qualify as equivalent.
> >>
> >> There's nothing to "pick and choose." The f-number means: the focal
> >> length divided by the physical size of the aperture. That's why it's
> >> written that way, and that's all it means.

> >
> > an f/number by itself is independent of any sensor size.

>
> Yes. Stop right there.


if you take a lens without a camera, there is no exposure. it's just a
lens, sitting on the table.

> > once you put
> > it on a camera, you *must* take into account the size of the sensor.
> >
> > you're also ignoring other characteristics of the image.
> >
> > if the noise and depth of field are different, the image is *not*
> > equivalent. you do not get to pick only one thing.

>
> You didn't stop where you should have stopped.


or more accurately, you're stopping prematurely, ignoring things that
matter. why is that?
 
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