Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Digital Photography > Should 4/3 lenses be half the size of full frame lenses?

Reply
Thread Tools

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

 
 
David J Taylor
Guest
Posts: n/a
 
      06-15-2011
"Neil Harrington" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
[]
> You cannot correct this by making the lens aperture larger, though. Your
> claim that it would take an f/1.4 lens on a Four Thirds camera to make
> the "equivalent" of an f/2.8 lens on full frame is obviously wrong:
> you'd get four times the photons (in the same time) all right, but you'd
> have to reduce exposure time proportionately in order to keep exposure
> correct, so the total number of photons would remain the same. You would
> gain nothing.


As the sensor area is one quarter on 4/3, you would get the /same/ number
of photons - one quarter of the area with four times the photons per unit
area.

If you reduce the exposure on the 4/3 camera, or are forced to because the
sensor overloads, you will reduce the signal-to-noise. If you follow the
argument through, it seems that you may be saying that any camera with an
f/2.8 lens is as sensitive as any other, and we know that simply isn't
true. Smaller sensors work less well at high ISOs.

Cheers,
David

 
Reply With Quote
 
 
 
 
David J Taylor
Guest
Posts: n/a
 
      06-15-2011
"Neil Harrington" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
> David J Taylor wrote:
>> "Neil Harrington" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed) ...
>> []
>>> You cannot correct this by making the lens aperture larger, though.
>>> Your claim that it would take an f/1.4 lens on a Four Thirds camera
>>> to make the "equivalent" of an f/2.8 lens on full frame is obviously
>>> wrong: you'd get four times the photons (in the same time) all
>>> right, but you'd have to reduce exposure time proportionately in
>>> order to keep exposure correct, so the total number of photons would
>>> remain the same. You would gain nothing.

>>
>> As the sensor area is one quarter on 4/3, you would get the /same/
>> number of photons - one quarter of the area with four times the
>> photons per unit area.

>
> But in one-quarter of the time, changing the exposure. Correct exposure
> on 4/3 is still the same f-number and shutter speed as it is on full
> frame, all else being equal. You can't just open up to f/1.4 to get all
> those extra photons.
>
>>
>> If you reduce the exposure on the 4/3 camera, or are forced to
>> because the sensor overloads, you will reduce the signal-to-noise. If
>> you follow the argument through, it seems that you may be saying
>> that any camera with an f/2.8 lens is as sensitive as any other, and

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

>
> Of course.


Yes, you can use a longer exposure on the smaller sensor camera to collect
the same total number of photons (and hence potential image quality), but
I would not describe the picture taking as "equivalent" in that case
(longer exposure means more movement blur, for example). It comes back to
what I asked in the first place: for the OP, exactly what does
"equivalent" mean. If it's purely exposure, then the same f/number will
do. If it's other factors like image quality at a certain light level, or
the same depth of field, then the same aperture will not produce the same
results.

I hope that helps, and I think enough has been said now., at least by me!

Cheers,
David

 
Reply With Quote
 
 
 
 
David J Taylor
Guest
Posts: n/a
 
      06-15-2011
"Neil Harrington" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
[]
>> Half of 36 x 24mm is 18 x 12mm,

>
> Not by any ordinary, usual or reasonable way of looking at it.


Half of 36 isn't 18? A quarter of the area.


>> approximately the size of the
>> four-thirds frame (in area). Approximately on quarter of the area,
>> yes. I was not using "half frame" in any specialised meaning, so
>> sorry for any confusion.

>
> I am using "half frame" in the way it has always been used in 35mm still
> photography, e.g. the various models of Olympus Pen and several other
> cameras commonly called "half-frame," which used an 18x24mm format --
> half of the conventional 24x36mm frame.


Perhaps you would prefer "half the frame size, i.e. one quarter of the
area"? I was using half in its common-day usage, nothing specifically
photographic, and have already apologies for any confusion.

Cheers,
David

 
Reply With Quote
 
Bruce
Guest
Posts: n/a
 
      06-15-2011
Paul Furman <(E-Mail Removed)> wrote:
>Bruce wrote:
>> Paul Furman<(E-Mail Removed)> wrote:
>>> Bruce wrote:
>>>> The light gathering power of an f/2.8 Four Thirds lens is identical to
>>>> an f/2.8 ...full frame lens
>>>
>>> With 1/4 the sensor size so 1/4 the print size.

>>
>>
>> That's only true if the Four Thirds sensor has a quarter as many
>> pixels as the full frame sensor.
>>
>> If the number of pixels is the same, the print size will be the same
>> for the same ppi at the printing stage. All that matters at the
>> printing stage is the number of pixels. The printer has no idea
>> whether those pixels came from a P&S, Four Thirds, APS-C, full frame
>> or medium format.

>
>In my first reply to this thread, I wrote: "the usable print size scales
>down for a given ISO rating". If you've got soft bright studio lighting
>with no dynamic range challenges and can use a low ISO, your scenario
>holds mostly true but you do see the noise and lack of detail with ever
>larger prints. If light is low, if there's important detail in the
>shadows and/or ISO needs to be raised, the difference can be dramatic.



Yes, it is certainly true that raising the ISO has a more dramatic
effect on image quality when using the smaller sensors.

 
Reply With Quote
 
David J Taylor
Guest
Posts: n/a
 
      06-16-2011
"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>

Cheers,
David

 
Reply With Quote
 
Wolfgang Weisselberg
Guest
Posts: n/a
 
      06-16-2011
Neil Harrington <(E-Mail Removed)> wrote:
> Paul Furman wrote:
>> Neil Harrington wrote:


>> You can't just squish the photons onto the sensor without changing
>> field of view. Hmm, actually you can, but it takes more glass, and
>> shortens the mount distance. Theoretically you could take a 50mm
>> f/2.8 FX lens and add a relay lens to squeeze it onto micro 4/3 but
>> it would likely be a large awkward expensive thing which was not very
>> sharp. I believe it might be possible to use a lens like this with an
>> telescope reducer lens to get a fast wide m4/3 lens:
>> http://www.flickr.com/photos/edgehill/5129933204/
>> http://www.celestron.com/c3/product.php?ProdID=359


> I remember your mentiong that sort of optical device before, Paul. But it's
> mostly all Greek to me. I do get (I think) the idea of a reducer lens
> increasing effective aperture by acting as a tele converter in reverse,
> though it sort of boggles my mind. But in that case the system would
> actually *become* the faster aperture, wouldn't it, just as an f/2.8 lens
> with 2x tele converter becomes an f/5.6 system?


Of course. The tele converter spreads the image onto a larger
area (thus less light reaches the sensor (and the f/number rises
accordingly), but you could use a larger sensor --- theoretically
at least). The reducer concentrates the image onto a smaller area,
the f/number shrinks accordingly ... and a smaller sensor than
usually for the lens without the reducer is needed, or you'll
get dark corners.

An f/2.8 fullframe lens with a 2x teleconverter (between lens
and sensor[1]) is a f/5.6 optic filling a 2x2 field of fullframe
sensors , the same lens with a 2x 'telecompressor' would be a
f/1.4 optic --- filling a "quarter fullframe" sensor.

The famous 50mm f/0.7 was a reduced 80mm f/1.0. IIRC there were
just 4 mm between lens and film.

-Wolfgang

[1] There are teleconverters and wide angle converters you can
screw in front of the lens, but they don't change the f/number.
Unfortunately, they reduce the image quality, which is why
you'll find them for P&S lenses (where you can't put them
between lens and sensor)
 
Reply With Quote
 
Wolfgang Weisselberg
Guest
Posts: n/a
 
      06-16-2011
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. 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.


ISO is ISO, but the amplification it needs to reach said ISO is
dependent on sensor quantum efficiency and sensor size.

-Wolfgang
 
Reply With Quote
 
Wolfgang Weisselberg
Guest
Posts: n/a
 
      06-16-2011
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?

- You have the same sensor area, and thanks to microlenses a very
similar effective fill factor.
- You incur SQRT(2) more read noise --- but read noise except
for the darkest areas has little influence on total noise.
- You have more information in a straight 12-to-6 MP downsample
than a 6 MP camera delivers.
- non-frame filling subjects (e.g. too distant for the tele end
and you cannot get nearer) are better resolved with 12 MPix.

The only real drawback is the larger image file size.

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.)

-Wolfgang
 
Reply With Quote
 
nospam
Guest
Posts: n/a
 
      06-16-2011
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.
 
Reply With Quote
 
nospam
Guest
Posts: n/a
 
      06-16-2011
In article <(E-Mail Removed)>, Neil
Harrington <(E-Mail Removed)> wrote:

> > If you reduce the exposure on the 4/3 camera, or are forced to
> > because the sensor overloads, you will reduce the signal-to-noise. If you
> > follow the argument through, it seems that you may be saying
> > that any camera with an f/2.8 lens is as sensitive as any other, and

>
> 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.

> 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
slower. then the exposure is the same, as well as noise and depth of
field.

> > 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.
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
comparing the first half of a string to the second half joe chesak Ruby 7 09-23-2010 03:34 AM
ie7 displaying only half of page (cuts page in half)... trint ASP .Net 4 09-11-2007 10:56 AM
Full Frame Lenses vs Small Sensor Lenses measekite Digital Photography 15 09-13-2006 03:36 PM
regexp that matches half then conditionally excludes the other half Mike Ballard Perl Misc 6 11-15-2005 03:26 PM



Advertisments