FourThirds- What it is and What it isn't

[drakon09]

Hi fellas, in view of the upcoming gathering on the 5 Apr, I'd like to take this opportunity to first explain and reinforce what is FourThirds about, as well as debunking certain myths.

Now this is not a scientific paper; neither am I hired by Olympus in any way. This is, to my knowledge, what FourThirds is and isn't; it will be phrased as much in layman speak as possible.

I hope all new adopters to this system would find this helpful; at the same time, feel free to correct my inaccuracies wherever they appear, and they will be corrected.

Thanks all.

First up on the next post, sensor sizes!

[drakon09]

Sensor Sizes for 35mm-equivalent or Similar DSLRs

Currently there are five different DSLR sensor sizes on offer, listed from the physically largest to smallest:

1. 35mm (36X24mm) - currently only adopted by Canon in their 5D and 1DS series, 3:2 aspect ratio
2. APS-C 1.3 crop - adopted by Canon in their 1D series, 3:2 aspect ratio
3. APS-C 1.5 crop - adopted by Nikon/Fuji, Pentax, Sony/KM, 3:2 aspect ratio
4. APS-C 1.6 crop - adopted by Canon for all other DSLRs below the 5D range, 3:2 aspect ratio
5. APC-C 1.7 crop - adopted by Sigma, 3:2 aspect ratio
6. FourThirds (18X13.5mm) - designed-for-digital system created mainly by Olympus and Kodak, 4:3 aspect ratio


Image Quality, Noise and Sensor Sizes

It is generally accepted that the larger the sensor, the better the image quality, the lesser the noise. The drawback is that the larger the sensor, the larger the camera, the larger the lenses. It must be noted that where image quality and noise is concerned, this is very general statement. A lot depends on HOW the image processor deals with the data coming from the sensor, e.g. although the FourThirds sensor is half the dimensions of the 35mm-sized one, the image quality is not 50% poorer nor is the noise "doubled".


Noise

Sensor noise is caused by heat. To boost ISO values is actually amplifying the sensor sensitivity, increasing heat and thus increasing noise. This noise shows itself as reddish grains on the image; the higher the noise, the more noticeable and more intense the grains.


Pixel Pitch and Density

To be more specific regarding the large sensors means better image quality statement, the factor really affecting that is the pixel pitch and density of the sensor. It boils down to this, larger the pixels are, the wider the dynamic range (DR) and the denser the pixels are packed in the sensor, the more noise it produces. This is really a very simplistic view, because sensor data transfer architecture plays a large role in this as well. The above stands true given all things equal other than pixel size and density.


Where FourThirds Stands

One of the premises of FourThirds is a smaller, lighter and cheaper DSLR system. While it must be noted that since it was established, the smaller and lighter system did not really emerge, the appearance of the E-400 in late 2006 and the new E-410 announced in PMA 07 has fulfilled that promise.

--- Next we will deal with how sensor sizes affect lens performance...

[drakon09]

How Sensor Sizes Affect Lens Performance

Sensor sizes affect lens performance in two ways: Depth of Field (DoF), and Focal Length (FL), but before that, we would first explain "Full Frame (FF) Sensors" vs "Cropped Sensors".


Full Frame Sensors

Full frame was originally used in cinematography to describe the film gate size of 35mm film. For DSLRs, it refers to the sensor size equivalent to a 35mm negative (36X24mm).


Cropped Sensors

Sensors smaller than full frame are normally expressed as a ratio of FF size against it (i.e. FF dimension size divided by smaller sensor dimension size, NOT the sensor AREA). The smaller sensors are called "cropped", because they use a proportionately smaller part of the image circle projected by a standard 35mm-system lens as compared to a FF sensor. This is described by the "Crop Factor". Lenses made specifically for smaller sensor sizes are a different proposition altogether.


Focal Length

What all this means is that in practice, the smaller sensor multiplies any given lens' focal length by the crop factor, e.g. a 70-200mm lens on a APS 1.5x sensor would equate to the apparent focal length and the equivalent Field of View (FoV) of a 105-300mm lens.


Depth of Field

Similarly, a smaller sensor would experience a proportionately increased DoF as compared to a FF sensor, e.g. a DoF at f5.6 on a APS 1.5x sensor would approximate a similar DoF at f8 on FF sensor.


Digital-Specific Lenses

The paragraphs above explain the relationship of the various sensor sizes against 35mm-system legacy lenses. Digital-specific lenses were development specifically for smaller sensors and projects a appropriately-sized image circle; therefore such lenses CANNOT be used on FF sensors and 35mm-legacy systems.

Once such lenses are utilized, the "Crop Factor" ceases to exist, because the image circle is now fully utilized by the sensor, and is no more "cropped". Because the needed image circle is now smaller, lenses can also be made smaller, and subsequently lighter.

However, for convenience (35mm-systems have been the standard for over 50 years), the focal lengths for digital-specific lenses are marked in 35mm-system equivalence.

Canon markets their digital-specific lenses as EF-S, Nikon as DX, Olympus as Zuiko Digital


Where FourThirds Stands

FourThirds sensors, being half the dimension size of a FF sensor, multiplies the equivalent FL and DoF by 2x, and since the image circle needed is theoretically a quarter the area of a FF image circle, lenses can be made much smaller, or made much brighter (larger aperture) as compared to legacy systems. FourThirds lenses are also marked in 35mm legacy terms for convenience as well.

[espion]

I think we need to think a little differently.

Tools are tools. A camera is a tool for various purposes: artistic, propaganda, selling, etc

The measure of a tool is the effectiveness and the ease with which you can achieve your purposes.

Now four thirds have been said to be designed for digital photography. What does this mean? What is the difference between film/slide and digital photography apart from the way the data is captured?

And so if you are into film then four thirds is the "wrong" tool, is it? And can you not also do digital photography with Canon, Nikon, etc?

So how much better - in whatever sense - does four thirds allow you to do "digital photography"?

And only in this context can we arrive at a meaningful understanding of all the technologies behind the four thirds standard, meaning know what are relevant and significant, and what are just hype and marketing.

Or maybe there is yet another context apart from "digital photography". Then it is surely interesting to hear what this is.

[drakon09]

It is no different from EF-S or DX; they are all digital-systems with lenses made specifically for digital.

What I'm attempting to do is to explain digital-specific systems against legacy systems retrofitted for digital; we do have first time DSLR users here new to all this. After all, FourThirds is only 6 years old.

As far as I'm concerned everything revolves around a constant; different manufacturers manipulate the various factors, but at the end of the day, it still equates to the constant.

The camera is nothing but a tool; this is fact. In this chapter, we are very privileged to have a choice of systems; as such, comparisons are inevitable, some fair, some not. This thread will attempt to address all these comparisons and what they really mean (I haven't posted this part yet). It is not an attempt to glorify or put down any particular system; do feedback if it does, it is to illustrate what it actually is, beyond all the marketing-speak.

One real difference (to me at least) between traditional film photography and digital photography is that one uses a darkroom, and the other uses a computer.

The other real difference is that digital has brought photography to the masses, the way film never did. It is more forgiving; people are more willing to be creative than to be correct. Of course there are always the downsides; wannabes intrude in territory once only trodden by people that put in blood and sweat to perfect their craft.

Thank you for your insights, espion. It will certainly influence the direction of the subsequent materiel in this thread.

[ykkok]

Originally Posted by espion I think we need to think a little differently. Tools are tools. A camera is a tool for various purposes: artistic, propaganda, selling, etc The measure of a tool is the effectiveness and the ease with which you can achieve your purposes. Now four thirds have been said to be designed for digital photography. What does this mean? What is the difference between film/slide and digital photography apart from the way the data is captured? And so if you are into film then four thirds is the "wrong" tool, is it? And can you not also do digital photography with Canon, Nikon, etc? So how much better - in whatever sense - does four thirds allow you to do "digital photography"? And only in this context can we arrive at a meaningful understanding of all the technologies behind the four thirds standard, meaning know what are relevant and significant, and what are just hype and marketing. Or maybe there is yet another context apart from "digital photography". Then it is surely interesting to hear what this is.

Agree with you totally, Tools are tools. But I think, drakon09 started this very thread to discuss about tools. As for other topics that everyone else would like to share, we always can create new thread or find other relevant thread in other categories.

[OlyFlyer]

Originally Posted by drakon09 Canon markets their digital-specific lenses as EF-S, Nikon as DX.

... Olympus as ZD or ED.

If this is about 4/3 than I think it should also mention 4/3 lenses. C & N are not 4/3.

Originally Posted by drakon09 Where FourThirds Stands FourThirds sensors, being half the dimension size of a FF sensor, multiplies the equivalent FL and DoF by 2x, and since the image circle needed is theoretically a quarter the area of a FF image circle, lenses can be made much smaller, or made much brighter (larger aperture) as compared to legacy systems. FourThirds lenses are also marked in 35mm legacy terms for convenience as well.

I would like to challange that part about lens sizes.

I know this is one of Olympus' arguments, but I think that is just bulls**t. If you look at the size of film equivalent lenses these are always considerably smaller than 4/3 lenses. Have a look at any of the OM 50mm lenses. Those are just tiny toys compared to the ED50mm which is designed for digital. In fact, if you look at the OM 100mm, even that is much smaller. And that, in spite the fact that most of those 50mm are much brighter that the digital ones also if you take the DoF factor into account. At larger focal length the size difference is even more obvious to the 35mm film lenses advantage.

I think all that about the possibilities of size being smaller or lens brighter than film lenses sounds good but it is nothing else than a marketing argument. Olympus never made such large number of dark and heavy lenses before as they do now. So, if it is possible to make them smaller and brighter, why not do it? Their lenses may be of high quality but bright are they not and nor are they lightweight, small.

BTW, sensor size is: 17.3mm x 13.0mm. Not that it makes much difference and actually your 18mm x 13.5mm is more precise to 4/3 than the one used.

[ykkok]

Film lenses need not have light path perpendicularly hitting the sensor as in digital.
Imagine this is needed for film, and I guess, those lenses should be way bigger than the current 4/3.

[Mikefellh]

I just tell people to go here:
http://www.four-thirds.org/

[Kid Shotter]

Our advantage is like this:50-200mm F2.8-F3.5=100-400mm F2.8-F3.5 in 35mm term.100-400mm F4.5-F5.6 is already 1.1kg,how huge will 100-400mm F2.8-F3.5??Another example is ZD 90-250mm F2.8 on E1 compare to Sigma 200-500mm F2.8 on 1DSMKII,how much is the weight difference?Over 10KG,that where the difference.

[cyuxiang]

Many people see photography as an art, while there are also those who see it as a science. We have books on lighting & exposure, & composition; then there are those reference manuals on technology & specifications of camera models line-up. I'm sure some of us here are just more technically inclined & would like to understand how things work in the backstage. I'm glad that drakon09 came up with this easily accessible summary right here in this forum, & it certainly paves the way for the meet-up too.

After this preliminary primary meet-up, I'll be more than happy to join in a photoshoot outing, which we can then discuss the artistic aspects of photography. Maybe that can be Part II of our newbies' introduction.

[OlyFlyer]

Originally Posted by ykkok Film lenses need not have light path perpendicularly hitting the sensor as in digital. Imagine this is needed for film, and I guess, those lenses should be way bigger than the current 4/3.

Yes. That is one reason why it is NOT possible to make 4/3 lenses smaller and faster than film lenses. That's why all the arguments that the lenses are actually small and fast is just bull***t. They are not small nor fast. May be smaller than other dSLR lenses may also be faster and higher quality for the same price but definitely not smaller or faster than OM or any other 35mm film lenses.

[microcosm]

Originally Posted by cyuxiang Many people see photography as an art,

I beg to differ... most people today do not see photography as an art anymore...

[cyuxiang]

Originally Posted by microcosm I beg to differ... most people today do not see photography as an art anymore...

Hmm, why is that so? When I walked around the 'Photography' section in Kino with its rows of huge hardcover picturebooks, it still gives me that mysterious feeling that I get with art... but yeah, I do realise that it's getting very commercial nowadays, at least.

[microcosm]

They know photography. They cannot feel photography. There is a huge difference in that.

[espion]

Originally Posted by microcosm They know photography. They cannot feel photography. There is a huge difference in that.

But you are not saying that there is no more art.

The relevant question then is to be able to see and discriminate which is and which is not.

Just because someone claims it is art does not make it so right?

[microcosm]

Originally Posted by espion But you are not saying that there is no more art. The relevant question then is to be able to see and discriminate which is and which is not. Just because someone claims it is art does not make it so right?

Art is subjective, and to discuss is to open up to a lot more arguments. Maybe when I am in the mood to start the discussions. No offense.

But at the end of the day, art is subjective.

[espion]

Originally Posted by OlyFlyer Yes. That is one reason why it is NOT possible to make 4/3 lenses smaller and faster than film lenses ....

But so what if it is bigger than film lenses but smaller than non four thirds ones?

But big or small does it matter?

Perhaps this is not the "relevant and significant" thing about four thirds.

Maybe so we should just let it pass and let it be, and let Olympus do and say anything, as long I get "high performance, affordable" lenses (and what is that?).

So then can ZD, Leica, Sigma deliver such lenses competitively compared to the other systems?

This I think is a more relevant four thirds issue.

So to answer drakon's question, what is and what isnt four thirds, four thirds isnt about lens' sizes, but better and more affordable lenses?

Maybe that is a real question.

[microcosm]

Interesting how the arguments has become, but let's not move away from the reason this thread was created. It is about what is and what is not about 4/3 System as from the originators of the system.

What is ideal/right/wrong is better left to another thread before the beginners get confused with all the extras we are adding from our experience as shooters...

[drakon09]

Wow, it is good to see that the thread had elicited all the responses from all the good people here. Since my last post here, I had a bottle of wine and a six-pack to wash it all down.

I'll try to address the advantages and disadvantages (and depending how to look at it, advantages can be disadvantages and vice versa) of FF-sized sensors against smaller ones in the next post.

But first, I'll need to edit the post about sensors, as I left out a very important factor, pixel pitch and density...