View Full Version : 4/3rds the smaller full frame system

20th July 2011, 12:39 PM
Something that gets my goat (slightly) when the subject of 4/3rds raises it's head on other forums is the immediate assumption that it's a 2x crop factor system.

I was always under the impression that 4/3rds was effectively a full frame system where the telecentric lenses were designed with the 17.3 x 13mm sensor in mind and nothing more.
In other words (please correct me if I'm wrong) unlike some APS-C systems you couldn't pop a larger format sensor into a 4/3rds body and a good proportion of the lens range would make use of the increased image circle.

I think part of this x2 crop conception is down to Olympus, marketing lenses as equivalent to 'X' focal length on 35mm 'full frame'. I think they would have been better served in the long run using the field of view equivalence.

Any thoughts?

20th July 2011, 12:50 PM
Surely Four Thirds is, as you say, a half frame camera system with purpose designed half frame lenses (quite a lot like the original Pen F, actually).

If you must compare it with old 35mm film, then yes you have to multiply the focal length in your head to make a comparison. I bit like you would do comparing a Pen F to a Nikon F :)

What confuses me is the uncharted waters of Nikon's various cameras and lenses. Does the Dxyz use a full size sensor or not? Does it have the built in focus motor or not? Which Nikon lenses could I buy for it that would fit on it but wouldn't work? Which of their lenses are the cheap and nasty range..? Which lenses are known to look nasty in the corners?

It's all too complicated. I will stick with Zuiko. Zuikos are either Good, Very Good or (I assume) Downright Amazing.



20th July 2011, 02:23 PM

On Wikipedia there is a comprehensive yet understandable description (http://en.wikipedia.org/wiki/Four_Thirds_system)of the various industrial standards used by various camera manufacturers. The description and list of pros/cons associated with a smaller sensor is reasonably unbiased (size/weight, depth of field, image quality).

4/3 system refers to both 4:3 aspect ration and also 4/3 inch size sensor. When used with Zuiko digital lenses it is a full frame system in that the lenses are designed to take full advantage of the sensor (or the other way around if you prefer).
In opposite to APS-C that is a "cropped" system designed to ensure backwards-compatibility with (larger than necessary) legacy lenses. Crop factor ~1.5, don't remember exactly how much. When using an OM legacy lens on a 4/3 body you also have a cropped system with a crop factor ~2.

Copied and pased from Wikipedia:
The terms crop factor and focal length multiplier were coined in recent years in an attempt to help 35 mm film format SLR photographers understand how their existing ranges of lenses would perform on newly introduced DSLR cameras which had sensors smaller than the 35 mm film format, but often utilized existing 35 mm film format SLR lens mounts.


jamie allan
20th July 2011, 02:29 PM
I agree with you both - it all appears to be a bit of a game of smoke and mirrors and is too confusing to get your head around. I've got a Zuiko 70-300 which has a large blue sticker on it saying it is the equivalent to 140-600 in 35mm terms. That just doesn't make any real sense. Increasing the magnification and lens quality whilst reducing the field of view on the lens and having a sensor that is physically just over a quarter of the area of a 35mm image doesn't make it a 140-600mm lens.
I think your idea of using field of view but also magnification factor as descriptive benchmarks would have been better. As well as that we should probably be using something like sensitivity or quality rather than the film term ISO.

20th July 2011, 03:03 PM
My own feeling is that it can really only be a true crop system if both the range of lenses and camera bodies (lens throat and mount) have the capacity to take a larger sensor and have the ability to make full use of the larger image circle.
This is physically impossible with 4/3rds and m4/3rds so it's full frame system :D

20th July 2011, 03:17 PM
Hi again,

I forgot to mention that I agree the "35 mm equivalent" isn't really fully adequate but since it seems that the focal lengths that were in practical use for 35mm system are well established and commonly referred to it makes sense for the consumers. I have even seen compact cameras marketed with specifications such as "zoom 28-112 mm F2.8-F4.0" - wow, that would a respectable telezoom. The correct figure should probably be something like 4 - 16 mm and probably you need to add a decimals to express with precision.

I have also seen cameras where the focal length is not even specified.

It becomes even more complicated to explain to the consumers since there are sensors with format 1/2.5", 1/1.8", 1/1.7", 1/1.6"

To draw a parallel: Speed limit on motorways in UK is 70 miles per hour if I am correct. If I bring my car to the UK I will need to use an equivalent of 112 km/h.

Lasty, the idea of specifying the angle of view is make senses from user/application point of view but may require a major education effort.
Parallel: Americans specify the fuel consumption in miles/gallon. Continental euros use liters/kilometers. Swedes use liters/mil (A mil is a national unit measure representing 10 km)

20th July 2011, 03:50 PM
Huw is absolutely correct, 4/3 is a full frame system. If Olympus ever design an interchangeable lens system that accepts 4/3 lenses but has a smaller sensor than 4/3, then that would be a crop sensor system.

It follows that both 4/3 and 36 x 24mm sensors are full frame. APS-C sized sensors which use lenses designed for 135 film, or developed from them are a cropped sensor system.

In my film days I occassionally used a panoramic back on my Bronica which used 135 film to produce an image 56mm x 24mm. That converted my Bronica and lenses into a cropped format system.

20th July 2011, 08:52 PM
Just to add given that it's a full frame system sometimes it's worth pausing to think what consistently high standard Olympus has achieved with their range of lenses.
I mean both optical performance, quality of build and operation.
Can you think of a bad or even average Zuiko digital lens?

20th July 2011, 09:05 PM
I don't ever remember anyone comparing the 50mm standard lens (35mm) to the 80mm medium format standard lens when 35mm came and medium format was still the popular choice.

It was just a standard focal length for that format that just gave a similar angle of view just as it should be for digital.

No one compares the 7mm standard focal length on compacts to 35mm and anyone shooting Phase One backs is not in the least bit interested what it's 35mm equivalent is, so why the obsession for comparing everything to a outdated medium like 35mm film, time to let it go.;)

Do you really need to know that this was taken on a Kodak compact at 17.7mm the eqiuvalant of a 90mm lens in 35mm terms.


jamie allan
21st July 2011, 08:28 AM
Great atmospheric image. The monochrome treatment works well. Where was this taken?

21st July 2011, 08:39 AM
"Yeah, I was using the 14-42mm (that's the equivalent of 5 and 3/8th to 14 and 3/4 inch on five by four plate)"