Duane Kuenstling
Active member
I see this all the time but don't understand what it means.
-
Welcome to the new forums! Please read this first. For known issues we are working to resolve, click here.
What exactly does 4/3 rds mean.
- Thread starter Duane Kuenstling
- Start date
D
Denny Colvin
Guest
D
Denny Colvin
Guest
FourThirds is the standard Olympus developed for its DSLRs, rather than building them on a 35mm camera base. See http://www.four-thirds.org/en/index.html . This includes lens mount, electrical connections, etc.
Central to this standard is the use of a 4/3 sized sensor (previous post).
Even more confusingly, the standard specifies an 4:3 aspect ratio.
Central to this standard is the use of a 4/3 sized sensor (previous post).
Even more confusingly, the standard specifies an 4:3 aspect ratio.
A 4/3ds sensor has the same size that a particular TV camera sensor used to have, which was fit in a glass tube that had a diameter measuring 4/3ds of an inch. Apparently this is still being used in the industry as a measure of sensor size.
For a better understanding of its size, it is good to know that the diagonal of a 4/3ds sensor is close to half that of a 35mm frame. In other words, its surface is approximately 1/4th of a 35mm frame.
The exact 4/3ds sensor sizes (WxH) are:
Sensor: 18mm × 13.5mm (22.5mm diagonal)
Effective imaging area: 17.3mm x 13.0mm (21.6mm diagonal).
For comparison, a 35mm frame is: 36mm x 24mm (43.3mm diagonal).
For a better understanding of its size, it is good to know that the diagonal of a 4/3ds sensor is close to half that of a 35mm frame. In other words, its surface is approximately 1/4th of a 35mm frame.
The exact 4/3ds sensor sizes (WxH) are:
Sensor: 18mm × 13.5mm (22.5mm diagonal)
Effective imaging area: 17.3mm x 13.0mm (21.6mm diagonal).
For comparison, a 35mm frame is: 36mm x 24mm (43.3mm diagonal).
Guy Parsons
Forum Pro
On a severely out of date page of mine is a picture of an arcane Vidicon tube with a bit of the same stuff as on the DPReview page about sensors.
http://homepages.ihug.com.au/~parsog/photo/sensors1.html
It is totally a pain and a pity that the modern digital camera industry insists on calling their sensor sizes by a ridiculous 50 year old standard. But I suppose calling something "4/3 inch" helps confuse the situation when it really is a 18 x 13.5mm sensor. Also "1/2.7 inch" sounds more impressive in a pocket camera than 5.3 x 4 mm.
But of course the "4/3 inch" name disappeared to become just "4/3" for the Olympus line. That seems to be accepted as a name now. As more makers join the club so to speak, there is a chance that the 4/3 idea will become a major camera standard.
The good bit is that the field of view factor compared to the arcane 35mm film cameras means a simple multiply by two of the 4/3 lens focal length lets you know how it compares to 35mm film. But you maybe already knew that.
Regards................ Guy
http://homepages.ihug.com.au/~parsog/photo/sensors1.html
It is totally a pain and a pity that the modern digital camera industry insists on calling their sensor sizes by a ridiculous 50 year old standard. But I suppose calling something "4/3 inch" helps confuse the situation when it really is a 18 x 13.5mm sensor. Also "1/2.7 inch" sounds more impressive in a pocket camera than 5.3 x 4 mm.
But of course the "4/3 inch" name disappeared to become just "4/3" for the Olympus line. That seems to be accepted as a name now. As more makers join the club so to speak, there is a chance that the 4/3 idea will become a major camera standard.
The good bit is that the field of view factor compared to the arcane 35mm film cameras means a simple multiply by two of the 4/3 lens focal length lets you know how it compares to 35mm film. But you maybe already knew that.
Regards................ Guy
Richard Pavek
Veteran Member
Four/thirds is a ratio, with the image being 4 units wide by three units high. Why do I say units? because the ratio is the same no matter what the units are. Remember the '645' format? (Minolta, Contax, Pentax, Mamiya & others) it is the same ratio. But the dimensions were (are) 6 cm by 4.5 cm. So, the shape of four/thirds is exactly the same shape as the earlier and still used 645 film.
In addition there have been sheet film of 3 inches by 4 inches and sheet film of 9 inches by 12 inches. Same ratio. (Personally I like this ratio better than the 35mm ratio.)
Hope that helps,
Richard
In addition there have been sheet film of 3 inches by 4 inches and sheet film of 9 inches by 12 inches. Same ratio. (Personally I like this ratio better than the 35mm ratio.)
Hope that helps,
Richard
D
Denny Colvin
Guest
...not FourThirds, the system, or 4/3", the sensor.
Richard Pavek
Veteran Member
Sorry,
The Oly sensor doesn't measure 4/3rds of an inch, not according to the chart you posted earlier. No dimension of the sensor measures 4/3". Not the horizontal, the vertical or the diagonal. Take the lens off your Olympus (assuming you have one) after locking the mirror up and look inside.
Richard
The Oly sensor doesn't measure 4/3rds of an inch, not according to the chart you posted earlier. No dimension of the sensor measures 4/3". Not the horizontal, the vertical or the diagonal. Take the lens off your Olympus (assuming you have one) after locking the mirror up and look inside.
Richard
D
Denny Colvin
Guest
Did you read http://www.dpreview.com/news/0210/02100402sensorsizes.asp ? 4/3" is the size of a Vidicon that could record an 18 x 13.5mm image. We're not making this stuff up!
Maybe you should you check your reading comprehension before making wisecracks...
Maybe you should you check your reading comprehension before making wisecracks...
Richard Pavek
Veteran Member
Danny,
18 x 13.5mm is a ratio of 4 x 3 (divide 13.5 by 3 and multiply it by 4 and you will get 18). It is not a measurement in inches. The fact that the lens is measured in millimeters makes that clear.
I was not making a wisecrack and my reading comprehension is pretty good, I believe.
Richard
18 x 13.5mm is a ratio of 4 x 3 (divide 13.5 by 3 and multiply it by 4 and you will get 18). It is not a measurement in inches. The fact that the lens is measured in millimeters makes that clear.
I was not making a wisecrack and my reading comprehension is pretty good, I believe.
Richard
D
Denny Colvin
Guest
Since you apparently can't comprehend Phil's explanation...
The sensor size designation started with TV cameras... the size (4/3" in this case) specifies the outer diameter of the Vidicon tube. The USABLE diagonal is about two thirds of this.
So, if the outer diameter is 4/3", and the usable diagonal is 2/3 of that, the usable diagonal is 4/3" times 2/3 = 8/9".
One inch is 25.4mm. 8/9" is 22.577777mm. The diagonal of a 4/3 18x13.5mm sensor is... (drum roll) 22.5mm.
The Four Thirds system sensor DOES have an aspect ratio of 4:3, but so does the 2/3" sensor on the E-10, and many other other smaller sensors.
The sensor size designation started with TV cameras... the size (4/3" in this case) specifies the outer diameter of the Vidicon tube. The USABLE diagonal is about two thirds of this.
So, if the outer diameter is 4/3", and the usable diagonal is 2/3 of that, the usable diagonal is 4/3" times 2/3 = 8/9".
One inch is 25.4mm. 8/9" is 22.577777mm. The diagonal of a 4/3 18x13.5mm sensor is... (drum roll) 22.5mm.
The Four Thirds system sensor DOES have an aspect ratio of 4:3, but so does the 2/3" sensor on the E-10, and many other other smaller sensors.
D
Denny Colvin
Guest
Four Thirds is a reference to the size of the image sensor. The image sensor for Four Thirds cameras is what is commonly referred to as a 4/3 type or 4/3 type sensor. These describe the type of sensor not the actual size of the light sensitive area, which is normally much smaller
The sensor measures approximately 22.3mm diagonally, not four-thirds of an inch, which would be about 33.87mm. Traditionally, the nominal size of image-sensing devices has been based on a method of calculation that was introduced when vacuum image-sensing tubes were first invented.
At the time, the outer diameter of these early 'vidicon' tubes was used to indicate their size. Unfortunately, this convention has remained despite the many advances in imaging technology that have since been made, and so the designation, "a four-thirds-inch sensor," can be a source of confusion. For this reason, many people now prefer to use the word "type" instead of "inch" when discussing the size of digital image sensors.
from http://www.olympus-europa.com/consumer/dslr_7045.htm
paultakeda
Senior Member
The 4/3" is a measurement, IN INCHES, of the OUTER diameter of the TV camera glass tube, of which the actual imaging plane is 2/3 the size.
By all rights the 4/3" TV camera tube could very well have captured a circular image exactly 2/3 the size of the actual camera tube, but circular screens weren't used.. instead, the TV standard was, you guessed it, 4:3.
CCD sensors continued to use this arcane/obsolete form of measuring and we're stuck with it. But be aware that 4/3" is the size of the sensor as defined by this standard. The 4:3 ratio of that sensor applies to all sensors that use this standard, including 2/3", 1/2", 1/2.5", 1/1.8" etc.
This was explained several times above, but after having to read Denny's continued attempts to explain this to you (all of them very clear and readable) I figured maybe you just need to read someone else's explanation for you to actually figure it out.
Mike_PEAT
Forum Pro
Most of the answers just talk about the ratio, but in terms of this camera series it also means the lens mount, the format, the whole standard created by Olympus and Kodak. See this site for the WHOLE story:
http://www.four-thirds.org/en/about/index.html
(dialup users may find it will take a while to load (I'm one of them), but it is worth it)
Rriley
Forum Pro
- Messages
- 21,846
- Solutions
- 1
- Reaction score
- 474
dang these uneditable threads
i meant to say, the APS C Image Circle
Riley
not all that counts, can be counted
i meant to say, the APS C Image Circle
--
Riley
not all that counts, can be counted
D
Denny Colvin
Guest
D
Denny Colvin
Guest
Olympus DOES say:
Four Thirds is a reference to the size of the image sensor. The image sensor for Four Thirds cameras is what is commonly referred to as a 4/3 type or 4/3 type sensor. These describe the type of sensor not the actual size of the light sensitive area, which is normally much smaller
The sensor measures approximately 22.3mm diagonally, not four-thirds of an inch, which would be about 33.87mm. Traditionally, the nominal size of image-sensing devices has been based on a method of calculation that was introduced when vacuum image-sensing tubes were first invented.
At the time, the outer diameter of these early 'vidicon' tubes was used to indicate their size. Unfortunately, this convention has remained despite the many advances in imaging technology that have since been made, and so the designation, "a four-thirds-inch sensor," can be a source of confusion. For this reason, many people now prefer to use the word "type" instead of "inch" when discussing the size of digital image sensors.
from http://www.olympus-europa.com/consumer/dslr_7045.htm
The image circle must surely be greater than 21.6mm, but where does it say it MUST be 33.87mm?
Gary Papilsky
Senior Member
http://forums.dpreview.com/forums/read.asp?forum=1018&message=22371336
Take a look here for a thread I started a while back which has some good examples. Thanks to all those who responded to that one.
--
Gary S P
When people are the art, and the art is the picture
http://www.garysworld.net
Take a look here for a thread I started a while back which has some good examples. Thanks to all those who responded to that one.
--
Gary S P
When people are the art, and the art is the picture
http://www.garysworld.net
Keyboard shortcuts
- f
- Forum