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Old Thursday 11th May 2006, 13:18   #1
Stuart R
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Question The Four Thirds System

Hi

Can somebody offer me a simple explaination as to what this is all about and what the implications are? I am about to move into the world of macro and have decided on the Sigma 150 macro (supposed to be a great lens from all reviews read) and this is available as a 4/3rd fit. I will use the lens with either a Nikon D50 or D70. Is there an adaptor that would allow the 4/3rd version to be used with these bodies or what? If used as 4/3rd, I have read that this will double the lens value, i.e. making the 150 into a 300mm. Or have I got it all wrong???

Thanks in anticipation

Stuart R
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Old Thursday 11th May 2006, 13:28   #2
Andrew Rowlands
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I think you have it wrong Stuart

If I've read it right (!), the difference in the 35mm equivalents is down to the sensor in the camera so a Bigma (50-500mm focal range) becomes the equivalent of 82-820mm (in 35mm terms) on a Nikon but it becomes the equivalent of 100-1000mm on an Olympus!

I'm sure there are a few pages on the web explaining the technicalities somewhere, maybe someone will post a link?

Cheers,

Andy.
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Old Thursday 11th May 2006, 14:30   #3
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Quote:
Originally Posted by Andrew Rowlands
I'm sure there are a few pages on the web explaining the technicalities somewhere, maybe someone will post a link
Hi Stuart,
I believe this is the official site .. click here
There are many other sites though... happy search .. I'm not a technician
Regards,
Max
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Old Thursday 11th May 2006, 14:58   #4
Stuart R
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Four Thirds system

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Originally Posted by gmax
Hi Stuart,
I believe this is the official site .. click here
There are many other sites though... happy search .. I'm not a technician
Regards,
Max
Hi guys
Thanks for the link - most interesting. So the sensor size is doubling in the camera body hence the doubling of the lens power. So if I was to buy a Kodak or Oly body with 4/3rd sensor and mount ( which I won't) this, with the Sigma 150 macro (4/3rd fit) would equal a 300 prime? If the mount is different on the body, are existing lenses going to be able to be adapted to use the forthcoming camera bodies that have the new 4/3rd sensor inside?

Sorry if I'm being a bit thick!

Stuart R

(PS max - see you also have the Tamron 200-500 . Just starting to get to grips with this lens and I like it a lot. Have just posted a couple of shots taken with the lens.)

Last edited by Stuart R : Thursday 11th May 2006 at 15:01.
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Old Thursday 11th May 2006, 15:14   #5
Andrew Rowlands
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A 150mm prime on an Oly/Kodak (and Leica/Panasonic soon) becomes the 35mm equivalent of a 300mm. The same lens fitted to a Nikon/Canon etc. becomes the equivalent in 35mm terms, of a 240mm.

A converter to use a 4/3rds 150mm prime lens on a Nikon/Canon will not work; the lens will be further away from the sensor and will not have the correct 'back-focus' to throw a sharp image onto the sensor. Even if it did work, it would still only give the equivalent of a 35mm 240mm lens!

Maybe I'll go and Google soon, somewhere out there should be an illustration or four that will tell the tale
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Old Thursday 11th May 2006, 15:27   #6
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Wooah there Stuart!

What we are talking about here is reducing the size of the sensor:
Traditional 35mm: 36 x 24mm
Nikon D50 etc: 23.7 x 15.7mm
Canon 30D etc: 22.2 x 14.8mm
Olympus: 18 x 13.5mm
Point & shoot cameras: typically in the range 5 x 4mm to 9 x 7mm

The smaller the sensor, the "longer" the lens acts, because what is actually happening is that you are only "seeing" a smaller and smaller part of the image. So, on your D50, with a 400mm lns you see an image that looks the same as you would see with a 600mm lens on a 35mm film camera or one of the Canon 1:1 crop bodies (5D, 1DS). With an Olympus-style "four thirds" system (stupid name!) you'd get the equivalent of an 800mm field of view.

[b]But[/i] every time you reduce the sensor size, two other things happen too: you alter the depth of field, and you reduce the resolving power of the sensor (a smaller sensor doesn't get as many photons falling on it and either has fewer pixels or more noise. We are in laws of physics territory here, and you can't get something for nothing.

The current wisdom seems to be that it's not possible with existing technology to get more pixels from a small sensor than are already available without increasing noise to unacceptable levels, so the only way to get better picture quality (with current technology) is to increase the size of the sensor.

So the 4/3rds system, essentially, is a sort of a half-way-house between the typical DSLR systems (Nikon, Canon, Pentax, etc.) and the point & shoot cameras, offering more potential than you will ever get from a P&S, but less than can be provided by a larger-sensor unit - and conversely, smaller size and weight than a standard SLR but bigger than a P&S.
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Old Thursday 11th May 2006, 15:33   #7
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A couple of graphs to illustrate:-
http://nordicgroup.us/digicam/dslrcriteria/index.4.gif
http://nordicgroup.us/digicam/dslrcriteria/index.1.gif
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Old Thursday 11th May 2006, 16:15   #8
gmax
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Quote:
Originally Posted by Stuart R
(PS max - see you also have the Tamron 200-500 . Just starting to get to grips with this lens and I like it a lot. Have just posted a couple of shots taken with the lens.)
Hi Stuart,
that sounds very interesting! I'll have a look at your shots ... I'm just putting all my efforts in trying to exploit this fine lens ... I'm very satisfied of it, but not getting tack sharp images yet ... I need more practice!

I was just talking to Sussex bird man who was perhaps willing to open a new thread on this lens: tips and advice on how to improve its usage! Stay in touch...

PS I noticed you used to use a S2 ... I was very satisfied with my S1 - excellent realistic colours!

Regards,

Max
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Old Thursday 11th May 2006, 20:33   #9
Stuart R
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Four Thirds system

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Many thanks to Andrew and Tannin - I think I get it now! Doh!

Cheers
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