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Old Apr 24, 2008, 10:03 AM   #1
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Having recently purchased an Evolt 510, I've taken the plunge into digital slr photography after many prior years as an OM2n 35mm photographer, (non-proffesional). I am pleased so far with my choice and find the camera a pleasure to use. One thing that I'm not understanding is the reference to 35mm equivilancy when referring to focal length. Anyone availible to explain why my 70-300 is considered a 140-600 mm? Thanks for any info.

Richard
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Old Apr 24, 2008, 10:15 AM   #2
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Richard, the answer is due to the size of the image sensor. It is smaller than 35mm film. Imagine shooting a light down on a piece of paper - the light hits the exact edges of the paper. That's 35mm. Now, take a smaller piece of paper and put it under the light - there is a lot of 'fall off' of light. If that light has an image, you in essence are getting a crop of the original image. Not unlike making B&W prints the old way - set up for an 8x10 print but substitute a 4x5 piece of paper for 8x10. The resulting exposure is a 50% crop.


Same type of thing going on here. For the same PHYSICAL focal length lens you're projecting onto a smaller sensor. In the case of Oly, it's like a 50% crop (if you were using full size optics). Oly has simply removed the extra optics so they don't create the extra light the sensor wont use.
So the result is you can use half the focal length (150mm) to get the equivelent field of view you would have gotten with a 300mm lens on 35mm film camera.If
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Old Apr 24, 2008, 10:26 AM   #3
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Thanks John !! Perhaps you could also "shed some light",pardon the pun, regarding depth of field . I'm use to being able to stop down to assure good focus when using 35mm equipment. Is there an "equivilant" with the E-510??
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Old Apr 24, 2008, 10:29 AM   #4
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Because of the image sensor, DOF is a bit different. Here's a handy calculator you can use. Just make sure you use t he PHYSICAL focal length - not the 35mm equiv. You can compare what DOF is like from film vs. different types of cameras for a given focal length and aperture:

http://www.dofmaster.com/dofjs.html
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Old Apr 24, 2008, 2:03 PM   #5
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Your 70-300mm on FourThirds is physically a 70-300mm...it just gives the appearance of 140-600mm on a 135/35mm camera.

The question you should be asking is why is 135 format equivalence used? So there's a common reference to compare things.

Using the example of the old C-700, it has a 5.9-59mm lens, while the C-750 has a 6.3-63mm lens. These numbers don't mean much unless you know the size of the sensor. To compare the two cameras a common reference is needed, and because 135 format is so prevalent in society that it is used as a common reference, and now you'd know that both of these cameras are 38-380mm in 135 format. The reason these two cameras use different lens focal lengths to get the same range is because they use different sized sensors.

Another example, in 135 format 50mm is said to be the equivalent focal length of the human eye (or "normal"). On FourThirds that would mean 25mm, and on medium format (645) format cameras that would be an 85mm lens to get the same focal length. If you physically measured each of those lenses you would see it's the mm that they are marked, but they all have the appearance of 50mm on a 135 format camera.

If all you use is one camera format you don't even think in 135 format anymore (unless you had to talk to someone else), but when using FourThirds I know 25mm is "normal", and if I use 645 I know 85mm is "normal". If I'm doing portrait shooting I'll use 50mm on FourThirds, 100mm on 135, and 170mm on 645.

It's just like I know that I would drive 40km/h on Canadian city streets, and 25mph on US city streets (unless otherwise marked)...I don't think "what's the equivalent of 40km/h...I know km is 1.6x the number indicated in miles, so I have to multiply the 40 by inverse of 1.6 to give me 0.625, so 40 times 0.625 give me 25 miles..." Instead I just look at the speedometer and go the speed indicated (in Canada & US speedometers are marked in both km & miles).

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Old Apr 24, 2008, 2:47 PM   #6
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RDH-Cincy wrote:
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I'm use to being able to stop down to assure good focus when using 35mm equipment. Is there an "equivilant" with the E-510??
You've received good answers above. But if you're wondering if you still need to stop down a 4/3 or any other digital lens to get maximum sharpness rather than just better depth of field, that hasn't changed in the digital world. The very good lenses are sharp even wide open, and the less-good lenses need to be stopped down at least 1 f-stop to be sharp, and maybe more. You get what you pay for, although in truth the Oly and Pana-Leica lensesin general are better wide open than the CaNikon lenses unless you have pro-quality CaNikon lenses.

Ted
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Old Apr 24, 2008, 2:50 PM   #7
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Mikefellh wrote:
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If all you use is one camera format you don't even think in 135 format anymore (unless you had to talk to someone else), but when using FourThirds I know 25mm is "normal", and if I use 645 I know 85mm is "normal".
Jeez- after 3 decades of 35mm film photography, even with the 4/3format I still think in terms of the 35mm equivalent. Are you saying there's still hope for me?

(grin)

Ted


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Old Apr 24, 2008, 5:12 PM   #8
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There'd better be hope for all of us. I went with the OM1 first then the OM2, bought my wife, then girlfriend the OM10.

Still used the OM2 now and then and have quite a few lenses for it. from the 50mm1.4 to a 600mm mirror. Even have a 5inch Celestron with a t-mount thatis really good.

But with the new camera and auto lenses I've become lazy. I have to work hard at taking better shots than the camera. Perhaps with that 70-300 and Riley's 11mm, I'd be set.

I still have to think in 35mm format though.
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Old Apr 24, 2008, 10:13 PM   #9
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RDH-Cincy wrote:
Quote:
Having recently purchased an Evolt 510, I've taken the plunge into digital slr photography after many prior years as an OM2n 35mm photographer, (non-proffesional). I am pleased so far with my choice and find the camera a pleasure to use. One thing that I'm not understanding is the reference to 35mm equivilancy when referring to focal length. Anyone availible to explain why my 70-300 is considered a 140-600 mm? Thanks for any info.

Richard
Hi,

Congratulations on a fine purchase. Everyone has already given you lots of great information relative to your original question. Given that you have extensive experiencewith a 35mm camera, I thought that at some point you might be wondering about the possible use of non four/thirds lenses on the E-510. You might like to give this a read when you have a chance. It's an article by Andrezj Wrotniak dealing with the use of Legacy Lenses on the Olympic E-xxx seriesDSLR cameras. It also goes into a great bit of detail on your original depth of field question and 35mm equivalancy question as well.

http://www.wrotniak.net/photo/43/any-lens.html

Hope you find it useful

:|

Zig






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Old Apr 24, 2008, 10:27 PM   #10
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I can't add anything to the excellent answers you've already received; except to say that if you've got a good selection of legacy Zuiko lens for your Om2, then consider a 4/3 adapter.Then download the available update from Olympus, and you can use the image stabilization (IS) built into the E510 with your OM2 lens. There is also an adapter available that includes a focus confirmation light.

Have fun with your camera!:-)
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