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Old Mar 21, 2010, 8:16 AM   #21
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A setup with Micro 4/3 should allow focus to infinity, which is why the adapters don't require corrective optics. The reason you have a narrower angle of view has to do with the smaller sensor size, not any change in distance from the sensor using an adapter, as the flange distance is shorter with a Micro 4/3 system.

You'll have the same thing with lenses that are specifically designed for a camera with a smaller sensor. That's why you'll find much wider lenses being used for kit lenses on digital camera with sensors that are smaller than 35mm film. See this Sticky for more information:

http://forums.steves-digicams.com/ge...op-factor.html

The focal length doesn't change with sensor size, but the angle of view does.

Basically, with a smaller sensor or film size, you'll have a narrower angle of view for a given focal length lens. With a larger sensor or film size, you'll have a wider angle of view for a given focal length lens.

The main reason for the so called "crop factor" is so that users of 35mm cameras have a way to compare the angle of view they'll have with a given focal length lens using camera using a smaller sensor size.

That's why most of the kit lenses for digital camera with APS-C size sensors start out at around 18mm. For example, an 18-55mm lens on a Canon model with an APS-C size sensor will give you roughly the same angle of view you'd have using a 29-88mm lens on a 35mm camera (multiply by 1.6x to see how angle of view compares).

With a 4/3 or Micro 4/3 system camera, you have any even smaller sensor size. That's why a typical kit lens for an Olympus dSLR model is around 14-42mm, which gives you the same angle of view you'd have using a 28-84mm lens on a 35mm camera (multiply by 2x to compare with an Olympus dSLR).

Note that Depth of Field is also impacted with a camera using a smaller sensor. The smaller the sensor or film size, the greater your Depth of Field for a given subject framing and aperture. That's why it's so hard to isolate a subject from distracting backgrounds using a typical point and shoot model (with very small sensors), because they can use a *much* shorter focal length lens for the same subject framing, giving you a lot more depth of field.

With an Olympus dSLR model (or other camera with the same sensor size), you'll have roughly the same Depth of Field at f/4 for a given subject framing that you would have using f/8 with a 35mm camera. That's because a shorter focal length lens can be used to get the same subject framing at a given subject distance, and the shorter focal length lens will have greater depth of field for a given aperture and subject distance.

IOW, figure about 2 stops difference (you'd need to use f/2 with an Olympus dSLR to get depth of field that's roughly as shallow as you'd get using f/4 with a 35mm camera). That can be undesirable if you're trying to isolate a subject from a distracting background, or a good thing if you want more depth of field for getting more of the frame in focus.

A camera with an APS-C size sensor will fall somewhere in between what you'd get with an Olympus model, as compared to a 35mm camera (or dSLR using the same sensor size as 35mm film). Figure a little over one stop difference with a camera using an APS-C size sensor. Again, that's because you can use a shorter focal length lens for the same subject framing at a given focus distance. For example, a 50mm lens on a Canon camera with an APS-C size sensor will give you the same angle of view you'd have using an 80mm lens on a 35mm camera.

If you want Depth of Field that's just as shallow for a given subject framing and aperture that you'd have with a 35mm camera, then you'd need to move to a camera using the same size sensor as 35mm film. For example, a Nikon D700, Canon EOS-5D Mark II or Sony A850 (and there are more models that use sensors as large as 35mm film, but these are the lowest priced current models right now).
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Old Mar 21, 2010, 10:15 AM   #22
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All adapters being sold on eBay these days are supposed to focus on infinity (according to the description), whether the lens is a 12.5mm TV or a 400mm zoom/prime. However, I have read some people complaining that they could not obtain infinite focus with their adapters, so I think some of the real cheap adapters may not have been properly designed/made for that particular mount. I've also read about tighten up the screws attaching the mounting ring as a solution to fix the infinite focus with one particular adapter (OM mount). Adapters are not just a piece of metal/plastic that allows one to attach a lens to the camera. They must be precise for that particular type of lens depending on the optics (lens construction). If the adapter is a millimeter too short or too long, infinity focus will not be achieved.

As I mentioned, I have a variety of lenses at different focal lengths, the longest being 135mm (I actually had two different brands) and they both focused on infinity. I have two different adapters (Pentax and Canon FD mounts) from two different eBay sellers and they both work flawlessly. One of the reasons they work so well is because there is no glass element to interfere with IQ.
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Old Mar 21, 2010, 10:22 AM   #23
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Yes, I can remember reading a note on a page yesterday about some adapters being designed poorly (too thick). In that case, it was with an FD lens to 4/3 adapter versus Micro 4/3 Adapter though (although I guess we could see that issue with some of the Micro 4/3 adapters, too).
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Old Mar 21, 2010, 10:40 AM   #24
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Quote:
Originally Posted by JimC View Post
Yes, I can remember reading a note on a page yesterday about some adapters being designed poorly (too thick). In that case, it was with an FD lens to 4/3 adapter versus Micro 4/3 Adapter though (although I guess we could see that issue with some of the Micro 4/3 adapters, too).
I'm sure we could, without a doubt. The issues I mentioned above were related to m4/3 adapters. Now, the proliferation of m4/3 adapters are way larger than any other system (including 4/3), so one would think that the manufacturers of those adapters have now designed their adapters according to the correct specs. Perhaps some of the real cheap ones being sold on eBay are the old "rejects". The two I have were cheap (less than $40/ea) compared to some of the most expensive ones, and they worked as designed.
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Old Mar 21, 2010, 10:50 AM   #25
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JimC -
Great explaination. I also use the "reverse logic" to explain the same thing establishing 35mm as the standard common denominator to equalize the various sensor sizes. Obviously, I ignore the depth of field and more advanced issues and concentrate almost exclusively on FOV.

That adaption is to address a more specific problem. As a Realtor and photographer, I teach a class to other Realtors to improve their photos and marketing (or hire me to do it for them). These are people whose idea of a camera is their cell phone or an inexpensive P&S, usually with a 35mm rather than 28mm equivalent. With realestate, 35mm is 'problematic' where 28mm is the barest minimum, particurally when they see photos on the powerpoint that also include examples from my Sigma 10-20. (subtle hire me). Likewise subtle hire me with flash discussion as I just happen to include a multi-flash off camera example to compare with direct flash and limited range flash of their P&S.

It is easy for them to recognize that the sensor size is different between their P&S vs my DSLR, plus a 35mm film camera I bring in, and the need for a multiplier creating the 35mm film as the common denominator for "equivalent" FOV. And while the 6mm stamped on the front of their P&S lens may in fact physically be 6mm, it is not a 6mm FOV, but may be a 35mm FOV. That is why when the are shopping for a new camera - always a question - pay attention to the manufacturer's 35mm equivalent spec where they have done the math for them and look for a model that offers 28mm or lower.
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