Adaptive Lenses Hyper-focal scale.

Jason Stamper

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Hoping to get some insight. So I have these two old Canon film camera lenses that I have been using with my G5 and a Fotodiox adapter, and absolutely I love them.

Anyway they have the hyper-focal scale printed on them, and with some intense experimentation (including a measuring tape) I have found them to be pretty much spot on. I have read posts on other sites that suggest you'd have to do math, or stop down on the scale for them to be right on a micro 4/3. I know there is a difference in "field of view" but the ACTUAL focal length is the same as on a film camera, you just see less. I don't think there is any difference in magnification, or is there? Again I have found my lenses work great simply reading the scale as printed. The depth of field is almost exactly what is printed on the barrel (and that is getting picky with a measuring tape).

So what gives?

BTW, I am not sure if it matters but I am using a Canon FD 28mm SC F2.8 and a Canon FD 50mm F1.8.
 

Jason Stamper

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Also, I know about the 2x crop factor on our lenses. Does that mean magnification is doubled, field of view is halved, or both? Does that have any impact on the hyper focal scale?


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bassman

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The 2x crop factor of the m43 sensor is just that: the field of view is halved. If you think of your 50mm Canon lens projecting an image on a 35mm piece of film, then the m43 sensor represents only the center of that image - it's cropped. Hence the term.

I don't know why hyperfocal distance would vary when you mount a lens on a camera with a cropped sensor - the lens doesn't know anything about the camera it's mounted on; it's still a 50mm or whatever. Hyperfocal distance is a particular DoF calculation ("from x to infinity"), and DoF is related to the FL of the lens, the size of the aperture chosen, the size of the print and the viewing distance from the print. This is what explains the common wisdom that you get twice the DoF on a 2x crop sensor camera: you're really using a shorter focal length lens to get the Field of View you want (eg 25mm rather than 50mm on full frame), and we always knew that shorter focal length lenses had a greater depth of field. Think about a 24mm at 2.8 on your Canon compared to a 50mm at 2.8 ...

It's also noting that "magnification" and "enlargement", are concepts from the film days which have very different meanings in the digital world. Taking enlargement first, that referred to the optical increase in size of the projection of an image from a transparent positive or negative film to a print media. The greater the enlargement, the greater the image was degraded. In digital, there is never any enlargement made. We take pixels from the sensor and remap them onto the display media - a screen or print, typically. So the relevant measure is between the number of pixels in the image we are displaying and the size of the display media, along with the viewing distance. This is insensitive to whether your 16MP sensor is m43, APC, full frame, or medium format. In fact, you will create an intermediate jpeg in most cases which is again divorced from the size of the sensor itself.

So magnification, in this digital world, is better thought of as "pixels on the bird". In other words, how many pixels are covered by the part of the image in question (in the idiom, the image of a bird). Thus a given lens which projects a 10mm image of the bird on a m43 sensor will have a different "magnification" effect depending on whether it's a 4MP sensor or a 16MP sensor. So while the size of the image projected on the sensor is important, without also knowing the pixel density (i.e., 16MP on m43, or 36MP on full frame), you don't know "pixels on the bird".
 

Jason Stamper

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Wow, bassman that is great information. I guess that means my original thoughts were correct before I got myself turned around reading some of these posts. I just could not figure out why the hyper focal scale would be off when mounted on micro 4/3. I guess you just explained why my scale works just like it was designed too. Also that is good information on magnification. I think the light might be coming on...

Thanks you so much.
 

Cruzan80

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You also need to remember, when looking at the f4/8/16 markings that they imply a print size and viewing distance in that as well. Distance should still be fairly spot-on.

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tkc9789

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If I may piggy bag this thread and ask a related question.
If I attach, say, a legacy 28mm lens. What FL should be set on the camera? Is it 28mm or 56mm? Thanks.
 

Duncan

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If I may piggy bag this thread and ask a related question.
If I attach, say, a legacy 28mm lens. What FL should set on the camera? Is it 28mm or 56mm? Thanks.
Use the actual FL; so in your example, set the camera to 28mm.
 

svenkarma

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Use the actual FL; so in your example, set the camera to 28mm.
Is this still the case if you're using a speedbooster? I assumed not, so have been multiplying by 0.71.
 
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