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Macro Questions

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Macro Questions

Postby Paz_Pazzaz » Mon Aug 27, 2018 9:33 pm

I've been working toward macro video lately. A lot. Not sure I've gotten there. I have some ideas that I am not sure are correct. Please let me know if you find my logic to be incorrect.

True macro is 1:1. That means the object photographed is captured on the film at exactly life size.

My micro 4/3 sensor is 17.3mm wide. Using a 1:1 macro lens, I should be able to take a pic of a ruler and fill the entire viewfinder screen at approx 17mm.

If I had an ultra macro lens, say a 2:1, I should be able to photograph the ruler and fill the screen with a perfectly focused area approximately 8mm wide.

Is that right?


+++++++++++++++++++++++++++++++++++

On this page, https://www.photographyblog.com/reviews ... cro_review



near the bottom, this quote:

"We used the lens with a full-frame camera in both its full-frame and APS-C formats. A full-frame sensor measures 36x24mm, so an object as little as 18x12mm will fill the frame of a picture."

On a full frame camera, shouldn't the object be 35-36mm wide or thereabouts?

Maybe they are talking about on the APS-C format?


++++++++++++++++++++++++++++++++++++++++++++

Also, is there a mathematical formula to figure out what ?degree? of macro you might get by using, say, a 100mm true macro lens in combination with a reversing ring? I've purchased a couple but haven't had much success with them in my experiments.

What about extension tubes?

I have some footage where I used a 400mm macro lens plus 31, 21, and 13mm 35mm extension tubes, a Canon mount to micro 4/3 adapter, and two micro 4/3 extension tubes, one 14 and one 10mm.

Is there a mathematical way to figure out the degree of "macro-ness" this combination would create?


thanks for your thoughts,

Paz
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Re: Macro Questions

Postby John 'twosheds' McDonald » Tue Aug 28, 2018 1:23 am

Good questions. I would be interested in the answers too. :-D
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Re: Macro Questions

Postby Bob » Tue Aug 28, 2018 4:27 am

True macro is 1:1. That means the object photographed is captured on the film at exactly life size.

At 1:1, the image projected by the lens on the film/sensor plane is exactly life size.

My micro 4/3 sensor is 17.3mm wide. Using a 1:1 macro lens, I should be able to take a pic of a ruler and fill the entire viewfinder screen at approx 17mm.

The image in the viewfinder might not show the entire capture area. Mirrored cameras typically display about 5% less or so. Mirrorless or electronic viewfinders and live view typically displays the entire capture area -- but, check your camera specs to be sure. So yes, 17mm would approximately fill the capture area width of that sensor.

If I had an ultra macro lens, say a 2:1, I should be able to photograph the ruler and fill the screen with a perfectly focused area approximately 8mm wide.

Again, yes, size wise approximately. However, focus is a different matter. The depth of focus will be narrow, if you're photographing something that isn't flat, you might not be able to get perfect focus across the entire area.


"We used the lens with a full-frame camera in both its full-frame and APS-C formats. A full-frame sensor measures 36x24mm, so an object as little as 18x12mm will fill the frame of a picture."

On a full frame camera, shouldn't the object be 35-36mm wide or thereabouts?

They are talking about using a 2:1 ratio. Earlier on the page they are explicit about this. On the second reference, they were sloppy and omitted that.


Regarding the APS-C vs FX issue. Remember, at 1:1 the projected image size on the sensor plane is the same as life size. The sensor format (APS-C or FX) determines what is captured. Since the projected image of a 1:1 macro lens on a FX sensor is the same exact size as the projected image of the same lens on an APS-C sensor. The smaller physical size of the APS-C sensor will capture a smaller portion of the image than the larger FX sensor. When the entire captured image is printed or viewed at the same size, the APS-C image will appear to be more magnified than the FX image by the crop factor.

More later...
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Re: Macro Questions

Postby sidd finch » Tue Aug 28, 2018 12:38 pm

Interesting. But what about the curvature of the lens. Would you have to calculate the curvature of the lens in the distance to the object? Unless you were using a non distortion lens.

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Re: Macro Questions

Postby Bob » Tue Aug 28, 2018 1:11 pm

Now that I've had some sleep, I can resume. :)

Regarding formulas: Yes, there are formulas you can use for the situations you described. But, they are just approximations due to the fact that real lenses are not theoretical simple thin lenses and don't behave like one. But, they can get you in the ballpark. If you want to know the actual magnification ratio you achieved, photograph a ruler and make the calculation.

Here are some sites you can use:

Extension Tubes (has a calculator)

Macro lenses, magnification, effective f/stop, depth of field

Macro reverse lens calculator

When using a reversing ring, keep in mind that the smaller the focal length of the lens, the larger the magnification. Longer focal lengths can actually reduce magnification.

For your 400mm example, add up the lengths of all the extensions and adaptors that increase the distance from the sensor and use that in the calculator. The greater the extension, the larger the magnification. But, the lens to subject distance decreases and at some point the plane of focus may get too close to the lens to be usable or even fall inside the lens. You will also have to contend with the change in effective f/stop and the reduction in depth of field.
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Re: Macro Questions

Postby Bob » Tue Aug 28, 2018 1:49 pm

Interesting. But what about the curvature of the lens. Would you have to calculate the curvature of the lens in the distance to the object? Unless you were using a non distortion lens.


The physical curvature of the lens is not usually an issue. What matters more is how well the lens is designed to keep the plane of sharpness flat. Macro lenses are better corrected for close focus distances.

Lens geometric distortion is a whole different issue.
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Re: Macro Questions

Postby Paz_Pazzaz » Thu Aug 30, 2018 9:20 am

Bob,

Thanks for confirming that my idea for testing macro with a ruler will work! And thanks for reading more carefully than I did where I got confused with the full frame macro width at 1:1 vs 2:1 !!!!

I'm not sure that I've achieved macro with my 400mm macro lens plus 6 adapters. I think it may be more like super telephoto. And I'm really surprised I was able to get anything at ALL with that many attachments. I think the fastest aperture for the lens is f/4. In retrospect it makes me wonder how I was able to have enough light. I think I'll go through that group of vids again and re-check what I said the settings were. (Yes, I talk to myself and tell myself what settings I'm using so I can learn which settings work best. :oops:) ((Crazy? Doesn't everyone talk to themselves????) ... Wish the camera would give me more metadata but I have come to realize that during a video I might change the settings while in progress.

Thanks for the formulae too. And especially the info that the longer the lens normally, the smaller the result when reversed. I didn't feel like I could get anything worthwhile out of the 400mm reversed. I'll be doing some testing on some of my shorter, higher quality lenses.

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