Best Equivalence - You are OK, I'm OK

Started Jul 17, 2014 | Discussions thread
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mostlyboringphotog Senior Member • Posts: 4,897
Best Equivalence - You are OK, I'm OK

DoctorJerry wrote:

I only wish I fully understood the points you were making. I shot 5 photos using my Panasonic LF1. One each at 640x480 pixels, 2048x1536 pixels, 2560x1920 pixels, 4000x3000 pixels, and 3264x2448 pixels. As I understand what is being claimed under equivalence, I should have needed different camera settings (ISO, Aperture, shutter speed or some combination thereof), but I did not. All were shot at the same shutter speed, ISO, and Aperture, 1/80 second, F2.0, and ISO 200. And since these were all shot using Panasonic's EZ zoom feature, I was using smaller chunks of the sensor as I used less of the sensor. I was NOT using the entire sensor, but, according to Panasonic, I was using smaller sections of the sensor as I selected fewer pixels (MP). So please explain equivalence as it applies to apperture with different sensor sizes. In this test, f2.0 was the same regardless of the size of the sensor I used, or in this case, how much of the sensor I used.

GB - If each of the five photos were all of the same scene from the same position shot with the same f-ratio and shutter speed, all cropped to the same framing and displayed at the same size with the same brightness, then those five displayed photos would be Equivalent.

mostlyboring - DJ, it's a interesting question so I started a continuing thread because I wanted a crack at answering that:

I used EZ zoom on FZ30 and a while ago and if my memory is correct there were more than a passing controversy as to if it was really a zoom or gimmick for Panasonic to mislead by claiming a longer FL than the lens actually is, etc, etc. It seems we the people just like to argue...

Anyways, it's not clear if you maintained the FOV (same scene) on different image sizes by zooming your lens and if you did not change any other settings, the image will have the same brightness (equivalent exposure). This is achieved in a zoom lens as the FL changed, the aperture (the opening that does not stop the light) is also changed to maintain the same F-stop. That's why you did not need to change other settings.

So the equivalent part is not that f/2 is equivalent to f/2 on the same FL (tautology), the exposure equivalency is that the f/2 at 50mm FL is equivalent to f/2 at 100mm FL. If the lens were marked with aperture diameter, instead, that number would have needed to be changed from 25mm to 50mm. If the zoom lens were designed with constant aperture diameter and not with equivalent F-stops, when you changed the zoom, you would have needed to change the shutter speed or ISO to maintain the same brightness.

Nonetheless, if you have zoomed, the equivalency built into the camera kept you from changing anything else to keep the photo looking about the same, however, depending on where you are focused, you could notice that DoF is difference; i.e. the background blurriness would not look the same.

If you want to keep the DoF the same and keep the same scene and other aspects of the photo, just peruse GB's great posts.

Now, if you did not zoom (did not change the FL) and the scene looks the same on a different image size, I can only assume that this is SW resampling like you can convert a JPG image to different pixel/inch. In camera, this is called digital zoom. Not sure but after maxing out even on the EZ zoom, I think it will continue with a digital zoom, but not sure. This would open up other contentious thread but for now I'll stop.

And if you don't understand a word of what I've said, it's my fault - you're TV is not broken

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