f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
xpatUSA Forum Pro • Posts: 12,424
Re: That "explanation" is so wrong...

Great Bustard wrote:

xpatUSA wrote:

Great Bustard wrote:

xpatUSA wrote:

Great Bustard wrote:

Take a photo of a scene from a particular position, with a particular focal length, f-ratio, and shutter speed. Then take another photo of the same scene from the same position with twice the focal length and the same f-ratio and shutter speed. Crop the first photo to the same framing as the second and display the photos at the same size. Which is more noisy?

For example, take a photo of a scene at 50mm f/5.6 1/200 ISO 1600 and another photo of the same scene from the same position at 100mm f/5.6 1/200 ISO 1600. Crop the 50mm photo to the same framing as the 100mm photo. Display both photos at the same size.

SD9, LO res, ISO 400, 70mm vs 35mm (zoom marks):

Noise display by ImageJ

Any conclusions to be drawn from this? GB? DC?

Can you go into more detail as to what the posted photos are? Thanks!

They are crops from pictures of my wellhouse, the which pictures were taken according to your suggestion quoted above.

Do the crops show equal portions of the scene, or are they 100% crops?

The shots were taken per your suggestion. By virtue of being in FastStone's comparison view, they were made equal portions by zooming the left side pane in, to be approximately the same size as the right. FastStone's comparison view allows zooming in separate panes independently when pushing the <ctrl> key.

I took a photo of the scene at 35mm f/8 1/350 ISO 400 and another photo of the same scene from the same position at 70mm f/8 1/350 ISO 400. Displayed both photos at the same subject magnification in FastStone Viewer's comparison window (the smaller image zoomed in but not smoothed).

When you say "same subject magnification", does that mean 100% view, or, for example, each crop showing 1% of the scene?

The 'crops' are virtual because of FastStone comparison settings used. I should have used a better term, perhaps. It's like when you view a Mighty Merrill file on your screen at 100% view, you see a 'cropped' view. If you look at the box above each histogram you can see the amount of zoom applied. From that, you can determine what you need, hopefully.

Took a screen capture ('Untitled-2') and opened it in ImageJ and took a histogram for each dark area, then screen-captured again for posting. Best viewed full size, of course. The bell curves should tell the story, do we think. The standard deviation at left being 40% of the mean, at right being 32% of the mean, what does that tell us?

I have nasty feeling that the zooming has negated my test and that ImageJ should not have been presented with a screen capture. I will do it with actual real crops instead and report in later.

[edit] it will be new images; I cleaned my CF card, duh [/edit]

I can answer that when I have answers to the two questions above.

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