Wide aperture - Pictures out of focus

Started Aug 3, 2014 | Discussions thread
Truthiness Regular Member • Posts: 122
ISO is not what you think

tedolf wrote:

Truthiness wrote:

tedolf wrote:

Truthiness wrote:

tedolf wrote:

Christof21 wrote:

AnthonyL wrote:

Jizzy wrote:

tedolf wrote:

So, stop down to about f/8 and you will get a DOF of about 8-10 inches.

Now, you have to ask yourself why did you spend so much money for a f/1.8 lens when you really can't use it wide open for the types of photo's you want to shoot!


Yeah, thats what I am asking myself now

Yes - just get a P&S - no probs with DOF there!

Or stop down the lens, same results. This is not a "problem"

There are some situations where you can't stop down. Like where you need a faster shutter speed to avoid subject motion blur, e.g. father/daughter waltz at a wedding.

You can always stop the FF down 2 stops compared to your beloved m43.

Ok, now what just happened to your shutter speed?

I kept it the same? What's the problem?

Went from 1/125 to 1/30 sec., didn't it?

No. Why woud it? If I feel like it, I'll up the ISO,

caught you!

Nope. You just are a bit out of your depth.

Now, what if you want the better dynamic range and lower noise of base ISO, or extended low ISO?

Why do you think your beloved Olympus OM-D_E-M5 (I assume that's your tool as you mentioned it earlier) has a better DR or lower noise at it's base ISO than for example Nikon D800 at ISO 400?


Here are some charts for your comfort. I added some helpful green lines:

I hope those help.

though I often shoot at ISO 100 (as I shoot raw and my camera is close to being ISOless).

So, you have a problem now don't you?

No. I do understand what noise is, where it comes from and how much there is it on different cameras. You might want to read http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/ as a quick primer on the subject.

Maybe you don't understand that 1/125 on both cameras, the m43 needs two stops faster f-stop to allow the same amount of light to be used to draw the image on the image plane.

not for proper exposure.

If the image created by both exposures are the same (they are), I can take images on both and apart from the aspect ration you would no see any difference in the FF 1/125 f/4 and m43 1/125 f/2 outputs. They would be identical. So if I were to blind test you, how could you say which has the "proper exposure" (whatever that means).

Thus the image quality will be the same with these settings (1/125 with f/4 vs. f/2).

It wont be the same, if you changed you shutter speed (moving subject) or your ISO (dynamic range, noise).

But different cameras have different DR and noise characteristics. Essentially FF has 2 stop advantage in all the relavant image quality metrics, thus stopping down 2 stops just equals the image qualities.

Sign, 1/125, f/4 on FF gives essentially IDENTICAL image to 1/125, f/2 on m43.

No it doesn't.

Yes it does.

It is two stops darker

Darkness and brightness is matter of processing, not an inherit propert of the raw-files or the captured image data.

If both sensor capture identical information (as they would, apart from aspect ratio and different sensor efficiencys etc.), how could you say that "one is darker"?

The FF lens at f/4 draws an identical (though scaled to be four times as large) image to m43 at f/2. Thus, the same amount of light is planted on the image plane. If the exposure lasts the same time, the image quality will be the same (disregarding sensor efficiency differences etc.)

None of that matters. What matters is motion blur, dynamic range and noise, and those things are not the same with those settings.

Actually if the senors have the same QE and read noise, they are.

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