F stop question
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Old 3 Weeks Ago   #1
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Default F stop question

I have been doing a lot of reading and see what other photographers are using as an Fstop in taking their photographs using Nikons and Canons. And a question has popped up in my head. For example a shot is made at 150th sec at F32. If I were to try to duplicate that in my EM1 would my set up be 150th sec at F16. I am thinking that if a 60mm lens on my EM1 is equal in focal length to a 120mm would this thinking apply to the F stop? Maybe a stupid question but it has been bugging me for a while and I thought I would ask here.

Thanks in advance.

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Old 3 Weeks Ago   #2
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Default Re: F stop question

The aperture f/[number] is effectively a fraction that represents the diameter of the entrance pupil of a lens, where f is the focal length of the lens, the slanted line is a fraction bar or a division sign, and the number is of course the number by which you divide the focal length to get the diameter of the entrance pupil. Most lenses these days are kept wide open for viewing and focusing and stopped down just before the shutter opens. You can actually see and measure the entrance pupil if you stand in front of the camera while the shutter is open, say, for a very long exposure, or by using the depth of field preview button that many camera models have.

Typically, the brightness of the lens' image will be inversely proportional to the square of the f-number, so a lens set at f/4 will have an aperture twice as wide as the same lens set at f/8, hence will let four times as much light through. The f/8 aperture will in turn let through four times as much light as a lens set at f/16. The intermediate f-numbers, e.g., f/2.8, f/5.6, f/11, and f/22, are sized to let through twice as much light as the next higher-numbered f-number and half as much as the next lower major f-number. A lens set at f/5.6 will therefore let through twice as much light as one set to f/8 but only half as much light as one set to f/4. Assuming the same shutter speed, a lens set to a given f-number will produce an image intensity as another lens, regardless of the lens' respective focal lengths. (There may be some necessary corrections for extreme closeups, small differences in the transmittance of different lenses, and so on, but these differences are negligible for most typical picture-taking cases.

The third leg of the exposure triad is the ISO rating of the film or imager, the first two being shutter speed and f-number. Unlike the other two legs, the imager (or film) sensitivity does not affect the intensity of the incoming light as the aperture does, nor the time the light is allowed to build up the image as the exposure time does. Rather, the ISO rating is a measure of how greatly the film/imager is affected by a specific time and intensity of light. Given the same lighting conditions, therefore, a given shutter speed, f-number, and ISO rating will produce a similar final image brightness regardless of the make or design of the camera or lens.

This, however, does not necessarily mean that the images will come from different cameras and lenses looking the same, even if their speed, f-number, and ISO settings and field of view of their lenses are the same. Typically, small-format cameras will have greater depth of field and some combination of less resolution, more pixel noise (or noise reduction artifacts) and less dynamic range - the ability to show detail in both the brightest and darkest parts of an image - than the larger-format cameras. The depth of field difference is the result of the combination of shorter focal length, smaller image size, and greater magnification to achieve the final as-viewed image. Some of the resolution degradation is also the result of the smaller image size because diffraction effects will have relatively a more deleterious effect on small images. The reduced dynamic range and greater pixel noise is partly the result of smaller active areas of the pixels, which in turn means fewer individual photons landing on each individual pixel. This results in relatively more noise because of greater statistical variations in the numbers of photons hitting neighboring pixels compared to the average. A smaller signal from each pixel also necessitates greater amplification from the smaller pixels, generating more noise. The better overall image quality and higher ISO capability for printable images is one reason that full-frame cameras are so popular despite their higher price. In my opinion, the difference between full-frame and APS-C sized imagers might be noticeable but isn't really that much for the same-vintage equipment, certainly less than that between APS-C and compact "bridge" cameras.
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Old 3 Weeks Ago   #3
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Default Re: F stop question

`


Quote:
Originally Posted by mike C View Post
...... question has popped up in my head. For example
a shot is made at 150th sec at F32. If I were to try to
duplicate that in my EM1 would my set up be 150th sec
at F16. I am thinking that if a 60mm lens on my EM1 is
equal in focal length to a 120mm would this thinking
apply to the F stop? .........
Things work, meaning the numbers scale down, just
the way you describe. And using f/16 to duplicate the
look of a FF f/32 image but scaled down to M43 you'll
need to adjust the exposure. So you lower the ISO by
2EV, which approximately improves the M43 format's
IQ to equal the IQ of the FF format [which is running
at an ISO that's 2EV faster].

So, it all works out more or less a zero sum game.


`
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Old 2 Weeks Ago   #4
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Default Re: F stop question

Scoundrel has a lot of the techie bits covered, but for the Olympus (and Panasonic, err, 4/3 format) everything is halved, or needs doubled to be in a FF equivalent, so if you are trying to duplicate a full frame 150mm f/32 image, you'd half both and end up at the Olympus 75mm at f/16... but of course the ratio (height/width) will be different because of the shape of the sensor...

Not sure why you'd shot at f/16 in the micro 4/3 world though, as diffraction can make the image appear softer... but that is a different topic.
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Old 2 Weeks Ago   #5
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Default Re: F stop question

Thanks everyone, it’s a lot clearer now.
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Old 2 Weeks Ago   #6
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Default Re: F stop question

Quote:
Originally Posted by Mr. Pickles View Post
Scoundrel has a lot of the techie bits covered, but for the Olympus (and Panasonic, err, 4/3 format) everything is halved, or needs doubled to be in a FF equivalent, so if you are trying to duplicate a full frame 150mm f/32 image, you'd half both and end up at the Olympus 75mm at f/16... but of course the ratio (height/width) will be different because of the shape of the sensor...
Speaking of which, when comparing image formats of different aspect ratios, when coming up with an equivalent focal length multiplier, do you scale the long dimension, the short dimension, the diagonal, or the image area? That is an issue I haven't been able to come up with a definitive answer on.

Quote:
Originally Posted by Mr. Pickles View Post
Not sure why you'd shot at f/16 in the micro 4/3 world though, as diffraction can make the image appear softer... but that is a different topic.
I agree, and I hinted at this problem with smaller formats in my previous post. In fact, I am reluctant to close down this much in my APS-C shooting, preferring to stay at f/11 or wider.
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Old 2 Weeks Ago   #7
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Default Re: F stop question

Yeah..... I was going to state that you'd get more "height" in the image with the m43, but then I thought "I wonder if that is really true, or if you get more width...or some of both"... I think you get more height, so width is half but height is like a bit less, but then maybe not.

I never go above f/11 on my m43 shots, but I know others who take great m43 images and use f/13 or f/16... but they are usually doing long exposures like 5 or more seconds, so not sure if longer exposure affects any diffraction, or makes it "better". Never tried and pixel peeped it to death to find out.

I think full frame the "norm" is f/16 to eliminate diffraction, right? Still, wonder why the one guy was using f/32... not even sure what lens in Canon or Nikon land does f/32. Maybe a lot of them do, but not so in m43 world...
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Old 2 Weeks Ago   #8
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Default Re: F stop question

I have a Sigma 50 mm f/2.8 macro that closes down to f/32. Then again, in extreme close-up and macro photography, depth of field can be hard to come by. That may be one justification for shutting down the aperture so tight. I use that aperture to inspect my imager for dust spots, which show up clearly at such an aperture.
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Old 2 Weeks Ago   #9
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Default Re: F stop question

Even the Olympus 30mm and 60mm macro's only go to f/22.... but that is probably small enough on the tiny sensor... Could do focus stacking in camera anyway (which I have not ever tried)
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Old 2 Weeks Ago   #10
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Default Re: F stop question

Quote:
Originally Posted by mike C View Post
I have been doing a lot of reading and see what other photographers are using as an Fstop in taking their photographs using Nikons and Canons. And a question has popped up in my head. For example a shot is made at 150th sec at F32. If I were to try to duplicate that in my EM1 would my set up be 150th sec at F16. I am thinking that if a 60mm lens on my EM1 is equal in focal length to a 120mm would this thinking apply to the F stop? Maybe a stupid question but it has been bugging me for a while and I thought I would ask here.

Thanks in advance.

Since you are just starting I am going to give you a place to start learning about the exposure triangle (Fstop-shutter speed-ISO) Look up the Sunny 16 rule. Look carefully at what is happening as the light changes sunny, shade etc (learn your full Fstops numbers)
Here's a link that will help you with almost any question you may have about photography ....and no un-necessary pedantics and jargon.

Cambridge-in-Colour
and
Sunny 16 Rule


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