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what is the meaning of stop down?

Skye Lee , Apr 08, 2009; 03:02 p.m.

i know what is f numbers it's the size of the aperture.
but when it says (in photography lesson (book or magazine) "f4 stoped down to f16" what is that mean?
set my lens aperture at f4 then what?
please help me.

thanks in advanced.


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Andy Szeto , Apr 08, 2009; 03:06 p.m.

It simply means to set the aperture to a smaller number. But remember you have to set the ISO or shutter speed accordingly to compensate. Hope this helps.

Mendel Leisk , Apr 08, 2009; 03:15 p.m.

Regarding: "f4 stoped down to f16"

"f4" id's the lens (it's max aperture", and "stoped down to f16" means to set it to f16.

The expression "stop" comes from past cameras with apertures that were opened/closed to preset metal tangs, or stops.

Peter Blaise , Apr 08, 2009; 03:29 p.m.


"Stop down" ALSO usually means "stop down metering", which means lens aperture setting must be manually stopped down to your specific choice of actual aperture for each shot in order to allow the in-camera through-the-lens metering to calculate an accurate exposure, and is required for proper automatic corresponding shutter speed setting for your chosen ISO sensor sensitivity when using non-camera-linked lenses such as old 42mm thread or other old manual aperture operation lenses on new Pentax KA mount cameras, cameras that otherwise "talk" to and know how to predict and operate modern electronic lenses that are designed to work on them. Modern automatic lenses don't need to have their apertures stopped down in order to meter properly. We often say:

  • Q: Can I use my dad's old film camera's manual lenses on my new DSLR?
  • A: Yes, but be prepared to use manual stop down metering (and a dark viewfinder that's hard to accurately focus through when the lens is stopped down to your choice of a taking aperture for each shot).

Andy L , Apr 08, 2009; 03:37 p.m.

It's also a bit confusing that higher numbers mean smaller apertures. The number on the aperture ring is actually on the bottom of a fraction: it's f/4 or f/16, where f is the focal length of a lens; so on an 80mm lens, f/4 means the aperture is 20mm and f/16 means the aperture is 5mm. So when you have a lens that maxes out at f/4 and you set it to f/16, you have stopped it down by changing to a higher number.

If this seems confusing, that's because it is :)

Rob C , Apr 08, 2009; 03:38 p.m.

Like everyone mentioned, stopping down means to adjust the aperture. Not sure how familiar you are with aperature, but it is the opening of the lens. Depending on how big the hole is, or the f stop, you either let more or less light in. The smaller the F, the bigger the opening. So a f/1.4 would be an extremely big opening, while at f/22 very tiny.
That is how exposure works. When you're in low light situation, you want more light to come in so your image would be bright, but when outside on a sunny day, less light in.

Lynn Jones , Apr 08, 2009; 05:37 p.m.

Well said Andrew Lynn, this is another Lynn, Lynn Jones.

The first couple of days teaching fundamentals of photography, I always ask if the students rember taking fractions in the 4th or 5th grade, I get stunned silence. As you have clearly stated, an f stop is merely the denominator of a fraction of the focal length, the numerator of which is 1. The same is true regarding shutter speeds.

As you say, the smaller the number the bigger the opening and vice versa. About 15 or so years ago, I sprang the same fraction of F question on more than a dozen photo instructors and they didn't know the answer, now they do!


John Williamson , Apr 08, 2009; 11:49 p.m.


Just to be sure, because there are a few possible answers, could you give the complete sentence or context from that remark in the photo book ?

I suspect, is it as Mendel said, it has to do with a lens and what the photographer set it to. For instance, ...

I can take out my 180mm f2.8 lens and ,based on how much light is in the scene, and what I want to do, I can twist the dial on the lens down to f16. That is called "stopping down to f16" from it's max open value of f2.8. It's called "stopping down" because each number is an f-stop. So, if adjust the lens f-stop down to what I want, I have "stopped down". Does that make sense ?

Of course the REASON to do that is to get a lot more things in focus than I would get , if I set it to f2.8.

Skye Lee , Apr 09, 2009; 04:16 a.m.

oh i get it. first of all, thank you to all of you for your kindly explained.
i did know what is f/number (stop) means few classes and other books i read didn't said like " at f4 stop down to f16" what i was confused on this sentence was "at f4" my photography classes teachers were never said it that way. they all said "stop down to f4, or f5, or f 16, and etc not like "at f4".... "to f16". now it's all clear to me what was that means. thanks everyone. oh and i don't have the book with me... i'm very poor guy who couldn't afford to buy a photography lesson book i had to went down to barn and noble to study it. when i read that line " at f4..stop..f16" i was like...
"......." "......" "huh???" "at 4??" lol.
thanks everyone.

Peter Blaise , Apr 09, 2009; 06:02 a.m.



"Photography" is never ending learning you're getting into. There is no "one" right answer that works for everything all the time, for instance:

Earlier: "... Of course the REASON to [stop down to f/16] is to get a lot more things in focus than I would get if I set [the lens aperture] to f/2.8 ... "

Allow me to "BUT" in here:

No. Stopping down the lens aperture does "deepen" the subject field plane of acceptable focus, BUT it also extends exposure time requirements at the same capture sensitivity, and so for moving subjects and hand held cameras, that might cause less accurate focus as we'd increase the risk of capturing movement, BUT with flat subjects, the additional depth of subject field focus may not be necessary, and the decrease in the image-signal-to-diffraction ratio at smaller apertures may cause the resulting image to lack clarity, BUT some image distortions due to the lens aberrations may be reduced with smaller "stopped down" lens apertures, and so the image focus may appear clearer at smaller lens apertures, BUT you could also raise capture sensitivity (ISO) when using smaller lens apertures to permit using faster shutter exposure times, BUT that might increase capture noise (film grain, electrical noise) so the image focus may appear less clear, BUT if the subject field plane of focus or the image plane of focus shifts at different lens apertures, then if you do not refocus after stopping down, the resulting image may appear less clearly focused (hence Zeiss/Contax had a focus bracket feature, but that also accommodated auto focus anomalies), BUT ...

See? It's never ending. There's no "one" right answer.

That's why we call the science and craft of photography ... an ART !

Enjoy, have some fun, ask as much as you can, the remember, Skye, that whole web world is your encyclopedia, and Google is your table of contents, and there are many places like this one, but also Wikipedia is a place you can leave your notes behind for others to learn from and comment on as you go.

Share some pictures!


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