Hi,It's complicated by the camera, usually. Stops run like this:.

1 - 14 - 2 - 28 - 4 - 56 - 8 - 11 - 16 - 22 and so on..

But they put in half or third values. Mostly you get third values. here they are for a small range:.

F28 - f32 - f35 - f4 - f45 - f5 - f56.

Then, of course, you get values for shutter speeds. Usually the main ones are (or should be):.

1 - - - 1/8 - 1/16 - 1/32 - 1/64 - 1/128.

But this looks wrong because they use 1/15 - 1/30 - 1/60 - 1/125.

And some use 1/25 and 1/50 and 1/100 and 1/200th..

Running in thirds we get: 1/125 - 1/160 - 1/200 and 1/250.

Best thing is to change the aperture as this makes life a lot easier. Or use EV compensation..

Regards, David.

PS To keep it simple I haven't mention the old "European" range but a search will soon add to the confusion...

One stop = 1/2 of the amount of light (be it 1/2 more or 1/2 less) that gets into the camera. This can be accomplished via the apature or shutter speed or even adjusting the light source.Good Luck..

Jellycat wrote:.

One stop = 1/2 of the amount of light (be it 1/2 more or 1/2 less)that gets into the camera. This can be accomplished via the apatureor shutter speed or even adjusting the light source.Good Luck.

A stop is half or DOUBLE the amount of light. So, 1/1000s is half the amount of light at 1/500s, 1/250s is double the amount of light compared to 1/500s. Both are 1 stop away from 1/500s, but in different directions. One half more light from 1/500s would be 1/333s which is not 1 stop..

For apertures, the rule is the same, but the numbers follow a square law. f4 is four times the light of f8, not double. So f4 is 2 stops from f8. So you need the square root of 2 (~1.4) to find the 1 stop values. That is where f2.8 and f5.6 come from. 8/1.4 = 5.6 (5.7 really) so f5.6 is 1 stop more light than f8.



Keith..

Http://photobucket.com/albums/v345/keith1200rs/..

Tony, 1 stop either doubles or halves the exposure parameters..

You can adjust by 1 stop by changing the lens aperture, the shutter speed or the ISO setting..

If you start by shooting at !SO 200 and leave the aperture and shutter speed alone, then shooting at ISO 100 will double your exposure and ISO 400 will halve your exposure. Both are a 1 stop adjustment..

If you start by shooting at 1/100th sec and leave the aperture and ISO settings alone then shooting at 1/50th will double your exposure and shooting at 1/200th will halve your exposure. Both are a 1 stop adjustment..

If you start by shooting at f11 and leave the shutter speed and ISO alone then shooting at f8 will double your exposure and shooting at f16 will halve your exposure. Both are a 1 stop adjustment..

Most cameras/lenses allow for either half or third stop adjustments to aperture and ISO settings and shutter speed settings are mostly 1 stop settings.http://www.pbase.com/tonysx..

TonyVV wrote:.

On my SLR camera the shutter positions from 125 goes down to 100,80, 70, 60, 50 etc. In my opinion 3 stops(positions) down should be60..

The opinion of the people who built your camera differs from yours .

"Stop" in this context is an abreviation of "f/stop" not "position" as you opine. f/stop (aperture) numbers are ratio between the focal length and diameter of the aperture opening. Traditional "full" stops are: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.

One f/stop change in lens aperture affects exposure by a factor of 2. Opening the aperture 1-stop (e.g. f/8 to f5.6) doubles the amount of light reaching the sensor. Closing the aperture by one full stop (e.g. from f/8 to f/11) reduces the amount of light reaching the sensor by 1/2..

1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 sec. are the traditional "full f/stop " speeds for cameras because each increment changes the exposure by a factor of 2 (with a bit of rounding between 1/125th and 1/60).

Newer cameras allow the shutter and aperture to be adjusted in 1/2 or 1/3 "f/stop" stop increments which is the source of your confusion..

To keep one's sanity it's helpful to memorize the traditional full stop aperture and shutter speed values and use them as benchmarks for the vaules in between..

CG.

Feel it - Shoot it - Understand it: Shoot with feeling always, then ask, 'How did I do that? How can I make it better?'. See: http://super.nova.org/DPR..

TonyVV wrote:.

I read a document recently that mentioned a shutter speed of 125that will be taken 3 stops down in a certain scenario, thereforethe shutter will then be 15..

On my SLR camera the shutter positions from 125 goes down to 100,80, 70, 60, 50 etc. In my opinion 3 stops(positions) down should be60..

To answer your question.

1/125 > 1/60 (1 stop) > 1/30 (2 stops) > 1/15 (3 stops).

Exposure is altered by adjusting the aperture (wideness of the opening in the lens), or by adjusting the shutter speed (length of time the shutter allows exposure for). ISO refers to the sensitivity of the film to light, or in the case of your DSLR, how much the sensor data is amplified before conversion into an image..

Increasing exposure (brighter) means either having the shutter open for longer, or using a wider aperture (F/smaller number), or using a higher ISO..

Every time you add a stop, you double the light getting to the sensor or film. With shutter speed and ISO this is pretty simple, halving the shutter speed (shutter open twice as long) will double the exposure (add one stop). Doubling the ISO will do the same (in terms of exposure)..

Aperture is a bit more tricky because it involves a root 2..

But a stop is concrete, it means something. A position is not necessarily an entire stop, a lot of cameras allow you to vary jumping in 1/3 stops or 1/2 stops etc. This is what you see on your camera. You may have moved your exposure 3 positions on your camera, but you only doubled the light..

But using a stop to refer to the doubling of light allows you to maintain exposure when altering the DOF using the aperture, or to alter the aperture to freeze the action a bit better..

Adam..

Http://www.uscoles.com/fstop.htm.

TonyVV wrote:.

I read a document recently that mentioned a shutter speed of 125that will be taken 3 stops down in a certain scenario, thereforethe shutter will then be 15..

On my SLR camera the shutter positions from 125 goes down to 100,80, 70, 60, 50 etc. In my opinion 3 stops(positions) down should be60..

I always thought that a 'stop' is the next position up or down. Howmuch is one 'stop' then..

Can someone please explain this to me..

John P..

'Any sufficiently advanced technology is indistinguishable from magic.'- Arthur C. Clarke -..

Plenty of people spent time answering your question. Don't you think it would be a good idea to acknowlegde this? Especially if you ever want another question answered.......http://www.pbase.com/tonysx..

I found this question on the aforementioned web site...............

""""Why are they called f/stops?.

I have no idea. I've never read an authoratative description of where the name came from. I have a vague memory that the defunct magazine Modern Photography did an article about it in about 1974 but my vague memory also seems to recall that it might have been the April issue."""".

F Stop is short for "Focal Ratio". For example, when a lens is set at "F-8", the diameter of the diaphram hole is exactly 1/8th of the distance from the optical center of the lens to the film plane, or 8 diameters to reach the film plane..

So, a 200mm lens, focused at infinity, and set to F-8, will have an aperture diameter of 25mm exactly..

Cheers!..

Hi,.

The usual abbreviation for focal length is "f" so the expression f/2 means what it says ie the focal length divided by 2..

Regards, David..

Lets get real technical, just for laffs. A 50 mm lens at f/4 gives a diameter on the front lens of 12.5mm giving an area of 122mm. The same lens at 1.4 is 35mm on the front lens giving an area of 961 mm. This is why you do not see a lens of 400 mm with an aperture of 1.4It would have a diameter of 285 mm..

That's the only post. I'll bet the original poster has not even read the replies yet.http://www.pbase.com/victorengel/.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Well on behalf of the original poster and everyone else (including myself) who has been enlightened by the answers I thank you all...

I have been stuck with this for awhile. Thank you. I have read books on adjusting 1/3 stop or 2/3 stop to compensate for green forests in low light etc., (Mr Green Jeans, et al). This clears that up.On to the next photographic challenge!..

I third that motion,.

I've never heard this explained as clearly as some of the posts posted here against this question..

Y'all have my thanks too d;-)..

There were some older cameras (and when a guy who has been in photography over fifty-years like I have calls a camera "old"; it is darn old!) that actually used plates with holes in them for exposure control. The plates slid into a slot behind the lens (or in between the lens elements) and had different size holes corresponding to say f/8, f/11 and so on (in those days - lenses with much faster than f/8 capability were rare or non-existent). In order to change f/stops; you removed the plate with the hole in it and replaced it with a plate that had a larger or smaller hole. You kept the f/stops in a nicely fitted wooden box..

Now for "T" (or "True") stop lenses. F/stops are mathematically determined by the relationship between the aperture and the effective focal length. There are slight variances between exposure with the same f/stop on different focal length lenses - and also on different copies of the same lens. With today's film and or sensors, this difference doesn't matter. However when one was using prime motion picture lenses and films with an ASA (older term for ISO) of 16 or slower, the difference could be noticed. This was especially noticeable when trying to cut an image shot with a normal angle lens with an image shot with a wide angle or telephoto lens.



Lenses using T/stops were developed. Each set of lenses had the transmission of light measured (not just mathematically factored) and so every lens in a T/stop set transmitted exactly the same amount of light at the corresponding T/stop as did every other lens. There was no difference between f/8 on a 50mm lens or f/8 on a 75mm lens "of that set". If the sets were mixed up, the accuracy of the T/stop did not hold true. As you would guess, the T/stop sets were astronomically expensive for their era..

I am full of trivia that no one cares about and sometimes I get a kick out of boring people like I just did..

Retired Navy Master Chief Photographer's Mate. I was a Combat Cameraman, Motion Picture Director, and a Naval Aircrewman. I also had experience in reconnaissance and intelligence photography. I have had considerable commercial photo experience in weddings and advertising photography. I am fully retired now although I dabble occasionally in dog portraiture. I presently use Canon DSLR cameras...

Rpcrowe wrote:.

Now for "T" (or "True") stop lenses..

Your explanations are fine. But I always understood that the T was an abbreviation for "Transmission"...

One interesting lens that has different light tranmission characteristics compared to what you'd normally have with it's aperture diameter and focal length is the Minolta (now rebranded as Sony) 135mm f/2.8 (T 4.5) STF.

You can read more about it here:.

Http://www.dyxum.com/...nses/SAL-135F28/Sony-AF-135-STF-SAL-135F28_review.asp.

JimChttp://www.pbase.com/jcockfield..