what does "stop down" mean?

[angelforever]

Hi evryone, sorry for the question but when reading about lens I find many talking about "One stop down" or "stop down"... can someone explain to me what it is about?
thanks.

 

[Chris R-UK]

http://www.photonhead.com/beginners/stops.php

Stopping "down" means decreasing the exposure, decreasing the amount of light reaching the sensor.
--
Chris R

 

[520man]

Hi evryone, sorry for the question but when reading about lens I find many talking about "One stop down" or "stop down"... can someone explain to me what it is about?
thanks.

My assumption these many years is that the term "stop" came from the aperture ring having clicks on it.



Normally you'd be looking through the camera's viewfinder and turning the aperture ring to adjust exposure. f2.8, f4, f5.6...as you turn the ring, it sort of clicks (stops) on those. That gave you a tactile way of knowing how many times you halved or doubled the exposure. Of course, you could stop the camera halfway between two of the clicks---say, a half stop or a third of a stop.

Same with the old shutter speed dials, but they were usually top mounted. 1 stop or click on the aperture was the same as 1 stop or click on the shutter speed. The ISO usually had a different system so you couldn't accidentally change it, since the sensitivity of the film couldn't be changed in mid roll, but it has full stops as well, doubling or halving.
--
Gear listed in profile under "plan."

Someone stop me before I buy again, please!
Dave

 

[dradam]

Hi evryone, sorry for the question but when reading about lens I find many talking about "One stop down" or "stop down"... can someone explain to me what it is about?
thanks.

A "stop" is a is a halving or doubling of light. This can be achieved with the aperture, shutter speed, or ISO (though people dont usually talk about ISO stops).

For aperture, the standard f-stop (different "stop" here) values are:

1 1.4 2 2.8 4 5.6 8 11 16 22 (a sequence of the powers of the square root of 2, if you're curious) and as the number gets bigger the opening gets smaller and lets in more light

Thus, since f2 is one stop faster than f2.8 it will let in twice as much light. f8 is two stops slower than f4 it lets in 25% as much light.

Likewise, with shutter speed, at 1/200 the shutter is open for half as long as 1/100 and so lets in half as much light so would be considered one stop different.

When people talk about "stopping down" a lens they are simply talking about moving the lens to a slower fstop (higher f number) and this is usually because lenses are sharper a few stops away from wide open (lowest possible f number)

 

[Hank3152]

1 1.4 2 2.8 4 5.6 8 11 16 22 (a sequence of the powers of the square root of 2, if you're curious) and as the number gets bigger the opening gets smaller and lets in more light

This just adds to the OP's confusion.........obviously a smaller opening lets in less light
--
Regards,
Hank

 

[dradam]

1 1.4 2 2.8 4 5.6 8 11 16 22 (a sequence of the powers of the square root of 2, if you're curious) and as the number gets bigger the opening gets smaller and lets in more light

This just adds to the OP's confusion.........obviously a smaller opening lets in less light

Yes, a typo indeed.

 

[Deleted1929]

"Stops" are units of exposure. For example,, when you double the ISO you add a stop. When you half the ISO you subtract a stop. Likewise when you half the shutter speed you loose a stop and when you double it you gain a stop.

With lens aperture you gain a stop by making the aperture wider by a certain amount and loose a stop when you make the aperture smaller by a certain amount.

The term "stop down" is only applied to aperture. Typically lenses are not at their best ( with exceptions ) when wide open ( at their widest aperture ). You would "stop down" to gain sharpness. Sometimes you might have a lens that has poor contrast when wide open and you might see someone say it improves when stopped down.

Aperture whole stops are easy to calculate.

Start with the numbers 1 and 1.4

Double them. - 2 and 2.8
Double the results - 4 and 5.6
Double those results - 8 and 11 ( roughly )
Double those results - 16 and 22

The sequence f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22 is the sequence in whole stops from widest aperture to narrowest.

You can have aperture values apart from these, but this is the reference sequence.

Likewise you have ISO values a stop apart 100, 200, 400, 800, 1600 - doubling each time.

You can read this for more information.

http://www.fredparker.com/ultexp1.htm

--
StephenG

Pentax K100D
Fuji S3 Pro
Fuji S9600

 

[Barrie Davis]

Hi evryone, sorry for the question but when reading about lens I find many talking about "One stop down" or "stop down"... can someone explain to me what it is about?
thanks.

The "stop" was a metal plate with a hole in it inserted into the lens through a slot in the side. It was called a "stop" for no other reason than because it "stopped" some of the light getting through.

Back then a series of different sized plate holes were used to allow different amounts of light into the camera during the exposure. The spare metal "stops" were kept in a little leather pouch that lived with the lens.

These days we use continuously variable iris diaphragms made of overlapping metal leaves. They act like the variable iris in your eye.

The act of choosing a smaller aperture called "stopping down" the lens.

Your eyes do this automatically.....

Go to the bathroom in the dark of night and position yourself in front of the mirror. Then switch ON the light and quickly look directly into your eyes in the mirror.... What you will see is the irises in your eyes instantly "stopping down" as they react to the sudden and unaccustomed brilliance!
--
Regards,
Baz

Well, I'll see your Cher, and your Streisand... and I'll raise you an Alice Babs!