A Tedious Explanation of the f/stop
The most important thing to know about these f/stop numbers is that, from each number to the next, the aperture decreases to half its size. Thus allowing 50%. This decision will dictate my f-stop. When you are setting your f-stop there is a huge range to choose from. The smaller the f-stop number the. In fact, each of the numbers in this sequence is a halving/doubling of the amount of light from its It is useful in relation to the adjacent f/stops.
Here, we describe a preliminary study on whether two widely-used tests of inhibition—the Stroop  and stop-signal  tasks—measure the same type of inhibitory ability.
Both tasks are often used to index prepotent response inhibition.
However, the extent to which they measure the same construct is unclear. In the classic color-word Stroop task see  for a reviewparticipants are asked to name the ink-color in which a color-word is printed e.
Interference, also known as the Stroop effect, occurs when the relevant i.
Compared to a neutral e. Facilitation occurs in the congruent condition where the two dimensions lead to compatible responses, resulting in faster and more accurate responses. Stroop facilitation and interference effects are usually attributed to word-reading being the more practiced and hence more prepotent stimulus-response dimension than color-naming. Accurate performance on incongruent trials is commonly thought to be achieved by selective inhibition dampening the fast automatic activation associated with word-reading, so the slower deliberate route associated with color-naming may be completed .
Stroop interference, measured by the difference in latency or accuracy between a the incongruent and neutral or b incongruent and congruent conditions, is typically taken to reflect inhibitory ability or efficiency. Such choice-reaction-time tasks typically involve centrally presented stimuli and manual key-press responses, and are commonly used in cognitive psychology to study individual, clinical and developmental differences in the inhibition of responses.
Other countermanding paradigms have been used to study the inhibition of saccadic eye or arm reaching movements to peripheral stimuli in both monkeys  and humans . Relationship between the Stroop and Stop-Signal Tasks Both the Stroop and stop-signal tasks can be seen as requiring the inhibition of a prepotent or well-practiced response.
Findings that performances on the two tasks are correlated with each other or load on a common factor support a common underlying construct .
In contrast, there is also evidence suggesting that the two tasks may index different constructs. Stroop and stop-signal measures of inhibition have been found to be uncorrelated or loaded onto different factors  ; exhibit different developmental trajectories  ; show different patterns of performance impairment in clinical subgroups e.
It has been argued that the two tasks may index different aspects of inhibition—e. Some have even argued that, other than the cancellation of motor responses e.
For example, it is possible that Stroop interference may be accounted for by proactive mechanisms such as sustained activation of goal or task representations . On the other hand, low correlations may also arise from measurement issues.
The literature sees a mix of accuracy and reaction time RT scores from different task variants, often computed in different ways across studies. Variation in task contexts Stroop effects can be elicited using a variety of stimuli, including the classic color-word version, but also with stimuli such as numerals and picture-word .
Whether Stroop interference is correlated across task variants can depend on the degree of similarity between tasks e. Stroop interference RT is calculated equally often as the mean latency difference between incongruent and neutral conditions, and between incongruent and congruent conditions.
The neutral control is sometimes preferred over the congruent condition which can be confounded by individual differences in facilitation effects. On the other hand, the congruent condition serves as a closer control for the incongruent condition in terms of stimulus-response dimensional overlap.
A weak or slow inhibitory process is hypothesized to benefit Stroop performance most at slower RTs, giving an accurate-trials RT distribution a negative skew, and a steeper interference delta slope . Though not conventionally used, the recent years have also seen Stroop interference begin to be examined in terms of inverse efficiency IE —an adjusted RT measure derived by dividing RT e.
Conventional RT measures are typically based on accurate trials only. The IE score adjusts RT performance for sacrifices in accuracy that might have been made in favor of speed.
A mean RT achieved with high accuracy will have a smaller IE i. The hybrid IE score may be especially useful when there are individual or developmental differences in speed-accuracy trade-offs, in which case accuracy and RT data can show different patterns of results . In the figure, several f-stops were skipped to better illustrate the point. Also note the scale above only shows full stops, disregarding fractional stops that exist between one full stop and the next.
Whole stops are important because they represent the admittance or blockage of half or double the light.
What is the aperture, f-stop?
Aperture and Depth of Field The aperture has a major role in determining not focus per se, but depth of field. The greater the f-stop number, the deeper the depth of the field is, meaning that more objects are likely to be sharp in frame. Likewise, the smaller the f-stop number, the shallower the depth of field is. The diagram below demonstrates the relationship between aperture and depth of field.
Assume that the camera is on the left side of the image, where lens and aperture readings are located. With a mm lens, the plain of critical focus is at 4 meters approximately 13 feet from the camera. The depth of field of an image produced at a given f-number is dependent on other parameters as well, including the focal lengththe subject distance, and the format of the film or sensor used to capture the image.
Depth of field can be described as depending on just angle of view, subject distance, and entrance pupil diameter as in von Rohr's method. As a result, smaller formats will have a deeper field than larger formats at the same f-number for the same distance of focus and same angle of view since a smaller format requires a shorter focal length wider angle lens to produce the same angle of view, and depth of field increases with shorter focal lengths.
The Relationship Between F-Stop and Shutter Speed
Therefore, reduced—depth-of-field effects will require smaller f-numbers when using small-format cameras than when using larger-format cameras. The larger number of elements in modern lenses allow the designer to compensate for aberrations, allowing the lens to give better pictures at lower f-numbers. Even if aberration is minimized by using the best lenses, diffraction creates some spreading of the rays causing defocus.
Light falloff is also sensitive to f-stop. Many wide-angle lenses will show a significant light falloff vignetting at the edges for large apertures.
Treating the eye as an ordinary air-filled camera and lens results in a different focal length, thus yielding an incorrect f-number.