yellow filter...?

[joe_hoyle]

<p>i have just got a hoya yellow k2 filter but it does not say how much i should increase the exposure to take the filter into account. Does anyone know? also is this the equivalent to a y2?</p>

<p>cheers</p>

[mukul_dube]

<p>I don't know about this k2 thing, but the filter factor for yellow is usually 1.5 or 2.</p>

[lilly_w]

<p>Mukul, it depends on which yellow filter is being used. There are various levels of density among colored filters. In generic terms they might be considered light, medium and dark/deep. Joe, you increase the exposure by the respective <em>filter factor</em> of a given filter. A K2 filter (medium yellow) has a <em>filter factor </em>of 2, which is to say 'double the amount of light', which equates to a loss of one stop. Light yellow has a filter factor of approx 1.2 to 1.5 (loss of 1/3 to 2/3 of a stop, respectively). Dark/deep yellow has a filter factor of 3 (loss of 1 2/3rd stops). Not sure what a Y2 is. Do a google search to learn more about the ratio between filter factor and # of stops.</p>

[craigd]

<p>If you are using a camera with a TTL light meter, the meter will adjust for the filter automatically. If you are using a non-TTL meter, then add 0.5 to 1 stop of exposure for a medium-yellow filter. Actually, shooting B&W film, I often simply ignore a yellow filter and the shots come out just fine; B&W film has more than enough latitude for it. I generally add one stop for an orange filter and two for red.</p>

<p>I think K2 and Y2 are the same thing -- different vendors use one name or the other. Both are basically a Wratten #8.</p>

[joe_hoyle]

<p>Thanks i have just had a look and there is a little thing on wikipedia which explains it. I also have a red 25a filter which i am told has a filter factor of 5. So 20% of light is transmitted, therefore i have to make up the other 80%. But then i don't understand how i can equate to this to the amount of f stops as it will be in 1/3 stop increments. </p>

<p>ahh!!</p>

[henryp]

<p>A K2 yellow filter is one stop (filter factor = 2).</p>

<p>Henry Posner<br /><strong>B&H Photo-Video</strong></p>

[joe_hoyle]

<p>I want to be as accurate as possible, i am studying the zone system and have just tested the iso of my film. I am shooting on a 5x4 shen hao.</p>

[craigd]

<p>Filter factors convert to stops pretty easily. Filter factors are multipliers, so a factor of 2 means half the light. One stop also means half the light (or double, going the other way). A factor of 4 means one-quarter the light. Two stops also means one-quarter the light (or four times). You get the idea.</p>

<p>The 1/3 stop increment issue is a non-problem. If you calculate that you need 1.5 stops and the closest you can get is 1.33 or 1.67, that's a difference of only 1/6 stop, which isn't likely to be noticeable.</p>

[Matthew Currie]

<p>Not entirely pertinent in this case, but since the subject arose, I will mention that not all through lens meters will read filters correctly. Older CdS meters, such as those on the old Nikon F, tend to underexpose a red filter by about a stop, for example, so if you're depending on the meter for a reading it's probably a good idea, at least the first time or two, to take an unfiltered reading and check if the filtered reading agrees with the published factor.</p>

[jim_jones3]

<p>For an A25a filter, I use three stops more exposure; for orange, two stops; and for medium yellow, one stop. It might not be precise enough for someone who exposes by the Zone System and uses a densitomiter on film, but is easy for this aging mind to remember. The precise filter factor should vary slightly with different light sources and film characteristics, especially with blue sensitive and infrared films. </p>

[steve m smith]

<p>I think I use the same numbers as Jim. Red = +3 stops, orange = +2 stops, yellow = +1 stop.</p>