Lens opening - sensor coverage?

[Key]

Originating here:

with a fully open diafragma you will have much more cover over your sensor

Not quite sure what you mean here. AFAIK all of your sensor is used at any lens opening; otherwise you would have a black edge, for instance. It is my understanding that wider open means the focused beams of light hitting the sensor are brighter: they originate from a larger surface. To compensate for this with a smaller opening, you lengthen the shutter speed. Am I missing something here?

Erik

[B767-300ER]

Not AFAIK

[wild weasel]

Hi Erik...

Good question, and you're right. i expressed myself the wrong way, i meant to say, figurly speaking. What i meant is, that with wide open diafragma (as you know of course) the whole picture is much more "verzadigd" in terms of light/brightness. I have made some with a fully open diafragma, resulting in a much brighter picture, but allso multiplying the light in the some what hazy conditions, craeting fog in the picture. I've made some extreme tighten diafragma shots (F16), resulting in high twinkeling lighst spots, but allso in a much darker totall picture, though i did do some good over exposing. seemed like my camera just couldn't handle it...

Did i do something wrong? byt the way, what does AFAIK mean? thanks for your feedback, very usefull!

Greets Menno

Originating here:

with a fully open diafragma you will have much more cover over your sensor

Not quite sure what you mean here. AFAIK all of your sensor is used at any lens opening; otherwise you would have a black edge, for instance. It is my understanding that wider open means the focused beams of light hitting the sensor are brighter: they originate from a larger surface. To compensate for this with a smaller opening, you lengthen the shutter speed. Am I missing something here?

Erik

[Key]

Hi Menno,

AFAIK = as far as I know
Your observations are interesting. With film, longer exposure generally means more saturation. Additionally, with very long or very short exposures, the reciprocity effects comes in: additional exposure is necessary, beyond meter indications (details checked in The Nikon Field Guide). I always wondered if any of these effects would exist for digital sensors. I cannot exactly say what your experience means in this respect, but it seems that small lens openings are better for contrast at night while a full opening makes haze more visible. I suspect this is due to the huge difference in light intensity of mentioned parts of the image.
Thanks!

Erik

[wild weasel]

Hi Menno,

AFAIK = as far as I know
Your observations are interesting. With film, longer exposure generally means more saturation. Additionally, with very long or very short exposures, the reciprocity effects comes in: additional exposure is necessary, beyond meter indications (details checked in The Nikon Field Guide). I always wondered if any of these effects would exist for digital sensors. I cannot exactly say what your experience means in this respect, but it seems that small lens openings are better for contrast at night while a full opening makes haze more visible. I suspect this is due to the huge difference in light intensity of mentioned parts of the image.
Thanks!

Erik

Hi erik,

i think that says about it all. Cause using a small opening created more contrast indeed, but it allso made the plane less visible, despite the fact i did some good over exposing (two full stops, but maybe i had to use more, will try next time). Using the full opening of the lens, made the plane very visible, but together with that, made allmost everything visible, including haze/fog. That's why it took me so long to find an acceptable compromise.......

Menno

[EC]

There is some discussion starting on a I think related topic on another site.l

http://www.luminous-landscape.com/essay ... rers.shtml

in short it says that with a CMOS sensor the actual pixel sits in at the end of a small "tube" on the sensor and that the light has to fall directly (as in paralel) into the tube to get the best exposure. The article suggests that with large 1,4 to 2,8 lensopenings the light from the outer rings of the lens is falling so diagonally on the relatively small sensor that most is lost because it comes in at an angle relative to the tube. But with a larger apperture I could also imagine that there is more light going paralel to the sensor as opposed to diagonally through the iris of the lens.

fact is that a sensor is not as flat as a film used ot be and in many cases more resembles an LCD display which also has a limited viewing angle.

For the moment I think we are still in a speculating fase.

rgds
EC

[wild weasel]

Hello EC,

Thanks for your input, to begin with. What you are saying sounds pretty logical to me, and makes sense. Though i have to say i do not have the CMOS sensor (it's a D200, think it still has a CCD sensor?), it will probably have the same effect. By the way, the pictures are made with a rather average lens with Aperture 3.5-5.6 and 4.5-5.6....which i have to say that the pictures were all shot on F13, to have this compromise between saturation and twinkling lights.

Funny thing is though, that what you explained down here, is exactly what went thru my mind in the first place, after i saw the results. I had something like, it looks like the light is not reaching the far ends of the sensor, when using a squeezed Aperture....

Interesting, i have to say....

Grtz,
Menno