if I have a proper exposure of 30 seconds at f 1.8 what time will i need at f/16 can someone send me a link about f stops and longer exposures ? thanks ...
2007-12-12 05:54:20 · 5 answers · asked by aaron 5 in Arts & Humanities ➔ Visual Arts ➔ Photography
Hi edwind , I was interested in doing star trails , and wanted to know more about the long exposure concept in general ..
2007-12-12 08:34:47 · update #1
also thanks everyone for the answers
2007-12-12 08:35:15 · update #2
The above answer are well off the mark.
The reason is that you also dealing with the factor of reciprocity failure after even a few seconds. Now this failure usually increases as the exposures get longer and longer.
The above numbers are incorrect as it isn't a stop of light between 1.8 and 2. But I suspect the over all reciprocity would be about a factor of 10 once you get into exposures above 30 mins.( This could mean that you are well into hours to get the right exposure)
Now different films/ processing combinations can result in different reciprocity factor. Most will publish the reciprocity factor for each film.
This also bring up an interesting question as i have no idea if reciprocity failure needs to be considered when shooting digital. I have read both pro and con on the matter and if I were doing an important shoot then I would do a test to answer that que3stion.
http://en.wikipedia.org/wiki/Reciprocity_(photography)
2007-12-12 08:45:42 · answer #1 · answered by Michael L 3 · 0⤊ 0⤋
The formula for this would be the EV formula
EV = log2 N^2/t
where N would be the f-number and the t would be the shutter speed.
I didn't count using that formula but it should take about 42 or so minutes to take the correct exposure under the same condition with f16. Remember that f1.8 is one third stop down from f2.
Edwin your list are correct IF ONLY the first f-number is on f1.4!
2007-12-12 15:03:37 · answer #2 · answered by dodol 6 · 0⤊ 1⤋
the thing you haven given is if your shooting film of digi,
long exposures film gives reproprosity failure, digi gives noise,
i would never use F1.8 for night shots, lowest i go is f8,
so without how long you want to expose for and the medium you are using how can anyone answer you?
as a general attempt for star trails use ios100, f11 for 1 hour - 3-4 hours
a
2007-12-12 17:32:29 · answer #3 · answered by Antoni 7 · 0⤊ 0⤋
Its simple to make a chart:
f1.8 @ 30 sec.
f2 @ 1 min.
f2.8 @ 2 min.
f4 @ 4 min.
f5.6 @ 8 min.
f8 @ 16 min.
f11 @ 32 min.
f16 @ 64 min.
I'm rather curious as to why you need (or want) such long exposures. Astrophotography? Experimentation?
Here are a few sites (from the 3.4 million listed for "long exposure photographers"):
thinkcamera.com
photo.net
fredparker.com
gorillasites.blogspot.com
Have fun!
EDIT!!
Mea culpa, DODOL, mea culpa. I shall give myself 5 lashes with a flash synch cord as penance. A coiled one since they are softer hehehe.
I guess Michael L told us didn't he!
2007-12-12 15:08:01 · answer #4 · answered by EDWIN 7 · 1⤊ 1⤋
30x2, x2, x2, x2, x2, x2
30 seconds doubled for each stop between 1.8 and 16.
Your exposure time increases geometrically with each smaller aperture change.
Long exposures get weird after a few minutes because of sensor noise (digital) and reciprocity (film)
2007-12-12 14:00:29 · answer #5 · answered by Mere Mortal 7 · 0⤊ 1⤋