[MacauEric]

有朋友對我說，做咩你成日都用大光圈呢？佢話光圈越大，相片周圍會比較散……，我今天去影夜景，於是就試試用細光圈，但係影出來的相就覺得唔清，好似加了soft 咁，我剛 post 了三張相，其中兩張都係用細光圈的，出來效果就真係唔係好滿意，煩請咁多位高手，幫幫忙解答小弟的疑惑，而 f/8 或再細Ｄ的光圈會係在咩時間用多呢？多謝幫忙！

[hytong]

Ususally lens perform better - sharper (in terms of contrast & resoution) when stopped down 1 or 2 stops from their max. aperture.
OTOH, depends on your format (film size), there is a limit to how small the aperture can get before diffraction around the aperture blade affects the picture quality. For medium format the limit is about f45 and 135 about f32. (But in fact, simply avoid the extremes.)
Having said the above, most lenses are optimized at f8 or f11 where you will find most lens tests are based upon. You will be able to see more of a difference with consumer zooms than prime lens or high quality zooms.

Hope this helps

[hytong]

e.g. http://www.nikonlinks.com/zoom_lens_reviews.htm

[MacauEric]

Thanks Hytong，我朋友都係玩開 nikon 的單鏡菲林機，所以當佢同我講話大光圈時相片周圍會散（我自己就唔係好覺），可能真係菲林的感光面積大細的問題，我的 DC 就真係冇得同菲林機比，但係如果照咁講，當我們大光圈時難做到像菲林機的淺景深，而當細光圈時又出不到細光圈應有效果，咁搞法，唉……，但係我就睇到很多網友 POST 上來的照都會用細光圈，如 F8 或更細，但出來的效果都好好，莫非係 S602 的問題，還是真係正如你條LINK咁講，真係要影很遠的東西，才可以發揮 DC 細光圈的效果？其實我都係新手一名，對單鏡機的認識都在書本上（實戰都係試過幾次！），所以睇完條LINK都唔係太明白，唔知仲有冇友朋可以俾ｄ意見呢！不過都真係好多 Hytong 兄的幫忙！Thanks!! :)

[hytong]

唉...
all I can say is different equipment serves different purposes, there are times a light weight, relatively inexpensive DC "will do" and there are times only medium format will do (large prints). As long as you are happy with the quality there is no need to upgrade. (Of course this standard changes - usually going up as you dig deeper.)

for the nigh shot you've mentioned, check:
1. is the scene foggy?
2. did you use proper support?
3. did you inadverently increased sensor noise (too high ISO)?
4. did you used any "Unsharp Mask" filter?

Remember picture quality depends largely on (in order of priority):
1. camera stabilization (proper technique / supports)
2. lens quality
3. timer / cable release (with SLR - mirror lockup)
4. film/ccd/cmos quality
from http://www.luminous-landscape.com/essays/tripods_&_heads.shtml

[lungdungyee]

I check your photo (大燈爖)and your photo is over-exposure!
Not your lens problem arr.
Why over-exposure?

[MacauEric]

Hi lunqdunqyee, 我又唔係好覺佢 over 喎？我當晚用細光圈都影了很多張，因為我唔想 post 太多出來，但係真係發覺大部份都係矇矇哋，如有時間的話可以去這個網頁內睇睇當晚的另外一些相，http://www.pbase.com/macaueric/macau_2003_jan_28，希望俾多Ｄ意見我，因為我都初哥一名，但我真係發現大光圈出來的效果比細光圈清很多和靚Ｄ，又唔該咁多位高手指點吓！

[hytong]

Could it be a matter of wrong focal point? Does your tool have manual focusing?
e.g. in Dscf0036.jpg I think you should be able to read the sign at 7 o'clock position (near the bottom) if focus is correct or depth of field is sufficient.

Could it be caused by excessive sensor noise after extended exposure time?

[lungdungyee]

do you mean the sharpness matter?
One thing is how to fix the DC to take pic? is ti tripod?
If so, the small aperature cause long time to exposure.
However, some tripod are not stiff enough and they vibrate, which causes not sharpness.
Besides, for the overexpose, you can see the light source *the blurr", I think If your photo reduce 1 EV, it might be good.