Sharpness Problem In Lake Shots

[Stu Engelman]

Hello,

I recently took some sunset shots of Lake Champlain from the South Burlington, VT shoreline. Most pictures came out very nicely, but toward the end I had a problem. While distant mountains were in sharp focus, the lake was not. Pictures taken earlier in the shoot did not have this problem. I don't think focal plane was my problem, as most of the lake portion is quite distant (i.e., the sharp focus for the distant mountains should have implied the same for most of the lake, but it did not in these latter pictures).

These end of shoot pics were hard to take, as the ambiant color and light value was changing by the minute. The sky was very bright, and the lake was quite a bit darker. Perhaps my sensor did not have enough dynamic range, but I have my doubts that this is the problem (clipping in the original RAW files was minimal). At any rate, HDR would not have been possible here as the conditions were changing too fast to permit captures that only differed in shutter speed.

These "problem shots" were all taken in manual exposure/focus modes, with attributes roughly at 1/500 second @ F5, ISO 100, 100mm focal length (using 40-150mm kit lens), and manual WB set using Expo-Disc neutral filter.

I've uploaded a downsampled copy of the post-processed photo (the post-processing had no effect on the issue at hand). I'll upload a 100% sample of the blurry lake region in a separate post.

Thanks, Stu

[Stu Engelman]

Here is the detail of the blurry lake w/o downsampling. Stu

[Stu Engelman]

Hello,

A final comment. The sky and clouds are quite sharp too. For some reason just the lake is out of focus.

Stu

[NewCreation517]

Hmm, well I'm not a professional but it would seem to me the combination of your low ISO and your relatively slow (compared the speed of water) shutter speed. While the clouds and sun wouldn't move a whole lot in 1/500th of a second, I think perhaps the waves would.

I'd try a higher ISO and a faster shutter speed.

[LiquidAir]

The lake sure looks out of focus to me. If you look carefully, you'll see that the highlights have been turned into small rings which are one of the common Airy disc patterns of an out of focus lens. At 100mm and f/5 you have less DoF than you think you do. If you focused at infinity, the closest features that will be in reasonable focus are about 350 feet way. It is also possible that you ended up focused slightly past infinity which would make the problem worse.

[bigpix]

These are fine for the settings you used........ the camera was focused on a point in the distance, the sun and clouds where with in the focus range, or on the same plane, but to get the water also in focus you would have had to shoot at f16 or f22...... what you have is lack of depth of field..... your equiptment is fine

[Stu Engelman]

The lake sure looks out of focus to me. If you look carefully, you'll see that the highlights have been turned into small rings which are one of the common Airy disc patterns of an out of focus lens. At 100mm and f/5 you have less DoF than you think you do. If you focused at infinity, the closest features that will be in reasonable focus are about 350 feet way. It is also possible that you ended up focused slightly past infinity which would make the problem worse.

Hi LA, thanks very much for your comment. I think your idea of focusing past infinity (i.e., past the horizon) may be a very logical answer. If this were what I did, the "near distance" of the focal range could have fallen near the far end of the lake, leaving only the mountains and sky in relatively good focus. Even with an aperture of F5, you can still get very good DOF for this type of shot (your 350 foot estimate is very close to what the lens manufacturer's DOF chart says), getting most of the lake in focus, as long as the focus is truly is on horizon. Of course, the focal near distance will move toward the opposite shore if the focal plane is extended beyond the horizon.

In short, an excellent answer. Your analysis most likely explains what happened.

Thanks very much! Stu

[Mikko]

Stu Engelman

Here is my take on the problem. The first thing is the aperture, to shallow, try some thing like F11, F16 or F22 to giver a deeper depth field. The second thing is did you use a tripod? If not I would try it again with a tripod to reduce movement and vibrations from your body.

Good Luck hope to see some re-takes.

MIK

[Stu Engelman]

Stu Engelman

Here is my take on the problem. The first thing is the aperture, to shallow, try some thing like F11, F16 or F22 to giver a deeper depth field. The second thing is did you use a tripod? If not I would try it again with a tripod to reduce movement and vibrations from your body.

Good Luck hope to see some re-takes.

MIK

Hi Mikko,

Yes, I did use a tripod. I really don't think aperture was the problem, as even at F5, almost all of the lake would be in focus, if I was focused on infinity (i.e., the horizon). I think the earlier reply from LiquidAir is the answer - I focused past infinity, which caused my near focal distance to get pushed toward the opposite shoreline. At F5, with a 100mm lense, I should be able to get clear focus from 100 yards out, which I obviously did not. This implies my focal plane was beyond the mountains on the other side of the lake.

Stu