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Picture quality query.

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Amalgam2 View Drop Down
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Post Options Post Options   Quote Amalgam2 Quote  Post ReplyReply Direct Link To This Post Topic: Picture quality query.
    Posted: 21 December 2016 at 17:10
I have been photographing a night time river scene recently, and I'm very, very pleased with the results. On reviewing the photos on my PC, I note some variation in the sharpness, ( at high magnification). I have looked at the aperture values, and decided that some wide values and closed down can be equally sharp. My conclusion is that the main factor must be the difficulty in adequate focussing in poor light conditions. My NEX3 preview screen shows the scene very grainy and makes for difficult focussing.I use a tripod and do try to pre focus on a "Sharp" edge. This seems to be ok most of the time. Do you agree that this is the case...and can I do more to achieve more consistency? Thanks Ian.

http://i1212.photobucket.com/albums/cc451/ipri/DSC08212_zpskd2mjnfe.jpg[/IMG][/URL]
 



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Miranda F View Drop Down
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 21 December 2016 at 23:20
It is a lovely picture. What do you think is wrong with it? (Maybe a little less sharp on the rhs?)

I can't get a zoom view on my PC, so I can only judge sharpness at full size, but it looks fine at that. I love the star-burst on the light source, BTW.

If you were expecting more sharpness, could you tell us what lens you used, aperture, shutter speed, etc?

It looks a wide-angle view so everything should be at infinity, which should ideally put the whole image equally sharp/blurred; if it hasn't done, then this might imply either field curvature or decentering-type issues or mounting (this cropped up in a different thread recently). Presumably you used a tripod, and the Nex3 doesn't have IBIS, does it?
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Post Options Post Options   Quote ratboy Quote  Post ReplyReply Direct Link To This Post Posted: 21 December 2016 at 23:51
Hi Ian, do you have the EXIF ? I know this scene well living not too far from here and given the wide angle and the distances involved shooting at around F8 would have kept everything razor sharp so it could be diffraction if shooting around F16 and above. Given it has been somewhat windy recently, is your tripod rigid and stable ? Even the smallest of vibrations from wind can cause an issue.

Do you use focus magnifier when focusing ? It helps particularly when focusing with a grainy live view image. Were you manually focusing ? I am assuming so. Can you remember where you chose to focus ?
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Post Options Post Options   Quote Steve-S Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 00:08

Agreed that more info (what lens? Camera/lens settings? etc...) is necessary to make informed comment.

You mention using a tripod -- did you also use the self-timer or a remote control?

Also agreed that a focus at/near Infinity seems likely to be most useful.
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Post Options Post Options   Quote Amalgam2 Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 13:41
Thanks....30mm sigma / 25 secs @ F 18 / 200ISO. I used a 2 sec timer setting .   regards

Miranda...thanks, I am delighted with it! never thought I'd be able to get this sort of pic. My comments re. sharpness were really just to confirm my own suspicion that extreme aperture setting were less important than a good focus point.I think I focussed on the group of buildings....At this distance (approx. 1/4 mile to the arched bridge) does the camera see every thing as Infinity?

Ratboy...I'm very local as well ( Newcastle Upon Tyne for non UK folk).I have a Sony NEX3...in the low light, half pressing the shutter brings a poor , grainy image..the semi auto focus kicks in, then with fine tuning with the focus ring, the image is magnified....and totally useless...so I just trust the auto and aim for an edge to force a decent focus......then off to the Crown Posada!

I do suspect a degree of chance in this light? Regards Ian
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Post Options Post Options   Quote Amalgam2 Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 13:48
PS..ratboy...I have a small pocket size tripod, which is great.Do any cameras allow some sort of way to show where the focal point was?...suspect a lot of smiles at this!!
 



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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 14:07
I think the f18 leads to some diffraction unsharpness. Also the slightest tripod instability or a bit of wind can lead to motion blur during the long exposure

Conventional dof at f16 with a 30 mm lens on APS-C is from 1,84 meter until infinity.

If you reduce the "circle of confusion" in the calculation to 0,005 mm (the size of 1 pixel) it's still sharp from 10,1 meter until infinity (when focusing at 11,25 meter).

So I'm not surprised that some of your pictures at larger apertures (so less diffraction and less chance of motion blur) turn out with better sharpness. Dof is not a problem at f8 either, even with a very small circle of confusion at 0,005 mm dof extends from ~18 meter to infinity when focussing around 22,5 meter which is more then plenty for this scene.

Technical aspects aside I like the picture, maybe crop off (or point slightly to the right) to avoid the busy yellow bright light and reflection on the left. The rest is nice and cool, both the scenery as well as the reflection in the water.    
Mind the bandwidth of others, don't link pictures larger then 1024 wide or 960 pix high, see here
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Post Options Post Options   Quote ratboy Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 14:35
Originally posted by Amalgam2 Amalgam2 wrote:


Ratboy...I'm very local as well ( Newcastle Upon Tyne for non UK folk).I have a Sony NEX3...in the low light, half pressing the shutter brings a poor , grainy image..the semi auto focus kicks in, then with fine tuning with the focus ring, the image is magnified....and totally useless...so I just trust the auto and aim for an edge to force a decent focus......then off to the Crown Posada!

I do suspect a degree of chance in this light? Regards Ian


As Pegelli said, the slight softness is probably diffraction. Even with a grainy image I normally still focus completely manually for scenes like this. With the camera on a tripod it's easy to do. Like your style though - take a shot and then off down the pub !
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Post Options Post Options   Quote Steve-S Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 17:49

Note that a very-grainy back screen is NORMAL in low-light and UNAVOIDABLE. Remember that it's displaying 24fps-30fps; effectively, the back screeen (or EVF) cranks-up its own ISO to compensate for the very-low ISO of the main sensor; it's probably similar to you shooting that scene at f/18 & 1/30 sec, with the ISO cranked up as-needed to compensate. Does that make sense?

As-noted wind can have a major impact on sharpness (especially with the little / lightweight tripods).

Also: road vibrations ! If you're on or near a roadway (or bridge!!!), passing traffic may vibrate the surface your tripod sits upon, as might buffeting wind from fast-moving vehicles).

In an industrial area, factory & shipping operations can cause similar vibrations to traffic.

In a building, slamming doors and kids' running feet (or adults heavy tramping) can shake things noticeably; I have even felt wind-vibrations indoors, shaking buildings!.

Make sure to minimize these and other possible external effects... You guys DO finally have your Wooly Mammoth Problem under control, right? Did you check over your shoulder as you shot?


===

Once you feel ALL the external issues are well-controlled, try these settings:

f/8 -- completely avoid diffraction

2 to 8 sec. shutter -- less time, since you have wider aperture; play around with the "right" setting for the conditions (which may be brighter or dimmer, depending on moon/stars/overcast/etc...)

ISO 200 -- should be fine; or 160, or 100, or 320... another item you CAN play with, to help nail the exposure.

Manual Focus -- Turn off the AF !   Manually-set to infinity-focus (the difference between 1/4 mile and infinity is largely inconsequential to a 30mm lens), then back off a bit (you want to back off because SOME lenses actually hard-stop the focus just "beyond" infinity). Since your depth of field is so large, you should still have everything in focus.

And let us know how it goes!


Edited by Steve-S - 22 December 2016 at 18:48
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Post Options Post Options   Quote bms44974 Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2016 at 18:28
and don't forget to turn SteadyShot off when on a rock-steady tripod.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2016 at 08:39
I've always liked taking night pics and I agree with most of the thigns said above, except that in film days I would usually be using 1/30 sec or so (maybe at f5.6-f8). In the days before decent auto exposure that worked in the dark, I would take a reading on a bright wall nearby, then back off so many stops for average brightness, then one more for reciprocity failure (100ASA film), and so on.

In film days I tended to use the Rollei 35 for this on a small tripod, usally on a brick wall. Today's digital cameras are so good you can almost hand-hold them, but you still need a firm base to avoid vibrations. I've tried it on bridges and these don't usually work with the vibrations.

But even in the best circumstances I wouldn't expect everything to be pin-sharp, and what you have looks pretty good to me.
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Post Options Post Options   Quote Amalgam2 Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2016 at 09:48
Thanks for all the help...Happy Christmas to everybody. More pics soon I hope! Ian
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Post Options Post Options   Quote Steve-S Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2016 at 16:47

One other idea... an "exercise" if you will...

You might want to try shooting the same *exact* scene (right down to tripod placement) during the daylight, modifying shutter & ISO as-needed but keeping the aperture down at f/18. Then open it to f/11 or wider, and modify shutter/ISO accordingly, and shoot again. Compare those two shots to see how they differ.

I bet you'll find some diffraction-unsharpness at f/18, but you'll have to zoom in & hunt a bit to spot it. I also bet there won't be much (if anything) outside your DOF at either aperture.

But keep the "exercise" in mind -- re-shooting the same thing, as a study-exercise, is often useful! A similar exercise is to look for new ways (angles, styles, etc) to shoot something...
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Post Options Post Options   Quote Amalgam2 Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2016 at 17:27
Thanks Steve...lots to think about. A bit jealous of where you live! regards ian
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