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Author Topic: How to get a sharp image front to back?  (Read 4071 times)
Jim2
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« on: September 01, 2012, 05:08:42 AM »
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I don't know what's wrong with what I'm doing, so I hope someone more knowledgable can help me.

I took just took this photo today at sunset and while I'm happy with the image, I'm not happy with the sharpness.


100% Crop attached.

My gear:
- Canon 1ds3
- Sturdy tripod (gitzo 3 series 4 section) + head (arca swiss cube)
- Singh Ray Grad ND (resin, not glass - and yeah it's not the cleanest - no scratches on it but it probably has some oily smudge but it is not noticeable - I did try to wipe it with a microfibre cloth the best I could - maybe I need a new cloth?)
- 24-105mm zoom
- Using Mirror lock up, cable release
- Shot at 24mm F/20 1.3s

It wasn't a windy day - from the image there is no 'shake'.

The exposure was underexposed by about 1 1/3 or 1 2/3 and then I adjusted exposure using Lightroom, and also Increased the "Fill Light".

So how can I achieve a nice clean / sharper image?
I want both the grass at the bottom (first 100% crop) and the mountain to be tack sharp.

What do I need to change?

« Last Edit: September 01, 2012, 05:12:25 AM by Jim2 » Logged
Slobodan Blagojevic
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« Reply #1 on: September 01, 2012, 09:11:08 AM »
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F/20??? There you go!

P.S. Google two words: difraction and hyperfocal

P.P.S. Nice image, btw
« Last Edit: September 01, 2012, 09:14:57 AM by Slobodan Blagojevic » Logged

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Praki
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« Reply #2 on: September 01, 2012, 10:09:05 AM »
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Hello Slobodan:
Googled the words and found some very useful info regarding hyperfocal distance. I am sure it will make my pictures sharper. Thanks for the same.
Praki.
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Slobodan Blagojevic
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« Reply #3 on: September 01, 2012, 11:30:34 AM »
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A couple of further observations:

1. There was absolutely no need to underexpose, especially not by that much. That results in noisy shadows, further robbing the image of cleanness/crispness. Check the Expose-To-The-Right (ETTR) concept by searching this site.

2. You should remove CA (chromatic aberration) in post-processing, quite visible in your corner crop. That would make the image a bit cleaner/crisper too

3. I would not say that sharpness (or alleged lack of) is a problem in your image. It looks sufficiently sharp to me. Yes, shooting at less diffraction-prone f/stops and using hyperfocal distance focusing would result in a slightly sharper image, but that would only be visible in a direct comparison and in huge enlargements and/or 100% pixel peeping.

4. Absolute sharpness, front to back, is overrated imho. It results in the lack of that three-dimensional feel many photographers are after. A slight decrease in sharpness across the field, i.e., from foreground to background, creates that 3D feel. Just ask Rembrandt. In that respect, your mountain crop appears sufficiently sharp.

5. Diffraction-induced loss of sharpness can be restored using deconvolution sharpening. Our forum member BartvanderWolf, is an expert in this field, so search for his post related to deconvolution. For instance, this thread: http://www.luminous-landscape.com/forum/index.php?topic=68089.0

« Last Edit: September 01, 2012, 11:33:42 AM by Slobodan Blagojevic » Logged

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ErikKaffehr
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« Reply #4 on: September 01, 2012, 04:10:52 PM »
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+1

Erik

A couple of further observations:

1. There was absolutely no need to underexpose, especially not by that much. That results in noisy shadows, further robbing the image of cleanness/crispness. Check the Expose-To-The-Right (ETTR) concept by searching this site.

2. You should remove CA (chromatic aberration) in post-processing, quite visible in your corner crop. That would make the image a bit cleaner/crisper too

3. I would not say that sharpness (or alleged lack of) is a problem in your image. It looks sufficiently sharp to me. Yes, shooting at less diffraction-prone f/stops and using hyperfocal distance focusing would result in a slightly sharper image, but that would only be visible in a direct comparison and in huge enlargements and/or 100% pixel peeping.

4. Absolute sharpness, front to back, is overrated imho. It results in the lack of that three-dimensional feel many photographers are after. A slight decrease in sharpness across the field, i.e., from foreground to background, creates that 3D feel. Just ask Rembrandt. In that respect, your mountain crop appears sufficiently sharp.

5. Diffraction-induced loss of sharpness can be restored using deconvolution sharpening. Our forum member BartvanderWolf, is an expert in this field, so search for his post related to deconvolution. For instance, this thread: http://www.luminous-landscape.com/forum/index.php?topic=68089.0


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Jim2
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« Reply #5 on: September 01, 2012, 05:18:24 PM »
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Thanks for the tips!

I think the _main_ problem is that I under exposed this image too much. I just saw the histogram too Sad

The next problem is diffraction but that's something I've been trying to understand better. I took some shots with different F stops, and when I took it with F16 compared with F22, the mountain in the far distance will appear less sharp on F16.
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Jim2
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« Reply #6 on: September 01, 2012, 05:34:48 PM »
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What should I do with the CA? While I am familiar with ETTR (my own fault for not doing it), diffraction (also my fault for doing otherwise), and hyperfocal distance, I haven't really looked into CA yet.

Should/Can I fix it with Lightroom, Photoshop, or Capture1? If so, how i.e. which tool? I guess I should google Smiley

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Frank Sirona
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« Reply #7 on: September 01, 2012, 06:02:59 PM »
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Hi Jim, nice shot. Regarding the reason for the lack of sharpness you observed, I believe there are two main things which are adding up. First, you have been using a zoom lens which might not be of prime quality - thatīs obvious from the red color fringe you see in the corner (already discussed as CA). A prime lens, in particular when stopped down that far, should not have any visible CA. As you know, while zoom lenses have become quite good recently, in many cases they still are not as good as a really good lens with fixed focal length.

Second, you stopped down far beyond the f-stop where the lens provides the best image quality, so diffraction is an additional problem. However, of course, shooting at a larger aperture reduces the depth of field, and I personally am a great fan of images that are tack sharp from the foreground to the horizon. While Iīm using a large format camera which allows to virtually stretch the depth of field by tilting the lens, a possible workaround for you would be to do "focus stacking". Following this concept, you are shooting at a favorable f-stop (usually stopping down 2-3 f-stops) and make two or three different exposures, one focussed to the background, one to the foreground and possibly one more focussed to the middleground. Then, the in-focus parts of your exposures are merged in Photoshop. Itīs not a lot of work, and this way you simply can squeeze higher image quality out of your equipment.

Best,

Frank
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Frank Sirona. Large format photography of the Desert Southwest.

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Jim2
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« Reply #8 on: September 01, 2012, 06:07:28 PM »
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Hi Frank,

Thanks for your tips. Can you please show me / point to me this 'red colour fringe in the corner' you're referring to?
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Frank Sirona
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« Reply #9 on: September 01, 2012, 06:15:40 PM »
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Actually itīs not in the corner, as I just realized - Iīm referring to the first of your 100% crops, where you see it where the grass overlaps the water. Typically you see color fringes along edges with high contrast - that means, when they are there at all, which they shouldnīt.
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Frank Sirona. Large format photography of the Desert Southwest.

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« Reply #10 on: September 01, 2012, 06:22:56 PM »
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Regarding focus stacking, hereīs a link with some examples. The merging of the different images can be made manually or by a software such as Helicon Focus.
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Slobodan Blagojevic
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« Reply #11 on: September 01, 2012, 06:38:19 PM »
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For fixing CA, Lightroom has a specific tool for it in the Lens Corrections tab.

As for where it is, I put several arrows to point it out. Usually there is a red component and a green one.

A very good, brief explanation for CA, hyperfocal focusing and difraction can be found here:

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

http://www.cambridgeincolour.com/tutorials/lens-corrections.htm

http://www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm




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Slobodan

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Slobodan Blagojevic
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« Reply #12 on: September 01, 2012, 06:48:38 PM »
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... when I took it with F16 compared with F22, the mountain in the far distance will appear less sharp on F16.

Only because you did not utilize hyperfocal focusing.

Check this out (from: http://www.dofmaster.com/dofjs.html). You will see that, had you used f/11, a stop even better than f/16 (for diffraction), you would have had sharpness from 2.91 feet in front of you to infinity! Nothing in your image appears to be that close to you.
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« Reply #13 on: September 01, 2012, 07:37:05 PM »
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You've already received some great advice.  I'll add to it a bit.

First and foremost, as has been mentioned, nail the hyperfocal point for maximum depth of field.  There are charts you can download or you can use an app to do the calculations.  Either way, make sure that you use a chart/calculator specific to your camera because the circle of confusion is slightly different for every camera and using the wrong one will give you a false hyperfocal point.

Secondly, most lenses have a sweet spot in the aperture range that runs from about f/8 to f/11 - give or take.  The image you posted should only require f/11'ish for maximum DOF if you use the hyperfocal point.  When possible, try to stay in the "sweet spot".  Not always possible but when it is, you want to use it to avoid diffraction issues.

Third, the 24-105mm is a damn sharp lens.  The whole "prime vs. zoom" was an argument back in the day but most pro level zooms these days are just as good as a prime of the same focal length.  There are exceptions but the 24-105 isn't one of them.  I use it for probably 60-70% of my images.

Lastly, you might consider some tilt/shift lenses.  Not cheap, but they're tough to beat when your primary concern is depth of field - whether it be shallow or deep DOF.  They're also the way to go for perspective control.

Hope this is helpful!
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Jim2
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« Reply #14 on: September 01, 2012, 09:09:43 PM »
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Thanks for the Hyperfocal distance info - I had another quick look again at it, especially this tool http://www.dofmaster.com/dofjs.html  My questions:

- When using a zoom lens, e.g. 24-105mm, do I use "105mm" as the focal length, regardless of zoom level? IF I need to use the actual focal length- I can only "guesstimate" the actual focal length based on the marker on the lens ring?

- Then will I also have to guesstimate the distance on the focusing ring since it's not all that accurate / detailed either? It also seems to be on a logarithmic scale rather than linear.
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Rajan Parrikar
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« Reply #15 on: September 01, 2012, 10:39:11 PM »
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I don't care about this hyperfocal distance idea at all for maximizing dof. When I'm not using Tilt-Shift lenses, I abide by Merklinger's thumb rule which, in most instances, works well.

http://jimdoty.com/learn/merkdof01.pdf

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Slobodan Blagojevic
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« Reply #16 on: September 02, 2012, 12:25:55 AM »
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...I abide by Merklinger's thumb rule which, in most instances, works well...

And that "thumb rule" would be...?
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Slobodan

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ErikKaffehr
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« Reply #17 on: September 02, 2012, 12:38:20 AM »
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You would use the actual focal length.

You are right about the focusing scale. I'm not really sure it's logarithmic but it is not proportional. This is due to physics and no malice of the lens designers.

Best regards
Erik

Thanks for the Hyperfocal distance info - I had another quick look again at it, especially this tool http://www.dofmaster.com/dofjs.html  My questions:

- When using a zoom lens, e.g. 24-105mm, do I use "105mm" as the focal length, regardless of zoom level? IF I need to use the actual focal length- I can only "guesstimate" the actual focal length based on the marker on the lens ring?

- Then will I also have to guesstimate the distance on the focusing ring since it's not all that accurate / detailed either? It also seems to be on a logarithmic scale rather than linear.
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ErikKaffehr
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« Reply #18 on: September 02, 2012, 12:47:58 AM »
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Hi,

Good suggestion from Slobodan, but you need to choose the circle of confusion according to your viewing distance and print size. The 0.03 mm is an old standard based on smallish print viewed at 25 cm. A large print viewed at short distance will be most demanding.

Diffraction can be compensated with proper sharpening, at least to some extent.

I have some write ups on the issue:

http://echophoto.dnsalias.net/ekr/index.php/photoarticles/29-handling-the-dof-trap

http://echophoto.dnsalias.net/ekr/index.php/photoarticles/29-handling-the-dof-trap

http://echophoto.dnsalias.net/ekr/index.php/photoarticles/29-handling-the-dof-trap

Best regards
Erik

Only because you did not utilize hyperfocal focusing.

Check this out (from: http://www.dofmaster.com/dofjs.html). You will see that, had you used f/11, a stop even better than f/16 (for diffraction), you would have had sharpness from 2.91 feet in front of you to infinity! Nothing in your image appears to be that close to you.
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Jim2
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« Reply #19 on: September 02, 2012, 04:41:18 AM »
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I went to the same spot again today to do some tests. Luckily the weather really sucked so I didn't have to worry about taking a "photo" but rather just experiment with focusing.

Here's what I did:
- F11 with lens set to 24mm
- According to the calculators, the hyperfocal distance is about 1.9xx metres

I took a series of images without changing the zoom / framing
1. F11 with the focusing ring set to "somewhat" 1.9m - the scale had 1.5m and 3.5m so I put it roughly in the middle (since the scale isn't linear anyway

Result: clearly nothing is in focus - front is very soft and so is the mountain

2. F11 with focusing set to almost infinity
3. F11 with focusing set to beyond infinity (basically all the way out)
4. F11 with my normal way of focusing (just focus on slightly further away to the closest object - which I noticed that the focusing ring is on near infinity - note the grass at the bottom of the image is roughly 10 metres from the camera)

The three methods above produced a similar result - everything is in focus except that it's not razor sharp, but reasonably sharp - this is before applying any sharpening but I think Lightroom applied a 'default' sharpening value of "25" which is applied to all the images including sample (1) above.

So my conclusion is that my way of focusing works for me, however maybe my lens sucks? Maybe it's a bad copy because it has fallen on to the concrete once.

How sharp is "razor sharp" for an image produced by 1ds3 or nikon d3x / d800e etc? Hard to compare different photos / scenes / lighting situation unfortunately. Is it the case that the only way to find out is to get a rental and try and shoot the same stuff with different cameras / lenses?

And here's the dirty question: will MFDB + technical camera (with tilt) totally solve the 'sharpness' issue?

The second problem as was pointed out above, was that my photo above was grossly underexposed so there is a lot of noise in the foreground grass since I had to add "Fill Light" to it.

The third problem as was also pointed out above, F20 does produce a softer image than even F16 or in this case where F11 would be just fine too. I usually take several shots at varying F stops just to cover all bases but in this instance I was too fixated over the clouds to remember doing it Sad

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