Focusing on Reflections in Water as it relates to a landscape image

[Mike Buckley]

I've been trying different shots with my wide angle lens and I can see that I can use the small apertures with no worries.

It may be that the difference in sharpness is of no concern to you, which would be understandable depending on how critical you're being. However, if it means you can't see a difference in sharpness, I would be surprised. If the sharpness is the same throughout all focal lengths at the smallest aperture as at the middle apertures, I would be exceptionally surprised. That's because that characteristic would be very unusual for that type and quality of lens.

This website reviews the sharpness of a Sigma 18-50 lens but I don't know if it's the exact model that you use. The reason I took a look at it is that the lens has been tested and the results are displayed in a graph at the right. The review indicates that variations in sharpness can be perceived, as I would expect.

When you click the blur graph at the right, an interactive graph is displayed in a new window. Set the focal length, as just one example, to 18mm. Then set the aperture to f/22. The lower the blur value, the sharper the image. Notice that the values in the corners are about 4 - 4 1/2 and the values in the center are about 3. Then set the aperture to f/8. The corner values change to about 2 1/2 to 3 1/2 and the center values change to about 0 to 1.

If I remember correctly, a change of value greater than 1 unit generally can be perceived when viewing the image. (I tried to confirm that information but found nothing about it at the web site. I'm positive that information used to be provided and seriously doubt that it has been removed.) The change described above in the center of the frame, which is the most important area, is a change of about 2 to 3 units, which I'm sure can be perceived. Moreover, I would expect this to occur.

If you're only posting your images in the small size required for use on the Internet, I wouldn't be surprised to learn that the sharpness differences displayed in the graph can't be seen. However, I would expect them to be seen when viewing medium to large prints at distances that are appropriate for the size of the prints.

[Brownbear]

Hi Mike,

Thank you for this. When I was referring to the larger apertures I was speaking in general and should've said that F8 seems to work very well and referring to my my most recently acquired new Nikon 10-24 mm lens. And yes, I will check for sharpness at full size.

I have a Sigma 18-50 mm lens, but since I acquired and a Nikkor 28-200 mm lens, but I think now that I have the wide angle lens (which covers the shorter focal distances) I will likely not use the Sigma lens very often.

Thank you.

It may be that the difference in sharpness is of no concern to you, which would be understandable depending on how critical you're being. However, if it means you can't see a difference in sharpness, I would be surprised. If the sharpness is the same throughout all focal lengths at the smallest aperture as at the middle apertures, I would be exceptionally surprised. That's because that characteristic would be very unusual for that type and quality of lens.

This website reviews the sharpness of a Sigma 18-50 lens but I don't know if it's the exact model that you use. The reason I took a look at it is that the lens has been tested and the results are displayed in a graph at the right. The review indicates that variations in sharpness can be perceived, as I would expect.

When you click the blur graph at the right, an interactive graph is displayed in a new window. Set the focal length, as just one example, to 18. Then set the aperture to f/22. The lower sharpness value, the sharper the image. Notice that the sharpness in the corners are at values of about 4 - 4 1/2 and the sharpness in the center is about 3. Then set the aperture to f/8. The corner sharpness values change to about 2 1/2 to 3 1/2 and the center sharpness changes to about 0 to 1.

If I remember correctly, a change of value greater than 1 generally can be perceived when viewing the image. (I tried to confirm that information but found nothing bout it at the web site. I'm positive that information used to be provided and seriously doubt that it has been removed.) The change described above in the center of the frame, which is the most important area, is a change of about 2 to 3 units. Moreover, I would expect this to occur.

If you're only posting your images in the small size required for use on the Internet, I wouldn't be surprised to learn that the sharpness differences displayed in the graph can't be seen. However, I would expect them to be seen when viewing medium to large prints at distances that are appropriate for the size of the prints.

[Mike Buckley]

should've said that F8 seems to work very well

That makes sense. Ahem, you mentioned that you are using "small" apertures. Please keep in mind as you communicate about this stuff that f/8 is not a small aperture. It's a mid-range aperture. As an example, your Nikon 10-24mm lens has f/29. That's a difference of almost 4 stops.

[Brownbear]

Thank you for clarifying. I referred to F8 as a small aperture simply because it is on the small number side. Good to know.

I would like to ask just one more question if I may, simply because these graphs are new to me.

When I view the center of the graph at F8 vs F22 it appears that the center of the image is the sharpest point of the image? If yes, does this mean that it is better to place the subject of interest at the center focus point, ie compose with cropping in mind instead of composing an image with the subject say at a 1/3 point, and also that this would be far more important for a wildlife shot close in when using a mid range or large aperture, then when composing a landscape image at a midrange aperture with a wide angle lens.

Also I didn't know that the aperture also effects the amount of chromatic aberration (a problem that I often encounter) and that in general choosing a larger aperture results in a less chromatic aberration? This particular graph is a bit complicated. And similarly at larger apertures I will see more vignetting and if yes, for some reason I think vignetting is easy to fix (easier than CA) in post processing via lens corrections?

Thank you.

That makes sense. Ahem, you mentioned that you are using "small" apertures. Please keep in mind as you communicate about this stuff that f/8 is not a small aperture. It's a mid-range aperture. As an example, your Nikon 10-24mm lens has f/29. That's a difference of almost 4 stops.

[ajohnw]

I recently got to play with a 7.5mm lens on my E-PL1 and on looking at the lens it has infinity marked and 0.25metre ... so I have placed the focus point about half-way between them and just press the trigger [ adjusting the aperture down, smaller, from f/8 when the camera protests ]. Makes life much simpler
Here I am sitting in the Railcar seat next to the man and the cruiseboat seems fairly sharp. One day I may just consult the tables to work it all out.

I will leave it to the experts to work out what the lens is equivalent to in an APS or FF camera
Even my palm seems fairly sharp as that hand holds the camera and presses the trigger.

Not on topic but wondered what you thought of the E-PL1. I bought one out of curiosity and immediate impression was revulsion mainly as it was used and came with constant AF on. Fixed that and less revulsion and then started playing in the menu's and began to like it. I bought the 1.4mp veiwfinder to avoid using the screen so much as anything on the screen also come up in it. In the end I concluded that it's a great little camera and lots of photography can be done with the usual 14-42mm on it but it does need reasonable light levels. So to get better controls - not keen on compact style - bought an E-P3. Came as a bit of a surprise even better and light levels not such a problem any more. The E-PL1 came with the 40-150mm on it so bought the 14-42 used. I still use both of them. They are very decent lenses. Just multiply the focal length by 2 for full frame which I expect you already know.

If they ever do one with tilt screen, pop up flash and built in viewfinder and still keep the size down I would probably buy one. Not that they will - no one would buy an EM-5. On the other hand I expect Oly would charge rather a lot for it. Too much probably.

There is a very good flickr group for the E-PL1, sadly I don't use the camera any more. 60 odd thousand shots some by capable people and well worth a look. All sorts of styles and subjects.

http://www.flickr.com/groups/e-pl1/

John
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[flashback]

Christina,
I'm late to the dance on this discussion but, has anyone suggested you download a DOF app to your smartphone? I have an android phone and I downloaded a DOF app from google play store. It's called DOF Calculator (icon is a black circle which is the front end of a lens.) I looked at a few and this one was the best (and easiest). It has a wide range of camera makes and models. It won't give you a technical explanation of WHY it works but the HOW is easier to understand.

[Mike Buckley]

I think most people would roughly refer to f/4 to f/1.4 as large apertures, f/5.6 to f/11 as mid-range apertures, and the others as small apertures.

When I view the center of the graph at F8 vs F22 it appears that the center of the image is the sharpest point of the image?

I'm not a gear head, but my understanding is that that's generally going to be universally true of all lenses at all focal lengths and all apertures.

If yes, does this mean that it is better to place the subject of interest at the center focus point, ie compose with cropping in mind

I would not advise doing that because, when all other factors are equal and not a concern, cropping reduces the maximum print size.

I don't know about the factors affecting chromatic aberration other than that it seems to be exacerbated in areas that are out of focus and in areas where dark pixels are adjacent to bright pixels. An example would be out of focus tree limbs against a bright cloud. Most software today makes it a lot easier to correct chromatic aberration than even five years ago, so I personally don't address it when setting camera configurations. Others may disagree.

I also don't know much about vignetting tendencies. If it occurs, I deal with it during post-processing (usually adding more intense vignetting ).

[Brownbear]

Thank you Mike. Truly appreciated, helpful and good to know.

I think most people would roughly refer to f/4 to f/1.4 as large apertures, f/5.6 to f/11 as mid-range apertures, and the others as small apertures.



I'm not a gear head, but my understanding is that that's generally going to be universally true of all lenses at all focal lengths and all apertures.



I would not advise doing that because, when all other factors are equal and not a concern, cropping reduces the maximum print size.

I don't know about the factors affecting chromatic aberration other than that it seems to be exacerbated in areas that are out of focus and in areas where dark pixels are adjacent to bright pixels. An example would be out of focus tree limbs against a bright cloud. Most software today makes it a lot easier to correct chromatic aberration than even five years ago, so I personally don't address it when setting camera configurations. Others may disagree.

I also don't know much about vignetting tendencies. If it occurs, I deal with it during post-processing (usually adding more intense vignetting ).

[ajohnw]

Thank you for clarifying. I referred to F8 as a small aperture simply because it is on the small number side. Good to know.

I would like to ask just one more question if I may, simply because these graphs are new to me.

When I view the center of the graph at F8 vs F22 it appears that the center of the image is the sharpest point of the image? If yes, does this mean that it is better to place the subject of interest at the center focus point, ie compose with cropping in mind instead of composing an image with the subject say at a 1/3 point, and also that this would be far more important for a wildlife shot close in when using a mid range or large aperture, then when composing a landscape image at a midrange aperture with a wide angle lens.

Also I didn't know that the aperture also effects the amount of chromatic aberration (a problem that I often encounter) and that in general choosing a larger aperture results in a less chromatic aberration? This particular graph is a bit complicated. And similarly at larger apertures I will see more vignetting and if yes, for some reason I think vignetting is easy to fix (easier than CA) in post processing via lens corrections?

Thank you.

I strongly suspect you can cope with this site Christina. The only odd number is lines per picture height. Bigger numbers mean better resolution. How lenses behave with aperture settings varies from one to another. Tests like these are fine but just represent a lens that was tested and they will vary. In a few cases by so much that the tester has sent them back. On sigma lenses there is no problem looking at Canon tests. It's best to look at the one that used a camera with the largest number of pixels but any one is a good indication of what a particular lens is likely to do. The tests often mention when diffraction kicks in but these don't relate all that well to how this will effect a photo.

Frankly I would expect most lenses to be showing the best across field resolution at F8 but that isn't always the case. Just how I feel things should be in an ideal world. On balance though the F8 - F16 are still likely to be the most usable. Wide open seldom is but that doesn't mean it shouldn't be used.

http://www.photozone.de/all-tests

He also mentions vignetting - light level fall off towards the corners of a shot. Many lenses have this and most software can correct it. 1 stop in real terms isn't worth worrying about.

Yes generally place the part that needs to be sharpest in the centre but it would be a sad world if that was essential. In the real world the important thing is that the camera is capable of capturing the detail where ever it is. That doesn't relate well to shots of resolution targets or the results of the above tests. In practical terms good in those tests is very likely to good enough. It depends on the detail in the shot. It's often relatively low.

Sigma to 18-50mm - Nikon 28-200 depends. Often zooms as wide as that have problems. Much depends on the lens.

Just noticed Mike has answered as well.

I can't use it but you might like to try the ViewNX2 that came with your camera for initial raw development. It should mostly remove CA for you. What I don't know is if it can save as 16bit TIFF for subsequent work. I would have thought that the Adobe software can do this as well.

John
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[Brownbear]

Hi Jack.

I don't have a smart phone, or even a cell phone but perhaps I will end up purchasing one, one day. I've just been asking a lot of questions because I'm trying to learn new things, I don't need to know the why for everything, truly.

Thank you for advising. Truly appreciated.

Christina,
I'm late to the dance on this discussion but, has anyone suggested you download a DOF app to your smartphone? I have an android phone and I downloaded a DOF app from google play store. It's called DOF Calculator (icon is a black circle which is the front end of a lens.) I looked at a few and this one was the best (and easiest). It has a wide range of camera makes and models. It won't give you a technical explanation of WHY it works but the HOW is easier to understand.

[Brownbear]

Understood and appreciated. I can also remove CA in Lightroom it is just that the function seems to leave the CA outline in a softer colour so I would prefer to avoid it, and perhaps I will try it out View NX2.

Thank you John.

I strongly suspect you can cope with this site Christina. The only odd number is lines per picture height. Bigger numbers mean better resolution. How lenses behave with aperture settings varies from one to another. Tests like these are fine but just represent a lens that was tested and they will vary. In a few cases by so much that the tester has sent them back. On sigma lenses there is no problem looking at Canon tests. It's best to look at the one that used a camera with the largest number of pixels but any one is a good indication of what a particular lens is likely to do. The tests often mention when diffraction kicks in but these don't relate all that well to how this will effect a photo.

Frankly I would expect most lenses to be showing the best across field resolution at F8 but that isn't always the case. Just how I feel things should be in an ideal world. On balance though the F8 - F16 are still likely to be the most usable. Wide open seldom is but that doesn't mean it shouldn't be used.

http://www.photozone.de/all-tests

He also mentions vignetting - light level fall off towards the corners of a shot. Many lenses have this and most software can correct it. 1 stop in real terms isn't worth worrying about.

Yes generally place the part that needs to be sharpest in the centre but it would be a sad world if that was essential. In the real world the important thing is that the camera is capable of capturing the detail where ever it is. That doesn't relate well to shots of resolution targets or the results of the above tests. In practical terms good in those tests is very likely to good enough. It depends on the detail in the shot. It's often relatively low.

Sigma to 18-50mm - Nikon 28-200 depends. Often zooms as wide as that have problems. Much depends on the lens.

Just noticed Mike has answered as well.

I can't use it but you might like to try the ViewNX2 that came with your camera for initial raw development. It should mostly remove CA for you. What I don't know is if it can save as 16bit TIFF for subsequent work. I would have thought that the Adobe software can do this as well.

John
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[ajohnw]

Nikon is a new excursion for me. If you look through the NEF challenge thread I started you will see lots of shots showing a pale outline around the building roof. I did it with 2 sliders manually that may be better than auto but it seems to me that ViewNX2 did the best job of all including PS users. Can't save or do much with the image so using it may or may not work out. Going on another thread downsizing in it isn't a good idea as that may leave artefacts in places that are difficult to reduce.

There is a site called kenrockwell.com. He passes judgement on just about any lens that will fit a nikon. Seems sound to me comparing with real tests. I picked out an old AF D type zoom on that basis and it was awful. Used for the NEF thread. The CA in the camera jpg was hardly noticeable and looked more like fringing. From raw red went one way and blue the other. Being fair to KR the lens was probably clapped out. I suspect the CA correction software doesn't adjust the brightness correctly so processing can bring up what it has left behind. Getting rid of it - maybe careful use of a blur brush at 400% view at least or possibly even cloning.

Colin's comment was that size reduction usually gets rid of the line. In many ways it's often best to process the full sized image. The last step is reduction and just enough sharpening to crisp things up a little. I always work like that but with the nef file I was after a full sized image and there was a lot of noise.

Edit
Fringing - It's a mostly blue outline at high contrast boundaries. Some software has a separate adjustment for it. Or did have as CA correction seems to be capable of achieving the same thing. These must be done of the full sized image. It can finish up as a horrible mess if done after cropping.

John
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[Shadowman]

Not on topic but wondered what you thought of the E-PL1. I bought one out of curiosity and immediate impression was revulsion mainly as it was used and came with constant AF on. Fixed that and less revulsion and then started playing in the menu's and began to like it. I bought the 1.4mp veiwfinder to avoid using the screen so much as anything on the screen also come up in it. In the end I concluded that it's a great little camera and lots of photography can be done with the usual 14-42mm on it but it does need reasonable light levels. So to get better controls - not keen on compact style - bought an E-P3. Came as a bit of a surprise even better and light levels not such a problem any more. The E-PL1 came with the 40-150mm on it so bought the 14-42 used. I still use both of them. They are very decent lenses. Just multiply the focal length by 2 for full frame which I expect you already know.

If they ever do one with tilt screen, pop up flash and built in viewfinder and still keep the size down I would probably buy one. Not that they will - no one would buy an EM-5. On the other hand I expect Oly would charge rather a lot for it. Too much probably.

There is a very good flickr group for the E-PL1, sadly I don't use the camera any more. 60 odd thousand shots some by capable people and well worth a look. All sorts of styles and subjects.

http://www.flickr.com/groups/e-pl1/

John
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I have the EPL-1 and like it, when I post images made with the camera I list the model. Has a decent bracketing function and RAW storage capability.

[jcuknz]

Not on topic but wondered what you thought of the E-PL1. [/url]John
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Briefly .... I hated it too becuase of the different menu layout from Panasonic but it is growing on me and while I only use it in the most basic way its IBIS suits the current manual bug-eye and it has been fun but not exactly satisfying when I coupled up a Pentax x2 converter, my Tokina 90-230 and of course the MFT to M42 adaptor ... crazy to expect anything of the combo I know But after downloading the manual I am finding my way around the menus and respect its performance after using my Penatx 50mm f/1.4 on it ... so if I use it properly I am sure it will deliver the goods.

EDIT ... PS. it does have a pop-up flash which I forgot to use as the railcar passed Port Chalmers and growth beside the track made getting a shot a bit of a fluke despite the RM crawling. I also have the VF-2 for it which I find very awkward though a neat idea.

[ajohnw]

Briefly .... I hated it too becuase of the different menu layout from Panasonic but it is growing on me and while I only use it in the most basic way its IBIS suits the current manual bug-eye and it has been fun but not exactly satisfying when I coupled up a Pentax x2 converter, my Tokina 90-230 and of course the MFT to M42 adaptor ... crazy to expect anything of the combo I know But after downloading the manual I am finding my way around the menus and respect its performance after using my Penatx 50mm f/1.4 on it ... so if I use it properly I am sure it will deliver the goods.

EDIT ... PS. it does have a pop-up flash which I forgot to use as the railcar passed Port Chalmers and growth beside the track made getting a shot a bit of a fluke despite the RM crawling. I also have the VF-2 for it which I find very awkward though a neat idea.

I had the manual lens craze too. It can be done even up to 500mm but only with the 7x magnified view on - hard to frame whatever is being shot. The Pen's only give IS when the shot is actually taken but with care it will cope with 500mm. Out of curiosity I did a search for E-PL1 focus peaking. Didn't look far but there may be some information about.. If there is it's probably one of the art filters as on the EM-5. There is a demo of what that one does on youtube shooting a teddy bear. A magnified view isn't needed. Using the art filter may mean throwing the jpg away but the camera will develop raw if I remember correctly if something is wanted on the spot. I think all Olympus m 4/3 can.

The focus peaking might turn out to be the shimmer thing. I found that if the camera is pointed at say a conifer the detail has a bright outline when some lenses are used and they are precisely focused. Most noticeable on an OM F1.4 50?mm - the lens that was actually better than nikons in it's day.

John
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