advice on poor image quality / contrast

[swifty]

To clarify, I meant the small drain (not the big ones) adjacent to the two sitting ladies, next to the knee of the one wearing black bottoms.
The cobble street leading up to the stairs is the easiest object to judge focus plane because the same object runs from near to far so you can see the defocus softening the further away from the plane of focus you get.

 

[one eye jack]

To clarify, I meant the small drain (not the big ones) adjacent to the two sitting ladies, next to the knee of the one wearing black bottoms.
The cobble street leading up to the stairs is the easiest object to judge focus plane because the same object runs from near to far so you can see the defocus softening the further away from the plane of focus you get.

I don't see any open drains (must be covered).Anyway it's immaterial..so where is the focus plain? The verital signage above the ladies seem a likely spot logically, midway into the frame.Must wait for TS to appear.


Edit: After some rethink, plane of focus as in science of optics where an object is in real world in relation to a lens focal plane image. Autofocus system in olympus camera (EPL6)
is based on contrast detection and image sensor is flat (image focal plane).Image sensor
does not use distance information like phase detection which is actually calculated by image processor.In contrast detection only point or area of highest contrast is deemed to be in focus which means it can be in error if photographer does not intend a particular
spot or plane to be his target as selected by autofocus sensors.In reality just like an image sensor does not detect/sense colour but only light intensity levels afforded by coloured filters over the pixel light gathering cell.

 

[swifty]

I don't see any open drains (must be covered).Anyway it's immaterial..so where is the focus plain? The verital signage above the ladies seem a likely spot logically, midway into the frame.Must wait for TS to appear.


Edit: After some rethink, plane of focus as in science of optics where an object is in real world in relation to a lens focal plane image. Autofocus system in olympus camera (EPL6)
is based on contrast detection and image sensor is flat (image focal plane).Image sensor
does not use distance information like phase detection which is actually calculated by image processor.In contrast detection only point or area of highest contrast is deemed to be in focus which means it can be in error if photographer does not intend a particular
spot or plane to be his target as selected by autofocus sensors.In reality just like an image sensor does not detect/sense colour but only light intensity levels afforded by coloured filters over the pixel light gathering cell.

I'm afraid this isn't correct.
There is always a plane of focus. You might not even have any objects in your framing that intersects this plane (in which case everything is out of focus) but there is always a plane of focus.
The 'contrast' in contrast detect autofocus (CDAF) doesn't refer to where the automated focus systems picks to focus, it refers to how focus is achieved for a selected focus point.

The automated focus system may well be picking an area of high contrast to try and focus on, but it still needs to achieve focus for those high contrast objects at its particular distance. Conversely, you can still achieve focus on an area with much less contrast with a CDAF system but it will just be more taxing on the system.
Similarly, a PDAF system may also have an automated AF point selection mode that asks the camera to pick a focus point for the user and it may well be an area of high contrast. What is being described here is how the camera's algorithm picks an area to focus on when the user hasn't selected a focus point himself, not how the focus is achieved which is what the contrast detect and phase detect are referring to.

In CDAF, after a focus point is selected, that patch is analysed as the camera moves the lens' focusing system back or forth. What this is doing is moving the plane of focus from near to far (or vice versa) until that plane intersects with the object you want to focus on. The system doesn't know when this will happen, it only analyzes the patch which will progressively increase in contrast as the focus plane moves closer to the object you want to focus on. This is what the contrast in CDAF refers to. It also cannot know when maximum contrast is achieved (in-focus) until it overshoots and the image starts to loose contrast again as it moves out of focus. It then racks back and forth around this distane until the algorithm is satisfied maximum contrast has been achieved for that AF point (patch). That's why CDAF systems have that little 'stutter' towards the end of the focusing sequence.
You can select whatever AF point you like and place it on whatever subject, whether high or low contrast and the system will move the plane of focus back and forth until maximum contrast is achieved for the patch that is being analysed. This basically corresponds with the plane of focus intersecting with your subject to be focused.

I don't have a photo editing tool on my work computer but if I get a chance later, I'll draw in approximately where the plane of focus is on the first image.

 

[one eye jack]

I don't have a photo editing tool on my work computer but if I get a chance later, I'll draw in approximately where the plane of focus is on the first image.

I use windows' paint.;p Thank you for the technical explanation Yes I have to agree with you that there IS a plane of focus but I think TS would appreciate more if you can tell him how he can improve his hit or keep rate rather than if he did not like what the camera chooses (focus plane) then tough luck and live with it.Ultimately it's how user makes use of the focusing sensors.Is one spot better than multiple spots.When and how,any special lighting conditions he needs to be aware of?

 

[thoongeng]

I'm afraid this isn't correct.
There is always a plane of focus. You might not even have any objects in your framing that intersects this plane (in which case everything is out of focus) but there is always a plane of focus.
The 'contrast' in contrast detect autofocus (CDAF) doesn't refer to where the automated focus systems picks to focus, it refers to how focus is achieved for a selected focus point.

The automated focus system may well be picking an area of high contrast to try and focus on, but it still needs to achieve focus for those high contrast objects at its particular distance. Conversely, you can still achieve focus on an area with much less contrast with a CDAF system but it will just be more taxing on the system.
Similarly, a PDAF system may also have an automated AF point selection mode that asks the camera to pick a focus point for the user and it may well be an area of high contrast. What is being described here is how the camera's algorithm picks an area to focus on when the user hasn't selected a focus point himself, not how the focus is achieved which is what the contrast detect and phase detect are referring to.

In CDAF, after a focus point is selected, that patch is analysed as the camera moves the lens' focusing system back or forth. What this is doing is moving the plane of focus from near to far (or vice versa) until that plane intersects with the object you want to focus on. The system doesn't know when this will happen, it only analyzes the patch which will progressively increase in contrast as the focus plane moves closer to the object you want to focus on. This is what the contrast in CDAF refers to. It also cannot know when maximum contrast is achieved (in-focus) until it overshoots and the image starts to loose contrast again as it moves out of focus. It then racks back and forth around this distane until the algorithm is satisfied maximum contrast has been achieved for that AF point (patch). That's why CDAF systems have that little 'stutter' towards the end of the focusing sequence.
You can select whatever AF point you like and place it on whatever subject, whether high or low contrast and the system will move the plane of focus back and forth until maximum contrast is achieved for the patch that is being analysed. This basically corresponds with the plane of focus intersecting with your subject to be focused.

I don't have a photo editing tool on my work computer but if I get a chance later, I'll draw in approximately where the plane of focus is on the first image.

Well explained.

I took the liberty to edit prollic's photo to paint in red the plane of focus

I use windows' paint.;p Thank you for the technical explanation Yes I have to agree with you that there IS a plane of focus but I think TS would appreciate more if you can tell him how he can improve his hit or keep rate rather than if he did not like what the camera chooses (focus plane) then tough luck and live with it.Ultimately it's how user makes use of the focusing sensors.Is one spot better than multiple spots.When and how,any special lighting conditions he needs to be aware of?

Go out and shoot more and you will understand. Most technical stuff can be googled nowadays, however many practical stuff have to be learnt through active practice in the field. I'm still learning every time I go out to shoot, even though I thought I have already grasped the technicalities. You could have answered your own questions if you shot enough in different conditions.

There is no best way for everyone, my way may not suit TS's. That's why there are so many settings and customisations available in the cameras. We do not know how proficient prollic is, so whatever has been discussed may just be gibberish or elementary stuff

In the absence of TS's replay, maybe I'll just share what I use - I usually set my autofocus point manually (press the LEFT side of arrow pad by default), with the small box option (press INFO button after going into autofocus point selection) so I can be more precise where I want the camera to focus on. I always try to move the focus point to nearest to my subject, however if I'm really short on time I may use the default centre box to focus then recompose

Olympus EPL6 also has the useful face and eye detection for autofocus point, which may suit many people better. As a friend said, you pay so much for the camera, have to make it work harder right?

(just to throw a spanner, the exif of the 2nd photo says it was taken with a 58mm lens :dunno: )

 

[swifty]

Thoongeng beat me to it But yep, I agree with where he's placed the focus plane.

IMO, the easiest place in the first photo to spot the focus plane is the pathway.
The arrow indicates the distance from camera from near to far. It is sharpest towards the bottom section and gradually falls off the further away from the camera (image plane) you get.

I've shaded in red where the sharpest region appears to be and have drawn and estimate of where the focus plane might be in solid red.

As can be seen, this is pretty close to the camera whilst most of the interest is further away. The close-ish focused distance has resulted in much of the image being out of the dof of the camera setting used.

TS could use Octarine's hyperfocal method. I plugged in the numbers on the linked site and if I did it correctly (I hope), it appears hyperfocal distance is around 10m for the focal length and aperture used.
The solid yellow line is another guess-timate of where 10m away from the camera might be (but I'm a bit crap at estimating distance). If the TS had focused on any of the objects around that depth, he would maximize his dof for the current settings.
However, this still won't get everything in focus for the composition presented. The two sitting ladies will still be out of focus.


There are no one or best way of doing things but a few things could help I think.

Firstly, composition-wise are the two ladies relevant to the image. If so, step back a bit and include them in the frame properly and get them focused. If not, then step forward and cut them out of the frame completely.

From a high position, pointing slightly down you'd get more close foreground which makes it more difficult to get everything in focus if that is the aim. Pointing the camera up a little will decrease the amount of foreground but you may also need to crouch a little depending on how you want to frame the shot.

I personally don't use hyperfocal distance for street photography. I like selective focus myself.
But I know many street photographers use a wide-normal focal length stopped down and manually pre-focus at the hyperfocal distance and shoot as is for every shot without changing the focus at all. This works well when there are plenty of light.

Back to the first image. Given the camera settings, I would focus on objects further away (because that is where the interest is) and I can afford to stop down and extra stop of aperture or two, even if I have to increase ISO and decrease shutter speeds accordingly because there adequate light in this scene for a bit of exposure flexibility. Stopping down has the effect of increasing DOF and most lenses are sharper across the entire field when stopped down a bit. You'd need to know where the sweet spot is for your lens by looking up reviews.

I wouldn't use the auto mode for AF point selection. Just use the centre one to lock and recompose. That way you're in charge of what you want to focus on. It works fine in most situations unless you're shooting very shallow DOF. In which case, do as thoongeng suggests and move the AF point to the closest one to the subject. This is what I normally do but like I said, if you're not shooting paper thin DOF, half-press focus lock and recompose works just fine.
There are situations where an auto-AF point selection would work very well. Eg. if you had an eye-AF mode whilst shooting portraiture.

In terms of shutter speed, it appears to be adequate at 1/250 for the focal length. I initially though there might be a hint of movement but on second thought, I think motion is quite negligible. The shutter speeds also assume good hand-holding technique. Using one hand held arms length in front of you and stabbing the shutter button might still result in some movement even if shutter speed appears to be adequate.

 

[swifty]

Image two.
The focus appears to be on the castle which is fine because that is the main interest. But usually DOF falls off quite quickly in front of the focus plane. I like the foliage just in front of the castle and would want to get that in focus so I'd focus on the trees instead and DOF should be adequate to extend to the castle as well. If not, then stop down a bit more but this will compromise other exposure settings a bit. In this composition, I don't really care if the water is out of focus.

I also noticed the exif says 58mm which is around 116mm FF equiv. Using the 1/2*FL guide for minimum shutter speed, you'd need around 1/230 for sharp images.
TS's shutter speed of 1/200 should be adequate with good hand-holding technique but if you're critical, then 1/200 might only be borderline adequate.

But generally the second shot seems mostly fine.
A quick edit of mine:

 

[thoongeng]

Thoongeng beat me to it But yep, I agree with where he's placed the focus plane.

Mine's only a 2 minute job heh... thanks for your detailed illustrations and explanations, good learning points

Hopefully TS (thread starter, ie prollic) makes good use of your efforts, or come back to clarify what points he is not sure about.

 

[Obscura56]

Wow, these are really helpful tips! Thanks, swifty and thoongeng!