Focus on Focusing
Derek Smith • 1 June 2022
Digital cameras use different methods of autofocus to obtain sharp focus on the subject.
DSLR cameras use a phase detect focus module below the sensor to compare light from a sub-mirror split into two separate images by prisms and micro-lenses in the AF sensor unit, each aimed at two lines on the AF sensor corresponding to the active AF point. If the images hit the two lines precisely, the subject is in focus, any distance between the two images tells the camera how much the lens is out of focus, the lens is driven until the images match, and accurate focus is thus achieved. In “Live View” many DSLR cameras use the contrast detect focusing pixels directly on the sensor.
Mirrorless cameras can use a contrast detection focus method, a phase detect autofocus, or a combination of both called a hybrid autofocus system, but without mirrors, or prisms, all the focus points are located directly on the sensor.
Contrast detect autofocus is the simplest system, it compares contrast areas within the subject, and moves the lens focusing elements backwards, and forwards until the highest contrast is achieved. Contrast autofocus is extremely accurate, but can be slow.
Phase detection autofocus (PDAF) pixel pairs are incorporated into the digital sensor and consist of partially covered sensors receiving light from either side of the lens, left, and right pairs. The camera compares both, and when they match, knows that the subject is in focus. If the subject is out of focus, it calculates how much it needs to adjust the lens to bring the subject into focus and drives the lens there.
Hybrid autofocus uses the phase detection to achieve close focus and finalises accurate focus with contrast detection.
Now, knowing all the technical details of camera autofocus is good, but how best to employ that knowledge? The best advice I can give is to get to know the various settings of autofocus that your camera has, and I shall use some images to illustrate those settings that I use.
Portraits – a lot of digital cameras have “face and eye” detect modes, and I’ve used this mode to good effect for photographing this model. My camera model has four autofocus selections, single point, zone, wide & tracking, and finally “all”, for this shot I used the wide & tracking selection, with the “face and eye” detection turned on to focus accurately on the eyes. Marika was photographed with the Fuji X-T20, and the XF50mm f/2 (75mm ff) lens f/4, 1/80, ISO 400
Derelict building – for this shot I used single point autofocus, I was taking practice images with my new Fuji X-T3 camera, and the XF35mm f/2 (50mm ff) lens, f/11, 1/52, ISO 1000. This photo is a technical failure, not being as sharp as it could have been, I needed a faster shutter speed, and should have either widened the aperture to f/8 or increased the ISO to 1600 to eliminate the shutter shake.
Robin – I was very pleased with this image, taken with the Fuji X-T3, and the XF70 – 300mm (105 – 450mm ff) using single point autofocus on the eye of the bird. Photo details: 434mm ff equivalent, f/8, 1/280, ISO 800.
Cadwell – my first outing with the Fuji X-T3, and the XF70 – 300mm lens, using the wide & tracking selection, and continuous autofocus, following the bikes with the camera as they come past, a technique known as “panning”. Photo details: 126mm ff equivalent, f/5.6, 1/300, ISO 200.
All images were captured in Aperture Priority mode, with the aperture and ISO adjusted to give the correct shutter speed (hopefully) for the scene. I very rarely use the “All” selection of autofocus as the camera focus can sometimes lock onto unwanted areas in the frame, a blade of grass in the foreground of a landscape perhaps, or the nearest tree. For a landscape scene, I usually use a single point autofocus point and focus a third of the way into the scene.
For macro images autofocus can be of use, but many photographers prefer to use manual focus, be aware that many lenses are “focus by wire”, which means that the lens focus ring does not control the focusing element within the lens directly, so there may well be a lag in obtaining focus. I find that manual focusing aids such as magnification, and / or focus peaking work well, and instead of turning the focus ring “rock” the camera physically slowly back and forwards until sharp focus is obtained.
DSLR cameras use a phase detect focus module below the sensor to compare light from a sub-mirror split into two separate images by prisms and micro-lenses in the AF sensor unit, each aimed at two lines on the AF sensor corresponding to the active AF point. If the images hit the two lines precisely, the subject is in focus, any distance between the two images tells the camera how much the lens is out of focus, the lens is driven until the images match, and accurate focus is thus achieved. In “Live View” many DSLR cameras use the contrast detect focusing pixels directly on the sensor.
Mirrorless cameras can use a contrast detection focus method, a phase detect autofocus, or a combination of both called a hybrid autofocus system, but without mirrors, or prisms, all the focus points are located directly on the sensor.
Contrast detect autofocus is the simplest system, it compares contrast areas within the subject, and moves the lens focusing elements backwards, and forwards until the highest contrast is achieved. Contrast autofocus is extremely accurate, but can be slow.
Phase detection autofocus (PDAF) pixel pairs are incorporated into the digital sensor and consist of partially covered sensors receiving light from either side of the lens, left, and right pairs. The camera compares both, and when they match, knows that the subject is in focus. If the subject is out of focus, it calculates how much it needs to adjust the lens to bring the subject into focus and drives the lens there.
Hybrid autofocus uses the phase detection to achieve close focus and finalises accurate focus with contrast detection.
Now, knowing all the technical details of camera autofocus is good, but how best to employ that knowledge? The best advice I can give is to get to know the various settings of autofocus that your camera has, and I shall use some images to illustrate those settings that I use.
Portraits – a lot of digital cameras have “face and eye” detect modes, and I’ve used this mode to good effect for photographing this model. My camera model has four autofocus selections, single point, zone, wide & tracking, and finally “all”, for this shot I used the wide & tracking selection, with the “face and eye” detection turned on to focus accurately on the eyes. Marika was photographed with the Fuji X-T20, and the XF50mm f/2 (75mm ff) lens f/4, 1/80, ISO 400
Derelict building – for this shot I used single point autofocus, I was taking practice images with my new Fuji X-T3 camera, and the XF35mm f/2 (50mm ff) lens, f/11, 1/52, ISO 1000. This photo is a technical failure, not being as sharp as it could have been, I needed a faster shutter speed, and should have either widened the aperture to f/8 or increased the ISO to 1600 to eliminate the shutter shake.
Robin – I was very pleased with this image, taken with the Fuji X-T3, and the XF70 – 300mm (105 – 450mm ff) using single point autofocus on the eye of the bird. Photo details: 434mm ff equivalent, f/8, 1/280, ISO 800.
Cadwell – my first outing with the Fuji X-T3, and the XF70 – 300mm lens, using the wide & tracking selection, and continuous autofocus, following the bikes with the camera as they come past, a technique known as “panning”. Photo details: 126mm ff equivalent, f/5.6, 1/300, ISO 200.
All images were captured in Aperture Priority mode, with the aperture and ISO adjusted to give the correct shutter speed (hopefully) for the scene. I very rarely use the “All” selection of autofocus as the camera focus can sometimes lock onto unwanted areas in the frame, a blade of grass in the foreground of a landscape perhaps, or the nearest tree. For a landscape scene, I usually use a single point autofocus point and focus a third of the way into the scene.
For macro images autofocus can be of use, but many photographers prefer to use manual focus, be aware that many lenses are “focus by wire”, which means that the lens focus ring does not control the focusing element within the lens directly, so there may well be a lag in obtaining focus. I find that manual focusing aids such as magnification, and / or focus peaking work well, and instead of turning the focus ring “rock” the camera physically slowly back and forwards until sharp focus is obtained.
Marika
Photo By: Derek Smith
Falling Down
Photo By: Derek Smith
Robin
Photo By: Derek Smith
Cadwell Park
Photo By: Derek Smith
Louth Photographic Society
Good Morning All I was having my lunchbreak on the Wolds last week and spotted this tree in a field next to me, it does give the impression it's looking at you. I hope you're all enjoying the summer break, time does fly by and it's time to get ready for returning to the club on the 9th of September. We start with mini lecture, 15 minutes on what you have been doing over the summer. If you want to take part, please email me and we will see how many we have. The September PDI competition is coming up as well on the 23 rd of September, Objects in the air and open, Harry will now start taking your entries, three entries in each subject with an (R) after one of them to be removed if there are too many entries. Derek sent the N&EMPF Exhibition entry forms out; I will again act as organiser for our club. The standard is very high so it's one for your best PDI's. We will view some last year's PDI's that made the grade on the 16 th of September. Regards Graham
NELPS organised an outing to the Trolleybus Museum at Sandtoft, there was some confusion with opening times, and a few of us arrived to find the gates closed, we went for a coffee!! Once inside and parked up we were welcomed by the volunteer staff, and began to take some photos around the site. A Grimsby trolleybus was running this morning, this bus had been painstakingly restored from a bare chassis, with great attention to detail, even down to sourcing the original moquette fabric to upholster the seats, it was great to be able to ride in a trolleybus again. Trolleybuses have a particular nostalgic memory for me, I lived in Uxbridge, on the outskirts of London, and the 607 trolleybus route ran past the end of my road, with a usual frequency of 5 minute intervals the buses were a common sight gliding along the main road. The 607 route was one of the longest in the country 11 miles to Shepherds Bush, taking about an hour for the journey. The trolleybus was whisper quiet, comfortable, and pollution free, and I took several trips on these. In comparison the conventional London bus the “RT” was not as quiet for longer journeys. The London trolleybuses, and eventually the London “RT” buses, were replaced with the iconic diesel fuelled Routemaster “RM” bus. I had an enjoyable visit, and many thanks to NELPS for organising the outing.
When we see a photograph what do we actually see? Does the image grab our attention? Does the image tell a story, or do we have to fill in the blanks with our own memories, and experiences? If we see a complete picture, or just a detail, which stirs our emotions most? At a recent competition a print was shown of fishing boats pulled up on the beach at North Landing, Flamborough, it was an excellent print, but the judge remarked “it’s just boats on a beach”. Do we feel the same emotion with a “normal” view, or do we want more, a storm raging, or fishermen launching the boats? Anyway, here are a few of my “abnormal” photos, first up a rusted bolt, you see I ask “who put that there?”, “what did it once hold?” Second, a vehicle excise disc, surely that stirs memories? Thirdly, a stone carved column, who carved the details? Was it shaped according to an architect’s brief, or a stone masons pattern? What emotions were felt by the stone mason? Lastly, a door handle. Where does this lead? How old is it, and how many hands have opened this door? Finally, I think that I’ve got my “mojo” back, I’ve been out more with my camera, and enjoying the experience, and surely that’s what photography is all about, the joy of capturing an image that pleases me.
The Exhibition will be in place from 10th - 29th September 2026
I was scrolling through the archives yesterday, and found these "Still Life" images. Still Life is an interesting photographic genre that requires good lighting, and compositional skills, but the results can be amazing. Here are four images of the genre, "Breakfast" showing cereal falling into a bowl, "Four Candles" (no not the ones from the Two Ronnies sketch), the moody "Decaying Tulip", and the simple but effective monochrome "Opener". Perhaps these images might give you some inspiration.
I joined the NELPS outing at Chambers Farm Woods on Wednesday. The NELPS visit to Chamber Farm wood and butterfly garden was well attended, with several members from NELPS, Grimsby, Dunholme and Louth, kind thanks to all that came, although it was very hot the butterfly garden, being rather full and slightly unkept did not let us down with butterflies, two less common were seen, a Comma butterfly and a humming bird moth, with loads of very lively common blue butterflies. Most of the insects in the butterfly garden were highly active, and by the time an insect was spotted, it was off!! I managed to just about get an image of the Comma butterfly, and nobody stood a chance with the humming bird moth, it was too fast. The dragonfly was more accommodating remaining fairly still posing for us. The next NELPS outing will be to the Peoples Park in Grimsby on Wednesday 19th, I'm busy on that day, but I will be attending the meeting at the Sandtoft Trolleybus Museum on Wednesday 26th. Many thanks to NELPS for organising these outings, it was a thoroughly pleasurable morning.
A visit to Whitby for a sunset picture didn't quite go to plan. Unknown to me today is the last day of the Whitby Regatta. Whitby in the summer is usually busy, but today it rivaled Time Square in New York. My planned shoot of the East Pier was a non-starter because for tonight only there's a fun fair along West Pier where I planned to shoot from. I had to re-think and resort to plan b, which was also a non-starter because the East Pier was closed as it was packed with fireworks. Plan c was OK though and I got an image I'm pleased with.
I've been up to RSPB Bempton Cliffs this week, and have taken some excellent photographs, the weather was fine, and the lighting was less harsh than usual. This pair were on the cliff top, obviously well established, and saw off this interloper trying to muscle in on their space, those beaks look very vicious. I hope that everyone else is having a productive summer break.
For club interaction, we are invited to these NELPS photo shoots. So lets start this club interaction, NELPS are now on there summer break, but it does not stop there. The NELPS club president has put together some outdoor photo shoots:- Lincoln 5th Aug meet at the Cathedral 11am Not forgetting the photo exhibition by Lincoln Camera Club in the Usher Gallery! Chambers Farm Wood & Butterfly Farm 12th Aug meet at 10am. Peoples Park Grimsby 19th Aug meet at 10am. Trolley Bus Museum Sandtoft 26th Aug meet at 10am Cadwell Park 10th Aug motorbikes, 24th Aug cars and both are track days so free to get in.
Sutton & Trusthorpe Camera Club have their annual Exhibition at the Meridale Hall, Sutton on Sea, on 29th / 30th August. Drink and a Home-made cake only £3!
