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
Yesterday evening the 17th April 2026 was the opening night for the Louth Photographic Society’s 70 Year Celebration Exhibition at the Louth Museum. The Mayor of Louth, Darren Hobson attended and was very impressed with the exhibition, who by the way is interested in photography. Some relatives of previous members, who are no longer with us, also came along. Julie Gough (Milli) and Bob Maddams represented the Museum. From the club we had 10 members, some with their partners. In all 20 people attended. A buffet and drinks were provided by the club which were prepared by Harry and his wife Karen for the night. Graham Harrison the President of the club gave the opening speech followed by Chris Birchmore, who was the member who first put the idea together. Members mingled, discussed the photographs and generally had a good time. Many thanks for all who attended and made it a night to remember.
Two female models were booked for our "Studio Night", which was held last night, and members were able to practice photographing the models in various poses, on the portrait set, or the fashion set. Our models Ginny, and Dina were very different in character, and appearance, but both were excellent models, and they posed easily in front of the cameras. The portrait set was lit with a flash speed light in a soft box, the fashion set was lit with constant LED lighting, the models changed outfits, and sets during the break. Both models are pictured here on the fashion set, Ginny in the red top, and large Doc Martin boots, and Dina in a softer fashion outfit. Members seemed to enjoy the evening, and for some glamour photography was outside their comfort zone, but it does give the opportunity to try something different.
It was a disappointing afternoon for Louth during Sunday's Fosters Challenge. One by one our submitted prints were dismissed, Graham Harrison's "Hairy Shield Bug", was too dark, "Trusthorpe Outfall" by Tony Gaskins had wind turbines on the horizon, and Tony's other print "Dawn Light Outfall Hornsea" was dismissed as the outfall was too close to the bottom of the frame. "Rudbeckia" by Harry Kerman fell as the judge felt that the third flower in the background was unnecessary. "Morning Sun Whitby" by Dave Turner was dismissed as the rising sun "caught his eye". Oh well, there's always next year. The winning print was a stunning portrait, "Maria" from Scunthorpe, which I felt had vibes of the Vogue magazine.
Good Morning All We had a really good week away last week in the Peak District, the good weather helped and we visited many places including Salford Quays and climbed to the top of Kinder Scout and Mam Tor. Last week at the club it looks like you were treated to some excellent coastal photography from member Tony Gaskins, Tony does a lot of long exposure photography producing stunning photographs. There is a report on our blog page with photographs from the evening. This week, Wednesday 15th April, is Derek's studio evening where we are invited to come along with our cameras, there is a £5 charge on the night to help pay towards the two models. The following week is a print competition, with the categories of "Circles" and "Open", you can send Dave Turner a list of your entries and bring your prints in next week. Today is the Foster Challenge at Nettleham village Hall, 1.30pm for 2pm, Louth has entered the competition as usual so it would be good to see a few members attending. Regards Graham
Our speaker last night was our very own member Tony Gaskins, who gave an excellent presentation "Coast 3" with some stunning visual images. Tony specialises in capturing long exposure coastal scenes, he related how beginning several years ago with a long exposure view of Whitby Pier he got the "bug" for long exposure photography. Much of his photography takes place along the Lincolnshire, and Yorkshire east coast, often arising in the early hours to catch a sunrise. Weather conditions dictate a lot of how the final image looks, and the long exposure style often creates a sense of calmness, and serenity, with pastel coloured skies, and milky seas. When the weather turns wild, the long exposure image presents a very dramatic scene with foreboding clouds. He recently travelled to Lewis & Harris island in the Outer Hebrides and took many images there, sometimes at sunny white sand beaches, and at other times moody bleak images as the weather closed in. Tony's technique requires a lot of patience, often spending hours at a location, with the camera mounted on a study tripod, and the ND filters on the camera permitting an exposure time of several minutes. Many thanks Tony for a very informative talk, well presented, and with some beautiful imagery.
Good Morning All Last week at the club we held a Local Nature and Open PDI competition, members Dave Turner and Steve Chapman kindly offered to judge the competition, thank you to you both, it was a good night and the entries were of a high standard giving you both quite a task. The results are on our website, but the two winners on the night were, Local Nature Tony Gaskins and Open Harry Kerman. This week, Wednesday 8th April, Tony Gaskins, one of our members is showing us Coast 3, a PDI presentation. Tony is an excellent photographer and spends many hours photographing our coastline. Aprils Print competition, Circles and Open is fast approaching, you can send your titles to Dave Turner when your ready and bring your prints in the week before the competition. Regards Graham
It was no April fools, when we held our PDI (Projected Digital Image) competition last night. The images submitted into this competition were off the highest quality. Dave Turner judged the Open category, which I think is always one of the hardest categories to judge, pitting landscapes, against nature, and still life, but Dave did a magnificent job, offering well founded critique of the images submitted. After the break, Steve Chapman judged the Local Nature category, (nature images taken within a 25 mile radius of St. James' church, Louth) Steve "held back" 10 out of the 18 submitted images, and gave those 10 images very careful consideration until he finally arrived at the 3 highest placed images. Steve commented that the submitted images were indeed of high quality, and he took his time to evaluate the submitted images and offered useful critique on each one. The competition made for a very interesting evening, and all members deserve praise for the quality of the submitted images. The website Competition page has been updated with the full results, and the top three images from each category. On this post is 1st placed Sedge Warbler, Cleethorpes by Tony Gaskins, in the Local Nature category, and 1st placed Hudson Bay Wolf, (Lincoln Zoo) by Harry Kerman, in the Open category.
Good Morning, All, Last week at the club member Chris Birchmore gave a presentation on MPP cameras which included some of Chris's collection of cameras and prints taken. There is a report on the evening on our blog page. Thank you Chris for an interesting evening. This week, Wednesday 1st April, we are holding a local and open PDI competition the local subject being nature, please if you haven't already, send your entries to Harry before midnight tonight. Members Steve Chapman and Dave Turner have volunteered to judge. Also on the Wednesday 1st April our Louth Photographic Society 70th anniversary exhibition will be open to view at the Louth Museum. Regards Graham
Chris Birchmore gave an informative, and interesting talk and demonstration of his medium format film cameras. at the beginning of the evening Chris gave a potted history of the origins of the MPP cameras he was showing us. The cameras take a 5 x 4" film stock, and looking at the cameras it seems incredible that photographers in the recent past could take excellent photographs with these. The MPP cameras were often used by the British Armed Forcies during the Second World War, and throughout the 1950s, and 60s, and some of these medium format were still being manufactured in the 1970s. The prints that Chris showed taken with these cameras were of excellent quality, with an amazing depth of field. Many thanks Chris for a fascinating evening.
Good Morning All Last week at the club we held a committee meeting, which was very productive, we made the final arrangements for the exhibition, charity night, and studio evening as well as other items on the agenda. We are holding an Exhibition opening night at Louth Museum on Friday 17th April celebrating 70 years of Louth Photographic Society. There will be a small buffet and cold drinks available, if any member would like to donate a bottle of wine to the occasion please hand it to Harry at one of our club nights. This week, Wednesday 25th March, member Chris Birchmore will be giving us a presentation. The following week is a local competition, with the categoriess of "Local Nature" (up to 25 miles radius from St James church) and "Open" (unlimited mileage) please send your entries to Harry before midnight, Sunday 29th March. Members Steve Chapman will judge the Nature category, and Dave Turner the Open category. Regards Graham
