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
It was our first meeting after the Christmas break, it was good to be back and the meeting was well attended. We held a PDI competition with the categories of “Insects”, and “Open”, our judge for the evening was Colin Lusby, who is a very experienced judge, and he gave many useful tips, and suggestions on how to improve our images for greater impact. Dave Turner took the well deserved top spot, in the “Open” category with his image of “Moody Llanberis”, landscape photography doesn’t just need a good view, the skill is in capturing the mood, the light, and the shadows, as well as the scene – Dave has captured the scene perfectly, it’s a view that anyone would love to hang on their wall. In the “Insects” category, Graham Harrison took the top spot with his perfectly sharp Willow Emerald Damselfly, this is a beautiful green iridescent insect pictured on a stalk, an excellent capture. The Competition page on the our website has been updated with the top three images in each category, and the score sheets.
Good Morning All I photographed this Treecreeper bird at Linwood Warren recently. We start back again this Wednesday 14th January with a PDI competition, the categories are "Insects" and "Open" to be judged by Colin Lusby of NELPS. The list of entries has been sent out and we have a good entry, fifty images altogether. The following week we hold our project night, "Prime Time", we have four members showing their images from the project. Regards Graham
The use of monochrome images seems to be coming back into fashion of late. Many of a certain generation will remember when monochrome was everywhere, television, newspapers, magazines, films, and our own photos (black and white film was less expensive), I remember in the mid sixties when the Sun newspaper (a broadsheet at that time) and the Daily Herald began a rivalry to publish the most colour photos into each edition. Monochrome images can sometimes convey a mood, and detail that’s not always evident in a colour photograph. Converting a digital colour image to monochrome can take a fair amount of skill, sometimes it’s helpful to visualise the image as a monochrome before even taking the photo, when editing the blacks have to be rendered as pure black, and the whites rendered as pure white, with a range of greys in-between, otherwise an image can look “muddy”. If your camera allows possibly try shooting some images in monochrome. Portraits, architecture, landscape, street photography, and trees often make the best monochrome images, and rarely wildlife, although my image of a lizard is quite effective. I shall be running a “Photo Editing” workshop on the 4th February, and members will have a chance to try converting colour digital images to monochrome.
Good Morning All I have been out a few times with my camera, there are a lot of Fieldfares around in large flocks at the moment, the only trouble is they soon take flight so are quite hard to get near, this one was from the car window. Our first meeting back in the New Year will be January 14th opening with a PDI competition, the categories are "Insects" and "Open" judged by Colin Lusby, please send your entries to Harry with a closing date of midnight the 7th January. The following week is the project night where members were asked to take part and using a prime lens take one photograph a month. Myself and Derek have done the project could any members who have taken part let me know please so I have an idea how much time will be left over. We are hoping to enter the N&EMPF club PDI competition and LPA club PDI competition, Harry as usual will organise an entry for us but if you can send him up to six of your very best PDI's when you have time, please. The main rule is it can't have been in the competition before. You may need to send them in two files as LPA use a size of 1920 x 1080 and NEMPF 1600 x 1200. The new project for this year is water, one photograph a month which includes water. The projects will be then shown January 2027. There is also the LPA individual PDI competition you may want to enter, Derek sent details a few weeks ago but information can be found on the Lincolnshire Photographic associations website. Regards Graham
So, why did I swap my Olympus OM-D E-M5 iii camera, and associated lenses for the Fuji XT-3 and lens system, and return to Olympus / OM Systems just a few years later? The Olympus E-M5 iii was, and still is a very capable camera, with a 20Mp micro four thirds sensor, and fully weather proofed, my camera upgrade path was to the OM-D E-M1 iii, but it would have cost me at least £1000, providing me with dual SD cards, and a few extra controls. It was cheaper for me to sell all my Olympus gear, and buy into the Fuji ecosystem, the XT-3 had the dual SD card slots, and promised to have improved image quality. The Fuji lens selection was extensive, and I bought a pair of zoom lenses, and a couple of prime lenses. Later on I bought the Fuji XS-20 as an everyday carry camera, but it was forever warning of overheating. I was content with the Fuji system for several years, I would liked to have photographed more birds, and wildlife, however the reach (focal length) of the 70-300mm Fuji lens was a limiting factor. I took some of my best photographs with the Fuji system, and the Fuji 16-80mm zoom lens was one of my favourite all-round lens. The turning point for me was the launch of the OM Systems OM-1, with a stacked BSI sensor, and subject detection AF, I could have chosen a Nikon, or Canon camera system but the lens selection was limited at that time for the latest mirror-less cameras. I sold all the Fuji gear, and bought a used OM-1 camera for £850, closely followed by a 12-45mm f/4 zoom lens, the 17mm f/1.8 prime (an all time favourite of mine) the 25mm f/1.8, and the 45mm f/1.8 prime. I’ve repurchased the Olympus E-M5 iii, as it’s a great small everyday carry for travel, and general photography. The lens I bought last year was the 60mm f/2.8 macro lens, which has enabled me to take some great insect photos. For bird, and wildlife photography I have been using the Olympus 70-300mm zoom lens, but I’ve just upgraded that to a OM Systems 100-400mm zoom lens, which is stabilised to 7 stops of IBIS on the OM-1, and is fully waterproof, and dustproof. As the micro four thirds sensor is smaller than a full frame sensor, you have to double the focal length to obtain an equivalent viewing angle to a full frame camera, thus the 100-400mm lens becomes equivalent to 200-800mm on a full frame camera. For this coming year I intend to be more focused (no pun intended) on landscape, and wildlife photography, watch this space. Whatever camera, or phone you’re taking photos with just enjoy your hobby, and keep learning and improving.
Good Morning All I hope you all had a very good Christmas and wishing you all a happy new year. I tried to find one photograph that summed up the year. Regards Graham
I hope that everyone has had a very good, and healthy Christmas. For our Programme for the New Year, I shall be running a photo editing workshop on 4th February, I will provide each participating member with an SD card containing example images for us to work together in editing. I shall be using three photo editing apps, which are all free to download and use, the first of which is: FastStone – This is the software that our Society uses for displaying images during our PDI competitions. The software is excellent for reviewing a file of .jpg images, basic edits, and resizing of images. The software is unable to develop RAW images, but does show a thumbnail preview which can be useful for culling a set of RAW images. Microsoft Windows only. Canva Affinity – This is excellent for developing a single RAW image, processing Focus Stacking, and Bracketed Exposure images. The software also can be used for layering, and compositing of images. I will be demonstrating the Focus Stacking, Bracketed Exposures, layering and compositing of images. You will need a Canva account to download this free software which runs on Windows, and Apple Mac. RawTherapee – This is an extremely complex photo editor, but I firmly believe that the software can rival anything that Adobe produces without the bloat, and cost. However the software has a steep learning curve, especially with the masking tools. One of the best features for me is the preview ribbon of a set of images at the top of the screen, I also like the tabbed editing tools, it is also possible to batch process basic edits onto a RAW file using a RawTherapee pp3 file. RawTherapee can be downloaded to Windows, Mac, and Linux. To gain the best from the workshop I would ask members to download all three software apps to their laptops. In addition there are YouTube tutorials on the use of RawTherapee, which I would encourage you to watch, and that way we can work together to understand how to produce the best results from the software. Wishing all our members a very happy, and prosperous New Year.
Good Morning, All, We had a very good last meeting before Christmas, thank you to my partner Jane for her hard work preparing the buffet, also thank you to Tony for preparing the quiz, there were some very good questions with Robin and Heather coming out on top with a fantastic 48 points. Thank you to Harry as well for running the raffle and to everyone who donated a prize. We now start our Christmas break but if you get bored there are things that you could be doing. The first meeting back on 14th January will be a PDI competition, with the categories of "Insects" and "Open", you can start sending entries to Harry now, remember three insect entries and three open entries with an (R) after one entry which will be removed if there are too many entries, but you may use it some other time. Derek sent information regarding the individual LPA PDI competition, it would be good if a few members entered. They do like you to go along on the day of the competition as well if you enter or just go along anyway if you didn't. The Print Of The Year (POTY) competition is held in February, so it would be a good time to look through your prints and sort some out ready. For newer members it may seem a funny time of year but our camera club year runs from the beginning of May to the end of April, all rules are under competitions on our website but the main one is that your entry hasn't been in a print of the year competition before, there are six subjects plus best mono in competition, this can be from any of the subjects. The subjects are Landscape, Pictorial, Nature, Photojournalism / Street, Record and Portrait. Regards Graham
The buffet and quiz evening was one of the highlights of our calendar, it's the culmination of the year's events before the Society takes a Christmas break. The buffet was excellently prepared by Jane, who is Graham's partner, with plenty of delicious food, pork pies, sandwiches, plum bread, with cheese, quiche, mince pies, and cake. Tony Gaskins produced an esoteric quiz, and Robin and Heather scored the most points with 48 points, I scored a miserable 17 points, but we all had a lot of fun with the answers. The raffle raised £47, with some members collecting more prizes than others, amid lots of laughter and banter. Overall it was an excellent evening, enjoyed by all. A big thank you to Jane for the buffet, Tony for the quiz, and Harry for organising the raffle. Wishing all our members, and readers a merry Christmas.
Good Morning, All We did go to the sand racing again last week, the weather was a bit overcast but as no sky is required for this kind of photography, so good action shots are still possible. Last week at the club we held our monthly competition, of prints, with the categories of "People" and "Open". There was a very good entry with some excellent prints. David Whitehouse came first in the People section with Dave Turner winning the Open section. All the results are on our website under competitions with a blog on the evening as well. This week our Christmas buffet and quiz night will be held. The buffet will be provided for you but feel free to bring a drink along with you (a beer or glass of wine if you wish). Dave Mann will also be providing tea and coffee. Tony is doing a quiz for us all so bring a pen and paper if you remember, Christmas jumpers are optional. Harry will be selling raffle tickets, and if you would like to provide a prize please bring it along and give it to Harry. Regards Graham
