Lens Sharpness, Focal Length, and Aperture

Derek Smith • 6 May 2024
In my experience it doesn’t matter what the size of sensor a camera has, most lenses will have a corner-to-corner optimum sharpness in the range of f/4 – f/8 aperture, often called “the sweet spot”. Camera lens design will often give a sharp performance in the centre at the widest aperture, for example at f/1.4, with the lens aperture resolving to sharper corner to corner sharpness as it is stopped down, then the performance deteriorates again becoming softer as the lens is stopped down further owing to diffraction at apertures above f/16, personally I wouldn’t push a lens on an APS-C camera much past f/11. 

Why does this matter? For landscape photography ideally a photographer would want foreground to background sharpness, and simply always choosing to select an aperture of f/10, or f/16 arbitrarily may not give the correct front to back sharpness required. This foreground to background sharpness is defined in cameras as Depth of Field (DoF).

Depth of Field is a factor of sensor size, closeness to the subject, and the focal length of the lens used, this attached image of a worm cast on a sandy beach illustrates perfectly the effect of DoF, shot at f/5.6 on an APS-C sensor, the band of sharpness runs through the focus point on the worm cast.

For macro photography a photographer often needs to be close to the subject, which reduces the DoF, requiring a photographer to focus stack the images. Many photographers opt for a small crop sensor of micro four thirds format from Olympus, or Panasonic, to maximise the DoF in this genre of photography.

Many of you know that I enjoy portrait, and fashion photography, DoF is critical as the focus should be on the eyes. A few years back, I succumbed to social media advice that I needed a full frame camera for portraiture, especially with an 85mm f/1.8 lens shooting wide open. Unfortunately, the DoF was razor thin, the lens a Sony FE 85mm f/1.8, and Sony A7 ii was heavy as a combination, and the large lens provided little room for my fingers on the handgrip, the Sony cameras were sold within a few months. On my last model photo shoot, with Ivy in Skegness, I used a new TT Artisans 56mm f/1.8 on my Fuji APS-C camera, shooting wide open the eyes were in focus but the ears, and nose were soft, stopping down to f/4 gave better focus on the face, but still retained a smooth out of focus background – bokeh.

I use an app called PhotoPills on my mobile phone, the app provides a tremendous amount of data relevant to photography including a DoF lookup, here are the results from my past, and current cameras, and lenses.

Camera                    Sensor           Lens                                              Aperture                  DoF
Fuji                            26Mp             Sigma 30mm                             f/1.4                          0.36m
Fuji                            26Mp             Fuji 16-80mm                            f/4 @80mm           0.14m
Fuji                            26Mp             TT Art 56mm                              f/1.4                          0.13m
Sony A7 ii                24Mp             Sony FE 85mm                          f/1.8                         0.08m
Olympus EM5        20Mp            Sigma 30mm                              f/1.4                         0.28m

Knowledge is power!! I know that any DoF greater than 0.20m for portraits will provide good definition on the face, without any softening of facial features. The Sigma 30mm f/1.4 lens allows for portraits to be shot wide open. My TT Artisans 56mm f/1.8 lens is probably best stopped down to f/4, also the benefit of stopping this lens down is that the lens will provide improved sharpness at this aperture.

Mark Denny has posted a YouTube video on this topic which some of you may find useful. 

In this video Mark discusses his mistakes in selecting aperture in landscape photography, he also touches on finding the “sweet spot” of a lens.

My photo of Jayne, “English Rose”, was taken with the Sigma 30mm f/1.4, shot wide open at f/1.4, the foreground petals are out of focus but importantly the eyes, and facial features are in sharp detail. This portrait of Fleur, taken in natural light with the Olympus EM5, and the Sigma 30mm lens, was shot at f/2 again preserving fine detail.

For landscape photography the image here is of the rocks in a bay at Flamborough, I can see on the set of images taken at this time that I’ve fallen into the trap outlined by Mark Denney of shooting at a fixed aperture, luckily in this case the selected aperture of f/8 worked on this image, with the Fuji 16-80mm zoom lens at 16mm, the foreground rocks are in sharp detail, and the background cliff still retains a lot of detail. 

Louth Photographic Society

by Derek Smith 9 April 2026
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.
by Graham Harrison 5 April 2026
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
by Derek Smith 2 April 2026
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.
by Graham Harrison 29 March 2026
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
by Derek Smith 26 March 2026
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.
by Graham Harrison 22 March 2026
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
by Graham Harrison 15 March 2026
Good Morning All Last week at the club we held our monthly PDI competition judged by Martyn Wrigg, the standard of entries was very high and well done to Tony Gaskins for a first in the Architectural Detail and Derek Smith for his first place in the Open. All the results are on our website under competitions. This week, Wednesday 18th March we will be holding a Committee meeting, just committee members for this one. The following week Chris Birchmore is the speaker for the night. Harry is now accepting entries for the PDI local competition, with the categories of "Local Nature" and "Open". We judge this competition in house so if you would like to judge one of the subjects please let me know. Regards Graham
by Derek Smith 12 March 2026
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by Derek Smith 12 March 2026
A PDI (Projected Digital Image) competition was held last night with the categories of "Architectural Detail", and "Open". Martyn Wrigg was our judge for the evening, and he competently judged the submitted images, although he diid surprise with some of his choices of placing, but that's a judges perogative. Martyn complemented members on the quality of the images presented, which had made some of his decisions difficult. First placed was "It's a Fixer Upper" in the Architectural Detail section, and "Dervish Musician" in the Open section. Congratulations to Robin Begley, who as one of our newest members submitted some impressive images, achieving a 3rd place in "Architectural Details", and 2nd in the "Open" category. All the results are now posted to our website Competition page.
by Graham Harrison 8 March 2026
Good Morning All Last week at the club member Steve Chapman gave us an insight into his life and especially his time at Ilam Park in Derbyshire photographing for the National Trust. Steve showed us many photographs he had taken of the people involved with the trust and the Peak District. The second half was dedicated to Steve's own work, some superb aircraft photography as well as many other subjects. There is a report on the evening on our blog page. This week, Wednesday 11th March we are holding a PDI competition, with the categories of "Architectural Detail " and "Open" to be judged by Martyn Wrigg of Barton. The following week is a committee meeting for the committee members only on that evening. For newer members we have two committee meetings a year. Regards Graham