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 16 July 2026
The LPA Battles competition was held last night at Axholme Camera Club, in Haxey Church Hall. I attended as the Louth Photographic Society representative, bringing the Battles prints with me. It was a closely fought contest with some excellent prints from Axholme, Barton, and ourselves. The judge for the evening was Steve Dormer, from Doncaster, and he was very relaxed in his judging of the prints, providing excellent critique on each print. At break time, Steve had held back a total of 13 prints for further assessment and award of higher points, Axholme, and Louth had 5 each prints held back, with Barton 3 prints. The attached photo shows all the held back prints on the print stand. At the end of the evening Axholme took 1 st place with, 266 points, Louth came 2 nd with 258 points, and Barton 3 rd with 251 points. As the prints were taken off the stand, one print remained, it was a Louth print titled “Sleeping” by David Whitehouse, this print was awarded 20 points, and the judge Steve was very taken with the image, well done David.
by Graham Harrison 12 July 2026
Good Morning All Last week members walked along the Swaby valley, we have done the walk before, but it is now very grown up with nettles, grass and brambles. Not put off Chris led us through the valley to Swaby, there were six of us plus three more who caught us up in Swaby. The butterflies we saw as I am finding out this year just don't want to settle but we did manage some photographs before returning and going for a drink in the Massingberd Arms. This week there is an LPA Battle at Axholme on Wednesday starting at 7.30, if anyone would like to attend, please email me for details or look on Axholme's website. We are not having a meeting in Louth this week, probably as well the way the football went last night and with the next match on Wednesday evening. Regards Graham
by Derek Smith 9 July 2026
Last night our members enjoyed a visit to the Swaby valley nature reserve. We crossed over two fields from South Thoresby, then followed the course of the Swaby Beck chalk stream through the valley, the public footpath was bounded by dense vegetation that hindered our progress at times. There was plenty to see around the reserve, myriad butterflies flitted around in a very lively manner, making for difficult photography, I spotted several small grasshoppers, and soldier beetles in the long grass, I tried to photograph a ladybird, but it was gone by the time I focussed on the creature. It was a very enjoyable evening, with good friendly company, and our camera skills were needed for the macro photography, these are a few of my photos from the evening.
by Graham Harrison 5 July 2026
Good Morning All Last week's outing was re-scheduled due to a clash with a certain world cup match, the good news was a victory for England, however we intend to still hold the outing on Wednesday 22 nd July. I did go to the Festival of Flight at the Shuttleworth collection, Old Warden last weekend. It was too windy for some of the old Biplanes, but we were treated to a four-and-a-half-hour display featuring many planes that I had never seen fly before. The De Havilland Comet was built to compete in the 1934 race from Britain to Australia, only three were built and it's good to see it flying, the aircraft design was quite advanced for 1934. This week, Wednesday 8th July, we have another camera club outing to the Swaby Valley, meeting at 6pm. Swaby is just off the A16 heading from Louth to Skegness. Regards Graham
by Derek Smith 2 July 2026
Last night’s Louth Photographic Societies outing to Kirkby gravel pits nature reserve was cancelled as some members preferred to watch some sporting gentleman by the name of Harry Kane. (Congratulations to the England team) The reserve is small, and simply laid out, a public footpath leads along a tree lined avenue to the river Bain at the back of the reserve. Historic sand and gravel extraction has left a large lake in the centre of the reserve, several ducks and waterfowl inhabit the lake and there is a bird hide on the shoreline. Returning to the road, there is a path running parallel to the road bounded by a hedge, insects of various types can be found in this area, damselflies, butterflies, and hover-flies are often prolific. Our outing to Kirkby Gravel pits is now scheduled for Wednesday 22nd July. Parking is on the verge by the roadside. Kirkby Gravel pits are fairly close to where I live, and it’s reserve that I often visit, these are some photos from a visit in July last year.
by Graham Harrison 28 June 2026
Good morning, All,  Last week at the club we had our monthly print competition, Trees and Open. There was a very good entry with a high standard of photography on show. Tony Gaskins was first in the Open and I managed a first in the trees, all the results are on our website and there is also a blog on the evening. This week, Wednesday 1st July, we are having an outing to Kirkby Gravel Pits, if we meet at 6.30 at the reserve, though you can arrive earlier as there are usually dragonflies etc around the entrance. If we walk straight ahead first, then anyone who arrives late can find us. I have struggled to find a map, but you can see the location on the Lincolnshire wildlife Trust website. Kirkby Grave Pits is also a good reserve for birds. Tattershall Road 1 mile south of Kirkby-on-Bain Woodhall Spa Nearest postcode LN10 6YN. Please note - postcodes are for the nearest registered address as we are unable to get postcodes for nature reserves.
by Derek Smith 25 June 2026
A print competition was held last night with the categories of "Trees" as the subject, and "Open". Our judge for the evening was Gail Wrigg from Barton who did an expert job. The first category to be judged was the "Open" with the high standard of prints making the choice of top placement difficult, and Gail held back 9 prints for further evaluation. There were some chuckles from members around one of Richard Hildred's prints of wooden electricity poles titled "In my previous life I used to be one of them" an "in" joke from Richard, which totally baffled Gail. After the break Gail judged the "Trees" category, with 7 prints held back this time for awarding of higher marks, the beautiful colours of some trees, especially the autumnal images contrasting with the stunning monochrome infrared prints from Richard Hildred. It was a great evening, with excellent prints on display, and the website Competition page has been updated with the full results. 
by Graham Harrison 23 June 2026
Good Morning All Last week we visited the nature reserves at Fir Hill quarry and Muckton wood. I have written a blog report on the evening which is on our website. You can always try something a little different like I did using camera movement. This week, Wednesday 24th June, a print competition will be held, with the categories of "Trees" and "Open" and is to be judged by Gail Wrigg.  The following week we have an outing to Kirkby Gravel pits. If you want advice on camera settings etc the outings are the perfect opportunity to ask other members while we all have our cameras. Regards Graham
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by Derek Smith 20 June 2026
Each year Louth Photographic Society begins a new project, one photo taken each month on a specific subject, that's 12 photos presented on "Project Night" in January. Last year the subject was "Prime Time" one photo each month taken with the same fixed focal length lens. This year the subject is water, the subject sounds easy enough, and I've completed 5 photos already, but I'm struggling a little with a photo for June. I'm currently on holiday in Corfu, an island surrounded by water which should be easy, but I'm yet to find the "definitive" photo for the project. These are my photos so far this month: Best regards Derek
by Graham Harrison 19 June 2026
Good Evening All