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By Eugene Struthers







When choosing a lens, it is fundamental to know what type of images you plan to capture. It is also important to be consciously aware of the conditions and time of day you will be working in. Because the conditions you will be working in will be dictated by light. Light is the main source over which we have no direct control. Indirectly, we can use strobes and flashes to artificially introduce light.


But once we can fully understand the capabilities and structural components of our lenses. And how they function in a way that will benefit us as photographers. Then we can take full control of any given lighting condition. Either with the assistance of a strobe or flash, as we balance them with ambient light.


Without going over what has already been discussed. I cannot stress how important it is, to have a working knowledge of how a lens's Aperture and Shutter speed work in conjunction with the camera’s ISO sensitivity to light. The counterintuitive nature of the Aperture may confuse some new to photography. Since a Small Aperture number (f/1.8)  produces a wider Aperture, which in turn will mean more light. , a large aperture number (f/22) produces a smaller, narrower aperture, which in turn means less light reaching the sensor.


If you need to go over this again. And require an in-depth explanation. Please click on the link below to be taken to the previous article I wrote on Aperture and Shutter Speed. It may shine some light on any grey areas you are not fully understanding.




Aperture & Shutter Speed: Click here

The process of actually picking a lens can be very daunting. Especially if you aren’t exactly sure what you are looking for. So to simplify the whole process. I have broken it down into easy-to-understand steps for you.




Example: 50mm f/1.8

                  18-55mm f/3.5 - 5.6

                  55-250mm f/4 - 5.6


The Focal length is represented by the first set of numbers.


The main point to remember before we proceed. That the Minimum Aperture of a lens is the same for all lenses, whether they are Canon, Nikon, etc. The second set of numbers you see above. Starting with the f/. These represent the number that we are mainly concerned with. This is the Maximum Aperture of the lens. So why is this so important? Why do you need to know about this extra information? And why are there two sets of f/ numbers instead of one, like some lenses have?








Prime lenses have only one Maximum Aperture, i.e. 50mm f/1.8


A Zoom lens has two Maximum Apertures i.e. 18-55mm f/3.5 - 5.6


When you purchase your digital SLR camera. It came with a “kit” Zoom lens of 18-55mm f/3.5-5.6. The lens is given with all new digital cameras by the manufacturer. This type of lens allows us to zoom in and out as it has two Aperture f/ numbers. And we can vary our focus on either. These are classified as having “Variable Maximum Aperture.


At 18mm, the Maximum Aperture is f/3.5


At 55mm, the Maximum Aperture narrows to f/5.6


This then allows us to vary our zoom and focal range to a point the same where between the two Aperture focal lengths of about f/4. (Try and memorise the Aperture settings)


If you are a professional photographer, you will be consciously aware of how the lens sometimes struggles to maintain focus when placed on autofocus. You can hear the lens tweaking and moving internally to try its best to focus, moving in and out. This is down to the variable maximum aperture zoom exposure settings within the lens constantly changing. And this is the main reason why a lot of landscape photographers use manual focus or a zoom lens with a “Constant Maximum Aperture”.


What is a Constant maximum Aperture?


This is a lens that has two sets of focal lengths (focal ranges) and one constant Maximum aperture. This means the Maximum Aperture remains the same and isn’t affected by how much the lens is zoomed in and out.


Example: 25 - 104mm f/4


The f/4 is the maximum aperture for both the 25mm and 104mm focal lengths and anything in between.


The type and location of the photography you capture will dictate which maximum Aperture lens to select.


Without stating the obvious. Lighting conditions will influence this decision process as well. As dark environments require a small f-number, and wider aperture, and bright-lit environments require a larger f-number and smaller aperture. If your lighting condition in your chosen location is constantly changing. Then you will require a lens that can quickly adapt and modify its aperture settings to accommodate the shift in light intensity.


If you are a wedding photographer, and you are constantly in different locations each week. You may find that the lighting conditions of the locations and environments that you find yourself in. Isn’t that great for capturing perfectly exposed images? Especially if you have a vicar on your back about not using a flash indoors in his church during the wedding ceremony.


Well, it would be easy if you knew how a lens works and which lens is suitable for a given condition and environment. This would explain why a lot of wedding photographers use lenses with a variable and constant maximum aperture. You have to weigh up your options and decide. How do I soak up all that ambient light in the church with just my lens and nothing else?  Whilst chatting up the bridesmaids.


However, your type of photography might be done out and about in the natural daylight. And there is no real need for you to purchase a lens with a wide aperture (small f-number). And you find that you can get by with a Maximum aperture of about f/4. Because bright natural sunlight is abundant.



There should be a 7th point on this 6-step guide to choosing a suitable lens. Which is mostly overlooked.


7th point



7) Match your lens's Aperture to the lighting condition of the environment you are working in.




Please follow the guide below to assist you.


   Lighting condition           Max Aperture                                                 Explanation & reason

I             Indoor                               f/1.4 - f/2.8

I             Overcast                          f/2.8 - f/3.5

I             Shade                                f/3.5 - f/5.6

I             Daylight                               Any

Ideal if you can't use a flash indoors. A wide aperture takes away the stress of shooting in dark locations and environments.

Mid way between light and dark. So challenging to a new photographer who will need to use a faster shutter speed to freeze motion.

You can get by on a shady day with a f/3.5 aperture. Depends if morning or afternoon shade and intensity of clouds and sun.

Day light sun shine, is the perfect conditions for any lens. Maximum aperture won't really matter. Down side maybe over exposed images, too much light.

Katja has recently purchased a new Canon 80d digital SLR camera that came with an 18- 55mm

f/3.5 - 5.6 kit lens.


At her local pub, a group of glamour models have found out about her new purchase. And have asked her to photograph them for a charity topless football calendar.


The calendar is for a local charity associated with a local hospice. To help send terminally ill patients to the USA for a holiday.

Katja knows how important this calendar will be to the girls, and she doesn't want to let them down.

She only has her kit lens and knows how to capture a proper set of images for their calendar. She will require a better lens. One more 
suited with the capabilities and functions to make the day a success.

She knows that she will need to be in the mix with the glamour models as she photographs them from the 
sidelines. And the only way she will be able to zoom in and out as they run around and across the field as they kick the football. Will be if she has a "Telephoto to telephoto lens". This type of lens will allow her to capture all the actions of the topless players. As the game heats up.

After reading Glamour-Photography magazine. Katja decides that as she has a Canon camera, the lens must be canon as well. She also
 knows that she will require a zoom lens so that she can get up close to the models as they play topless football on the field.


Katja isn't too sure what maximum aperture lens to purchase. So she does a bit of research on the internet and decides. That she would need a Maximum aperture, just to cover herself. As the weather hasn't been that great in the UK. And she kind of knows that it is bound to rain or drizzle or just be an overcast day. So she isn't going to take any chances. 


She isn't too confident with her new camera, and she doesn't want the added extra worry about lens settings. So she decides on a lens with a constant maximum aperture. So that she can have full control of the settings herself. This will allow her to put all her focus and attention on capturing crystal-clear images of the topless players as they run around the field.


Katja decides on: Lens mount: Canon

                               Lens focal length: Telephoto

                               Lens type: Telephoto to telephoto zoom

                               Maximum aperture: f/2.8  /   Zoom aperture: Constant


         See you all

next month

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