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By Eugene Struthers

The extra features that are present on your digital lens are important to your success as a photography. Do you really need them? And if they weren’t present on the lens would it make any difference to you in capturing great images. Probably not because they are not that essential. Then why have them on a lens?


If you compare this to when you purchase your first new car. The salesman in the auto showroom will run through a list of functions and specifications about the car, highlighting characteristics that you will probably never use or will probably forget about after a week. That is until you actually need them. And you find yourself on the side of the motorway reading the instruction manual.


The main purpose of a new car is to get an individual from point A to point B safely. If a car keeps us dry when it rains and warm when it is cold. The rest is kind of irrelevant. As long as the car doesn’t break down. We will be happy. Are the extra features of air conditioning, electric windows, a sunroof, Satnav or even blue tooth wireless essential to our trip from A to B. Probably not. Will they make our journey any different? Probably yes. The car's features will contribute to us having a more enjoyable journey, and we will derive a benefit from their use indirectly.


Okay! Lets, break this down so you will fully understand what a feature is. The Satnav above is a feature and drivers derive a benefit from its use as it provides them with voice-activated directions.


This is pretty much what the feature's on our lens do as well. Each feature provides a benefit when being used, and this in-turn makes a photographer more efficient and successful onward on his journey.


Listed below is an outline of the features and benefits to look for when purchasing a lens.

Internal Zoom


These are usually specialist lenses which can be very expensive.


The zoom of an external lens will move as the length of the lens moves from wide-angle to telephoto. You can physically see and hear the mechanical elements of the lens components move.


An internal zoom lens is classified as a length of lens that is constant.


This means you don’t see any moving elements as the lens is zoomed in and out. The movement of all the mechanical elements occurs within the barrel of the lens. This makes the lens a lot faster and smoother. As it is not reliant on the external components to move and operate. The actual movement occurs with the glass optical lenses within the barrel of the lens. The internal zoom does not affect the balance of the camera when the camera and lens are put onto a tripod. The external lens can slide if pointed directly downwards. This can be a real inconvenience, especially if you are trying to capture landscapes from a high vantage point and your lens keeps sliding out. And you find you have to keep holding the zoom ring to lock it in place.  As there is no external movement, internal zoom allows movement in any direction. Ideal if you want to capture a city at night from the 8th floor of a tall tower block.       


Image stabilisation


The main purpose of image stabilisation is to allow photographers the added ability to capture images under lighting conditions that were once considered way too low for capturing crystal clear images. It allows a photographer the ability to capture images at a shutter speed three or four times lower than what was previously thought possible.


The rule of thumb for capturing handheld images is. You should hand-hold a camera at a shutter speed lower than is the equivalent focal length of the lens. Which means. If you have a lens of 300mm. You shouldn’t be hand-holding it at speeds slower than 1/300, a 50mm lens slower than 1/50.


But once we put image stabilisation into the equation and try to capture sharp images of still objects at 300mm, we can lower the shutter speed down to as little as /60 and still get crystal clear images.


The common misconception is that it enables you to freeze fast-moving objects at a slower shutter speed. This isn’t true. Image stabilisation only allows you to capture sharp images for static subjects at slower speeds. Your moving objects will still be blurry and shaky even if the image stabilisation is turned on.


There are three main types of image stabilisation systems on offer:


ISO stabilisation


This is the cheapest and easiest form of stabilisation a manufacturer can add to a camera. It is managed by the camera's firmware and is usually termed “digital image stabilisation”. This type of image stabilisation allows the camera to check the focal length and shutter speed being used and make a decision whether the two will create a sharp image. If it calculates that the image won’t be correctly processed to create a sharp image. The camera's sensitivity will be raised, which in turn will increase the shutter speed. The image will be captured, and the appropriate shutter speed used whilst the ISO has increased. It is not uncommon for noise to be introduced as the ISO increases.


Sensor stabilisation


The sensor stabilisation method also uses the focal length and shutter speed to make a calculation, but instead of adjusting the sensitivity ISO. The camera physically moves the sensor.


Lens stabilisation


This works by shifting the lens group towards the back of the lens on a plane perpendicular to the optical axis.


The two gyro sensors within the lens, one on the pitch “turns upwards and downwards” and the other on the yaw“ turns left and right”. These notice the speed and angle of movement and the information is fed to a microprocessor which computes the necessary adjustments to make to the lens group. This then changes the light's angle of refraction so that it hits the sensor in the correct place. This usually occurs when the shutter release button is half depressed.


Please check before purchasing a lens with image stabilisation, as your camera may already have it built in as an operating function.    


If you can’t afford an image stabilisation lens. Try increasing the shutter speed so it is higher than your lens's focal length. Or just increase your camera sensitivity ISO. Which may increase your chances of getting more noise in your images. If that isn’t working for you. Introduce a flash to freeze motion. Perhaps use the most obvious solution, a tripod. It that fails, try a shutter release cable or put your camera on a time release setting.

Silent autofocus 


You have probably noticed that when your lens focuses. It makes a mechanical whizzing and grinding sound. Similar to that of a going up-and-down lift.  


If you work as a private investigator or an investigative journalist or any other profession that requires discretion. Then this the best lens for you. As the lens won’t make any noise and give your location away by a loud, noisy lens.


The silent autofocus system is a ring-type USM designed and fitted in the circular barrel of a lens. It has a micro USM motor, rotor and gear drive that are combined into one. Which make it ideal for capturing fast action, the system has a smooth focus and fine sped control.



Canon – Ultra Sonic Motor (USM). Canon was the pioneer in this field.

Sigma – Hyper Sonic Motor (HSM)

Tamron – Ultra Silent Drive (USD)

Minolta, Sony- Super Sonic Motor (SSM)

Olympus – Supersonic Wave Drive (SWD)

Pentax – Supersonic Dynamic Motor (SDM)

Panasonic – Extra Silent Motor (XSM)

Tokina – Silent Drive Module (SDM)


The main advantage of using a ring USM, is that the motor is built into the lens. Which in turn makes focusing a lot faster than a standard lens.


They are a lot quieter than standard or cheaper lenses. Which makes them ideal for wildlife photographers who spend hours locating an animal just so they can get up close and capture it in complete silence. So as not to frighten the animal with strange sounds and noises.  


The only disadvantage being.


A “Silent autofocus lens will cost you a lot more than a convention standard lens.

The lenses are generally heavier than those of standard lenses as well.

Full-time manual focus


On every SLR digital camera, there is the option of switching from autofocus to manual focus. When you are in one, you are locked out of the other option.


To go back and forward, you have to flick the switch.


The modern lenses equipped with a manual focusing ring and a distance scale can operate a full-time manual focus. This means that even though your lens is engaged in autofocus, without flicking a switch. You can override this function and make fine-tuned adjustments. It is a very handy function to have if you are very specific about maintaining focus and depth of field.


Does it warrant the extra expense that it will cost you? Well, that depends on if you will use it more than other photographers. Instead of using full-time manual focus, you could use the back focus button.


Click here: Back focus method 1Back focus method 2 ,  Back focus method 3

Superior lens optics


If we were to deconstruct a lens and break down each of its components and elements. We would find that the general consumer lens has less, whilst the professional range has more.


The superior lens optics function more smoothly, the minimum and maximum apertures open and close quicker, there isn’t any lag time in shutter speeds, and there are more aperture blades to produce a more effective background blur “bokeh” effect. They don’t have your standard aperture blades. The superior lens usually has rounded aperture blades, which produce more pleasing specular highlights. They have low-dispersion elements, which focus different wavelengths of light at different distances behind the lens. High and low-dispersion glass elements can reduce chromatic aberration. Most of them have fluorite elements and are especially good at reducing colour chromatic aberrations, but they cost a small fortune. Internal focusing means that elements move inside the lens barrel to focus, so the physical length of the lens doesn’t change during focusing, and the front of the lens doesn’t rotate (handy when using orientation-sensitive filters like polarisers and graduated from ND filters). A superior lens has glass elements coated with anti-reflection material to reduce the glass interface in the lens from producing reflections and flare that can affect and reduce contrast and image sharpness, whilst reducing the amount of light that hits the camera sensor. The lenses have several elements and groups that assist the photographer in correcting image distortion and sharpness. Superior lenses have been produced to allow the photographer the ability to make micro autofocus adjustments.


I go into this topic in a lot more detail in the Click here: Photography course

Non-rotating front element

We know that most lenses rotate when we focus. That is a given. We can even hear them making a mechanical whizzing sound as the barrel of the lens turns.

The front glass element rotates to achieve proper focus and exposure. If we place a piece of tape at the top front of the lens and then focus again. The tape will rotate with the barrel of the lens, and it will no longer be at the top. Depending on the focus position. The tape may be at the side or at the bottom.

The one problem that this poses to photographers, especially those that use polarising filters when shooting landscape images. A polarising filter is an expensive piece of gradient glass. They usually come in two forms, either as a direct attachment to the front of the lens. Whereby, the filter is circular in design and is fixed directly onto the lens casing itself. These become a part of the lens after they are screwed in place. The second, more expensive option, is mostly used by landscape photographers. Is to have square block filters that slide horizontally into a specially designed bracket that covers the front of the lens. As a separate attachment. They fit tightly onto the front of the lens.  

Polarising filters change the intensity of the light entering the lens and how the sensor interprets that light information.
Click here: Filters If you need to know more about filters.

It is important to set the polarising filter so that the darker glass gradient is at the top whilst the lighter part is at the bottom. As you can appreciate. This is done to darken the sky, make colours richer, and appear more vivid whilst adding clarity and contrast to images with liquid and vegetation.  

If the lens rotates, we 
are unable to predict the exact position where the darker and lighter parts of the filter are. We will be using a filter which we have no control over. Which will defeat the purpose of purchasing it in the first place. And as you can imagine, this can cause a lot of frustration. As we won't be able to accurately predict precisely at what position the gradient of the filter glass will be. Our lens will turn the filter as it focuses. The landscape photographer will have to stop and adjust the filter, refocus, and then attach the filter again, and then refocus again. Which won't place the filter in the right position as initially intended.  

Lens manufacturers have stepped in and resolved this issue by developing a lens that has a non-rotating front element. So by attaching a filter to this type of lens. There will be no turning front elements, and the filter 
stays in a fixed position on the front of the lens.   

We do use polarising filters in glamour photography. Especially for fine art nude images done in conjunction with stunning landscapes and urban environments.

Don't worry, We cover filters in more detail later on in the advanced photography course.




To fully understand what a “Crop factor” is. We first have to have a base reference point from which to work from. In the photography world, this base reference point is the 135 photographic film. The 135 film was introduced to us by the Kodak company back in 1934, and it comprised a cartridge of film, with a gauge of 35mm. They came in several different types of emulsions, sensitivities (film speeds), colours and monochrome negative and positive, etc.



The term 135 format, refers to a 36 x 24 mm film, which is commonly known as the 35mm format. The 36 x 24 mm format is common to digital sensors and typically referred to as a “Full frame” format. In the digital world, “full frame” sensors are the same size as this film. A film frame with a width of 35mm. The camera of this photography format was commonly and collectively known as a 35mm camera.


The value is not used as a focal length measurement but as a measurement of the dimensions of the frame of the film. The film image area measures 24 x 36mm, but the strip is 35mm wide. So when we refer to it in photography as a 35mm film or the size of the sensor, we are not referring to the lens focal length.



The 35mm camera is and always will be the world's most popular camera format. The 35mm allowed us to think of a field of view given by a lens at a certain focal length, and we could visualise what the image should look like. In the 35mm Camera world, a lens with a focal length of around 50mm would provide a normal field of view, similar to how the human eye would see it. Lenses with a shorter focal length would provide a wider view, and lenses with a longer focal length would provide us with a narrower – telephoto view.



Skip forward a couple of years with the arrival of the first digital camera. And camera manufacturers had a huge obstacle to overcome. Most sensors in the early days were a lot smaller than the 35mm film. Images seen through the lens of any particular focal length had a different field of view than that of the same lens on a 35mm camera. The 50mm no longer had a normal field of view, it resembled that of a telephoto.


Photographers decided that they needed to know the 35mm equivalent field of view of various lenses when attached to a camera with a digital sensor smaller than a 35mm film.


They needed a system of calculating a defined, precise measurement that could be applied to any lens that they attached to their camera.



They knew that around the lens produced a circular image circle. And that the sensor at the back of the camera captures a rectangular portion of this image circle. They also realised that when they used a 35mm film as a standard, any camera with a sensor smaller than a frame of 35mm would cover a smaller portion of the image circle produced by the given lens. This would change the field of view. Cutting or cropping those sections “portion” of the image out. This was termed cropped. They knew that this cropped field of view would need to be calculated and given an equivalent lens focal length. They devised a ratio for calculating the “crop factor” of the diagonal dimensions of a camera’s sensor. Manufacturers provide the horizontal and vertical dimensions of a sensor. So by using the horizontal and vertical dimensions, and a bit of maths taught to us in high school. We can use “Pythagorean theory” to calculate the diagonal dimension.

“In a right-angled triangle: the square of the hypotenuse is equal to the sum of the squares of the other two sides.”









































So why is this important?



Each camera sensor has a different “Crop factor” and this affects our field of view


So if we used a 50mm Canon lens on a Canon APS-C camera. We would know that we would need to multiply the crop factor (1.6) by the focal length of the lens to give us our actual field of view. Calculated at 1.6 x 50 = 80mm


And if you wanted just a 50mm lens. All you would need to do is divide the 50mm by 1.6 (50/1.6 = 31.25mm) to give you the normal 50mm framing.


If you don’t want sections of your image cropped out, and you want the exact field of view that your lenses focal length will give you. Then choose a full-frame camera.


If you don’t mind doing maths, every time you put a new lens on your camera. Then don’t purchase a full-frame camera. But be conscientiously aware that your focal length will change according to the lens and sensor of the camera you are using.



If you are still confused.


Click here: Full frame “Crop factor”



Put in what we know: 


Calculate squares: 


Take 81 from both sides: 




Square root of both sides: b = √144


Calculate: b = 12




We already know that a Full-frame sensors are based on the dimensions of a 35mm which are 36mm x 24mm.


So it would be logical to assume that                        would equate to 


So the calculation would give us:                                                     (Full frame sensor dimensions)


So how would you calculate the crop factor diagonal dimensions for a camera with a smaller camera sensor.





A Canon APS-C sensor which has the dimensions 22.2 x 14.8 mm which would equal √(22.22 + 14.82) = 26.68mm



The Crop factor would there for equal: 43.27 divided by 26.68 = 1.6

                              576  + 1296 = 1872                               Square root of 1872 = 43.3mm​



Full-Frame or 35mm Diagonal / Crop Sensor Diagonal = Crop Factor


   Sensor size         Sensor dimensions         Crop factor


   Medium Format         53.7mm x 40.4mm                       0.64


   Medium Format        43.8mm x 32.9mm                        0.79


   Full Frame 35mm      36mm x 24mm                                1


   APS-H                            27.9mm x 18.6mm                       1.3


   APS-C                             23.6mm x 15.6mm                       1.5


   APS-C (Canon)             22.2mm x 14.8mm                       1.6


   1.5″                                18.7mm x 14mm                          1.9


   4/3″                               17.3mm x 13mm                           2


   1″                                   12.8mm x 9.6mm                          2.7


   2/3″                                8.8mm x 6.6mm                           3.9


   1/2.3″                            6.17mm x 4.55mm                        5.6


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 is brand loyal and doesn't know anything about third-party lenses. So she decides to purchase a Canon lens. To get her through the topless calendar day. She knows that she will probably purchase a third-party lens as well in the future. But has no rush to do so immediately. 


When it comes to lens features. Katja doesn't have a clue where to start and what to look for. She decides to leave it until she has gained enough experience in the basic functions of her camera first.


Katja decides on: Lens mount: Canon

                               Lens focal length: Telephoto

                               Lens type: Telephoto to telephoto zoom

                               Maximum aperture: f/2.8  /   Zoom aperture: Constant

                               First or Third party lens: Canon lens

                               Extra features: Needs to do more research


         See you all

next month

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