Camera Lenses and Filters

Camera Lenses and Filters

Caveman Camera Club

April 20, 2016

A lens is a “transmissive optical device which affects the focusing of a light beam through refraction.”  A camera lens is a group of lenses used to focus light onto the sensor.

What do those numbers and abbreviations on lenses mean?

Numbers followed by “mm” means the focal length of the lens.  Examples:   85mm, 24-105mm, 70-200mm.  They may be on the inside of the filter ring or outside at the front usually.

Numbers that look like a ratio – for example 1:1.8 or 1:4 or 1:3.5-5.6 – show the maximum (wide open) aperture (like f/1.8 or f/4).  When there is a range, it indicates that when the lens is zoomed  wide, it will be at the lower number (like f/3.5) or zoomed telephoto, it will be only at the higher number (like f/5.6).

Numbers with a diameter symbol ∅, a number, followed by mm (e.g. ∅ 72mm) or just the number and mm (67mm) is the diameter of the opening for filter threads.  Not to be confused with the focal length of the lens.

(BTW, the ∞ symbol means infinity, which for our photographic purposes essentially means about anything from about 100 ft on to the stars and beyond.)

Some Important Lens Abbreviations


DX = lenses for APS-C size format

FX = lenses for full-frame format

CX = for use with mirrorless system

VR = Vibration Reduction

AF-S or SWM = silent wave motor for focusing

and for many more, google “Nikon abbreviations”


EF = fully electronic, designed to cover the 35mm full-frame circle

EF-S = for use with APS-C size sensors

EF-M = for use with mirrorless cameras with the like mount, APS-C size

IS = Image Stabilization

USM = UltraSonic Motor or silent wave motor for focusing

L  =  “Luxury” or the professional grade lenses (has red ring)

and for many more, google “Canon abbreviations”

Each has many more of their own abbreviations, and other brands of cameras and lenses can have a many other specific abbreviations.  You must see what that brand means by their terms.  If nothing else, google the brand for information about its terms.

Speaking of Focal Length

Focal length, simply put, it means the distance in millimeters between the front lens and the sensor, though this is not always literal due to the use of the various individual glass lenses within a camera lens.  The normal, non-exact, nomenclature – usually translated in terms of full-frame (similar to 35mm film) sensors – is as follows

Fisheye = an extremely wide angle of view, normally between 8mm to 15mm.  They may be circular within the frame of the image or show an entire frame with distortion, also.  They take in about 180̊ field of view or less.

Wide angle = 12 mm to about 35mm.  They have a wider field of view and tend to magnify distances between objects and allow for a greater depth of field (what is in apparent focus).

Normal = approximate the field of view the human eyes sees naturally, or about equal to the diagonal of the digital sensor.  It’s considered about 45mm (or 28 on an APS-C camera).

Telephoto = medium at about 70mm to about 300-600mm or more.  The angle of view is smaller (narrower field of view) and it appears as though the objects are compressed.

For different sizes of sensors, like the small micro four/thirds and APS-C or the large medium formats, the lengths are shorter or longer respectively.

“Macro” (or micro in some cases) lens is technically, a lens with the ability to focus an image on the sensor that is at least as large as the subject, i.e., a magnification of 1:1.  The term is often used generically to mean “close up.”

Switches on lenses

Your lens may have several switches on it or it may have none.  One is probably the VR or IS on and off switch.  When you are hand holding your camera, the switch should always be on.  When you have it on a tripod, the switch should always be off.

Another switch on the lens may be the A – M or A/M-M (or AF-MF) switch for the autofocus function.  This is not to be confused with your exposure dial settings nor other focus settings on your camera.  “M,” of course, means manual focus – where you rotate the focus ring in order to achieve focus where you want it.  “A” means the camera/lens will automatically focus using the selected autofocus points (a lesson in itself, almost).  If you try to manually focus when on the A setting, it will revert back to what it wants to focus on automatically when you hit the shutter release, thus negating your manual focusing.  If the lens has an A/M or AF-MF setting, then your manual setting will override the automatic when you hit the shutter release.

Some telephoto lenses may have a focus limiter that will focus on subjects within a certain range so the camera doesn’t waste time hunting throughout the entire focus range of the lens.  For example, it may allow you to switch between 1.2m-∞ or 3m-∞.  (It’s not a big deal.)

Also, some telephotos may have a Mode 1 or 2.  One is where it is trying to stabilize your camera motion in up/down and sideways directions.  Two is set for up/down only and is for a panning movement.

Filters for Digital Camera

First, look at the diameter of your lens (like ∅ 55mm – not the focal length – and buy filters that size or larger.  If you have several size lenses, you can get a step-up ring that is to adapt a larger filter down to a smaller diameter lens.  But I don’t think it’s too bad of an idea to have a set for each diameter lens.

What Filters Should You Really Have in Your Tool Kit?

Circular Polarizer

UV or “protector” filter.

Neutral Density if you want to slow time and water down.

Split NDs are used to darken light areas, like the sky and allowing normal light coming through the clear glass.

What Filters Are Options, Maybes?

Star filter

Round Split ND’s aren’t all that effective.

Additional Accessories

Teleconverters or tele-extenders come in usual flavors of 1.4X, 1.7X, or 2X.  They will magnify the focal length of the lenses they are added to by those amounts.  But there is a cost – one to two stops of light.  There is also the financial cost, which may be cheaper than buying a new and longer lens, but it is a place where you get what you pay for.  For maximum compatibility, go with the brand of your camera or lens.

Lens hoods can help to keep some direct sunlight off your lens.  Sun hitting directly on your lens or filter is what causes the flare spots or lines in an image.  The tulip-shaped hoods, however, have limited usage because they are not wide enough on normal or wide angle lenses to block very much.  It is best to use a hat or something, as long as you prevent the sun from hitting the lens itself.  A deeper hood for a telephoto can be more helpful.  A hood can also take some of the impact if you drop a camera, but you normally shouldn’t really be doing that.

Use micro-cloths for lens cleaning, but first use a brush, like that on a LensPen to brush off any flecks of material.  Use your breath for the moisture and rub gently, in a circular motion.  Lastly use the carbon end of a LensPen to clean off oil and other substances.  I use it for my glasses all of the time.

Camera bags come in all flavors and are beyond the reach of this class.  As the size of your collection of you equipment grows, so will the needs of your camera bag.  You can consider have a master bag at home for virtually everything.  But when you’re going out for a specific shoot (like to hang with Gene at the bars photographing beautiful singers and dancers in low light), then bring just the equipment you need in a small bag. [Be very careful with your gear – it can get stolen.]

Physically Switching Lenses on Your Camera

Have you seen those little blurry dark spots in the skies of your pictures (where they are most visible)?  They are dust spots on the sensor, usually created when you switch lenses in an unclean environment.  RULE #1:   Switch lenses only where the camera is protected from dust or moisture (like in your car after the air has settled).   #1a: If you can’t be in a clean environment, protect the lenses and camera as much as possible, like getting out of any wind, enveloping them in a jacket, etc.  RULE #2:   Be prepared with the new lens and make the switch just as quickly as possible so the inner part of your camera is exposed for as few seconds as possible.   #2a: also keep the camera end of the lenses protected quickly so dust doesn’t settle in them.  RULE #3:   If your camera doesn’t have an automatic dust shaker-offer, then use a baby snot syringe bulb (unused) to blow off the sensor (after locking up the mirror) without touching it.  NEVER use canned air – it can leave a permanent residue.  Don’t blow in your camera interior with your mouth.  There are sensor cleaning kits, but be very, very, very careful with them.  Better to have a sensor cleaned by a professional (and no, Photo Den doesn’t do anything but the baby snot blower).

Lens Buying Advice

Consider seriously what do you need a new lens for. Can it do something you need or want to do that your current lens can’t?  Are you now shooting low light when you didn’t before?  Do you need a long telephoto to shoot the lions in Africa?  Or maybe the sharpest macro that you can get.  If you have a well-thought-out reason for something, then go for it, but NOT just because it’s the latest and hottest.  Do YOU need it for the kind of work you do?  For a one-time experience – like a long telephoto for a trip to Alaska – consider renting a lens.  One of the best agencies that I’ve seen is .

  1. You get what you pay for. The $200 bargain will not measure up to the similar $2,000 lens.  I definitely won’t get into the details of the physics of optics, but you are paying for sturdier quality material – metal, not plastic – and much higher quality glass, glass coatings, and more elements that have been computer designed.
  2. You can get very decent prices, though on some very good, sharp glass with many prime lenses – those that don’t zoom. A good prime lens might be an 85mm f/1.8 or a 35mm f/1.4 cheaper that you could with fast zoom lenses.  It costs more to do all of the adjustments of all of the elements when you have a zoom lens, especially on the telephoto end.  Primes are generally very sharp, but after being accustomed to a zoom, you have some adjustment to do – you essential zoom in and out on your feet!
  3. Those very wide range zoom lens (like a 18mm to 270mm, or others) are complicated and costly. If you find what looks like a lens with a very wide zoom range, that may look way cool but the quality is not as good as if you’d purchased two shorter- range zooms.  Especially be fearful of any that is cheap, within the $1-300 range.  (Refer to #2 above).  One common thing that manufacturers do to hold down the cost is to have the widest aperture (like f/3.5 or f/4) available when you’re at the wide angle end of the lens (such as 18mm or 24mm) but as you zoom up into the higher number like 200mm or 300mm, the lense will only allow say f/5.8 or f/8 to be the widest.  This creates problems for you as the shooter, but it makes the camera cheaper to build.  So a better quality zoom lens will have the same wide f/stop throughout the entire zoom range.
  4. READ REVIEWS – see what other people think of them. DPReview is good, and I personally like Ken Rockwell a lot.  You don’t need to understand all the technical testing, but be sure to look at the summary.  Look at user reviews, but don’t trust everything you see there.
  5. Lastly, be very cautious of LBA – Lens Buying Addiction. Trust me, it can cause spousal conflict.  (Also, try hiding a purchase and see what happens!)

Gene Rimmer   Caveman Camera Club