Extra Features of a Digital SLR Lens

From Image Stabilization to Silent Focus

Didn't think there was this much to know about a digital SLR lens did you?

Well, here's some good news. We're almost done.

This is the next to last step that you have to take when choosing a lens for your digital SLR camera.

By now, you should have found your focal length, decided bewteen a zoom, prime or specialty lens, and determined what you'd like for the maximum aperture of the lens.

Now we're on Step 3 Part 2.

The finish line is in sight!

Here's the list of the extra features that we're going to cover:

Silent autofocus
Full-time manual focus
Non-rotating front element
Crop reduction
Superior optics
Image stabilization
Internal zoom

Silent Autofocus

When some lenses focus, they make a grinding noise like a bad transmission.

If you enjoy taking discreet photos or don't want your subjects to be aware that you've got a camera aimed at them, this type of focus will give you away every time.

Some lenses come with silent autofocus systems.

Common names for this include Ultra-Silent Motor (USM) and Hyper-Sonic Focus (HSF). All that these really means is the lens is dead quite when it is focusing.

Quiet focus is also an essential tool for wildlife photographers, where a skittish deer would be alerted to your presence with the autofocus motor grinding away.

Full-Time Manual Focus

This feature is less essential, more nice to have.

On most lenses, if you want to switch from autofocus to manual focus you have to flick a switch on the lens.

Want to go back to autofocus? Flick the switch.

There are a special set of lenses that feature full-time manual focus. This means that even if the autofocus for the lens is engaged, you can still focus manually to make fine-tuned adjustments.

Since autofocus systems don't always get it right, having the ability to focus manually all the time is helpful.

Non-Rotating Front Element

On some lenses, the front of the lens rotates when you focus.

If you put a piece of tape at the top of your lens and then focused on your subject, the tape would not longer be at the top.

So the front spins around. Big deal.

It is a big deal if you are a landscape photographer trying to use a polarizing filter on your lens.

A polarizing filter changes the light entering the lens depending upon how it is oriented. Let's say that you set your polarizing filter just how you want it.

Now you focus, and the polarizer spins around. It is no longer capturing the same image as before, so now you have to re-set it.

In fact, you'll have to re-set it every time you focus. See the problem here?

If you know for sure that you're going to take landscape photos with your digital SLR, you're probably going to want to use a polarizing filter at some point.

Make sure that the lens you get has a non-rotating front element.

Crop Reduction

Remember digital SLR crop factor? If not, you can learn about it on the page where I define digital SLR terms.

Some lenses are designed to reduce this crop factor. While they cannot eliminate it completely, they can adjust for it.

Essentially, the lens is designed so that the back (the part that attaches to the camera) is closer to the digital SLR sensor.

Since the back of the lens is closer to the sensor, it reduces the amount that the small-sized sensor crops out of the image.

There is one big drawback to this type of lens: it won't work with your film SLR camera.

If you sold your film SLR on eBay already, then no big deal. If you'd like to continue to use that camera from time to time, then a digital-only lens is not going to work with it.

Superior Optics

Not all lens optics are created equal.

Some lenses are designed with special optics that adjust for distortion, reduce flare and stray light from entering the lens and are designed to produce images with maximum clarity.

These lenses all come with different names, but the bottom line is exceptional optics inside the lens.

For example, Canon's lenses are part of the L series while Nikon used the term "ED".

The easiest way to tell is by price. Any one of these lenses is going to cost significantly more than a lens without the superior optics.

Image Stabilization

A select group of lenses include image stabilization (also called vibration reduction).

The stabilization helps when you are holding the camera in your hands and taking photos at slow shutter speeds.

Typically, this would result in a blurry photo, but with an image stabilization lens you can get clear shots. The stabilization corrects for the fact that the lens is shaking around.

This is especially helpful on lenses with long focal lengths (100mm or greater) since camera shake is magnified at long focal lengths.

You are going to pay a huge premium for an image-stabilized lens, but if you take a lot of photos in low-light conditions and don't want to attach the camera to a tripod all the time, this is the way to go.

Note: Image-stabilized lenses are not necessary with digital SLR cameras that include built-in anti-shake.

Internal Zoom

Last but not least (you still with me?) are lenses with internal zooms.

This really is a specialty feature, but it can make a difference. If you have a zoom lens with an external zoom, the length of the lens changes as you zoom from wide angle to telephoto.

With an internal zoom, the length of the lens is always a constant.

This is helpful for 3 reasons: first, internal zooms tend to be smoother and faster than their external counterparts.

Second, an internal zoom does not affect the balance of the camera. If you have your digital SLR attached to a tripod and use an external zoom, the changing length of the zoom changes the center of gravity of the camera.

Finally, external zooms can "slide". This means that if you are pointing the camera toward the ground, the lens will zoom in unless you are holding onto the zoom ring.

Internal zooms stay put no matter which way they are pointing.

The World's Most Expensive Digital SLR Lens

Finally, the part we've all been waiting for!

Here's where you get to see what lens features would cause you to pay top dollar.

Each one of these features will add to the price of your lens:

Long focal length
Wide maximum aperture
Silent autofocus
Full-time manual focus
Non-rotating front element
Crop reduction
Superior optics
Image stabilization
Internal zoom

So what's the most expensive lens you can buy?

Something like this might be close:

A 200mm to 600mm f2.8 maximum aperture zoom lens with silent autofocus, full-time manual focus, a non-rotating front element, crop reduction, superior optics, image stabilization and internal zoom.

Do lenses like this exist? You bet!

Camera	Lens	Price
Canon	Canon EF 400mm f/2.8L IS USM Super Telephoto Lens	$6,600.00
Nikon	200-400mm f/4G IF-ED AF-S VR Lens	$5,000.00
Pentax	Sigma APO 300mm f/2.8 EX DG HSM Lens	$3,000.00
Minolta	Sigma 50-500mm f/4-6.3 EX RF HSM Lens	$970.00
Olympus	300mm f/2.8 Super Telephoto ED Lens	$7,000.00