Will a filter cause more or less damage when lens is dropped?

Question

I recently dropped my camera bag from around waist level to the ground. The ground is somewhat padded (carpet) and the bag itself has padding (the typical messenger type of bag's padding). The camera was in a facing down position (lens towards the ground). I was shocked to find that after the drop my filter was completely shattered. I don't know how much damage was done to the lens yet as it is in the repair shop now. But just from looking at it the lens is not cracked, but possibly scratches.

So I guess the question is, in a situation like this, will it likely to have more or less damage with the filter? On one hand the filter broke and not the lens, but on the other hand the filter glass might have damaged the lens in itself.

I'm asking specifically to cases such as a drop and big impact damage (lens bumping to a wall etc).

Answer 1

So, the common idea is that the UV filter helps to protect the lens element from damage. Stores love to push that concept, a lot, and I think it stems from trying to actually get rid of them in the digital age when it didn't really need them. They've now managed to create a sustained market for UV filters despite the fact the UV part of it is meaningless. Kudos to them, I suppose, but I think it's a waste of money and I'm not the only one.

So, in the scenario you just described, you may now be out the cost of the shattered filter and possibly the cost of a front element replacement, though this is not as expensive as you might think. Filters are not strong glass, unlike your lens element, and so it is entirely possible that had the filter not been there there would be no harm done (though you may have calibration problems, that depends). You may still not have significant damage, as a result of the filter, it takes a lot to make a lens useless, but you never know.

For me, I don't use them. A lens hood is far more effective in blocking significant contact with the front element. If there is some likelihood that I might be in a massive sandstorm or something, then maybe I'd slap on a UV filter, but probably not.

As further food for thought... A filter is another piece of glass. Cheap ones can degrade image quality, but all of them run the risk of light reflection creating ghosted reflections in your shots. When I start to add up the plusses and minuses, I'm not seeing a lot of plusses for the filter.

Answer 2

Even if the front element gets a few scratches on it, the effect on image quality is negligible. This is because light from each part of the scene strikes every part of the front element (unless something is causing vignetting). Although hard to believe, it really takes a LOT of damage for image quality to be noticeably degraded. Check out these pictures taken with a "slightly damaged" lens!

The assumption that any impact that shatters a thin, flat filter would have shattered the lens' front element had the filter not been installed is a false one. Most front elements are much thicker than flat filters, made of more resilient materials, and shaped in a way that gives them more strength (compare the shape of most front elements to the shape of an egg). Just because the filter shattered does not prove the front element would have. It can take a lot of abuse to scratch, much less shatter, the front element of most lenses.

One must also consider the possibility that a shattered filter and the resulting shards of glass and sand-sized grains can actually contribute to more damage than might otherwise be the case. This question concerns a filter that was shattered inside a camera bag that filled the internal parts of a very nice lens with the equivalent of sand. The lens had to be sent in and disassembled to clean out all of the tiny pieces of shattered filter that had gotten inside the lens.

Of greater concern when a lens takes a dive is the alignment of the elements in the lens. Some lenses have a reputation for tolerating abuse fairly well, such as the Canon EF 24-105mm f/4 L IS. Others, like the Canon EF 24-70mm f/2.8 L, have a reputation for getting out of alignment at the slightest bump. Often this is due to the way a lens is designed. In such a case the filter makes little difference. The ring will receive the lion's share of the force and transfer it to the front of the the lens housing that it is screwed onto.

A much better way of protecting your lens from impact is through the use a of a lens hood. Not only will a hood often keep objects away from your lens' front element, but in the case of heavy impact the plastic most hoods are made out of will flex and soften the impact force transmitted to the lens itself. And hoods contribute to better image quality in certain environments. A "protective" filter, on the other hand, can only reduce the optical quality of the lens.

On the other hand, when shooting in daylight, UV from the sunlight passing through your lens will inhibit the growth of fungal spores that may be (hint: are) in your lens¹. The filter stack directly in front of the sensor has a fairly strong UV filter anyway, so there's no real benefit to preventing UV light from entering your lens unless it is constantly exposed to sunlight 24/7/365, and there's a definite benefit to at least periodically allowing UV light through the lens.

For a fuller run-down of the various questions here that address the protective filter/no protective filter decision, please see the multiple links included in this answer to is uv filter a must?

_{¹ Fungal spores are everywhere on the surface of the earth, including the skin of most animals and the leaves of most plants. They require three things to multiply: Moisture, organic matter (provided by almost every kind of dust), and the absence of UV light.}

Answer 3

UV filters are frequently used specifically because they offer a cheap front element that can protect a lens from damage. (That said, there is debate on if the loss of quality that can occur from using a front element is worth the protection afforded by them.) I suppose in theory it might be possible for a filter to cause damage in a fall, but they are far more likely to prevent damage and save a lens.

A fall is a very complex action and no two are ever going to be the same, but lets talk a little about some of the mechanisms involved. Glass (or any other solid material) breaks when it is deformed beyond its tensile limit (how much it can stretch). With a front element or lens, this could occur from a side impact deforming the case to the point that the case itself deforms the lens and breaks it or from a direct impact against the lens element.

If the impact is on the side of the camera, a lens filter isn't going to do just about anything to help absorb the damage as most of it will be absorbed by the case itself. It adds a little additional material to spread the force over, but the overall impact is likely going to be insignificant.

In the event of a direct impact however, it is guaranteed to reduce the energy involved in the collision with the main element. Energy can't be created or destroyed so the energy the lens picks up during the fall has to go somewhere. Similarly, both the deformation and the breaking of the front element require energy to be expended. That energy that they absorb is energy that can't subsequently go in to damaging the front element.

Now it's impossible to tell if there might be other damage as a result of the filter. It is possible that the glass from the filter might scratch the lens element (though generally front elements are hardened and should resist this.) It's also possible that a piece of glass from the element could get lodged in such a way between the ground and the lens that it could increase the concentration of force in one area, but that would simply be bad luck. Similarly, it is possible that the direction of the fall could be altered by the front element breaking in such a way that it hits a weaker part of the front element causing more damage with less energy than if the lens had not had the front element.

Those are all random freak chances though. In general, the less energy in a collision, the less damage there is likely to be. The front element will absorb a substantial amount of energy in any direct impact with the front of the lens and thus generally reduce the amount of catastrophic damage incurred, potentially tipping the balance between a scratch and a crack.

It also does prevent minor scratches and keeps dust off the lens, but these are probably insignificant next to the impact of a flat front element being added to the optical system (though it does help offset the image quality loss a little.)

Ultimately the question of if a lens filter is worth it or not as a protection measure is very debatable due to the impacts on quality and the fact things like lens hoods have a bigger impact on absorbing energy, however the fact is that much more often than not, a front filter should reduce the damage in a fall where the impact is directly on the front of the lens.

Answer 4

My bag fell going through security at the airport. When I picked up my Fuji 100-400 I was distressed to hear the sound glass. The lens is fine, the filter shattered absorbing the shock. It removed easily and I carefully got the shards out. I'm sold on good filters.

Answer 5

A filter protects a front element from finger prints and getting scratched in normal use cases. However, when you run into a blunt object or drop the lens, the filter shatters and can cause much more damage to the front element than when there's no filter attached.