Filter merits

[marstar]

Hi everyone.

I was looking in my local camera superstore for a protective filter for my lens and couldn't help but noticing the gajillion other types and styles available.
I've never really paid them much thought until recently and was hoping someone had some experience or insight on the merits and demerits of using filters.

I'm most interested in C-PL filters and was wondering if ...

A: What are the downsides to leaving this filter on full time? And IF there's a negative effect, can it easily be fixed in post with LR4 or PS?

B: To my understanding, these type of filters help reduce glare and reflection of glass, metal, water, etc while increasing saturation (perhaps I messed that up....). Can the same result be duplicated in post without a filter?

The store I visited basically only carries Kenko brand and BW (a little over my budget).
The store clerk recommended the Kenko Zeta EX or CPL.

The lens in question is a Nikkor 16-35 F4

Any thoughts?

[Mike Buckley]

A: The filter will decrease the amount of light entering the lens by about 2 stops. (There are situations when you will want those extra two stops of light. Knowing your camera model and its highest ISO that can be used without producing noise that can't be handled during post-processing would be helpful on that point.)

When you are using the shorter focal lengths of your lens and including a blue sky in the morning or afternoon, the polarizer can create an uneven appearance in the sky that can be difficult to eliminate in post-processing, especially if your post-processing skills are at the novice level.

B: Your understanding is mostly correct. Reducing glare and thus increasing the perception of saturation in a scene can be accomplished during post-processing, but doing so can be very difficult, whereas it's really easy to accomplish that using the polarizer. Reducing or eliminating the reflection cannot be done using the filter; that can be done in post-processing but in most cases it can be very difficult and time-consuming, so much so that you will usually be better off making a different photo.

There is always going to be a debate about whether any filter should be used for the purpose of protecting a lens. I personally feel that a lens hood does a far better job of protecting a lens from both falling and bumping into things. It's also a lot less expensive than many filters, especially a polarizer.

If you feel the need to use a filter expressly for the purpose of protecting the end of the lens, most people would use a UV filter because it's cheaper, does not reduce the amount of light entering your lens, and helps reduce blue light at high altitudes and haze. Be aware that many people argue that putting anything in front of your lens that is not necessary for making the photo risks degrading the image quality of your photo (a polarizer, a neutral density filter, a graduated neutral density filter, a star filter and perhaps other filters can be necessary in certain situations).

[DanK]

Mars,

You have may have started a new iteration of the Great Filter Wars. There must be 10s of thousands of postings on the web arguing for and against protective filters. Apart from that argument:

1. CPL filters are very useful, and many of us consider them an essential tool. I almost always carry one, but it is rarely on my lens because of the loss of light. I use it when I am concerned about glare and remove it otherwise.

2. Regardless of the type, only use high quality multi-coated filters to avoid flare and glare. B+W is a very good brand, but very pricey. I have no idea how high quality the Kenko filters are. All of mine are either Hoya, which is a very standard brand, or Marumi, which is harder to find but sometimes cheaper.

Now, for the argument about protection: The "petal" lens hoods that are used with most zoom lenses don't offer much protection, and none against liquids. I have used high-quality UV filters for protection most of the time for decades, and I have had a few ruined by stuff that would otherwise have ruined the front element of my lens. I've done some tests, and my conclusion is that with lighting behind you, the loss of quality is negligible. On the other hand, if you have light in front of you, there is a good chance that a filter will cause some degradation, and I take it off under those conditions, e.g., doing night photography.

Recently, for that reason, I was using my most expensive lens, a 70-200 f/4 IS, without a filter. I have absolutely no idea how this happened, because I really baby my equipment, but the next time I took it out, I found scratches on the front element.

I'll post two test shots. They were taken identically, except that one had a Hoya UV filter on and the other didn't. I can't tell you which is which because I no longer remember. If you like to pixel peep and want the fill size images, you can find them here.

So, it's just a matter of how risk averse you are, and how careful you are when you use your gear. My own personal preference is to risk a tiny degradation of the image in many cases for the protection, but I still go filterless when it is likely to matter more.

Dan

[Manfred M]

I usually leave my CPol installed on my lenses all the time when I am shooting outdoors. What they do for me totally outstrips the loss of a couple of stops most of the time. I will remove them when it is quite dark out and I need the additional speed. I have a number of the, so I don’t have to switch when I change lenses.

Unlike Mike, I rarely use lens hoods because they get in the way when using a polarizer and frankly a hood can actually increase the likelihood of damage to a lens. The only time I tend to use a lens hood is when it is raining or snowing. I will sometimes use them when I get lens flare (but often just use my hand to shade the lens).

1. The are great for reducing / eliminating glare from NON-METALLIC surfaces:

a. Removing or reducing glare from glass and water; and

b. Removing reflections from leaves. Your images of grass and trees will be “punchier” when you shoot landscapes with a polarizer.

2. It can darken skies, but only when you are shooting in a direction when the sun is not directly behind or in front of you. The polarizers have maximum effect when you are at right angles to the sun.

WARNING: Using a polarizer with a wide-angle lens will give you awful looking skies. As the polarizing effect varies based on the angle to the sun, you can get banding as the sky does from light to dark.

If is easy to overdo the polarization effect and you can get unnatural looking skies, especially when you have set your polarizer to have a maximum effect. Dialing this back a bit can help a lot.

I also use two other types of filters. Neutral density filters that allow me to either shoot with the aperture wide open (gets me a shallower depth of field) or reduce shutter speed to introduce motion blur (I also use a tripod for this type of shot).

I also use graduated neutral density filters which vary from a higher density that reduces to no density. These are useful for landscape work by reducing the brightness of the sky. If you have sufficient range, you can emulate this filter in post-production, but only if your camera’s sensor can handle the dynamic range of the scene.

[Mike Buckley]

a hood can actually increase the likelihood of damage to a lens.

In what circumstances? I ask because I can't think of any.

[HenkB]

I agree with Mike. I use lens hoods as much, or more, for protection as for flare control. I lost some shots to a UV filter. What seems to happen is that the filter and glassy sensor and the low pass filter directly over it just reflect light back and forth along the lens barrel sufficient to wash out the contrast in the center of the frame. Ugh. Remove the filter and the effect is removed. Lesson learned. That was several years ago and, without filters, I haven't lost the front element of a single lens since. I have broken some lens hoods which I have been delighted to replace.
As to the CPL, Mike's core suggestion (which he soft pedals a bit) that leaving such a filter on all the time creates as many problems as it solves is sound. Your understanding of the capabilities of the CPL is slightly flawed; CPLs will not reduce glare from metal to any substantial extent. Reflections from glass, painted surfaces (using non-metallic paint), leaves, etc will be effected. But the effect is not universal. Besides controlling polarized light, the response of CPLs (or linear polarizers, for that matter) is highly polar. The CPL will be most effective when, as the light source is rotated around the subject, the subject is illuminated at 90 degrees to the lens axis. Doesn't matter sideways or from above or below. 90 degrees is the ticket. At 0 or 180 degrees there is hardly any effect at all. This suggests that at most angles other than 90 degrees (or nearly) the CPL's response is sub-optimal and therefore its candidacy for permanent resident status on the end of your lens should be considered a long shot.

[Downrigger]

I found Dan's comments helpful - in this case meaning they articulate well and agree with my (less informed and experience-based) biases. I am outside a lot, often in desert, and I'd rather get the itty bitty bits of "dust" and grit (lots of which is as hard as, or harder than the glass) that inevitably get on the front of the camera off a $100 filter than the leading surface of a $1500 lens.

I like the effects of polarizers on bright days, especially around water, or snow, just like good polarizing sunglasses. The effects on seeing what's under the water surface for relevant shots are striking, and the reason fishermen love them. On wide lenses though you get weird sky effects since the sky is differentially polarized in relation to the angle of view from the sun so shots with lots of sky get different degrees of polarizing effect across the image. I wouldn't put one on a wide-zoom very often - and if you leave it there as a protector, you may not notice when you're getting unwanted variations in effect across the spans of sky in your shots.

Thus I have them for my midrange lenses, and only use them when I want polarizing effect, which can be very nice. (but not always - for instance a dappled glare from breeze-rippled water can be a wanted effect). I might put one on for the day on a sunny day, with lots of natural polarization in the sky and landscape, and lots of glare, but otherwise would use just for solving specific issues for specific shots/compositions.

And I definitely fall into the camp of folks paranoid about inadequately protecting my lens itself so always have a UV/haze on every lens. If it's off, I feel like I am playing football without a helmet. It's possible that those more advanced than me respect their lenses too much to add otherwise superfluous glass.

[Manfred M]

In what circumstances? I ask because I can't think of any.

Simple mechanics Mike:

1. The lens is longer with the lens hood in place, increasing the risk of hitting something;

2. Because they are longer and you do hit something with them, you are applying a longer lever arm to the "incident". Longer lever = higher force = higher risk of damage. This is the principle as to why we used levers (something called the mechanical advantage). Think of trying to remove a cork from one of your famous wine bottles by just trying to pull it out; it’s hard work. We employ a cork screw, which is essentially just a lever, to increase the force to help remove the cork. It’s exactly the same principle at play here..

3. When you apply a force to a material like a lens hood, it deforms and bounces right back. This is knowns as elastic deformation. Other than a bit of sound and if you could measure it, a tiny bit of heat is generated, your lens hood will bounce right back, having transmitted the force if the collision into the sensitive elements inside the lens.

To absorb energy (and protect delicate components), you need something called plastic deformation, i.e. the energy is absorbed by permanently deforming the material (that is the purpose of that nice foam that your lens is packed in when it is shipped from the factory. Look at car bumpers; they crush in a collision and absorb the energy from collisions or any kind of helmet with the energy absorbing foam.

So the fact that when you dropped the lens, nothing got deformed worked out well. The problem is that you don't know if there was any hidden internal damage to the lens, but the lens hood held up well...

[Mike Buckley]

Thanks for the information, Manfred. All of it makes sense at least theoretically. I question whether it has much practical application but cannot come close to proving or disproving it. I'll continue using my lens hoods for the simple reason that the one time I needed it to protect my lens, it seems to have done that very well when I suspect the lens would have been ruined if the hood had not been in place.

[Green Mountain Girl]

While looking at screw-on hoods, I realized that hoods are made of a variety of different materials. The standard ones that come on my Nikon lenses are a heavy plastic. I know someone who likes metal hoods. Then there are the rubber lens hoods - my first thought was "how can rubber protect when it will bend?" Now I see that with the impact = lever = damage concept, perhaps rubber would be a good solution! Protection + resilience --> less trasference to the lens.

I am still learning, and this kind of discussion is interesting. Especially since I am an advocate of using lens hoods, own UV filters but don't use them all the time, and own a circular polarizer which I use selectively. Planning on buying a grad ND filter and holder - just one to start with, probably more later.

Any comments on the rubber lens hoods?

Susan

[Manfred M]

Thanks for the information, Manfred. All of it makes sense at least theoretically. I question whether it has much practical application but cannot come close to proving or disproving it. I'll continue using my lens hoods for the simple reason that the one time I needed it to protect my lens, it seems to have done that very well when I suspect the lens would have been ruined if the hood had not been in place.

Mike - the truth is that we really can't tell what will happen in a specific situation. The physics (mechanics) can be used to predict general outcomes, but that doesn't mean that in "typical" scenarios a lens hood, used the way you and many others do, will not have a beneficial impact (pun intended).

While everything I have written is technically correct, having a lens drop on its front element may protect the rest of the lens by having it "absorb energy" and break, but the lens would be totally useless.

In your case, the hood did transfer the force of the fall to the other parts of the lens assembly, and as long as the forces that were exerted did not exceed the design parameters of the affected lens components, all is good.

I experienced a situation with my 80-400mm where the hood was the cause of the accident and the way it fell (really a relatively short distance), also caused damage to the lens. The lens hood came off partially during the initial incident (got hit by a closing door; it would likely have cleared the door if I hadn’t had the hood on). I dropped the camera and the partially dislodged lens hood drove straight into the filter on the lens when it hit the ground. This shattered the filter and as luck would have it, the filter was made of a harder glass than the front element of the lens creating a tiny scratch. It doesn’t affect the image quality at all, but sure screws up the resale value of the lens and I had to replace the $100 filter.

[Shadowman]

Not one mention of the skylight filter? Works similar to a UV but depending on the tint can change the appearance or hue of the sky.

[Manfred M]

Any comments on the rubber lens hoods?
Susan

Main advantage is that they collapse quite nicely for storage. Disadvantage (assuming that there is a good fit; i.e. no vignetting) is that rubber does break down over time.

[DanK]

rubber hoods are not generally good for zooms because they are not petal shaped and are therefore more likely to vignette. The petal shape arises because the hood is cut out for the four corners that extend farthest from the center of the image.

[benm]

I think the petal-shaped hoods are to save on material costs, otherwise the hood would need to be much larger. But in any case, a hood on a zoom works best at the wide end. As you zoom towards the long end the hood is not as effective.

[Green Mountain Girl]

Well, I guess that means rubber hoods are not such a good thing! It was just a thought...

[Manfred M]

I think the petal-shaped hoods are to save on material costs, otherwise the hood would need to be much larger.

That would be not be true. The resin costs are not that great a factor and the amount reduced by going to a petal shape would have a negibible cost on the product. The amortization of the mould itself would probably be the highest cost (high pressure injection molds, even on a fairly simple product like a lens hood would run into several hundred thousand dollars. The second largest cost is likely to be production cycles on the injection moulding machine.

Finishing operations will also add to the cost (all of my lens hoods have had mould flash and sprue material is removed), some of my higher end hoods have springs and catches and all of them have identification and other marks applied to them.

[DanK]

I think the petal-shaped hoods are to save on material costs, otherwise the hood would need to be much larger. But in any case, a hood on a zoom works best at the wide end. As you zoom towards the long end the hood is not as effective.

It's just geometry. Because the frame is rectangular, not circular, the maximum angle that is viewable in the frame is in the corners. The minimum is in the center of the long side, which is the closest part of the perimeter to the center of the frame. That's why petal hoods are longer on the top and bottom than on the sides.

Longer hoods will be more effective in reducing flare than shorter ones, regardless of focal length, because longer hoods lop off a larger proportion of the arc in front of the lens, and therefor reduce the arc from which light can cause flare to occur. The importance of focal length is that a longer focal length has a narrower FOV and therefore can accommodate a longer hood. That is why the hoods on telephoto primes are so long. In the case of zooms, the hood has to accommodate the shortest focal length, so they are short. Petal-shaped hoods allow more length top and sides than you could accommodate with cylindrical hood, but they are still often shorter even at their maximums. For example, the hood for my 100mm macro (prime) is cylindrical, about 3 inches (8 sm) long. My 15-85 extends to almost as long a focal length, but the length of the hood is a bit over 1 cm at the cutouts of the petal, 2.5 cm on the sides, and 5 max on top and bottom.

[Hero]

I think the petal-shaped hoods are to save on material costs, otherwise the hood would need to be much larger. But in any case, a hood on a zoom works best at the wide end. As you zoom towards the long end the hood is not as effective.

If anything, the petals are there so you don't need a long hood for the long end and a wide hood for the short end.

[Mike Buckley]

that doesn't mean that [it]...will not have a beneficial impact (pun intended).

And a very good one at that!

Now that I have read your example of how the lens hood caused your gear to be caught in the door when otherwise that might not have happened, I'll be sure to take my lens hood off every time I get in and out of the car.