5.16.2011

Keep your lenses clean. Don't keep cleaning your lenses. And for God's sake don't stick a filter in front of them!!!!

See how blurry the photo got over on the left side?  That's because I had a UV filter on the front of my lens for protection and..........

Okay, not true, but..... I've experimented many times over the last few decades and I've proven to myself that filters in front of lenses degrade the quality of the final images.  Here's how I understand it all:  Every air to glass interface causes a slight loss of resolution and contrast.  This tends to make a lens look "flatter" and less sharp than it could be.  Lens designers have understood for over a century that adding more glass elements increases the compromise.  In the 1940's and 1950's they were willing to compromise things like corner sharpness and flatness of field so that they could design lenses with fewer corrective optics that had much more "snap" and "sparkle" than lenses of equivalent focal length designed with more elements.  

Everything in lens design and manufacture is a compromise.  If you add more elements you can correct for more distortions but you inevitably compromise contrast or resolution.  And contrast/resolution is an equation.  You can have one or the other or a mix but not high apparent acutance and high resolution in the same design.  Really.  Macro lenses need to have flatter fields and greater correction of geometric distortion.  They have more elements.  But in order to keep the image quality very high they have slower f-stops and smaller elements.  Smaller lens elements are easier to machine with high accuracy than larger elements.  They are easier to correctly assemble in barrels.  Faster lenses have bigger elements.  According to optics expert, Erwin Puts, every time you double the diameter of an optical glass element you increase the manufacturing complexity by something like a factor of 8X.

The creation of the "cemented pair;" two elements bonded together, is an attempt to reduce the number of air/glass interfaces to cut down on light loss and the tendency to increase "veiling flare" at each intersection.  Lens coatings are also an attempt to cut down on light lost at the interface of each element. They also prevent (by the process of wavelength interference) light from hitting the element and bouncing back to cause ghosting on the surface of the glass element thru which it just emerged.  Yikes.  A lot of design goes into making glass and coatings that nullify various wavelength "bouncebacks".  

Practically speaking, when you buy "L" glass or premium Nikon or Leica or Zeiss glass you are buying a system that's tweaked like a race car.  Really.  Like a Formula One race car.  It's optimized to produce stunning images as part of an overall optical system.

So you drop a few grand on your dream lens, put it on a tripod, lock up the mirror and trigger the shutter with an electronic cable release and.........you don't see the huge difference between the deluxe optic and the old beater you've had in the bag for years.  You know why?  To use the race car analogy you just put on aftermarket hood scoops, spoilers and fancy wheel covers on your race car when you stuck the damn filter on the front!!!  You introduced two air/glass interfaces that the lens designer didn't include in his calculations.  His computer didn't compute for them either.  You added weight and drag to your race car.  

And to make matters worse the coatings on the filter may interfere with the coatings on the lens and cancel out parts of the spectrum that you might really like to have on your imaging sensor.  They also introduce more chromatic aberrations because now the various color frequencies don't line up as well on the imaging plane.  

The idea behind the desire to use a filter is to protect the front element of the lens.  In days of old, when people would sit around on their davenports and immerse themselves in the latest novels of Nabokov and Kerouac while sipping cognac,  the coatings and the glass used on lenses was......soft.  Rigorous and frequent cleaning degraded the coatings and could scratch the front surface of the glass which led to flare and other nasty optical business.

But lenses have been hardcoated for years and years (five decades?).  And the infinitely expensive fast telephoto lenses from Nikon, Canon and Leica are designed with a neutral front element that is, essentially a built in protective filter.  The difference being that the systems were designed with that component as an integral part.  Not an after thought that's only benefit is to increase the commission of your camera sales person or to increase the margin on your internet purchase.

Finally, too many people who decide they must have the glass make the stupid decision to save money and buy cheap filters.  Back to our analogy, it's like putting retreads on a Ferrari.  You might be able to go but you won't be able to go fast.  

If you live in constant fear that your lens will become damaged you have obviously spent too much money on your lens and should return it and buy something that won't cause you unbearable emotional distress should it become damaged.  Really.  Like buying a nice car and always having to park it across three spaces because you don't want it to get door dinged.  It's karmic.  It's the quickest way to get your car "keyed."  And your fear for your lens attracts calamity to your lens like a magnet.

Stop.  Take the filters off the lenses.  Shoot like a real man.  Or a real woman.  And if your lens is destroyed then make sure you have a good story to go along with the loss.  That's the way it's done.

I've been doing this for 25 years and I've never had a front element damaged.  The protective filter is an urban legend.  It's also a huge profit add-on for the camera sellers.  My advice?  The only filter we really need in the digital days is a circular polarizer.  And that should stay in your pocket til you need it for something aesthetic.  

added after:  Here's what Lloyd Chambers, noted writer about optics, has to say about the filter imbroglio:  http://diglloyd.com/articles/Filters/quality.html

32 comments:

Kyle Batson said...

Fantastic article. I stopped putting protective filters on my lenses after I saw a video where someone smashed a hammer down on the front element of his lens and it didn't cause any noticeable damage.

Tom Devlin said...

Amen.

Jim said...

Hear ye, hear ye. The best protection for your lens is to put the lens cap on when you aren't using it and be careful when you are.

kirk tuck said...

Arrrrrgh. Filters be for babies. (pirate accent implied....).

Michael Ferron said...

Glad ya said it. Only filters I use are maybe a yellow on the occasions I shoot B&W film or a polarizer when the situation dictates it.

Albano Garcia said...

Excellent article. I use lens hoods, no protecting filters. I've seen many of my earlier photos ruined by filters, and even a whole vacation shoot from a friend ruined by his cheap non coated uv filter (it was in the film days, he saw the fog in a lot of his photos when he got them back from the lab. He never used a protective filter anymore).

kirk tuck said...

Kyle Batson, I loved your rangefinder street shots. Came across them years ago.

obakesan said...

+1 in agreement

andrew korlaki said...

if you use a decent filter made of optical glass (Canon, Leitz, B & W etc) it won't degrade image quality..

Use a cheap filter and it will...

Shoot motorsport without a filter? Never......

mbka said...

Same here, no filters, and use lens hoods whenever I can. I had so far one accident with a lens in 30+ years of shooting. I dropped the lens while changing it. It fell on the filter thread and got a ding there, and that was about it. Work in salt water spray or with sand blowing needs to weigh the trade-offs carefully though.

Anonymous said...

I never used filters; found them to degrade image quality. Then my 3 yr old started putting his fingers (covered with grease, food, PBJ) on my lenses. At that point I discovered that Nikon filters don't affect image quality much, unlike other brands.

Gino Eelen said...

Lens hoods not only offer mostly adequate protection, they also improve image quality by preventing oblique light rays that don't contribute to the actual image from hitting the lens front element and bouncing around inside the element(s), interfering with rays that do form the image.

Lens hoods = increased image contrast, increased protection, win-win, no-brainer!

Ct Photo said...

Uv filters we don't need no stinking Uv filters

Shotslot said...

+1, good rant!

Anonymous said...

Took me years to come to this conclusion but totally agree. And ... if you have a hood on the lens anyway there's all the protection you'll need if/when you knock camera against anything. Simple.

The obvious exception being the Leica M8/8.2 with the necessity of having to use UV/IR filters. I've found from personal experience even if intending to convert .dng files to B&W that the resulting file carries more detail if shot using a UV/IR filter on the lens. There is even a solution to this though - It's called the M9! (Or just use a film M. lol)

Can anybody spot me £5000 .... pretty please? :-)

Royce said...

I always neglected to follow the advice to use a UV filter. I don't remember if this was because I had read someplace that it degraded image quality or if I was just too lazy to buy one. It's nice to hear that I did the right thing all these years.

Craig Yuill said...

Several years ago I took some test shots with a 50mm Nikkor where the sun was shining on the front of the lens. I took shot with and without high-quality Heliopan filters. I carefully examined the shots and found that there was no difference between filter and no-filter shots I took. I was delighted to see that flare was no problem. I think that keeping things clean, as you mentioned in your Zeiss 21mm, is the key to getting the most out of a lens.

That said, I have been going largely filterless for several years. Lens hoods are what I use for protection. Like you, I have to admit, I haven't found not having a filter to be a problem. None of my filterless lenses has gotten damaged. But I agree with other posters that putting on a filter where sand and debris might fly towards the lens would be a good safety measure.

John H said...

Amen brother! And what about all of those people you see walking around with their lens hoods reversed ... or those who take the lens cover off only to take a shot (or two) and then promptly place it bask on again? I just want to walk up and slap them :-) (just kidding of course!)

Mike said...

Kirk,

On a related topic, what are your thoughts on how and with what to clean lenses? I don't mean of dust, I mean of the stuff I've run into at some venues - beer, bodily fluids, etc. I've been loathe to pull filters off when shooting in environments like that simply because the subject of cleaning methods and materials seem to be vague and often full of contradictory opinions.

Christian said...

I was photographing with another photographer once who told me about a time when he dropped a lens. It had a UV on the front to protect the lens. The inside of the UV flaked glass into the area between the UV and the lens and the lens barrel distorted slightly where the UV attached, making it nearly impossible to remove the filter.

He no longer shoots with a filter "to protect the lens" and only uses one when it will genuinely enhance the image.

He does leave a lens hood on instead just in case he drops another. The plastic hood might break some of the fall without a corresponding risk to the lens itself.

Anonymous said...

I was using a filter on a really nice lens and I dropped the len. The filter cracked and cut into the lens element. The lens was a total loss. Had I used a hood and no filter I am convinced the lens would be with me today.

Bob.

Paul Glover said...

"Protective" filter use is a set of paradoxes:

If you have a cheap lens, why spend almost as much on a high quality UV filter to "protect" it? But buy a cheap filter and your cheap lens just lost some image quality it probably couldn't afford to lose.

If you have an expensive lens, even an expensive filter will compromise it in some cases, and a cheap filter? Forget that!

I shoot an old Canon FD system. Many of my lenses cost less than a high-quality UV filter. I almost always use a lens hood, which offers protection with the added bonus of helping to improve the image in some cases! I have ND, polarizer, orange and green filters which are used as necessary. I have an 80B which I never use because I can correct the color cast as I scan my negatives. If I'm in blowing sand or spray I'm going to be more concerned with keeping crud out of the focusing helicoids which a UV filter isn't going to help with.

Chris said...

I used to keep a circular polarizer in my pocket but found the slight temp different between the back surface of the polarizer and the air between the front lens element caused the polarizer to fog up.

Bold Photography said...

The only filter in my bag is a Rodenstock CPL... and with the right lighting, it can cause flare and reflections.

With the right conditions, though, it can do amazing things.

Simply Divine Photography said...

I was told this same thing by a photography instructor and took the UV filters touted by the sales-people to "protect my expensive glass" off of all my lenses...so WHY, yesterday, did I let them, sell me yet another UV filter for my latest lens...going now to take it off! Lesson learned the second time around??? It's the last UV filter I will ever buy!!!
Thanks for the reminder ~

atmtx said...

Kirk,

A great informative writeup. I once googled for the effect of UV filters on image quality but did not find any articulate articles. I'm guilty of using filters... I guess I'll be using them less now.

Thank you.

Jonathan said...

I wonder if the amount of a degradation of the filter is related to the angle of view of the lens? With a long telephoto lens, the light rays will be entering the lens almost perpendicular to the filter. With a wide lens the rays will be entering at a much flatter angle, which might show up some interesting effects. Think about looking through a house window straight-through, or at an angle.

Of course this doesn't affect whether the filter causes flaring or reflections, but it might make me remove the filters from my wide lenses more readily than my telephoto lenses.

This is just a "thought experiment" on my part - can anyone give any information on this, backed up by science?

fotoplek@yahoo.ca said...

Good advice! i take with a piece of sugar..
if you bump a lens,the filter part is trashed. better less sharpness and longer life lenses.
Of course here at this blog it's new systems all the time..
Leica lenses are soft esp the old ones.
use a filter! my 1954 Summicron is still mint.

David Bateman said...

very true about the hard coating. I have tried to shoot uv, here you take your lens and pollish it till your arm is knumb to get the coating off for more uv entry. I worked hard and did not get the coating off an olympus 35mm macro. I was recommende to use a dremel tool! This seems common in UV circles.

Damen said...

I keep a condom over my lens. I seem to be in a photographic rut. There is a distinct lack of variety in my photos.

Kyle Batson said...

Kirk, thanks. Though I've never shot with a rangefinder and have only been doing street for 2 years at most. Are you sure you're talking about me? My street photography: http://www.flickr.com/photos/95931944@N00/sets/72157624906018119/

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