Sunday, August 28, 2011

What is a stop?


One of the main keys to good photography is exposure. This is also one of the big mysteries.  When I am teaching classes and we are using manual mode the first question is what should I set my camera to for the exposure?  What the person wants to know is three settings, ISO, shutter speed, and aperture.  My stock answer is “it depends”, because it really does depend. The big key is what effects are you looking for in the photo. The other answer could be, “the combination that gets you the proper exposure”. The reason for this is that there are many different combinations that will get you a proper exposure.

You can go a fast shutter and wide aperture and you stop motion (either the subject or camera shake) and get a shallow depth of field. You can go with slow shutter and narrow aperture and you get a very large depth of field, but if something moves you get blur. You can go fast shutter, narrow aperture, and a high ISO, and you get big depth of field and stop motion, but you also get digital noise in the photo. It is all about what affects you want (or compromises you are willing to make) to get the shot. So it really does depend.

As you are trying to find the right combination you will move the settings of each of these three settings in specific and related increments. The measurement for exposure is the stop. You might have heard the phrase “bring your aperture down a stop”, when people are talking about the exposure. Or when reading about vibration reduction (Nikon term – for Canon it is image stabilization – and for Sigma lenses it is optical stabilization) you might see the phrase “gives 4 stops of stabilization” (more on what that means in a minute). At the very basic level a stop difference means you are either doubling or halving the light that gets to the film or image sensor (yes it is the same for film and digital). Initially everything was pretty much measured in full stops. Technically you could have infinite adjustments for shutter and aperture, but the industry has agreed to increment things in either full stops, half stops, or third stops.

Well this probably sounds all boring and mathy. I suppose it is. But if you can at least get a good basic understanding of the relationship then it will help you pick and adjust your settings. It will also help when purchasing equipment. You will see references to stops regularly. You will also need to know the basic increments when evaluating different equipment.

So let’s start with an example or two on how this affects your actual photography shoot. Say you are out doing a shoot of some kids. You want a clear clean photo without digital noise. So you set ISO to 100 (the lower the number the less noise). You initially set your f-stop to f/8 because that is the real sweet spot of the lens (this is a whole different discussion on lens quality and construction). You adjust your shutter speed until the light meter shows a proper exposure and you end up with 1/60th of a second. Not a bad setup, except that kids are constantly moving. So you might be lucky to get one good photo out of five. The rest are blurry from motion. So you think “I need to get to at least 1/250th of a second. This is a change of two full stops. You know you don’t want to adjust ISO because you don’t want the digital noise. So you need to adjust aperture. Well if you move from f/8 to f/4 then you are dropping aperture by two full stops. You can now go to 1/250th of a second for shutter and still have a proper exposure. Tada, you have now used all that mathy stuff to get you where you need to be.

Or let’s say you are shooting with a 50mm f/1.8 at f/1.8 and the depth of field is just too short (a fast lens is not always the solution). So you increase by a stop and a third to f/2.8 to get a little more depth of field. Again, ISO is always a last resort adjustment. If you were at 1/500th of a second for shutter you would need to drop to 1/200th of a second to keep the same exposure.

To be a little honest here, I don’t have all the different numbers memorized.  I know some of them, but not all of them. I use a chart when writing. When I am “in the field” doing shoots what I simply do is to count the number of clicks I am making in the first adjustment to know how many clicks to make in the other adjustment. So if I increase shutter by two clicks then I will decrease aperture by two clicks. Then I chimp a couple shots (take a shot and look at the LCD screen and go Ooo Ooo Ooo) to see if I have what I want.

Another place that this knowledge of stops helps is with choosing new equipment. Let’s say you are trying to decide between a 55mm to 200mm zoom lens that is f/3.5 at 55mm and a 50mm f/1.8 lens. Well you are going to get two full stops more light with the prime lens. This means you could go from a shutter speed of 1/30 and move to 1/125th for a shot. This could be the difference of using flash or increasing your ISO to get a natural light shot. Don’t forget that your depth of field shortens up, but maybe that is OK.

Let’s talk again about vibration reduction. You have two lenses that you are considering. Both are the same focal length and aperture capabilities. One has vibration reduction that says you will get three stops of stabilization, and the other does not have that. Keep in mind that image stabilization only affects movement in the camera and NOT the subject moving. If you get the lens without the VR and you need to shoot at 1/500th to get a still photo, then you could get the VR lens and shoot at 1/60th and still get a clear blur free photo. This is especially important with telephoto lenses. The rule of thumb is that you always want to be at least as fast as the reciprocal of the focal length. So if you are shooting a 200mm lens you should be at least 1/200 or faster. For a 500mm it would be 1/500th or faster. So now you can decide if that extra $400 is worth it to be able to handhold the lens at 1/60th of a second. The numbers (three full stops of reduction) are not just numbers, but have actual meaning for your shooting.

Exposure compensation is also measured in stops. So when I talk about that in the next blog post what we talked about here will make a lot more sense.  One other point, Remember that ISO is the last refuge to get a faster shutter or narrower aperture. Digital noise is the bain of digital photography. In film you would get grain. Surprisingly at times grain could be a good thing. Digital noise is almost never good. So that is why digital cameras don’t have an ISO priority setting. You will almost never adjust that. That is starting to change with the high ISO capabilities of some of the newest cameras. And full frame sensor cameras are better at high ISO than crop sensor cameras. But you will want to still go as slow as possible for ISO to get your best looking shot.

Have fun shooting and take some time to practice making these adjustments back and forth to get used to them. 


Thursday, August 18, 2011

Creativity and the Lensbaby

Recently I got a Lensbaby lens. I picked the least expensive model, the Muse. I will say it is a very interesting little lens. The thing with the Lensbaby is that it does not give you typical photos at all. The lens has different optics that can drop into the main lens body. The double optic is the clearest of the lenses. And from there you have the single optic, the plastic, etc. Each one is softer. They also have a sweet spot of focus and the rest of the image falls off into interesting blurs. This is not blur like out of the depth of field blur. This is much more artistic than that. You get very unusual photos with it. I think I like the lens a lot, but it is a temperamental bugger too. Here is a shot I took with the lens.


Notice how the person is in focus and a lot of the rest of the picture is blurred. Even the sax, which is in the same focus plane as the person is out of focus. This is the idea of the sweet spot. The interesting challenge with the Muse is that you have an accordion rubber tube that you need to squeeze to compress to focus. And you also have to tilt the thing around with your fingers to get the sweet spot in the right place in the frame. And while holding it in place you then need to depress the shutter without losing the setup. It is quite the gymnastic stunt with your hands to pull it off. Sometimes it does not work as you would want, getting things not really where you want them.


Here instead of the man's face being in focus I slipped and got the shirt. Not quite what I had in mind. I suppose in some respect it is not a bad photo, but totally not my goal. Some of the photos were even worse. I will say that it takes a lot of practice to get the Muse to work the way you want it to. I am hoping to get the Composer at some point, hoping to have more control over it than I do with the Muse. We will see. But I will say that when everything clicks and you get the shot you want it is just a stupendous thing.


So I know I will keep shooting with it and see if I can get to the point of being more consistent. The Muse is nice in the sense that it is very spontaneous. So for something like a concert that is always moving there is a fluidity to using it that works really well. Recently another photographer said to me "one thing nice about the Muse is that you will NEVER get that same shot again... ever!" and I suppose she was right. There really is never a way to ever truly duplicate the shot exactly the same way a second time.

Tuesday, August 16, 2011

Organization of photos

I often get questions about how to organize photos. This was always a challenge with film. It is even more of a challenge now with digital. Now we can quickly amass thousands of photos to try to keep track of. So how does one organize all of those photos? Well I am sure there are a lot of different ways to do it, but here is what I have worked out over the years and seems to work really well.

The first thing I do on my hard drive below my pictures folder is to create a folder for each year. So I have a 2011 folder and a 2010 folder and a 2009 folder etc. Obviously then the photos that are taken in a particular year will go below that years master folder. This way if you can remember what year the photos were from then you will know right where to start. It also helps when trying to figure out if that vacation to XXX was in 2008 or 2009. Solves many a family discussion.

Now below the year folder I create folders for each event. I name the folder with the four digit year then the two digit month and the two digit day followed by the name of the event. So it might be like "2011-08-30 Daughters Birthday party" for a folder name. This will make the folders fall in order through the year. And the name helps find the event. I love to use Photoshop Elements to get the photos on the hard drive because I can also tell the program to name each of the photos with the same name as the folder. That way I don't have a bunch of photos just named DSCXXXXX. I am starting to use Aperture to import photos. I am thinking there has to be a way to get that program to do the same, but have not found it yet.

Sometimes you will have an event that spans several days. An example would be summer vacation. So at that point I do a folder in the year that is titled the year and month. So like "2011-08 Summer Vacation" and then below that I would put folders for each special event for the vacation or maybe just put all the photos in that same folder. This is where giving the pictures a common name helps. So you could name the photos in groups like "beach day" and "dinner at Panchos" inside the summer vacation folder. That way it is easy to find the main event and all the photos from that event are all together.

So there is how I organize things. I am sure others have some cool tips too. Feel free to put them in the comments. I look forward to hearing what you all do.

Thursday, August 4, 2011

Understanding lenses and apertures

I teach beginning photography at a local community ed program (might be starting with a second one too). One of the things that constantly comes up is apertures and why some lenses can get wider apertures than others. And then, to make things even more complicated, why some lenses don't seem to always have the same setting for the widest aperture. So let's talk a little about aperture and see if we can figure this out without getting too geeky. 

First, just so we know we are all on the same page, aperture is the opening in the lens that lets the light through into the camera body. In almost all cameras this opening is variable and can be adjusted. The measurement for the opening is called the f-stop. This is where we could jump off the cliff into sheer geek heaven, but I will resist. At a high level the number you are looking at is a fraction. It is the ratio of the opening to the focal length of the lens. This is why it is always written as f over something. So you might have f/8 or f/3.5. See how the number is at the bottom of the fraction? This is why the smaller the number the bigger the hole. So if you have a smaller f-stop you have a wider opening. It is one of those funky math things. OK, pressing the geek off button now. 

So the first thing we can see is that the aperture is something that is in the lens. The size of the aperture is always a function of the lens, never the camera body. Just like shutter speed is all about the camera body and not the lens. Oh, I am talking specifications of equipment here. It made sense in my mind... haha. When lenses are put together then each one will have certain limitations of aperture. When you purchase a lens you will see an f-stop listed for that lens. The value listed will always be the widest that the aperture can open up. Typically people really don't worry about how far they can stop down a lens. They want wider open most of the time. So you have to dig deeper into the specs to find the smallest the aperture will go. 

The fastest lenses.... oh wait, maybe I should explain fastest here. Photographers will refer to a lens as either fast or slow. This is not an indication of how quickly you can put it on and off the camera. They are actually talking about how wide the aperture will go. The wider the aperture will go then the faster you can set the shutter speed for a proper exposure, everything else being the same. So the aperture of a lens in indirectly fast or slow because of the effect on shutter speed. Thing of aperture and shutter speed as being a tug of war or a see saw relationship. If you set a proper exposure, then you change either aperture or shutter, then the other needs to change as well but in the opposite direction. 

OK, back to fast lenses. So the fastest lenses will be prime or fixed focal length lenses. (GEEK ALERT) This is all about optics and lens design and the number of elements in the lens. And.... oh wait... no geeking out. OK, you just need to trust me on the design thing. The prime lenses can simply open up wider than a zoom lens. So like my favorite lens in my bag is my 50mm f/1.8 prime lens. It is an extremely fast lens. I can get natural light shots with a decent shutter speed and a very slow ISO like this one. 


This shot was able to be taken without a flash indoors just hand holding the camera. This is the benefit of a fast lens. Notice also that the background is blurry. This is a secondary feature of wide open apertures. It may be good or not depending on the photo you are taking. The other thing about primes is that they only have a single f-stop listed for the widest aperture setting. Some zooms are that way too. They will only list a single f-stop. They will also have a very big price tag. 

So most zooms have two numbers listed on them. A common kit lens to go along with entry level DSLR cameras is an 18 -55mm f/3.5-5.6 lens. Ahhh see the two numbers for the f-stop? I won't complicate this with more geekyness other than saying remember how we talked about the aperture measurement being a function of the ratio between the opening and the focal length of the lens? Well on less expensive lenses the actual aperture will only open so far. Now as you change the focal length of the lens you start to change that ratio. The aperture does not actually change inside, the focal length changes. So in effect you change the f-stop of the lens without touching the aperture. In really expensive lenses they have a way to get around this to actually change the aperture as you change focal length so you can maintain the same opening to focal length ratio. So that lens I just talked about has a maximum opening of f/3.5 when you are at 18mm and a maximum opening of f/5.6 when you are at 55mm. 

So here is the interesting thing. Let's say you are shooting manual mode on your camera. You are at 18mm and set yourself to f/3.5 for the aperture and say are at 1/250 of a sec for shutter speed. Then you decide to zoom all the way in for a close up. You forget to check your light meter and readjust your shutter speed. So you are now at f/5.6 at 1/250th and your picture ends up one and a third stops too dark. Opps, that was not intended or expected. If you are shooting in aperture priority then the camera will automatically adjust your shutter speed down to 1/100th of a second. If you are shooting sports you now have a blurry picture. Hmmm, this is getting a little complicated. Well that is one of the challenges of a zoom lens. I am mentioning it to make sure you stay mindful of what will happen. 

This is one of the benefits of a DSLR is that you can chose a prime lens that is very fast for some shooting, and a zoom when aperture is not as important. I am a huge fan of bridge or superzoom cameras. I personally thing that Fujifilm makes the best of them. Their top of the line bridge camera is the HS20EXR. Since it is a bridge camera it does not have interchangeable lenses. So you are stuck with an f-stop range of f/2.8-5.6 on it. Not a bad lens at all. But it is what it is. Oh that camera has an effective focal range of 24-720mm. WOW!!! Talk about incredible zoom! Oh I am starting to drift from aperture. 

So now you know what the term fast lens means, why some lenses have two numbers for aperture, and why some people love prime lenses. I hope this helps a bit.