Flags in the mist

When do we need Long Exposure Noise Reduction?

Roger Clark had some comments about Canon cameras and Long Exposure Noise Reduction. He basically wonders if we really need it most of the time. And he suggests that you can just take a series of separate dark frame exposures at different temperatures and just keep those to manually subtract from the image in Photoshop. The noise map apparently doesn’t change very quickly.

Why do we even think about using Long Exposure Noise Reduction (LENR) or as it is more generally known dark frame subtraction? Sensors heat up as they are used, if we are talking a typical short exposure, maybe 1/100th of a second, the sensor doesn’t heat up very much. But once the exposure lengths get into the multi-minute range that sensor will get hotter. And a hot sensor is a noisy one.

Astrophotographers actually cool their sensors down, sometimes to very low levels–hundreds of degrees below zero–to hold down noise. That option isn’t open to us. But taking a dark frame image essentially maps the noise generated by the sensor and you can have the camera automatically subtract that from the image. Hopefully this reduces the overall noise in the image. The dark frame file, captured separately by shooting a shot with the lens cap on, can be subtracted later in post production.

The problem with letting the camera do the subtraction, is that it doubles the duration of exposures and seems to me it may heat up the sensor even more since you are keeping it on twice as long. That also uses up the battery faster.

Doing some exploration on the web, and this pertains to Canon DSLRs mainly, there is some info on the matter. Canon suggests on their European site:

The long exposure noise reduction performs a dark field subtraction – in other words, it calculates the fixed pattern noise and then removes it from the image you have just shot. In practice, it’s not worth turning on unless you are planning on taking images with an exposure time of more than 2 to 3 minutes.

Andy Frazier a well known night photographer and Nocturnes member suggests an even longer duration, 5 or 6 minutes. And DPReview has reported no benefits on the Canon 40D with or without LENR for 30 second exposures. Joe Reifer has some tests on the Canon 5D where he suggests you have a problems around 8 minutes or so. And that noise becomes a problem on older Nikons around 3 minutes. But the 5D is older technology now, superseded by lower noise sensors and Nikons too have better sensors. Joe Reifer has some comments about the Nikon D200 here.

So from all this I’d say that we probably don’t need to worry too much about sensor noise on shots less than 4 or 5 minutes on newer Canons and probably something like that on newer Nikons. And possibly for even longer exposures. This would depend on the age of your camera, older models could be noisier. If you need to know where the break is you should do some tests on your own system. Any of you using other brands may want to think about using Google to see what noise characteristics your model is.

Not using LENR will certainly speed up operations at night and let me capture twice as many shots.

Rainstorm

Taking a look at the different systems

The two biggest companies in the business of making Digital Single Lens Reflex (DSLR) cameras are Canon and Nikon. Between them they control something around 85% of the market. The smaller actors are Sony, Pentax and Olympus and the tiny actors are Sigma and Fuji.

Not only are Canon and Nikon the companies with the biggest market share but they are the two companies that have been making DSLR bodies the longest. They have more lenses and accessories available for their equipment than any of the rest. Pentax was a very important company in the Film SLR market. They introduced the first popular SLR camera many years ago. But they failed to get involved in the change to digital until recently. Olympus made film SLR cameras but also is a late comer to the digital world and they also made a very foolish decision when they move to digital. They have locked themselves into a smaller sensor size than the other companies. The use the 4/3rds system which is a half sized sensor.

Sony has made sensors for the Nikon bodies for years but has recently decided to jump into the DSLR market themselves. The top of the line Sony is getting very good reviews.

Lenses

Let’s take a look at what is available in the lens market for the various brands. This will include the manufacturers own lenses and the main third party lens manufacturer’s offerings (Sigma, Tamron and Tokina).

This is not an exhaustively researched table and could well be off a bit.

Canon and Nikon are more or less tied but the others lag far behind. Canon produces about 5 or 6 new lenses a year and they have much more money and a larger staff than the smaller companies. How many years would it take for Pentax or Sony to catch up with Canon and Nikon at the rate of 4 or 5 lenses a year.

Flashes

Looking at available flashes, flashes that fully support the camera electronics and exposure control:

We see the same story. Nikon does a little better than Canon, but all of the others are left in the dust. Again this is a quick reference table from the manufacturer’s websites and B&H. So errors are possible. Sony hotshoes use the old Minolta style that is incompatible with almost all other flashes.

Macros come in different focal lengths, generally running from 50mm to 200mm. The shorter lenses are lighter and cheaper but have a short 1:1 focus distance which makes doing bugs difficult since they fly off. Longer lenses are expensive and heavy but have a longer focus distance. Looking at some popular lenses, let’s see what the availability is for different brands.

Only the manufacturers own lenses are counted. Sony, Pentax and Olympus only have short macros. One of the Canon lenses is a super macro.

Another common lens used by bird photographers especially is  a 300mm lens. These come in two apertures f/4 which is cheaper and lighter and f/2.8 heavier and a lot pricier. Again looking at what the manufacturers offer:

Again Nikon and Canon have the better selection and prices as low of much lower than the other three. The Canon and Nikon lenses have Image Stabilization the others do not.

I just randomly spot checked some of the more popular lenses. I didn’t try to look at consumer grade lenses, I’m sure they all have plenty of 70-300mm and 18-200mm type junk lenses.

Image Stabilization

This is the last subject I’ll look at in my biased overview. Canon and Nikon have both settled on in-the-lens stabilization. The other three have in-the-body stabilization. While at first glance it might seem to be better to have stabilization in the body, that does not turn out to be true for lenses where you really need stabilization.

The reason for that is that the body stabilization can only work on short lenses because these systems work by moving the image sensor to compensate for lens movement. The longer the lens the longer the distance the sensor has to move and once you get beyond 100mm or so the sensor cannot move far enough to compensate for lens movement.

The in lens system works by moving elements inside the lens. Thus each lens is optimized for it’s focal length. Canon has an explanation here. Bob Atkins has a general overview here.

Another benefit of the lens stabilization is that you can see the stabilized image in the viewfinder, not the case with the in-body IS. Of course Canon and Nikon have a big investment in IS lenses so that comes into the calculation too.

The truth of the matter is that you don’t really need IS on short lenses. Most people can handhold a 18mm lens down to 1/20th of a second or so. But those long lenses are heavy and hard to hold and they really need IS.

So What?

So what does this mean? When you buy into a DSLR system you are not just buying a camera body. For example, I have one good camera body and one old one. Say they are worth $1400, more or less, right now. I have 6 lenses, a 1.4X extender and some extension tubes. Total value around $4000. (Darn my wife better not read this). So switching to a new body would be fairly painful, but replacing all those lenses  would be impossible. And unlike a lot of other photographers I do not have a lot invested in dedicated flash units. So a serious photographer can easily have four to six times the cost of the bodies he has, tied up in other gear.

So buying into a system, where you soon hit a wall when you want to add a new item that you just have to have, can cause real pain. If that item doesn’t exist for your system. I just listed flashes and lenses above but there are many other system accessories. Wireless triggers, remote controls, intervalometers, focus screens, vertical grips, wireless transmitters and the list goes on and on.

I mentioned the Sony non-standard flash above.I know one budding photographer who found herself unable to use studio flashes with her new Sony camera. She had to sell it at a loss and buy a different brand.

Think!

So think long and hard about buying into one of the lesser brands if you have the least idea that you will get serious about photography. Yes some of the cameras are decent, and maybe some of the lenses. But overall the systems are not. If you are sure that you won’t ever want to expand what you have, then buy whatever you fancy.

—UPDATE —

Roger Clark suggested that I should point out that Canon has prime lenses in 200, 300, 400, 500, 600, 800 and maybe 1200mm (rumored to be available if you will pay them to make one) and Nikon has 200, 300, 400, 500 and 600mm primes. Sony, Pentax and Olympus all have no prime lenses longer than 300mm. This is important for bird, wildlife (think of that African safari you always wanted to go on) and sports/action shooters as well as photojournalists. They all want and use long prime lenses.

Canon also has a couple of very fast f/1.2 lenses and you can even occasionally pick up a 50mm f/1.0 (used only, since they are out of production). These are popular with wedding shooters who shoot in dark rooms using available light.

—Another Update—

The final step in buying a camera is to go to a shop that has the models you are looking at and try how they feel in your hands. People often have love at first touch with a certain model. And these cameras are quite different in how they sit in your hands. The lower grade models are on the small sized end and may be too small for someone with big hands. But other models may be too big for someone with small hands. The control layouts are also different. How it feels to you is a major consideration.

White Egret

What is the problem with Point & Shoots?

Point and Shoot cameras (P&S) have a number of defects and many of them can be traced to the small sensor size in the bodies. A DSLR sensor is about the size of a large postage stamp but P&S sensors are the size of a fingernail. Those tiny sensors have just as many pixels squeezed onto them as the larger DSLR sensors have. That means the pixels are tiny and very close together. Sean McHugh explains this in more detail. Roger Clark goes into great technical detail about this issue on his website. Some of the problems caused by these small sensors:

• High apparent noise level and diminished ISO
• Loss of Depth of Field Control
• Decreased dynamic range

The high noise apparent noise (see below for a comment from Roger Clark) level of these small sensors mean that even tho the camera manufacturers may show higher ISO values in the camera controls those high ISO values are unusable.
Depth of Field (DOF) is how photographers control the zone of sharp focus in an image. It is one of most important creative factors that photographer use to control what the viewers see. A photographer can show a person in sharp focus but throw everything behind that person out of focus and thus concentrate the viewer’s attention on the subject and not the background. And because of the physics of small sensors and the lenses that they use on those cameras you are unable to control DOF. Everything in the image will be in focus, period.

(Note on this: see below for a comment from Roger Clark)

You can see this for yourself by playing with this calculator. For example at 55mm and at f/4 a Canon DSLR has a zone of focus of 1.1 feet at a distance of 10 feet. A Nikon Coolpix P90 has an infinite zone of focus. When you use this calculator you need the real focal length of your camera’s lens not the 35mm equivalent. Usually dividing the shown focal length by 8 or 10 will get you in the ball park. So a P&S that show 60mm is probably actually around 6 or 7 mm in reality.

The dynamic range (DR) of an image is how much difference exists between the deepest blacks and the brightest whites that the image will show. DSLR cameras with 14 bit processors will have a distinctly higher DR at low ISO and will maintain higher DR all the way thru their usable ISO range. P&S cameras start of with lower DR at low ISO and this drops rapidly as the ISO is increased.

Other defects

Some other defects of P&S cameras are:

• They limit the user to jpeg files
• They have small memory buffers
• They use a slow focusing mechanism for the lens
• The camera processors are slow
• They have long shutter delays
• They use up batteries quickly

DSLR cameras can use raw format for the image files. These raw files have many advantages. Too many to go into here but they are a vast benefit to serious photographers. Michael Reichmann’s Luminous Landscape has a good article on the subject. There were a few P&S cameras that allowed the use of raw format but manufacturers have mostly eliminated that feature on most of them. The only apparent reason would be to drive people to buy a DSLR to get raw. P&S cameras all capture the image in raw but convert the raw images to jpeg before you can get to the file.

There are actually people who hack the firmware on cameras to add raw capability and I notice there is a list on Yahoo devoted to that subject. I have been a bit perplexed by those hackers since I don’t know what you could do with a P&S raw file. Raw files are not images, they are the actual data that the camera sensor captured. A raw file converter takes that file and converts it to a real image. But no commercial converter software will take any of those P&S raw files.

A memory buffer is where the camera stores the file until it is fully written to the flash card. DSLR can often hold 20 or more images in a buffer but P&S are lucky to hold a couple of files.

DSLR cameras use a lens focus method that depends on the camera having a mirror, called phase detection, P&S cameras have no mirror and are stuck with a much slower method called contrast detection.

DSLR cameras use a fast processor, sometimes involving dual processors that are much more powerful that the microbrains used in P&S cameras. And of course they can make use of the much greater amount of memory in the camera.

All the points above are the cause of one of the major points of irritation on P&S cameras. The very long period of time that elapses between the time the shutter button is pressed and the camera actually takes a photograph. On some of the worst examples this can be one full second. And by the time the camera actually makes a photograph that special thing that junior was doing is only a memory. This is called shutter lag.

The shutter lag on DSLR bodies is usually around 0.05 seconds or so. Pressing the shutter button most of the time fires the shutter instantly. This comes from the fast focusing lens, the fast processor and for multiple shots the big buffer. Current DSLR cameras can shoot somewhere between three and ten shots every second. And keep that up until 20 or more shots have been captured. Something between a half of a second and one and a half seconds to capture five shots. A P&S takes between six seconds and 25 seconds to capture 5 shots.

And last thing I’ll mention is the incredible way P&S cameras eat batteries. A DSLR will be able to take thousands of shots on one battery charge. The batteries last for days or weeks depending on how many shots you take. My sons Canon G series camera uses the same type of battery as my Canon 40D and he is using the battery charger all the time. The 40D body is much larger than the G and the lenses are vastly larger and heavier and move faster but the batteries last much longer.  I doubt he can get 200 shots on a charge. And that camera is no different than other point and shoots in that respect. I don’t know why it is, perhaps running the LCD kills the battery. But they go fast.

Should most users move to DSLRs?

In my opinion and despite all the advantages of a DSLR, I think the answer is no. DSLRs are darned hard to use, the manuals are thick and you cannot ignore what is in them. Manufacturers add all sorts of ‘shooting modes’ to the lower end DSLRs to try to pretend that these are super P&S cameras but they are not. And many people who buy them expecting that they can continue their point and shoot practices are soon unhappy with their new and expensive DSLR.

I often hear complaints by new DSLR owners that their cameras are producing ‘bad’ images. Well the images are fine but the DSLR user has to understand how to make good images, he has to do a lot more thinking and has to understand photographic technique. Plus most DSLR images need post processing, you have to learn how to use Photoshop Elements or even Photoshop (there are a lot of other software packages out there) to make great photographs.

And obvious solution to the problem of people wanting something better than a P&S and the complexity of DSLRs would be a automated camera with a large aps-c sized sensors and LCD focusing. People have been calling for this type of camera for years. But no manufacturer will make one. It is a mystery, perhaps DSLR manufacturers do not want to introduce a model that would compete with their DSLRs. But there are camera companies that do not make DSLRs or if they do sell darned few of them. Why don’t they produce such a model?

If you are serious about being a better photographer, then of course a DSLR is the only way to go in their price range right now. But be prepared to work hard to master the camera, read the manual, buy a book or two and shoot a few 1000 shots before you begin to get a good feel for using the camera. Having a background in film SLR cameras will make the switch easier but it will still be difficult.

Next up: comparing DSLR systems

—UPDATE—

Roger Clark has this comment:

“The correct way to put this is that the small sensors actually have LESS noise
at all levels, from shadows to highlights.  The problem is that the small pixels collect so little light that they have very LOW SIGNAL.  The factor that we see in images is not absolute noise but signal-to-noise ratio.  So the small pixel cameras have low signal-to-noise ratio at all levels from shadows to highlights compared to the larger pixel DSLRs.”

use that link to his site above to get a much fuller discussion of this.