So you think you want a DSLR...

When you're looking at a picture and think it's an SLR, it's just the effect of a good lens and sensor. It's not necessarily an SLR. It can be a rangefinder, a mirrorless interchangeable lens camera even a large sensor compact.


In this post, I will explain:

• What makes a DSLR different from simple compacts (size, mirror)
• Usability differences (viewfinder and specific AF points)
• CDAF and PDAF focusing methods (CAF, specific points vs full sensor)
• DSLR Alternatives (MILC/large sensor compact)
• Large Sensor Compacts (a few options)

I've seen several people say they want a DSLR after viewing another person's pictures. The problem is there are several cameras out there that can give the effect they want, but they only recognize the almighty DSLR as the means to it.

Don't get me wrong - for the most part, a good DSLR is a superior option, but think of the average person using their camera to take a picture of their family. Be it a phone or compact camera, they're not bothering with how they're focusing, ISO, Aperture etc. They're also not taking the picture with their eye up to the camera, as there's most likely no viewfinder.

What makes it a DSLR...
So right off the bat, there's a usability difference. The "R" in DSLR is reflex. It refers to the action of the mirror that the user looks through when taking pictures. 

 

In the above left diagram, the ray of light coming in hits the angled mirror and focuses on the blue line. This line contains the focusing screen, and auto focus sensors. Light passes through here to a prism or mirror then through the viewfinder. The "problem" with this is focusing is done at fixed points (see diagram on the right). Some of these points are more sensitive than others (usually center point) meaning in tough conditions, only those points will focus. This leads to the common act of focusing with the best point(s) -AF sensors at the center- and recomposing the shot.

This type of focusing is called Phase Detect. Now you need to be concerned with which points are active. Otherwise you wont focus on what you're taking a picture of! When the shutter button is pressed, the mirror flips upwards, and light hits the sensor.

NB: credit Anandtech for AF points diagram.

The other aspect is the sensor size - but this isn't exclusive to DSLRs. It's just that no DSLRs use the tiny sensors found in phones and common compact cameras.

What makes simple cameras easier?

There's more work involved in simply focusing with a DSLR. Why? Well to be fair, you can get the similar "problems" with higher end compacts that let you select focus. I'm calling it "problems" because it's really control.

A good compact/phone camera generally autodetects faces removing the need to worry about how to focus. With small sensors, scenic shots generally have so much depth of field it doesn't matter if they're a little off. i.e. most everything is in focus. 

Focusing of these cameras is done directly on the sensor. In phase detect (DSLR), the light from the lens is directed to a focusing screen with AF sensors. The sensors manage focus. In small compacts, phones, and mirrorless interchangeable lens cameras, the focusing is done by the same sensor taking the picture. The advantages are the entire area of the sensor can be used to focus. Think of it as having AF points everywhere, all with the same maximum sensitivity.

Also, since the entire sensor is active, image processing can be used to detect stuff like faces, or smiles, so it can automatically focus on people's faces, and autosnap if they smile.

This type of focusing is called Contrast Detect.

Why use one or the other?

It sounds like Contrast Detect (CDAF) has some advantages over Phase Detect (PDAF) by using the sensor. It does, but that's not the entire story. There's some disadvantages too.

CDAF uses the entire sensor, PDAF is restricted.

CDAF gets the full image, so it can detect faces, objects etc.

CDAF uses the sensor itself where PDAF can have alignment issues and focus a little infront or behind the sensor.

PDAF can determine if an object is infront or behind the current focus plane, and will focus faster generally.

PDAF can perform Continuous Autofocus - i.e. focusing on moving objects for multiple shots currently much better than CDAF.

Using the reflex mirror means there's ZERO latency tracking moving subjects. A CDAF LCD can lag behind the actual movement.

In general, DSLRs will use PDAF. Their CDAF implementations are quite slow. When using a DSLR, you will be restricted to using the viewfinder. The advantage is this actually helps keep camera shake down. the disadvantage is you need to be MUCH more mobile. Especially with little kids.

DSLR alternatives

There are alternatives of course that can give equal image quality to DSLRs, but provide CDAF (there's also rangefinders, but lets not go there...) focusing for ease of use. These cameras are large sensor compacts and mirrorless interchangeable lens cameras.

If you're buying a DSLR but only use the kit lens, get your money back. You're wasting your money. The kit lens is a dark and generally not very sharp lens. The entire point of getting a DSLR or any interchangeable lens camera, is to change the lens to your need.

Mirrorless Interchangeable Lens Cameras (MILC) have the same size image sensor as a DSLR. Micro Four Thirds sensors is slightly smaller, but still comparable in image quality. MILC cameras are smaller - as they don't need the space for the mirror or prism. As a result, there are also less constraints on the lens. i.e. the designer can start putting lenses closer to the sensor.

As with most CDAF based cameras, the rear screen can be used to compose and select focus point(s). This makes it easy to just stand normally when holding the camera at an angle to shoot. Being electronically coupled, these screens can even come on hinges to make it even easier to shoot below, and of course, there are options for regular viewfinders. A camera like the Panasonic GX7 or Olympus OMD-EM5 give both options - a viewfinder and rear viewscreen.

Large sensor compacts do not have a sensor as big as these. Their sensor is small in comparison - however many of them have fast lenses. If you don't want to spend money on lenses, this is probably a better option. The difference between a lens listed as F1.8 and a lens listed as F3.5 is you get 4 times as much light in the same area covered by the lenses. 4 times the light means a faster shutter for less shake, and better freezing of motion. It means lower ISO for less noise - less grainy pictures in low light. It also means more depth of field control, which is subject isolation. Don't expect a lot from compacts though.

My perspective

I've used several cameras, and currently have a Canon 5D and Olympus EP3 as my main cameras. The 5D is full frame, having a much bigger sensor (almost 4x the area).

As far as usability goes, the EP3 wins hands down. CDAF is generally slower - but that's comparing it against the best really - do you have $$$$ for the best?

Focus is lightning quick, and because it can focus an snap the picture based on where I touch the viewscreen, composition is much easier. Taking pictures of my kid running about is much easier.

For quality though, there's no contest. The 5D's pictures take on a whole new meaning to bokeh comparing against the EP3. This is due to the larger sensor really. If I could get the same quality in a mirrorless body, I would no longer have a need for the SLR.

Some solid mirrorless cameras:

• Olympus - any 16MP cameras (12MP use an older sensor). EPL5, EM5, EM1 etc.
  These cameras are of the Micro Four Thirds standard.
• Panasonic - their 16MP cameras - again, the older 12MP cameras have an older sensor which is noticeably worse in low light.(G6, GX7, GX1, GM1). These cameras are of the Micro Four Thirds standard.
• Sony - Sony's NEX system uses APS-C sensors. The same sensor gets used by Nikon and Pentax in their DSLRs and Leica's M8. Lens options include NEX, and sony'd DSLR mount lenses via an adapter.
• Fuji - The fuji EX series is a capable low light system. AF historically lagged behind NEX and MFT. Lens range is somewhat limited, but they have decent options. Fuji has the right lenses needed to round out your range, but options less than NEX and MFT.
• Samsung - The NX series uses Samsung's own sensor. It's good, but RAW files are huge, and take a long time to process after shooting. Lens range is limited.

Olympus and Panasonic have clear advantages in lens availability as both are using the same Micro Four Thirds (MFT) advantage. The main lens on my Olympus camera is a Panasonic 25mm f1.4. So not only can you use either brand on any MFT camera, but they've been doing mirrorless the longest, resulting in a much bigger list of available lenses in the mirrorless category.


Some solid large sensor compacts:

• Panasonic LX7 - excellent low light capability, due to the larger than average sensor (1/1.7") and brightest lens in this category (F1.4-2.3).
• Olympus XZ-1 - Good low light from 1/1.7" sensor, and F1.8-2.5 lens.
• Canon powershot G15 - Large compact, but good quality. 1/1.7" sensor and F1.8-2.8 lens. Loads of options, especially with CHDK - canon hack development kit.
• Sony RX100 - doesn't get much better. 1" sensor and F1.8-4.9 lens great image quality, but this is a pricey option, easily costing as much as a cheap older DSLR + lens.
• Pentax MX-1 - decent camera, fast lens, large sensor - you get the gist.

So in summary!

• If you're not going to buy a better lens, go with Large Sensor compact cameras.
• Looking through a viewfinder to compose shots can be restrictive on movement.
• Mirrorless cameras use the rear LCD normally to compose and can be quite comfortable to use this way.
• DSLR advantages over mirrorless are mostly in how they track moving subjects. No lag, AF sensors provide better Continuous AF (usually).
• Most of what you notice with good pictures is the result of a bigger better sensor and good lens (faster aperture, sharper).

Hope this helps!