The difference between “point and shoot” and DSLR camera

The difference between “point and shoot” and DSLR camera is something many people ask. Here is a clear description of the difference.

Single lens Reflex

There are several important differences. The first one is that it is an SLRSingle lens reflex.  What does this mean?  Essentially that behind the lens there is a mirror, which reflects the image through a prism for you to see through an optical viewfinder. If there is no optical viewfinder, it is not an SLR.  There are some newer cameras that  have interchangeable lenses but are not SLRs – see the Sony NEX, Olympus Pen, and other similar models.  These cameras generally have a sensor sized similarly to an SLR, but lack the mirror/prism that SLRs have.
Believe it or not, there have in the past been digital SLR cameras with fixed, non-removable lenses and small sensors, such as this Olympus:
In an SLR, this means that the sensor or film is behind a physical shutter AND a mirror.  When you take a photo, the mirror flips out of the way, the shutter is opened, and then the exposure occurs.  This differs from a point and shoot camera because there is no mirror, and in the P&S, the sensor is actually on.  The image you see on the P&S LCD screen is from the sensor.  Modern SLRs can sort of duplicate this in “Live view” modes, but the experience is non-optimal in most cases.

The next major difference between a digital SLR and a point and shoot is the focusing system.
In a point and shoot camera, the sensor is always on, always receiving an image.  The way they focus is simply looking at the contrast in the image in a certain area, and it adjusts the lens until the contrast increases.  This is because if something is out of focus, it is more blurry, and therefore a solid line does not appear – it tweaks the focus until there is more contrast. There is no technological reason why the point and shoot camera could not focus anywhere in the image, but typically there are computer algorithms that make a best guess as far as what you are taking a photo of.

SLR focus systems work differently.  Because the sensor is not receiving a signal, the input from it can not be used.  The autofocus system is actually in the area where the prism is!  Essentially, it works on the same concept as the point and shoot systems.  It looks for contrast.  But it can’t focus just anywhere.  It has sensors, which are basically lines (-) (|), crosses (+), (X), or even the + and X combined.  The focusing sensors ONLY work along those lines, and they, again, are detecting contrast, but this time in a MUCH smaller part of the image.

This has a major advantage – you can precisely choose what point you want to be in focus.  It is also MUCH faster than the autofocus systems in point and shoot cameras.  But it also has some limitations.  If you have a – sensor and you are trying to focus on a horizontal line, it will not work, because there is no contrast!  This is not a major issue in use.  That is where cross shaped sensors come in – they are much more likely to be able to grab on to contrast.

The Focus system

This focus system is MUCH more precise than the ones found in point and shoot cameras, because it gives you much better control of what is in focus.  This is very important with an SLR, because SLRs have larger sensors, larger lenses, and larger aperture (light openings) than point and shoot cameras, so there is much LESS in focus.  So it’s much more important to be able to focus on an exact dot.  If you’re shooting a portrait, you want the person’s eye to be in focus, not their nose!

This is the viewfinder from a pro digital SLR.  See all the focus points?  There are always many ways to control the way autofocus works on digital SLRs – even relatively low end models.  You can use them in full auto mode where it picks from them all, or go so far as simply choosing one focus point if you need exact focus accuracy.

Low end SLRs use the same kind of focus system, but have less focus points, less focus points with cross sensors, and less computing power and focus options.  For example, my Canon 7D, a midrange SLR, has five different modes for choosing focus points, whereas a Rebel may have 3.

There are other differences too, which tend to be ergonomic – but the main functional differences are the presence of the reflex mirror and the way autofocus works.  The other differences are of functionality and ergonomics that are side effects of the design of an SLR, and the needs of the people that use them (controls, flash hotshoes, and the like) – There’s nothing stopping anyone from making a point and shoot digital camera with flash hotshoes that use the same flash systems as SLRs (Canon and Nikon do, actually, look at the G12 and high end Coolpix cameras to see).

A camera does not need to have interchangeable lenses to be an SLR, but every SLR these days does have interchangeable lenses.  As I noted before, there are other types of cameras that can produce similar image quality to digital SLRs, but are not.  They are either rangefinders, which are manual focus only (Leica makes rangefinders, primarily), or are similar to the large sensor interchangeable lens cameras I had mentioned earlier – and those cameras use autofocus systems that are the same as found in point and shoot cameras.

There is your overview on The difference between “point and shoot” and DSLR camera

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