how does an SLR outperform a non-SLR

[rookie1010]

Hello,

I was wondering why a SLR out performed a non-SLR.
I mean it is just about where the view finder is looking at, right?

If that is the case, should not all digital cameras be focussing at exactly the same scene that will be captured,
by virtue of this should they not all be classified as SLR's.

 

[f95toli]

There are many answers to that question.
First or all, SLR=Single Lens Reflex.
When you look throught the viewfinder of an SLR you are acutally NOT looking at what the sensor (in a digital SLR) will "see". What you are seeing is actually the image reflected by a mirror in front of the sensor.
Hence, the sensor is not "active" until you press button. When that happens the mirror moves out of the way and the light from the lens hits the sensor (this is the reason why even digital SLRs are somewhat noisy, what you hear is actually the sound of the that moves the mirror).

Another, major, reason is that the sensor in a SLR is much bigger than in a digital compact. The has, of course, to do with cost but it is also due to the fact that in a digital compact the sensor is also responsible for "recording" the image that is sent to the viewfinder and for various technical reasons it is difficult to make sensors that are both good at this and good at ecording the actuall image when you press the button (on reason is that the sensor in a compact must be much "faster" than in an DSLR)

 

[Matthias99]

I think an SLR, by definition, has to have the film/sensor facing directly at the thing being captured. Many compact digital cameras don't do this, and bounce the image off one or more mirrors/prisms first.

Also, "SLR" has become somewhat of a definition of the feature set of a camera; if it can't take different lenses, and doesn't have manual controls for f-stop/ISO/etc., most people wouldn't consider it an "SLR". A camera with all the "professional" features and the ability to swap in "professional" lenses would probably still be marketed as an "SLR" even if it didn't technically use a single-lens reflex system.

But yes, a digital point-and-shoot camera should always capture exactly what you see on the screen if you are using a live preview mode. Some digital SLR cameras also offer similar features.

http://en.wikipedia.org/wiki/Digital_single-lens_reflex_camera

 

[rookie1010]

thansk for the reply,

so in a compact(i guess that is the name for a non-slr) the sensor has to go from viewing mode to ecordig mode, and hence it is not god at capturing the image at that point in time. so with reference to a digitial slr, it is the instant of time which is affected.

whilst in a non digital non slr the viewfinder is not exactly focussed, is that right? in such a case is there a major difference in the performance?

 

[ScottMac]

The prime difference in an SLR (Digital) versus a non-SLR / Point & Shoot is the sensor.

Most P&S cameras have a 3/8" sensor ... most digital SLRs have a sensor about the size of an APS frame - a little smaller than a 35mm film frame. A digital SLR sensor pixel is much larger than a P&S sensor pixel.

The smaller sensors are more noise prone/less sensitive, especially at higher (pseudo) ISO settings. There are some other differences in terms of accuracy, depth of field & such.

In film cameras, some of the traditional "better" cameras are not SLR (Leica, Zeiss ...) - the mirror-flipping mechanism makes the cameras larger and more prone to mechanical errors. OTOH, SLRs tend to give a more accurate preview of what your picture will capture ...

Like everything else, there are plusses & minuses for each side, and it tends to boil down to preference and features desired for specific application.

FWIW

Scott

 

[rookie1010]

thanks for the replies,

so the multiple reflections of non-slr's degrade the image. i guess that is how non-slr's work in general.

so all point and shoot cameras are non slr's?, am i correct in saying that all digital point and shoot cameras are slr's, at least in their live previe mode. i guess in their normal mode, the sensors are not located inline and the image needs to be again eflected through mirrors/prisms before it is captured?

is the difference between the performance of an slr and a non-slr the preview one gets, and the final picture quality is pretty much the same?

 

[f95toli]

No, it has nothing to do with reflections. It is just that SLRs can use better sensors.
You can also use really good lenses for SLRs which makes a huge difference. Lenses in compact tend to be small,cheap and cover a very wide range. Therefore the image quality tend to suffer. Compact that use eg. 28mm prime lenses tend to give better results than cameras 28-300mm "superzoom" lenses.

However, it is possible to build relatively small high-quality cameras cameras (with matching optics). A famous example is the rangefinders from Leica.
Lecia recently released their first digital rangefinder and as far as I have seen it can produce some really good results. Unfortunately it is VERY expensive.

 

[rookie1010]

thanks for the reply,

so for digital cameras, SLR vs non SLR is dependent upon the sensor quality?

and in analog cameras it is the number of reflections, correct?

waht is a rangefinder?

 

[f95toli]

No, in most film-based compacts the viewfinder doesn't actually show what the film will record so there are no mirrors or prisms (meaning no reflections).
For small distances the difference between what the viewfined and the film "sees" can be quite large (due to the parallax error).

The reason for the lower quality of compacts is simply due to the quality of the optics and to some extent the quality of the film itself. "Good" film tend to age quite quickly and should preferably be kept refrigerated so it is not as conventient to use as the type usually used by "happy snappers" in compacts.


Rangefinders

 

[rookie1010]

thanks for the reply,

i thought the rectangular viewfinder indicated what would be captured on the photo, i guess what you are saying is that rectangular viewfinder is incorrect(because of the parallax error)

is the viewfinder and rangefinder the same thing?

is the difference between the non slr and slr digital cameras just down to the sensors they have?

 

[Mark R]

With SLR cameras, the viewfinder (the thing you look through) shows you (almost) exactly what the film/sensor will see. As has already been said, a mirror goes between the sensor and lens, and diverts the light to the viewfinder. When you take the picture the mirror moves out of the way. This allows the visible image in the viewfinder to match the captured image without parallax, be very similar in magnification and identical in focus/depth of field.

Compact cameras don't have the mirror mechanism - so have a seperate viewfinder, which gives an approximation to what the main lens will see. It's inaccurate due to parallax error, may be inaccurately matched for magnification/zoom, and cannot show the focus position or depth of field.

In order to deal with the focus problem - some manufacturers invented rangefinder cameras. These added a rangefinder mechanism to the viewfinder. This makes it possible to see the distance to the subject, so that the main lens can be precisely focused on the object of interest.

Now that autofocus is practical for compact cameras, rangefinders are unnecessary.

One advantage of digital sensors is that it is possible to get a live preview - this means digital compact cameras can produce a precise preview (without parallax and showing focus) of the scene. The problem, is that the LCD image often isn't sharp enough to focus with (this is the case with my compact canon - although it has a manual focus function, it is unusable because the screen resolution isn't anywhere near good enough) - and some sensors need significant time to switch from live preview mode to full capture mode.

I'm not aware of any cameras that reflect the image between the lens and the film. Although there may be some, every camera I've seen places the film/sensor immediately behind the lens. This isn't the case with video cameras, where high end cameras use a series of coloured mirrors to reflect red, green and blue light onto 3 seperate CCD sensors. This allows higher resolution and less noise. A standard full colour sensor throws away 2/3 of the light it receives in its filters. 3CCD systems use 100% of the light, diverting each of the different colours to a dedicated unfiltered sensor. This three sensor/mirror arrangement is expensive and bulky, so is reserved for pro and pro-sumer video cameras.

With conventional film cameras - the image quality is really dependent upon the quality of the lens and the quality/sensitivity of the film. A cheap moulded glass fixed-focus lens isn't going to give the same quality as a precision aspheric ground, multi-coated, lens made from special refractive glasses. Similarly, consumer grade film isn't going to give the same resolution, colour and contrast as pro film - but it's cheaper, and is designed to age well, whereas pro film is designed to be used as fresh as possible, kept refrigerated, developed immediately after shooting, etc. There are compact film cameras of outstanding quality (e.g. Leica) - because they use precision engineered lenses - however, they still suffer from the same limitations as other compact cameras - mainly that you don't see exactly what gets recorded on the film.

In terms of digital cameras - the SLRs are bigger, designed for a higher price point, and so can use bigger, more expensive sensors. With image sensors, size is king - Bigger gives you less noise and/or better resolution - which are both the major limiting factors in digital image quality. Base model dSLRs use APS size sensors (23 x 15 mm). Pro-level SLRs use larger sensors (up to 36x24, or even larger for studio cameras e.g. 49x37 mm). The other major selling point of digital SLRs is their flexibility - interchangeable lenses mean that you can choose the lens best suited to your subject - e.g. a very high magnification zoom lens for sport or wildlife, or a very wide angle lens for architecture or landscapes - or your budget e.g. a $250 general purpose lens for a beginner, or a $2000 high-magnification 'telephoto' lens for a pro who must have the best, sharpest picture of a charging wildebeest. There are other minor differences between the dSLRs and non-SLRs - again, the higher price allows more functions: better autofocus sensors, better shutter mechanisms with better precision or range of speeds, etc.

 

[Mday]

The term SLR, by definition, only refers to the relationship between the optical viewfinder image and the film image.

In practice, SLR brings a few more goodies into play. For digital SLRs, this typically means a larger sensor which generally has less noise than compact and subcompact sensors. Other incentives include full manual functions (also available on compacts) and larger buffers for higher frames per second. Also, not ALL digital SLRs have removable lenses, but 99% of them do. The first digital SLRs did not come with removable lenses.

 

[Madwand1]

The biggest practical difference is the sensor size, not the SLR vs. non-SLR difference per se. Most people with high-end digital range-finder class cameras would consider themselves as having equally good or superior cameras to SLR cameras.

Bigger sensor => lower yields, much higher costs, and bigger bodies and lenses => additional cost.

Smaller sensors, getting smaller and smaller => the reverse.

Full-frame digital has otherwise the same format as cropped-format APS-C digital, but much higher cost -- just due to the sensor cost. Look at medium-format digital prices to see this factor magnified further.

Bigger sensor => [some complex optical effects], less noise and better low-light capability This is the main difference you'll see in the difference in pictures from one class of cameras to another, and even in the digicam class of cameras, it's often worthwhile to choose cameras with bigger sensors than the others.

AFAIK, there are no cameras in the digicam class which have sensors close to the size of even cropped format DSLR's.

 

[Mday]

FYI: CMOS is dirt cheap to make, and has relatively high yield.

 

[OS]

Originally posted by: Mday
The term SLR, by definition, only refers to the relationship between the optical viewfinder image and the film image.

In practice, SLR brings a few more goodies into play. For digital SLRs, this typically means a larger sensor which generally has less noise than compact and subcompact sensors. Other incentives include full manual functions (also available on compacts) and larger buffers for higher frames per second. Also, not ALL digital SLRs have removable lenses, but 99% of them do. The first digital SLRs did not come with removable lenses.

that's pretty good summary, in the past with film cameras, how you previewed pictures was either with an SLR view, or a secondary viewfinder on a point and shoot. The secondary viewfinder by it's nature has inferior optics and has parallax error, so the image you saw was probably not the picture you took. SLRs on the other hand, since they use the film lens to also preview the image, is most accurate.

however, in the day of digital cameras, the LCD preview already uses the image lens ane sensor to preview the image, thus kind of rendering moot this traditional advantage of SLRs.

But as mentioned in practice, SLRs are typically designed with removable lenses and accessory flash shoes, so you have better hardware still. The flipside is you can just as easily build a digital camera that is NOT SLR, and still have removable lens and flash shoe.

 

[rookie1010]

thanks for the reply,

so a rangefinder aids a compact camera.

and a digital slr also uses mirrors with the film

the original SLR was built to solve the parallax problem, correct?

and there is no parallax problem in digital cameras since the LCD preview already uses the image lens as a sensor to preview the image

 

[Vee]

Originally posted by: OS
The flipside is you can just as easily build a digital camera that is NOT SLR, and still have removable lens and flash shoe.

There is the issue that the ccd is then continually exposed to whatever goes through the lens. (like accidentally being pointed towards the sun). And that the ccd's vulnurability to dust will increase.

 

[Vee]

Originally posted by: rookie1010

and a digital slr also uses mirrors with the film

No, a digital slr doesn't use film. It uses a ccd.
It does use a mirror though. Only difference between a digital slr and a traditional slr is that the traditional slr used film behind a shutter, instead of a ccd.

the original SLR was built to solve the parallax problem, correct?

Not really. The issue was interchangeble lenses. The slr makes it possible to see what goes onto the film through the lens. And thus make it possible to compose, focus and expose accurately. And this regardless whether you have attached a microscope photographing bakteria, makro lens photographing ants or bees, normal lens, wide angle for landscapes or interiors, portrait lens for portraits, tele for sports, long tele for birds, or telescope for the stars and planets.

and there is no parallax problem in digital cameras since the LCD preview already uses the image lens as a sensor to preview the image

emm... since the LCD preview already uses the image sensor (ccd) to look through the lens.

 

[rookie1010]

so the original SLR was used for interchangeable lenses and that is still the case.

parallax solving was a nice byproduct of the original non-digital SLR which no longer needs to be solved, correct?

 

[imported_Hamzter]

So DSLR cameras still use a mirror, right? does this mean it actually has 2 sensors in it, one for the image capture and one for the preview? or do they just not give you a preview and you use the viewfinder?

 

[Mday]

Originally posted by: Hamzter
So DSLR cameras still use a mirror, right? does this mean it actually has 2 sensors in it, one for the image capture and one for the preview? or do they just not give you a preview and you use the viewfinder?

MOST DSLRs do not provide preview options. Sony (I think) came out with one that does, but it uses the same sensor.

Why no preview options?

Including a 2nd sensor would introduce parallax, unless you introduce a new path for the light. This will also make the optical viewfinder much darker, which is bad. And including a 2nd sensor would make them more expensive.

Using 1 sensor to take the picture and provide a preview introduces problems related to noise. And some sensors have limited life time due to light (UV, etc) materials (mostly dyes as far as I know).

 

[Mday]

Originally posted by: rookie1010
so the original SLR was used for interchangeable lenses and that is still the case.

parallax solving was a nice byproduct of the original non-digital SLR which no longer needs to be solved, correct?

That is mostly correct. If you dont use the optical viewfinder in digital cameras, there is no parallax. SLR-like digital cameras actually use an electronic viewfinder.

And, not knowing the history of SLRs, I don't know if the first SLRs had removable lenses. The first digital SLR actually had a non-removable lens.