Why do Digital Cameras use SLR (DSLR)?

[Anour]

Fellows
My understanding of SLR, before digital took over, was that it showed exactly what the film would have seen without the error of a view finder.

Now that we have a "chip" instead of film that sees the image before saving it and an EXACT duplicate of that is available electronically on the LCD (on back of the camera or viewfinder) , what is the point of having an SLR mirror anymore?

Thanks
Anour

[timmciglobal]

dSLR's do NOT (in general) have life previews (IE: LCD's which show you image as your composing a shot)

dSLR's have mirrors because at top is a prism or pentamirror that shows you the reflected image. No LCD in the little viewfinder, just glass and a mirror.

They have them because the size plates they use require a lot of energy and heat up quickly if left exposed constantly (IE: like P&S do during live preview) and thus would be impracticle) Panasonic and Olympus do have live preview MOS sensors which do both have LCD and mirror but they acheive that at cost of bright viewfinder using a partially transparent mirror.

Tim

[coldrain]

The Panasonic L1 and the Olympus E-330 do not have a partially transparent mirror. The L1 only has live preview when the mirror is up and out of the way.
The E-330 either has the mirror out of the way and preview via its big sensor, or preview via a small sensor located near the view finder.

If you want to show what you see through the lens in a view finder, you just need to have a mirror in front of the sensor. This is one big reason for "SLR". Another, like Tim said, is that the sensors get too hot for live preview. They are bigger than the onces in compact digital cameras. And a 3rd reason is that electronic view finders just never can approach optical view finders in judgeing things in the image.

[Riley]

as to, what is the point of an slr anymore

the place we are at with dSLRs we have arrived at via evolution
for the moment, the slr is the tool that offers the most flexibility
interchangeable lenses, wide / normal / tele /macro
system options such as TTL flash / ring flash
together with these features, the slr has enhanced sophistications
like faster more accurate autofocus
like more accurate and more extensive metering options
higher and more useable iso

now remember slr film cameras only had an optical finder via the prism
no LCD on the back at all, there is still a core of photographers that will prefer the finder to the LCD. but as EVF's become better and more useful, we wont need the slr at all, well not for the reflex prism anyway
but we are not at that place quite yet

the moving mirror actually makes some things more difficult
the more sophisticated cameras need to be able to meter and focus when the is mirror down, and when the mirror is up. adding complications and sometimes duplication of systems
the mirror also adds an amount of shake or vibration
and it makes a noise, making candid shots harder to achieve
it adds an amount of shutter lag, and adds cost and weight to the camera

Riley

[timmciglobal]

Your right coldrain, my mistake. It uses a poro mirror and a second CCD. The mirror doesn't go up during one of the live modes for that.

Tim

[Anour]

Thanks Timmciglobal , Riley and Coldrain for your informative comments.

I understood three reasons for DSLR (from your comments):
1) DSLR Sensor gets hot if left on (like P&S)
2) It was an evolution of SLR (maybe to encourage professionals to switch)
3) Optical image is better than LCD for judgement (maybe because it is really 3D)

I am not a professional photographer, just love photography. However, as a technocrat who earns his salary by predicting the impact of technology in an engineering field (not related to photography), I still do not see a FUNDAMENTAL reason for having that moving part (mirror) with all its complications.

Reason #3 above is fundamental and would probably help extend the mirror life in the market but sensors getting hot is just a matter of technology. It is just a matter of time before better sensors with fraction of their present power consumption (cause of heat) would be available. I do not know what percentage of professional photographers have switched to digital but, if not the majority, that will be a matter of time too.

My prediction (as an outsider) is that the "moving part" is on its way out and professional cameras become smaller (in body) with full lens interchangeability and gadgets.

How off am I in my prediction ?

[Riley]

Anour I think you are spot on
its just a matter of time and availability ot the technology
that said, some photographers have a tendency to resist change
which presents some obscure solutions

Riley

[Norm in Fujino]

How off am I in my prediction ?

No one knows but the shadow (i.e., only time will tell). There is talk in some circles that electronic viewfinders will eventually replace the mirror, but that time hasn't come. Current evf technology simply isn't up to the visual quality of an optical vf.

[cwphoto]

Personally I'd prefer to use a Pellicle Mirror than go to an EVF.

Today's EVFs just don't cut it for pros or discerning users, but we already have the technology to do away with the moving mirror. It never really went mainstream manly due to the loss of 2/3rd f-stops to the media, but with today's clean-free high ISO sensors I reckon it's time for the Pellicle Mirror to make a comeback.

I would buy two pro-level cameras immediately for this feature if it was on the market.

[forno]

i think it will be a long time before there is a EVF that can pan as well as a OVF and even longer for it to be accepted