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Elie
12th January 2004, 10:05
Hi Guys, I need to know whar SLR stands for and what it really does.

Sorry I am not all that into photography and want to broaden my horizons a bit.

Many thanks in advance,
Elie

Tjalfe
12th January 2004, 10:15
To the best of my knowledge, which I am sure will be corrected by someone more into photography, SLR means Single Lens Reflex . it means that there is not a seperate viewfinder from the main lens. so that when you look through the viewfinder, you see out through the main lens, though a mirror, which also doubles as the shutter. This means that you see through the viewfinder exactly what will end up on the film, or the CCD.

az
12th January 2004, 11:49
Yes and no ;)

SLR means single lens reflex (as opposed to Twin Lens Reflex (http://photographytips.com/Images/xtwin-lens-reflex-yashica.jpg) and Rangefinder (http://www.perkowitz.net/photo/gear/rangefinder/rangefinder.sm.jpg) cameras) for the reasons Tjalfe posted. But the mirror does not work as the shutter (it is too slow, and not precise enough. Also, it swings up, this would expose the lower part of the film slightly longer). The mirror flips up, shutter opens and closes, mirror flips back down.

With digital SLRs it's the same, only there's a sensor in place of the film. There are also "SLR-like" digital Cameras, like the Minolta Dimage 7x and A1. They're called SLR-like because they look and feel not entirely unlike SLRs, and have an electronic viewfinder that also looks through the lens (via the sensor).

AZ

Tjalfe
12th January 2004, 11:57
bah.. I was close ;)
I do recall the mirror being used as a shutter in some old( read really old) cameras my friend has.. at least it looked like it was . My Olympus C-730 Digital camera is using one of those SLR kind of digital viewfinders using the CCD.. it works pretty good :)

az
12th January 2004, 12:36
See, that's the difference: My digicam was twice as expensive, and its EVF is scheisse ;)

AZ

SpiralDragon
12th January 2004, 12:53
heh... i almost forgot what slr stands for ..... shame on me...

VJ
13th January 2004, 00:30
Originally posted by az
There are also "SLR-like" digital Cameras, like the Minolta Dimage 7x and A1. They're called SLR-like because they look and feel not entirely unlike SLRs, and have an electronic viewfinder that also looks through the lens (via the sensor).


Just for completeness: the Olympus E10 and E20 use a prism instead of a mirror. This allows light go to the CCD, but also to the viewfinder. As a result, these cameras have an optical trough-the-lens finder, but still allow the lcd to be used as preview. A disadvantage was that both viewfinder was relatively dark (only half of the light coming the lens goes to the finder) and that only half of the incoming light hits the CCD.

More commonly on digital photography forums (and as az used), "SLR" is used exclusively for cameras with an optical true the lens finder (mirror); cameras with EVFs are referred to as "SLR-like".
(because of the mirror and shutter, the lcd on a digital SLR can ony be used to review pictures, not to frame them; a feature that is possible on an SLR-like camera)



Jörg

az
13th January 2004, 04:53
BTW, Minolta's digital SLR this year will have a mirror and is rumored to still allow you to use the LCD to preview, just like the Oly E-x0, by either using mirror lockup or a half-see-through mirror. Built-in (into the body) image stabilization ("Anti-Shake", which shakes the CCD, like in the Dimage A1) will also likely be in, and "one feature unnamed will be a big surprise". I am curious what the inventors of the Autofocus SLR and Anti-Shake will bring us this time :)

Prototypes will likely be shown at PMA in a month, it will be available at Photokina.

AZ

VJ
13th January 2004, 05:16
Originally posted by az
BTW, Minolta's digital SLR this year will have a mirror and is rumored to still allow you to use the LCD to preview, just like the Oly E-x0, by either using mirror lockup or a half-see-through mirror.
Hmm, half-see-through mirror is difficult (bear in mind the reflection and the refraction; Olympus used a prism). Mirror lockup would mean the camera doesn't have a mechanical shutter, but uses an virtual electronical one (taking into account the recording of the CCD for the specified shuttertime ). Of course, there is nothing wrong with this (IIRC Nikon used this in D1 for shutterspeed faster than 1/1000th (could be wrong about this speed though)); but it does limit the CCD to be used:
http://www.dpreview.com/learn/Glossary/Camera_System/Sensor_01.htm
it must be an interline sensor, not a full frame (not to be confused with the size of the sensor, see above url) sensor.


Built-in (into the body) image stabilization ("Anti-Shake", which shakes the CCD, like in the Dimage A1) will also likely be in, and "one feature unnamed will be a big surprise". I am curious what the inventors of the Autofocus SLR and Anti-Shake will bring us this time :)
It could be something similar to "X3 Fill Light" like in the Sigma SD10 (or Digital DEE in Nikon Capture software), where the image is analyzed and exposure is corrected. An example is a person in front of a bright background (e.g. a window): his face will be too dark. X3Fill Light (and DEE) adjust the exposure of the face (and other items), so that the exposure is ok, without blowing out the background. X3 does it in hardware (!), Nikon DEE is in postprocessing on computer.

Or it could have to do with serial photos. I believe the Minolta A1 is one of the best when it comes to high FPS shooting (not in its full resolution, only when a fast CF card is used).

Or portable mass storage devices ?



Jörg

az
13th January 2004, 05:59
Originally posted by VJ
Hmm, half-see-through mirror is difficult (bear in mind the reflection and the refraction; Olympus used a prism).

I only know Minolta has at least one patent for this.


Mirror lockup would mean the camera doesn't have a mechanical shutter, but uses an virtual electronical one (taking into account the recording of the CCD for the specified shuttertime ). Of course, there is nothing wrong with this (IIRC Nikon used this in D1 for shutterspeed faster than 1/1000th (could be wrong about this speed though)); but it does limit the CCD to be used:
http://www.dpreview.com/learn/Glossary/Camera_System/Sensor_01.htm
it must be an interline sensor, not a full frame (not to be confused with the size of the sensor, see above url) sensor.

Why could you not use a mechanical (electronically controlled) shutter then? Professional SLRs have had mirror pre-lockup for quite a while now, to prevent "mirror slap", and you would only need to keep the shutter open for as long as you used the LCD. Mirror lockup could work automatically using Minolta's Eye-Start sensor. I don't know about full-frame sensors, but the Dimage A1 needs a progressive sensor, since interlaced won't work with AS.


Or it could have to do with serial photos. I believe the Minolta A1 is one of the best when it comes to high FPS shooting (not in its full resolution, only when a fast CF card is used).

The Dimage 7 series had this, the A1 has abandoned it (I don't know why, might have to do with the full frame sensor). I can shoot at 7fps at 1280x960 (so VERY reduced resolution), the Dimage 7Hi can keep this up for 106 shots in "fine" quality. It was rumored that the Minolta "Zeus" DSLR would have a buffer for 36 full-resolution pictures, at 3.5 fps. But I don't think that's true :) Well, I guess in a week we'll know :)

AZ

VJ
13th January 2004, 06:10
Originally posted by az
I only know Minolta has at least one patent for this.

aah... I didn't... :)


Why could you not use a mechanical (electronically controlled) shutter then? Professional SLRs have had mirror pre-lockup for quite a while now, to prevent "mirror slap", and you would only need to keep the shutter open for as long as you used the LCD.
It has to do with the sensor type; if a sensor doesn't need a shutter, a manufacturer isn't likely to put one in the camera. Why would you, if you allow live LCD preview (which would mean the shutter would have to stay open). The easiest approach is that the imaging works the same, whether the mirror is down (viewfinder), or the mirror is up (live lcd).

In the Nikon D1, there was a mechanical shutter that was used for slower speeds, when the speeds got higher, this shutter opened for too long, but the electronic shutter kicked in. This is not a scenario you can use when having live preview.


The Dimage 7 series had this, the A1 has abandoned it (I don't know why, might have to do with the full frame sensor).
No, a full frame sensor wouldn't allow a live preview (which the A1 has).

How is that, in 1 week ? PMA is a month away...


Jörg

az
13th January 2004, 06:17
The A1 also has that combined mechanical/electronic shutter. And if Nikon could do it in the D1, Minolta can use it too in their DSLR, I think :) Just close the shutter very shortly before opening it for the shot.

I menat in a month, not in a week, sorry :)

AZ

VJ
13th January 2004, 06:28
You are correct... it is listed in the specs as mechanical and electronic
http://www.dpreview.com/reviews/minoltadimagea1/page3.asp
yet it offers live preview... Strange...
It doesn't need a mirror, as it has an EVF; but why would it need a mechanical shutter... :confused: it has got to be open as soon as you want a preview (in EVF or on the LCD)... :confused:

Nikon in its D1 didn't offer live preview the electronic one was only present to have faster speeds than the mechanical one would allow.

Or could the CCD in the A1 have different modes, something like this:
1. live preview mode
2. user presses shutterbutton
3. shutter closes, CCD changes mode
4. shutter opens, photo is recorded, shutter closes
5. CCD changes mode and shutter is opened
And then an electronic shutter to acchieve higher speeds...?


Jörg

az
13th January 2004, 07:32
I think it is exactly as you think :) I know the electronic shutter is used only for very fast speeds (I think <1/4000 s).

AZ

rubank
14th January 2004, 09:52
Just for the record:

see-through mirrors is nothing new. In the sixties Canon had a (moderatley successful) SLR model named "Pellix", that had a nonmoving, see-through mirror. This mirror refelcted as little as ~10% of the incoming light to the viewfinder. Hence, the viewfinder was somewhat dark, not as much though as you would think (compared to the competition of the day).
Nowadays new focusing screen technology has given brighter viewfinders (Minolta being the first to introduce such a device, called accute-matte, if I recall correctly, in their XD-7 model. This model was later to be more or less rebadged to Leica R4).

rubank

Elie
14th January 2004, 12:18
Wow thanks guys!
Understood loud and clear!

Maybe I should start a new thread ont he differences between Foveon and CCD LOL :)

Thanks again!

Cheers,
Elie

az
14th January 2004, 12:50
Simple :)

The photodiodes on a CCD sensor cannot see colour, they only see light intensity.

On a traditional ("Bayer") CCD sensor youone photodiode per pixel, and an array of colour filters in front of the sensor, one colour for each photodiode (green, red, green, and blue - yes, 2x green, because the human eye is more sensitive to green than to other colours). So each photodiode can only see one colour. Colour gets interpolated, which is no big problem, because (as you probably already know from video) the human eye is more sensitive to luminance (brightness) than to chrominance (colour). This only introduces problems for certain patterns, resulting in moiré or reduced resolution.

The Foveon X3 sensor has THREE photodiodes per pixel, behind each other. This works because certain frequencies of light penetrate silicon a little deeper than others, reaching the second or third sensor. The 3 megapixel X3 sensor actually has 9 million photodiodes (3mp times three).

AZ

Marshmallowman
14th January 2004, 18:15
CCD = "charge coupled device"...not really a diode :)

az
14th January 2004, 18:33
I don't know why, but they are called photodiode (at least on dpreview, and I think I've seen it somewhere else also).

AZ

VJ
15th January 2004, 00:33
Yup, the individual pixels are called photodiodes.

Most cameras use GRGB (green, red, green, blue) as az stated, some cameras use CMY (cyan, magenta, yellow), and now Sony is using a different layout: RGBE (red, green, blue, emerald)
http://www.dpreview.com/news/0307/03071601sonyrgbeccd.asp
This is the sensor in the F828.

The Foveon has the disadvantage that - while some frequencies penetrate deeper in the silicon - the colour positioned the lowest does get less light.
http://www.foveon.com/X3_tech.html
This leads to more noise in green and red (most in red), than is present in blue.

It is clear that this has opened a discussion: the Foveon reads 1 pixel at one position, whereas the traditional bayer sensors need to apply specific interpolation between a pixel (=1 colour) and it neighboring pixels (=another colour). Suppose Foveon have a sensor with 1 million pixels: it reads 3 x 1 million photodiodes; a bayer sensor that would do this has 3 million photodiodes.

The discussion then concerns:
Which is the sharpest ? (bayer: sensors are spread over an area, this benefits the sharpness, but the interpolation has a negative effect on it)
Can Foveon state they have a 3 megapixel sensor ?
(no: only 1 million individual positions / yes: 3 million photodiodes)
Can the bayer sensor state they have 3 megapixels ?
(no: the 3 million pixels are not independant / yes: 3 million photodiodes)


Jörg

Marshmallowman
15th January 2004, 02:51
Indeed it is my mistake:suprised:

I keep thinking of things they used to be (non silicon)