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Old Mar 18, 2004, 6:57 PM   #1
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Default understandign actual pixels

Hi,
I am fairly new to all this digital stuff and am confused on pixels, or maybe not.... I'm hoping someone can let me know if i understand this correctly.
As I understand it there are basically 2 types of sensors out there that being the standard which is in most cameras and now the new foveon type in the Sigma's.
I understand it that the Sigma (foveon) it has 3.4MP per color totalling 10.2 so in reality what I would really get is 3.4MP of green, red and blue colors.
The other is really just colored filters for lack of a better description over the pixels. By that I mean that out of a set of 6 pixels you have 3 green, 2 red and one blue therefore a 6MP sensor is really producing 3MP green, 2MP blue and 1MP red.

This is why the Sigma images seem to have a lot better clairity as in any given color there are more actual pixels than what would be in a 6MP chip after they are all divied up into seperate colors therefore it would take an 8MP chip to exceed only the color green and still lack in the blue and red?

Am I understanding this correctly?

This leads me to my next question, how does Fuji come up with 12MP using a 6MP chip? Are they doubling up on the greens or something silly like that?
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Old Mar 18, 2004, 8:32 PM   #2
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Your problem is that there is a difference between a pixel (what appears on your computer screen) and the thing that actually senses the light (which is actually called a photosite.)

Each photosite samples the light at that given point on the sensor chip. The range of light each senses covers (portions of, I bet) either the red, blue, or green areas of the spectrum. There is no direct correspondence between the number of photosites and the number of pixels. Obviously, the more photosites you have, the more data you have that can be turned into pixels, but as you see with the Fuji you don’t have to have as many because you can interpolate the data from the photosites to make more pixes than you have photosites. If you do it well (both in software and in photosite layout on the sensor) it works. If done badly, well… the picture will look bad.

The reason there are more green sensors than red or blue is because the human eye is more sensitive to the green area of the spectrum. That is just how our eyes developed. Since we are more sensitive to greens, sensors that do a better job representing greens in a picture look better (i.e. we sense green color problems more than other color problems is how I see it.)

Why the Foveon produces such a good picture is an interesting question. My take on this (and I could be wrong) is that because the same actual beam of light is read for red/green/blue, this produces a better reproduction of reality. In a CCD or CMOS sensor, the green sensor is next to the blue, and so on. This means that the exact beam of light that is used to read “green” is not the same light used to read “blue”. I bet that makes a difference (but a subtle on) that the software in CCD/CMOS cameras try to emulate but don’t do perfectly.

In the case of the Fuji, I have always assumed that they are reusing photosites and combining adjacent ones in different combinations to produce more pixels out of the same number of photosites. Part of their magic is in the layout of the photosites on the sensor. Are these “manufactured” pixels (like when PhotoShop interpolates an image to a larger size) its not the same, but its similar. But one could say that unless you are using a Foveon, all pictures are a combination of different light beams.

Does that help? Feel free to ask more if I’ve only confused you more.

Eric
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Old Mar 19, 2004, 6:20 AM   #3
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Hi Eric,
Yes, your explination helps a lot, much appreciated!
The reason I am trying to understand all this stuff is because I am looking to upgrade my point and shoot Olympus 4040Z to a DSLR and I want to get the best value for the coin. By value I mean great looking pic's, I dont much care for extra bells or whistles that some cameras have such as the ability to make mpeg's. I do like to control all the settings manually or as many as I can anyway, maybe just because that's what I am used to doing and feel most comfortable with. I have no lenses so no matter which way I go I will have to invest in those. I guess its not really a bad thing though because it allows me to choose from all manufactures rather than getting something just because I happen to have other equipment that is compatable with it. Curious, If you had $5K saved up, which camera would you recommend buying and why? What I am looking at is the camera, a lense or two for starters, batteries and media. I have the bag, tri-pod, flashes and all that kind of stuff.

Thanks again for the explination, I value your opinion.

Ken

Olympus - OM2-N, 4040Z
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Old Mar 19, 2004, 10:45 AM   #4
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I am glad I could help.

If you really like full control (including switching lenses for particular situations) then a DSLR is a good choice. They also let you choose how much money to spend on lenses. People might talk about there really expensive lenses (I will below) but you don’t have to get them. A DSLR can be used to produce stunning hang-in-a-gallery quality pictures, but that cost lots of money. You don’t have to do that, and can buy cheaper lenses that fit your needs… keeping the cost down.

First I'm going to give you background. I do avian photography for fun. I don't have kids, I don't photograph my extended family (my brother & sister give me pictures they ged of their kids.) So I don't take "kid play sports" or "kid having fun in the backyard" or "kid looking cute in the high-chair" picture. I take picture of distance, skittish animals that (I think) can look lovely and do photogenic things.

I don't know what type of photography you do. So my choices and reasoning (which I'll list below) might be absolutely useless for you. If you take loads of indoor pictures of kids smiling and looking cute, then this info won't help. If you take pictures of soccer games, then my info will be of more help.

If I had 5K to spare and I was starting out, I would have to choose to go in one of two types of directions.

1) Either the Canon 10D or the Nikon D100 (I guess the D70 should be on the list, but I honestly don't know enough to say if it replaces the D100 or just augments their product line below it.)

2) Buy a professional quality body (Canon 1D, 1D-Mark II, Nikon D1h, Nikon D1x) This would leave very little for anything else, and would probably mean that the 5K wouldn’t be enough. But it would be enough to hold me for a month or two while I save a bit more any buy the rest.

#1
This would leave me enough left over to buy a Lexar 40x 1G WA CF card, an extra battery & a big powerful flash (I have the Canon 550EX, the largest hot-shoe flash Canon makes) and an external battery pack for the flash (maybe the flash and body.) A good tripod and ball head.

But what about the camera body & lens? Well, when I compared them, the D70 didn’t exist. I saw the 10D & D100 were the same cost. The reason I went with Canon was because the lenses I wanted (Canon 100-400 vs. Nikon 80-400) was cheaper and better (optically & AF speed.) Also, the really big expensive lenses (500mm & 600mm) are cheaper and include Image Stabilization. In fact, Nikon really only started to push VR (their version of IS) into more lenses. This is a great help when hand-holding shots. So at the time Canon’s IS is in more lenses and that is a good thing too.

So I choose the 10D and the 100-400L lens. I use that lens about 95% of the time. While it isn’t amazing, it is very good, and has served me well.

#2
I could benefit from a better AF system than the 10D has. To get that, I have to buy something better. But the leap in price is very high when you go above that. I’d have to buy used or not get anything but the simplest lens and save more money for better lenses. I would be tempted to go this way, but the reality is that I shouldn’t. Camera bodies get replaced quickly, the depreciation is so fast its scary. Good lenses last a long time and hold their value.

Does that help? How exactly would you use the camera? That is what really matters, but what people rarely say (much to the annoyance of the regulars at this forum.)

Wait a second. If you have flashes, then you are already partially invested into a system. What flashes do you have?

Eric
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Old Mar 19, 2004, 12:00 PM   #5
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Hello again,

Well, to answer your question of what I would use the camera for. I enjoy cave photography when I can. I say that because so much of the neet stuff is in places that are not easily reached. Hauling in a bunch of equipment just isnt feasable at times so I only do it when I can. Besides, it's a minimum 6 hr drive to the nearest cave one way and I'm not getting any younger. A typical cave trip ranges anywhere from 4 - 12 hours and thats a long time to be lugging stuff around all while climbing over huge rock piles or belly crawling through elbow deep mud all while trying to keep the camera out of the dirt. Suffice to say its also low light at best. Focusing can also be a huge issue in these conditions mainly because you can't see very well what it is your looking at. I currently use multiple (4 at any given time) Vivitar 285HV flashes as they are bright and easily adjustable. All I do is set them up with what I call a bug, its a small round sensor about the size of a nickel and it sets off the flash when it see's a flash. The idea is that they are set up in places further down a passage and then light the entire area up for the shot. It works quite well unless you have a camera that attempts red eye reduction of some other sort of pre-flash. I tend to do more close up or macro stuff in general either in the cave or outside such as a photo of a flower or insect. I don't do weddings, seldom do people shots unless its just a quick snapshot just for kicks. Most any camera I get will do fine in these situations should they arrise and therefore wotn be much of a consideration in what I end up geting. I would like to get more into distant stuff however the 4040Z doesnt do a very good job of this, agian its just a general point and shoot IMO. The lense I have on my old OM2 is a Tokina 35-200 with macro capabilities, also have a 2X when I need to go beyond the 200MM which works great for the distant shots such as a bird in a nest way up in a tree on the other side of a ravine. Have a couple other general use lenses as well that I picked up over the years none of which are compatable with DSLR's made these days. This has suited me for many years, and still does well when I use it. I think I would be quite happy with the 100-400 you mentioned and then get a lense for macro and maybe a 2rd to cover the 35-100 range after I've saved up some more coins.

Going forward I want to get a lot more into photo's on the surface, old buildings - houses - barns, nature shots - flowers - animals, sunsets, shots of objects from odd angles like the one I snagged a couple weekends ago of some moss inside an old beer bottle. That was a toughie for my 4040Z! Had to shoot through the neck of the bottle catching the moss all while trying to get the camera to not focus on the bottle itself. I was quite happy with the results, will upload to my web site and post the link here so you can check it out just for kicks.

No doubt I will find other stuff that I will want to photo once I get some decent equipment, not that the 4040Z's bad... its just really limiting me, my creativity and thus my fun, basically I jsut wnat to do all the fun stuff I used to do with my OM2. To bad its film....

One last thing, I have big paws so whatever I get needs to have a good feel or grip. The Canon feels good to me so that is something I will need to consider as well. Haven't had a chance to hang on to a Nikon, Fuji or Sigma yet but hope to soon.



Ken
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Old Mar 19, 2004, 12:34 PM   #6
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The Fuji's sensor is unique in that the pixels are not laid out in a square grid like other sensors; they are in a honeycomb layout. Because each row of pixels is partially nested in the row next to it, it's only a half a pixel distance to the next row of pixels. I guess I should be using the word photosites instead of pixels but I'm too lazy to go back and change it. Anyhoo, because it's only half the distance, you don't need to upconvert to figure out what's in the next line. That's how I understand it anyway. What I'm really impressed with is the new sensor going into the Fuji S3. It has a big and a small sensor on each photosite - the big one is real sensitive so it captures the shadows, the small one is not, so it captures highlights without blowing them. Kind of like having high-speed film (big silver halide grains) and low speed film (small silver halide grains) in one.
If I had $5k to spend, I would get the Canon EOS-1D MII that's coming out soon. I got to play with one at the WPPI convention. On high speed, it's like firing a machine gun. It looks like Canon paid attention to what everyone wished they had. It wouldn't leave much $$ for lenses, but I have 2 Canon lenses to keep me occupied until I gould afford some L glass.
Since it looks like you do a lot of spelunking, (hehe, I used a cool word) is it more important to you to have a lightweight camera or a durable one? The 10D is not too heavy. THe Canon 1D series are built like tanks. Heavy, but so durable you could use one to pound in nails. The D100 and I suppose the D70 I think are close to the 10D in weight and build. I've never used a d2H, maybe someone can tell us how sturdy it is. The Fuji is a great camera but it's plastic. I dropped mine once and the only thing that saved it was the Sunpak flash it landed on. (bye bye flash)
OK I'm done rambling.
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Old Mar 19, 2004, 2:08 PM   #7
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Hi LTBerry,
Thanks for the info on the Fuji sensor. That would explain to some extent how they are getting 12MP out of the 6MP sensor. I supose the rest is made up in software.
As for your question, I would opt for durability vs weight.
Thanks much for the reply!

Ken
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Old Mar 19, 2004, 2:42 PM   #8
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Yes, the S3 Pro looks to be going in a great direction. Much better dynamic range. To me, it has been one of the annoying thing about most digital cameras, too small a range.

If I had the money, I'd seriously consider the 1D-Mark II as well. I could get it, but I think I'd be better served with a monster lens. And at least for awhile it's one or the other.

Caveboy_Ken

Well, that description is certainly not the usual answer to my question. This changes things some.

The easy thing first: The D100 is physically smaller than the 10D, so while you should check it out, it might not fit your hands. Still, its a good camera and has great battery life so its worth considering.

Wow, for that usage... humm. Difficult choice. You obviously need a decent wide angle and light. Very light. You're on your feet for 4-12 hours on those trips? Weight will really matter, which is difficult. Every DSLR will be much heavier (after all the lenses) than a fixed zoom camera. But the image quality should be better. So if you can deal with the weight, keep going.

Your camera has in 35-mm equivalent of a 35-105 f1.8-f2.6. That is what you are used to, so you'll need at least that. It will be next to impossible to match that, though. If you normally shoot at the larger f-stop range, then it won't matter (greater depth-of-field.)

For trips that long, you might consider a battery pack (or at least extra batteries!) I don't know how many pictures you take, but if you run out way in the cave, there is nothing else you can do. Something like a Quantium 2x2 or a Digital Camera Battery might be a good idea. The same logic applies to extra CF cards.

You can get a hotshoe flash that also as an AF-assist light for focusing. The Canon 550EX does that and I bet Nikon has one too. The range isn't staggering, but it isn't bad (I forget how far.) Works great and won't trigger your off-camera flashes.

The 100-400 is a nice lens. Sigma finally came out with a similar lens with optical stabilization that is cheaper and looks good. You might consider that to save money. I don't know if it's as good as the 100-400, but it isn't bad from what I've seen.

For buildings and such, the same wide angle you use in the cave will be fine.

It does sound like you need to seriously consider build quality of everything. You'll be giving them a beating. Unfortunately, the most rugged DSLRs are all the pro models, which are really expensive. But if you think the 10D is rugged enough, it is certainly a good camera.

Eric
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Old Mar 19, 2004, 5:57 PM   #9
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Grin, yea, most folks look at me really strange when they realize where I go and then really freak when they realize that I just draged in about $1.5K worth of camera stuff through the mud. Thanks to Pellican everything stays nice and dry not to mention very well protected. While weight certainly plays into how tired one gets when caving I think I would still opt for durability as I can always stop and rest whenever needed. We do move all that fast either and typically rest often so its not as bad as it sounds. I've got to be realistic here... I have to consider the fact that it's highly likely that my new $5K investment won't be seeing any mud any time soon and if it does it will be in wide open passages such that you would find at Mammoth Cave where the mud can stay on my boots where it belongs. There are some great shots that can be had at Mammoth which do not require and crawling at all too get to. So that being said I have to look at this all differently in that I'll be using the camera most on the surface. That pretty much solves the low light issue and I do have access to more powerful flashes should the need ever arise. Now those babies are heavy!!! but that's another story for another day.
My Tokina is 35MM-200MM @ F: 3.5-22 (for 35MM film), It would be nice to get something lensewise that falls somewhere near that range, whatever that equals in the digital world.
I'm thinking that most of the stuff I would shoot could be handled with that range. I'd get another lense just for the macro stuff.

I need to learn how to figure out the equivilent lense for DSLR based on the Tokina that I have now for my OM2. Any suggestions on where I could find a good explanation?

Ken
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Old Mar 19, 2004, 6:22 PM   #10
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pelican makes good stuff. I've never had to get one, but I know they are what I would get if I ever had to.

Actually, finding the equivalent of that lens is easy.

First off, an f-stop is an f-stop. So don't worry about that. You stated the fstop range a little odd. f3.5-22 is the range of max to min. But is it f3.5 for all focal lengths for the largest aperture? It could be, but F3.5 is a of an bit odd choice. But you can get lenses that are always f2.8, that are 80-200, and then a second one to cover the close stuff, or you can get something like 28-200mm f/3.5-5.6. It's not stunning quality, but it isn't bad.

Now, about the focal length. There is one way to calculate it, and 3 different "constants" in the calculation depending on the camera.

Because the sensor is smaller than film, lense seem to act like they are longer focal lengths than they really are. This is refered to as the "crop factor" (other terms are also used, but they can be misleading.) Since the crop factor is based on sensor size and many cameras share the same sensor size, the "factor" is the same among many cameras.

Canon 1D, 1D-Mark II = 1.3x crop factor
Canon 10D, Digital Rebel, D30, D60 = 1.6x crop factor
Nikon D100, D70, D1x, D1h, D2h = 1.5x crop factor

How you use the number is simple. Multiply the focal length range by the "crop factor" and you can the effective range of the zoom.

My 100-400L on the 10D is equal to a 160-640mm on a film camera.
My 100-400L on the 1D is equal to a 130-520mm on a film camera.

If the range is A to B and you put it on the 10D, its the same a (A * 1.6) to (B * 1.6). If you already have the "film" numbers, just divide and you'll get what you'd need on the digital to be the same thing:

X *1.6 = 100 x = 100/1.6 = 62.5
Y *1.6 = 400 Y = 400/1.6 = 250
So to get the same as a 100-400 on a film camera I need a 62.5-250mm zoom on my 10D.

On my 10D, the equivalent of your Tokina is 21-125. Canon doesn't make that lens, though. They make a 28-105, 28-135, 24-70. Sigma might, though.

So you just use the proper crop factor based on what camera body you are thinking about.

Does that help?

Eric
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