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Old Jan 15, 2003, 1:24 AM   #1
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Default Optical zoom v. more megapixels

When I raised the question of the relative merits of more zoom versus more megapixels, the discussion started to include thoughts about digital zoom - which was fair enough because I hadn't said that I was trying to elicit a comparison of more optical zoom with more megapixels.

But I wonder if there are any further thoughts on the topic if we're just comparing more optical zoom with more megapixels?
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Old Jan 15, 2003, 5:43 AM   #2
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I use an Olympus C-700 with 2.1mp and 10x OPTICAL zoom (2.7x digital zoom)...I bought it before I knew the C-730 was coming out which has 3.3mp and also 10x optical zoom. Had I'd known about the C-730 was actually coming out in the next month, I would have waited for the extra megapixel but not only for that reason but because the C-730 has more features...even at the cost of $200 more (compared to what I saved on the older C-700).

I could have bought other cameras on the market but I wanted the long zoom, plus I wanted a "camera"...not an electronic box.

2mp is good enough for 8x10 (most printers can only print 8x10 or smaller anyway if you consider photo formats except for banners).

There's also the arguement of optics/camera features vs. electronics/computer features...many people buy cameras by looking at the electronic features, I looked at the camera features, lens diameter (bigger lens lets in more light), optics, type of viewfinder, ability to add lens filters, etc.
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Old Jan 15, 2003, 5:56 AM   #3
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I'm not sure where this is going so I'll keep my post very simple!

My objective is to record an image (forget whether it's an optical zoom or not), transfer it via some media to an output device, monitor, printer, brain implant etc. What matters is what resolution maps to the output device to give acceptable pic quality. So high Mpix count for say a 10X zoom printed at 10X8 and wide angle are the same, assuming fine detail exists in both the wide and tele shots.

Now, if you're saying what post processing comparison can be made with the more expensive optical alternative, you still need the minimum res. for the output device. So the issue becomes: will more pixels to start with, to provide the same equivalent res. on a print after electronic zoom, be more expensive and convenient than a big lens?

I've left out a lot of other factors. You assume the fixed lens can resolve the detail to start with and the MegaMegaPix ccd will see it, and the processing will be transparent. So it's not just whether the ccd image can be enlarged electronically afterwards or not.

I could say I'd always trust the glass first, unless contrained by size and weight. But I know large cheaper lenses suffer geometric distortions and shading not present with electronic zoom.

So here's an example, I'm shooting architecture or maybe text in macro, or other situations needing flat geometry. Possibly, I might just trade off some electronic zoom for a more linear picture.
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Old Jan 15, 2003, 11:02 AM   #4
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Let me describe in a different way what I'm trying to get at .

Suppose you want to take a picture of something - say a duck sitting on it's nest among the reeds at the side of a pond.

And suppose that to be able to see the duck on its nest, you have to stand in one particular place on the opposite side of the pond.

At that distance, the duck and nest occupy only a small part of the image captured by a non-zoom lens.

You have though, two cameras. One is a 2-megapixel one with a high quality, 10x zoom lens and you zoom it to its full extent so that your duck picture fills the screen and needs no cropping. The other camera is a 6 megapixel camera with a good non-zoom lens. You take a picture with each camera, and later you crop the image from the 6 megapixel camera to get a picture that covers exactly the same picture as you got from the 2 megapixel, zoom camera.

Now, my question is - how will the uncropped image (from the zoom camera at 10x zoom) and the cropped image from the 6 megapixel camera compare? I assume that the answer would be different if I'd specified a non-zoom camera that had 4 megapixels or, at the other end of the scale, 12 megapixels.

I expect that there's a mathematical formula that gives the answer, but I'm mathematically challenged. Is there a simpler way to explain it all?
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Old Jan 15, 2003, 5:44 PM   #5
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Start from the output requirement and work back, not from what you've convinced yourself to buy! Say you want a 6x4 print, printed at Walmart at 300dpi. Assuming no cropping, your framed 10X good quality lens tele shot, on a steady tripod, only needs 2Mpix. Any more would give some, but only slight improvement.

Your high Mpix cam is working at an equivalent 1/10th the image size with a standard lens (remember we fixed the output print size and res. first). So to cut out the same image size and res. quality, you will need to start with a print 60"X40" at 300dpi. For native ccd resolution this requires a cam of some 216Mpix which seems a very big number, memory card and pc to go with it!

I've left out noise, other stuff like sensitivity, compression artefacts, and the ability of your standard lens to resolve the fine detail (unlikely) after you magnify the cut out with your duck sat on its nest.

Don't think these 216 Mpix cams exist yet. Go for the zoom glass, you're going to need a tripod so what's another bit of kit. Shooting significantly more picture area to crop in post is incredibly wasteful on resources. Lenses are cheaper!

BillDrew will explain the square law relationship of Mpix to image size. But if I haven't made the wrong assumption for the zoom mag. or an arithmetic mistake, working back from output print size and res. is easier for me to understand.
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Old Jan 15, 2003, 10:33 PM   #6
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I understand your question. I am a little slow about understand some of the answers. If you divide the horizontal resolution of the larger image by the horizontal resolution of the larger zoom camere, you would have a ratio. (1.6 for a 5mp to 2mp camera) If you multiply this ratio times the larger photo, you would have the zoom that would compare to the camera with teh larger zoom. For instance a Dimage 7 (i or Hi) with 200mm would compare to a 2mp camera with 320mm on the tele end (1.6 X 200). You can figure this out for the 5700, etc yourself.

Now your question is how will a cropped photo compare to a lower resolution photo if they both cover the same subject area and have the same size. The cropped photo will be sharper and better or the same depending on the subject matter. The cropped photo is using the center part of the lens. Most distortions and imperfections occur nearer the edge of the lens. The center of the lens in the best quality. Although most telezoom photos do not require great detail. Because there is less in the scene and it is bigger, the fine detail is not usually required. Which is why teles on 2mp cameras or crops from 5mp cameras at full zoom work so well.

If the greater telezoom camera and the high res camera cover the same area at the same size (as your question states), then obviously the higher resolution camera has more capablilities than the greater tele camera. If the parameters of your question are kept, the high res camera can do everything the longer tele can. Plus it can do all the wider photos and at the wider zoom settings, the greater number of pixels will greatly improve the photo. It would be very unusual for every photo with a camera to be taken at maximum tele. And if was, then you do not need a zoom, just a fixed tele or prehaps an 8X teleconvertor on a fixed lens.

All this is in answer to your quesion. In reality, other things have an effect also. Things like the speed of the lens, the shutter speeds available, image stabilization, bracketing available, best photo, and other features than will effect the quality of your photo. Purchasing a camera based on one spec would most often be a futile exercise. But as a conveerstaion topic, it has in interest.
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Old Jan 16, 2003, 2:04 AM   #7
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Hey Demmy, I haven't seen a post from you for almost a year, welcome back, we can sure use your expertise...Johnny :!:
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Old Jan 16, 2003, 6:23 AM   #8
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I use both types of cameras and I like the big or long zoom camera because it is much easier to frame the photo. The size of your LCD is, in my opinion, a factor in this as the process starts with what you can see.
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Old Jan 16, 2003, 9:04 AM   #9
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The math isn't complicated. In essence, 2 times the pixels is the equivalent of 2 times the zoom for distant subjects. In essence this is what "digital zoom" is all about. It takes your lovely 4 MP picture, and accomplishes a "2x digital zoom" by removing half of the pixels (specifically those around the edges of the photo). The subject is twice the size, but the end result is effectively a 2MP picture.

You can crop any high-resolution photo into a lower-resolution, "zoomed" photo (whether the camera has digital zoom or not). That's simple enough. But there other factors to consider. For example, if you only have a 2MP camera, regardless of the zoom, you aren't going to get good large prints (well, you might with fractal-based software, but not printing the raw file). The point is, a 4MP, 4x optical zoom camera and a 2MP, 8x optical zoom camera may be completely equivalent for capturing subjects at a long distance (where you are forced to crop on the camera with less optical zoom), but for larger prints of close subjects, the 4MP camera will produce superior results.

With the proliferation of 8x and better high-resolution cameras, it's fortunately not always an either/or proposition.
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Old Jan 16, 2003, 11:23 AM   #10
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Quote:
Originally Posted by walkerjks
... 2 times the pixels is the equivalent of 2 times the zoom for distant subjects. ...
Not quite: twice the pixels will give 1.4 (square root of 2) times the zoom. To get twice the zoom, you need to have four times the pixels.

If you double the focal length, you halve the field of view. Field of view is a linear measurement (height or width)while pixel count is area (height times width).
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