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Old Jul 22, 2009, 11:53 AM   #11
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that's where my comment about resolution came in.

If the base image (the full image you take when zoomed in) is 3000x2000px and you crop a tiny little piece out of the middle, you may only have a frame thats 300x200 left over. If you were to stretch this highly cropped image to fit on a 8x10 page when it was printed, you'd see the loss of quality.

There are a lot of factors in play here...
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Old Jul 22, 2009, 12:08 PM   #12
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But I thought the last one should win? Because we can crop it using photoshop repeatedly and be able to see the word "Steve" printed on the poster far far away. Am I right?

Cropping repeatedly is going to probably result in a nearly unusable image. You're much better off framing the image the way you want it, rather than cropping to achieve the desired framing.

As was mentioned, there are too many factors at work here to give you a definitive answer. Lens quality, sensor size, and lots of other things all come into play, and ultimately i don't think any of the scenarios you present will produce a usable image of even poor quality.

What exactly are you trying to accomplish?? I see you posted similar questions a couple of years ago.
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Old Jul 22, 2009, 1:11 PM   #13
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Cropping repeatedly is going to probably result in a nearly unusable image. You're much better off framing the image the way you want it, rather than cropping to achieve the desired framing.

As was mentioned, there are too many factors at work here to give you a definitive answer. Lens quality, sensor size, and lots of other things all come into play, and ultimately i don't think any of the scenarios you present will produce a usable image of even poor quality.

What exactly are you trying to accomplish?? I see you posted similar questions a couple of years ago.
I just a newbie who is interested into optical zoom and is amazed how a tiny small lens without any protruding lens (Referring to panasonic 35-2500mm camcorder) can compare to a huge aperture like 300mm 2.8f. I am into birding and concert and now need to choose whether to upgrade my SX10 to DSLR. When I use SX10 for capturing bird, it is not enough. And when I crop it, it result in blurry image. And to my horror, I realised SX10 has a crop factor of 4 which effectively mean that I am buying a 150mm lens. That why I was thinking should I buy a DSLR and a 300mm lens. Then after I shoot, I will crop the photo and I wonder whether this will result in a better image than my SX10.

My hypotechnic question about trying to see the word "Steve" on a poster far away is another clearer way to pharse this question, in my opinion
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Old Jul 22, 2009, 1:43 PM   #14
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I just a newbie who is interested into optical zoom and is amazed how a tiny small lens without any protruding lens (Referring to panasonic 35-2500mm camcorder) can compare to a huge aperture like 300mm 2.8f. I am into birding and concert and now need to choose whether to upgrade my SX10 to DSLR. When I use SX10 for capturing bird, it is not enough. And when I crop it, it result in blurry image. And to my horror, I realised SX10 has a crop factor of 4 which effectively mean that I am buying a 150mm lens. That why I was thinking should I buy a DSLR and a 300mm lens. Then after I shoot, I will crop the photo and I wonder whether this will result in a better image than my SX10.:
ok, first, quality glass costs. the tiny little lens and the tiny sensor on the SX10 cannot compete with fast expensive glass. Though the 35mm equivalent focal lengths may be the same, the reduced sensor size and less-optically-perfect lens will reduce the quality of your image.

Yes, that lens on the camcorder is a 150mm lens, but when combined with the tiny sensor (that has the very high "crop factor") it will result in a much more "zoomed in" picture (hence the 2500mm focal length value they state)

the 150mm on a dSLR with a crop factor of 1.5 (which will net you a 225mm lens) will produce a MUCH wider angle of view (not zoomed in NEARLY as far), you'll have to crop it even more to get the same image (ie, you might have used 1/4 of the image off the camcorder, but you'll likely need 1/50th of the image off the dSLR, sorry I haven't the time to figure out exactly how much of the image you'd end up using to get the same frame.

in my opinion, the larger sensor in the dSLR, combined with some very good glass would be the best choice, especially if you anticipate needing to shoot in low light (concerts) or high motion (wildlife).

Here's the catch, as a random example of a quality lens capable of low light performance in the 500+mm range: the AF-S VR Zoom-NIKKOR 200-400mm f/4G IF-ED retails for about $6000 USD. (200-400mm on a camera with a 1.5x crop factor will yield a lens that behaves like a 300-600mm lens)

On the cheaper end, the Tamron SP AF 200-500mm F/5-6.3 Di LD (IF) (which will yield a 300-750mm lens on a camera with 1.5x crop factor) retails for about 1200USD but lacks image stabilization making it impossible to take clear shots hand-held when zoomed in.
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Old Jul 22, 2009, 2:03 PM   #15
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Each time you crop a photo so that it looks like you used twice as much optical zoom (double the focal length), you end up with about 1/4 the original resolution in pixels.

So, you can't crop a lot and still have much detail left, depending on the resolution of the image you're starting out with (which I haven't heard you mention yet for the video cameras you're looking at).

For example, if you cropped an image from an 8 Megapixel Camera taken at a 35mm equivalent focal length of 400mm to make it look like you used twice as much optical zoom (equivalent to 800mm), you'd only have 2 Megapixels out of the original 8 Megapixels left.

So, even a 2 Megapixel Camera with an 800mm lens (and I mean a lens with the same angle of view you'd have using an 800MM lens on a 35mm camera) could give you the same number of pixels representing your subject as an 8 Megapixel Camera using a [35mm equivalent) 400mm lens, if you cropped the image from the 8 Megapixel camera so that your subject occupies the same percentage of the frame, if the other characteristics of the cameras are roughly the same (lens quality, noise levels, dynamic range, etc.), which they rarely are.

See this article on Telephoto Figure of Merit for more details:

http://www.digicamhistory.com/Figure%20of%20Merit.html

It sounds like you need to browse through our Digiscoping/Digital Photomicroscopy Forum and get a feel for the cameras that work well with an adapter in combination with a higher powered telescope if you really need a lot of detail at the focal lengths you're asking about.
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Old Jul 22, 2009, 10:19 PM   #16
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Thanks all for answering my query. Appreciated it a lot.

Hi JimC, I read the figure of merit article you provided twice. I was wondering why didn't the author considered crop factor? For example, some camera has smaller sensor size and higher crop factor. Some camera has bigger sensor size and smaller crop factor. Using the formula, SDR-H80 has a FOM of 3133942579200 which is 10X bigger than normal digicam with 10x zoom. However, I feel this may not be a fair comparsion as H80 has more than 20x crop factor.

For example, a full-frame DSLR vs olympus DSLR. A Nikon normal DSLR has 1.5X crop factor while olympus DSLR has 2X crop factor. Why would birders rather pay a lot more for 100mm extra than to get a olympus DSLR?

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Old Jul 23, 2009, 1:51 AM   #17
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Do yourself (and me) a favour, stop referring to crop factor. Find a chart with actual sensor sizes and use that for reference. Crop factor is only a useful concept when you are using lenses that can be mounted on a range of cameras which have different sensor/film sizes. From the way you are using the expression it seems to be causing you confusion.

Bigger sensors capture more actual photons.

If you can get the angle of view you are looking for this is a good thing. More photons mean lower noise and better picture quality.

It is also a bad thing because big sensors need big lenses. No-one does bird photography using medium-format digital backs. The simple reason is that the lenses required to get the small angle-of-view that you need would be incredibly large and unbelievably expensive.

As a general principle you simply cannot crop down a (seemingly large) image with a wider angle of view and maintain good quality. You are much better off using a smaller sensor and a lens designed specifically for that sensor. You can think of this as optical zoom trumps digital zoom. ALWAYS.

Taking pictures of birds with still cameras is a silly and exceedingly expensive game. This is true of wildlife in general. At any given price point, if your interest is primarily in the animals (rather than in photography) then you will do much better with a video camera. Still bird photography requires a great deal of skill, a great deal of luck (and therefore patience), and a great deal of money.

For the specific application of birding:
For $1000 you can only get a very poor set of gear for still photos, but an okay video camera. For $10,000 you can get a good set of gear for still photos, but a very good video camera. For $20,000 you can get an excellent set of gear for still photos and a stupendously good video camera.
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Old Jul 23, 2009, 4:23 AM   #18
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Hi JimC, I read the figure of merit article you provided twice. I was wondering why didn't the author considered crop factor?
It's an older article and was geared primarily towards point and shoot camera models where manufacturers normally give the 35mm equivalent focal length (and I mean the focal length you'd need to use on a 35mm camera to get the same angle of view)

IOW, you'd want to use the 35mm equivalent focal lengths for calculations so that you've got a common measurement between different camera types. The resolution of the sensor, and the angle of view of the lens are the two main variables you're looking at. Those calculations are just geared towards using the 35mm equivalent focal lengths (the focal length you'd need to use on a 35mm camera to get the same angle of view). If you have 10mm lens on a tiny 12MP Sensor that gives you the same angle of view as a 100mm lens on a larger 12MP sensor, you'll still have the same number of pixels representing your subject. ;-) The quality may be a bit different (noise, optics, etc.), but that's not what the calculations are looking at.
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Old Jul 23, 2009, 9:49 AM   #19
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A nice link that talks about this comparison http://www.ophrysphotography.co.uk/p...ameandcrop.htm
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Old Jul 23, 2009, 2:29 PM   #20
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A nice link that talks about this comparison http://www.ophrysphotography.co.uk/p...ameandcrop.htm
Unfortunately that link is full of half-baked data and erroneous conclusions.

1. His conclusions about cropping are half-baked. There are a very wide range of variables which he is not controlling for.
2. His section about DOF is complete rubbish. He clearly doesn't understand the first thing about it.

His photographs are very good however, which just goes to show that you don't have to understand the technical stuff in very great detail in order to take great photographs.
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