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Crop Factor

Carny

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I understand crop factor (I think anyways), but I see it referred to so often I start second guessing myself. The confusion comes when people talk about gaining 1.6x extra reach on their lenses. If I take a picture of a bird using my 800mm lens on my 1Dx and 7D, isn't the bird the same size in each shot? It just fills more of the frame on the 7D, right?

So, here is what confuses me. I have these two shots. If I crop the one from the 1Dx to match the 7D will the image not be as good as the one shot straight from the 7D? Or is it because after cropping you have to stretch what's left to get back to the full size, and have done a digital zoom sort of thing.

I just don't get how and image from the 5Dii cropped to match a 7D pic wouldn't still have better IQ.

Hopefully someone will understand what I'm getting at and explain it to me or repost it in a way that others can understand and respond, lol
 
One thing that would probably help would be two shots taken the same way with the same lens on a ff and crop body. I looked but can't find that.
 
If you consider sizes in mm (or inches), yes, projected on the two sensor will be the same size. But here we have pixels sizes, so "it just fills more on the frame" means that is larger -in pixels-, unless the larger sensor has 1.6x more pixels (linear), which typically is not.
7D has 18MP. If you have a full frame camera with 18•1.6•1.6=46MP, then when cropping you obtain the very same result. 1Dx has 18MP (so, physical pixels are much larger!), so by cropping you end up with much less pixels.
However, image quality is not only resolution: those less pixels will have much less noise than 7D pixels, so from that point of view IQ will be still better. If you need the same reach, you use a longer focal length, which will give you same resolution, less noise.
 
Think about it as loosing field of view instead of gaining focal length. You don't really gain extra zoom power, you simply lose some of your field of view, which mimics a greater focal length. Take a 4x6 note card. Draw a picture that takes up the entire card. Now put a 3x5 note card in the center of that picture, trace the edges onto your 4x6 and then cute the area around the square off. Now hold the picture a little closer to your face. That's basically how it works. When you view the images on your computer it'll usually automaticaly adjust them to a size to fit your screen.

The 4x6 before it was cut was your the picture on your full frame body, the post-op 4x6, now a 3x5 is the picture on a cropped sensor. The picture is smaller due to a smaller sensor, but it essentially just cut the edges off. To answer your question about the 7d vs the 5D Mk II... the picture taken with the 5D cropped down exactly to the 7D size will be essentially the same with very minimum difference in DOF, and some added dynamic range. The larger sensor allows the higher dynamic range. That, added with the benifit of a "true" field of view (based on 35mm film focal lengths) gives you some of the advantages of a full frame body.
 
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Both motor have difference crop factors:

1dx - 1.3 crop factor
7d - 1.5 crop factor.

Use the crop factor and multiply it by the focal length:

1.3 x 800 = 1040 mm
1.5 x 800 = 1200 mm

This is what the focal length of your lens will behave like with these cameras.

On the 5dii there is no crop factor so 800 = 800mm
 
It's a Nikon FX/DX illustration but it still shows what is going on with 'crop factor'. FX is a full size image sensor and DX is an APS-C (crop) size image sensor:

FxDx.png
 
Both motor have difference crop factors:

1dx - 1.3 crop factor
7d - 1.5 crop factor.

Use the crop factor and multiply it by the focal length:

1.3 x 800 = 1040 mm
1.5 x 800 = 1200 mm

This is what the focal length of your lens will behave like with these cameras.

On the 5dii there is no crop factor so 800 = 800mm

You should research your info sometime. Because the 1Dx is full frame.

1D cameras are 1.3x, 1Ds cameras are full frame, and the new unreleased 1Dx is full frame.
 
"Crop factor" is simply a way of thinking about a camera's "format" as compared to a 35mm film camera.

Film cameras are classified by film size... 35mm, 6x6cm, 4x5in and so on. This classification is referred to as "format."

35mm film cameras had become the standard in most households, both for point-and-shoots and the more advanced rangefinder and SLR cameras.

Digital cameras are similar in size to 35mm film cameras, but do not all have the same format. Those that DO have the same format are considered "full frame" cameras. Those digital cameras with a format smaller than a 35mm film camera are considered "crop frame" cameras because they have a sensor size smaller than a 35mm negative or slide.

The larger the camera format, the longer the lens focal length necessary to obtain what approximates the "normal" view of the human eye. This focal length is referred to as a "normal" lens. In other words, the focal length of a normal lens is determined by the camera format; what's normal for one will not be for another.

Since digital formats are commonly compared to the 35mm film format, a crop factor (a simple equation: focal length x n = effective focal length) may be employed to communicate the difference.

I hope this is helpful.

-Pete
 
Both motor have difference crop factors:

1dx - 1.3 crop factor
7d - 1.5 crop factor.

Use the crop factor and multiply it by the focal length:

1.3 x 800 = 1040 mm
1.5 x 800 = 1200 mm

This is what the focal length of your lens will behave like with these cameras.

On the 5dii there is no crop factor so 800 = 800mm

You should research your info sometime. Because the 1Dx is full frame.

1D cameras are 1.3x, 1Ds cameras are full frame, and the new unreleased 1Dx is full frame.

I googled it and that is what popped up. Maybe it said 1d and i misread.
 
It's a Nikon FX/DX illustration but it still shows what is going on with 'crop factor'. FX is a full size image sensor and DX is an APS-C (crop) size image sensor:

FxDx.png

I understand this part of it. I don't see why you get extra "reach". This example shows that clearly. The center portion isn't magnified any more, it just doesn't have the extra around it and fills the frame better.

If you took that portion and blew it up to be the same size as the ff image, then it would be bigger. But is that really better than doing the same thing in reverse? You could crop the ff image and end up with the same result, couldn't you?

It just kind of seems like you really aren't gaining anything unless you are wanting to make big prints, then I could see where it would come into effect. Having to do with the total number of pixels.
 
"I googled it and that is what popped up."

Google results are not necessarily correct answers. Anybody can say anything they want anytime anywhere on the net. If its said enough times or accessed enough times then Google will put that near the top of the page, but that does not equate to accuracy.

As in anything, evaluate the source of your information before accepting it as fact.
 
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(Rant start) The first digital camera came into being around 1975 or so (Kodak) and this discussion about crop factor has been going on since about a day and half later. There is lots and lots of information about this all over the place, this forum included. (Rant over)
 
You could crop the ff image and end up with the same result, couldn't you?

Yup. Thus the term "crop frame camera." And you do understand correctly about the loss in size, requiring a greater degree of enlargement to produce the same size print.

What IS different is "angle of view" when using the same length lens on the two different format cameras and filling the frame with the same subject. For example: If you photograph a car, bumper to bumper, with a 50mm lens on a "full frame" camera, and then make the same photo, bumper to bumper, with a 50mm lens on a "crop frame" camera, you'd realize a greater distance from the car would be necessary, changing the angel of view. The 50mm is considered "normal" on the full frame camera, but it is a slight telephoto on the crop frame camera because it's a different format.

Does this make sense?

-Pete
 
(Rant start) There is lots and lots of information about this all over the place, this forum included. (Rant over)

"I googled it and that is what popped up."

Google results are not necessarily correct answers. Anybody can say anything they want anytime anywhere on the net. If its said enough times or accessed enough times then Google will put that near the top of the page, but that does not equate to accuracy.

As in anything, evaluate the source of your information before accepting it as fact.

So, you go on a rant about a thread no one forced you to read, reply even though you are sick of the subject and state there is tons of information about it all over the internet, immediately after you discredit info on the net. I think you may have just got some sort of forum triple double or something, lol.
 

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