Focal Length question

I'm not sure if this will be worded correctly so bear with me.

Let's say you have a picture taken at 100 mm. Is there a chart or guide saying what % crop is needed for that picture to look like it was taken at 400 mm or 500 mm? Baiscally, if this same picture was taken at 400 mm, how much more "zoomed in" will it look.

I know with a large crop the quality won't be comparable but I'm not concerned about that. I just want to know what length is needed.

It will scale linearly. That is, the ratio of the longer lens to you lens is the percentage of the frame to reduce. For instance, if you have a photo shot with a 100 mm lens, a 300 mm lens is 3 x narrower in angle of view. So, 33% of the frame, horizontally and vertically, is what a 300 mm lens will show. As you can tell, the difference betwen 100mm and 200mm is much bigger than the difference between 400mm and 500mm.

Exactly what I needed to know. Thanks

edit

http://www.juzaphoto.c​om …al_length_compa​risons.htm

Juza has this technique that I find very usefull... maybe it can help you

Alex_Venom wrote in post #9498019
http://www.juzaphoto.c​om …al_length_compa​risons.htm

Juza has this technique that I find very usefull... maybe it can help you

Cool. Thanks

Someone correct me if I am wrong but I think that the relation between FL and size of the frame is not linear. I think it is exponential, because you are talking about the area of the frame. That is why to cut in half the area of a frame you use a 1.4x teleconverter (square root of 2) and if you want to cut it in 4 you use a 2xTC. That also explains why you cut the aperture by exactly one stop using a 1.4 TC, because you are getting half of the frame area or in other words half of the light.
If we start with 100mm + 1.4TC = 140mm ; 100mm + 2TC = 200mm. That is not linear but exponential. That also explains why the difference between 10mm and 20mm (only 10mm) is huge, but the difference between 400mm and 500mm (100mm!!) is not so noticeable.

^^ you would be correct if I phrased my response talking about area, but I didn't...I talked about linear dimensions, which do scale linearly. (half the frame size in each direction = 1/4 the area)

I was curious about how the FL relation really is so I decided to actually measure how wide the field of view was at different focal lengths. I used a measure tape and took pictures at 25, 50, 100, 200 and 300mm. These measurements are not exact but are pretty close. The result is a curve and not a line.
X axis is focal length in mm, Y axis is actual measurement of the FOV in mm.

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http://www.tawbaware.c​om/maxlyons/calc.htm

Perhaps something like this may also help.

juanpafer wrote in post #9499499
IX axis is focal length in mm, Y axis is actual measurement of the FOV in mm.

What distance from the target was the camera?

The advertised focal length of most lenses these days is only accurate (and then only to about ±5%) when the lens is focused at infinity. If you were close in, that could drastically skew the chart.

The camera was about 12 ft away from the target.

From Canon's specs: Angle of View:

50mm f/1.4: 46 degrees (actual focal length 52mm)
100mm f/2: 24 degrees
200mm f/2.8: 12 degrees
400mm f/5.6: 6 degrees

There might be very small variations in the AOV due to small variations in the actual focal length vs the stated focal length, but the relation of AOV is directly inversely proportional to focal length (which I really should have said in my first response.)

There will be variations based on the distance of the subject in actual subject captured, but it's still pretty linear
At 12 feet distance, a
50mm lens will capture 5.34 feet diagonally.
A 100mm lens will capture 2.55 feet diagonally (1/2.09...not QUITE 1/2, but close)
A 200mm lens will capture 1.26 feet diagonally (1/2.02. from the 100mm...darn close to what it should be)
A 400mm lens will capture 0.63 feet diagonally (Exactly 1/2 of the linear dimension of the 200mm lens)

juanpafer wrote in post #9499499
I was curious about how the FL relation really is so I decided to actually measure how wide the field of view was at different focal lengths. I used a measure tape and took pictures at 25, 50, 100, 200 and 300mm. These measurements are not exact but are pretty close. The result is a curve and not a line.

And a good thing too, since the relationship is not linear!
When you double the FL, you halve the linear FoV, etc.
Here's the graph you want:

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Jman13 wrote in post #9500828
From Canon's specs: Angle of View:

50mm f/1.4: 46 degrees (actual focal length 52mm)
100mm f/2: 24 degrees
200mm f/2.8: 12 degrees
400mm f/5.6: 6 degrees

There might be very small variations in the AOV due to small variations in the actual focal length vs the stated focal length, but the relation of AOV is directly inversely proportional to focal length.

There will be variations based on the distance of the subject in actual subject captured, but it's still pretty linear
At 12 feet distance, a
50mm lens will capture 5.34 feet diagonally.
A 100mm lens will capture 2.55 feet diagonally (1/2.09...not QUITE 1/2, but close)
A 200mm lens will capture 1.26 feet diagonally (1/2.02. from the 100mm...darn close to what it should be)
A 400mm lens will capture 0.63 feet diagonally (Exactly 1/2 of the linear dimension of the 200mm lens)

The change in angle is linear, but would the % of frame be linear (... looking for my protractor)?