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Misra
01-13-2005, 06:11 AM
I am very new to this stuff, but George very kindly gave me the basics of the crop factor. I have just bought a Nikon D 70 with the following lenses:

(i) Sigma 18-125 f/3.5-5.6
(ii) Nikon 70-300 f/4-5.6 ED
(iii) Nikon 50mm f/1.8

I was also informed that the crop factor for a D 70 is 1.5. Therefore, the Nikon 70-300 lens would, on a non digital film camera become a 105-450.
Is this true? Also, at 300mm the lowest f stop is 5.6. Does this mean that i would get a lowest f stop of 5.6 at 450mm?

And finally, if i were to take a photograph on a normal film camera with a lens zoomed out to 450mm (at 5.6 f stop), would the result be similar to the photograph that i would get with my digital at 300mm (5.6 f stop)?

I am not sure if my question comes out clearly. Sorry :)

TenD
01-13-2005, 07:01 AM
The crop factor comes from the fact that the Sensor in a digital camera is smaller than a frame of 35mm film. This means the digital slr crops out the center portion of a given lenses field of view, but the image is still at the full resolution of the digital sensor. This crop factor gives a lens on a digital SLR a smaller field of view than it would have on a film SLR, giving it the same field of view of a longer lens when compared to a film SLR. So when placed on your DSLR the 50mm has the FOV of a 75mm lens on a film SLR.
Michael Reichmann explains this much better than I can:
http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml

D70FAN
01-13-2005, 01:38 PM
I am very new to this stuff, but George very kindly gave me the basics of the crop factor. I have just bought a Nikon D 70 with the following lenses:

(i) Sigma 18-125 f/3.5-5.6
(ii) Nikon 70-300 f/4-5.6 ED
(iii) Nikon 50mm f/1.8

I was also informed that the crop factor for a D 70 is 1.5. Therefore, the Nikon 70-300 lens would, on a non digital film camera become a 105-450.
Is this true? Also, at 300mm the lowest f stop is 5.6. Does this mean that i would get a lowest f stop of 5.6 at 450mm?

And finally, if i were to take a photograph on a normal film camera with a lens zoomed out to 450mm (at 5.6 f stop), would the result be similar to the photograph that i would get with my digital at 300mm (5.6 f stop)?

I am not sure if my question comes out clearly. Sorry :)

The article pointed to, by TenD (thanks TenD) covers it in detail, but I think you have the idea down pretty well.

Have fun with the new D70.

One additional FYI: When you look at the EXIF information (during editing), the lens will still report the "actual" FL of the lens. So the 70-300 will still be "reported" and recorded as 70-300 (not 105-450).

dwig
01-29-2005, 06:05 AM
...I was also informed that the crop factor for a D 70 is 1.5. Therefore, the Nikon 70-300 lens would, on a non digital film camera become a 105-450.
Is this true? ...

Close but you have the math inverted. The convention is to compare digital-to-film rather then film-to-digital.

To start with, a 70-300mm lens on a standard 35mm film camera is 70-300mm and, on a digital camera, is also 70-300mm, period. The so called "cropping factor" is a way of comparing the fields of view a lens yields when used on cameras with differing "image receptor" sizes with the standard 35mm image size of 24x36mm as the reference standard. dSLR's generally have sensors smaller than this causing the lenses to give greater image magnification when used on dSLRs than when used on standard 35mm film SLRs.

With a dSLR with a cropping factor of 1.5, a 70mm lens yields the same field of view as a 105mm lens on a standard 35mm film camera. This also means that the field of view the user of a 35mm SLR sees with that 70mm lens is the same as you see with a 47mm lens on your dSLR with a 1.5 cropping factor

ktixx
01-30-2005, 10:57 PM
I clicked the link posted above and read the article, however I still have a question that I don't think the article covered. I purchased the Sigma 18-125 DC lens for my Canon 20d. I took a shot with the camera and mentally marked the frame that I saw in my viewfinder, then I looked at the picture on the lcd and it captured everything (or close to everything) that I saw in the view finder. Because it is specifically made for Digital Cameras is the crop factor already accounted for with the DC lenses?
Ken

dwig
01-31-2005, 12:07 AM
I clicked the link posted above and read the article, however I still have a question that I don't think the article covered. I purchased the Sigma 18-125 DC lens for my Canon 20d. I took a shot with the camera and mentally marked the frame that I saw in my viewfinder, then I looked at the picture on the lcd and it captured everything (or close to everything) that I saw in the view finder. Because it is specifically made for Digital Cameras is the crop factor already accounted for with the DC lenses?
Ken

You misunderstand. The crop factor is an attribute of the camera body, not lens, and is a measure of the difference in the field of view that is recorded by the digital camera in question and that of a standard 35mm film camera using a lens of the same focal lenght.

scalia
01-31-2005, 01:56 AM
I clicked the link posted above and read the article, however I still have a question that I don't think the article covered. I purchased the Sigma 18-125 DC lens for my Canon 20d. I took a shot with the camera and mentally marked the frame that I saw in my viewfinder, then I looked at the picture on the lcd and it captured everything (or close to everything) that I saw in the view finder. Because it is specifically made for Digital Cameras is the crop factor already accounted for with the DC lenses?
Ken

Hi Ken,
crop factor has nothing to do with the viewfinder. That's viewfinder coverage you're talking about.

ktixx
01-31-2005, 02:16 PM
You misunderstand. The crop factor is an attribute of the camera body, not lens, and is a measure of the difference in the field of view that is recorded by the digital camera in question and that of a standard 35mm film camera using a lens of the same focal lenght.


Hi Ken,
crop factor has nothing to do with the viewfinder. That's viewfinder coverage you're talking about.

I realize the crop factor is an attribute of the camera body, and I do understand what viewfinder coverage is, I guess I just didn't ask the right question, so let me ask a different one :p.
From what I understand when you put a 35mm lens on a digital camera you run into a problem because the Sensor is too small to capture the entire image, therefore there is a "crop factor" that you account for (IE: a 100 - 300 mm lens has the equivalent of 160 - 480 on the 20D (1.6x factor)) so my question is, when you are looking through a 100mm lens are you seeing the image as if you are looking through a 160mm lens? My second question is, because I have a sigma lens specifically made for digital cameras, has the lens been specially made to fix the problem with the smaller cmos?

D70FAN
01-31-2005, 03:17 PM
I realize the crop factor is an attribute of the camera body, and I do understand what viewfinder coverage is, I guess I just didn't ask the right question, so let me ask a different one :p.
From what I understand when you put a 35mm lens on a digital camera you run into a problem because the Sensor is too small to capture the entire image, therefore there is a "crop factor" that you account for (IE: a 100 - 300 mm lens has the equivalent of 160 - 480 on the 20D (1.6x factor)) so my question is, when you are looking through a 100mm lens are you seeing the image as if you are looking through a 160mm lens? My second question is, because I have a sigma lens specifically made for digital cameras, has the lens been specially made to fix the problem with the smaller cmos?

1. The camera mirror is sized to give you the same crop. So size-wise it is the same as the imaging target. Yes, you see the image at 160mm crop factor TTL.

2. The Sigma DC lenses (and Nikon DX, etc.) are built to fit the image to an APS-C sized sensor, but the lens is just smaller and lighter (theoretically) due to the smaller target coverage (smaller diameter and shorter barrel) and if you use it on a 35mm camera you will get some vignetting because of this. Other than that it is the same as any other 35mm SLR lens. So you still have to add the crop factor.

To summarize: Using the Sigma 18-125 DC as an example:

1. It will cause vignetting when used on a full 35mm film or full-frame 35mm digital camera. AND will show the image uncropped at 18mm-125mm when used with full frame 35mm sensors. All 35mm and dSLR lenses are still Focal Legth (FL) rated based on a 35mm target. Hence the crop factor on all dSLR and SLR lenses.

2. When used on a dSLR with APS-C sized sensor it will not show vignetting (hopefully) and will show the image as if it were a 28.8mm-200mm on Canons 1.6X crop cameras, and 27mm-187.5mm lens on Nikon and other 1.5X crop sensors.

Hope that helps.

ktixx
01-31-2005, 09:56 PM
1. The camera mirror is sized to give you the same crop. So size-wise it is the same as the imaging target. Yes, you see the image at 160mm crop factor TTL.

2. The Sigma DC lenses (and Nikon DX, etc.) are built to fit the image to an APS-C sized sensor, but the lens is just smaller and lighter (theoretically) due to the smaller target coverage (smaller diameter and shorter barrel) and if you use it on a 35mm camera you will get some vignetting because of this. Other than that it is the same as any other 35mm SLR lens. So you still have to add the crop factor.

To summarize: Using the Sigma 18-125 DC as an example:

1. It will cause vignetting when used on a full 35mm film or full-frame 35mm digital camera. AND will show the image uncropped at 18mm-125mm when used with full frame 35mm sensors. All 35mm and dSLR lenses are still Focal Legth (FL) rated based on a 35mm target. Hence the crop factor on all dSLR and SLR lenses.

2. When used on a dSLR with APS-C sized sensor it will not show vignetting (hopefully) and will show the image as if it were a 28.8mm-200mm on Canons 1.6X crop cameras, and 27mm-187.5mm lens on Nikon and other 1.5X crop sensors.

Hope that helps.

Definitely helps, thank you George!