This is a fairly rough presentation that I am working on the explain to my 2nd year students the differences.

1. AKA…the DX Crop Factor
Dx vs. Fx
in terms of 35mm film
DSLR Chip Size

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Photo by Drew Loker

3. 35mm Film sets the standard
• 35mm film measure 35mm x
24mm
• When the first Digital SLRs came
out, they had the form factor of
the film cameras, but the sensor
size was half the size of a film
negative…resulting in a change in
the field of view.

4. 35mm was NOT perfect
• 35mm film measure 35mm x
24mm which is approximately a
2:3 aspect ratio
• This mean that what you see is
NOT what you will get EXCEPT
for 4x6s.
– 2:3 = 4x6 20x30 (or .66 factor)
– 2.5:3.5 5x7 = (.71 factor)
– 3:4 = 6x8 (or .75 factor)
– 4:5 = 8x10, 16x20 (.8 factor)

5. Sensor Sizes: 35mm vs. APC vs. P&S

6. Lens Focal Lengths
• A stated lens focal length was
based on the size of the image
area.
• So, a 50mm lens (the yellow
circle) on a 35mm negative
(blue box) was designed to
cover the entire negative.

7. Lens Focal Lengths, cont.
• But the same 50mm lens was
MUCH larger than the DX
sized sensors. So, what the
user saw (I.e. field of view)
was similar to that of a longer
lens, specifically, a 75mm
lens.

8. Lens Focal Lengths, cont.
• Then lens manufactures “got
smart” and designed a lens
with an opening just big
enough to cover the size of
the sensor…thus the DX lens
was born.

9. Lens Focal Lengths, cont.
• The only problem is if you try
to use a DX lens on a full
sized sensor.
• You literally get a circle from
the heavy vignetting of the
lens on to your image.

10. FOV Crop – A benefit?
• This resulting 1.5x crop factor is
perceived by most as a benefit…if
you are wanting to shoot LONG…
and a disadvantage if you are
wanting to shoot wide.
• 70-200mm lens has an effective
FOV as a 105-300mm. 300mm is
good for sports and wildlife.
• 18-55mm is actually a 27mm-
82mm…so not really a wide angle
lens.
• 10-20mm lens is actually a 15-30.

11. Camera Companies Release FX
• In the last couple of years, both Nikon and Canon
have released professional level full sized sensors.
(ok…Canon was first). But the consumer cameras
have YET to see a full size camera resulting in
even more confusion to the focal length Field of
Fiew Crop.
• Some lens are designed only for DX sized
sensors…other lenses will work on both.
• The smaller sized lens is good for portability…but
bad if you ever upgrade to a different camera.

12. Not all cameras have the same
FOV Crop Factor
• Crop factor simply means you take the
stated focal length and multiply it times the
factor number. I.e. FL x 1.5 = effective
FOV.
• Nikon has been consistent with all of it’s
APC sized bodies with a crop factor of 1.5
• Other camera manufactures have produced:
1.7, 1.6, 1.3, etc.

13. Popular Nikon
DX lenses vs. FX lenses
• 18-200 = 27-300
• 18-55 = 27-82
• 12-24 = 18-36
• 28-105
• 24-120
• 24-70
• 14-24
• 300
• The above lenses will not work
on a FX body.
• If the above lenses are used on
a DX body, then the FL has to
be multiplied by 1.5
* Note: There are other lens manufactures with even more focal length…and some of those are designed
to work with both FX and DX…or just DX. Generally, DX lenses are smaller and less expensive.

15. Comparison of Cameras
FX = Full Frame
35mm Equivalent DX = APS
Nikon D40
Pentax ist
Canon Rebel xti
Nikon D3
Canon Mark Id3
P&S = APC
Canon A85
Canon 570
Nikon
Coolpix
Just about
all pocket
P&S
cameras
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