Technical Help Please - Crop Factor

Olympus 12-40mm f/2.8 Pro

08/27/2007 08:51:21 PM · #1

I am trying to work out the crop factor of my digital camera. I am learning more about my camera but this has me stumped.... "DLSRs have physically different sized sensors. Sensors smaller than one frame of 35mm film have a mulitplying effect on the focal length of a lens. On a camera with a 1.6 field of view mulitplier, a 100 mm lens would be equivalent to 160mm lens because of a crop factor". I kinda understand about 1/2 of this quote. Could someone explain this to me in laymans terms. My spec's state that my sensor size is 22.5 x 15.0mm. How do I use this infor to work out my crop factor.

Thanks in advance for taking the time to read and help.

slickchik

OM System OM-1

08/27/2007 09:01:33 PM · #2

I believe the Canon DSLRs all have a 1.6 crop factor with the exception of the full frame cameras like the 5D and 1D. So you would have a 1.6 crop factor on your 30D.

Message edited by author 2007-08-27 21:02:07.

cryan

Nikon D700

Sigma 24-70mm f/2.8 EX DG Macro for Nikon

08/27/2007 09:01:53 PM · #3

Just multiply 1.6 to what ever focal length your lens is at the time. This will give you the "crop factor". The term crop factor is a very misleading term. The sensor is actually about the size of what APS film used to be.

Message edited by author 2007-08-27 21:02:26.

08/27/2007 09:25:58 PM · #4

Thanks. How I can figure our the crop factor, what would be the formula? How does 22.5 x 15mm = 1.6?

08/27/2007 09:33:10 PM · #5

Also, is crop factor only used to work out minimum shutter speeds for handheld shots? Eg. Shoot with lens at full zoom of 80mm. 80x1.6=128 so minimum shutter speed for a handheld shot would be the closest to 128, being 1/125?

Message edited by author 2007-08-27 22:21:56.

Canon EF 70-300mm f/4.5-5.6 DO IS USM

08/27/2007 10:20:50 PM · #6

Bump

Message edited by author 2007-08-27 22:30:41.

cpanaioti

Canon EOS-40D

08/27/2007 10:27:03 PM · #7

The 1.6 refers to how the sensor size relates to 35mm film.

Full Frame means the sensor is the same size as 35mm film.

Message edited by author 2007-08-27 22:27:48.

Atropos

Nikon D40

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6 ED

08/27/2007 10:28:50 PM · #8

Nope. It has nothing to do with the shutter speed. The focal length is like the zoom power of the lens. For instance, 350mm would be a 10x zoom on a 35mm camera, or 17mm would be roughly 0.5x zoom (a nice wide angle).

Canon EF 70-300mm f/4.5-5.6 DO IS USM

08/27/2007 10:32:05 PM · #9

Originally posted by cpanaioti:

The 1.6 refers to how the sensor size relates to 35mm film.

Full Frame means the sensor is the same size as 35mm film.

So does this mean at 1.6 it is larger than 35mm or that 35mm is 1.6 larger than my camera.

cpanaioti

Canon EOS-40D

08/27/2007 10:33:42 PM · #10

Originally posted by Monique64:

Originally posted by cpanaioti:
The 1.6 refers to how the sensor size relates to 35mm film.

Full Frame means the sensor is the same size as 35mm film.

So does this mean at 1.6 it is larger than 35mm or that 35mm is 1.6 larger than my camera.

35mm is 1.6 times larger than the sensor on the 30D.

scalvert

Canon EOS-5D Mark III

Canon EF 24-105mm f/4.0L IS

08/27/2007 10:39:08 PM · #11

Originally posted by Monique64:

Thanks. How I can figure our the crop factor, what would be the formula? How does 22.5 x 15mm = 1.6?

This is easier to figure out if you understand the REASON for the crop factor...

In a traditional film camera, the lens exposes a circular image area (cropped into a rectangle) on a 35mm film negative, which must be enlarged to make a 4x6" print. The sensor in your 30D is smaller than 35mm film, so the lens is exposing a much smaller rectangle within that circular image area. Much more is "cropped" out, and the smaller image has to be enlarged 1.6X more to make the same 4x6" print. The extra magnification required to produce the same size print has essentially the same effect as using a lens 1.6X longer.

So... if you just pretend that every lens is 1.6X longer, you can calculate minimum shutter speeds the same way you would for a film camera. Hope that helps.

cpanaioti

Canon EOS-40D

Canon EF 70-300mm f/4.5-5.6 DO IS USM

08/27/2007 10:39:17 PM · #12

edit to remove film size - numbers didn't look right

Message edited by author 2007-08-27 22:42:35.

jdannels

Nikon D300s

Sigma 30mm f/1.4 EX DC HSM for Nikon

08/27/2007 10:42:12 PM · #13

Originally posted by Monique64:

You are right it is used for this also. :) Many photographers used 35 mm for so long they wanted to know what was equivalent in terms of perspective on a digital camera. For example on a 35 mm camera lets say you were used to using a 50 mm lens. If you wanted that same field of view on your 30D to get the same perspective you would have to use the crop factor to find an equivalent match focal length. So you would divide 50 mm/1.6=31.8 mm. This means if you had a 31.8 mm focal length lens it would show you what a 50 mm lens would on a 35 mm camera.

From digital SLR to 35 mm SLR conversion
(digital focal length)*1.6=(35 mm focal length)

From 35 mm camera SLR to digital SLR conversion
(35 mm focal length)/1.6=(digital focal length)

Hope this helps

Message edited by author 2007-08-27 22:43:15.

scalvert

Canon EOS-5D Mark III

Canon EF 24-105mm f/4.0L IS

08/27/2007 10:46:17 PM · #14

Originally posted by Atropos:

Not quite. A 50mm lens on a full frame camera requires about a 1/50 shutter speed to be "safe." The same lens on a 30D would effectively magnify everything (including shake) like an 80mm lens. Thus, you'd want a 1/80 shutter speed to be safe.

Also, I'm pretty sure zoom ratios are just that: ratios... and not always compared to 35mm. A 28-112mm lens is 4x, but so is a 36x144mm lens.

Atropos

Nikon D40

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6 ED

08/27/2007 10:46:19 PM · #15

I didn't know of that technique, I feel pretty dumb now. I usually just up my ISO if I can't get a good handheld shot, never knew there was a formula for estimating what shutter speed you should use dependant on your focal length.