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Magnification, sensor size and crop factor 25 Disember 2009

Posted by azmirul in Astrophotography, Photography.
Tags: , , , ,

setelah study dibuat, akhirnya berjaya juga aku memahami secara “kasar” macamner nak calculate magnification power bila guna webcam/camera bersama telescope. rupa2nya semuanya amat bergantung kpd sensor size yg akan menentukan crop factor dgn perbandingan dibuat berdasarkan format film 35mm.. patutler field of view (FOV) bila guna webcam semakin kecil berbanding bila guna DSLR.. ini disebabkan sensor webcam yg amat kecil iaitu dlm 4mm diagonal (utk SPC900NC) berbanding DSLR iaitu 26.7mm diagonal (EOS 350D).  So, utk full frame sensor yg hampir sama dgn standard film 35mm (43.3mm diagonal) akan memberikan FOV yg lebih besar. So, ada kemungkinan wide-angle lens utk 35mm camera menjadi normal lens utk DSLR camera!

Berikut adalah beberapa calculation yg aku buat.. ni berdasarkan apa yg fahamler.. kalo tak tepatpun, aku raser masih bleh digunakan utk buat perbandingan.

Magnifaction of Telescope Apex 90mm with Philips SPC900NC Webcam:

  • crop factor for Philips SPC900NC is 10.8
    ( 35mm diagonal/sensor diagonal = 43.3/4 = 10.8 )
  • 35mm equivalent telescope focal length when using spc900nc
    ( 1250mm focal length * 10.8 = 13500mm )
  • magnification calculation (divide by 50mm) is 270x
    ( 13500mm/50mm = 270x  )

Magnifaction of Telescope Apex 90mm with DSLR Canon EOS 350D:

  • crop factor for Canon APS-C sensor is 1.6
    ( 43.3/26.7 = 1.6 )
  • 35mm equivalent telescope focal length when using Canon EOS 350D
    ( 1250mm focal length * 1.6 = 2000mm )
  • magnification calculation (divide by 50mm) is 40x
    ( 2000mm/50mm = 40x )

Common crop factor:

  • 35mm film = Diagonal (43.3mm) = 36 x 24 mm ( Crop factor 1 ), 3:2 aspect ratio
  • DSLR with Canon APS-C sensor = Diagonal (26.7) = 22.2 x 14.8 mm ( Crop factor 1.6), 3:2 aspect ratio
    eg crop factor calculation = 43.3/26.7 = 1.6
  • Typical compact digital camera = 1/2.5″= 5.76 x 4.29 mm ( Crop factor 6.02 ), 4:3 aspect ratio
  • Common camera phone/ webcams/ digital camcorders = 1/6″ = 2.40 x 1.80 mm ( Crop factor 14.14 )
  • SPC900NC webcam = 35mm diagonal/webcam sensor diagonal = 43.3/4 ( Crop factor 10.8)



In digital photography, the image sensor format is the shape and size of the image sensor.In particular, image sensors in digital SLR cameras tend to be smaller than the 24 mm x 36 mm image area of full-frame 35 mm cameras, and therefore lead to a more narrow angle of view.

Lenses produced for 35 mm film cameras may mount well on the digital bodies, but the larger image circle of the 35 mm system lens allows unwanted light into the camera body, and the smaller size of the image sensor compared to 35 mm format results in cropping of the image compared to the results produced on the film camera. This latter effect is known as field-of-view crop; the format size ratio is known as the crop factor or focal-length multiplier.

Because of their larger sensors, DSLRs can generally take high-quality pictures at ISO 1600, 3200, or even higher speeds, while compact cameras tend to produce grainy images even at ISO 400.

As of June 2009, most consumer-level SLRs use sensors around the size of a frame of APS-C film, with a crop factor of 1.5-1.6. A notable exception is the Four Thirds System of cameras, mostly made by Olympus, which use smaller sensors with a crop factor of 2.0. Some professional DSLRs use full-frame sensors, equal to the size of a frame of 35 mm film. Many different terms are used in marketing and describing these sensor formats, including the following:
-Full-frame digital SLR format, with sensor dimensions nearly equal to those of 35 mm film (36 × 24 mm)
-Canon’s APS-H format for high-speed pro-level DSLRs (crop factor 1.3)
-APS-C refers to a range of similarly-sized formats, including
-Nikon DX format, Pentax, Konica Minolta/Sony a, Fuji (crop factor 1.5)
-Canon entry-level DSLR formats (crop factor 1.6)
-Four Thirds System format (crop factor 2.0)

Most DSLR image sensor formats approximate the 3:2 aspect ratio of 35 mm film. Again, the Four Thirds System is a notable exception, with an aspect ratio of 4:3 as seen in most compact digital cameras (see below).

The most common sensor size for medium-format digital cameras is approximately 36 × 48 mm, due to the widespread use of Kodak’s 22-megapixel KAF-22000 and 39-megapixel KAF-39000 CCDs in that format.

As of December 2007, most compact digital cameras use 1/2.5″ size sensors.

Sensor sizes of around 1/6″ are common in camera phones, as well as in webcams and digital camcorders.


In photography, the 35 mm equivalent focal length is a measure that indicates the angle of view of a particular combination of a camera lens and film or sensor size. The term originates from the time when the vast majority of photography was done with 35 mm film.

Most commonly, the 35 mm equivalent focal length refers to the diagonal angle of view.

On any 35 mm film camera, a 28 mm lens is a wide-angle lens, and a 200 mm lens is a telephoto lens. However, now that digital cameras have mostly replaced 35 mm cameras, there is no direct relation between the focal length of a lens and the angle of view, since the size of the camera sensor also determines angle of view, and sensor size is not standardized like film size was.


In digital photography, a crop factor is related to the ratio of the dimensions of a camera’s imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a standard. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame’s diagonal (43.3 mm) to the diagonal of the image sensor in question; that is, CF=diag35mm / diagsensor. Given the same 3:2 aspect ratio as 35mm’s 36mm x 24mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the square of the crop factor.

This ratio is also commonly referred to as a focal length multiplier (“FLM”) since multiplying a lens focal length by the crop factor or FLM gives the focal length of a lens that would yield the same field of view if used on the reference format.

Using an FLM of 1.5, for example, a photographer might say that a 50 mm lens on his DSLR “acts like” its focal length has been multiplied by 1.5, by which he means that it has the same field of view as a 75 mm lens on the film camera that he is more familiar with.

Because of this crop, the effective field of view (FOV) is reduced by a factor proportional to the ratio between the smaller sensor size and the 35 mm film format (reference) size.

This narrowing of the FOV is a disadvantage to photographers when a wide FOV is desired.

Smaller, non-DSLR, consumer cameras, typically referred to as point-and-shoot cameras, can also be characterized as having a crop factor or FLM relative to 35 mm format, even though they do not use interchangeable lenses or lenses designed for a different format. For example, the so-called “1/1.8-inch” format with a 9 mm sensor diagonal has a crop factor of almost 5 relative to the 43.3 mm diagonal of 35 mm film.

For example, the Canon Powershot SD600 lens is labeled with its actual focal length range of 5.8–17.4 mm. But it is sometimes described in reviews as a 35–105 mm lens, since it has a crop factor of about 6 (“1/2.5-inch” format).


The SPC900NC uses the same Sony ICX098QB CCD sensor as the Toucam Pro’s with a pixel size of 5.6 x 5.6 microns (=0.0056mm), which allows a high resolution (320×240 Pixels non interpolated). This table shows the chip is a 1/4″ Type which has 659 pixels horizontal x 494 pixels vertical, in a 14-pin Plastic DIP package with a CXD2450R Combined timing pulse generator, and a primary colour mosaic filter mounted.



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