The Difference Between a Camera Phone Lens and a Traditional SLR Camera Lens

One of the readers of this blog asked a question of how come a camera phone lens is much smaller then a traditional camera. 

So I decided to post this question to Dr. Mustafa Abushagur who is the Director Microsystems Engineering at RIT.  He has been working in the field of optics for 25yrs and is a  Fellow of OSA and SPIE.  So here is what he had to say about this question:

The aperture size and focal length of the lens plays a role in the quality of the image to be captured. Camera lenses are usually identified by their f/number (f/#). The f/# is defined as the ratio of the focal length to the diameter of the aperture. In single-lens reflex (SLR) camera the aperture size (entrance pupil) can be adjusted to change the f/number providing more flexibility to the photographer in capturing the image. Changing the f/number controls the amount of light falling on the imager and allows for creating the proper lighting condition. Changing the f/# also changes the depth of the field (the range at which the image will be focused on the imager). The smaller the f/number the larger range of depth of field. The f/# for SLR lenses ranges from f/1 to f/128 or larger. The smaller the f/#, the faster the lens and the more expensive it will be. Smaller f/# requires extensive corrections for the aberration (deviation from sharp image). Good quality images vary with f/number of the lens. It is found that f/numbers between f/5.6 and f/8 gives best quality images for most typical applications. Cell phone cameras have a fixed f/number which limits the imaging conditions that will be available to the photographer. This affects the lighting condition and ultimately the quality of the images taken by cell phone cameras. Cell phone cameras by their compact nature have very small aperture stops and focal lengths. Also their aperture stop is fixed. As an example Nokia 6600 cell phone has a camera with 3.5 mm focal length and f/2.8 which results in an aperture with 1.25 mm diameter. This f/number does not give large depth of field so only few subject will be sharp in the image. This is very clear in the image shown here.

I would like to thank Dr. Abushagur for taking the time to answer this question.  Some thing I wanted to note about the image he included here on the left is about its depth of field.  If you notice some of the flowers are in focus and others are out of focus.  This is a great example of depth of field and how in current camera phones it is limited and creates images similar to this.  In future posts I will cover more on this topic.

Comments

[geographer47]

The 640x480 image is decent for a snapshot. It definitely shows the depth of field limitations, but there is only so much focal length after all.

[Babu]

Hi, I would like to hear your expert opinion about Omnivision's proposed Wavefront Coding camera lenses. Have you heard anything about this and do you think it will work for camera phones? What are the benefits and drawbacks?

Thank you very much.

[Alex]

Nice article. Even such photo dummy like me understood the idea!