Looking for lens with very low f-stop number

[rjseeney]

Originally Posted by dumathecheetah

Hi JohnG,

Thank you and the other posters in this thread--very useful information.

I too am looking for a cheap low f-stop lens to get for my D40x to better achieve the blurred background effect (and to use in low lighting conditions). With respect to your post, I have a few questions: What is a "1.5 crop" camera? Is the D40x a 1.5 crop camera? If so, and if I'll be limited in my ability to take a close-up shot of something (within a few feet of it) with a Nikon 50mm f/1.8D lens, given everything else the same about the camera shot conditions, will having a lens with a lower f-stop limit (e.g., 50mm f/1.4 AF-S lens) be able to compensate for the cropped picture and give me a wider left-right field of view?

I'm sorry if it's unclear what I'm asking. Please let me know if so.

Thank you in advance.

To answer your question, no. A 1.5 crop camera refers to the sensor size, being smaller than the size of film. It is a reference point only to help those familiar with 35 mm cameras to understand how the field of view is affected. When mounted on a DSLR, you have to multiply the focal length by 1.5 to get the effective focal length of the lens. so a 50mm lens on a DSLR has a field of view of and functions like a 75mm on a film camera. Lower f stops do not affect field of view, or close focus distance of a lens. The only way to get a wider field of view is to get a wider lens.