Effect of Filter Diameter

[mcraige]

When chosing between two lenses, should you consider the filter diameter? I'm looking at 2 lenses, both 50mm F1/4, but one has a filter diameter of 55mm and the other has a filter diameter of 77mm. Common sense says the one with a 77mm diameter should allow more light in. Am I completely wrong here?

 

[HPS3]

Filter size doesn't affect the amount of light getting to the sensor. F1.4 is f1.4.

 

[photo_chick]

Yes, a wider diameter lens lets more light into the barrel, but the amount of light getting to the sensor is determined by the diameter of the aperture. The physical size of the aperture is determined by dividing the focal length by the f stop number (ex. 50/1.4 = 35.71mm) and has nothing to do with the diameter of the elements. The larger diameter lens element comes into play in other areas, like sharpness. For example a larger diameter lens could project a larger image which would mean less vignetting issues and fewer problems with corner softness. The element diameter can also affect how a lens flares. That doesn't necessarily mean the larger diameter element is better though.

 

[HPS3]

Danielle, very well put!

 

[mcraige]

Thank you very much for the replies. This cleared up the confusion I had.