AboutDavid Barry Expertise I have a lot of experience in most traditional forms of photography, so I`m quite knowledgeable about things like camera types and formats, techniques, exposure, film types, colour, filters, lighting, standard colour and black and white developing and printing.
I do not make recommendations about brands or models, and I am not a camera technician so I may not be able to tell you what is wrong with your equipment if it`s not working .
I also know a little about digital photography and imaging with scanners and digital cameras, so ask me and I will answer if I can.
Experience Experience in the area
I have been seriously involved in photography for over 25 years, including about 4 years as a professional, as well as 2 years providing administrative service to government photographers, requiring interpreting photographers' requirements and trade technicalities for those unfamiliar with such.
I have successfully trained several beginners in photography, helping them to become competent in basic techniques.
Organizations belong to:
None at present, but have been in about 4 camera clubs, having won or had placings in 2 club competitions.
Publications:
A lot of my photos have been in educational / training manuals, books and some photography magazines, as well as 2-3 dozen images been on the Web so far.
Education/Credentials:
Completed 4-year diploma in professional photography technique at Sydney's Technical College
Awards and Honors:
3 placings and / or merits in camera club competitions.
Expert: David Barry Date: 9/8/2007 Subject: lens brightness
Question I understand that the 'f' rating for a lens specifies how "bright" it is and, therefore, how well it is likely to autofocus dependign on the lighting conditions (i.e. an f2.8 lens is "brighter" than an f4 lens and so is better suited to working in lower light levels).
My questio is, does lens diameter (i.e. filter thread size) have any influence on lens "brightness"? Is an f4 lens with a 77mm diameter "brighter" than an f4 lens with a 58mm diameter?
Thanks in advance
Answer No, the physical outside diameter of the overall lens does not necessarily influence the 'brightness' as you call it.
It is the diameter of the aperture inside the lens, relative to its distance from the film/sensor, which governs the brightness.
The 'f' rating (as you call it) is a ratio of the aperture diameter to the distance from aperture to film / sensor.
So f4 aperture means the diameter of the aperture is a quarter of the distance from aperture to film / sensor
