That's the whole point of the "f/" numbering system. It means that the effective diameter of the entrance pupil is directly related to the focal length..
A 400mm lens at f/8 has a 50mm effective entrance pupil diameter. At 32mm lens at f/8 has a 4mm effective entrance pupil diameter. The shorter focal length gathers more light at the same entrance pupil size, but the effective entrance pupil is smaller. Hence, the same amount of light gets through at the same f-number..
(The exact amount of light that gets through varies slightly depending on lens construction and such, but the variance is so small that it is universally ignored for still photography.).
So yes, the same shutter speed applies at a given f-number (and ISO exposure index) regardless of focal length...
In addition to the light available, you also need to check the impact of focal lenth on shake when you finally want to select shutter speed. The longer the lens, the higher the chance for a blurred pic.http://budding-nature-photographer.blogspot.com/..
As Doug indicated, the beauty of measuring aperture with f-stops is that, because they incorporate focal length, they're consistent. If you consider the "sunny f/16 rule" for instance, it works because f/16 exposes your sensor to the same amount of light regardless of the focal length of the lens..
On any given lens, an aperture of f/4 (for example) means an opening whose diameter is the focal length of the lens divided by 4..
- DennisGallery at http://kingofthebeasts.smugmug.com..
Light travels so fast, that any difference, in distance, between the sensor-film and subject is negated..
Remember, photography is light. How much, what temperature, what direction, how harsh, etc..
Dave PattersonMidwestshutterbug.com'When the light and composition are strong, nobodynotices things like resolution or pincushion distortion'Gary Friedman..
Irrespective of Focul length particular "f stop" permits same lights....
Example : 35mm f8, 50mm f8 and 85mm f8 allows same light at any instance....
But shutter speed controls the quantity/amount...http://www.flickr.com/photos/9734068@N05/sets++++++++++++++++++++++++++++++++++++++++D50 - 18-70 - 70-300 VR - 50/1.8 - 80/1.8 - 90/2.8 MacroSB-800 - Filters - Tripod - Monopod - CS2 - Cam Bags++++++++++++++++++++++++++++++++++++++++..