2x zoom lens with same absolute aperture instead of extender ?

MitchAlsup wrote:

But you are not measuring the size of the entrance pupil! You are measuring how much of the lens can be seen through the viewfinder--which needs to be the whole lens (or the manufacture would save money by making the lens smaller.

You can observe the size of the entrance pupil by opening up the aperture all the way and see how much of the view finder you can see from the front of the lens. Hint: its a lot smaller than the size of the objective. The objective is large because it has to fit multiple entrance pupils across its face in order to fully illuminate the off axis portions on the sensor.

That is exactly the objective / entrance pupil diameter. This IS the test to measure the objective diameter. This website tells how to measure the diameter of objective of binoculars. This is valid for telescopes as well and ... cameras. A DSLR woth OVF is just a.... telescope with objective and eyepiece, regardless of how many mirrors, lens elements or baffles are in the light path. Any obstruction will be shown in the projection image on the objective site.

http://www.cloudynights.com/topic/431279-the-flashlight-test-for-aperture-illustrated/

[quote] Not for long lenses. The 300/4L IS for example has a front element which measures 75 mm. The various 200/2.8s (71.4 mm entrance pupil size) are similar. The effect you describe is increasingly true as the lens covers a wider field of view - the EF-S 10-22mm f/3.5-4.5 for example has an entrance pupil of approximately 3 mm (at 10 mm zoom) but it has a 50 mm front element.

[/quote]

This is indeed correct.