A standard light loss test for 35mm adapters?

[snodart]

Is there such a thing?

This post from DVinfo seems to make some sense, but the test would not take into account the difference in light loss between various 35mm lenses (not to mention the different aperture size at various f/stops for different focal length lenses).

1.Take a white piece of paper. Fix it on the wall
2. Light it evenly from one or two fixed points. Use a strong light
3. Install your 35mm adapter.
3. Using a tripod, move the camera until the piece of paper fills the frame, then stop.
4. Set the zebra of your camera to, say, 80% IRE
5. Use the longest exposure time available 1/50th or 1/25th second
6. Open the 35mm objective to full open.
7. If your light is strong enough, the frame should be filled with zebra patterns.
8. Close slowly the iris of the camera until the zebra pattern disappears totally.
9. Note the f-stop.
10. Take off the 35 mm adapter e.g. Letus 35
11. Using roughly the same focal length angle of view as your 35 mm adapter objective, move the camera until the piece of paper fills the frame.
12. Close the iris until the zebra pattern disappears from the frame.
13. Note the f-stop value of the camera iris.
14. Note the difference in the f-stops measured.
15. You have then a rough overall measurement of the adapter's light loss.

The DVXuser 35mm adapter shoot out article briefly mentions a test done in which the 35mm lens was not attached to the adapter (quoted below). This test would seem flawed as well since light would find its way through the adapter and around the outside of the GG. So the actual make up and reflectiveness of the adapter's interior would account for some of the differences. Also, I don't uderstand what exacly the subject was while the adapter was on the cam (without the 35mm lens). It would have to be the blank GG since it is translucent, and not the white surface that was used for the camera-only reading.

Before I get into any of the down falls with the SG35, let me say it is a CLEAR winner with regards to light loss. When tested with the unit only (35mm lens not attached as this will vary from user to user), the light loss was only a 1/2 stop. It excelled in the exterior night shots, whereas the Letus35 Flip was nearly useless (more on that later).

In all honestly, I don't see anything under 1.5 - 2 stops of actual light loss being that big of a deal unless the set up is being used for low light shooting (ie: run-and-gun documentary). I would still like to know though if there is a "standard" test used for 35mm adapters.

Thanks for any input.

 

[j]

That to me also seems flawed, isn't that the difference between a spot meter and an incident meter?