Understanding light loss equation!

jgastelb

jgastelb

Well-known member
I'm kind of curious to understand the equivalent of the light loss between dvx/hvx with and without the Letus Extreme.

For example:
If I were to use the camera and Letus Extreme with a 50mm fd 1.4 lens and film a white wall and got a marker reading of 50% with both lenses wide open, then what F-stop would match this reading when taking off the adapter and shooting with only the native lens (no nd filter applied) at exactly the same angle, lighting, zoom, and so forth?

I know the claim is that there's a 1/2 stop of light loss but each lens loses its own share of light on top of the adapter. I'm just trying to visualize it. Does this make any sense?
Thanks for any tips.
Jgastelb
 
You wouldn't want to film a white wall at 50%- you need to use a 18% grey card (you can buy them at your photo store, or at filmtools.com. To figure out what your total light loss is with the adapter and the lens attached you would need to do the following test:
How To Video
How To Article

With the 1.4 or 1.8 lens you are loosing just over a stop of light. So for example, if your meter set at 320 ISO (Speed of the HVX bare) gave you a reading of f11, then for one stop less then that the correct exposure would be f8- ISO 200 (roughly the HVX + Letus Extreme + 1.4 or 1.8 Lens)

-Ryan
 
The 50% example was just a starting point.

What I did last night was to film the white wall with the Letus FE with all lenses wide open and based on the practicals available got a marker reading of 15%.
Without the adapter, about the same framing, same lighting, to get 15% with just the dvx lens I had to change my iris to a F5.6.

Do you see what I mean? I'm trying to simplify it so that I can see what it equates to in the lamest terms. This means that with the 50mm fd 1.4 canon lens I used and the adapter I see what the native dvx lens sees at F5.6. I don't quite understand the f-stops as much but I can see how it translates from one to the other. Make Sense?

I'm trying to see what to expect with the Extreme newly improved light loss so I can adjust my dvx by itself and get a pretty good comparison while waiting for it to be delivered. Though I did get the Economy but it should be close enough according to the makers.

Oh, and I don't have a light meter so.... There's that.
Jgastelb
 
PaPa said:
how exactly are you measuring the percentage?
Click to expand...

Marker in the dvx100b instead of zebras. Focus on the same area. The look of it in F5.6 was pretty close. But remember that was with the Letus FE which loses 1.5 stops though.
 
J, that's why we only test and and quote light loss with a 50mm f1.4 lens attached! In other words, on your test, you'd expect to close down your bare DVX .5 to .7 stops after removing the Brevis35 "system" which would include the 72mm achromat, Brevis35 and 50mm f1.4 lens.

In both tests you would not change the DVX distance from the test scene, only zoom in or out for the identical framing.
 
I understand what you mean. I would not change the distance either. Only the zoom as you mentioned.
I think that a lot of new people to this whole thing never understand that when someone says it loses a whole stop or whatever most of the time they're not including the lens choice since it could be a number of them.
Jgastelb


Dennis Wood said:
J, that's why we only test and and quote light loss with a 50mm f1.4 lens attached! In other words, on your test, you'd expect to close down your bare DVX .5 to .7 stops after removing the Brevis35 "system" which would include the 72mm achromat, Brevis35 and 50mm f1.4 lens.

In both tests you would not change the DVX distance from the test scene, only zoom in or out for the identical framing.
Click to expand...
 
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