I might be wrong, but... try it yourslef Bill. Get a FAST lense (1.4 or better) and a Beattie and let us know the findings. (moving it is not relevant for the purpose)
Although on the surface it may not make much sense to get more light out of a source adding a lens and a focusing screen, the results seem to contradict "common sense": (or don't they?)
http://dandiaconu.com/gallery/ALL-CL...A0660TU?full=1
We all could "smell the brightness difference" if holding a lense close to skin on a sunny day..... (imagine a poor ccd's opinion on the matter)
Who said is the other way around? Give me the "offender" and I'll ... hmmmm, ....just you watch.....

The Daves' camera said it's the other way around. The more he closes his SLR iris, the wider his camcorder's iris opens.

Originally Posted by Bill Porter
The more you close the SLR, the more the camcorder will open its iris,not the other way around.

Originally Posted by Dan Diaconu
Who said is the other way around? Give me the "offender" and I'll ... hmmmm, ....just you watch.....

Originally Posted by Bill Porter
The Daves' camera said it's the other way around. The more he closes his SLR iris, the wider his camcorder's iris opens.

Guys, maybe I do not understand you enough, but you both are saying the same... More I close SLR, more iris open on Cam.

Dan is saying the opposite:

<<If the camcorder "reads" in AE say... 4 (iris) for a certain scene, than with the converter (and lens wide open-which ideally should be 1.2, hehehe....) close the iris on the SLR lens till the camcorder "reads" again 4. If the SLR has a 1.4 (as max), the camera should have at least the same reading through the Fresnel and the lens @1.4 as all by itself. >>

I have never used a fresnel so I can't say whether he's right or not, but your numbers (Daves) disagree with what he is saying.

Guys, guys, guys... I still do not understand, how someone can say "My adapter is loosing 2 stops" - its nosense, I think. So long until you say "My adapter is loosing 2 stops at 50mm with 1:2" or something like that. Today I have tried lens 1:1.3 and I have F2.4 with adapter and F2.0 without adapter, both at 1/50s. Next interesting thing is, that this lens does not produce any vignetting !

It's not nonsense, because your adapter hás less light-loss with the 1.3 lens. The light-loss depends on the lenses used and the GG together. With most telephoto lenses you'd loose much more light.
The only real question is: does the adapter give too much limitations compared to the camcorder without the adapter. The answer is probably, yes if you loose 4 F stops and want to shoot indoors. No if it looses 2 F stops or less in any circumstances.

But thats the point... If some one says "my adapter has 2 stops light loss", he told nothing - if he will not tell also the type of lens. Right ? With 1:1.3 my adapter is gaining about half F stop... But this does not mean, I will gain with 1:4 too.
Whats the point of this issue ? If someone come here, to DV and starts to read... And he see : ManA : hey, buddy, my wax adapter is loosing 2Fstops. and then ManB: hey, dude, my spinning CD is loosing 0.5Fstops... But he do not know one important thing... manA is using lens 1:4 at 50mm, manB is using 1:1.2 at 70mm. In case both will use 1:1.4 at 50mm, manA will say 0.5Fstops and manB will say 2Fstops (example). See my point ?
Maybe Im still completely wrong. I just want to undersand it.

I guess this is the answer for me... So... If someone tells his adapter has 2Fstops loss, its zero predicative value, until he mention the lens he is using...

Hi Daves,

I have not look at adapter threads for while.

You're saying with F4 lens losing 1/2 stop and with F1.3 lens gaining about 1/2 stop.

That is about 1 stop difference, although there is 3 stops difference bwtween the lenses. It not make much sense.

I was originally wrong about adapters. I thought at F1.0 lens does not lose any light. Is not the case.

You're right, you can gain F stops with adapter, if these are the measurements and yes, if someone says they lose stop or two it does not make sense if is not referenced to something.

You're right you must reference light gain or loss to certain F-stop of 35 mm lens.

If everyone did testing same way, e.g. at F2.8 of 35 mm lens then we would have some reference to which compare adapters.

There may be some discrepencies, F-stops are related to dimentions of lenses, how much light goes through lens is measured in T-stops.

If your 1.3 lens was made for larger format, that may explain descrepency in your measurements.

Radek

The lens is from some kind of movie projector, I get it for free, when throw away some projectors from very tiny old local cinema.

It could been 70 mm projector or medium format slide projector. That would make sense.

GG will naturally lose light. It is 35 mm lens that is responsible for gaining light, also condenser lens. To see how much GG and condenser, which make 35 mm system, are losing, you could measure amount of light coming off 35 mm lens, then add GG and condenser to see how much light have then. May lose 3 F-stops.

When P+S talks one or two stops, is probably on Canon or other interchangable lens camera and adapter uses relay lens.

Radek

True! But we have a different story when it comes to focusing screens!!!! For the same lens, (let's say a 1.4/50), some GG will lose between 1 to 3 stops and a good focusing screen will gain some 1/2 to 1 stop) Big difference! Why do you think Nikon, Canon, etc use focusing screens in SLR and Digital cameras instead of just GG?

Dan, it is physically impossible to start with a set amount of light and gain more in the process of scattering :)

Actually the screen always loses light but the 35 mm lens is capable of increasing the amount of light compared to the camera lens.

Radek

Quite possible! I was just pointing out that you can't end up with more light than you put into the system (which is what the post sounded like it was saying - not sure if it is or is not).

I think what Dan is trying to say is that if you were to measure the amount of light that a particular lens captures it would read a particular F-stop on a light meter. However, keep in mind that at the back of this lens the light is not uni-directional. It's being spread out in all directions away from the back of the lens. Now, if you were to put a focusing screen between the back of the lens and the light meter you are capturing some of those light rays that would otherwise pass the light meter without being read. The screen captures those light rays and makes them unidirectional. In this case you would most likely gain F-stops.

It's not saying that you're reading more than what's coming in. It's saying that your losing less light due to the fact that you're capturing those rays that would have normally gone right by the light meter, or in our case, the CCD's in the camera.

One must keep in mind that if you're going to compare light loss between all of our different adapters, there has to be some sort of standard. Otherwise you have no way of comparing. You wouldn't try to benchmark one computer to another with one playing the newest Splinter Cell game with all the detail,s effects, audio, etc. turned on while the other one is playing the first Doom game ever made. It's not a fair comparison.

Probably everyone has a 50mm lens. Probably most of us here have Canon lenses. Why not record what the F-stop is with the lens attached to the adapter and camera, then again with your focus-screen/ground-glass/whatever in place. Then you'll get an idea of what you're losing, and at the very least, you might be able to figure out a better way of capturing more of those light rays that would otherwise not be seen by your cameras CCD's.

Court