Does Letus Extreme lose more light than Brevis

OK, this will be unusual post from me, as you have seen we never defend our products, just let the users judge. But I have to jump in to comment on this.

Barry, you don't need to test further, there is no need, as I know exactly what happened. And you would find out exactly the same result if you do the same test on the same GG.

This is the very reason we had to recall about the first20 Extremes when it entered the production version. We mistakenly assembled the test ground glass (the see through ground glass) to the Extremes. With that ground glass, you would see the same phenomenon. I hope Dennis didn't ship a lot of these GG already.

Here is the way you can prove it, if you have time, of course:

1. Take a piece of glass about 1-2mm thick
2. cut it to the size of the GG holder
3. use the sand to hand sand it, just a little, and let all the aerial images to pass through
4. Put it on your adapter (replace the current GG of course)
5. Do the same test like in the video, you'll see it perform "better" than the demonstration in the video.

The problem? You just let the whole aerial images to pass through the GG and this is the worse thing that a 35mm adapter can do.

OK you have just tested the one extreme of the GG.

Now do the test again, but this time, sand the GG really well (or get the piece of GG from Flip Enhanced or SG Pro or Extreme, they are about the same see through level, which is almost none). Do the same test again. Uh oh, I cannot get that "cool feature". But this is what you want for a 35mm adapter.

I hope this will put to rest this phenomenon as it is a known thing. All DIY adapter builders out there should experience the same thing.

Please do not email me regarding this until you do the steps above. Have fun disproving me ;)
 
Well, CF1Le, CF1L or CF1 can be found in every one of our units sold worldwide over the last 18 months. We've not had a single complaint of aerial image pass-thru...and they all perform much the same as this one. I've made it very clear that CF2/Le and CF3/Le have a different response curves and bokeh rendering. CF1Le is purpose designed for maximum light efficiency. The "e" versions that we're currently shipping have been carefully engineered to replicate that very flat response you see as we stop the 35mm lens down...and this is consistent across the line.

In our extensive testing comparing shots using actual film vs. the same lens on the Brevis adapter, we also developed a very accurate matrix of the relative differences in bokeh rendering across the f-stop range...and from this first study evolved our entire imaging element line.
 
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defend? who's attacking?

who is this?

anywho... I find that that is a cool thing about the GG that let's lots of light get though... better yet I find it is excellent that you can replace the GG's...

I would love to get a third party like Barry to tell me what the pitfalls of the Brevis are as he will most likely do it objectively and in POLITE fashion... also I pray he tells me how to get the best out of a Brevis because if it seems simple enough for full days I will likely go with it

I am not 100% about this but it seems that so long as you know how to avoid hot-spotting and you are pleased with the image then the Brevis with CF1Le allows you to manipulate your DoF to great extent without affecting exposure and it might allow for 2.8 glass to be used as if it were faster...

please, PLEASE do tell me if there is something bad about light getting straight through the glass... I SURE do need help from people that know far more than me... without a DP I would be, well.. a bit worried... I'd be just fine, but I am the first to admit that I am not a cinematographer... so please tell me about things I don't know, but do so objectively and for the good of ALL users
 
I guess it is light that passes straight though the GG

And wouldn't it be guided properly by the lenses, I mean it is correctly directed by the elements of the first lens, and you are only recording the correct sector of the GG, so if you can get enough grain and DoF accent (and all other attributes being sought) from a lower amount of grain then so be it... right??
 
Yeah, I can in one term: Hot Spot.

The ground glass is basically see through, and you need an actual screen to retain the image, right? If you barely have a screen to project the image, the rest of the image passes through and all of the light is hitting the iris in the first place.

That's why Phillip managed to stop down a Vibrating GG adapter to F8 and not see any grain... cause there's barely an actual surface that nets enough image to keep it from spilling. I can see a few things wrong with it: Namely the difficulty in controlling color rendition and light in general.
 
Unfortunately, there is no perfect adapter. We listen to our customers, and the R&D programs we undertake are based on their requests. It's also true that keeping costs down means that not every feature I'd personally like to see, can be integrated into the system at it's current price point. I suspect that Hienle, and Wayne would say the same thing about their products. You'll also find many folks are understandably biased towards what they've spent their hard earned money on. Barry has his own opinions toward adapters and cameras, based on his own experience with them. Competition is a good thing....and the only danger is being caught standing still. Btw, it is technically impossible for light to pass straight through any of our imaging elements. The waveform monitor performance shows that the Brevis flip (as Barry mentioned) is showing no hot spotting at all. The waveform monitor response is nearly dead flat...and it cannot be more graphically demonstrated. This is a very difficult thing to achieve, which is why you don't see too many test like this. Can I say it again? There are lots of great adapters out there and if you have one of them, worry more about learning their quirks and optimizing your experience with them. I think I've demonstrated that a few minutes with a few basic tools of the trade can be very helpful in understanding the lenses, adapter and camera that you're dealing with.
 
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but the hot-spot only occurs at a specific aperture... so if you can avoid it and you need to use slower glass then this is the answer, right?

Is the hot-spot not present with the CF3Le?
 
Btw, it is technically impossible for light to pass straight through any of our imaging elements.
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It was also technically impossible for the Brevis to be brighter until it was explained in a better way.

Can I say it again? There are lots of great adapters out there and if you have one of them, worry more about learning their quirks and optimizing your experience with them. I think I've demonstrated that a few minutes with a few basic tools of the trade can be very helpful in understanding the lenses, adapter and camera that you're dealing with.
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You can say it again. There's gonna be drawbacks at the price point. We just wanted to know how the Brevis managed this feat.
 
Every lens itself has a degree of edge fall-off as well as "hot spotting" and it gets worse as you get to the wider angle lenses. This behaviour also changes with aperture, and with some lenses, is actually worse when they are used wide open. On a wf monitor, this looks like a gently sloping hill. You are taking what is essentially a circular wave and trying to get it to normalize an a planar surface...which is why lenses have all those elements crammed into them.

The line you're seeing on an evenly lit white board in this test is flat all the way to f5.6. Looking at the aperture at f5.6 it is 25 times smaller (5 squared) with respect to surface area..and this is very difficult for any optical system to deal with. In other words, no adapter can fix this unless it can dynamically and differentially alter it's gain value across the focussing plane. There are a few things I won't discuss about the unit, but I have no problem showing you the manifested behaviour of the system :-)
 
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Losing light with adapters is one of the side effects of using adapters. It's a tradeoff. It's a tradeoff in design I would imagine and a tradeoff that the end user would need to consider based on their needs.

Less light loss in an adapter is also likely to be a tradeoff in exchange for a less film like representation due to the less dense diffusion, right? To get a more film accurate bokeh, an adapter would lose more light as a side effect, would it not?

So, it isn't so much a lose the least amount of light is best, or a get the most film like representation is the best.... It depends on what the end user is looking for ultimately. Someone shooting a film under controlled circumstances would probably look for the most film like bokeh, etc, etc. Someone who shoots run n gun style stuff or weddings, or is simply just after the shallower DOF an adapter can offer, might not be as concerned with film like representation, and might just want to get the brightest adapter they can find without too much tradeoff in picture quality. Others might wish to live somewhere in the middle.

The advantage to the end user is that there are some really great options to look at in the adapter world for us. When the Letus Extreme came out, it really upped the game for everyone. Letus went from being an affordable flip option to being a very competitive all around product. And, every adapter maker now offers a flip option of one sort or another, and there are some very good adapters out there now, dollar for dollar. Every one is upping their game.

Depends on what you are after, and just wanted to clarify that light loss is only one factor to consider with adapters. Not the be all end all.

With concern to what this thread has been largely about, which is the non-linear light loss of the Brevis (and possibly other adapters to some extent... I'm sure people will be testing it now), the question is... why is it happening... what are the tradeoff's going to be, and how will they effect the shooter based on their individual needs.

Later,
Jason
 
So far, all the testing and argument for a numbers guy like me only tell me that:

The GG in question is inefficient for fast lenses and the amount of light lost is grater at wide aperture since you don't gain anything by using brighter and usually more expensive lenses.

Assuming that the adaptor looses only 0.5 f, then the ASA raring would be about 200 at f 4.0.
Then at f 2.8 it lost 1 full stop and the ASA rating would be 100.
At f 2.0 it lost another f stop and the ASA rating would be 50,
At f 1.4 the rating would be 25.

Don't take me wrong I think the Brevis is a great adapter. They have as far as I know the only Back Focus adjustment and image centering. I just think that the wide aperture phenomenon is a negative for that particular GG.

I love to have the actual ASA rating as use on that test. I know that most videographers don't have any idea of what this is because you use monitors to determine exposure, but without it you can't compare apples to apples.
 
Okay, then, key question for Dennis: does this "non-linearity" of f-stop response apply only to the CF1-series screens? If so, that would go a long way towards explaining it, as Hien and Michael have said. If there's less effect the more diffused the ground glass is, that all starts to make a lot more sense.

Thanks to all who have participated in helping us get to the bottom of this, or more towards the bottom of it at least!
 
As far as I can remember he said that the other elements have different curves. It sounded like one of them might be a middle ground and the third has direct light basically completely avoided by design... I am not sure at all where they fall but it seems that this is something that the guys at Brevis have been completely aware of from the get go and have been developing the current GGs and are developing up coming GG's with this in mind.

Not knowing much at all about optics and such I did understand the powerfully ability of being able to exchange elements... after all this is where our curves reside together with grain and other added qualities that we are asking for in order to emulate film. It was also evident to me that they were serious and had budgeted for R&D of multiple GG's... I think all is possible... whhhell... maybe not all, I really dunno... but this is the biggest selling point for me still to this day: possibilities

Someone equated the change of the GG to changing film stock... and that's an ability that is (was?) missing when using cameras which cannot emulate film all on their own to that greater degree which we are now used to achieving.

If I end up buying into the Brevis with my little money it will be mainly because I believe they will continue to provide me "new adapters" for only the cost of a different GG.

(and I plan to completely understand how to use, how they work, and how to teach my DP to use one before I buy any) hehe... :thumbsup:
 
US, in about a week we'll have our complete 8-part Brevis "Video University" online which will go a very long way in helping you with your quest for knowledge :-)
 
I think I have a very good idea of how to perform the initial set up and use the Brevis to get the most out of. I say this based on what I've learned and read about it on this thread mostly. But just like with my HVX, knowing how to use it is not enough. So I will be glad to have the VU available if get a Brevis.
Same goes for photography, and just like with your DOP when you direct, knowing how to make and speak with visuals is not enough. You still want and need a pure breed DOP that you can lean on when you doubt yourself or when you simply ran out... I feel the need to MASTER all that I am responsible for, and as a Producer Director I feel that means knowing 100% about the medium before hand. Not so I can do the job of holding the chisel, but because I feel it is my responsibility to know how and why when you are the sargent and your soldiers are on the trenches. Because if you are asked which way to charge, you HAVE to know.
I becha I could go out today with one all alone and come back with some very compelling footage, but there is a long way to go before I can feel that based on my knowledge I might have gone to film school in the past. It is tough to be self-taught, but not so tough when you have DVXuser in your bookmarks and good threads in your User CP. Thank you guys for allowing me to take part in this discussion. I don't like to read from the sidelines even when I don't have much to add because I feel I can learn much quicker if I put my understanding to the test and under your scrutiny.
 
Douglas Villalba said:
The GG in question is inefficient for fast lenses and the amount of light lost is grater at wide aperture since you don't gain anything by using brighter and usually more expensive lenses.

Assuming that the adaptor looses only 0.5 f, then the ASA raring would be about 200 at f 4.0.
Then at f 2.8 it lost 1 full stop and the ASA rating would be 100.
At f 2.0 it lost another f stop and the ASA rating would be 50,
At f 1.4 the rating would be 25.

Don't take me wrong I think the Brevis is a great adapter.
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I'm not sure how you got those figures. For arguments sake, if f4 is 200 asa with the Brevis, then f1.4 would be pretty close to 200 asa too. The adapter isn't doing things backwards - you're not losing more light the wider open you are. And the benefit of stopping down is that the 35mm lens will almost always perform better 2 or 3 stops down from wide open (eg, f4 vs f1.4).

If my 50mm is at f4 with the Brevis then theorectically it's performing better than when it's on the SGpro at f1.8, and my Brevis setup is still more sensitive. My early opinion is however that the SGpro is aesthetically more pleasing, so I'd use that when I have plenty of light.

Dennis, I'm interested to hear your developments on the bokeh front, however would a trade off be greater light loss? And I'm not sure I want to be changing out screens - I'm sure many are ok with it but it's not for me.
 
StMad said:
I'm not sure how you got those figures. For arguments sake, if f4 is 200 asa with the Brevis, then f1.4 would be pretty close to 200 asa too. The adapter isn't doing things backwards - you're not losing more light the wider open you are. And the benefit of stopping down is that the 35mm lens will almost always perform better 2 or 3 stops down from wide open (eg, f4 vs f1.4).

If my 50mm is at f4 with the Brevis then theorectically it's performing better than when it's on the SGpro at f1.8, and my Brevis setup is still more sensitive. My early opinion is however that the SGpro is aesthetically more pleasing, so I'd use that when I have plenty of light.
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You would be correct if when you open from f 4.0 to any other f stop the light would change linearly also.

In the case of this GG you don't see any changes when you open more than f 4.0.

Think about it.
if the SGpro is 1.8 when the Brevis was at f4 in reverse since there is no change when the Brevis is from f 1.4-f 4 the SGpro is still at 1.8

You are no loosing light you are just not taking advantage of a wider lens.
 
StMad, about not wanting to exchange the GG. I think you own multiple adapters so this may not apply to you. But for those with very limited budget, I think that a little break to take the Brevis off the adapter and exchange the GG in a place with no air movement other than your air gun might be worth it.

Say I go to Fargo and I film my day exterior stuff on the snow and frozen lake on a sunny day but that same day we shoot into the night with the full moon :) and just a few lights... then maybe I will want something a bit less translucent to start with and change the GG at dinner?

Wouldn't this help me avoid the hot spotting during the day if the first element was a bit more like the G35's M2's and Letu's... then at night using the translucent one help me get the most out of a smaller crew and kit?
 
Hey guys, I'm happy to see this discussion has risen beyond - you guys are nuts! that's impossible.... etc etc. It seems that most of you are recognizing the phenomena is real. Thanks at last!

Thanks Jason for a great extremely simple test that revealed what we have been saying for a long time. I never bothered to look at the more closed apertures because I had other stuff to do, but that is very interesting. it would be cool top\ compare a few adapters at different apertures.

A couple of quick thoughts:

1. This is not a hot spot or vignetting - I repeat it is not something that indicates a crappy image from the Brevis. It might be related to vignetting but the image is FINE. I have very rarely seen a professional video camera reproduce a flat field as a flat line on a waveform. There is generally some fall off due to the optics.

2. It is a function of the GG or Diffusion Screen not the Brevis mechanism. The Brevis CF2 & CF3 are more linear than the CF1.

3. This seems most directly related to how dense the diffusion quality of the screen is. More diffuse = more linear. Redrock is very diffuse and more linear than any of the others in my tests.

4. Hold on to your seats fellas. The most interesting thing I noticed was that at least between f1.4 to f2.8 there is also NO DIFFERENCE IN DOF OR SHARPNESS of the 35mm lens. This is why I have always described it as "the adapter doesn't appear to even see the extra light from the wider aperture at all." How this might pertain to more closed apertures is worth testing.

5. You can decribe this phenomena many different way and as a glass half-full or one half-empty. If you want you can even drive yourself nuts trying to compute the ASA changes involved.

However, if you care about speed, the important thing is to realize the Brevis CF1L is clearly faster at 2.8 than the denser adapters, but they begin to catch up with high speed lenses wide open. You can draw your own conclusions for your purposes depending on what lenses you like and what f stop you want to run them at.

I hope that you are all beginning to realize that as Dennis mentioned there is a whole world of unusual optical phenomena that come with these adapters. Some that warrant further discussion include:


A. Why Denser screens seem to produce lower apparent DOF - i.e. Same 35mm lens/ Same f-stop: The denser screen will usually have lower DOF.(When I first mentioned this people also yelled "scientifically impossible etc." but now it seems to be accepted here as a fact.)


B. Why do different screens seem more well suited to tele or wide lenses or to different size video cameras. This is particularely something where Dennis claims he has designed his screens to optimize for different situations. This may get into trade secrets though.

C. Why in the world do higher 35mm apertures or video shuttter speeds produce more "static grain" on the image. I have trouble visualizing this, especially the f-stop thing.

D. What's the deal with so-called corner to corner flat field focusing and its absence most of the time in my experience.
Its the whole sharpness issue altogether. Sharpness and corner to corner sharpness are not neccessairly the same.

E. i have found that the way different screens handle extremely bright objects varies quite a bit, and this is a real difference in the kind fo image you can get from these contraptions. the issue is rarely mentioned here though it can be important I think.
Thanks,

Lenny Levy
 
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