Extreme Vs Brevis
- Thread starter johnnyspack
- Start date
jenningsp
Well-known member
Brevis claims CF1 has 0.7 stops of light loss with a 50mm F1.4 lens. and they say the flip module has 0.2 stops of light loss.... so in total that 0.9 stops.
the letus EX claims 0.5 stops of light loss without a lens.. so with a 50mm F1.4 it should be 1.5 stops of light loss. - which has been proven
the designs are almost identical. so you'd probably have to zoom in about the same amount on both. the difference would be inconsequential.
the 0.6 stop difference is probably because of the GG. the letus would have better bokeh because of this. but you could put CF2 in the brevis which loses an extra 0.5 stops, so they would be even....
the letus EX claims 0.5 stops of light loss without a lens.. so with a 50mm F1.4 it should be 1.5 stops of light loss. - which has been proven
the designs are almost identical. so you'd probably have to zoom in about the same amount on both. the difference would be inconsequential.
the 0.6 stop difference is probably because of the GG. the letus would have better bokeh because of this. but you could put CF2 in the brevis which loses an extra 0.5 stops, so they would be even....
Dennis Wood
DVXuser Sponsor
Lenny did some testing: http://www.dvxuser.com/V6/showthread.php?t=116755
Zoom in is not the same necessarily as vignetting and image centering can affect zoom-in levels dramatically. On most cams means more light loss. Linearity of light loss is also a major factor ... at f2.8, the Brevis is still trolling along at .5 stops loss in Lenny's tests...so assume .7 stops at f2.8 if a flip module was installed.
Zoom in is not the same necessarily as vignetting and image centering can affect zoom-in levels dramatically. On most cams means more light loss. Linearity of light loss is also a major factor ... at f2.8, the Brevis is still trolling along at .5 stops loss in Lenny's tests...so assume .7 stops at f2.8 if a flip module was installed.
starcentral
Veteran
Yeah can someone explain how an adpater would have different light loss using a different f-stop on the lens? This doesn't make a lot of sense... ?
"So here are the results with an 85mm/f1.4 Nikkor on my HVX.
@ f1.4 Brevis lost about .5 stop
SGPro .6 stop
Letus 1 stop (corrected to N72 maybe .85)
f2.8 Brevis .5 stop
SGPro 1.2 stops
Letus 1.5 stops"
"So here are the results with an 85mm/f1.4 Nikkor on my HVX.
@ f1.4 Brevis lost about .5 stop
SGPro .6 stop
Letus 1 stop (corrected to N72 maybe .85)
f2.8 Brevis .5 stop
SGPro 1.2 stops
Letus 1.5 stops"
Lenilenapi
Carbonite Member
I can't explain it any more than I attempted to do in my report.
It is an observable fact at least on an HVX with f1.4 Nikon lenses. I have double checked this many times.
Its got its pros and cons as I mentioned.
In the 35mm adapters because we are re-photographing from a distance an image on a diffusing screen - it just seems that many of the typical behaviours we expect from lenses seems to change.
Why do different screens give us different DOF? Never heard of that before either, but again it is an undeniable observable fact. I've published my best guess on the f-stop issue.
"I don't really know why this occurs but my own completely unscientific theory is that because the Brevis CF1L does not scatter light a great deal that the increase in the f stop doesn't have any light to gather from the sides of the lens. Its just a guess though. "
It is an observable fact at least on an HVX with f1.4 Nikon lenses. I have double checked this many times.
Its got its pros and cons as I mentioned.
In the 35mm adapters because we are re-photographing from a distance an image on a diffusing screen - it just seems that many of the typical behaviours we expect from lenses seems to change.
Why do different screens give us different DOF? Never heard of that before either, but again it is an undeniable observable fact. I've published my best guess on the f-stop issue.
"I don't really know why this occurs but my own completely unscientific theory is that because the Brevis CF1L does not scatter light a great deal that the increase in the f stop doesn't have any light to gather from the sides of the lens. Its just a guess though. "
Dennis Wood
DVXuser Sponsor
This property of CF1 and CF1Le with near zero loss as they're stopped down from f1.4 to f2.8 is inherent in their design, and easily confirmed by any Brevis users. It's a huge plus from my perspective as you can dial out edge softness on your 35mm lens with no light loss penalty 
starcentral
Veteran
I'm still confused. If the brevis is .5 loss of light then a lens at f1.4 results in 1.5 stops of light, at a setting of f2.8 a total of 2.5 stops of light, etc.. How can it be the same???
Barry_Green
Moderator
I think there's simply way too much confusion over this whole subject. Anyone with a Brevis or SG Pro who can stand to part with it for a week so I can get to the bottom of this? :thumbsup:
Jason Ramsey
Admin
Didn't Dennis offer you a flip version in a post a while back? I hope that offer still stands... Shouldn't be too long now before they are out..
I will say, that the difference in light change on my Brevis from 1.4 - 2.8 also appears minimal compared to the change when I stop down beyond that. Also using the marker function of the HVX, the percentages don't change at all, or very little in the 1.4-2.8 range, but then change noticeably beyond that...
But, this is a completely non-scientific, just an observation with my untrained naked eye.
Late,r
Jason
I will say, that the difference in light change on my Brevis from 1.4 - 2.8 also appears minimal compared to the change when I stop down beyond that. Also using the marker function of the HVX, the percentages don't change at all, or very little in the 1.4-2.8 range, but then change noticeably beyond that...
But, this is a completely non-scientific, just an observation with my untrained naked eye.
Late,r
Jason
starcentral
Veteran
Hold on - are we talking about fstop of the STOCK lens, or fstop of the 35mm lens?
If we're talking about the fstop of the stock videocamera lens then definitely zoom will play a factor in overall brightness.
If we're talking about fstop on the 35mm lens then like I said before, varying light loss seriously makes no sense.
And now for something completely different.. PS Technik mini35 footage www.starcentral.ca/demo.htm LOL
If we're talking about the fstop of the stock videocamera lens then definitely zoom will play a factor in overall brightness.
If we're talking about fstop on the 35mm lens then like I said before, varying light loss seriously makes no sense.
And now for something completely different.. PS Technik mini35 footage www.starcentral.ca/demo.htm LOL
Barry_Green
Moderator
That's the thing -- I want scientific observations. Brightness compared with evenness of illumination, etc. Vignetting and hotspots. Actual f-stop calculations, with test charts and proper engineering tools. Actual answers. Answers for how much the adapter itself loses, and answers for how the adapter interacts with any particular given lens. Using the same lens on all adapters, and all adapters on the same camera (not multiple cameras, but the same one) to eliminate all variables. Controlled lighting conditions, a lightmeter that's reading out in footcandles and a waveform monitor that's showing IRE...
Lenilenapi
Carbonite Member
I hope someone does do more exhaustive tests especially with a lightmeter. Likewise that someone else looks at vignetting, DOF, Bokeh and sharpness. Another interesting thing would be look at how each adapter and screen might change the gamma differently. Its alot to do though and you need to be very careful.
I have no doubt that some differences will emerge with different video cameras and different 35mm lenses. However I am pretty darn sure my tests within the limits I explained were legit. I would call them scientific Barry, though they did not test everything - thus I call the f-stop loss approximate because I didn't use a lightmeter.
However, they were all done with the same lens on the same camera on the same day observing waveform changes looking at a test chart. I don't think that vignetting on my tests was an issue as the charts looked pretty flat with an 85mm. That's one reason I chose it.
One reason I wanted to do this was because I was sick of people making conflicting claims for adapters they had neveer compared head to head. I didn't have any axe to grind either as I invested in all three.
One thing I will stand by absolutely is that changing the fstop on a 35mm lens on a Brevis CF1L between f1.4 to f2.8 will show virtually no change. When I first noticed this I thought of it as a liability though.
Starcentral - The lack of an f-stop change makes no sense to you because you haven't seen it. But once you see it you will realize it is a fact. Then you'll begin changing your understanding to make sense of it.
In other circumstances (lenses video cameras etc.) people may well get different results - perhaps the Letus may lose less light for example. There must be some reason why many people have sworn that it loses only 1/2 stop. But if you look at my tests - when I corrected for the zoom in factor on my HVX (because the Letus was offset) then I estimated .85 stop at f1.4. That's close enough to 1/2 stop to remain consistent for me.
- Lenny Levy
I have no doubt that some differences will emerge with different video cameras and different 35mm lenses. However I am pretty darn sure my tests within the limits I explained were legit. I would call them scientific Barry, though they did not test everything - thus I call the f-stop loss approximate because I didn't use a lightmeter.
However, they were all done with the same lens on the same camera on the same day observing waveform changes looking at a test chart. I don't think that vignetting on my tests was an issue as the charts looked pretty flat with an 85mm. That's one reason I chose it.
One reason I wanted to do this was because I was sick of people making conflicting claims for adapters they had neveer compared head to head. I didn't have any axe to grind either as I invested in all three.
One thing I will stand by absolutely is that changing the fstop on a 35mm lens on a Brevis CF1L between f1.4 to f2.8 will show virtually no change. When I first noticed this I thought of it as a liability though.
Starcentral - The lack of an f-stop change makes no sense to you because you haven't seen it. But once you see it you will realize it is a fact. Then you'll begin changing your understanding to make sense of it.
In other circumstances (lenses video cameras etc.) people may well get different results - perhaps the Letus may lose less light for example. There must be some reason why many people have sworn that it loses only 1/2 stop. But if you look at my tests - when I corrected for the zoom in factor on my HVX (because the Letus was offset) then I estimated .85 stop at f1.4. That's close enough to 1/2 stop to remain consistent for me.
- Lenny Levy
starcentral
Veteran
When you say full 35mm frame, do you mean 36x24mm or 24x18mm?
36mm requires less zoom, but produces inaccurate FOV of the actual 35mm lens being used.. man a whole other debate on its own...
starcentral
Veteran
Papa, do both do 24mm - I remember that one of the 35mm adapters did really wide.. forget which one that was.. SGpro, M2 or Brevis?
Jason Ramsey
Admin
Brevis and Letus will do the "VistaVision" frame size... the SLR frame size. Dennis is also advertising the flip module for the Brevis as being able to do 10% wider than SLR frame size.
I'm not sure about the others. Lenny mentions it in his comparison thread though... I want to say that the SG could handle SLR frame size, but don't quote me. Redrock, I have no idea on. All of these have flip module's coming soon though, so their useable frame size may be likely to change with the SG and the Redrock as well.
EDIT: all of the adapters do the smaller 24x18 size (the 35mm cine frame size).
later,
Jason
I'm not sure about the others. Lenny mentions it in his comparison thread though... I want to say that the SG could handle SLR frame size, but don't quote me. Redrock, I have no idea on. All of these have flip module's coming soon though, so their useable frame size may be likely to change with the SG and the Redrock as well.
EDIT: all of the adapters do the smaller 24x18 size (the 35mm cine frame size).
later,
Jason