View Full Version : B4 Pro Relay Lens Light Loss?
July 29th, 2010, 07:11 PM
I am prepping an indi feature and we are considering using the B4 Pro Relay with my Letus Elite on my Sony PDW-700.
I don't have access to a relay lens to test. Does anyone know how much light loss there is using the relay and the elite units?
The film is all night exteriors, and we will be using Zeiss CP2 at f2.1 to 2.8.
I currently rate the PDW-700 at about an 800 asa, and I can't really afford to loose too much light to the relay and elite.
Any insight or experience appreciated.
Ben Ruffell (http://www.ruff.co.nz)
July 30th, 2010, 05:56 AM
I can't speak for the B4 relay myself as I have not used it. You may or may not have read or heard of Philip Bloom or Tom Guilmette. Both have used the Letus products and have published reviews on them.
Philip's site can be found at Philip Bloom - DP, Director, Filmmaker (http://www.philipbloom.co.uk). Tom's site is Home « Tom Guilmette (http://www.tomguilmette.com)
Whilst it was not shot on the Letus, the feature "Dear Wendy" is worth renting on DVD as this was shot using a custom HD camera/Pro35 rig. The behind-the-scenes featurette is worth a look. The DP was Anthony Dod Mantle, now more popularly known as the DP for Slumdog Millionaire
If you are on the operator end of a PDW-700 it is unlikely that there is anything meaningful for me to add.
July 30th, 2010, 02:41 PM
I have had a look at the video reviews. They are good to see - but I really need to know the light loss. I have emailed Letus several days ago, but have yet to receive a reply.
Thanks for the tip on the "Dear Wendy" film, I will have a look. I have used the Pro 35 with an F900 on a commercial. It's a great unit, but I cannot rent one here and I own the Letus Elite already.
July 30th, 2010, 11:19 PM
Letus' own claim on their home website is for their 2/3" Professional relay lens, 3/4 stop brighter than the P+S Pro35 2/3" relay. The Letus relay lens is wide-open at f1.5.
There is also their 2/3" compact relay lens which wide-open is f1.8.
My following comments are opinion only, based on practical use but no measurements or testing and should be disregarded if more accomplished people than myself reply here.
I think your practical limiting factor will not be so much loss through relay lenses themselves. You might regard their performance as on par with the original camera-recorder lens.
It is the loss through the adaptors which is the main issue. At the wide-end of lens aperture settings you are likely to use during a night shoot, I expect a real-world 1.5 f-stops of light loss. Claims vary across adaptor brands and models.
The 800ASA sensitivity claim for your camera. Is this at 0db gain? Adding gain may increase sensor noise.
I understand that your camera uses the HDCAM codec and that it is more robust than the compressed formats I am accustomed to. You therefore may have much more gain to play with before things deteriorate.
Sensor "noise" when a camera is gained up, is additive to fine detail changes between each frame of image from a groundglass. With cameras like the Sony EX family, Sony Z1, where long GOP systems are used, apparent sharpness is sacrificed for frame rate. I found that setting gains of more than 6db degraded the image too much.
If you are using still-camera lenses on front of the Elite, you will likely find that you lose sharpness and contrast in the widest 1 to 1.5 f-stops of these lenses. The Noct-Nikkor 58mm f1.2 and Nikon 28mm f1.4, which are about the best of the Nikons, still seem to flare over that last 1/2 f-stop.
I don't know how well the Letus relays perform wide-open for sharpness, flare and contrast. The Professional 2/3" is claimed to be a 12-element lens and the Compact 2/3" is claimed to be a 9-element lens.
Your lighting choices will also be a factor. You may lose performance either in white-balancing the camera or gels on lights.
The SI2K, is regarded as a 200ASA daylight 2/3" sensor camera. It is a single CMOS versus the 3 x CCD sensor found in your camera. It apparently has most sensitivity in the red channel. If white-balanced to tungsten lighting and gained up, it may develop gain noise initially in the blue channel so it is best given as near to daylight as possible by adding a colour-balancing filter on front ( about a 1/3 stop light loss) or gelling the lights.
How your PDW-700 behaves when gained up is not something I know.
A DP published a test of the Pro35 a few years back. The light loss at f16 was almost zero and increased as apertures were opened up. I think he also went into the settings of the camera which enable calibration for particular lenses and generated one for the Pro35. With most groundglass adaptors there is a practical wall at f5.6 where tighter apertures are likely to provoke groundglass artifacts. In low light conditions this will not be a issue for you.
My inclination, based on the performance of the Nikon 85mm f1.8 as a relay ( not necessarily a fair reference ) is to give any relay lens an allowance of a half f-stop.
My conservative estimate on performance :-
0db gain, f2 on a f1.4 front lens = 0.6 f-stops, plus 0.5 f-stop leeway on the relay lens, plus about 1.5 f-stops through the adaptor, plus 0.3 f-stop colour adjustment becomes an approx f2.9 light loss assumption for consistant sharpness and contrast outcomes at the wider-end of the front and relay lens iris settings, versus the camera's expected performance through its own lens at 0db and default colour setting.
In low lighting, your lens choices will become limited. The 14mm rectilinear stills wide lenses people seem to like to use indoors are f2.8 which is sweeter at f3.5.
This could seriously impact your lighting budget.
You could of course shoot with everything flat-out open and camera gain up and get more, but there would be visible differences if you are able to vary exposures across the shots in different lighting conditions. You will also run into the drawback of 35mm lenses when used wide-opn, the razor thin depth-of-field which is a nightmare to keep focussed on moving subjects.
You will definitely need the fastest stills lenses you can get to trade off f-stops to get back into the sweet spot of those lenses.
I expect you may run into a grey wall if you try to stretch the blacks. An ultracon filter on front helps.
Your experience and knowledge are likely superior to mine, so if any of my comment is redundent, please forgive the loss of minutes of your life reading something you may already know and perhaps better.
August 2nd, 2010, 06:08 PM
Really good advice. Very much appreciated.
August 3rd, 2010, 12:14 PM
We aims to please, however, I know just enough to be a danger unto myself. Hopefully the likes of Charles Papert, Chris Barcellos, Philip Bloom and Tom Guilmette will put their own opinions which will be more valid than my own.
Please let me know how it works on the big camera. I am examining it for the SI2K but short of actually having one in hand and testing it, I do not know how much of the large groundglass area on the Letus Extreme (Elite) I would lose with the B4 relay. It is a big chunk of cash to put out on a chance. It is also apparently optimised for 3chip cameras and their prism splitter. The SI2K is single CMOS and a B4 lens apparently has to be optically corrected to work on single chip cameras to best effect.
I am able to get adequately sharp results with a hack relay using Nikon primes but I have also been chasing a larger than movie standard area off the groundglass and getting soft corners from the same Nikon primes in a quest for better "apparent" sharpness. What I have seen posted from the Letus relay on the Ultimate has been looking encouraging so far.
Here are some of my test clips to a 2/3" single sensor with the Letus Extreme, the usual outdoors back yard stuff that makes real industry professionals cry in their cups for the future of the industry when they see it posted. This is with hacked Nikon-mount lenses for relay. I would expect the dedicated B4 Letus relay to the 3-chip sensor to be better than the Nikons to the single-sensor.
August 3rd, 2010, 03:05 PM
FYI I asked Cinevate about their relay lens last week, here is the reply:
Thank you for getting back to us on this. Unfortunately we had to decide to cancel the relay unit due to rapidly changing market conditions. We are still about to release a limited run specifically for the SI-2K hi-def camera, but we had to abandon the version for the B4 mount.
August 3rd, 2010, 10:53 PM
Thanks for that bit of info. Dennis' lens is apparently a special unique short-throw zoom which enables adjustment of the area of the groundglass framed. It might be usable with a PL - B4 adaptor, but how to fit it on back of the Letus Extreme/Elite and whether it would be okay for the Letus achromat and internal condensor and possibly longer optical path would be a guesswork unless Dennis has tested his relay with a Letus and can vouch for the result.
August 4th, 2010, 08:08 PM
Jeff Regan at Shooting Star Video has lots of experience with that equipment and he can rent it.
Shooting Star Video (http://www.ssv.com)