July 19th, 2007, 03:42 AM
Finallly a rent house bought the 16m lens adapter HZ CA13. I am the first one who is renting the piece to shoot a commercial tomorow. Is there anything I need to know about this adapter? Are there any 'don't do this' things with this piece of glass? How do I backfocus with a fix lens?
Thank you for sharing your experience,
July 19th, 2007, 12:42 PM
I'm out of town and this is probably the last time I'll have internet access for a week, so I'll give you as many tips as I can think of right now from my personal experience and then you'll be on your own.
First of all, you should make sure you have a backfocus chart like DSC's Fiddleheads (http://www.dsclabs.com/resolution.htm), or a standard Siemen's Star (http://www.temple.edu/fma/referencelibrary/manuals/SiemensFocusStar.pdf).
You'll also need a measuring tape.
Backfocusing on the HZ-CA13U (aka COPLA) is easiest with longer focal lengths. I always rent a 32mm or 50mm to set the backfocus.
Of course before you rent any prime lenses your 1st/2nd A.C. should confirm the quality and collimation of the primes at the rental house, and ensure that the lens is not focusing near or far. Setting the backfocus on one lens won't help when swapping primes if that lens is not properly collimated.
Most reputable rental houses maintain their lenses and will have a projector on-site to check the lenses before they go out.
The backfocus procedure is fairly simple and you should conduct it everytime you change locations.
Mount a long focal length lens (32mm or longer) and set the witness mark to a focus distance of say 15' (or 10' - varies depending on make and focal length of prime lenses.)
Now with your measuring tape set the backfocus chart at exactly that distance from the focal plane (continuous line etched around the circumference of the COPLA adapter.)
Open the aperture all the way and compensate with ND filters or shutter speed if over exposed.
Loosen the backfocus adjustment knob and slowly turn until the backfocus chart is sharp.
Mount each lens you've rented and confirm that they also appear sharp at that focus.
DOUBLE CHECK: Move your backfocus chart to a closer distance that corresponds exactly to another witness mark. I will usually use 3' or 6'.
Recheck your lenses at that distance. You can now take note if a particular lens is focusing closer or further.
Some things to consider when choosing lenses:
Depth of Field:
The COPLA has a maximum usable aperture of roughly F/2.8. This is because of the optical invariant (aka Lagrange Invariant) and the fact that the maximum aperture on the HD100/200/250 is F1.4. You can read more about this topic in this thread (http://www.dvinfo.net/conf/showthread.php?t=83854&page=2&highlight=optical+invariant) taking note of the calculations presented by Ryan Damm and myself.
The bottom line here is that there is absolutely no advantage to renting hi-speed T1.3 lenses. They will not give you shorter depth of field or higher transmittance than the much cheaper T2.1 Standard speed lenses. Opening past 2.8 on the prime lens will have absolutely no effect on depth of field. The maximum aperture is set at F/2.8.
T stops versus F stops:
Prime lenses are marked in T stops which corresponds to actual transmittance of the lens. This means that even though a T marker says 2.8, the F stop might actually be closer to F/2 and a half. There is really no way of knowing, so to be on the safe side consider the T stops to be equivalent to F stops for all DoF calculations. I generally shoot at T2.8 or T4.
You can use standard 16mm circle of confusion values (.0005") when reading from depth of field charts.
Transmittance: Here's an important one. JVC has been quoted as saying that the adapter has less than a 1/2 STOP loss. This is partly true. The optics in the adapter do technically lose some transmittance through dispersion/refraction... whatever.
The reality is that because of the design of the adapter (it is essentially a reducing lens) the Optical Invariant (see link above) comes into play again and thus the reduction of image size results in an increase in transmittance of about 2 STOPS. The net result (2 STOPS minus 1/2 STOP) is a 1 and 1/2 STOP INCREASE in transmittance. Yes... it's true. You actually GAIN light. Setting the aperture to T2.8 will give you an equivalent transmittance of about T1.7
I shot a short film a couple weeks ago with an interior scene and our largest light (bounce) was 1000W. I actually employed the ND1 filter (1/4 transmittance - 2 stop loss) just to bring the exposure down and allow me to shoot at T2.8 instead of T5.6.
It sounds counter-intuitive, but it's true.
Field of View/Angle of View:
You can use equivalent FOV/AOV charts for 16mm and they will apply to the horizontal range of the 16x9 frame. I've found in comparison tests that the COPLA actually captures a slightly larger angle of view than 16mm transmitted guides into the overscan areas, but if you follow the safe action guides in the VF it will be about the same.
I generally will rent at least a 9.5mm (for nice wide shots without distortion), a 16mm (for 'standard' medium shots) a 25mm or 32mm (for close-ups) and sometimes a 50mm (for extreme close-ups/telephoto.) The 50mm is good to have just for quick backfocus testing if you can afford it.
Any lens will work. The format does not matter (s-16, 16 or 35mm). Anamorphics and other specialty items like tilt/shift will also work. If you can mount it on an Arri SR, then you can mount it on the COPLA.
Assuming you have 15mm/60mm "mini" rods then you can also rent lightweight follow focus and matte box, etc. I find that my graphite rods that came with my Cavision matte box are just slightly outside of the 15mm diameter spec for film accessories and I therefore always rent a pair of aluminum rods.
It is also recommended that you use a lens support on adapter, especially if you plan to attach zooms, anamorphics, Cooke S4 or Zeiss Ultra Prime lenses.
One last note is that you should make sure they rent the COPLA with a PL port/body cap. The plastic cap that ships with the COPLA is not very stable and falls off easily.
July 19th, 2007, 05:26 PM
My English is very poor, I don't know those words which can express my feelings of gratitude for your professional help.
Thank you very much Tim Dashwood.
God bless you,
July 19th, 2007, 10:49 PM
That was great, Tim- maybe this should be a sticky..Eugen, hopefully you will post some footage from your shoot.
July 22nd, 2007, 05:53 PM
I shall post some footage the moment they start broadcasting the commercial.
One thing I can say for now is that the HZCA13 adapter worth the money.
I didn't get that 'sticky ..Eugen' joke Robert, you know.. my English.
All the best
July 23rd, 2007, 01:03 AM
Yes Eugen, I was simply suggesting to Tim that he may want to make his very informative reply to your inquiry a "sticky"; in other words, a "full time" message posted in a way that remains visible always in a particular forum. This would serve as sort of a " mini handbook" for the HZ.
Look forward to seeing your project footage. Thanks for sharing!
July 23rd, 2007, 05:33 AM
I am sorry Robert, I got it wrong.
In less than a week I'll share some footage.
All the best,
July 23rd, 2007, 09:43 AM
I'd love to rent this adapter, where can you rent one?
Many thanks, Josh