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Periscope Lens On A Big Set

Published : 9th October 2004


I'm shooting a commercial where there are a few shots that call for a pericope/boroscope lens, but would love some input on the different options. I've checked the archives, but the parameters of this job are a bit different than most that have been discussed thus far.

I have two shots in particular that I need this tool for. One starts looking straight down and booms about two feet down to within inches of a surface and tilts up slightly. The focal length is approximately 25-35mm. Here I'm concerned about being able to keep the camera away from the surface to avoid shadows, as well as to be able to achieve very close focus. The second shot is a floor level dolly back from an object that starts very close (within inches) and pulls back 2 to 3 feet and is about the same focal length (apologies for the lack of specifics on distances and lenses, but they are based on the clients' wishes to decide those things on set).

What I'm struggling with is trying to avoid lighting rather large sets (despite the close up nature of the shots, they occur in a large space) to a T8 or above which is what would be required to use the T-Rex, Revolution, or even the Optex Excellence (though I realize this lens only requires a 5.6).

I'm thinking of using the Century Periscope with Ultra Primes or S4s (and a Macro lens when I need close focus). That lens seems to give me the lens position options and the ability to keep the camera away from the subject without having to light to the deep stops that the more specialized lenses like the T-Rex and the Revolution require. I don't nee the ability to go underwater or do the cool panning moves that those lenses allow one to do, but am I missing something here?

As usual, thanks for the input.

Rob Barocci
Director of Photography



>am I missing something here?

I think so, isn't the stop in this case determined by the periscope and not by the prime you put on it.

IE the periscope has a max ap of T5.6 or so and it doesn't matter that the prime on it is faster.

I think

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based
www.cinematography.net



Geoff Boyle writes :

>I think so, isn't the stop in this case determined by the periscope and >not by the prime you put on it.

>IE the periscope has a max ap of T5.6 or so and it doesn't matter that >the prime on it is faster. I think


Correctomundo.

The Century V-35 has an effective max of 5.6, the fastest Cinewand is 2.8.

Brian Heller
IA 600 DP



"I think so, isn't the stop in this case determined by the periscope and not by the prime you put on it"

According to Century, you set the taking lens at T2.8 and then use the periscope to set the exposure. The range there is T4-45, so there is just a stop loss. At that point I'm a bit conflicted though, since I would be more comfortable stopping down one stop from the open position of the Century periscope which puts me at T5.6, which is the same stop as the Optex and only 2/3 of a stop open from the T-Rex.

How do you feel about using the Optex and/or the T-Rex wide open?

Rob Barocci



>How do you feel about using the Optex and/or the T-Rex wide open?

Hi Rob,

I always put a little stop in over wide open on these scopes as a general rule although I haven't had the pleasure of using the T-Rex. I find that wide open everything seems just a little bit softish. And I always find the end result sharper than it appears through the scope.

The T-rex and the Revolution have more options as you previously mentioned but they can often make things much easier to adjust when setting up the shot. On the other hand, they can make things much more complicated very quickly if you don't keep the camera/lense move very simple.

One note to consider may be the DOF you will need when focused closely. That may be a determining factor at what stop you end up working with as well as how much focus pulling you will need to do when you pull out. Unfortunately none of these rigs seem to have any DOF charts as far as I know.

I almost always use 500 ASA stock (5279) when shooting 35mm with these rigs. And, when necessary, I have rated it at 1000 ASA for large set considerations and correct the underexposure in telecine. Haven't had the chance to shoot '18 with any of the scopes yet.

Hope this helps a little.

Jim Sofranko
NY/DP



Although some scope rigs accept 35mm primes when used on the tip they can be the cause of shadows when working within inches simply because of their size. With many of these periscope / borescope set-ups the taking lens on the tip is usually as small as you can get it, I usually use a C-mount 10mm Switar, or even a endoscope/pinhole affair to fit into small places on 16mm format, I often find that 16mm super speeds cover 35mm format. Normally one stops down 2 stops to kill flare and give us flatness of field on the tip lens and then stops down 8-11 on the body of the scope for the best results.

The Optex scope is different and an interesting one indeed.

Tony Scott the optical engineer who designed it spent seven years to get it right, where as most scopes are hybrids from many bits the Optex Excellence is purpose built. It has its own lenses that are smaller than normal primes and very good optically; a 10,14,20,28, and 40mm that's in the testing stage. They have no iris for stopping down; this is done with the body of the scope. The stop is also a function of the format; 2.8 for Super16, 5.6 for 35 & HD. Wide open it can render 150 line pairs on axis and 80ish edge to edge - the same sort of performance one would expect from primes. One stop in the edges are noticeable better, after that diffraction quickly takes over and the image starts to fall off. It was designed for shooting wide open or a stop in.

The feedback on the Excellence has been all very positive. More that one DP has mentioned it will cut with primes. The 90 degree prism may come in handy for your shoot to keep shadows out of frame.

Phil Savoie
BBC Natural History Unit

http://www.bbc.co.uk/ - World Wide Wonderland



Geoff Boyle writes:

>isn't the stop in this case determined by the periscope and not by the >prime you put on it.

Put any two things in series and the lesser of the two will dictate the limits of the combined system.

But will the periscope *determine* the T-stop, or merely limit it? Do you multiply the two stop numbers, add them, or ignore the greater (transmission-wise) of the two? Never having used relay-lens systems I'm not sure how to calculate the net T-stop.

This will probably be embarrassingly obvious once someone explains it.

Dan Drasin
Producer/DP
Marin County, CA