Some resource notes for Letus Extreme

[Bob Hart]

Copied below are some notes I posted over on indieclub.com for an operator who is thinking of going the Sony EX3/35mm adaptor route for an indie feature to be shot in Iraq. That discussion is here :-

http://www.indieclub.com/icmessagebo...8112106&page=1


My notes are by no means the be-all-and-end-all. My usual caveat of not being an industry professional or necessarily knowing anything about that which I talk about, again applies.

If you read anything which is bad practice or patently wrong, please correct it over on Indieclub and here.


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Ahmed.


Firstly, you may have already done the research so please ignore my comments if you have.


Some questions and quick tricks if you are using a Letus Extreme/Elite/Ultimate 35mm adaptor with the EX3.

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Are you also buying in the 1/2" direct relay lens or using the camcorder's own lens?

If you are using the camcorder's own lens, then make sure you buy the Letus version with the "special achromat" for the EX1/EX3. This special lens takes care of a corner-softness issue associated with the 1/2" Fujinon lens.

If you are buying used off eBay, make sure the seller does not just wrap the case but packs the adaptor in soft padding in a box, then packs that box inside another box in more padding.

There have been instances of the heavy prism and the achromat becoming chipped due to violent handling during shipping.

I strongly recommend you also buy a rods and baseplate support system if you have not bought the "production bundle". Letus sell their own kit and Zacuto also made a kit.

When assembling the adaptor to the camera for the first time, I find it helpful to have another person assisting. I position the camera to face directly upwards and lower the adaptor onto the camera so there is no bending load on the front of the lens.

In this position, it is easier to adust the rods and baseplate without having to worry so much about the weight of the camera and adaptor damaging things whilst they are not yet firmly fixed in place.


After setting the relay focus by the factory recommended method, I find it helpful to use a resolution chart and to trim the relay focus with the groundglass motor running. If done carefully it is good for about another 50 lines of apparent resolution over setting the relay to the stationary groundglass texture with the motor stopped.

Relay focus must be set with the camcorder iris at its widest so the camcorder's own lens depth-of-field is as shallow as it can be. This makes sure the relay focus is spot on and already best for any low-light situation where eveything in the optical path has to be wide-open.

The image resolves sharpest somewhere within the five micron or so thickness of the groundglass texture, not at the surface.

Sharpness is best when you are zoomed back off the groundglass as far as you can without seeing an edge of the adaptor. It is hard with the EX1/EX3 because the LCD screen and viewfinder cannot be set to an underscan view.


When you finally adjust the position of the camera on the rods and bridgeplate, you need to do this with the camera on your tripod, the tripod head bubble showing perfectly level and a true horizon or perfectly horizontal line indoors to aim at.

Set the horizon across the centre of the image and re-adjust until it is perfectly level. If you do not do this, when setting up the tripod and then mounting the camera, you may find that horizons become skewed. This is often not apparent until you are editing. By then it is too late.


Helpful stuff can be found here :-


Home « Tom Guilmette

Philip Bloom - DP, Director, Filmmaker ( Philip is now a convert to the Canon 7D and 5D DSLRs).


The clips can be found on the youtube if you search for philipbloom and tguilmette.


Here's a few clips of my own

CONGORO - SLOWMOTION TEST. OVERCAST AND RAIN CONDITIONS By Bob Hart On ExposureRoom

ROIDING THE EXTREME. - ADDED LATERAL CENTERING ADJUSTMENT. By Bob Hart On ExposureRoom

For practical reasons, there is little point to modifying the Letus Extreme like I did. The Letus Ultimate has horizontal and vertical adjustment already built in.

SONY PMW-EX1 - LETUS EXTREME TRUCOLOR V2 TRIAL By Bob Hart On ExposureRoom

Beech Baron Touch and Go at Jandakot Airport Western Australia By Bob Hart On ExposureRoom

FOURNIER CLOSE-UP By Bob Hart On ExposureRoom

This last clip was short with a mirror telephoto lens with fixed 10.5 aperture. With the Letus Extreme/Elite, you will get groundglass artifacts (flickering grain). With the Ultimate, you would get away with it.

You should not use a tighter aperture than f5.6 with any 35mm adaptors.

My personal preference is to use the switchable camera ND filters to enable my camera iris to be manually set in the ballpark of f4 -6.3. This seems to be its sweet spot and the front lens aperture seems best at f2 -f3.5. Of course you can use it wider if you really want to make the depth-of-field very shallow.

My personal preference is not to make the depth-of-field really shallow just because I can, but for the screen story to give me a reason to do it.

Many still-camera SLR lenses flare and go soft over the last half to one stop of their range. Ideally you should use fast lenses capable of f1.4 or even f1.2, so that you can close down to their sweet spot, yet still shoot wider aperture than f5.6.

Your summer outdoors lighting conditions are probably like our Pilbara and Kimberley in Australia, very bright but dulled down a little by airbourne dust and haze. You may find you need to add a ND filter in front of your 35mm lens. With the EX1 and EX3, there sometimes can be infra-red light getting through to the sensor when more ND filters are added. This sometimes causes colour to be added to blacks.

If you run into this problem you may beed to buy in a Schneiider Optics or Tiffen infrared filter.

On your shoot, you need to make sure somebody includes the 35mm adaptor in the call, because the operator will forget to turn it on sooner or later.

"Camera or turn-over" - "rolling", - "Letus" - "on" , - "sound" - "speed", - "action".

Switch the motor off between takes. The little vibrator motor may wear out too soon if you leave it in continuous duty, especially in hot conditions.

Switching off after every take also gets you into the habit of not leaving it switched on overnight, flattening the batteries and wearing out the motor. A good habit at the end of the day's shoot, is to remove the batteries. Make sure you don't forget to store them with the adaptor.

After each new setup, it is a good idea to check if the groundglass motor is actually operating by taking the lens off the front and looking at the groundglass moving or pressing your ear against the adaptor and listen for the vibration. Don't just trust the red light. The motor may stall on power-on if the batteries are nearly flat.

You may find a motor which will not start, usually flat batteries and somebody did not bring spares. Sometimes it will start if you point the camera directly at the ground or vertically at the sky, and then may keep running when the camera is returned to the shot. Chances are that the motor will draw down what is left in the batteries quickly, so you may only get one or two more shots.

It is very important to check the relay focus every time after the camera has been shut down and moved. These cameras are good but every time you shut down and switch on again, the lens focus may move just that little bit from jolts and knocks, also when the camera checks itself starting up again.

It is also easy for the focus ring to get moved by somebody just having a look between takes. I put a small strip of gaffer tape on the zoom and focus rings. Don't rely on the EX1/EX3 autofocus to trim the relay focus. Sometimes it will try to focus on sharp objects in the groundglass texture, spots of dust or on subjects through the groundglass and may not be sharp. YOu will not notice until you are end the edit suite and it will be too late.

It is also very important to check the front lens focus for every shot with a siemens chart held up alongside the actor or subject. The viewfinder and LCD on these cameras are good but still not good enough to focus reliably by eye. If you have a monitor screen with underscan, use it but still use the focus chart as well.

It can be helpful to glue a siemens focus chart on on the back of of the clapper/slate. Don't fasten one to the microphone pole as it may whistle or rumble in the wind or when the boom man becomes tired and gets the shakes.


I don't regard myself as an industry professional. I don't have enough produced work under my belt to make that claim. There are people here who can express in far fewer words what I have described here so please test my comments against the opinions of others.


You may find these discussion threads helpful.


Sony XDCAM EX CineAlta Forum at DVinfo.net

Let Us Discuss Letus Forum at DVinfo.net

Tapeless Video Recording Solutions Forum at DVinfo.net


Please keep us informed about your project and its progress. All the best with it.

[Damian Heffernan]

Thanks Bob for the awesome tips. They'll be very helpful.

I recently got a letus for my EX1 and the first few test shots I've done seem to be to be a bit, well, cloudy. That's about the best way I can describe it. I was a bit surprised by the light loss inside so took it outside and shot some flowers and stuff in the yard. The bright sunny shots looked OK, but when I shot something in a little lower light the image seemed to become foggy or cloudy looking.

Is this normal and do people using letus manipulate in post?

Here's an unedited still. Sorry if I'm hijacking the post but I thought it there's someone with a tip to avoid this you'd be the man.
http://img514.imageshack.us/img514/4103/flowersml.jpg

[Bob Hart]

Don't feel you are hijacking. Nothing asked, nothing gained.


The image appears a bit over-exposed for my personal preference. It is desirable when controlling light onto the groundglass to use a ND filter in front of the lens as well as the lens aperture ring.

This helps diminish flare and resultent loss of apparent contrast occurring within the groundglass texture. Some might contend that I am talking out of that vacuous space somewhere behind me.

My guess is you had an 85mm f1.4 or f1.8 on the Letus and you shot with the lens wide-open. My wild guess at a personal preference with that shot would have been to use about f2.8 - f3.5 on the front lens, ND1 on the camera and maybe f6.3 or f8 on the camcorder iris and "shutter off". The camcorder iris setting would depend on the lighting. As I said, my wild guess.

The EX1 and EX3 have a monochome histogram display option and zebras. Either is worth selecting "on" and becoming accustomed to if not already your practice.

There are wiser DOPs who post on dvinfo.net who are worth a read, the likes of Chris Barcellos and Charles Papert who can put you right on best practice. Use the dvinfo.net search function to find their comments.

Whatever lens you use on front, most will tend to flare or lose contrast in the last half to one f-stop to being wide-open.

A groundglass image has less apparent contrast anyway. It is part of the image aesthetic. Your relay focus seems to be okay. You might be zoomed in a bit far which will lose you a bit of apparent sharpness.

You lose some with a groundglass image relay anyway but you lose less, the wider the view of the groundglass you can get before picking up an edge. Depending on the combination of camcorder and achromat (the lens in back of the Letus) there is a point where you might cause left edge or corner softness if you try to go too wide. Some wide lenses will also throw an image which is darker in the corners. It is all about balance and compromise.


With any camera image groundglass or otherwise, there is always that little bit of grading and adjustment you can do to sweeten the image.

With groundglass work, you could probably get away with about 15 points of sharpen if you shot default sharpness on the camera.

If you are using Premiere Pro, under the timeline playback monitor screen you will see a littie logo on the right which looks like three coloured balls in a bunch. When you mouse over this, it will say "output". Clickon it and it will give you a dropdown list. On that list click RGB parade and this will draw a three coloured graph.

Use your effects for black level and white level, to draw the waveform closer to the bottom for black and closer to the top for whites, maybe bring in a slight amount more colour saturation.

You probably know all this already so please forgive the ramble.

Philip Bloom sings the praises for the Magic Bullet plugin which apparently automates this process with some presets. I've not used it so I don't know it.


Just use and use. Get the practice in until you are able to reflexely operate both systems and not have to work stuff out when you shoot.

With a 35mm adaptor, your camera is now taking a picture of a picture. It is important that the picture it is looking at on the groundglass is the best it can be. You have only about three to five stops of real world light management available on the front end with the lens blelow the f5.6 wall, depending on how fast your lens on front is. You have more if you use ND filters on front. Groundglass adaptors do swallow light, some more than others, so in most instances you will be looking for light rather than wanting to lose it.


There might be some stuff in this thread to interest you.

http://www.dvinfo.net/forum/let-us-d...g-extreme.html

Don't be tempted to operate on your Letus Extreme though. Unless you function at the level of the compulsive-obsessive as do I, there is probably no significant advantage to be gained versus the risks of damage, dirty optical surfaces etc..

[Damian Heffernan]

Thanks Bob. Awesome advice - followed and to great success. I'll post a still up when I get a chance to pull it off the camera but even through the viewfinder I could see the difference.

I had never thought of changing the aperture on the camera after setting the focus on the ground glass (you're instructed to set the ground glass focus with your own aperture wide open). I left the camera wide open and then used a 50mm at 1.4. I used the histogram before and did play around with the exposure but it still looked "cloudy" I had the Camera's ND on 1 setting which is 1/8 or something from memory.

Once I changed the Camera to 6ish, the lens to 2-4 it all became much better. Markedly better actually.

[Bob Hart]

Damien.


Glad it helped. I initially thought your lens was a 50mm but then recalled my own adaptor which I forgot I had modified for a wider view which brings the 85mm field-of-view a bit closer to that of the 50mm on your unmodified Letus.

Sometimes, if you want to ND down but keep your sweet spot on the camcorder lens iris and a preferred wider aperture on the front lens, you can put a coin sized circular piece of ND gel between the back of the front lens and the front glass of the Letus. I've used ND lighting gel but can't guarantee it is optically accurate.

You could put it in the front of the front lens itself but if you have any sunlight falling directly on the surface of the gel you may get flare or fogging from surface defects and dust.


Enjoy.