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Old January 7th, 2012, 06:38 AM   #1
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Focus assist and DOF adapter

Hi,
Just waiting on getting an SGBlade DOF adapter rigged up to my HM700 - does anyone know if the Focus Assist function will continue to work while the adapter is attached.
Also has anyone had experience with a DOF adapter and the 700/750/790? Not much evidence on here.
Cheers
Keith
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Old January 7th, 2012, 09:47 AM   #2
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Re: Focus assist and DOF adapter

Focus assist will most definitely help and should be used to best effect with a large siemens chart, a4 or foolscap paper size with wide bands not thin ones which are harder to see in the small LCD screen. A larger monitor will be helpful. I can speak for the JVC GY-HD*** camera family. I understand, maybe wrongly that the HM-700 performs comparably. If the HM-700 is natively a 1280 x 720P camera, then I strongly recommend you use that option. Using a higher pixel count output may introduce some aggravation of anty groundglass artfifacts which creep in.

Others will argue against me however my final personal preference was to add about three points of sharpening when shooting the the groundglass. There are valid reasons for adding sharpness (detail) and for reducing it. The short GOP codec of the JVC GY-HD*** family was more robust at dealing with any "grain" effect from the groundglass and a little more tolerant of added detail. It is a matter of personal preference and perhaps scoping out your locations first before deciding upon a style. Skeletal white branches in a snow covered forest will look dreadful and flickery with higher detail (sharpness settings).

From vague memory, I think Wayne's groundglass was a little more forgiving of hard detail (sharpness settings) but may have slightly less transmmissive of light. I lost touch with the specs on most adaptors. I think they all shook down to closely comparable in the end.

I strongly recommend where possible to use a measuring tape if you can for focus. This will be of doubful utility if the lens focus witness marks do not match the actual distance of subject from focal plane. There are ways of adjusting this which I won't detail now.


Try to stay in the ballpark of f2.8 - f4 with the front lens when controlling light. Use ND in front of the front lens if you can and use in-camera ND for another layer of light control. Most 35mm stills camera lenses tend to go soft and flary in the last half to one stop to fully wide.

So to maintain the sweet spot of the lens, you desirably should choose a f1.4 lens.

Set the iris any tighter than f5.6 and you may see groundglass artifact in certain conditions. Shutter speed faster than 1/60th sec may also introduce artifacts, thouigh often in good lighting and a wider iris you can get away with 1/100th sec.

These and some faster lenses are fairly available as genuine older Nikon manual lenses in the focal lengths 28mm (dreadfully expensive), 35mm, 50mm, 55mm ( f1.2 ) 58mm ( f1.2 Noct-Nikkor - dreadfully expensive), 85mm. With f2.8 lenses, especially the wider angle lenses, there is a risk of corner brightness falloff or vignetting.

The JVC is not the most light sensitive camera on the block, so you may find yourself having to add light. That is a value-adding consideration you likely will already be addressing if you intend going for a "filmic" look. Poor lighting and setup can make even the finest film camera image look bad.

Even now, with care, the JVC/35mm adaptor combination, properly set up can still look sweet compared to the new tech now out. There is a lot of work and vigilence required as you are managing in effect two exposure and focus systems.

How good groundglass imaging can be is shown by three feature movies, "Kandahar Break", "Merantau" and "Monsters".

If you have difficulties, feel free to post a "help me" here or in the Special Interest Areas > Alternative Imaging Methods threads below.

Wayne's adaptor, properly set up and carefully managed should be able to resolve at or maybe a little beyond the limit of the JVC which is natively 1280 x 720.


As for the EX1/3 special achromat, this was shot as a test of an odd direct relay thing I was trying with Nikon lenses on the JVC GY-HD111. I was using the special achromat and there did not appear to be any edge softness issues. With the camcorder's own lens it may be a different story. After the tests, I returned to favouring the camcorder's own lens.

http://exposureroom.com/members/DARA...fa25d62896f0f/

Last edited by Bob Hart; January 7th, 2012 at 10:20 AM. Reason: error
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Old January 7th, 2012, 11:27 AM   #3
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Re: Focus assist and DOF adapter

Thank you so much Bob, more information than I could have ever hoped for. I bought all three of the versions of ground glass for the Blade (called rotorazors) - different versions of the glass allow shutter speeds to 1/500th and up to f22 and offer different levels of bokeh and light loss.
I guess I need to spend a lot of time experimenting.
Thanks again Bob.
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Old January 8th, 2012, 01:44 AM   #4
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Re: Focus assist and DOF adapter

Looks like you have it pretty much covered. I recommend you do as much timewasting casual shooting as you can to simply build up the reflexes to second-nature so you are not then distracted on a purposed shoot.

When you initially set up and play with the system I recommend you hook up to a large domestic TV so that from the outset you know and can choose the "rotorazor" which best suits you. My vague recall is that Wayne's adaptors were disc based so they will be more tolerant of faster shutter speeds and tighter apertures.

If intercutting groundglass image and direct-to-camera image of the same subject or location, my personal preference would be to use the finest grade of "rotorazor" in the kit of three.

There is not a lot of point to shooting at f16 or f22 just because you might be able to. I think you will find the image will have a harder less colourful look to it for other reasons which are a bit longwinded to go into. Keyword "diffraction", similar reason for not shooting 1/3" sensors with camera'S own iris set at f16 versus using in-camera ND.

Maintain about f3.5 on your front lens, f4-f6.3 on your camcorder, use in-camera ND to control light within those ranges. Add light with reflectors or artificial sources if you can in preference to opening apertures fully wide.

As well as the flare issue, it is the nature of a groundglass to "amplify" bad focus as in making it look more apparent. Most lenses wide-open go a bit softer.

My personal preference is to use ND filters in a mattebox on front when you can afford them or camera weight is not an issue. ND filtering before, not after the groundglass seems to help reduce flare within the groundglass a little and the flags on the mattebox are a basic rule for minimising lens flare. Groundglass flare and lens flare reduce contrast.

A groundglass rig is not ideal for handheld work and will ruin your back and arms pretty quick. The older JVC GY-HD*** camera family was more kindly because you could move the sidefinder forward a little to keep balance for shoulder holding. The PS Technik Mini35 had this feature designed in for their JVC kit.


As for groundglass-imaged projects, I had forgotten about this one, only a trailer so far. As far as I recall, they shot the trailer with a mix of Panasonic 2/3" direct-to-camera and via a P+S Technik Pro35 adaptor.

Exile Movie Trailer - YouTube

Adaptors on the EX cameras can still return a very good look against Canon 7Ds, though with much inferior light performance. They don't alias anywhere near as bad, if at all.

35mm adaptors dead? ( go to bottom of page ) - handheld, bad focus, forgot to turn GG motor on in some grabs, just a fun day scoping a location. We actually shot it on the SI2K 2/3".

Roiding The Extreme ( scroll down a bit and there are some grabs from EX1/Letus footage. ) Wayne's adaptor I think has a fairly wide camera view of the groundglass. By taking a slightly wider than normal camera view of the Letus groundglass, I was able to get it to resolve at the practical ability of the EX1 camera. A page or two back in this thread there are two grabs of Lemac resolution charts with the Letus. Wayne's finer grained "rotorazor" should be able to get close to that for you.

My recall is that he used acrylic material for his disks after trying optical glass. If the rotorazors get grubby, do not clean them by polishing as you may modify the groundglass surface.


Not too far down the track may be the instant affordability of used REDs. They seem to be devaluing faster than motor cars.

It is heartful that Jim Jannard seems to have not imposed a market preserving buyback and destroy policy as part of the upgrade path to the EPIC.
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Old January 9th, 2012, 11:53 AM   #5
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Re: Focus assist and DOF adapter

Again Bob, a really insightful post, thanks again for taking the time out to respond. I am really looking forward to putting the Blade to use.
I will definitely start by having a mess around at home, hooked up to a nice 37" monitor - good tip!!! If there is any footage that is worthwhile I will post it here.
Best wishes from Liverpool!!
Keith
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