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Old June 6th, 2007, 01:33 AM   #1
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Newbee ?'s About Focusing & Zooming

I've been searching around for an answer to these ?'s but they're probably SO SIMPLE they're not even addressed.

How does using a 35mm adapter affect focusing? Do you focus with the lens attached to the front of the adapter or do you focus using the camcorder's auto and manual focus controls? (I THINK you lock your camera's focus on the adapter's focusing screen and manually focus the attached lens. That makes sense to me, but it also means saying goodbye to autofocus.)

And how does using a 35mm adapter affect the camera's zooming ability? Is some of the range lost?

Thanks much guys!

-Peter
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Old June 6th, 2007, 01:39 AM   #2
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Peter,

Once you get a "lock on" the ground glass/focusing screen on your adapter, you won't be using your cams zoom/focus and macro adjustments anymore. Only your iris and speed may be adjusted to a certain degree, depending on your adapters capabilities, your FOV is now dependent on your attached 35mm lens(s) capabilities.

Hope that helps,


Ted
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Old June 6th, 2007, 02:02 AM   #3
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Ted,

So if I wanted the ability to zoom, putting a zoom lens in front of the adapter (instead of a fixed focal length lens) should work, right?
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Old June 6th, 2007, 02:09 AM   #4
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that is correct.
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Old June 6th, 2007, 02:34 AM   #5
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Two more quick ?'s. I can "lock the camera down" at any focal length, I just lose the ability to use the camcorder's zoom while shooting, correct?

And I guess I must rely on the LCD screen image to tell if I've properly focused. Seems like that could be challenging on a small screen like the HV-20's. (Although I just read the HV-20 has a Focus Assist feature that magnifies the LCD image 2X.)

Thanks much for the help!
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Old June 6th, 2007, 02:50 AM   #6
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yes you have to use the camera to tell if you're properly focused. most use a field monitor, but the lcd should do just fine.

i'm guessing "the camera's focal length" is the camera's zoom. yes, once the camera is zoomed in, you can't use it anymore or else you take the chance of either messing up the focus on the camera or more vignetting. i would say once you focus on the screen, get a sharp focus and no vignetting leave it as it is. you can still use other settings on the camera, just not the zoom or focus feature after it's set.
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Old June 6th, 2007, 03:42 AM   #7
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Rich, I'm sorry but I just want to get some clarification on one point.

The HV-20 has a focal length from 6.1 to 61mm. Can I choose anywhere along that range to "lock down" the camera, or is there some recommended or optimal focal length that the camera should be set at when mating it to the adapter?

Thanks again!

P.S. FWIW, I'm considering the Cinevate Brevis35.
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Old June 6th, 2007, 04:39 AM   #8
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There is an optimum setting, when coupled with a particular adapter.
For instance, in my case, I have a DIY mid format lens adapter coupled to a HD100, my setting is 20mm on the zoom, focus set at infinity and full macro. Thats my "constant" lock down setting, i can however, tinker around with my iris opening, and speed, to some degree.
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Old June 6th, 2007, 05:12 AM   #9
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The general rule is, you zoom your camcorder in to fill the frame with the 36x24mm image. It then stays locked in this position.
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Old June 6th, 2007, 10:57 AM   #10
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There are adaptors and adaptors.

Some project a full 36mm x 24mm still-camera sized frame onto the groundglass as Wayne suggests. Others project a smaller area, some in the ballpark of 22mm to 24mm wide.

Larger image generally means a potentially sharper image, wider field-of-view, the most profound creative depth-of-field options possible but introduces some other issues which require some additional optics and careful design.

Smaller image size means simpler but potentially reduced resolution for a given groundglass texture grade, reduced field-of-view/creative depth-of-field options but some sharpness recovery through having to use fewer optical elements.

The 22mm - 24mm image size, whilst smaller than the still-camera image frame is faithful to the traditional 35mm motion picture frame image size and accompanying image aesthetic.

Some adaptors flip the image. Some do not. There are some practical reasons but moving groundglass flip adaptors do not project the 36mm x 24mm image on the groundglass and image area from these is more often in the 22mm to 24mm wide range.

Like all rules, there are exceptions and rules can sometime be flouted.

The recommendation of not messing with the camcorder zoom is a good one. Unless you have "allscan" mode for the camera viewfinder or an underscanning monitor, it is too easy to spoil your shot by picking up a frame edge or vignette when playing with the zoom.

However, with some adaptors more than others, you might be able to use a little bit of camcorder zoom adjustment to assist composition but probably not more than about 5mm as changes in sharpness or the aesthetic of the relayed groundglass image become too apparent.

As a ballpark, you might need to be in the longer (telephoto) region of your zoom range, say 45mm to 55mm, maybe a little wider if your camera has a 1/4" and not 1/3" imager.

For best light gathering performance, a wider zoom setting, stronger close-up lens or dioptre and shorter groundglass to camcorder distance is better. There are also some practical limitations here too. Too close may cause edge/corner softness, edge/corner brightness falloff, or distortion.

Several factors interact, principally, the size of the projected image on the groundglass, the native field-of-view of the camcorder, ability of the camcorder/chosen close-up lens to focus and frame sharply the projected image.

The alternative adaptors currently being sold all represent their designers' take on the best compromise of all these interactions.

Once the operator has got past shooting everything at f1.4 or f1.8 in an inch-wide depth-of-field and has worked all these wild focus pulls out of the system, real-world lens aperture settings begin to prevail as the working choice.

At this point, variations in designs begin to show their individual benefits and deficits, become a concern to some operators and a joy to others, depending on the individual operators' own creative preferences.

Last edited by Bob Hart; June 6th, 2007 at 11:10 AM. Reason: error
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Old June 10th, 2007, 12:47 AM   #11
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Quote:
Originally Posted by Bob Hart View Post
There are adaptors and adaptors.

Some project a full 36mm x 24mm still-camera sized frame onto the groundglass as Wayne suggests. Others project a smaller area, some in the ballpark of 22mm to 24mm wide.

Larger image generally means a potentially sharper image, wider field-of-view, the most profound creative depth-of-field options possible but introduces some other issues which require some additional optics and careful design.

Smaller image size means simpler but potentially reduced resolution for a given groundglass texture grade, reduced field-of-view/creative depth-of-field options but some sharpness recovery through having to use fewer optical elements.

The 22mm - 24mm image size, whilst smaller than the still-camera image frame is faithful to the traditional 35mm motion picture frame image size and accompanying image aesthetic.
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Bob, you wouldn't happen to know if the Brevis35 projects a 36mm wide image or a smaller ~24mm wide one?

Thanks!! You've been a great help.
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Old June 10th, 2007, 02:38 AM   #12
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The Brevis does indeed use a full frame (36mm x 24mm).
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Old June 10th, 2007, 04:41 AM   #13
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Thanks Jon!

Poking around the Brevis webiste I couldn't find a direct answer, but I did find a post concerning DOF tables. It mentioned that the one closest to Brevis would be the one for Vista Vision, which is 36 X 18.3mm. Thanks for the confirm!

... Interestingly, Vista Vision is still used for special effects work even today. E.g. Spiderman 3 used it for some FX shots. Why, IDK?
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Old June 10th, 2007, 08:47 AM   #14
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Vistavision. - for same reason as bigger groundglass is better in an adaptor.

The proportionate size of each film grain relative to the image size is smaller so initial resolution (if several generations of optical work is done) is greater to compensate for generational losses.

The larger format also lends to cropping, digital panning, stabilisation etc.. If a considerable amount of the image area has to be stripped away the resolution suffers less.
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Old June 10th, 2007, 09:49 AM   #15
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Great thread. I have few questions that I'd like everyone's opinion on.

I have an SG35, which I am just beginning to use more often. I'm wondering if I can use my digital SLR lenses without any negative impact, or if I need to stick to 35mm SLR lenses. I have a Nikon mount, but I imagine the answer is the same for Canon too.

Also, I have been focusing on the GG with it stopped; not spinning. I find that I can do a "grain" focus. The only problem is, the DOF is so limited that I find I can focus on different layers of the GG. Should I use a spinning GG for my focus instead?

Finally, is there a way to provide aperture control on my Nikon autfocus lenses? The iris want to stay closed. BTW, what are you using to keep it open?
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