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

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

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?

that is correct.

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!

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.

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.

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.

The general rule is, you zoom your camcorder in to fill the frame with the 36x24mm image. It then stays locked in this position.

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.

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.
...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.

The Brevis does indeed use a full frame (36mm x 24mm).

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?

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.

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?

I am going to get chastised for this but here goes.

I have found - and a DP here in Perth also found likewise with the Mini35-400, that sometimes, focus on the groundglass texture of the stationary groundglass puts you in a very precise "ballpark" of where the relay (camcorder) focus should be and that you can then cheat just a little extra sharpness by focussing on the actual projected image which is made using a Siemens star or similar large target normally used for setting backfocus on ENG cameras.

This requires you to mess with both the focus of the SLR lens on front and your relay focus until you get it spot on. There is a sting in the tail of doing this with home-mades. If your groundglass is passing aerial image, your focus by this method can sometimes drift way off.

With the Sony HVR Z1P, I have found that through the +7 Century Optics dioptre I have used, also the +4, a ten second burst of the camcorder autofocus works as well as the manual focus/human eyeball to small LCD screens and faster at getting to the optimum relay sharpness point, leaving you only to get the SLR focus on the Siemens star at its sharpest.

The same sting in the tail applies. The autofocus will sometimes get enough aerial image to chase a totally way off setting and you have to bring it back manually.

A bonus is that you don't have to set the SLR lens iris at f11 or tighter to provoke the groundglass texture to show itself.

Because my disk motor has a small amount of end-float and stabilises after getting up to speed, I give the autofocus a touch to trim the relay focus after starting the disk motor, then lock it off by switching back to manual. I have the manual focus ring taped to avoid bumping it off. This also helps to maintain a fair average optimum if your disk is running out.

...
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.
...[Deleted Original Post] Paul, my original reply was not accurate. Here's a link from the Brevis FAQ's:

http://www.cinevate.com/phpBB2/viewtopic.php?t=183&highlight=digital+sensor

Essentially, the answer ranges between maybe to probably not.

I can't imagine why a DSLR lens would be any different. Nobody I know has actually said otherwise. And I believe you mentioned focusing with it spinning or it not, Wayne has suggested you focus on your image while it's stopped and then turn it on.......I believe. I think he said that a long time ago.

Focusing on the groundglass when it is stationary is the recommended method for all moving groundglass adaptors.

DSLR lenses most likely will have a narrower available field-of-view. Depth-of-field for a given aperture setting and focal length should be the same. You may even get a slight sharpness bonus depending on the quality of the lens.

A Nikon 12mm - 24mm f4 zoom for digital cameras will give you an adequate image at the 24mm end but becomes vignetted at 12mm on the full 36mm wide still-image frame. For a 24mm wide motion picture image frame, it is fine but being a rectilinear lens tends to be a bit stretchy into the corners.

I'm thinking the DX lens will produce a small image on the GG. Is that correct?

What is the impact of having to zoom in on a smaller image?

Peter, the Brevis imaging element will actually allow a FOV wider than 36mm with fast 35mm film SLR lenses. Several rental shops use our PL mount (the new one), which is designed for lenses projecting the much smaller 35mm cinema film image size. The Brevis adapter is designed to accomodate the full range of frame sizes from 16x22 to 24x36. I use and test with a set of LOMO cinema lenses designed for the Konvas 35mm motion film camera. Every video camera and 35mm lens has their own unique issues, but we've pretty much sorted them out at this point.

The sensor size of a nikon DX is 15.7mm x 23.7mm if memory serves correct. This would suggest that if it's a fast lense and edge fall off is not an issue, it would be similar to using the 35mm motion film lens...and would be worth testing.

Most people are shooting 16:9 format either SD or HD. This video frame is basically superimposed onto the lens' projected image...and you would zoom in as appropriate. The trick is keeping edge falloff to a minimum so that you can use, or exceed in our case, the full image size possible with a given format lens. This is why the Brevis is configured with different imaging elements depdending on the type of cam being used.

Paul.

http://www.youtube.com/watch?v=WokhLQv7fQE

This clip includes some Nikon digital 12mm - 24mm f4 zoom lens still lens images.

Fall-off along the left edge is due to confinement of the prism path and the centre of the lens mount is a bit low as viewed (high on the adaptor).

The clip was sent up as a DivX so might take a while to convert.