35mm framing distance test for DVX/HVX

[Toenis]

I`m dong a research do find out camcorder lens to 35mm frame (GG) distances for different makes and models and create a reference list for those who plan to build a 35mm DOF adapter (http://en.wikipedia.org/wiki/Depth_of_field_adapter).

Please download and print out this pdf (http://www.autonomicum.com/researchdocs/35mm_framing_test.pdf) and follow the instructions.
Or just draw a 36x24mm rectangle and try to focus your camcorder on it.

So which is the smallest distance to fill the 35mm frame with HVX and DVX?

Or even better how big should be GG for camcorder to focus as close as possible on a frame like 35mm.
As far as I know from Dan`s MPIC design the HVX200 can not focus on 36x24mm frame as close as can the DVX so for HVX there should be even wider GG?

Your help is greatly appreciated,
Tõnis Liivamägi

[Dennis Wood]

Toenis, a good idea. I've sent the same instructions to some of my testers. There are couple more factors to consider:

1. What is the camera's equiv. focal length at full zoom out?
2. What is the minimum focus distance?
3. What is the actual effective frame size of your adapter?
4. How fast is your 35mm lens?

For many adapters, you will need to zoom in even tighter than a 24x36 frame due to light falloff at the edges. Slower 35mm lenses may also project a smaller usable image (free of vignette) area due to their smaller rear aperture. The diffuser in the Brevis is engineered to allow less zoom in by 16:9 cams like the HVX.

This test will help....and adding the other points in the database will make it even better.

[Toenis]

Good points Dennis,

I`m about to get a HVX to my company and wondered if it is possible to make or purchase a full frame (36x24mm) DOF adapter for it as DAN`s MPIC apparently does not work so without additional macro on HVX lens.

Just wondering how big should be the GG to fill the frame with HVX in closest macro setting.

Let`s assume ideal conditions without any hotspots/light falloffs on GG frensel setup and with aperture f1.2 on slr lens.

As far as I nkow FX1/Z1 has closest focusing distance of 10mm at focal lenght of ca 40mm but for those I also don`t know if 35mm frame fills the frame or not...

Regs,
Tõnis Liivamägi

[bklyndv]

Is it just me, or are the pdf's dimensions all wonky? The 36x24mm frame dimension is way off, both at 100% on screen and printed out... or are the dimensions measured on the diagonal?

[Barry_Green]

You don't want 36x24mm anyway. That's still-camera frame size. You want to match motion picture 35mm film, and the movie frame size is 24x18mm in 4x3, and about 22x12mm in 1.85:1.

[bklyndv]

Is that true? Since we're working with 35mm still camera lenses, and since you're looking to get the largest frame dimensions possible, while suffering no vignetting (to reduce the magnification of grain), aren't you trying to push the image to greater dimensions if possible?

I'd love to be wrong. That would give me greater design freedom...

- jim

[Barry_Green]

Are you trying to match the look of 35mm movies or not? If you are, you want to match the 24x18 frame size.

If you're just going for an arbitrary frame size to try to get the shallowest DOF possible, then use whatever. But if you want to match the field of view and DOF of 35mm movie film (which is the design goal of the mini35, and frankly should be the design goal of any 35mm adapter IMO) then use 24x18.

[bklyndv]

OK. So in theory the GG could go as small as, say, 26mm diameter and you'd be set.

Thanks for the help :)

- jim

[j]

I think in order to maintain the correct focal length to what a lens is marked as,you would want to use standard 35mm frame size, wouldn't you?

Hmm.... Interesting question. If you use a 35mm still lens (say a 50mm standard), but crop the projected image, it would appear more telephoto, like putting a 35mm lens on a 16mm camera.

The question then is, are you trying to emulate 35mm motion picture DOF, or 35mm still DOF?

[petri63]

I guess that yes, it depends what you are trying to achieve.

I personally feel restricting the frame to specific dimensions is a limitation. Whether you zoom in on 24x18 or larger, the DOF is the same, which is that of the 35mm still lens that’s in front of the adapter. The more you zoom in, the more grain you are likely to see. So I prefer to work with as much image as possible from the GG, whether in 4x3 or 16x9.

I must admit I don’t know much about 35mm movie film, though. Why would it be difficult to emulate the field of view of such film using 35mm still lenses?

[j]

A 35mm still camera negative is wider than a 35mm movie frame. In effect, it's the same as Zooming in a bit on a 35mm still negative. Not that much difference, but some.

A 50mm lens is a 50mm lens weather it's on a bolex, panavision, nikon or IMAX. It's effect is different, as is it's field of view. The user just has to keep in mind how it is being used.

[petri63]

OK, thanks for the info.

From a design point of view, I still believe it is best to have as much GG surface as possible for the image. If a 35mm still lens provides a larger usable frame, the better IMO. I really don’t see the difference in field of view as an issue.

[Barry_Green]

I personally feel restricting the frame to specific dimensions is a limitation. Whether you zoom in on 24x18 or larger, the DOF is the same, which is that of the 35mm still lens that’s in front of the adapter. The more you zoom in, the more grain you are likely to see. So I prefer to work with as much image as possible from the GG, whether in 4x3 or 16x9.
But this discards all 35mm movie film parallels. Cinematographers know what field of view a 50mm lens will give them, but on your adapter it won't. They know what DOF they should have, but on your adapter, it won't (because, with the wider frame of the still frame, you'll have to get closer to have an equivalent field of view, which means shallower DOF for equivalent framing). DOF charts and panning frame rate charts and all other movie reference charts in the ASC manual would become inaccurate if using your product.

To some that will be a big deal. To others it'll be irrelevant I guess. But you should at least be very clear as to what your product emulates so someone knows beforehand. Again, the mini35 was designed around the full academy 24x18 frame because the goal and intent was to emulate 35mm movie film.


I must admit I don’t know much about 35mm movie film, though. Why would it be difficult to emulate the field of view of such film using 35mm still lenses?
It's not difficult at all. Just limit the frame size to 24x18 and you'll emulate it exactly.

[Barry_Green]

A 35mm still camera negative is wider than a 35mm movie frame. In effect, it's the same as Zooming in a bit on a 35mm still negative. Not that much difference, but some.
Actually it's a huge difference. The 35mm still frame is TWICE as large as the 35mm movie frame.

35mm still frames are 36x24mm. 35mm movie frames are 18x24mm.

[petri63]

Thanks, Barry. Very informative. Actually, I’m not making commercial products, even if I made a few project adapters for my own use. But the point is made that users should know what to expect.

I guess it makes a difference for the more serious cinematographers.

I’ll try and find some info on these charts and manual, I’d really like to read more on the subject.

[Dennis Wood]

The downside of the movie frame size on a 35mm adapter is that you run low on F/stop shutter speed choices before visible grain is an issue...and that's in SD. Using a 24 x 36 size will mean a fair bit more leeway on the prime's f/stop settings. Those have been my (rather limited) observations so far building these things. It also reflects 0 experience/history shooting motion film.

I sure have wrecked a lot of 35mm still film though.:Drogar-BigGrin(DBG)

[Toenis]

Is it just me, or are the pdf's dimensions all wonky? The 36x24mm frame dimension is way off, both at 100% on screen and printed out... or are the dimensions measured on the diagonal?

Just don`t let your printer to stretch the file before printing it out. Pdf is in A5 landscape format and it should print out on every office paper format out there.

Interesting that nobody actually haven`t talked about what this thread was ment for.

Please help me out tell me from how far/close it is possible to focus on a 35mm frame 36x24, 24x18 or what so ever.

Thanks in advance,
Tõnis Liivamägi

[pywl]

OK maybe dumb questions, but is there a set distance that the DVX has to be to the GG and then to the lens? If there is a distance then what all factors come into play on adjusting this limit (macro, etc, etc)??? I trying to learn as much as I can before I try to create one of these things.

[bklyndv]

Flange distance is what's most crucial -- this is the distance from the "face" of the lens mount to the diffuse surface of your GG. Typically somewhere around 43mm, but different for all lens types.

From there it's a matter of your vid cams minimum focus distance to zoom in on the projected image, which can be augmented with a macro or achromat.

[Policar]

Barry, I respectfully (very respectfully) disagree. Partially.

On the mini35, you're using motion picture lenses to get 24X14mm or whatever and (in my experience) if you're shooting indoors, shooting at about T1.3-T1.6. (F1.2-F1.4). You loose a ton of light because of the GG and because you're zoomed in to Z99 (f2.8 rather than f1.6, a full 1.6+ stops). Let's say you're using a 50mm lens.

On the "homebuilt35" you're using 35mm SLR lenses to get 36X20 (16X9) or whatever, and I doubt anyone is using lenses much faster than f1.4-f1.8 or else they have too much money and should be renting panchros or something. Light loss is slightly less (f2.4 at about Z75) and I find microwax to have a tiny bit less light loss than the mini35's GG. Let's say you're using an 85mm lens (about equivalent to 50mm supes35).

Let's compare grain, DOF, effective focal length, light loss, etc.

Grain: the mini35 should have less since the lens is open to f1.4 (let's assume f1.4 for the 50mm motion picture lens, f1.8 for the 85mm SLR lens). But it's zoomed in to a smaller area, so the grain structure will look similar. Assuming similar ground glass, we'll call this about a tie.

DOF: The mini35 at 50mm f1.4 will have a deeper depth of focus by a noticeable amount, but not by a ton. If the 85mm lens were at f2.0 it would be about a tie, and light loss/grain would still be similar.

Effective focal length: Again, close. Medium telephoto portrait.

Light loss: Similar (f1.4+f2.8 versus f1.8+f2.4, although obviously this isn't linear addition).

So, overall, using the full image plane makes sense to me. You get similar results. Slightly shallower DOF (imo, this is bad as often as it is good), but similar grain, light loss, framing, etc. if you take into account that you'll need to use longer lenses.

Also, where can you get a 17mm SLR lens that opens up to f1.4-f1.8? You can get a 28mm f1.8 sigma which will give similar results if you use the full SLR-sized imaging circle. Otherwise, you're stuck and would have to buy real motion picture lenses to get a fast wide angle.

Just my opinion, but fast wide lenses are important to me.

[bklyndv]

So, did anyone ever post the DVX minimum focal distance results? Did I just miss
them?

[Toenis]

No. Not a single reply about DVX or HVX minimum focal distance.
Actually I haven`t got no replys at all fom dvxuser, pana3ccduser or dvinfo forums.

Thanks anyway,
T.

[Inexistence]

There has to be one brave individual out there
willing to find the minimum focal distance.:)

[PaPa]

it depends on the zoom.

[j]

I did some diopter tests that also tried out different lens to GG distance. I used an image that was the same size as a camera negative in width, but a little higher due to 4:3 NTSC ratio.

http://emrl.com/j/projects/

[j]

How do you measure the lens to GG distance? In most cameras there is a marking where the film plane is, but I couldn't find one, so I measured to the 72mm lens thread.