Some MINI and PRO questions

[John Jay]

Hi Mizell

Does the MINI with the SLR mount allow the full image circle 43+mm to be captured?

Is a Sony B4 relay lens available or at least a Nikon to B4 mount adapter so that the MINI can be used with 2/3 chippers or is the PRO the only way with B4?

[Mizell Wilson]

John,

We do not cover the full 43mm, the Mini35 itself captures the full 35mm image circle, but what reaches the camera is more like the TV Safe Area on a 35mm ground glass.

There is not currently a direct Nikon to B4 adapter that I am aware of. We do have a Nikon mount for the PRO35 though.

mizell

[John Jay]

The Mini35 itself captures the full image circle, but reaches the camera is more like the TV pumpkin on a 35mm ground glass.>>


thats good - but it will require debarrelizer or 55mm in post to pull out the bulge

[Mizell Wilson]

John,

I'm not quite sure what you mean. No post process is needed on the images the Mini35 create, depending on your final aesthetic. As far as adjusting the image, spherical lenses need no correction. If you're using anamorphic lenses then an unsqueeze needs to effected in post.

mizell

[John Jay]

Mizell,

My comment is in relation to the distortion when macro-focusing on a full 35mm image, viz

http://img.villagephotos.com/p/2004-...7/DSC00094.jpg

(ignore the banding which is due to a bad fluor.)

does your last post infer that the Mini35 somehow corrects for this?

[Mizell Wilson]

John,

I forwarded this thread on to my technician to try to get you a better answer and a couple of issues cropped up.

I was mistaken in my answering of your first question. The Mini35 does not capture the full image circle of the still frame, or 43mm. Rather, it captures the Academy 35mm motion picture frame, approximately 32mm.

The Mini35 does not introduce any type of barrel, or other, optical distortion. If the lens you are using has a distortion, it will be represented by the Mini35 and some post tweaks will be necessary. Do keep in mind that with the Academy 35mm frame, lenses that otherwise distort in the still world may not distort with the Mini35, or at least not as badly.

Does this get closer to your original questions?

mizell

[Charles Papert]

Mizell:

Is there a formula that defines the relationship between the stated focal length of a given still lens with the resulting equivalent focal length of a 35mm cine lens? Assuming that the DV image is compared to 1.78 framing shot in 35mm and transferred to tape. My assumption is that due to the significant difference in target size between a still frame and Academy, the still lens will deliver a narrower field of view than it's numerical counterpart in the cine world, but I'm wondering by how much, and especially when the Mini35 system is taken into account.

[Mizell Wilson]

Charles,

Based on another conversations in this forum, of which I think you were a part, it was determined that from the 1/3" CCD (1/4" in reality) to Academy is approx. 4.5x and that from 1/3" to 35mm still is approx. 7.2x (based on the horizontal)

If we all agree on these number, at least for the sake of this post, then from Academy35mm to still would be approx 2.7x

So, theoretically, if we are shooting with a 50mm lens on our Nikon or Canon still lens, then we would want an 18.5 on the film camera....but that don't make any sense...at least as I type it...cuz the reverse would mean that if we are shooting Academy with a 50 we would need a 135 on the still camera.

I'll have to talk this out with Guy and look at some numbers.

mizell

[Barry Green]

There is certainly a difference, but it depends on what you're using it for.

"My assumption is that due to the significant difference in target size between a still frame and Academy, the still lens will deliver a narrower field of view than it's numerical counterpart in the cine world"

Well, no, the field of view seen through a given lens is determined by the imager size. So a 25mm still-camera lens on a movie camera will deliver an identical field of view as a 25mm movie-camera lens on the same movie camera. 50mm is 50mm is 50mm... doesn't matter where it's sourced from, whether a still camera or a movie camera or whatever, the focal length is still the same. The circle of illumination will likely be larger on the still-camera lens, but that just means there's more of an image to be seen by the larger imager size -- the optical properties (magnification, etc) will be identical between the various lenses of identical focal length.

But, a 25mm lens on a 35mm still camera will have a much wider field of view than a 25mm lens on a movie camera (because of the smaller imaging size on the movie camera).

[John Jay]

Mizell

thank you for your response, I could not see the variable geometry necessary to give 43+mm within the Mini35 envelope.

Another question...

I have been given a quote of two hours of Top Quality German lathe/machinist time for a Nikon to B4 mount. If I decide to go this route, would, in your or your technicians viewpoint, it be possible to use the Nikon 55mm Macro lens to filter screw into the Mini35 Configuration so that , well sorry, I can save momey viz the PRO35

I am also considering the Sony 990 1/2 inch medicam with the Pentax K mount which might screw into the Mini35 with the associated macro lens

What do you suggest, apart from PRO35 which will seriously eat into a three cam shoot



P+S academy is 27mm corner to corner :)




PPS Charles

the formula is FOV = 2*arctan (x/2f)

x = image diagonal
f = focal length
FOV = Field of View

Remember Acadamy sound track eats into FOV

[Charles Papert]

Thank you, gents.

I should have been more specific here, I was only referring to the Mini35 in practical use. So when I said that the still lens delivers a narrower field of view than a cine lens of the same focal length, I meant when attached to a Mini35: all I am interested is comparing the final image size that appears on the monitor.

The forumula I'm looking for would be a simple magnification factor for still lens to cine equivalent. Mizell, using your figures I came up with 1.6x for the factor: given that x=1/3 imager and is a constant, and the relationship between cine and still is 4.5x and 7.2x respectively, so dividing the two gives 1.6 as the magnification...am I doing that right? It seems closer than 2.7. By this logical, a 50mm still lens would give the same field of view as an 80mm cine lens. This feels right to me.

What I don't know is whether the edges of the image captured by the DV camera off the groundglass of the Mini35 has common framelines with that of a 35mm camera. If not, the mathematical formula will not be necessarily accurate. What this means is that a 50mm cine lens on the Mini35 will not necessarily deliver the field of view of that same lens mounted on a 435, given comparable presentation.

Probably the easiest way to test this is to line up a test chart on the Mini35 and then move the same lens over to a 435 or equivalent with the focus planes lined up neck by neck, and see what the images on the monitor deliver. Have to keep that in mind next time I check out one of these puppies at a rental house.

[Mizell Wilson]

1.6 definitely sounds closer to me, but I would have thought we were subtracting the variable rather then dividing. I'll see what Guy and I can work out today.

[Barry Green]

<<<-- Originally posted by Charles Papert :

By this logical, a 50mm still lens would give the same field of view as an 80mm cine lens. This feels right to me.

-->>>

Hi Charles,

Obviously I'm not following you here. A 50mm still lens is going to give the same field of view (on the mini35) as a 50mm cine lens.

We had the mini35 with two lens adapters: PL mount and Contax still-camera mount. I mounted an 85mm Ziess PL lens on it, then an 80mm Zeiss still lens on the Contax mount. The field of view was nearly identical.

The still lens projects a larger circle of illumination, but the mini35 only sees a 22 x 16mm window of that circle. The movie lens projects a smaller circle of illumination, which the mini35 sees all of.

So technically the still lens could display a wider field of view, but the mini35 doesn't see it, it only sees the center. Same as using a c-mount 18mm lens or a PL mount 25mm lens on a 16mm camera: the PL lens is going to have a larger circle of illumination, because it's designed to support the 35mm movie frame size, but the 16mm lens is only going to see the smaller central 10mm x 7.5mm window. Which is the same window that the c-mount lens would illuminate. And a 25mm lens on 16mm is going to look like a 25mm lens, whether it's PL mount, or c mount, or adapted from a still camera, it's still going to have the same DOF and FOV characteristics as any other 25mm lens.

But as far as field of view, once it hits the gate of the camera, lenses of equal focal length are going to deliver equal fields of view, whether they're sourced from still or cine cameras.

[Mizell Wilson]

Barry,

What we're trying to hash through is the conversion factor for achieving similar compositions between formats e.g. If I am shooting on my SLR with a 50mm, what lens would I need on my Arri 435 to achieve the same composition given the subject to focal plane distance is the same.

It has been determined through other posts and marketing materials the diff between 1/3" CCD and SLR 35mm is 7.2x and from 1/3" CCD to Academy 35mm is 4.5 (both approx.)

Let's say we are shooting with a 100mm lens on our 435. Given the same camera position, what lens would I need on my XL1s to achieve the same composition? Using our conversion factor, we come up with a 22mm.

To go the opposite direction, let's say we are shooting full zoom on the XL1s, or 88mm. To achieve the same composition on a 435 I'd have to be hanging a 400mm.

You are correct in saying that a focal length is a focal length is a focal length, there has just been much confusion about what a "conversion factor" is. Many people are told that if you use the mechanical adapters, like the Canon EF, that your lenses become more telephoto then you are used to, by 7.2x. The mis-information comes from the fact that, as we are all agreed, the focal length doesn't change, but since the chip is taking so much smaller of a cookie cutter, that the AoV changes, not the focal length.

The real problem is that these "conversion factors" get thrown around by too many people that don't have a 35mm motion picture or SLR background, making them (the conversion factors) useless. If you do not have an internal picture, as many operators and DPs have, of exactly what that lens' composition would be in one of the other formats, then don't worry about what the compostition would be in another format.

Hope this clears up the confusion.

mizell

[Mizell Wilson]

John,

To get back to your question about the lathe time, I'm still not quite sure what you're trying to achieve.

Could you please send Guy (guy@zgc.com) and I (mizell@zgc.com) a more detailed e-mail so we can address your issue.

thanks,

mizell