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JVC PL Adapter questions


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#1 Ben Saunders

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Posted 05 May 2009 - 10:01 AM

I have a couple of questions about the JVC PL Cine lens adapter:

-The adapter is meant for 16mm lenses. What is the result when 35mm lenses are used instead? My best guess is that the focal length effectively (almost) doubles, but the dof stays the same. Is that correct? I'm trying to figure it out so I can reliably calculate for framing and dof.

-I'm also looking for input as to how the adapter affects light. Using the same lighting setup I compared the adapter with a cine lens to the regular 18x zoom lens. To get the same exposure levels the zoom lens was opened up several more stops than the cine lens. This seems counterintuitive and I'm hoping someone with experience with the adapter can help (Tim?)

-Thanks!
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#2 Rohan Dadswell

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Posted 23 May 2009 - 04:11 AM

I haven't had a chance to test the PL Cine lens adapter yet but as far as lenses go - a 50mm lens is a 50mm lens. (a 25mm is a 25mm, a 100mm is a 100mm etc.)
A 50mm lens designed for 35mm will give you the same field of view & the same depth of field as a lens designed for 16mm cameras when used on the same camera.
The differences come from when the field of view of a 50mm lens on a 35mm camera is compared to the same lens on a 16mm camera.
So you shouldn't have to change any calculations for your framing or DoF - just use 16mm camera settings

Edited by Rohan Dadswell, 23 May 2009 - 04:15 AM.

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#3 Lew Fraga

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Posted 24 July 2009 - 12:02 PM

I'm having this same debate myself - do I go with the lens I already own (Ang 25-250 w/PL mount), or buy/rent one MADE for 16mm. I want to buy the PL mount adapter, but not sure just how severe a crop it will be.

While a 50mm lens (or ANY lens for that matter) won't "change focal length" there WILL be a crop - THIS is the question Ben wants answered. The shorthand is to say there is a focal magnification - like the 1.5x magnification factor describing 35mm lenses used on APS-C DSLRs - when in fact there's no change in focal length, but a cropping of the image - therefore "equivalent to" a focal length change/magnification.

(see attached image - if this works)

The only way I'm going to know for sure how severe the cropping will be is by getting the adapter in my hands andd slapping on my lens.

I want the more shallow DoF from my Ang lens, but I just may have to get a "made for 16mm lens" because the cropping might make mine unusable.

-Lew

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#4 Mitch Gross

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Posted 24 July 2009 - 12:41 PM

It is not that complicated. A given focal length -- say a 25mm -- will look the same on this adapter whether it is a lens designed to project to the 16mm sized image area or the 35mm sized image area. You just won't be using that extra projection. Your 25-250 zoom will look the same as it would if you stuck it onto a 16mm camera, which has a much smaller image area than a 35mm camera. On a 16mm camera, the lens that would give the similar Field of View to a 25-250 on a 35mm camera would be about a 12-120.

The depth of field and field of view characteristics are not locked together on this adapter because it uses arial imaging instead of projecting onto a surface and rephotographing like a Mini35, Letus or RedRock Micro does. The field of view will be the same as 16mm, but the depth of field will be that of the camera's original 1/3" sensor. The point of this adaptor is not to affect depth of field, it is to allow the use of superior optics.

There are a couple of bonuses to using a true arial imaging adaptor. The first is that the image quality is outstanding, with excellent resolving power and contrast. Another is that because in the end it is essentially a big magnifying glass, taking a large image and squeezing it down to a smaller area, it effectively brightens the image by about a stop and a half. Compare this to rephotographing devices that always consume light.
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#5 Lew Fraga

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Posted 27 July 2009 - 06:59 PM

I fully understand that the optics of each lens used will not change - from focal length to depth of field. The answer I've literally been looking for is very simple, but (and please understand I've had this frustrating conversation many times with people) the answers given to me are just the ones above - versions of "focal length doesn't change" or "lens characteristics don't change".

Here is the exact question I'd LOVE to have answered - looking at the above image for illustrative purposes, what might the crop be when using a 35mm motion picture film zoom lens (as opposed to one specifically designed for versions of 16mm - standard or Super16)?

The crop - and ONLY the crop - are the questions I have about this adapter.

The above image is as literal as I could illustrate it - the size of the projection is for a MUCH larger imaging area - therefore cropped when using a smaller imaging DEVICE - get it? My worry is that after spending $4k just so I can slap my 25-250 on there, the actual image recorded by the camera will be such a teeny fraction of the whole lens' capable projection that it's worthless.

A second question - which might clear up what I'm asking, or give a different perspective - is of the adapter itself - is there a relay/resizing/enlarging or shrinking lens element which when using a lens designed for 35mm film that would resize the image to the pore appropriate imaging size of a 1/3" CCD?

-Lew
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#6 Mitch Gross

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Posted 28 July 2009 - 12:05 PM

Lew, I'm trying to make it as simple as possible. If you want to get a general sense of what the field of view would be using this adapter on a 1/3" camera such as the JVC, look at the image from your 25-250 on a 35mm camera and then divide the image into four: halfway left/right and halfway top/bottom. One of these quarters is about what you'll get.
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#7 Lew Fraga

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Posted 28 July 2009 - 12:48 PM

Ah yes - sorry - I get it now - it really IS that severe, but in a different way of gauging it.

Well, looks like I either drop the notion of getting the PL adapter, or add the notion of getting a lens designed for 16mm cameras...

Thanks Mitch-

-Lew
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#8 Ben Saunders

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Posted 04 August 2009 - 09:06 AM

I must disagree with Mitch-there is a significant difference in depth of field when using this adapter. The adapter provides 16mm depth of field, which is quite a bit shallower than that of the 1/3" chip sensor with a standard video lens. Tim Dashwood did extensive tests in a review of the adapter that showed a big difference in the depth of field characteristics. I can send or post a link if you'd like to look at it (he has pictures).
As for framing, I have found a way to account for the cropping. When renting 35mm lenses I put the focal length of the lens in the 16mm window of my director's finder. I've found that to be pretty accurate. Hope that helps.

Edited by Ben Saunders, 04 August 2009 - 09:09 AM.

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#9 Mitch Gross

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Posted 05 August 2009 - 11:22 AM

Tim was incorrect. The adapter is an arial imager and therefore does not alter the depth of field of the camera sensor because there is no rephotographing going on, only demagnification. This is physics. There is no magic going on here. The only possible change in apparent depth of field is that in using high quality optics instead of the "free" inexpensive zoom included with the camera, the improved resolving capabilities of the glass can make the difference between what is and is not in focus more apparent, thereby creating the perception of a shallower depth of field.
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#10 Lew Fraga

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Posted 05 August 2009 - 01:04 PM

"...does not alter the depth of field of the camera sensor because there is no rephotographing going on, only demagnification. This is physics."

Hang on - first part incorrect (unless that isn't what you literally meant), second part right.

The incorrect part (again, unless that isn't what you literally meant) - no one is saying it alters the depth of field of the sensor because depth of field is not dependent on the sensor, or even the sensor size - it is dependent on the physics of the lens being used (hence, the second part "right").

While I don't own my Eclair ACL anymore, I could tell a DEFINITE difference between the DoF characteristics of my Ang 12-120, and my 25-250 on an Arri 35III when the shots were framed the same.

THIS is why I would prefer to use my lens designed for 35mm motion picture film rather than a lens designed for 16mm/S16mm motion picture film. The smaller the destination size (image sensor/CCD/film frame - doesn't matter) the lens is designed for, it will inherently have a deeper DoF. The larger the destination size, it will inherently have a shallower DoF. Ever use medium format lenses on an IMAX camera - or just on a medium format camera for that matter - it's really shallow and a nightmare to pull focus on the fly. And using a large format camera you have to work VERY hard at getting a head and shoulder shot completely in focus - that's a LOT of light to get a deep enough f-stop.

It IS physics, but the sensor itself does not in any way define the DoF - the design of the lens being used does.

Objects further away from the focal plane in my 12-120 were still fairly focused at T4 while the same shot (framing and distance from camera) with my 25-250 at T4 had those objects definitely more out of focus. BUT, at least using the 12-120 they would go out of focus MORE than with my lens that came with the HD110 - which is where the desire for a film lens adapter comes in.

If this wasn't true, there wouldn't be this emerging business of trying to come up with the best one (P+S, RedRock, Letus, Brevis, etc).

-Lew

Edited by Lew Fraga, 05 August 2009 - 01:06 PM.

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#11 Tim Carroll

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Posted 05 August 2009 - 07:15 PM

The incorrect part (again, unless that isn't what you literally meant) - no one is saying it alters the depth of field of the sensor because depth of field is not dependent on the sensor, or even the sensor size - it is dependent on the physics of the lens being used (hence, the second part "right").

While I don't own my Eclair ACL anymore, I could tell a DEFINITE difference between the DoF characteristics of my Ang 12-120, and my 25-250 on an Arri 35III when the shots were framed the same.


Boy, you guys are really confusing yourselves. Mitch is dead on right. The size of the sensor TOTALLY effects the Depth of Field. Just like the size of the film image TOTALLY effects the Depth of Field.

Lew, you are looking at this from some bassakwards angle when you make that statement "I could tell a DEFINITE difference between the DoF characteristics of my Ang 12-120 (on your Eclair ACL), and my 25-250 on an Arri 35III when the shots were framed the same." Of course you could tell the difference, the image size on the film of your ARRI 35III is like four times the image size on your Eclair ACL, that is why the DOF is so much shallower on the 35mm film compared to the 16mm film. It's got nothing to do with the lens design. Using your ACL, if you took that 25-250 lens and set if at 25mm, with a Tstop of 4, and take the 12-120 lens and set it at 25mm, with a Tstop of 4, you would have the exact same depth of field on the image captured on your 16mm film. Doesn't matter which lens, size of captured image on the film makes the difference with Depth of Field.

Same with digital sensors.

The reason the depth of field is shallower when you use one of those RedRock or P+S adapters is because the adapter focuses the image on a ground glass that is the same size as a 35mm frame of film, which is much larger than your 1/3 or 2/3 inch sensor. You are just photographing the 35mm size image on the ground glass, you are capturing that larger image, with all it's shallow depth of field, with the sensor on your camera. That is why the depth of field is more shallow.

Best,
-Tim
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#12 Lew Fraga

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Posted 05 August 2009 - 09:44 PM

Okay - first lemme say I get what you're saying. If the 12-120 were zoomed in to 25, it should have pretty much the same characteristics as the 25-250 at 25.

I have noticed it to be different - that's what I'm saying, yes. That the bigger format lens gave me a shallower Depth of Field.

Yes, I'm arguing that the image capturing area (the actual sensor or film behind the gate) itself is not "in itself" what determines the Depth of Field (I know you realize that as well - it's part of my misunderstanding of that statement that I want to understand your point and why I'm still at it - undoubtedly very annoying, I know, sorry) because in my feeble mind it's merely where the image being projected by the lens "lands" regardless of how large an image circle the lens was designed to project - the above attached picture is what I'm getting at as far as that notion. If you attach a PL mount adapter to any 16mm camera, mount a 35mm camera designed lens, it will project a much larger image circle than needed - resulting in a "cropping" for the final exposed image.

The back-theory behind my continued arguing is about framing/Field of View between different format cameras and their corresponding lenses - in the same tight room, with the same camera placement, you will end up with different focal lengths per format to achieve the same Field of view, and yes, I'm agreeing the larger the intended format, the shallower your Depth of Field will get for that same Field of View (which is where I think I'm looking from the opposite end from what you're saying and not seeing the common ground). And if proven wrong, I will appropriately bow my head and say "thank you" - just saying that what I've noticed between the cameras was when going up to 35, the same framing of a shot gave me a shallower Depth of Field (which to me was a more pleasant image). Maybe this was entirely my perception, but it's what I saw and felt I got. Not mm, but framing.

This is also why I feel Tim Dashwood had a noticeable shallow Depth of Field in comparison to using 1/3" format intended video lenses.

The main thought/problem/challenge in my responses is the desire to use lenses designed for larger formats/projection circles on a teeny little actual capturing area.

Yes, I'm stuck on the lenses - based on them being designed for larger or smaller formats - which is also why I'm arguing about the adapter systems (Letus, Brevis, etc.) thought. I'm about to get nit-picky - understand that this is for clarification - not the "adapter", but the lens in front projects the image onto a ground glass. And yes, I agree the lens in front was designed to project a much larger image circle - larger format. And the lens in front (PL mount 35mm based, Nikon, Canon, whatever you use), for the same Field of view with a stock video lens, will give you a more shallow Depth of Field

The lens photographing the ground glass is not determining the Depth of Field, and neither is the CCD/CMOS sensor, the lens projecting onto the ground glass is determining that (the lens capturing/photographing/framing the ground glass itself is merely photographing a flat field, yes) - the point of those adapters is to use the FRONT lens' characteristics which are not easily (if ever) achieved with the video lenses. The final recorded image will be exactly the same if recorded on 2/3" or 1/3" CCDs - they are merely recording what the lens at the very front is projecting, and you merely frame the ground glass to get the same crop.

And when using the PL mount adapter (going back and denoting the original post) from JVC, if I were to slap my 25-250 on there, I would never be able to get a wide angle view. The PL mount adapter was with the intention of using flavors of lenses designed for use with 16mm - not 35mm (@ 4x larger projected area).

Yes, it's very possible I'm arguing the same thing but from the opposite end as though it were different - I'm actually trying to figure that out over this thread because I know it HAS become confusing to me at least. Yes, I know there is too much mis-information around (especially on the web), which is why everyone here wants to make sure they have it right. I'm obviously a little confused and I want to make sure I have it right - sorry for the headache.

-Lew

Edited by Lew Fraga, 05 August 2009 - 09:48 PM.

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#13 Tim Carroll

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Posted 05 August 2009 - 10:10 PM

Lew,

This is the last post I am going to do on this topic. Not sure why you're not getting this, but there are only so many ways to try to explain it and we all only have so much time in the day.

Here's an explanation from Wikipedia, maybe it will make more sense to you.

DOF vs. format size

To a first approximation, DOF is inversely proportional to format size. More precisely, if photographs with the same final-image size are taken in two different camera formats at the same subject distance with the same field of view and f-number, the DOF is, to a first approximation, inversely proportional to the format size. Strictly speaking, this is true only when the subject distance is large in comparison with the focal length and small in comparison with the hyperfocal distance, for both formats, but it nonetheless is generally useful for comparing results obtained from different formats.

To maintain the same field of view, the lens focal lengths must be in proportion to the format sizes. Assuming, for purposes of comparison, that the 4×5 format is four times the size of 35 mm format, if a 4×5 camera used a 300 mm lens, a 35 mm camera would need a 75 mm lens for the same field of view. For the same f-number, the image made with the 35 mm camera would have four times the DOF of the image made with the 4×5 camera.

In many cases, the DOF is fixed by the requirements of the desired image. For a given DOF and field of view, the required f-number is proportional to the format size. For example, if a 35 mm camera required f/11, a 4×5 camera would require f/45 to give the same DOF. For the same ISO speed, the exposure time on the 4×5 would be sixteen times as long; if the 35 camera required 1/250 second, the 4×5 camera would require 1/15 second. The longer exposure time with the larger camera might result in motion blur, especially with windy conditions, a moving subject, or an unsteady camera. Adjusting the f-number to the camera format is equivalent to maintaining the same absolute aperture diameter.

The greater DOF with the smaller format can be either an advantage or a disadvantage, depending on the desired effect. For the same amount of foreground and background blur, a small-format camera requires a smaller f-number and allows a shorter exposure time than a large-format camera; however, many point-and-shoot digital cameras cannot provide a very shallow DOF. For example, a point-and-shoot digital camera with a 1/1.8″ sensor (7.18 mm × 5.32 mm) at a normal focal length and f/2.8 has the same DOF as a 35 mm camera with a normal lens at f/13.


http://en.wikipedia..../Depth_of_field

Best,
-Tim
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#14 Lew Fraga

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Posted 05 August 2009 - 11:27 PM

Tim-

I actually came back downstairs because I just realized the opposite side - yeah, my total experiences and thoughts are based on using the lenses FOR their destined format sizes. Because yes, if you take a 50mm lens for 6x7, a 50mm lens for 645, a 50mm lens for 35mm, and a 50mm lens for 16mm, and capture them (if you magically find the adapters) on the 16mm film frame you will end up with the same image.

So yeah, you're right, I was looking at it backwards - trying to figure out how it would apply if an adapter could project the entire lens' projected image circle to a smaller size captured by the recording format (in this case a 1/3" sensor). If I could get the same framing with larger format designed lenses, basically (Mamyia 50mm for an RZ lens has a 81 degree angle view, and a Nikon 50mm lens have a 46 degree angle view - but given their target recording format you will be physically closer or further away to get the same shot - hence the change in DoF).

I haven't read your post yet because I'm sure you're right. So, bowing head, saying "thank you" and now I'm gonna go back and read your post.

Again, sorry for the headache-

-Lew
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