MFT only with manual iris lens ?

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Gabriele Turchi

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MFT only with manual iris lens ?

PostSun Dec 30, 2012 11:23 am

Just read this on prolost blog

""""you’ll find that the “dumb” MFT mount won’t control your sealed-up, no-manual-iris-ring lenses. So the MFT BMC will only work with the subset if MFT glass that has a manual iris ring. Or, more likely, you’ll use the MFT mount as a permanent home for a PL-mount adapter. At which point you will be back to selecting among lenses optimized for a larger sensor"""""

is it true ? so only manual iris lenses ?


ps: i am not familiar with MTF lenses " when for a lens spec they write : 15mm --->equivalent to 30 mm (in 35mm format) it means that visually looks like having a 30mm mounted on a full 35mm format ? if yes : a normal wide angle on MTF would be a 10mm ? (but those are listed as fish eye ...)

thanks

g
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Christian Schmeer

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 12:14 pm

Hi, yes it's not possible to use automatic MFT lenses, as the MFT lens mount on the BMCC is passive (=does not control the iris or focus automatically, as there are no electronics).

The real focal length of a 15mm lens used on a BMCC would be 34.5mm because of the BMCC's small sensor (15mm x 2.3 crop factor)
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Gabriele Turchi

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 1:24 pm

thanks christian

but here is my doubt : a MTF panasonic 15mm lens mounted on the BMCC MTF : does it look like a Canon 15mm lens mounted on a 5D full frame ?

meaning : is a 15mm MTF lens a very wide angle lens ? (all the 10mm MTF are declared fish eye ..)

thanks

g
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Elliott Balsley

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 4:13 pm

Gabriele Turchi wrote:a MTF panasonic 15mm lens mounted on the BMCC MTF : does it look like a Canon 15mm lens mounted on a 5D full frame ?

No. A 15mm lens on a 5D will give a much wider field of view than the same 15mm lens on the BMCC (or any other 16mm sized sensor). The 5D is even larger than 35mm movie film.

Gabriele Turchi wrote:is a 15mm MTF lens a very wide angle lens ? (all the 10mm MTF are declared fish eye ..)

Where did you hear that? There are a few MFT lenses in that range that are not fisheye. Many of them are zooms, and there aren't a ton to choose from, but you can find many threads about this topic. For example: Panasonic 7-14mm f/4 or the Olympus 12mm f/2.
Whether or not a lens is considered a fisheye is not necessarily correlated with focal length (although it usually is). At this extreme wide focal length, it's difficult to build a lens that keeps lines straight. That might explain why you are finding more fisheyes than normal lenses.
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Gabriele Turchi

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 4:32 pm

Elliott Balsley wrote:No. A 15mm lens on a 5D will give a much wider field of view than the same 15mm lens on the BMCC (or any other 16mm sized sensor). The 5D is even larger than 35mm movie film.


This is a bit confusing to me ..(because you mention the same lens , but i mean 2 lenses )

What i mean is :

15mm MTF Panasonic Lens on Blackmagic MTF mount Camera FOV
vs
15mm canon lens on a canon Full Frame camera FOV

so you are saying that the canon lens on the canon camera would have much wider FOV?

ps: on B&H , searching for all the MTF lens , anything below 10mm (and even 10mm) is called fisheye ..

thanks

g
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Elliott Balsley

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 4:48 pm

A 15mm is a 15mm, no matter what kind of mount it has. The difference would be the size of the area it can fill on the sensor. So while the Panasonic lens might not cover the whole sensor of a Canon 5D, the Canon lens will certainly cover the BMCC sensor, and the FOV will be the same between the two lenses.

Cheers
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Gabriele Turchi

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 5:31 pm

i see ..

thanks

i tough because of the fact that those lenses are built for smaller sensor , the naming (like 15mm in this case ) are adapted to the standard (in this case Micro four thirds ) ...

so i guess that to have a wide angle lens on MTF a 8mm is needed ...

are u sure that 8mm that not distort the image exist ?

thanks

g
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Elliott Balsley

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 7:49 pm

Micro 4/3 is a very new mount, so the lens choices are limited. But people have been shooting on 16mm for a long time, so there are hundreds of wide angle lenses for this format. There are also a plethora of B4 mount lenses for 2/3" HD cameras.
For example, the Zeiss Ultra 16 set goes as wide as 6mm.
One benefit of the MFT mount is that it can accept adapters for almost any kind of mount, so you can use older PL lenses, etc. I'm not very familiar with the current lineup of MFT lenses, so I couldn't help you there. But for comparing focal lengths between formats, I would recommend the pCam app for iPhone.
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rick.lang

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 9:40 pm

Gabriele Turchi wrote:thanks christian

but here is my doubt : a MTF panasonic 15mm lens mounted on the BMCC MTF : does it look like a Canon 15mm lens mounted on a 5D full frame ?

meaning : is a 15mm MTF lens a very wide angle lens ? (all the 10mm MTF are declared fish eye ..)

thanks

g


This may help you visualize the different field-of-view a given focal length can have on various size sensors:
http://www.abelcine.com/fov/

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Gabriele Turchi

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 11:02 pm

thanks rick

i was familiar with that calculator ,
what i was uncertain was if lenses made for other standard are named (focal length) in relation of the standard , but i guess not

ps: the FOV calculator is great , but a bit miss leading in this circumstance because for example lenses made for MFT (for example 8mm ) won't work on 35mm , so those will be the equivalent of the wider (without distortion ) lenses for 35mm

even tough i am not sure about 8mm lenses for MTF that have no distortion , but other members here said that exist

thanks to all
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rick.lang

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 11:44 pm

Gabriele Turchi wrote:thanks rick

i was familiar with that calculator ,
what i was uncertain was if lenses made for other standard are named (focal length) in relation of the standard , but i guess not

ps: the FOV calculator is great , but a bit miss leading in this circumstance because for example lenses made for MFT (for example 8mm ) won't work on 35mm , so those will be the equivalent of the wider (without distortion ) lenses for 35mm

even tough i am not sure about 8mm lenses for MTF that have no distortion , but other members here said that exist

thanks to all


You just need to remind yourself that the focal length posted on the lens is the same focal length on any camera regardless of whether it is mounted on a full-frame 5D or a MFT or a S16 sensor. The FOV you capture on the different sensors is determined by the physical dimensions of the active sensor area. The smaller the sensor, the smaller the FOV for a given lens.

As you point out, not all lenses will have a large enough image circle to cover all sensors. For example, a Canon EF 25mm lens is designed to cover all sensors up to the full-frame size. But if you mount that 25mm lens on a true MFT camera, the FOV is halved on the smaller sensor and the image captured will be as if you had cropped the lens by a factor of 2. The image and FOV will look as if it was a Canon 50mm lens but remember it is still a 25mm lens.

A lens like the Canon EF-S 18-55mm is designed for the smaller APS-C sensor. Te image circle will not fill a full-frame sensor, but the focal length is 18mm regardless. The widest part of the lens is 18mm but the sensor has a smaller diagonal and results in a smaller FOV as if you were seeing a crop of 1.6 so you can think of the lens as behaving as if it were 29-88mm lens in terms of FOV.

On the BMCC as you know the FOV is reduced by a factor of just under 2.3 so a lens with a true focal length of 15mm will capture a smaller image due to the 2.3x smaller FOV. So the image FOV looks as if it was a 34mm lens mounted on a full-frame camera.

This is an oversimplification of comparing the image on various sensor sizes just to try to clarify the issue of FOV. It gets more complicated when you discuss perspective which is different than FOV. As I understand it, if you really wanted to duplicate the perspective you would see from a full-frame sensor on the BMCC's sensor, you would need to physically back away from your subject 2.3x the distance you had placed the full-frame camera. Hope I have that right. Not always going to be possible of course but may be practical for medium to close-ups. Or block your talent to suit the lens.

As for the very wide lenses, true they are often fish-eye lenses and that may be an effect you want. But if you want your vertical lines to look straighter, then check to see the lens specifies it is a rectilinear lens. Most rectilinear lenses will still have some distortion (perhaps you are familiar with the terms pin-cushion or barrel effect) but the best lenses will have no discernible distortion.

Rick Lang
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adamroberts

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Re: MFT only with manual iris lens ?

PostSun Dec 30, 2012 11:53 pm

I posted a long explanation about focal lengths in this thread with many addition post by other that will probably be helpful:
viewtopic.php?t=3649
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Elliott Balsley

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Re: MFT only with manual iris lens ?

PostMon Dec 31, 2012 10:25 am

Rick, I disagree with you about the perspective thing. If you change the focal distance (subject to camera), the perspective will change, along with the psychological impact of the shot. Keeping the same focal distance will match perspective between two different sensor sizes, provided the FOV matches.
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rick.lang

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Re: MFT only with manual iris lens ?

PostMon Dec 31, 2012 5:11 pm

Elliott Balsley wrote:Rick, I disagree with you about the perspective thing. If you change the focal distance (subject to camera), the perspective will change, along with the psychological impact of the shot. Keeping the same focal distance will match perspective between two different sensor sizes, provided the FOV matches.


Elliot, I was thinking of the situation where you use the same lens on a full-frame sensor and the BMCC for instance. So the FOV is changed if you keep the cameras at the same distance from the subject. If you wanted the BMCC to emulate the same view and perspective, I thought you would need to back up 2.3x the distance to the subject. I can see backing up would give you the same view but also see the perspective may be different for example a face will appear more flattened as you back away even though the face fills the same portion of the image seen.

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