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    #31
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    Combat - you touched on the hot button issue of "equivalence". You are correct and people just do not want to hear it. They want to see f2.8 on their lens. DOF is the only constant in the imaging world and it would be great if everything was re-tooled to reflect that - I just bought a 10cm DOF lens... But, it will never happen.


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    #32
    Senior Member puredrifting's Avatar
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    Quote Originally Posted by Bassman2003 View Post
    Combat - you touched on the hot button issue of "equivalence". You are correct and people just do not want to hear it. They want to see f2.8 on their lens. DOF is the only constant in the imaging world and it would be great if everything was re-tooled to reflect that - I just bought a 10cm DOF lens... But, it will never happen.
    Isn't DOF always a variable? Always dependent on FOV, imager size, focal length, subject to focal plane distance?
    It's a business first and a creative outlet second.
    G.A.S. destroys lives. Stop buying gear that doesn't make you money.


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    #33
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    Depth of field is a product of: (1) f-stop, (2) focal length, and (3) focal distance.

    Sorry, my last post was simplistic. Even accounting for f-stop, a lens for a bigger sensor would still be bigger and heavier, because of the greater focal lengths. Instead of a 7-140mm, you have a 14-280mm.

    Now the interesting thing to me is that the physical diameter of the apertures would be the same. A 25mm f/2 and a 50mm f/4 both have an aperture 12.5mm in diameter. If you wanted that 50mm to also be f/2, then its aperture would have to be 25mm. That's double the diameter of the shorter lens, which is quadruple the area. That's why these lenses for larger sensors get big fast (I think). I'm not a lensmaker, and there seems to be many other variables. Some 25mm lenses are bigger than 50mm lenses, for instance.

    All that to say, I think I largely agree with those who wish more was done with the 4/3 format --- not only by Panasonic but the other manufacturers. It is an open format, so more makers could have taken it up, and our lives would have been easier. Instead most continue to make their own lens mounts.


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    #34
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    Quote Originally Posted by morgan_moore View Post
    THis looks good - at 1lb five elements and designed for the job it should be better than the internal dubler.

    ONe thing Im not up to speed on is the 2/3 lenses are (or are not??) landing the coloured light at different planes to function with three chips. (This would cause colour fringing on a single chip - my 'film' was abound with colour fringes amongst many abberations)
    Yes, most B4 lenses were designed for cameras with three 2/3-inch sensors and a prism to split the incoming light into RGB wavelengths for each.

    The better B4 mount optical adapters for single-chip sensors will correct for this design of the B4 lenses.

    For example, IBE Optics makes B4 to single chip conversion lens adapters for both Micro 4/3 and Super 35 image circles, although they tend to be kind of expensive. The Micro 4/3 variant (model HDx2 Mark II) has a 2.2x conversion and sells for about $2500: https://www.ibe-optics.com/en/produc...-mark-ii-10171

    The B4 to PL mount adapter for Super 35 sensors (HDx35 Mark III) has a 2.7x conversion and goes for about $4300: https://www.abelcine.com/buy/lenses-...ptical-adapter


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    #35
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    Quote Originally Posted by puredrifting View Post
    Isn't DOF always a variable? Always dependent on FOV, imager size, focal length, subject to focal plane distance?
    I do not see it as a variable in its absolute form - usage. A FF camera with a certain f-stop lens at a certain FL & distance creates a certain amount of area in focus. Then take a different camera/lens and recreate that certain amount of area in focus. The two cameras might have different numbers and sensor sizes but the user/buyer can judge how easy for difficult it was for that camera/lens to achieve the area in focus.

    Basically, f2.8 on a FF camera is not the same as f2.8 on a 1" sensor etc... One could easily see this if they were compared with the DOF number at the given aperture of f2.8 Sort of like a guide number for a flash. Very complex but as ISO improves, DOF will become pretty much the only separator between cameras, sensors and lenses.


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    #36
    Senior Member Run&Gun's Avatar
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    Quote Originally Posted by davedv View Post
    Yes, most B4 lenses were designed for cameras with three 2/3-inch sensors and a prism to split the incoming light into RGB wavelengths for each.

    The better B4 mount optical adapters for single-chip sensors will correct for this design of the B4 lenses.

    For example, IBE Optics makes B4 to single chip conversion lens adapters for both Micro 4/3 and Super 35 image circles, although they tend to be kind of expensive. The Micro 4/3 variant (model HDx2 Mark II) has a 2.2x conversion and sells for about $2500: https://www.ibe-optics.com/en/produc...-mark-ii-10171

    The B4 to PL mount adapter for Super 35 sensors (HDx35 Mark III) has a 2.7x conversion and goes for about $4300: https://www.abelcine.com/buy/lenses-...ptical-adapter
    The HDx35 was worth every penny I paid for it, however long ago that was, now. And I think it was even more back then. Maybe closer to $5K, if memory serves... I think at the time, the Fuji 19-90 was the only “ENG” option for s35 cams. But I think I’ve only used it a few times since getting the 17-120, several years ago.


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    #37
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    Quote Originally Posted by Bassman2003 View Post
    I do not see it as a variable in its absolute form - usage. A FF camera with a certain f-stop lens at a certain FL & distance creates a certain amount of area in focus.
    Well, knowing the focal length and aperture is all you need to know to ascertain how much DOF it will have.

    But yeah - I could see an additional figure being offered. A number that indicates how much DOF there is at maximum aperture and a fixed distance to make it easier for the buyer to compare. But...how often are people choosing between different formats anyway? If you're shopping options within the same format, it's irrelevant. And would they report the figure based on a fixed focus distance from the sensor or based on a focus distance that offers a medium shot of a person with that FOV.


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    #38
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    Yes, it is more of a buyer's tool or a way to counteract some marketing. But as evidenced by Canon releasing f11 long lens primes, clean high ISOs are changing the game. Who cares if you have an f2.8 or f4 lens in terms of light gathering, DOF is kind of the only separator.


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    #39
    Senior Member ahalpert's Avatar
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    Quote Originally Posted by Bassman2003 View Post
    Yes, it is more of a buyer's tool or a way to counteract some marketing. But as evidenced by Canon releasing f11 long lens primes, clean high ISOs are changing the game. Who cares if you have an f2.8 or f4 lens in terms of light gathering, DOF is kind of the only separator.
    Eh....it depends on how clean you want your footage and also the lighting conditions you'll be shooting in. There will always be a penalty or at least a difference to pushing the ISO. Even the vaunted abilities of the A7SIII are heavily aided by noise reduction, which, of course, softens the footage.

    f/11 will probably always be a daylight lens IMO. And the additional challenge is that if you're shooting stills of birds in flight, you really want to keep your shutter speed very high. I really think that the only reason they launched those lenses was because the faster variants are ungodly expensive, large, and heavy. But it just so happens that such lenses are often used in bright daylight conditions anyways.

    I think people get a bit absolutist about things like - oh, now you can push the ISO so you don't need to worry about aperture. Everything is on a spectrum and there will always be a threshold for acceptability. On my S1 at ISO 51200 shooting HD 60p 1/120 f/2 on dark dance floors, there was an acceptable level of noise for the application (wedding films). But not for most narrative film standards and probably not for most documentary standards if you were shooting/displaying in 4K at large viewing sizes. I couldn't even acceptably film those scenes at f/4 or I would have stayed on my 24-105 the whole time.

    But sure, it becomes easier and easier to use a slower lens.


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    Quote Originally Posted by ahalpert View Post
    Well, knowing the focal length and aperture is all you need to know to ascertain how much DOF it will have.
    And focal distance. If you focus the lens on something far away, the depth of field is deeper than if you focus on something up close. That's why the old cinematography depth-of-field charts included focal distance (example).

    For example, if you focus on something 6' away, your DOF might be 3'. But if you focus on something 16' away, your DOF might be 10'.

    Each lens has a certain focal distance where DOF is at its maximum. Some people might think it is when you set the lens to infinity, but actually it is a little bit less than infinity, and it is called the hyperfocal distance.


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