I have no idea how you could have come across two 500mm lenses, except one isn't really a 500mm. If you have a moment, send a link to the product's page on Adorama or B&H or Amazon or wherever you like, so I can see what you're looking at, because I have never seen a "full-frame-equivalent focal length" used in place of the actual focal length of a lens. Canon doesn't, and I suspect Nikon doesn't either.
On May 29, 2012, at 1:04 PM, Howard Jones wrote: > Ok then explain to me why I have a 500 mm lens that fits my Nikon that will > give the same as a 750mm lens designed for the camera. The sensor has cropped > the image coming through the back of the lens and effectively changed the > focal length. > > I can buy a 500mm lens designed for my camera and that will give me the field > of view of a 500mm. > > So I now can have 2 500 mm lenses on the same camera but with completely > different results depending on which one I use. > > I assume I'm missing something here, but as there are 2 lens types available > for my camera, one designed for it and one that happens to use the same mount > both 500mm isn't there 2 possible results from a '500mm ' lens? > > It's this scenario I'm talking about, and I believe the one that has sparked > the thread in the first place. > > H > > From: Joe Laude <[email protected]>; > To: Nuke user discussion <[email protected]>; > Subject: Re: [Nuke-users] Arri Alexa sensor size - camera tracking question > Sent: Tue, May 29, 2012 9:50:20 AM > > Alex is correct. The cone of light coming through the lens doesn't change > because of the sensor. The sensor determines how much of that light is > recorded as an image, but an 18 is an 18 on any sensor. A bigger sensor will > give you a wider fov when you're shooting, but that's irrelevant to the > figures you put into Nuke after it's been shot. The lens is still an 18mm > lens, and you don't need to convert it to something else. > > Joe Laude > (507) 251-7006 > Sent from my iPhone > > On May 29, 2012, at 1:49 AM, Alex Fry <[email protected]> wrote: > >> It doesn't matter what sensor the lens is designed for, it's focal length >> remains the same. It is what it is. >> >> What are you basing 27mm on? A crop factor of 1.5? Relative to what? A 35mm >> still camera? >> >> 35mm stills equivalent focal length descriptions should have no place in a >> discussion about tracking footage from a movie camera, they only exist as a >> crutch for stills photographers who grew up using their focal lengths as >> working slang to describe a particular field of view. >> >> >> >> On 29/05/2012, at 6:23 PM, Howard Jones <[email protected]> wrote: >> >>> I'd agree with Randy here. If the 18mm prime is not designed for the film >>> back then it would have an equivalent focal length of, in your example of >>> 27mm (though that is just based on your example. ) >>> >>> However if it is a prime lens designed for the chip, then it is an 18mm >>> lens, so no conversion necessary. >>> >>> However again, the solve you would get should work either way, but the >>> relation between the point cloud and camera will vary and will begin to be >>> an issue for objects that should be close to the camera. >>> >>> That is you can double a focal length and move an object twice as far away >>> in nuke and it should look the same, except for objects very close, when >>> distortion artefacts creep in, and I don't mean lens distortion >>> characteristics here before any one jumps in, I mean if you stick a sphere >>> right next to the lens and have a super wide angle, that isn't the same as >>> an object further away with say a standard lens size. (eg 50mm for 35) >>> >>> So you can track and try 2 solves with 2 different lens lengths, and if >>> there are objects close to camera you should see a difference in shape of >>> any test spheres etc, otherwise it should still lock. >>> >>> I couldn't find anything quickly online to confirm your film back sizes, >>> but someone has created a whole set of presets for cameras (Nathan?) which >>> are very useful on nukepedia. >>> >>> H >>> >>> From: [email protected] <[email protected]>; >>> To: Nuke user discussion <[email protected]>; >>> Subject: Re: [Nuke-users] Arri Alexa sensor size - camera tracking question >>> Sent: Tue, May 29, 2012 7:21:12 AM >>> >>> He is right. >>> >>> T-Mobile. America’s First Nationwide 4G Network >>> >>> ----- Reply message ----- >>> From: "Darren Coombes" <[email protected]> >>> To: "Nuke user discussion" <[email protected]> >>> Subject: [Nuke-users] Arri Alexa sensor size - camera tracking question >>> Date: Tue, May 29, 2012 01:01 >>> >>> >>> Thanks for the reply Alex, I'll have a look. We have someone here saying >>> that the 18mm lens would not be an 18mm lens in our tracker settings, I >>> just want to make sure what they are saying is right. >>> >>> Cheers. >>> D. >>> >>> On 29/05/2012, at 4:57 PM, Alex Fry wrote: >>> >>>> The "crop factor" is described by the sensor measurements you input. >>>> Your 18mm lens is still 18mm, no conversion is necessary, your field of >>>> view has changed, but not your focal length.. >>>> An 18mm lens has a different field of view if its mounted on micro4/3, DX, >>>> super35, 35 stills, 70mm or medium format, but it remains an 18mm lens. >>>> >>>> Have a play with Nuke's camera node, tweaking the focal length, haperture >>>> & vaperture knobs to get a feel for the relationship they have to each >>>> other. >>>> >>>> -Alex >>>> >>>> On 29/05/2012, at 4:27 PM, Darren Coombes <[email protected]> >>>> wrote: >>>> >>>>> Hi, we have some plates shot with the alexa on a 18mm prime lens. >>>>> I Need to camera track this material. >>>>> >>>>> On the Arri website, it says the sensor size for the alexa is 23.76 x >>>>> 13.37mm when using the ARRIRAW setting with 1.78:1 aspect ratio. >>>>> >>>>> in the camera tracker settings, would I put the film back size as 23.76 x >>>>> 13.37mm? >>>>> And then I guess i need to find out the crop factor for that sensor size >>>>> and use that when entering the focal length of the lens? >>>>> >>>>> So if we shot on a 18mm lens, and theoretically the crop factor was 1.5 >>>>> (not sure what the actual crop factor is yet), you would times 18 x1.5? >>>>> and that would give the right focal length? >>>>> >>>>> Can someone point me in the right direction with this? and is my theory >>>>> of this right? or am i missing something? >>>>> >>>>> Thanks. >>>>> >>>>> Darren. >>>>> >>>>> >>>>> >>>>> Darren Coombes >>>>> >>>>> Compositor >>>>> >>>>> www.resolutiondesign.com.au >>>>> >>>>> >>>>> resolution: sydney australia tel: +61 2 9360 9908 fax: +61 >>>>> 2 9360 8908 >>>>> 22 burton st: east sydney: 2010 post office box: 614 darlinghurst: 1300 >>>>> abn: 3305 196 1856 >>>>> >>>>> 2010 Silver One Show Entertainment Award: Online Branded Entertainment >>>>> 2009 Gold Promax/BDA Award: Best Broadcast Design Image Spot >>>>> 2009 Winner Creative Review Hotshop Award: Post Production / VFX >>>>> 2009 Finalist Creative Review Hotshop Award: Broadcast Design >>>>> >>>>> >>>>> The information transmitted, together with the attachments, is intended >>>>> only for the person or entity to which it is addressed and may contain >>>>> confidential and/or priviliged material which may be subject to >>>>> copyright. Any review, retransmission or other use of, or taking of any >>>>> action in reliance upon, this information by persons or entities other >>>>> than the intended recipient is prohibited. If you received this in error, >>>>> please contact the sender and delete the material from any computer or >>>>> network. No warranty is given by the sender that any attachments to this >>>>> email are free from viruses or other defects. >>>>> >>>>> >>>>> <Unknown.jpeg> >>>>> >>>>> _______________________________________________ >>>>> Nuke-users mailing list >>>>> [email protected], http://forums.thefoundry.co.uk/ >>>>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >>>> _______________________________________________ >>>> Nuke-users mailing list >>>> [email protected], http://forums.thefoundry.co.uk/ >>>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >>> >>> Darren Coombes >>> Compositor >>> >>> www.resolutiondesign.com.au >>> >>> >>> resolution: sydney australia tel: +61 2 9360 9908 fax: +61 2 >>> 9360 8908 >>> 22 burton st: east sydney: 2010 post office box: 614 darlinghurst: 1300 >>> abn: 3305 196 1856 >>> >>> 2010 Silver One Show Entertainment Award: Online Branded Entertainment >>> 2009 Gold Promax/BDA Award: Best Broadcast Design Image Spot >>> 2009 Winner Creative Review Hotshop Award: Post Production / VFX >>> 2009 Finalist Creative Review Hotshop Award: Broadcast Design >>> >>> >>> The information transmitted, together with the attachments, is intended >>> only for the person or entity to which it is addressed and may contain >>> confidential and/or priviliged material which may be subject to copyright. >>> Any review, retransmission or other use of, or taking of any action in >>> reliance upon, this information by persons or entities other than the >>> intended recipient is prohibited. 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