September 7, 2012

Watch This Zeiss Video to See Examples of Lens Focal Length and Angle of View on Full-Frame DSLRs

Crop factor is one of those terms that really shouldn't exist, but it does because it makes it very easy to immediately multiply what a particular lens will look like on a sensor that is smaller than full frame 35mm (or Vista Vision in motion picture terms). The correct term, angle of view, isn't used nearly as much thanks to the popularity of cameras like the Canon 5D Mark II, which uses lenses that have a larger diameter image circle than motion picture lenses do. Angle of view is platform agnostic, but crop factor is the term used everywhere (even by us, admittedly). Zeiss has made a video showing the angle of view of their full frame lenses mounted on a full frame camera. There is no crop factor since these are native lenses, but when we refer to crop factor, you can use the video below to see the equivalent focal length we're talking about.

I would like to never use crop factor again, since it changes depending on the lenses in question and the platform, but since it has become the standard online, it will be hard to move completely to angle of view. Either way, the video is a good representation of what you can get out of particular lenses depending on the chosen focal length and the format (full frame in this case). When talking about crop factor, for the most part it is related to these focal lengths and angle of views, so video can help give a clearer picture of exactly what we're talking about when we use that term.

For example, when we're discussing a camera like the Blackmagic Cinema Camera, we take about it having a 2.3x crop factor. This means that no matter what lens you mount on the camera, if you multiply the focal length by 2.3, you can use the video above to determine what that lens will look like on that camera. While this can get confusing, it's helpful for some people who have come over from DSLRs and have been only using full frame still lenses.

B&H also thinks we would be better off just using Angle of View, and here's a chart from Allan Weitz to show you exactly what's going on:

What do you guys think? Would you like to see all mention of crop factor go away? Should No Film School move to simply referring to lenses by the correct term, angle of view?

Links:

[via Carl Zeiss Lenses -- Twitter]

Your Comment

34 Comments

Hi, great article, as usual. Perhaps it would be ideal if you could tell all of us who are not yet familiar with the reason why one is the correct term and how the other originated. Thanks.

September 7, 2012 at 5:06PM, Edited September 4, 10:54AM

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Fernando

I'm not sure where it originated but it gained popularity with DSLR cameras when shooters needed a quick way to figure out how to understand the effective focal length of their old full frame lenses on their new APS-C digital cameras (which was the only option until a camera like the 5D).

Angle of view is the correct term because angle of view is a visual measurement that does not change - 1 Degree to 180 Degrees.

September 7, 2012 at 5:11PM, Edited September 4, 10:54AM

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Joe Marine
Camera Department

But you can't sell lenses by AOV...

September 7, 2012 at 6:58PM, Edited September 4, 10:54AM

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Pippy

I can see it both ways but, coming from a stills background where I shot nearly everything on a Nikon F2 and Kodachrome or Ektachrome, since I am so familiar with what a 50mm looks like on a full frame camera, 'crop factor' is an easy way for me to figure out what the field of view will be on any smaller sensor camera out there without actually having to look thru the viewfinder as long as someone can tell me what that 'crop factor' is. After all, we are, essentially, cropping into the image circle being projected into the camera from whichever lens is in question. So, I reckon I don't have a problem with the usage of 'crop factor'.

September 7, 2012 at 5:59PM, Edited September 4, 10:54AM

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dixter

I think the only thing wrong with referring to crop factors is that you are comparing to something that has never been a standard for film or video (aside from VistaVision). What's far more annoying is "35mm equivalent focal length". Focal length is focal length. It doesn't change because of your sensor and isn't a good substitute for an angle of view. So I would prefer to simply see an actual focal length and sensor size; i.e. 35mm/APS-C.

September 7, 2012 at 8:10PM, Edited September 4, 10:54AM

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In the long run crop factors are referring to what the image will look like. On set, when a director says "put a 25 up there and let's go" there's a shared knowledge of what the image will look like, given where the camera is located.

I've never used FOV to discuss shots and I haven't seen anyone who does. That doesn't mean that it doesn't happen. But it's kind of a moot point cause at the end of the day lenses will continue to be sold in metric and Directors and DPs will know that if they're shooting on a 60D, a "35mm" will look like a "56mm".

September 7, 2012 at 9:30PM, Edited September 4, 10:54AM

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Travis Jones

Actually Angle Of View is and has always been used in the feature film world, particularly by Set Designers and Production Designers when figuring out backings, estimating shot coverage, and designing effects shots like foreground miniatures and so on. Laying out shots by specifying angle of view is helpful when you're not sure what format is going to be used. Also, laying out or planning shots using architectural plan and a lens angle finder like this one: http://thedesignersassistant.com/2012/06/04/the-quick-view-ii-going-goin... , is a good way to see exactly where you're going to run into problems with a shoot, particularly at a practical location where you don't have wild walls like you would on a set. You'll know right away whether you can actually get that shot that's in your head.

September 13, 2012 at 3:54PM, Edited September 4, 10:54AM

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I like what Jay said above. But I don't mind crop factor. It sprang up out of the DSLR space. And that is essentially what is happening, You are not changing the effective focal length of the lens you are simply cropping the resultant image. As if you had a 35mm film camera and chose to crop out the center of the image to say the 1.6x for an APS-C. I have always had a problem with angle of view because the focal length of the lens does more than just change how much of the picture you can see, it changes the relationship of the foreground to the background, which does something different to the image than simply cropping a wider focal length. The issue for filmmakers is that the term "crop factor" is based on 35mm still camera's so we are talking about a system of knowledge and experience that is different than the standards in filmmaking and video. APS-C has a virtually no existant crop fact compared to Super 35 film stock. So in that world it has no crop factor.

But its something that is easy to understand. APS-C has a 1.6 crop factor, in reference to 35mm still film. That doesn't mean my 35mm lens now acts like my 50mm lens on my old Canon AE-1. it means I am cropping the resultant image by a factor of 1.6. Its just something to know and move on and make the images you want to make.

Now the fact that we call it a 35mm or a 50mm lens to begin with is false, because those are numbers that are not actual descriptors of the lens but an invented system to recreate the actual distance you placed the lens from the film plane on an old bellows camera. Now there's an interesting can of worms to open.

Or that the ISO settings are numbers that are invented because photographers were used to the old ASA system. there is no reason that were we inventing that on it's own we would have used that number system to describe some thing that is multiplying the sensitivity of the sensor.

or the fact that most all TV signals are 4 bits luminance channel and 2x 4 or 2 bit color channels. Color works in RBG, why not use 3 color channels. We use this system because of the hold over from Black and white TV. They had to be able to broadcast a signal that would not disrupt what the old B&W sets were doing but could add in the color information. That is changing with the advent of digital TV's and really the mandate on Digital broadcasting, but the legacy of that system is rampant on our codecs and how we compress video.

We are constantly plagues by old hold overs that are no longer relevant except for that that's what all the pros knew and didn't' want to have to learn a new system when it came out.

September 7, 2012 at 9:41PM, Edited September 4, 10:54AM

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That's just the way the game works. We can't completely re-invent the way people work every time technology takes a step forward. Then no one would be able to us it when it first comes out.

September 7, 2012 at 9:43PM, Edited September 4, 10:54AM

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The problem with crop factors is that they are different for almost every sensor out there. Check out the chart above - I updated with a link to a B&H article describing exactly what I'm talking about.

September 7, 2012 at 11:21PM, Edited September 4, 10:54AM

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Joe Marine
Camera Department

Yes the Crop factor is different for each camera, but the reference is the same. 35mm film. The thing is to know your camera and what it can do (read what are it's strengths and limitations). I think a lot of this will shake out as the tech get's cheaper. The Black Magic Cinema camera is a smaller sensor because it was what they could afford to hit the price point they wanted. I'm sure they would have rather used an APS-C or better a Super 35 sensor but, it was currently too expensive. This is still relatively new tech. These camera's came into their own in the last 8 years. 10 at most. It will shake out.

Also I don't see Angle of View as the 'correct' term. That doesn't describe the relationship of fore to background. And also some properties within the depth of field considerations.

Like I said. I don't consider my 50mm an 85mm cause I shoot on a 7D. I consider it a 50mm, that's been cropped by 1.6. I wish I could afford a full frame, but currently I can't. That's the deal. But I spend half my time as a photographer, so I have a different view than those who are only or primarily filmmakers.

September 7, 2012 at 11:52PM, Edited September 4, 10:54AM

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the measuring of the field of view of a sensor/lens in mm (and in 35mm equivalent mm) always sounded funny to me.

but i recently found out that not all same mm lens (on the same mm sensor) have the same field of view (measured in degrees).

whats worse is that i was searching for a measurement of a lens field of view in canon aps-c sensors (in degrees) and i couldnt find any.
most places didnt mention FOV in degrees and some that did, mentioned the number provided by the manufacturer (that was not correct) and not their own measurement.

we are all used to using mm and crop factors. thats ok. field or angle of view should not replace those numbers.
but i think lens reviews must have field of view measurements in degrees

September 7, 2012 at 10:22PM, Edited September 4, 10:54AM

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You know what's funny? You mention Field of View here, and maybe that's exactly what you meant to say, but most people confuse Field of View with Angle of View. They are both angles and have a relationship, but aren't the same measurement. This is a good explanation though:

http://martybugs.net/blog/blog.cgi/learning/Field-Of-View-And-More.html

I think when you make terms that are so easily misunderstood, they just fall out of use.

September 8, 2012 at 1:15AM, Edited September 4, 10:54AM

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Actually the post you link to specifically states that FOV is NOT an angle, whereas AOV is.

The internet is rife with confusion on this topic. So much so in fact, that I think the correct answer has been lost. You have Wikipedia stating that AOV and FOV can be used interchangeably, and yet they link to sources that clearly state they can't be. Some people claim FOV is an angular measurement, and some claim on AOV is, and that FOV should be a distance. It's a real mess :)

June 5, 2017 at 4:49PM

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Daniel
72

I found this interesting, crop factor works for me, but I can see the point of everyone speaking the same "industry talk" and using the same measurements. It's not always easy to get people to change. We still use foot, gal, inch, yards,mph in the US. Even when the rest of the world has gone metric. Changing an accepted terms is hard to do, but if you don't Then you get a world like we have in the US now where you end up needing both English and metric. We should have gone all metric years ago (IMO). As a manufacture of gear in the camera world we run into this all the time dealing with parts. Kind of funny when you think about it. Your have an all metric DSLR camera, but the tripod screw in the bottom is 1/4 inch x 20 English thread. How did that happen? Try and find 15mm raw aluminum rod in the US, good luck. In film making which is very much global now having everyone use the same terms would be best. It's the implementation of it that's hard to do.

September 8, 2012 at 8:32AM, Edited September 4, 10:54AM

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I wish you would use the cine term Super 35mm rather than the photo term APS or add it to the list. Super 35 was used before APS sensors first appeared and it comes from the cine world. Most movies from early 1990s to now were filmed on super 35mm.

September 8, 2012 at 9:00AM, Edited September 4, 10:54AM

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tttulio

Honestly, I think this just has the potential to confues things further. Crop factor and focal length are solid standards, and contain a lot more information than just the AOV. It also tells you about depth of field for instance.

Besides this, in many cases switching to AOV won't help anyway. Plenty of people use full frame lenses on APS-C for instance, in which case you need to apply the crop factor. And that could be confusing since you need to know whether it's a full-frame or APS-C lens to work out what the AOV is going to be. Focal length is useful precisely because it doesn't depend on what camera you use it on. You know what the lens is, you know what your crop factor is, job done.

Furthermore, an understanding of focal length and crop factors, I feel, significantly improves your understanding of optics and photography. It's important to understand aperture, depth of field, compression and so forth.

September 8, 2012 at 9:27AM, Edited September 4, 10:54AM

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Luke

AOV is an interesting measurement but iplimenting it as a standard would be practically impossible. If I am shootong Canon APS-C and my director asks for 46 degree AOC prime (50mm full frame equivalent) just where am I going to find a 31.3 mm lens?

Or is the suggestion that lens manfacturers make a 46 degree lens for every format?

September 8, 2012 at 12:29PM, Edited September 4, 10:54AM

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Matt

No, you would never refer to lenses by their angle of view, the angle of view is used to know how wide a particular lens would be on your particular format.

September 8, 2012 at 2:24PM, Edited September 4, 10:54AM

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Joe Marine
Camera Department

Just talk in full frame (35mm) equivalent focal distances and every MFT or APS-C owner knows how to do the math on his own (and what lens to put on for each shot).. it is not rocket science
(for all my lenses, i know what the FF equivalent is)

September 8, 2012 at 12:46PM, Edited September 4, 10:54AM

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Jay

Since some have brought up the subject of lens compression (optical), if a 50mm lens from the FF world is placed in front of a Super 35 sensor, it's angle of view is more like that of a 75mm lens, correct? Approximately 1.5 crop factor.

I would like to know then, will that 50mm, now being cropped in camera by the sensor size, yield the same or different optical compression as a 75mm lens (if that focal length actually exists) on a FF camera? Or, will the inherent optical compression of any particular lens remain the same, regardless of crop factor? I would assume the latter but, would love to hear from an expert on optical properties.

September 8, 2012 at 1:53PM, Edited September 4, 10:54AM

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dixter

Short answer: a 50mm on a 1.5 crop will give exactly the same image as a 75mm on full frame (with the single exception of depth of field).

Compression is not actually an optical factor per se. It's more to do with distance and perspective. Things which are far away tend to be compressed as our perception of space is kinda logarithmic. If you think about how perspective works this makes sense; imagine a grid at ground level extending into the distance. As the horizontal lines get further away, they take up less and less space. The nearest two lines to you might be separated by, say, 5 degrees of your AOV, but the furthest ones are all bunched up together. It's down to trigonometry.

So, farther things are compressed. Thus it's not your focal length that matters, really, but your distance to subject. Focal length effectively draws attention to compression, however, since you're only looking at things which are further away. You can see this in a wide angle still - crop and enlarge something further away, and you'll see compression. This is exactly what crop factor does.

Um... that got longer than I planned. Hope it's relatively clear...

September 9, 2012 at 5:11PM, Edited September 4, 10:54AM

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Luke

It does make sense relatively...
So, are you saying that, if someone painted a huge grid on the ground at the salt flats in Utah, and I photographed it from eye level with a 75MM lens on a FF camera and then, a 50mm lens on a 1.5 crop factor sensor, the lines would look different on each image?

September 9, 2012 at 10:11PM, Edited September 4, 10:54AM

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dixter

And, will the 50mm on the 1.5 crop factor sensor have more or less DOF than the 75mm on FF if both are set to the same aperture? I'm assuming the 75mm on FF would have less but, I really couldn't say...

September 9, 2012 at 10:20PM, Edited September 4, 10:54AM

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dixter

what's interesting to me is that nobody talks about how crop factor changes depth of field (DOF), which changes with crop factor as well. If I shoot on FF with 35mm lens set to f4.0, then to get everything equal on APS-C, I need 24mm lens set at f2.8.

This creates problem for crop factors above 1.6.

On Black Magic Cinema 2.3x crop factor to get equivalent DOF to Full Frame 35mm lens set at f4.0 ( which is my favorite setting ) you would need lens 15mm with f1.4 which doesn't really exists.

FF 24mm set at f4 would need on BMC 10mm set at f1.4....

So DOF needs to be recalculated as well when moving between crop factors.

September 8, 2012 at 5:16PM, Edited September 4, 10:54AM

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Everything apart from DOF looks identical. Perspective, AOV, compression etc. Compression is a function of perspective and distance; to frame the same shot with 75mm FF and 50mm 1.5 crop your setup is exactly the same (distance to subject etc) so those factors are the same.

Focal length only affects two things; depth of field and "zoom". Zoom is identical to cropping an image (albeit in reality cropping changes resolution, but I'm talking theoretically), hence crop factor.

Depth of field is a function of focal length, aperture, and focal distance. Increasing focal length decreases DOF. Increasing focal distance increases DOF. Increasing aperture (decreasing f-stop) decreases DOF. Crop factor therefore doesn't affect DOF. However it means you use a wider lens to achieve the same shot; this is a decrease in focal length and therefore an increase in DOF. Thus DOF is deeper FOR THE SAME SHOT on a crop sensor, but this is only because you're using a different lens.

September 10, 2012 at 1:17PM, Edited September 4, 10:54AM

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Luke

Sorry, that was meant to be a reply to dixter!

September 10, 2012 at 1:18PM, Edited September 4, 10:54AM

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Luke

Okay, I've got to jump in on this one. Now, don't take this as an assertion of facts, but my understanding is that the only way focal length influences depth of field is through background magnification. I have not tested this myself, but I have watched tests wherein the same shot is taken with two different focal length lenses, but identical aperture and focal distance. The depth of field on the longer lens appears shallower than the shorter lens, but when background objects in the frame are compared on a 1:1 pixel basis, they are identically soft. The difference in the shorter lens is a lack of magnification, which optically makes background objects appear sharper. Now clearly as a DP you are concerned with the whole image, and your subjects are either sharp or not, but...it does make me question the above conclusion that the only difference between the 50mm and the 75mm would be DOF. I'm not sure there would be any appreciable difference beyond optical inconsistencies between the lenses themselves. That's theory though. If anyone has actually tested this I would like to see it.

September 11, 2012 at 1:18AM, Edited September 4, 10:54AM

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I'm not quite sure what you're suggesting. You say that the DOF does appear shallower, but things are just as soft as each other?

Regardless however, it's unassailably true that the same frame, shot with 50mm on a 1.5 and 75mm on FF, will have shallower DOF on the 75mm lens. This is why phone cameras have extremely deep DOF, and more expensive, larger-sensor cameras have shallow DOF.

September 11, 2012 at 12:04PM, Edited September 4, 10:54AM

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Luke

I guess what I'm saying is that I have read very strong assertions that focal length does not in fact affect DOF. It is something photographers used to argue about endlessly. For example:

http://www.film-and-video.com/dofmyth.htm
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
http://www.luminous-landscape.com/tutorials/dof2.shtml

Now, you make a good point because observably, large sensor cameras (because they are using longer focal length lenses) are capable of shallower depth of field. You really can't argue with that, and it would seem to contradict the above arguments. To that end, I dug further and started reading a very technical paper published by Zeiss themselves.

http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_35_Bokeh_EN/$File/CLN35_Bokeh_en.pdf

It seems to say that these guys have a point, but there is more to it....then launches into some physics and geometry that goes over my head. I'll have to spend some time on this one with a dictionary and a math textbook. We'll see....

September 11, 2012 at 2:52PM, Edited September 4, 10:54AM

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It's just occurred to me that by "background magnification" you perhaps are talking about compression again? If so, this doesn't change anything - as I've explained above, compression is a function of distance and perspective, not focal length; nor does it "interact" with DOF. Applying a crop factor affects compression identically to increasing focal length.

September 11, 2012 at 12:10PM, Edited September 4, 10:54AM

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Luke

I started with a DSLR and in my oppinion you learn the tools your working with and adjust to it. I do spend a lot of time trying to learn what the profesional standards are and adhere to them as much as possible for the day I upgrade to a Pro Video camera and I want my product to be as profesional as possible you have to make adjustments because the crop factor focal length does'nt have exactly the same look as a lens with the equivalent focal length on a full frame so you go for a look you like with what you have and keep every thing adjusted to get your framing compatible with how a fullframe shot would look on screen and do the best you can and hope that your audience will like it. I plan my shots with that in mind and my results are not bad not what I wihs for but good enough while I am learning the craft. one thing I recently learned after a very kind person let me try 1 of his L series lenses on my T3i is even my Rebel can get a very good shot when all camera settings and setup are right a good lens makes a world of difference the quality of the video clip was far better than anything I have done before the clarity was outstanding so for you guys like me still using standard canon glass invest in better glass as soon as your pocketbook can handel it now Im really motivated.

September 13, 2012 at 4:29PM, Edited September 4, 10:54AM

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Gary Simmons

This is quite handy tool for comparing FOV on different cameras >> http://www.abelcine.com/fov/

September 14, 2012 at 9:16AM, Edited September 4, 10:54AM

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Janitor

I don't mind using crop factor, because I don't know the angle of view of a 30mm on my APS-C camera - but I know what it looks like. So with crop factor I can determine the angle of view better, because I can compare it to my knowledge of how the picture looks on my camera. I still don't know the numbers for the angle of view.

However I wouldn't mind learning the angle of view numbers if everybody changed their mind and used angle of view in degrees from now on. It would just mean I'd have to learn how many degrees my 30 or 50mm show on my APS-C camera - then I'd have that reference again and I'd be able to compare it to other sensor sizes and focal lengths.

The biggest problem with crop factor and "35mm equivalent" is that people think a 50mm on APS-C "equals" a 85mm on full frame. That is truely not the case, because the 50mm is still a 50mm on every sensor, and that means it is still not a good portrait lens, although the angle of view on APS-C is the same as the angle of view of an 85mm on FF.
If people got that distinction, then it doesn't matter what words we use to compare lenses and sensors, I think.

September 14, 2012 at 10:23AM, Edited September 4, 10:54AM

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Heiko

On the contrary, in terms of being a "good portrait lens", 50mm on an crop DOES "equal" 85 on full frame. The only thing that's different is depth of field. What makes a good portrait lens is perspective. Perspective depends on distance to subject, NOT focal length.

The appealing thing about an 85mm on full frame is that it "flattens" a face due to compression. That compression is only there because for the same framing, you must be further away with an 85mm than with, say, a 50mm. A crop factor does exactly the same thing - with a 50mm on a crop you must be the same distance away to achieve that framing, so the compression and perspective is the same as an 85mm on full frame. Again, the ONLY thing that changes is DOF.

September 15, 2012 at 9:49AM, Edited September 4, 10:54AM

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Luke