Relative Focal Length, Angle of View, and CCF Chart

[J Davis]

relax barry, don't be on the defensive. I like your chart

[Ryan Patrick O'Hara]

Wonderful chart Barry, thanks for doing this. I'm sure the time you spent making the chart will save you 100x that in the long run.

Just curious about the equivalent focal length numbers, I was trying to do a quick conversion of the HPX-170 zoom lens range regarding FoV. I'm sure there are charts out there that include 1/3" chip cameras, but as your chart includes the AF-100, I am hoping to just confirm. Right now, I'm looking for zoom lenses for a possible documentary, and I'm quite happy with the range the HPX-170 has given me in the past.

My question is... should I simply divide the 2/3" chip information by two in order to attain the equivalent focal length in 1/3"?

This may see like an obvious, but if I recall, terms like 1/3" and 2/3" are not the exact size of the chips thus I'm not sure if a 50% reduction is the most accurate math.

Thoughts?

[Barry_Green]

I'd have to calculate it out. You'd be in the ballpark by dividing the 2/3" numbers, but it wouldn't be exact...

[Multi-Media]

Thanks for providing CLARITY where contention prevailed.

[groveChuck]

I was trying to do a quick conversion of the HPX-170 zoom lens range regarding FoV. I'm sure there are charts out there that include 1/3" chip cameras, but as your chart includes the AF-100, I am hoping to just confirm. Right now, I'm looking for zoom lenses for a possible documentary, and I'm quite happy with the range the HPX-170 has given me in the past.

I don't shoot 35mm motion, but started (many years ago) shooting 35mm film stills (that, and Super and Regular 8).
I've never weighed in on the "crop," FOV, etc. but that's my... "frame" of reference.
50 is medium ("normal" or close to the human eye), 28 is wide, 85+ tele.

But it's not just in the post-5D world that 35 stills (or FF) is used as a reference point.
B&H uses 35 stills for their 1/3" equivalents:

FROM B&H: Panasonic AG-HPX170
Lens Leica Dicomar 13x Zoom
3.9-51mm f/1.6-3.0
(35mm Equivalence 28-368mm)
72mm Filter Diameter

And I too like the HPX170 range.
So all I need is a Canon FD or EF 28-368mm, and while you're at it, can you make it a constant 2.8, please?

[Brian@202020]

B&H has a nice chart for stills cameras on their site to show the relative focal length needed on various stills cameras to achieve certain fields of view. But it's not very adaptable to the AF100 or cinema cameras.

Here I've put together a chart that shows the sensor sizes of common video and film formats, their Cinema Crop Factor as related to Academy Aperture 35mm Cinema Film frame size, and normalized for 16:9 image shape. It's not all that easy to put together a field of view chart when comparing different aspect ratios, so I normalized all the sensors for their widest 16:9-shaped field of view.

Without further adieu...
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I want one with all the RED ONE (4.5K, 4K, 3K, 2K) 16x9 sizes added as well as 1/4, 1/3, and 1/2 16x9 sizes. Also the exact 7D/t2i/60D, 1D, 5D, and Sony NEX 16x9 sizes would be nice, hell maybe the Nikon 16x9 sizes too. I might just make one. I'm a junky for numbers. Loved math class as a kid

[bhdfield]

I understand the x2 crop factor of the AF100 sensor. But I'm trying to wrap my head around whether that crop factor has any bearing on f-rating of the lens. So my 50mm f2 that I used on my Letus, will now have the effective focal length of 100mm on an AF100. But does that somehow mean that its DOF characteristics will be that of an f4? Or will its wide open DOF be the same as I had with it on the Letus? Sorry if that's a stupid question - my background is video, so I'm learning this stuff as I go.

[Barry_Green]

I think a wise investment in these days and ages, would be in the stocks of Tums and Rolaids. Because every time I hear the words "crop factor", I reach for an antacid...

Simple answer -- the crop factor doesn't change the imaging characteristics of the lens in any way. It only chops off the sides of the frame. So your 50mm lens will deliver 50mm DOF on any camera you put it on.

If you want to match 100mm/f4 "full frame" DOF, you could either doube the distance from the subject with the AF100 (but that'd change the perspective) or you could stay at the same position but open up the iris a couple of stops.

[RGBaker]

I understand the x2 crop factor of the AF100 sensor. But I'm trying to wrap my head around whether that crop factor has any bearing on f-rating of the lens. So my 50mm f2 that I used on my Letus, will now have the effective focal length of 100mm on an AF100. But does that somehow mean that its DOF characteristics will be that of an f4? Or will its wide open DOF be the same as I had with it on the Letus? Sorry if that's a stupid question - my background is video, so I'm learning this stuff as I go.

Yes, no and sort of.

The lens remains a 50mm f2. If you are using a 35mm still frame as your point of reference (and I understand -- we switched temperature scales over thirty years ago here, and I can talk Celsius with the best of them ... but I still convert quietly in my head to figure out what the temperature 'really' is) then yes, your angle of view is changed to effectively match that of a 100mm lens on a 35 still camera. But your aperture remains f4, and the depth of field calculation is still based on f4. But here the water muddies ...

As an example, the 50mm f2 lens focussed at 3 metres will have a depth of field of focus of 43cm (roughly 18 inch depth of field focussed at 10 feet) and you presumably know what field of view your lens delivers on a 35 still frame at that distance. The same lens, still 50mm and f2 but mounted on a device that delivers a 'crop factor of 2' (sorry Barry) still focussed at 3 metres will now have a depth of field of focus of 21cm (roughly 9 inch depth of field still at 10 feet) -- but your subject now is twice as big in the frame compared to your other camera. So to deliver the same field of view, and to have your subject fill the frame the same way, you'll have to double the distance to camera (assuming that's what you want) so now you move the sticks back to 6 metres and focus on the subject. The depth of field of a 50mm lens at f2 on a camera with a crop factor of 2 focussed at 6 metres is 86cm (near enough 30 inches at close to 19 feet). So the behaviour of the lens, though rigidly predictable, is not 'the same'. On the other hand, if instead of backing the sticks up you'd swapped lenses, putting a 25mm f2 lens on so the subject filled the frame the way you expected from your days as a 35mm stills photographer you'd still focus at 3m, still shoot at f2 ... but your depth of field would now be 90cm or very nearly 36 inches.

Shorter lenses will deliver wider angles of view; larger apertures (lower f numbers) will deliver shallower depths of field of focus ... but the precise details do need to be calculated based on the combination of focal length, aperture AND (sorry Barry) crop factor.

HTH

Cheers,
GB

[bhdfield]

LL 3 copy.jpg

Thanks for your very thorough reply! So, for the included example here, with a wall at my back (and in this case shot with a 50mm f2.8 wide open, mounted to a Letus/HVX shooting full frame), in order to create exactly the same look (in terms of DOF and subject size) on an AF100, I would need put on an even longer lens, like an 85mm and back way the hell up, through the walls (I say jokingly), thus giving me the same DOF and subject size. Obvioulsy I cannot shoot or move through solid walls, so if I want to shoot the same shot on my AF100, getting not only the same size of the subject, but also narrowing the DOF back down to what it had been here on my Letus, could I use a faster lens (say, a 25mm 1.4) opened wide, and then have something close to that shallow DOF I had with the 50mm 2.8/Letus? Is there a chart resource (or simple calculator software) that would allow me to calculate contingencies such as this? Published formulas? I know the sorts of shots I like to make, and what I needed to do to get that look with my current setup, but now I need to know what sort of lenses will allow me to achieve that kind of DOF with an AF100. Thanks for your info RGBaker, and Barry, I hate to make your head spin buddy, but there will be plenty of former HVX/ old ENG guys like me with these new cameras that will have to learn the ways of the still shooters. Thanks!

[RGBaker]

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Is there a chart resource (or simple calculator software) that would allow me to calculate contingencies such as this? Published formulas? I know the sorts of shots I like to make, and what I needed to do to get that look with my current setup, but now I need to know what sort of lenses will allow me to achieve that kind of DOF with an AF100. Thanks for your info RGBaker, and Barry, I hate to make your head spin buddy, but there will be plenty of former HVX/ old ENG guys like me with these new cameras that will have to learn the ways of the still shooters. Thanks!

If you've an iPhone there are apps that will do the depth of field calculation for you. Very handy. In the example you've given, I think maybe you are going the wrong way with lens suggestions? If the shot was originally a 50 @ 2.8 on 35FF at a distance (I'm guessing) of about 1m, you had a field of focus of about 6cm (ear to tip of nose), and you want to duplicate with an AF100 you'd be looking for a lens of roughly 28mm at a similar distance (I pick this rather than a 24 just because they are more common -- and because Barry has taught me that the actual crop factor comparing at 16:9 is actually 1.9) if you could select f2 you'd have a dof of 7cm. All near enough to make it work. A shorter lens would do the job, you'd have to stand a little closer and open it a little wider -- a longer lens say 35mm would force you to step back a little (maybe half a metre) but you'd get the same dof at f2.4. Where the short lens really let you down is when you are further from the subject -- a distance to subject of 4 metres and suddenly you've got a dof of almost 3 metres with a 20mm at f2.

There's an app for that -- in fact there are scores. Play with the free ones to see what you like -- some of the highly regarded ones cost a few bucks, though nothing ridiculous.

Cheers,
GB

[bhdfield]

Thanks so much GB. I am following your explanation and learning these photography basics. One thing that still puzzles is the fact that when I look at various DOF calculators, when you adjust the theoretical image sensor size, the DOF goes down with sensor size, given all other values remaining unchanged. This is counter intuitive to my basic understanding of issues of smaller sensors, but I understand we may not be comparing apples to apples in such a scenario. In fact, I can't figure out why these calculators would show any change of DOF with different sensor sizes at all. I would think (based on my limited understanding) that I could simulate what will happen with my Nikon lenses on the AF100, by simply using my Letus/HVX, and zooming in with the HVX on the Letus ground glass film plane to an area of approximately the same size as the AF100's sensor. Thus cropping the virtual "sensor" area. As Barry suggested, the DOF is the DOF being projected out the back of the lens, and DOF shouldn't change. It just lands on a smaller space. But alas, those DOF numbers change in the calculators when you change sensor size. Then I read about Circle of Confusion, appropriately named I think.

[tflak]

Thanks so much GB. I am following your explanation and learning these photography basics. One thing that still puzzles is the fact that when I look at various DOF calculators, when you adjust the theoretical image sensor size, the DOF goes down with sensor size, given all other values remaining unchanged. This is counter intuitive to my basic understanding of issues of smaller sensors, but I understand we may not be comparing apples to apples in such a scenario. In fact, I can't figure out why these calculators would show any change of DOF with different sensor sizes at all. I would think (based on my limited understanding) that I could simulate what will happen with my Nikon lenses on the AF100, by simply using my Letus/HVX, and zooming in with the HVX on the Letus ground glass film plane to an area of approximately the same size as the AF100's sensor. Thus cropping the virtual "sensor" area. As Barry suggested, the DOF is the DOF being projected out the back of the lens, and DOF shouldn't change. It just lands on a smaller space. But alas, those DOF numbers change in the calculators when you change sensor size. Then I read about Circle of Confusion, appropriately named I think.

I've been using a Circle of Confusion of 0.015 for the GH1 and it seems to have worked out pretty well in various DOF calculators.

[Darren Levine]

Great chart, good to see people talking about this topic, lotsa folks get very confused about it because of the lack of info, so this is great

[d.w.vaughn]

I ordered an AF100 (B&H tells me I am first on their list). My college-aged son will use it first for a movie project. I have an old FujiFilm S2Pro digital still camera with a crop factor of 2 (similar to the AF100 as compared to 35mm still film). Am I right that my son should be able to use the S2Pro with different Nikon lenses to scout locations and scene set ups and the S2Pro images should be very similar in terms of field of view and depth of focus to what he will get with the S2Pro? I believe so based on the discussion above but wanted to confirm. Thanks.