1/4 inch sensors. Even harder to shallow DOF?
 

It's hard enough with the 1/3rd inch sensors without a 35mm adaptor. Will it be even worse with the v1s chips?

The short answer is yes.

Depth of field basically is related to three things--aperture, distance of subject from background and size of the imaging area. The smaller the imaging area, the greater the depth of field. To minimize it you would have to shoot with your aperture wide open and move in significantly closer than the same shot you might do with a larger chip camera. For example, if you shoot a head and shoulders interview with a 1/3" chip camera, aperture wide open, your background will generally be soft enough to pop the foreground. With a 1/4" chip camera, to get the same effect you would have to make it a much tighter shot, just the head.

As you said, it's difficult with a 1/3" chip camera. I usually like a shallow depth of field when shooting interviews on location, because people are always walking by in the background. This is easy to do with a 2/3" chip camera, but often I'll do that kind of thing with a smaller camera. What I try to do is light the subject so the background will go down one to two stops. It's not the same as a shallow depth of field but does separate the subject adequately.

There was an article about still photography I saw last month with the headline: How Digital Photography Is Changing the Way We See Our World. It was about depth of field. Everybody's dumping their 35mm still cameras for 2/3" chip digital still cameras; and the same subject shot with a 2/3" chip camera is going to have a lot more dept of field than the same thing shot with a 35mm camera. We're accustomed to seeing pictures and films with backgrounds deliberately soft to direct our attention to the subject, but that is beginning to change with digital. Orson Welles would be a happy camper today. The thing that could change this trend in still photography, anyway, is that 35mm size chips are starting to appear in cameras like the Canon 5D.

If you wish to limit the depth of field (ie to have the subject rendered
sharply with the fore and background softly out of focus) you need to have
the following in place.

1) Use a camera with the biggest gate possible. A 10" x 8" plate camera is
best, a modern camcorder with 1"/6 chips is worst.

2) Use as long a focal length as possible

3) Use as wide an aperture as possible

4) Have the subject as close as possible

5) Have the background as far away as possible

6) Use the highest definition medium available

If you take a 35 mm film camera, it's 'standard lens' will be 50 mm, and can
be as wide as f/0.95 A 'standard' focal length on the TRV950 (say) is a
miniscule 3.6 mm, with a maximum aperture of f/1.6 - one and a half stops
smaller.

Back to item 6). I've only just added this to my DOF requirement list as
HDV has shown quite clearly that because the focused object is so much
sharper in HD than SD, the differential between sharp and unsharp is now
much more strikingly obvious.

tom.

To compare the DOF between 1/4" and 1/3" sensors I did some calculations:

Assuming you had this setup:

• FOV: 100mm lens (in 35mm terms)
• Aperture: f/2
• Distance to subject: 5 feet

The DOF would be:

1/4" sensor:

• Actual focal length: 10.4mm
• Circle of Confusion: 0.003
• Near focus distance: 4' 7.4"
• Far focus distance: 5' 5.5"
• Depth of field: 0' 10.1"

1/3" sensor:

• Actual focal length: 13.9mm
• Circle of Confusion: 0.004
• Near focus distance: 4' 8.5"
• Far focus distance: 5' 4"
• Depth of field: 0' 7.5"

Super35mm Cine:

• Actual focal length: 68mm
• Circle of Confusion: 0.019
• Near focus distance: 4' 11.3"
• Far focus distance: 5' 0.7"
• Depth of field: 0' 1.4"

Obviously the 1/4" sensor will have deeper DOF than a 1/3" sensor but at this subject distance and aperture, it is only about 35% more. Compare to Super35, the 1/3" sensor is about 535% more. IMO, the difference in DOF between 1/4" and 1/3" isn't really that as great.

DISCLAIMER: These DOF calculations are only valid for the shot setup I described. DOF does not change linearly so you'd have to do the calculations again if you wanted to check another setup. The circle of confusion for each format was also estimated. And feel free to re-check my calculations. It's always possible I made a mistake.

A 100mm lens at 5 feet is going to be a very tight shot.

Yeah, that is a fairy tight shot. I'm curious if it changes much so let's try it at 50mm and 5 feet:

Given:

• FOV: 50mm lens (in 35mm terms)
• Aperture: f/2
• Distance to subject: 5 feet

The DOF would be:

1/4" sensor:

• Actual focal length: 5.2mm
• Circle of Confusion: 0.003
• Near focus distance: 3' 8.9"
• Far focus distance: 7' 6.5"
• Depth of field: 3' 9.6"

1/3" sensor:

• Actual focal length: 6.9mm
• Circle of Confusion: 0.004
• Near focus distance: 3' 11.8"
• Far focus distance: 6' 8.5"
• Depth of field: 2' 8.7"

Super35mm Cine:

• Actual focal length: 34mm
• Circle of Confusion: 0.019
• Near focus distance: 4' 9.2"
• Far focus distance: 5' 3.1"
• Depth of field: 0' 5.9"

So in this shot, the DOF of 1/4" sensor is about 39% more than the 1/3" sensor. The 1/3" sensor is still about 5 times more than S35. This is all assuming I didn't make a mistake somewhere.

That's close to 40% more depth of field with the 1/4" sensor, which is quite a bit. I think throwing in super 35 confuses things a bit. There's already a pretty big difference between a 1/3" and a 2/3" chip's depth of field. Shooting with a 1/3" chip camera, it's difficult to soften the backgroun on most shots, unless you're shooting wide open with a pretty tight shot, like a head and shoulders interview, with the background well beyond the depth of field range. And even then, you can't blur it entirely as you can with a 2/3" chip camera under the same conditions. I think with a 1/4" chip camera you can forget about a soft focus background most of the time unless you use one of the spinning ground glass adapters.

And that's not a bad idea for people considering this camera. The Redrock M2 is about $1200, I believe. You can pick up old pre-AI Nikkor lenses really cheap. Instead of spending 500 bucks (or whatever the actual price may be) for the Sony wide angle adapter, spend more and get the Redrock and a Nikkor 24 or 28mm for you wide angle, a Nikkor 50mm and 105mm, and you'd be fixed for most of what you might want to do in terms of production. Maybe an 80mm too would be nice.

Fascinating! It's great to see the numbers. Is it possible to show comparisons for 1/4", 1/3" and 2/3" rather than/as well as Super35? How significant is the jump from 1/3" to 2/3"?

Many thanks, much appreciated.

I don't do the math, but the jump from 1/3" to 2/3" chips is probably bigger than the jump from 1/4" to 1/3" I think. Using his 50mm lens at 5', which is still pretty close, from 1/4" to 1/3" is 39%. I'd guess that from 1/3" to 2/3" would be closer to 50%, but that's just a guess.

When shooting with a 2/3" chip camera, I find it easy to soften the background when shooting interviews. I usually have to shoot at a -3db and use an external ND filter so I can go wide open. For a typical chest-up shot, it's easy to blur the background so you can't see people's expressions when they walk past. With a 1/3" chip camera, I can soften the background so the subject "pops," which is nice, but I can't blur it all the way out as with a 2/3" chip camera.

Bill,

I have been shooting Beta formats (SP, SX, DIGI) all my working life and to suddenly start using a z1 1/3" chip camera is a shock to the system, ignoring the obvious problems with button positions, lenses etc. it's the difficulty in getting a shallow DOF that's been to toughest to get used to. I understand all the maths and why but it does change the way you shoot substantially!

I have a Letus35 flip enhanced and it is very nice, of course it adds a lot to the length, weight and balance to the camera. Low light is bad news too. The problem with suggesting fixed length lenses above means you can't shoot like it's a video camera anymore, no quick reframes etc. Unless every shot and take is set up and planned you really do need a fast zoom lens for these GG adaptors. I have a 35-70mm, it's not long enough but it does give me that flexability I need if I am shooting an interview and need to tighten up or shooting something quite reactive...

You have a good point--nothing wrong at all with using a 35mm still camera zoom with something like the Letus, M2, etc. But the act of using one of those devices is going to slow you down--the combination of the weight and rails, and the upside down viewing is going to mean you're almost always on a tripod, rather than hand held guerrilla video style shooting. That 35-70 is a pretty good range for lots of normal shooting and would be a good lens to have. I'd say thorow in a 24mm and a 105 for the times you could use them.

I agree with you about culture shock. Every time I get involved with a small camera it's a new learning process. I can still move a lot faster with a 2/3" chip camera.

that's why i went with the flip letus! upside down on top of all the fiddly buttons, don't think i could have coped with that... makes me feel like a beginner again as it is! i have it on rails, and with a cavision rod type shoulder support. my god it is front heavy but it kinda works and it lets me take it off the tripod for handheld stuff. Shame there is no cheap and easy way to use it with my fig rig. With it mounted to my a1 i can take it off the shoulder support and almost use it like a director's viewfinder, just a fair bit bigger. I support the bottom of it with my right hand and focus with my left. You can get some effective guerrilla type shooting that way, don't think i will try that with my z1! Would need arms like Popeye for that!

A woman commented today that that was an amazing looking rig (yes, she used rig!) it certainly does look pretty serious!

The Letus flips the image right side up? I didn't know that. How do you find the image quality with it?

Most people using these gadgets seem to be attaching a 7" LCD monitor, upside down, over the camera, or out to the side. Zacuto makes a nice setup for that.

yeah it does and very well too, it adds a few more inches but it works well and i don't have the problem the producers having to turn the monitor upside down when they log the rushes off the tape!

Dennis Wood is making a flip module too for his Brevis, that would be worth looking at i imagine too!

That's good to know too. The Brevis looks very nice and eats up less light, from what I've read.

Glad to help! I ran the numbers for 2/3" below. I'm not exactly sure what the size of a 16:9 2/3" sensor is so I just used Fujinon's 35mm-to-2/3 16:9 multiplier factor of .254. From that I estimated the circle of confusion to be .0076.

For the heck of it, I also added 1/2" sensor based on Fujinon's 35mm-to-1/2 conversion factor of .178.

Here are the results:

Given:

• FOV: 50mm lens (in 35mm terms)
• Aperture: f/2
• Distance to subject: 5 feet

The DOF would be:

1/4" sensor:

• Actual focal length: 5.2mm
• Circle of Confusion: 0.003
• Near focus distance: 3' 8.9"
• Far focus distance: 7' 6.5"
• Depth of field: 3' 9.6"

1/3" sensor:

• Actual focal length: 6.9mm
• Circle of Confusion: 0.004
• Near focus distance: 3' 11.8"
• Far focus distance: 6' 8.5"
• Depth of field: 2' 8.7"

1/2" sensor:

• Actual focal length: 8.9mm
• Circle of Confusion: 0.005
• Near focus distance: 4' 2.4"
• Far focus distance: 6' 2.2"
• Depth of field: 1' 11.8"

2/3" sensor:

• Actual focal length: 12.7mm
• Circle of Confusion: 0.0076
• Near focus distance: 4' 4.5"
• Far focus distance: 5' 10"
• Depth of field: 1' 5.4"

Super35mm Cine:

• Actual focal length: 34mm
• Circle of Confusion: 0.019
• Near focus distance: 4' 9.2"
• Far focus distance: 5' 3.1"
• Depth of field: 0' 5.9"

If anyone sees any errors, please feel free to correct them.

It's got a 20x zoom lens, so shallow depth of field isn't too bad at all.

heath

That's right--if you want an ECU of a person's eyeball and nose, then the depth of field would be pretty shallow.

Quite right Bill. Heath - the longer the focal length of the lens the tighter you'll frame, that's all. You must combine this with big gates (chips) to get useful photographic differential focus.

tom.

With JVC's 30p one had to shoot in a manner appropriate to the frame-rate. With the V1, we will have to learn HOW to shoot with deep DOF.

But, I'll say that for every person who needs minimal DOF there are ten who will be shooting in situations where max DOF will save the shot by keeping good focus.

Minimal DOF is most relevant for those shooting 24p. For every person who shoots 24p, 100 or even a 1000 will be shooting 60i. IMHO, the future is HD at 720p60, 1080i60, and in late 2007 -- 1080p60.

I am constantly surprised by "filmmakers" shooting video trying to emulate the film medium of Hollywood. Personally I see these cameras a different medium in themselves and see the differences between film and video as positives to be explored rather than negatives to be worked around e.g. with expensive clunky 35mm adaptors. In my view the small, lightweight high quality camera packages are liberating and far outweigh the considerations of shallow depth of field.

Some of the greatest filmmakers and if not the finest of our time, Abbas Kiarostami, regularly use Deep Focus as a device.

...getting back on topic, I thought I read that the 1/4 inch chips were arranged such that their effective area was the same as 1/3 inch CCDs. I'm pretty sure I'm not going mad. Always a possibility though... But if true should mean little or no difference between DOF of previous cameras such as the Z1.

TT

Welcome to the marketing circle of confusion, Tony. If you haven't read Rushkoff in awhile, it might be a good time to pick up a copy of "Coercion." It's all about corporate control.

Sony does, indeed, say that by rotating the chips they get the same imaging area as with 1/3" chips. And my first thought was the same as yours: If that's true, then the depth of field should be the same too, and a 3.5mm lens should be a really nice wide angle lens. But it isn't and it isn't. That superwide lens, in fact, is very close to 40mm, in real lens terms. So, you're shooting with a 1/4" chip camera. Even Sony can't violate the laws of physics. Maybe the 1/4" CMOS chips provide a picture quality equivalent to 1/3" CCDs, but they're not the same size. There's electronic magic going on there that I could never hope to understand, but 1/4" is still 1/4". I'm not knocking the camera--hell, I might even buy one one of these days.

As far as emulating film look, that may be the reason some people use shallow depth of field. I don't. I use it selectively depending on the shot. For example, I had a shot of different size wine glasses lined up, a very tight shot, filling the frame. I shot wide open, dropping the background a couple of stops, backlighting the glasses and with about a 1 foot depth of field. That popped everything nicely. You can't do that with a 1/4" chip camera, or a 1/3" chip camera for that matter. Shallow depth of field can be very useful. When shooting interviews in public places, I like a shallow depth of field so when people walking by in the background look at the camera, you can't tell what they're doing. You can do that, just barely, with a 1/3" chip camera, but most likely not with 1/4".

I think if a guy wants to use a 1/4" chip camera for serious moviemaking, then he would be very interested in one of the spinning ground glass adapters. Not for everything, but for some shots. Those gadgets wouldn't be all that bad to use if they get the flip thing done. I've read that the Brevis may have a right-side-up model soon. If the V1 turns out to be a successful camera, which it very well might be, then I'd guess the sales of the ground glass adapters would soar. Time to dig through my old still camera bags and see how many pre-AI Nikkor lenses I can come up with....

You raise good points about limited DOF Bill, and here's another. Probably the most difficult image to successfully compress to MPEG2 for DVD is a field of waving grass. I've tried it and no way is it as smooth and clean as the original MiniDV master.

So to give DVD players an easier time, have as much of the frame as soft and blurry as you can make it - that way the compression gets used where it's needed, and BCU of faces with out of focus backgrounds and foregrounds look pin sharp and beautifully detailed.

tom.

True. Also in film-originated shots like that, when a person is running across the frame, the background is usually a little softer, so you don't really notice the strobing if the pan is too fast.

If somebody (like Redrock or Cinevate) would make a 35mm adapter than allows you to shoot right side up, then that would certainly make the V1 a much more desireable camera for low budget movie work. Same for any 1/3" chip camera. Shooting upside down isn't so bad, actually--it would be like using a view camera again.

The industry could build more versatile image flip functions in the cameras, not only EVF flip, but also actual image flip. Upside-down issue wouldn't be an issue, but for now, we have to deal with it.

Deep DOF is especially painful in wide shots in SD, when all the background details are in focus or so, but the camera resolves them like some sort of moving pulp. In HD it does not hurt so much. Background detail is resolved in much more pleasant way, but I absolutely don't mind larger sensors :) 1/3" vs 1/4" matters and 35mm adapter is not always handy.

yeah totally agree.

Such a shame sony went with 1/4 chips. Completely put me off. My Letus35 is great but heavy, cumbersome, fiddly and only for stuff close to me. So if I "running and gunning" I can't get something far away without taking the letus off. Not a simple thing with rods etc..

I think people's desire for 3CMOS 1/3in. cam stands a good probability of being satisfied within a number of months time. There's always a method to a company's apparent 'madness'..

just an opinion.

Hard to say, but it's possible. Sony invested in new technology and will probably wait to gain profit from that before introducing larger version. 1/4" ClearVids sit in FX7 also. Sony's choice of 1/4" size was primarily about cost effectiveness. 1/3" would bump up the price much more above XH-A1 level.

I agree. A 1"/4 chip has an area of 8,17 sq mm, whereas the 1"/3 chip has an area getting on for twice that: 14.52 sq mm.

Such a surface area demands a much bigger and heavier lens, as can be witnessed by comparing the TRV900's 12x zoom with that of the 12x zoom fitted to the VX2000.

tom.

Don't forget, it has a 20x lens so getting the shallow DOF isn't hard.

heath

Yes, but longer lens changes the perspective completely and it forces you to move the camera away from the object. Then we don't feel and don't perceive the images the same way as with the camera truly in close distance to objects.
There is a world of difference between true CU and zoom, even if both bring background out of focus similarly.

You miss the point Heath. It *is* hard, and the amount of zoom you have makes far less difference than the area of your chips.

Look at it this way. The max telephoto of the 12x zoom VX2100 (using 1"/3 chips) is 72 mm. The max telephoto of the 20x zoom FX7 (1"/4 chips) is 78 mm.

But the FX7 is f/2.8 at that focal length whereas the VX2100 is half a stop faster at f/2.4. There really is no contest - even with the 20x zoom the VX wins the differential focus competition hands down.

tom.

We have the camera right now and I was able to do some shallow DOF by zooming in and opening up the iris.

heath

If you zoom in tight enough you can get a shallow depth of field with any camera, but in practical use, you usually don't want to shoot that tight. If you want to check out something for yourself, zoom back to the widest angle you have, open up all the way, and move the camera in extremely close, so you have the same image area at wide angle as you did when zoomed in all the way. Your depth of field will be the same.

I know what you're saying Bill, but remember the FX7's lens is a good 1.5 stops faster at wide-angle than it is at telephoto. The dof will only be the same if you stop fown to f/2.8 at the wideangle end.

tom.

And, you can add an ND filter to enable you to open more.

BUT, remember, that you never want to shoot fully open with ANY lens.

And without doing the math -- you likely want to never close below f/5.6. This is also a function of chip size and it is f/8 for 1/3-inch cameras.

And, yes that means you should ideally shoot between f/3.6 and f/5.6. Just like a movie camera with a prime lens. :)

Except maybe high-speed primes at night, and that's only because you have to. And they're very expensive because they're designed to function well (as is technically possible) wide open. Depending on your settings, your DOF might be a couple of inches, requiring one darn good focus-puller.

I have a wide angle lens on my Panny GS, and I can usually get it to do a nice portait setup (subject in focus, background out).

what is a panasonic GS? If it is a 1/4 inch setup, surely you must be 3.5 miles away from your subject to get that effect!!

Just been viewing my first stuff shot on my Sony a1, letus35 adaptor on my hd tv. I was blown away by the fact I have lost very little detail, I just have a a really really beautiful shallow DOF now!

Derek, you may well have a wide-angle converter on your GS Panasonic (with its 1"/6 chips) but you're not using it in the wide-angle mode when you get that differential focus effect, now are you? Your converter is a zoom-through, right?

So take it off and zoom some more - that way you'll get shallower depth of field - but of course you'll have to crop your portraits a lot more.

tom.