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

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Old October 13th, 2006, 09:18 AM   #1
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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?
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Old October 13th, 2006, 09:45 AM   #2
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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.
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Old October 13th, 2006, 09:55 AM   #3
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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.
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Old October 13th, 2006, 11:59 AM   #4
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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.
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Old October 13th, 2006, 12:19 PM   #5
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A 100mm lens at 5 feet is going to be a very tight shot.
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Old October 13th, 2006, 12:49 PM   #6
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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.
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Old October 13th, 2006, 01:08 PM   #7
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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.
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Old October 13th, 2006, 02:51 PM   #8
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Quote:
Originally Posted by Tim N Le
I'm curious if it changes much so let's try it at 50mm and 5 feet...
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.
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Old October 13th, 2006, 03:04 PM   #9
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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.
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Old October 13th, 2006, 03:45 PM   #10
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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...
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Old October 13th, 2006, 04:10 PM   #11
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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.
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Old October 13th, 2006, 04:21 PM   #12
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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!
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Old October 13th, 2006, 04:34 PM   #13
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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.
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Old October 13th, 2006, 04:36 PM   #14
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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!
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Old October 13th, 2006, 04:40 PM   #15
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That's good to know too. The Brevis looks very nice and eats up less light, from what I've read.
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