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Old December 1st, 2010, 08:28 AM   #1
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Quality of footage beyond f.4

Hi,

I wonder if someone can give me some practical advice; Iíve searched these pages to find some resolution but to no avail as yet!

I understand that my V1 is not going to be the best camcorder to use in low-light situations, however, when I use it indoors, without 3 redheads or other video lighting, Iím going to need to open my aperture beyond f4.

But when I do, the resulting image is far too fuzzy and soft to be classed as ďHigh DefinitionĒ, in my opinion. Some users seem to suggest that this is a unique attribute of this camera, and have used it to positive effect, like softening faces of people. However, surely only having nice, crisp images when the aperture is closed upwards of f4 canít be right?

Can someone tell me if thereís a setting I can change to enable the image to retain itís crispness - and HD quality - with the aperture open wide? I havenít even started using the gain yet!

Thanks very much
Steve
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Old December 1st, 2010, 11:26 PM   #2
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Steve, I sold my V1 a while back but from my recollection I never noticed any softness beyond f4. That is pretty surprising to me. The only issue I ever had was a mis-adjusted back focus which Sony Service fixed for me.
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Old December 29th, 2010, 11:44 AM   #3
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Steve - something's really amiss if you find wide apertures soft on your V1, and I suspect that it's either a back-focus issue (return to Sony for a fix) or the camera's suffered a fall and the lens is out of alignment with the chip block assembly (highly unlikely).

Modern camcorders are generally sharper wide open than they are stopped down. The image will be vignetted for a couple of stops, but at least diffraction is way off. Your V1 uses tiny ľ'' chips, so you shouldn't shoot at smaller apertures than f/4 - certainly at the wide end of the zoom - unless you really can't avoid it.

I suggest you plug your V1 HDMI into a good big TV and use that as a viewfinder. Lock the gain but let the shutter speed ride on auto. Then, with the camera firmly supported, vary the aperture and watch the picture. Does it suddenly blur? Do the edges go first?

Record what you see while telling the mics, and when you send the camera for repair, include this test tape to show the technician you're on his wavelength.

tom.
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Old January 5th, 2011, 07:00 AM   #4
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Thank you, I really appreciate the advice and will give it a go in the next couple of days.

Just one query... when you say "shouldn't shoot at smaller apertures than f.4, certainly at the wide end of the zoom", please can you clarify what you mean by this?

Many thanks again
Steve
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Old January 5th, 2011, 10:22 AM   #5
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Certainly Steve. Let's talk about diffraction - where light doesn't bend as we'd expect it to when it meets a sharp edge. Now lets look at light entering a lens - any sharp edges in there on the way through those 15 elements to the chips? Nope.

Now we stop the lens down and what have we done? We've introduced a very sharp edged object (the diaphragm blades) and when light hits these it doesn't carry on in a nice straight line - it deviates, and this deviation means the image it forms isn't as sharp.

A lens is (theoretically) at its sharpest at maximum aperture. Let's say that's f/2. Of course all lenses vignette the image wide open, so the image will only be correctly exposed in the centre of the frame - it could easily be 2 stops under-exposed at the edges.

So we stop down to f/2.8. Now the edges are only a stop under-exposed (and BTW, your zebra stripes will show this with alarming clarity). Stopping down helps in other ways too. When you have 15 elements (and very many of them float about because they're used for zooming, OIS and internal focus) then miss-centering becomes a real production tolerance problem. Stopping down hides the damage miss-centering does.

OK, now we go to f/4. The image is evenly illuminated, miss-centering is hidden and diffraction losses are hard to detect with such low resolution (1920 x 1080) chips. But stopping down further doesn't improve on the vignetting problem, all it does is give the light this sharp-edged object to overcome.

Diffraction losses are focal length dependent too, and the rule is this - the shorter the focal length, the more damage diffraction does. So cameras with tiny chips are more at risk simply because they use shorter focal lengths for the same angle of view.

A 50mm lens for a full-frame SLR might well have an f/22 minimum aperture, but lots of camcorders have lens focal lengths in the 4 - 40mm range, so their internal (and undocumented) ND filters are designed so as to force them to shoot at apertures wider than f/4. The Sony PDX10 was like that - 1/5" chips, f/4 at wide, f4.5 at full tele. Replay of the tape might say the frame was shot at f/8, but that was just extrapolation of the density of ND applied.

So, with the V1 comes into this category, and if you fit a wide-angle converter you have to be even more careful about shooting apertures, because the camera you're using ever shorther focal lengths and the camera is calling upon you to insert the ND and not doing it itself.

tom.
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Old August 14th, 2011, 06:00 AM   #6
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Re: Quality of footage beyond f.4

This thread is a little old, but I can totally relate to it. I have an FX7 that I bought in 2007, and have the exact same problem.
It took me a (long) while to understand what it was. I usually mostly shoot outdoors in good light, and was delighted by the FX7's images in most cases.
I've had the occasional indoor shoot that always did end up fuzzy. The sensitivity of the FX7 is awful anyway so I just put it down as "simply don't do that" without really looking into it. That's until I also got a few unsharp shots in less than ideal light outdoors, where I decided to look into it a bit more, hook the camera to my HDTV via HDMI, and do some tests.
And there we are, at any focal length indeed if you want a sharp image you should close to F4 or more. Any more open and it starts getting fuzzy. Knowing that I tested indoor shots again, and indeed you'd better up the gain to 6-9dB and maintain F4, even if the image is noisy it is sharp and definitely looks better (at least to me).
So my outdoor shots were simply getting fuzzy when I was opening the lens too much (I'm usually using the dial in Exposure mode, and wasn't particularly looking at aperture before that).

That's one of the reasons that pushed me to change for an EX1R. Most of what I shoot is things that are happening quickly in front of me, in very uncomfortable environments, having other things to do at the same time or just before/after, and having to concentrate on aperture not getting wider than F4 is just one thing too much.
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Old August 14th, 2011, 07:39 AM   #7
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Re: Quality of footage beyond f.4

You've sort-of turned the thread on its head Andre because whereas we were saying that wide apertures are good and small apertures are bad, you're suggesting that apertures from f/1.6 to nearly f/4 are best avoided. That is what you mean when you say. 'concentrate on aperture not getting wider than F4' is it not?

The small but perfectly formed Panasonic SD900 video camera uses the internal ND filters and for most of the camcorder's life it's shooting at maximum aperture. This design parameter shows the confidence Panasonic have in their 12x zoom lens and chip block assembly, and the production tolerances must be superbly controlled to shoot all day at f/1.5 and 3.45mm. At first I poo-poo'd a focal length stated to 100th of a mm but now I'm less sceptical. I now believe the tight production tolerances mean that all their cameras come off the production line with this focal length.

So what happens when you shoot movies? Well the camera shoots at maximum aperture and if it gets brighter more and more ND is applied. Its the same in manual or auto - you think you're shooting at f/4.5 (say) but you're not - you're shooting at whatever the maximum aperture is for the focal length you've set. That's f/1.5 at wide stopping smoothly (ramping) down to f/2.8 at full tele.

So the lens 'stops down' (using ND) to f/5.6 and only if it gets brighter still do the aperture blades start to close. You can see that scenes shot at an indicated f/8 are actually shot at f/4, bringing with it the dof that comes with f/4.

So I'm surprised that your FX7 is soft (or 'fuzzy' you say), when used wide open. I would have thought that competition meant Sony have the same production tolerances as Panasonic.

tom.
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Old August 14th, 2011, 08:46 AM   #8
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Re: Quality of footage beyond f.4

Quote:
Originally Posted by Tom Hardwick View Post
we were saying that wide apertures are good and small apertures are bad
You were, but it seems to me you got it backwards, and the OP is seeing the same problem as I do:

Quote:
Originally Posted by Steve Joseph
when I use it indoors, without 3 redheads or other video lighting, I’m going to need to open my aperture beyond f4.
But when I do, the resulting image is far too fuzzy and soft to be classed as “High Definition”, in my opinion.
Quote:
Originally Posted by Steve Joseph
Can someone tell me if there’s a setting I can change to enable the image to retain it’s crispness - and HD quality - with the aperture open wide?
He's indeed having softness when wide open from what I read here.

Quote:
Originally Posted by Tom Hardwick View Post
Well the camera shoots at maximum aperture and if it gets brighter more and more ND is applied. Its the same in manual or auto - you think you're shooting at f/4.5 (say) but you're not - you're shooting at whatever the maximum aperture is for the focal length you've set. That's f/1.5 at wide stopping smoothly (ramping) down to f/2.8 at full tele.

So the lens 'stops down' (using ND) to f/5.6 and only if it gets brighter still do the aperture blades start to close.
No no no! What you describe would actually require having a grad ND filter in the camera, otherwise how would it gradually adapt exposure without you seeing steps without touching the iris, gain or shutter? No camera that I know of has this, and it wouldn't even be really physically possible to achieve (a grad ND that would be rotated within the lens to vary light input would cause uneven exposure across the frame unless huge)...
Cameras that have ND filters have them in steps, with a manual lever on the body that will mechanically slide the filters in or out of the light path, with usually 3 to 5 steps, which obviously can't be done during the shot (you see the filter slide in, and obviously the exposure changes by a huge step). The FX7 for example has 3 choices that you switch between using a mechanical lever, ND off, ND1, and ND2. ND off obviously clears the light path, ND1 slides in an 1/4 ND filter, and ND2 slides in a second 1/4 ND filter, making a total of 1/16.
Your SD900, like most consumer camcorders, doesnt even have any ND filter at all.

Shutter, aperture and gain as displayed on a camera are always real values, just like on a still camera! It wouldn't make any sense "tricking" the user by giving him some fake aperture value that would try to correspond to one, but done otherwise...

The optics of a video camera are just the same as with a stiill camera. The only difference is that with a stills camera you'll allow yourself to vary 3 exposure parameters, shutter, iris and ISO(gain). That gives enough latitude not to require ND filters for most uses. For video, you try to keep shutter speed constant, and (grossly) between 1/50th and 1/100th, to allow for motion blur in the image. So as you can't play on that, you're left with gain and aperture. Gain will usually stay at 0dB as much as possible, so you only have aperture left to adjust exposure. Obviously that's not enough to handle the wide range of lighting conditions, especially in bright light, so to cope with that you require ND filters. But between the ND "steps" your camera offers, what you use to adjust your exposure is aperture.

You should have a close look at a rather high end camera with mechanical controls. For example on the Sony EX1, the iris control on the lens barrel directly mechanically operates the iris. It doesn't go more "real" than this. The ND lever mechanically slides filters in or out of the light path. Gain is set in steps either in the menu or on a 3-position switch on the body. Shutter speed is hidden in the menu, as you'll normally not touch that. Should you want to, it would be in steps too. So the only thing that allows "continuous" fades that you can vary smoothly during a shot is the iris. Values that are given on the screen are obviously "real" ones, and you'll have to check by yourself that your ND/iris combination is where you want it, for example in "medium" light if I want shallow DOF I'll rather use ND2 and F3.5, but could just as well use ND1 and F9 if I wanted a lot of DOF.

As your SD900 has no ND filters, it will mostly play with aperture to adjust exposure in standard lighting conditions, maintaining shutter speed at the standard values (1/50th for PAL, 1/60th for NTSC) and gain at 0dB. If it's too bright, it will cheat by increasing shutter speed. If it's too dark, it will boost gain.
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Old August 14th, 2011, 09:11 AM   #9
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Re: Quality of footage beyond f.4

You say, 'no, no, no!' quite loudly Andre, but are you saying this from guesswork or experience? Guesswork, because this is precisely how the Panasonic 900 works in its video mode. In still picture mode the twin V iris blades do stop down as the display would indicate, but that's because the camera can vary the shutter speeds with impunity, whereas in the video mode 1/50th sec is the default.

There's no need for a grad ND within the zoom - ND is slowly introduced as you turn the iris dial. The display says you're going from f/2.8 to f/4 but in fact you're still shooting wide open and more ND is blocking the light path. Of course the ND is placed right alongside the aperture blades so the filters are completely and utterly out of focus - so the edge is not seen creeping into frame. And they only move in 'steps' in the manual mode - in auto they smoothly float about of course.

And you're quite wrong to suggest, 'Shutter, aperture and gain as displayed on a camera are always real values, just like on a still camera! It wouldn't make any sense "tricking" the user by giving him some fake aperture value that would try to correspond to one, but done otherwise...'

The Sony PDX10 (along with a host of other cameras) gave 'false' info about the aperture being used. The design intent was to feed the user with aperture values he'd understand, and for most of the camera's life it shot at f/4.5 with lots of internal ND applied.

You're quite right about the EX1's exposure controls and I'm not disputing the fact that all cams with user operated ND filters give accurate aperture readouts. All I'm saying is that cameras that use internal ND don't give reliable (read: accurate) aperture readouts, either in the v'finder or on the video files themselves.

tom.
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Old August 14th, 2011, 10:26 AM   #10
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Re: Quality of footage beyond f.4

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Originally Posted by Tom Hardwick View Post
There's no need for a grad ND within the zoom - ND is slowly introduced as you turn the iris dial. [...] Of course the ND is placed right alongside the aperture blades so the filters are completely and utterly out of focus - so the edge is not seen creeping into frame. And they only move in 'steps' in the manual mode - in auto they smoothly float about of course.
How is ND "introduced"? What would that or those variable ND filter(s) that "float about" look like to you? How could filters that each have a fixed value come and go without creating steps? How could the 10+ required mechanically fit inside that small camera?

Have a look at the lens diagrams in the service manual.

PANASONIC HDC-SD900 TM900 SM Service Manual free download, schematics, eeprom, repair info for electronics

Last edited by Andre Bernet; August 14th, 2011 at 11:23 AM.
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Old August 15th, 2011, 03:40 AM   #11
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Re: Quality of footage beyond f.4

OK, it's gloomy and the 900 camcorder has its twin iris blades fully open, let's say at f/2. It gets brighter and the auto diaphragm mechanism slides a tiny sliver of ND material in from the bottom of the diamond (so it effectively ND's the top of the frame first, but as I say it's so out of focus that the entire frame has some light soaked by the ND). As you film in auto this ND floats in and out to control the light that hits the chips.

In manual mode you turn the iris ring and the mechanical blades stay wide open, but the ND's cover more and more of the open iris blades as you 'stop down'. You go from f/2 to f/2.8, f/4 and then at f/5.6 the ND covers the entire aperture. All this while (even though the camera is still shooting wide open) the aperture readout in the v'finder is displaying the imaginary and extrapolated f numbers that you and I recognise.

You ask how the 10+ NDs could fit inside the camera, but do you now see how it works? Oh, it would be so much easier to show the stripped down Panasonic I have here.

If it gets brighter still then there's no more ND to introduce, so the aperture blades start to close. This means that when f/8 is displayed the iris blades have actually stopped down to f/2.8. Of course there's a very good reason for this, and that is the designers are trying desperately to keep you from using small apertures - and this is because they rob you of so much sharpness when you use tiny 1/4.1mm chips.

Thanks for the service manual link Andre.

tom.
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Old August 15th, 2011, 12:47 PM   #12
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Re: Quality of footage beyond f.4

OK, yes if you had photos of the stripped unit I'd love seeing them :)

I'm an electronics engineer and have been following imaging technologies for quite a while now, and this being a really good idea I'm surprised that I've never seen any white paper, tech document or even marketing claim about that!

Anyway, we're way off topic there, the topic matter was lens softeness at wide apertures, not diffraction losses at small ones :)
On the FX7 the loss at small apertures (F8-F11) is nearly unnoticeable, yet between F4 and F1.8 it quickly gets really awful, I know all lenses are softer wide open, but that's really stretching it too much.
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Old August 15th, 2011, 01:06 PM   #13
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Re: Quality of footage beyond f.4

To get back on topic and to answer Steve's original question - yes, it's not right that your lens (when shooting at apertures wider than f/4) gives images so soft that you're wondering if they should even be called hi-def.

Steve - modern camcorder lenses are designed to give very good results indeed wide open (see my posts on the Panny 900), and camcorders that use tiny ľ" chips such as your V1 shouldn't be used at apertures smaller than f/5.6 if you're after the sharpest pictures.

Have you tried the brick wall test? Tripod, cam perpendicular to a brick wall, wide-angle, SSSS off. Tell the mics what you're shooting at, keep the gain constant and vary the shutter speed and/or NDs to let you shoot at all apertures from f/1.6 to f/11. Wite the cam into a big, good, HD TV and critically analyse the results.

If you're really finding that your lens is soft then there's the possibility that the back focus needs adjustment. You should notice vignetting till you stop down to f/3.5 (your zebras will show you this). You haven't dropped the V1 at any time? The lens doesn't rattle when you shake it?

tom.
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Old August 15th, 2011, 01:48 PM   #14
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Re: Quality of footage beyond f.4

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Originally Posted by Tom Hardwick View Post
Have you tried the brick wall test? Tripod, cam perpendicular to a brick wall, wide-angle, SSSS off. Tell the mics what you're shooting at, keep the gain constant and vary the shutter speed and/or NDs to let you shoot at all apertures from f/1.6 to f/11. Wite the cam into a big, good, HD TV and critically analyse the results.
It's pretty much what I've done. Put camera in front of a subject, manual focus, vary iris. Done that at several focal lengths, not just on widest FL. Image is consistantly softer wide open, becomes better as iris is closed, and F4 is where it becomes like it should. When soft, manually focussing shows there's leeway on both sides, but the best I can achieve is still awful.
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Old August 16th, 2011, 03:14 AM   #15
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Re: Quality of footage beyond f.4

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this being a really good idea I'm surprised that I've never seen any white paper, tech document or even marketing claim about that!
I had a Canon 310XL Super-8 camera in 1976 and this used internal ND. Back then cameras couldn't shorten the shutter speed in bright conditions and as the Super-8 frame is a pretty small 'chip' (5.4 x 4.1mm) ND was used to avoid physically tiny apertures.

I'm pretty sure tech documents avoid talking about this because as photographers we like to think that we've 'chosen' to shoot at f/4 (say), especially if you've forked out thousands of dollars on your new Sony NX70, Panasonic HMC40, Canon XA10 and so on. Of course internal ND means you're not shooting at f/4 even though v'finder readouts and file replay insist you are.

But this shouldn't unduly concern us. Undocumented ND is there to give us sharper pictures, full stop. And it's a lot better than faffing about with vari-polarisers as you have to with Sony's VG10.

tom.
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