Focus on the Z1

[Matt Davis]

Originally Posted by Simon Ash

Can you explain, Z1 lens's sweet-spot is between f2.8 and f4 - if it's wide open, you're using all of the glass, not the best bits?

A lens will have a maximum aperture, and a minimum aperture. With the lens wide open, you're going to be using all the glass, right up to its edges, and whilst the centre of the lens will be as perfect as the manufacturer can make it, the edges (especially on mass produced and cheaper lenses) will have 'issues'.

Setting aside Depth of Field for a moment, the temptation may be to stop down to use only the middle bits of the lens, but as the sensors are so small, you're going to bump into some limitations of the physics of light and sensors that you don't get in 35mm cameras and up (to the 'absurdo reductum' of a pinhole camera). As I've not had breakfast yet, I'll simply point you here:

http://broadcastengineering.com/infr...port_choosing/

About half way down.

So you can't stop down too much, especially with small sensor sizes, and you don't want to use the wide-open aperture if you want ultimate resolving power (e.g. sharpest images), so there's a Goldilocks area, a sweet spot between wide open and where diffraction artifacts kick in (f6.8 seems an interesting number that crops up inside the Z1's menus), which is around f4. Yes, it extends to about f5.6 but at the expense of DoF which is very desirable to most Z1 shooters, and f2.8 at the wider lens settings crops out the edges of the lens.

[Simon Denny]

Thanks Matt great read.
I have done some testing on the Z1 and focus has to be spot on, dont do fast pans, the lens has a hard time when trying to focus on trees,plants anything with a lot of small detail in large areas such as farm crops.
The ideal range for getting a great picture in my opinion is about 1-5 meters from talent any longer on the lens and it's harder for the camera to focus.
Lock down manual focus at all times, forget trying to auto focus on moving objects.

Cheers
Simon

Oh i forgot, adding sharpness to the downconvert does help. Cheers

[Matt Davis]

... I think we may have got a little distracted about Goldilocks and the three apertures...

If you thought focus was good filming huge vistas of gently waving crops, or vast expanses of rippling water, and you did all this on HDV, then although the lens is doing a good job, the codec (HDV) will turn it into soup.

The mushiness you see isn't the lens doing a bad job (but as any Z1 shooter will know, autofocus really loves backgrounds and hates faces), but it's an aftereffect of how HDV works. HDV can be easily stressed - shaky footage, lots of fast motion, lots of motion within a frame, lots of very subtle gradation, all this will tip HDV down the drain and leave you bruised.

This is probably why so many broadcasters have been so scathing about HDV whilst leaving XDCAM-HD unmolested (the extra 10 Mbits make a difference). It's precisely these amazing Hi Def vista shots that make HD compelling to punters and makes Z1s panic.

[Simon Denny]

Yeah mushiness is where it's at. Oh well i'm stuck with it now and just have to make the best i can with this camera.

Simon

[Matt Davis]

Originally Posted by Simon Ash

just have to make the best i can with this camera.

Be assured that when you do your interviews, if you set the camera way back, zoom in nice and tight, shooting around f2.8 (add ND and even a polarizer if you have to outdoors), you'll get something that should cheer you up no end. Especially with that smidge of sharpening.

The Z1 is a great 'talking heads' camera. :)

[Simon Denny]

What about recording in SD? is there any inprovment in quality or is HD to SD downconvert better?
I was reading in here somwhere that downconverting has a better image? but i dont see how as SD is 720/576 no matter which way it is, isn't it?

Simon

[Matt Davis]

Originally Posted by Simon Ash

What about recording in SD? is there any inprovment in quality or is HD to SD downconvert better?
I was reading in here somwhere that downconverting has a better image? but i dont see how as SD is 720/576 no matter which way it is, isn't it?

Recording DV or DVCAM instead of HDV makes sense when shooting fast moving action on a Z1, needing a speedy turnaround or you're working within a SD environment - 75% of my work is still DV/DVCAM.

Shooting HDV, editing in an intermediate codec such as ProRes, Cineform or DNxHD, then outputting to Standard Def does provide you with a nicer image especially when dealing with subjects with strong colour (theatrical lighting, CG and chromakey) because you don't downsample to DV - rather, you downsample to uncompressed, or a 4:2:2 codec such as DVCPro50.

HDV is a 4:2:0 codec with big blocky pixels for colour. The Z1's flavour of HDV is interlanced, and deinterlacing loses 25% of your resolution. The Z1 is known for a 'clean' image but you tend to use Gain more because of the lower sensitivity. So, by shrinking the image from 1080i to SD 4:2:2, you get better colour sharpness, the grain is less noticable, and you can hide the loss of resolution in deinterlacing by the downscaling of the image.

When plied with enough beer and given an appropriate platform, I'd say that HDV makes for SD done right (4:2:2) so long as you're aware of what HDV doesn't like. For my own productions, I shoot HDV for SD, but I'll repeat that most of the time I'm shooting DV for clients because HD just hasn't got the demand in Europe yet.