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#16 |
Inner Circle
Join Date: Mar 2003
Location: Billericay, England UK
Posts: 4,711
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Thanks for the link - interesting thread Nick.
There's nothing special about 'video lenses' as Sony seems to infer - all lenses suffer from diffraction losses the smaller the aperture that's used. In theory all lenses are at their very best wide open, but in practice flare from the interior of the cylinder, vignetting of the frame and decentering of the elements ensures this is never so. Our Z1s have a 'sweet spot' in the aperture scale at f/4. Any wider than that and the lens vignettes the corners of the frame, and the zebras can clearly show that wide open the edges of the frame are a good 1.5 stops under-exposed. Of course for general movie making this doesn't matter a toss and can even be used to good effect - 'highlighting' the object in the centre of the frame quite nicely. If you use your camera for making panoramas you'll quickly notice that frame vignetting makes matching up sucessive shots very difficult. Cameras that have automatic (and generally undocumented) internal ND generally stop the lens closing below f/4 these days, the ND taking over as the owner thinks he's stopping down. (Sony PDX10, A1 etc). This is to stop diffraction blurring the image, a problem that is exacerbated by short focal lengths. Pinhole cameras (remember them?) needed a tiny hole to keep the image sharp(ish), but not so small as to have diffraction take precidence. So with our tiny chips and short focal lengths (and even shorter focal lengths if you use a wide-angle converter) you must stay well clear of small apertures. In fact our Z1's menu offers you the option of not allowing you to stop down past f/5.6 or so. If you're shooting HDV, take this option. I'm much less afraid of using maximum aperture than I am of using minimum. But never be afraid to experiment I say. Video is the greatest of teachers. Opening slo-mo shot on Splash was a Canon 1014E at 60 fps. tom. |
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#17 |
Regular Crew
Join Date: Sep 2004
Location: Bangkok, Thailand
Posts: 189
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I think you mean in the picture profile? You can limit the iris to no smaller than F11, F6.8 or F4 in there.
I have often shot with a picture profile limiting the iris to F6.8 and will do this religiously from now on. I have my maximum gain in PP1 set to 12dB and I'm going to keep sharpness at 9 as well from now on having read comments from DSE and others about the over-sharpness of HDV cameras and noticing this myself in my recent footage shot with no picture profile set. I'm also wondering about a bit more colour. I notice a lot of people choosing around +2. What do you do? |
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#18 | |
Regular Crew
Join Date: Sep 2004
Location: Bangkok, Thailand
Posts: 189
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Quote:
Just wondering about this because I'm cutting my macro footage now and a lot of it is not quite sharp. Some of such footage may well have not been on infinity focus. Last edited by Nick Hope; October 20th, 2007 at 10:07 AM. |
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#19 |
Inner Circle
Join Date: Mar 2003
Location: Billericay, England UK
Posts: 4,711
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If you fit a close-up lens it simply means that infinity as marked on your lens is a lot closer. You can still use the camera's focusing quite happily, but of course adding the extra element(s) brings with it pretty nasty abberations. Generally the centre of the image should be ok, but it's the edges that suffer. Stopping down helps, but then again the more you stop down the more you head towards diffraction. You can't win.
So many manufacturers are making their lenses 'tele-macro'. The HC7 is a case in point - you have to use max telephoto (because of vignetting) but it does allow great closeups from a distance. tom. |
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#20 |
Regular Crew
Join Date: Sep 2004
Location: Bangkok, Thailand
Posts: 189
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Thanks Tom. Well the achromatic Century diopter is definitely sharper around the edges the single-element diopter I was using before. But I'm only getting razor-sharp clarity and detail on the occasional shot. Many of the other macro clips shot with the Century are ever so slightly blurry, but still usable. The blurriness can't be seen on the camera's LCD. Only on my 24" monitor. A winning combination of lighting, iris, focus and distance from subject is pretty difficult to achieve (particularly underwater!).
I wish the exposure metadata could somehow be captured along with the footage, not just displayed on the camera during playback. Would make it much easier to learn from mistakes. Attached is a still from some of the better underwater footage with the Century diopter. I guess that slug's about 2 inches long. |
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#21 | |
Wrangler
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Quote:
I'll also second what Tom says about lenses and sweet spots. He mentioned you can tell that edges are underexposed vs. the center of the image and I have confirmed this while using a waveform monitor. You'll see the edges droop down on the scope until you close down to around F4, at which time the line becomes flat. As a general rule, the sweet spot kicks in around 2 stops down from wide open on most every zoom lens I have used. -gb- |
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#22 |
Inner Circle
Join Date: Mar 2003
Location: Billericay, England UK
Posts: 4,711
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The 'everso slightly blurry' shots - these can't be blamed on dof problems or on very slight miss-focusing (i.e. it's sharper somewhere else in the shot)?
Greg - all lenses vignette the edges wide open - primes as well as zooms. tom. |
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#23 | |
Regular Crew
Join Date: Sep 2004
Location: Bangkok, Thailand
Posts: 189
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Quote:
(Will post some finished edited footage in due course) |
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#24 | |
Sponsor: Schneider Optics
Join Date: Aug 2007
Location: Van Nuys, CA
Posts: 387
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Quote:
Send email with a BOLD title that say "SCHNEIDER CLOSE UP CONVERSION". Thanks, Ryan Avery Regional Sales Representative Schneider Optics |
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