Sharpness Issue

[Greg Crawford]

OK, I could place this in the zoom lens section... But I think it deserves it's own special page.

One of the shots I did in October for my short film is of a girl in a cave. It's a close up of her face (pitch black) the door opens and the light comes streaming in.

Although the image is sharp it's not blazingly sharp, as I saw it in the viewfinder.

Yes, I was following all the rules, zoom in focus, and pull back. and yes I adjusted the my eye to the lens before shooting. Focusing the lens at infinity in the widest position. Tweaking the viewfinder to my vision, in bright daylight.

We were shooting this shot at F2.0 - F2. 8 The girl was lit with one light . The 1K focusing spot light was gel'd with a Chocolate filter. We used a couple of flags to act as a door. As the flags were pulled away the light struck the girl across the face simulating a door opening.

I shot the scene in both Ektachrome T-120 and T-200 negative stock. On a side note, I have not scene the Ektachrome results yet, but I can tell you that with just a little ambient light, (60 watt bulb) you can see the outline of the girl and a can since the background. Amazing. it's about 4-5 stops under indicated exposure.

The camera us a Nizo 810 Macro.Could it be that there is a slight focusing differences between film plan and eye sight plan?

Or could the Chocolate light be causing a focus shift?

[Alex]

Backlighting can make a shot look "softer". Dropping the black level on your video image can make the shot look "sharper". (although not below 7.5 IRE)

Any oils or dust on the lens will make the shot look softer when doing backlit shots. And yes, the back focus on the camera can be off. It's also possible that anything below a certain f-stop, say below an f 4/2.8 split, may look soft, especially on backlit shots.

Video/TV also tends to show underlit warm tones as fuzzy, and bluer parts of a shot as sharper.

If you have access to a columnator, you can check backfocus. Places like U.T. Photo (in Burbank California, 818 area code) can check for backfocus on your super-8 camera, and apparently, can make some adjustments on some cameras.

It would be interesting to see if you could squeeze a higher f-stop, say a 2.8/f4 split, if that helps with the sharpeness issue.

[Alex]

Another answer is, glare on the lens can make the image look softer.

[lightfeat]

If you need to produce the sharpest images, it is always wise to remember that all lenses have an optimum aperture for sharpness, which varies between lenses. Some non-zoom telephoto lenses are optimum at f2 so that they can be used to create very short depths of field, but most lenses are optimum at about f8 or f5.6. That is why reaal pro cinematographers always adjust light levels, not f stop. They work to an optimum f stop of usualy f8. Try it - it works!

From what I've seen of the T200, it's nicer and sharper the brighter the conditions, such as overcast day, or shaddowy day, or well lit street at night. Same goes for the 500.

Precise collimation of the prism splitter and viewfinder is always a possible problem, but not an easy one to resolve, unless you can find a lens expert to correct it. Arri GB corrected my Arri 16mm camera collimation, but at a cost, and that camera is set up to be easily adjustable with expensive micrometer acurate equipment. I don't think super8's are, but I may stand corrected on this.

More light, stop down - no-one will ever know it's brighter, but it will be sharper. I realise this is impossible in a cave with natural light......

I hope this was helpful to you.

Lucas Lightfeat.

[Greg Crawford]

I wrote this post, then went to dinner ...thinking about the problem, I might have missed the most obvious point.

At F2.8-2.0 the depth of field is so short, my actress might have moved after I focused on her.

Thank you both for your ideas...I am aware of the sweet spot for optimum sharpness and could not go for it at the time. Cranking up the one and only light to F5.6 or F 8 would increase the spill in this small room , we were using. With an over all brighter light level I could never convince anyone we were in a cave. I know Host Board will censer the word I would rather use...****eon.

I probably should not worry , having shot another 4 or 5 takes on the Ektachrome. And I know I evaluated focus from time to time.

On the flair or back light issue. The room was very dark no other illumination other than the key to my right high and a single 60 watt bulb on my left lights at 10 and 2 o'clock, in back of the camera. There was a small window high above the actresses head...maybe it did kick up a little flair?