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Old October 5th, 2006, 09:58 PM   #1
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Back focus?

This is at full wide, open, shutter 1/60, 30p, panamatch(i think), focused infinity.

Is this the best the lens gets with that distance? This was on a tripod so..

Also, I've noticed quite a bit of magenta and green edging, is this normal?
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Old October 6th, 2006, 01:43 AM   #2
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That does look a bit soft to me. How did you set up the focus on the shot? Did you zoom it in, focus, and then zoom back out? If so, yes, you probably need to check your back focus.

If you set your focus wide like that, well, you might be in for the same learning experience I had. :P HD is not as tolerant of minor focus errors as DV is. Might just take some practice. Maybe play around with your focus assist and peaking?

I know the stock lens, while not perfect, is capable of producing some pretty crisp images.

As for your magenta and green edging, it's called Chromatic Aberration. (Is that spelled right? Doesn't look like it. Anyways...) It's normal. Every lens has it, to some degree. Cheaper lenses, like the stock lens on the HD100, are more likely to exhibit some CA at full zoom, than, say, the $12,000 (MSRP) 13x lens. There are ways to avoid it. The easiest is to avoid using full zoom. I usually try to keep my zoom below 80%, although I've never had CA problems, even at full zoom.
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Old October 6th, 2006, 03:45 AM   #3
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As far as my experience with this lens goes, focus at infinity, really means very very far away...not 30 or 40 or 50 feet. My guess is that your shot would've looked good if you'd turned the focus ring a tiny bit to the right.
Of course...if you zoomed in,focus and then zoomed out, and it looks like this... that's a back focus adjustement you need to do.
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Old October 6th, 2006, 05:45 AM   #4
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Yes, HD is more difficult to focus, but I think this might be a back focus issue. The distance should of been okay for infinity. Of course I could be wrong, but first double check your back focus to elliminate it as a problem.
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Old October 6th, 2006, 10:34 AM   #5
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I zoomed all the way on the bride and focused on that. My first guess is the back focus. Maybe I'm not understanding the steps to adjusting the back focus. If anyone cares to tell me, I'd appreciate it, just incase I'm not reading the material right. Oh....just read something -- What is the usual distance you adjust to in regards using the siemens star?
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Old October 6th, 2006, 11:30 AM   #6
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Quote:
Originally Posted by Matt Setnes
What is the usual distance you adjust to in regards using the siemens star?
3 meters

The important thing when back focusing: open the aperture all the way!
This will shorten your depth of field as much as possible when setting the backfocus.
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Old October 6th, 2006, 12:05 PM   #7
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This is what I figured, but then I stumbled upon this

http://www.mediacollege.com/video/ca...ack-focus.html

Stating 70 feet, and i read another where it says 75 feet
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Old October 6th, 2006, 11:41 PM   #8
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If I may jump in and ask a quick back focus question... How do you guys monitor your video when you are back focusing? I have a big 30" Apple Cinema display so I plug my HD100 directly into iMovie so I can have as large an image as possible for the wide angle view where the Siemens Star gets tiny.

I use iMovie instead of FCP because the FCP Capture window seems stuck at one size, and the iMovie window can be made pretty big.

What I'm REALLY wondering is: is there some way (either in iMovie, FCP or some other app) to greatly enlarge the image on my monitor so the tiny wide angle star fills up the whole screen? this would make back-focus setting much easier.

Also-- has anyone else noticed that the back focus/macro ring is a little loose even when it is screwed down tightly? it seems there is still wiggle room in the ring that can slightly change your back focus even after you have carefully set it.
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Old October 7th, 2006, 01:52 PM   #9
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I use the same Dell 24" widescreens that I use for my editing. Just plug the component out from the camera into the monitor, and voila. I actually use them for field monitoring, as well. Well, semi-field monitoring, given their power requirements.
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Old October 7th, 2006, 03:04 PM   #10
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Just an interesting aside - I talked to a Fujinon rep and he said that if you crank the focus all the way out to "infinity" you will in fact have eveything go a bit soft. I guess they put a bit of wiggle room in the far end of the lens to account for extreme temperatures and other things that affect the lens physically. This is so you can always get to "infinity" - even in extreme conditions - but to do it they have to give you a bit of room past infinity under normal circumstances.

I also agree about the back focus thing - It is crucial with HD to have good back focus.
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Old October 7th, 2006, 09:43 PM   #11
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Quote:
Originally Posted by Burk Webb
but to do it they have to give you a bit of room past infinity
Wow, I wonder how far that is. :)

Richard
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Old October 8th, 2006, 06:37 PM   #12
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I'm sure many (including myself) have had good luck with 3 meters. The manual mentions to use at least 3 meters.

I'm starting to wonder based on a recent shoot... which was an important one I might add!, if 3 meters is far enough. The manual has it listed as its minimum.

It doesn't take much error of back focus to have your wide shots go soft.
A small amount of error will have your image plane fall behind or short of the camera's CCD when changing focal length.

I'm starting to think it's safer to use the siemen chart at 25' or more.

Matt, by the way, based on how you set your shot, it appears that back focus was off on your camera.

I've learned my lesson the hard way.
Always check back focus carefully (with a good monitor) before any important shoot. Also, check it if there is a temperature change.

Last edited by Steven Thomas; October 9th, 2006 at 08:55 AM.
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Old October 11th, 2006, 01:30 AM   #13
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Do I really need to invest into an HD monitor to calibrate the back focus right now? Maybe I'll take it over to Circuit City once in a while ( : Otherwise I'll attempt using a SD tv for this.

Does this mean infinity should be avoided when shooting HD, especially with this lens?

Here is another shot, I set it this time again with about 12 feet. Obviously this distance isn't working well.
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Old October 11th, 2006, 01:36 AM   #14
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Just re-read my post...I sound like an insane person.

It sounded so much better when the Fujinon guy was saying it...
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Old October 11th, 2006, 01:38 AM   #15
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haha, yea. I guess I will call the guys up.
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