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-   -   focusing with manual 16x lens (https://www.dvinfo.net/forum/canon-xl1s-xl1-watchdog/2333-focusing-manual-16x-lens.html)

Josh Bass June 9th, 2002 04:00 AM

focusing with manual 16x lens
 
I recently purchased the manual 16x lens, and I just want to make sure I have this straight (and not only because I've misplaced the instructions).

When focusing, you first critical focus, and the zoom out wide for the back focus. The way I understand it, you loosen the screw (or screw thingy, don't remember it's official title) on the back focus ring, which is the same ring with macro button on it. You then use the ring to focus the wide shot, and retighten the screw. This ensures throughout your zoom range that you stay in perfect focus. Is this right?

What happens if you don't back focus every single time, and only critical focus?

I have the hardest damn time telling if the wide shot's in focus or not. I don't know if it's me or the color viewfinder.

Ken Tanaka June 9th, 2002 10:30 AM

You only need to adjust the back focus occasionally, not with each shot. Setting the back focus is a maneuver that enables the lens to maintain focus throughout its zoom range. Re-adjust whenever you find that the lens is not doing so.

Chris Hurd June 9th, 2002 11:22 AM

Back-focus is something you should very rarely have to do. Back-focus is a correction to a misalignment. Don't adjust it unless you have a problem.

Wide shots can be difficult to focus properly because of pixel averaging. Wide shots in general will tend to look soft, which is common for DV.

Set your back-focus up properly one time, lock it down and then *leave it alone.* You'll have fewer problems this way. Hope this helps,

Josh Bass June 9th, 2002 11:41 AM

Alright, fair enough. How come, then, when I set it, the picture still looks blurry towards then end of the zoom when I zoom back in from being all the way wide

Chris Hurd June 9th, 2002 11:55 AM

It sounds like you may have thrown out the back-focus when you were adjusting it... the lens comes from the factory pretty much all set up. If you have changed the back focus, then it probably doesn't look right... or if you haven't messed with the back-focus, then it's possible that it did ship from the factory not properly set up.

Can you take it into Pro-Tape there in Houston tomorrow morning? Somebody there should be able to help you get it set up the right way... and then... leave it alone! ;-)

Hope this helps,

Charles Papert June 9th, 2002 03:16 PM

Chris' advice is no doubt sound, being the man when it comes to all things XL1...

My two shekels on the subject of back focus is that it should be checked each time you switch lenses i.e. the standard 16x to the manual 16x (unfortunately the standard lens doesn't have a back focus adjustment; have users found it to have the back focus issues that the first generation had?). Using an external monitor will make finding the exact setting much easier than the color finder.

Temperature changes may require touching up the back focus, which can be a result of external influence (taking the camera from indoors to outdoors) or just from the camera body heating up over a period of use. In the HD world, it requires tweaking several times a day. I can't say as I've experienced too many problems using the 14x manual lens on the XL1, but I'm so used to making the adjustment I don't even really think about it (having the B&W viewfinder makes it a snap, so to speak!)

This all said, for many users it is a set-and-forget thing, as Chris indicated.

Josh Bass June 10th, 2002 02:46 AM

Wow, I had no idea. I thought adjusting the back focus was something to be done every time you crically focused, otherwise the option would not be so easily available. Can anyone recommend an easy way to adjust it (short of taking it somewhere), e.g. putting a subect so and so feet away and focusing on that while fully wide?

Chris Hurd June 10th, 2002 07:05 AM

Here's a procedure:

http://www.isorainbow.com/tech/backfoc.html

Josh Bass June 10th, 2002 10:25 AM

Thanks.

Don Palomaki June 10th, 2002 07:04 PM

Back focus can be set in the standard lens using a target and a RM-95 adjusting controller. Not a procedure for the faint of heart. The lens mount includes temperature sensors and compensation circuits that help keep backfocus on.

Putting the lens ona different camcorder body may require a different backfocus adjustment.

David Slingerland June 11th, 2002 04:17 PM

get flange focal chart
 
get your self a flange focal chart and focus should not be a problem, another way would be to look for a glimmer on lets say a cooking pan or anything witch will reflect.

Josh Bass June 12th, 2002 12:52 AM

Thanks for all the advice. I think I have it now, though. I reset the back focus last night and then zoomed in and out several times, and each time I came back to full telephoto, I was still in sharp focus (or at least as much as you can tell using the color lcd), so I guess problem solved.

Kai Leibrandt June 17th, 2002 06:34 AM

one thing i have really found helpful with adjusting backfocus on my manual 16x is to connect an external monitor, or better still a laptop through firewire. this gets you the sharpest picture I found, and circumvents the action-safe cropping problem of the XL1 viewfinder).
The problem with this is it's hard to do on the road (unless you use the latop), but I found it much quicker than trying to guess focus using the EVF.

Kai.

Charles Papert June 17th, 2002 11:08 AM

Josh:

Just want to clarify your results:

>>I reset the back focus last night and then zoomed in and out several times, and each time I came back to full telephoto, I was still in sharp focus>>

If the back focus was out, it would go soft at the wide angle end, not telephoto. But I'm assuming in this instance it was good at both ends, so all appears to be happy in your world.

Josh Bass June 17th, 2002 11:34 AM

That sounds right. . .but I remember someone in another post talking about the ISII lens and saying that when he/she critically focused, and would zoom out and then zoom back in, sometimes the image would go soft, and that he/she had to send to the factory to "get the back focus adjusted." Maybe I read it wrong. . .highly possible.


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