weird xl2 focus issue with manual 16x lens at DVinfo.net

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Old December 24th, 2006, 08:50 PM   #1
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weird xl2 focus issue with manual 16x lens

Hey, guys (and gals) has anyone else experienced this? I used to have an XL1s, and since I bought the 16x manual lens, used it almost exclusively. Now, with the XL1s, I was used the the fact that when fully zoomed out/wide, no matter where focus was set, you were always in focus.

With the XL2, same lens, seems it ain't necessarily so. Seems like closer than a certain distance (haven't figured out exactly what this distance is) to your subject, even when wide/zoomed out, you have to set the focus barrel to the closest possible distance for it to be in focus. Now, to clarify, I'm not talking about a situation where you'd have to use the macro focus, I'm talking 3-6 ft from a subject. Again, in this same situation, with the XL1s and same lens, the subject would be in focus. When out of focus in these instances, it's very slight, not always noticable in the viewfinder, only when viewed on an NTSC monitor.

Conversely, let's say I'm 50 feet from a subject, trying to get a very wide shot. Now I have to set the focus to infinity, even when fully wide, or it'll be slightly soft, same deal-- can't really see it in the EVF, only on a monitor.

Has anyone else noticed/experienced this? I reset the back focus on the lens the first time I observed this phenomenon, and it checked out fine, yet I still have this issue.

Is the XL2 so sharp compared to the '1s that these slight differences in focus are noticable, where they weren't on the other camera? Unless my lens is going wonky on me.
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Old December 24th, 2006, 09:19 PM   #2
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Pardon me, if you've already done this. Try resettng back focus a couple of times at various distances, one near, and one far. Use a maglight with the lens focus cowling twisted all the way off, so it's a point source, or go to DSCLabs.com and get a Siemens star printed out that you can focus on. Be sure that everything is locked down. Are you using the FU-1000, with the peaking cranked? If possible try using a larger monitor in addition to the B&W one. The stock Canon LCD onboard monitors are shite, mate. Completely unusable.

Also, are the previous situations at a deeper f/stop? Always check focus wide open.
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Old December 24th, 2006, 09:21 PM   #3
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How pathetic is that? It's Christmas Eve and I'm on friggin' DVinfo.

Time for more vino and wrap presents.
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Old December 24th, 2006, 10:44 PM   #4
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ho, Ho, HO!!!

Mark,

Not to worry, Santa's says you've been a good boy - perhaps under your tree is a B&H gift certificate for a shopping spree...

Merry Christmas, Michael (yeah, another sick puppy in your club)
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Old December 25th, 2006, 12:57 AM   #5
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Nothing wrong with being here tonight. I'm a Jew, so it's just "eve".


What do you mean about different distances? Do you mean set the backfocus with the camera 6 feet from the chart, and then 25 feet from the chart, or something?

You're saying do the maglight thing only if I don't have access to the star? I have a backfocus star from somewhere printed out and hung on my wall, that's what I use to set it.


Sorry, when I set the back focus, I always use my NTSC monitor to judge the sharpness(es), didn't mean to imply I was judging off the EVF.


I've been doing a lot of shooting lately wide open (at f1.6), so yes, I notice the issues at that stop. Good question about deeper stops, no way to tell after the fact, is there? I'm gonna it's definitely more noticable at the more open stops.

No FU 1000. I have the FU. . .um. . .stock XL2 viewfinder. Let's be honest, "completely unusable?" certainly not! Not particularly easy to work with, but it's something.
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Old December 25th, 2006, 08:55 AM   #6
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JOsh,

I shoot with the 16x manual on my Xl2. I always check the back focus before a shoot. It CAN change over time, based on atmospherics... and 'getting bumped around' a bit. But yeah, it sounds like you have a back focus problem, and no, it's not xl2 specific. Or at least it's not specific to ALL xl2's.
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Old December 25th, 2006, 10:40 AM   #7
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The whole point in having a lens with a 'back focus' adjustment is so that it can be used on different cameras and therefore minutely calibrated for the tiny differences in distance between the rear element and camera's sensor plain. The procedure for checking this is also known as 'lens tracking'.

In theory you should always check back focus everytime you change the lens between cameras, and in fact everytime you take the lens on or off.

The procedure for checking is normally to open the iris open fully use ND if required to see the picture. Fully zoom in on a distant, detailed subject preferably at the infinity end of the lens and check focus using the front element of the lens. Once you're sharp fully zoom out and assess the focus on a monitor or trustable viewfinder. If slightly soft then adjust the rear element until the picture is sharp. Check your lens 'tracks' focus all the way by zooming in to the tight end and back out a couple of times.

After that you're good to go, if not you may have a problem with the lens itself ?
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Old December 25th, 2006, 01:15 PM   #8
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Right.

The the thing is, I never take this lens off, so it should be fine. I'll mess with it later.
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Old December 25th, 2006, 03:16 PM   #9
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Quote:
Originally Posted by Josh Bass
Right.

The the thing is, I never take this lens off, so it should be fine. I'll mess with it later.
Yes but the rear element can work loose over time and needs checking from time to time.
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Old December 26th, 2006, 09:16 PM   #10
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I meant that the maglight trick can be used if you don't have a star. Because it's a point source, it's easier to tell if it's unsharp at the wider end of the zoom. Yes, about six feet is good. I think a lot of times, I just do it there and then call it good. I find it harder to tell at the longer distances.

I have found that the back focus can shift as things heat up/cool down. It's a good idea to check periodically throughout the day, possibly more frequently as the day warms up, or cools off. It seems to be more necessary than with other camera/lens set ups. Humidity can also be a factor.

Yes, having a big monitor always helps.
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Old December 26th, 2006, 09:18 PM   #11
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Originally Posted by Michael Nistler
Mark,

Not to worry, Santa's says you've been a good boy - perhaps under your tree is a B&H gift certificate for a shopping spree...

Merry Christmas, Michael (yeah, another sick puppy in your club)
Hee, hee. Thanks Michael.

Yo, Daddy Bass! I'll be Home For Purim.
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Old December 27th, 2006, 02:35 PM   #12
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So I rechecked back focus. I think even before I adjusted it, it was spot on, but I redid it just for grins.

when I zoom in and critically focus on something, it stays sharp throughout the zoom range, but the original issue still persists.

Basically, if I'm all the way zoomed out, if an object is, say, between 1 (or whatever the minimum near focus distance is with the lens before you have to engage the macro) and 6 ft, I set the focus barrel to it's closest setting, and it's sharp. If the object is 6ft to infinity, I set the barrel to the infinity setting, and it's sharp.

Seems to have something to do with the way this lens breathes, but I never noticed it with the XL1s, only with the XL2. I give up. Seems to work fine other than that.

I was just used to not having to think about focus when fully wide, i.e. if I'm on an ENG style shoot and I don't want to have to worry about things going soft, I just stay wide and move around and shoot. Now I have to think about it.
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Old December 31st, 2006, 01:55 PM   #13
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Pretty normal behavior if you ask me... the lens does breathe quite a bit. The XL2 is MUCH MUCH sharper than the XL1s, you are noticing that more than the lens I suspect.



ash =o)
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Old December 31st, 2006, 02:41 PM   #14
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So that's all it is, then? Have someone else observed this?
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Old December 31st, 2006, 07:09 PM   #15
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If you want infinity focus... put it on infinity =o) pretty easy. As stated, the XL1s allowed you to cheat because of the lack of sharpness... you can cheat even more in 16:9 on the XL1s which is very soft compared to the XL2.



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