Even More XL2 Lens Problems

[NewBee]

Hi Folks,

Just wanted to make certain that everyone is aware that the BF issue seems to be cropping up with the 3x Lens as well. I have read/heard that Canon was unable to address this issue for at least one of its customers.

What does this mean?

BF like issues have been reported for the 20x, 3x, and Century Optics .7x Lenses.

Unfortunately, C. Hurd seems to continue to avoid full discussion of these issues on his board. Not trying to cause trouble. Just trying to be candid and honest ... :-/

Thanks In Advance

[Zim]

what is a BF issue?

[scharky]

BF= Back focus ie. when you zoom in and get exact focus, and then zoom back out the image goes out of focus. All I can say is that the back focus issues have to do with the lens itself, and canon should adjust it for you if you are unable to like on the manual lenses.

[NewBee]

Yes BF=BackFocus. Canon *should* be able to adjust it for you. However, I have heard of several instances with the XL1s where this was not the case. I have also now heard of a situation with an XL2 where canon was unable to resolve the BF issue on the 3x Lens ...

Between the problems with the Century Optics .7x adapter and the problems being reported by folks with the 3x combined with the issues reported on the 20x, this seems to be a rather nagging problem ... :-/

It deserves serious discussion and consideration. Especially if you are considering purchasing an XL2 ...

[Chris_Hurd]

Howdy from Texas,

<< Unfortunately, C. Hurd seems to continue to avoid full discussion of these issues on his board. >>

Gee whiz. I'm "avoiding" that issue only because I have absolutely nothing constructive to add to it. If I knew something about it or if I had any advice or assistance to lend to it, then of course I would do that. But in all honesty I don't know a damn thing about it, so what would you have me say? I'm not an apologist for Canon, I don't work for them, I have no secret inroads with them or any real way to help out with this issue. The best thing I can do is to provide the discussion platform for that problem, and I'm doing that. If there is any other way I can help out, please tell me so here, or on my boards, or by private email and I'll do what I can.

For the most part though, if I don't have a clue about something then I try my best to keep my mouth shut about it (lots of people will tell you this doesn't always work for me though). Otherwise I'd be doing more harm than good. Of course I'm open to any and all constructive criticism, but accusing me of "avoiding" an issue is a little harsh. I'm not avoiding it; I just don't have anything helpful to say about it (sure wish I did, though). Hope this clears things up a bit,

Chris Hurd
San Marcos, TX

[icicle22]

I have now had my 20x lens reset to factory specs and according to them the camera is "properly calibrated" for Backfocus. And indeed this seems to be true. However with the .7x WA from century it is indeed still exhibiting the backfocus issue. In addition on shots that I am able to get focused very good I am still seeing a softness and haloing around the outer edge of the frame. I see none of this with the 20x alone. So the WA from century is showing an Unnacceptable ammount of "distortion/blurriness" around the perimeter. I even bought a 2nd CO .7 wa to test and it behaved exactly the same.

Here is a link to a .7x CO adapter on the DVX100 that shows the softness I am referring to. This is not my camera but an image that shows what I am seeing.....except a little worse.

http://www.icexpo.com/dvx100/Century_7_full_wide.bmp

In fairness this is at its worst when the iris is wide open and the camera is pulled back as wide as possible. However I never had these issues with the Xl1/XL1s and the .6x century. Sure there was a little barrel distortion but not blurriness. I am going to test this in really well lit areas and see if it goes away when I stop way down. But as of this moment it seems as though there is a limitation on how much you can open the iris before the image starts to "soften" too much. I know lenses have "sweet spots" that are usually in the f4-f5 range where they are their sharpest. But this would have to be considered a "sour spot" where the image is too soft.

Incidentally I spoke with a knowledgable rep from canon and was told that with all zoom lenses you will get a focus shift when testing for backfocus as a result of the iris closing in the telephoto range. In other words if you zoom in all the way the iris stops down to f3.4. Then you focus based on that aperture. As you zoom out the iris opens back up to f1.6 and you depth of field decreases and your focus shifts and can go soft. While this makes sense to me now I am wondering why for years I didn't have to compensate for this on the Xl1 or DVX that exhibit the same aperture shift. I just zoomed, focused, zoomed out and everything was great!

I am not flaming about this at all. I just want my focus to stay constant and currently it is not. In my early tests this issue is alleviated by shooting with the exposure at f3.4 to start so that when you zoom the aperture doesn't change. However I am frequently in environments where I need to open up the iris all the way to properly expose the images. And in these cases I have softness with the WA adapter. Without it there is no focus shift or it is so miniscule I cannot detect it.

Please feel free to add to this as I am trying to determine how to work this all out!

Peace!

[icicle22]

http://www.iciclestudios.com/images/xl2/compare.jpg

Here is a comparison shot with the .7x and the 20x alone. I see significant distortion and softness on the sides of the .7x but none with the 20x. Pay close attention to the yellow network cable wrapped up in the upper right. Also note the person standing in the distance. Isn't this too soft to be acceptable? It started out in perfect focus but as I backed out these annomalies reared their ugly heads!

thanks!

[NewBee]

My sincere apologies Chris,

As I have mentioned in the past, I am really not trying to cause trouble. It does seem that a pattern is emerging though with respect to BF issues on the XL2 lenses.

It sounds like this is not the "softening" or "pixel averaging" problem that you referred to on the board. If I recall correctly, I think I remember posts where you have referred folks to the manual 16x Lens if they had concerns regarding BF on the 20x. Unfortunately, if problems exist on both the .7 WA and the 3x, then this provides some serious questions regarding WA functionality on the XL2.

Once again, *PLEASE* believe me when I tell you this: "I am really not trying to cause trouble or start a flame war" I am really interested in the XL2 and think it provides some beautiful images. However, these are very legitimate questions that I would like to see discussed/addressed.

From a consumer standpoint, this is a major concern. Especially if I am going to comit to spending $6,000-$7,000 of my hard earned dinero.

Apologies if I have offended you in any way. That is not my intent.

Humble Apologies and Peace :)

[Barry_Green]

Isn't this too soft to be acceptable? It started out in perfect focus but as I backed out these annomalies reared their ugly heads!
That's horrible.

Would have been nice if you could have framed the shots the same, so we could see how much of the difference is attributable to the presence of the .7 vs. how much is just due to the images being smaller/below the threshhold of rendering cleanly.

But I gotta say, that doesn't look too good...

[scharky]

Yeah that looks really bad. It's hard to say who is at fault. It seems that Century optics keeps blaming the lens and canon keeps saying that the lens is fine. Can't say I have any advice for you except for keep on them. This is not acceptable for a $4500 camera and a couple hundred dollar wide angle adapter. I have used Century optics products in the past, and have always been happy with them, and have never seen anything that bad, except with a cheapo ebay wide angle lens that a friend had. Good luck to you both.

[icicle22]

That's horrible.

Would have been nice if you could have framed the shots the same, so we could see how much of the difference is attributable to the presence of the .7 vs. how much is just due to the images being smaller/below the threshhold of rendering cleanly. *

But I gotta say, that doesn't look too good...



You mean zoom in with the wide angle adapter as to get the same "FOV" as the 20x alone? I was standing against a wall so I could not back up any farther with the 20x. Hence the reason why I would use a WA adapter in the first place.

[icicle22]

*This is not acceptable for a $4500 camera and a couple hundred dollar wide angle adapter. *

A couple hundred dollar wide angle adapter????? try $599-$749 for this depending on where you get it. I expected a lot better. I will post a comparative shot with the .6x to see how it looks. I got the .7x because the .6x softened the image a little. But the .7x has been a step backwards thus far.

Thanks!

[Barry_Green]

You mean zoom in with the wide angle adapter as to get the same "FOV" as the 20x alone?
Exactly. I know it's not the normal circumstance for you to use the lens under, but it'll help eliminate some variables and determine much more definitively if it's the presence of the .7 that's causing the problem.

[icicle22]

http://www.iciclestudios.com/images/xl2/compare/index.htm

take a look at these. they are not exactly framed the same but I don;t think you need to be to see there is something wrong. And just to clarify I can reproduce this on 2 different .7x adapters so it is highly unlikely that it is defective.

I always heard that the .7x was sharper. This doesn't jive with that theory.

[Barry_Green]

I'd say that's just unacceptable. *There's something wrong going on there. Definitely have Bill Turner take a look at the photos, I'm sure there must be something out of whack somewhere. If not, and that's the way it's "supposed" to look, the Century just doesn't look like a usable solution for an XL2 user!