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-   -   flange back problems with XF300 (https://www.dvinfo.net/forum/canon-xf-series-4k-hd-camcorders/488241-flange-back-problems-xf300.html)

Reinhard Kungel November 30th, 2010 09:56 AM

flange back problems with XF300
 
Hi together,

had the feeling for several times, that sometimes XF300 is not really sharp in picture.

Today I took several shots of the bavarian mountains and made some test. Back home in my editing-suite I was shocked to see, that some shots really are not sharp. Actually this is nearly impossible, because it is not a interchangable lens. Canīt believe it, but in fact, it is. By the way: it was a little bit cold, around minus 10 degree (Celsius), but I had the problems also at normal temperature (around 20 degree Celsius).

The way I made the test: Zoom-in into a tree, which is around 300 Meters away, then I focused manually (infinite looks sharp), zoom back, then I changed focus in steps from invinite down to one meter. The shot looks sharp betwen 1-2 meters. But actually the distance is around 300 Meters. Strange.

regards, Reinhard

Steev Dinkins November 30th, 2010 02:27 PM

I also noticed focusing issue phenomena with the XF305. Here's some of the results of my testing:


More detail is in this post:

In short, I am finding that the lens is not parfocal when aperture is open more than f3.2, and the ND filters make this problem worse. Aperture closed down past f3.2 essentially eliminated the issues.

My end conclusion was to double check all focusing if aperture open faster than f3.2.

Chris Hurd November 30th, 2010 02:34 PM

Diffraction (soft focus) can occur not only at extremely
small apertures but open apertures as well, in some
conditions. Is it possible that's what you're running into?

Reinhard Kungel December 1st, 2010 12:48 PM

Hi Chris,

used stop was around 4. Canīt imagine that this stop can cause problems.

regards, Reinhard

Reinhard Kungel December 1st, 2010 12:55 PM

Hi Steev,

might be the same problem. Canon wants to check the camera. Hope to know more in some weeks.

Reinhard

Jeff Lower December 1st, 2010 06:36 PM

I'd love to hear what they have to say once they get back to you about it.

Reinhard Kungel December 2nd, 2010 04:52 AM

Hi Steev,

what I really donīt understand: how can ND-Filters downgrade sharpness?
Canon is building high-end-lenses.

Josh Dahlberg December 6th, 2010 01:11 AM

Hi Reinhard,

I'd be very interested to hear more on this. I've run into exactly the same problem a number of times - just the other day I zoomed in for critical focus on a subject 30m away, pulled wide for the shot, only to find in the studio the clip horribly out of focus. This happened a few times on the day, always outdoors with NDs engaged and f2-5.6 range.

Even with the 4" screen and magnification on it can be difficult to focus manually if you must stay wide. Very irritating.

I've owned a number of 1/3" cameras (XHA1, XL-H1, Z5 et al) and never run into anything like this...

Reinhard Kungel December 8th, 2010 04:47 AM

Hi together,

today Canon Germany was calling me by phone. They told me, that they canīt find any focal problems.
They made test, inside and outside (minus 4 degree celsius) and everything went fine.

Thats all I can say for the moment.

regards,

Reinhard

Steev Dinkins December 8th, 2010 11:27 AM

Quote:

Originally Posted by Reinhard Kungel (Post 1596161)
today Canon Germany was calling me by phone. They told me, that they canīt find any focal problems. They made test, inside and outside (minus 4 degree celsius) and everything went fine.

Interesting. What I'm wondering is if they specifically tested for parfocal focusing accuracy throughout the entire focal length zoom range. You'd think that would be a given, but maybe not.

Perhaps, guaranteeing parfocal accuracy seems to be a challenge with this high of a resolution camera. Anyone have an EX1/EX3 to compare lens parfocal quality/behavior?

So far, I love the lens image quality itself, but the lack of constant aperture, lack of near focus consistency through zoom range, and questionable parfocal performance are all bummer points.

Reinhard Kungel December 11th, 2010 05:20 AM

Today my XF300 came back. A letter from Canon Service tells, that they made several tests for a whole day, but couldnīt find any problems concerning focus. Not to draw wrong conclusions from, but the AF-Button of my XF300 now is switched from manual to automatic. I never use automatic-AF and I just hope, they didnīt made the test on AF-Mode.

Steev Dinkins December 11th, 2010 11:25 AM

Quote:

Originally Posted by Reinhard Kungel (Post 1597368)
I just hope, they didnīt make the test on AF-Mode.

Now that would be sadly comical. I think I'm going to do some further tests to really understand the behavior of parfocal performance, or lack thereof. I haven't had issues with shorter ranges of zooming. Its just going full telephoto, establishing focus, then going all the way wide, when at low f-stop that is not keeping focus.

Regardless, I'm so impressed with the image quality and highlight handling in post, I'm getting an XF300 as a camera B.

In short, I'm developing a very ingrained habit of using that magnification button to confirm focus, and not making as many assumptions as I did with the HVX200. The resolution is incredibly higher, and focus is more critical now than ever.

Josh Dahlberg December 11th, 2010 06:28 PM

"Its just going full telephoto, establishing focus, then going all the way wide, when at low f-stop that is not keeping focus."

Yes that's a good definition of the problem Steve... things can go horribly awry when doing so! But this is really quite frustrating as it's standard procedure for many (inc. me).

It's quite hard to fathom how the Canon techs couldn't replicate this with your camera Reinhard, given that it's not subtle, it's really obviously out of focus when you do what Steve describes. Bet you wanted to pull your hair out when you got that letter.

I don't find magnification on the XF powerful enough to confirm focus - it works much more effectively on my 5DII.

Reinhard Kungel December 12th, 2010 04:21 AM

"I don't find magnification on the XF powerful enough"

Hi Josh,

I confirm. You are right. With my EOS-550 itīs much more easier (higher factor).

Don Palomaki December 12th, 2010 08:41 AM

A single frame grab at full zoom and full wide rather than the video might be easier to judge.

Did you send Canon a sample video illustrating the concern? Sometimes that helps them see what the issue is! A picture being worth 1000 words.

Reinhard Kungel December 12th, 2010 01:47 PM

Shure I did. But unfortunatelly they couldnīt reproduce the problem.

Alex Footman December 19th, 2010 11:46 PM

I know I'm jumping in a little late here, but this revelation about parfocal problems really dampens my enthusiasm for the XF300. In my work I need to trust that focus will stay sharp, and given the extreme lighting situations where I am I routinely shoot fully open and as closed down as possible plus ND filters.

Given that I won't be able to trust manual focus to stay sharp through the zoom range, how have you found the autofocus? Is it useable or does it hunt? I still use an XHA1 and AF mode is useless because of hunting issues.

Reinhard Kungel December 20th, 2010 02:12 AM

Hi Alex,

Iīm one of these old-fashioned guys who only use manual focus. I never trust in automatic, never. But as you say: if theres is no guarantee in manual focus, than it becomes difficult.

Reinhard

Robert Turchick December 20th, 2010 07:47 AM

The AF really depends on the situation. As with all cameras, light makes a huge difference. I have mostly been using mine in full daylight or controlled lighting shoots. I shot a series of auditions for a tv show and just for grins decided to try the face detection AF mode. Not a critical shoot so wasnt concerned if it messed up. To my amazement, it never missed. I mean not once! I then used it for a greenscreen TelePrompTer shoot where the actor would be walking around a bit. Dead perfect! This is the real deal and not a gimmick! Not saying I'd use it all the time but for certain types of shoots, it makes life insanely easy! On a recent shoot, my XF found itself flying on a glidecam 4000 and I suggested to the operator to leave it in face detection AF mode. Worked great!
Since discovering how well it does work, the only times the AF had a problem were in unlit indoors situations (chasing my kids around the house) and one shoot where the background was too bright (used the backlight feature and it helped) So in extreme lighting conditions, use manual. But give the face detection mode a try (I use the instant mode) and as long as the white box is around your talent, you are perfectly focused!

Doug Jensen December 20th, 2010 08:05 AM

Robert, I agree 100% with your assessment of face detection. It's not for everyday use, but it really does work in the right situation.

James Miller December 28th, 2010 03:46 AM

Doesn't adding a nd behind the rear element change the lens characteristics? I know if I use anything thicker than a gelatine filter behind the lens the lenses does not function as parafocal.

Are all these issues found after ND's are flicked on? Are the ND's too thick?

Alex Footman December 28th, 2010 04:41 AM

Robert,

Thank you for testing this out and posting about it. I have no shame in declaring that this feature will make my life easier. Given the situations I shoot in (no preparation, managing sound levels and ad-libbing interview questions on the spot) trusting in auto-focus would take a big load off my mind. Starting to take this camera seriously, especially if there's a good telephoto adapter on the market. Also, a trustworthy AF takes a lot of the sting out of the single-ring configuration.

Brian Drysdale December 28th, 2010 04:42 AM

In cameras with built in ND filters, there is always a piece of optical glass in the image path otherwise you will get back focus problems. The rear ND filters have to be manufactured to a tight specification to avoid thickness variations, although this doesn't mean that one or more sub standard NDs got into the system.

This would be best tested by shooting with a fully open aperture and testing each ND filter for back focus variations. You'll need to control the lighting level for the correct exposure,

If there appears to be a variation between ND filters I'd send the camera back to Canon.

James Miller December 28th, 2010 07:37 AM

Brian, yes sorry I didn't account for the clear optics in the image path, still if it not a problem before switching to the inbuilt ND's the ND's are at fault. You would have thought this would have been tested when the camera went in for service.

I had a bad copy of a Canon 2.8 70-200mm IS that had slight play (about 1mm) on the zoom ring not the focus ring, and would shift a pin sharp image out of true just by rocking the play.

I wonder if you are finding any slack on these lenses?

Alister Chapman December 29th, 2010 10:58 AM

I've experienced similar problems on my EX cameras after bumpy journeys or shipping, clearly rough handling and shocks can upset the focus tracking. With the EX it's just a matter of running the back focus routine in the service menu to restore accurate focus tracking.


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