Back Focus Issue with the EX1????

[da//media]

Hi ,
I am curious, I have seen a couple threads were members have complained of a back focus issue on the EX1...

not really familiar with this term, what exactly is back focusing in lamen's terms?

also another question:
would my image res. be worse if I put both ND filters on with my iris open (f1.9-f9)
or would it be better if I was to put one ND filter on and close the iris down more (f9-f16)
I have heard that running the cam at f16 or around there cuts down on clarity badly.

can someone clarify this for me?
thanks
Matt

[basspig]

Backfocus is the ability to maintain the lens elements in focus throughout the zoom range. The issue that myself and at least one other user have discovered with the EX1 is that when you focus on a distant object at max tele, and then back out to wide, focus is lost. That means the lens failed to maintain proper backfocus.
In the XDCam EX, the problem was found to be connected with the use of the ND filters.

Lenses tend to be sharpest at wide open apertures. The reason the image softens at small apertures (high f-stops) is due to a phenomenon known as diffraction--light bending around the iris blades (usually 6 blades that open and close like... well, an iris). This diffracted light makes up a percentage of the total light passing through the iris. When the iris is wide open, that's a very small percentage that is diffracted, so the image circle projected on the imager is maximally sharp. When the iris is almost closed, the unobstructed area is very small, so a larger percentage of the light passing through is diffracted (bent) around the iris blades. This results in a softening of the image.

[See tukka]

I just got my ex1. Amazing camera but I´m also suffering with back focus problem...Should I test the auto back focus calibration in the camera?? Does do any good? Does it affect my warranty??

[da//media]

So now would this issue still be applicable when utilizing full manual focus with the camera??

Matt
DA//MEDIA

[Barry_Green]

It's a problem if you want to employ the traditional technique of zoom-in, focus, zoom-out and shoot.

If you want to focus at the same focal length you're shooting in, then it's less of a problem. But it's very difficult to get precise focus on a wide-angle shot; it's much easier to get pinpoint focus by zooming in. That's where the problem comes in though; the lens isn't holding that focus when you zoom back out to shoot.

[Stevet]

I just read from the "other" forum that someone sent in their EX1 for the back focus issue. It came back fixed.

[matthew77]

And, to add to what Barry said, if back focus is off in the "wrong direction" it might be impossible to find a point within the range of your lens focus, where the image is sharp.

Especially true at wide angles.

[rainermann]

Hi
there are massive backfocus problems, when you use an ND filter! Please try it for yourself: ND1 or 2 on, zoom in - focus - zoom out - out of focus! Without the ND filter there are less problems. I know about a lot of people here in Germany having that problem. A few of them send it to Sony but got it back unrepaired: Sony told them it is a problem they don't have a solution yet and they need to communicate with Japan first.

[DeeZiD]

I corrected the Backfocus Issue myself with AutoFB Adjust and ND2 on.
Just tried again today with F1.9 and ND2 - still ok :)


regards Dennis

[matthew77]

Now that you've done that, how does it work with ND Off? That's the real test.

[DeeZiD]

It is working as before with no ND filter.

Dennis

[Stevet]

Hi
there are massive backfocus problems, when you use an ND filter! Please try it for yourself: ND1 or 2 on, zoom in - focus - zoom out - out of focus! Without the ND filter there are less problems. I know about a lot of people here in Germany having that problem. A few of them send it to Sony but got it back unrepaired: Sony told them it is a problem they don't have a solution yet and they need to communicate with Japan first.

Apparently not massive,
tried it, my camera's fine.

This would of been noticed on day one since 99.99% of everything I focus is done by zooming in focusing and pulling out.

[basspig]

It is working as before with no ND filter.

Dennis


I tried BF adjustment with ND1 and it threw off the backfocus with no ND, so if you're checking on LCD, better to check on larger monitor--you'll see it's a compromise between ND and no ND--everything is soft in both settings.

[matthew77]

There is definitely a problem with your guys' cameras.

Like Steve, I just tested mine (again) and it's perfect with all filter settings.

[da//media]

but technicaly this issue only happens with autofocus??
cuz when I manual focus my EX1.....zoom in and set the focus, then zoom back out and zoom back in it is still in focus.... or maybe thats not the problem i should be looking for??

matt

[basspig]

I never used autofocus in daily shooting. It hunts too much. So I, and others, are observing the problem in FULL MANUAL mode.

I spoke with a technician at Sony today about my camera. Bottom line is they don't yet know what the backfocus problem is being caused by, but Sony Japan is working on it as a HIGH priority.

He was less encouraging about the CA problem, but did acknowledge that the printout of a single frame showing the problem demonstrates that it exists, though he was unable to observe it with testing in the shop.

I mentioned the battery draindown issue and the matter is also being tackled by Sony engineering.

He sounded optimistic that Sony will find fixes for at least two of the above issues. He said they are actively working on solutions for these problems and something should be forthcoming soon. I don't know how soon. I've got a busy shooting schedule this month, and an even busier one in April. I expressed that I do not wish to be spending thousands in rental fees (in fact, I just drove into the city to return a rental this afternoon). Hopefully we can work something out for a loaner, if this is going to take several weeks.

[See tukka]

I´m a little afraid of adjusting the backfocus myself. I bought the camera from US and i´m from europe so I don´t have warranty here. Can I make worse by doing it myself?? I need to bring the camera to US for repair some day this year. Where is the sony repair center in NY??? or is there any?? Can I send email there? anyone got email adress?? What is the estimate for repair of the backfocus cause I can´t stay in the US for very long cause it´s quite expensive to live in hotel in manhattan:)

Thanks guys,

[basspig]

The repair center is in San Jose, California. And they don't yet have a solution for the BF problem. Hopefully, that will change VERY soon. Rentals are expensive!

[Stevet]

The repair center is in San Jose, California. And they don't yet have a solution for the BF problem. Hopefully, that will change VERY soon. Rentals are expensive!

Hmm..
Seeing I just read a post from someone I believe overseas said he sent his camera in for this very back focus issue and it came back fixed!

[Lenilenapi]

I just saw some serious backfocus problems on a wide shot f the Golden Gate bridge. I must have used the ND though I don't recall my f stop or filter settings.
Will try again with external ND filters.

This bothers me esp along with the CA problem

Lenny

[robfilms]

not having the camera, i ask the following out of ignorance:

if internal nd1 & nd2 somehow "cause" the backfocus issue, would the use of external nd filters also "cause" the loss of backfaocus?

has anyone access to a set of screw-on or drop-in nd filters that they could test?

as always, thanks to all for discussing the camera's issues.

i'm sure/hopeful that work around solutions will soon be developed.

be well

rob

[matthew77]

rob,

Filters won't affect backfocus when put on the front of the lens. Technically, they will affect forward focus, but so little that it's negligible.

The effect on focus on either end is maybe half a millimeter. In front of the lens, that is essentially zero. In back of the lens, that's a huge amount, especially at wide angles.

[robfilms]

matthew77-

thanks for the info.

since filters won't affect backfocus, a screw-on/drop-in nd filter would cut the light allowing a low f-stop (and the resulting narrow dof) while not losing focus.

would the above be a decent work-around for the current nd1/nd2/backfocus issue?

thanks in advance

be well

rob


rob,

Filters won't affect backfocus when put on the front of the lens. Technically, they will affect forward focus, but so little that it's negligible.

The effect on focus on either end is maybe half a millimeter. In front of the lens, that is essentially zero. In back of the lens, that's a huge amount, especially at wide angles.

[matthew77]

Absolutely, it's really the only workaround if your internal filters are screwy. But at a great cost to the convenience and speed that the internal filters provide.

My filters work fine - so I think this (clearly annoying) backfocus thing is only on some cameras.

But I wonder if it's a failure that will happen over time to the cameras that are currently working.

[robfilms]

matthew77-

which filters do u use?

screw-on?

drop-in?

if so, which matte box fits the ex1?

thanks in advance

rob

[matthew77]

rob,

perhaps you misunderstood - my internal filters work fine so I don't need to use external ones (for ND).

I haven't purchased a matte box for my EX1. For what I do I shoot everything clean and adjust in post.

There are others (phil bloom?) who have a lot of experience with matte boxes and can tell you more.

For the occasional use of a polarizer, I use a screw on. Mostly this means losing the factory matte box as many filters are too thick to allow it to be put on top of them.