Weird image softness/ghosting when shooting towards the sun.

[Joe Holt]

Ok. I realize that most of the experienced XL2 users have probably moved on but I'm posting this in the chance someone can shed some light on a little mystery I'm experiencing.

I am a free lance camera operator for the local school district and one of my duties is to shoot and edit all high school athletic events for delay broadcast on cable television. I've done this for three years now and the cameras we use are XL2s. We have 3 of them with identical set ups with 18X lenses.

Here's the weird thing. When shooting softball and baseball I have to shoot towards the setting sun so the scene is heavily backlit. Now I'm not shooting directly into the sun as I'm not getting lens flares. What I do get is a strange double image/soft focus when I'm zoomed in. It isn't really just soft focus as some areas of the image are sharp while others are blurry and even look like some form of ghosting. It happens with all three cameras in exactly the same way. It doesn't matter if I'm using ND or not or if I have a polarizer. It always does this until the sun drops behind the hills. Again. I am not getting lens flares. It seems to me that somehow light is reflecting within the lens causing this strange ghosting. I know I should post a frame grab but don't have access to footage right now. Maybe I can post one later if I know someone is actually interested in seeing it. So here's my main question...

Has anyone else experienced this?
Is there anything I can do to alleviate this (that I haven't already tried)

Thanks in advance for the help.

BTW: I think this is my first post in about 7 years. I forgot how much great info there was here.

[Bob Hart]

My imagining is that even with ND, your lens aperture may still be chosen as f16 or even tighter in the environment you were shooting in by yourself or camera auto. As well as any internal reflection between sensor and lens optics or within the lens itself, an optical phenonema known as diffraction may become a big factor in this issue you are having. Diffraction is a bigger problem with smaller sensor cameras apparently. There is also the complication of having a threeway prism split in the optical path. CCD sensors also smear vertically any highlights. If the image is all highlight as in shooting against the sun, then there will be masking blur and a vertical definitions within that blur which will look like ghosting.

There was a publication on the Sony VX1000 way back when Noah was a pup, which suggested that no tighter than an f5.6 aperture was the preferred way to go with 1/3" sensor cameras.

There's not much I can suggest as a remedy but I would be tempted to use a ND6 soft grad filter or even ND9 if it can be had as a soft grad filter, to kill off the bright sky but leave you with the players still visible. You would need to elevate your camera position sufficiently that you can have their heads in the darker portion of your image, backgrounded by the play area or crowd.

The grad filter might best be a 4x4 in a mattebox versus a screw-in or clip-on style as the vertical position in a 4x4 mattebox can be adjusted.

Heed the wiser people than I on this topic.

[Don Palomaki]

Can you post a frame grab showing the issue, and give us the camera settings (aperture, shutter, gain, zoom setting).

As noted above apertures smaller than f/5.6 will start to show diffraction issues..

Without seeing the image it is hard to say, but any chance it is a back-focus issue?

[Bruce Watson]

Originally Posted by Joe Holt

Now I'm not shooting directly into the sun as I'm not getting lens flares. What I do get is a strange double image/soft focus when I'm zoomed in. It isn't really just soft focus as some areas of the image are sharp while others are blurry and even look like some form of ghosting. It happens with all three cameras in exactly the same way. It doesn't matter if I'm using ND or not or if I have a polarizer. It always does this until the sun drops behind the hills. Again. I am not getting lens flares.

And yet, you are describing lens flare. The sun doesn't have to be in your frame to induce lens flare. All it takes is for the sun (or the stadium HMIs for that matter) to be lighting all or part of the front element -- so the sun itself can be well outside your frame. This is why we have lens hoods and matte boxes. Or assistants who can stand in the right place and block the sun from shining on your lens with their body, a hand, or a hat.

[Khoi Pham]

Bob is right, that is lens diffraction, you should shoot in aperture priority or Av and set your aperture at f 4 to 5.6 and let the camera do the rest.

[Joe Holt]

Thanks for the quick and thoughtful responses. I would like to post a frame grab but I only shoot for them part time and don't have ready access to the footage. I will be back in there on Friday and will be shooting towards the sun again so I will try to verify the aperture and set it to 5.6 . I usually shoot everything on full auto and so I bet the iris is clamping down even though I am using the highest ND in the lens. I've never had this problem before and I used to own a VX1000 and likes to shoot with my subject's back to the sun and use a reflector for a fill . Never saw this phenom until now. Of course that wasn't a 18x lens either.

I'll report back after Friday. Thanks again for taking the time to help me solve this mystery.

[Don Palomaki]

What portions of the image are soft - e.g., foreground, back ground, moving objects, all, only in camera moves?
What portion show ghosting?

What is the Noise Reduction setting. (some of what you describe sounds like image artifacts of a High internal noise reduction setting - see page 69 of the user manual).

[Joe Holt]

First, I would like to thank all those who have responded. We did have a softball game to shoot yesterday but unfortunately it was overcast so I could not recreate the conditions. I have attached several frame grabs.

The shots of the scoreboard show a good example of the phenom I have been talking about. This was shot at a baseball game earlier in the season. The camera is on full auto and the lens is zoomed all of the way in. As the day prograsses (notice 7th inning frame grab) the problem mysteriously disappears. I changed nothing. The only thing that changes is the sun muves from 45 degrees (shooting towards it) to about 90 degrees.

The two shots with the runner on base and the girls heading into the dugout were shot yesterday. (bright, overcast) I had the camera on full maual with 1/16 ND and the iris set to around 4.6 (it changed as the day progressed). Looking at the frame grabs in these, looks to me like I have a back focus issue but these lenses do not have a back focus adjustment. (That I know of) I turned noise reduction off and had the camera set to a preset with cine gamma and color. (if that matters to anyone).

Finally, I mispoke earlier... The lenses we are using are 3 identical Canon 20X Zoom +5.4-108mm L IS 1:1.6-3.5.

Thanks again for all of the responses. Joe

[Bob Hart]

Looking at those frame grabs and I am really tossed for a burton. Absolutely no clue what's going on.

I would normally expect to see a backfocus artifact as a round area of soft focus but this is almost a vertical band. The three way prism split of the image may have something to do with that however. The prism is oriented vertically. On groundglass 35mm adaptors, a tight image path through prisms will cause edge brightness fall off parallel to the sides.

The soft area is offset to right of centre as viewed. (optical axis offset to left). This is consistent with Sony and Canon 4:3 MiniDV cameras of the vintage so I would not fret over the offset. I expect that all your cameras will be doing this with maybe a littlle variation from fair wear and tear.

If the artifact occurs identically with all cameras using the same model lenses then it is likely something which is designed in and cannot be fixed, only avoided.

The cure may be for the fittings on the back of the lenses to be adjusted by either an internal adjustment or if there is no internal adjustment, adding or removing shims between the mount on the back of the lens and the lens body, a tiresome and fiddly business best done and possibly only doable in a workshop.

It seems this is an old and wellknown issue with the XL2 and this lens combination :-

http://www.dvinfo.net/forum/canon-xl...us-clunks.html

There may be an unholy combination of incorrect backfocus and diffraction going on. The lens iris when wide open will make a backfocus problem more apparent. With the iris tight at say f16, diffraction might also become more apparent zonally if the backfocus is off.

I also note that this lens becomes slower by around two f-stops from wide to zoomed fully in. In a wider shot, the image will be brighter, zoomed in, it will be darker. How that affects the diffraction traits of a lens would be anyone's guess unless they are an optical engineer. My imagining is that a diffraction trait would become more aggravated by zooming in if the lens is already set at about f16.

I understand, maybe wrongly, that the servo system on the XL Canon auto lenses of that vintage may be mechanically switched from a single drive motor and that both zoom and focus may not be operable at the same moment, but either one or the other.


My personal experimental preference for the moment would be :-

For the brightest part of the day depending on conditions, use an ND3 or ND6 filter in front of the lens which might hopefully reduce internal flaring within the lens, use a mattebox with flags to keep as much of the side light out as possible. I cannot remember now if the XL2 has an internal ND system.

If there is one, then I would use the ND3 on front and trim ND with the in-camera ND to try to keep the lens aperture at about f5.6, for two stops wider, one stop narrower before needing to switch in more or less in-camera ND.

The only other time I have seen a vertical soft artifact like that was when a strainer wire from a pole was getting in the shot but was almost invisible through being out of focus when the lens was zoomed in.

I wouild also select image stabilisation "off". Air bubbles have been known to move into the image area of fluid prisms used for optical image stabilisation. I would not expect to see such a defect across three lenses.

[Don Palomaki]

If the XL2 is like the XL1, the back focus adjustment for the automatic lens is an internal electronic setting that is stored in the camera, and is temperature compensated as well for the lens/body temperature. I believe that the adjustment tends to be a match of the lens to the camera body, so swapping lenses among bodies could cause less than optimum back focus.

Back focus is adjusted using the modified Sony RM90 (If I remeber the number) - "Remote Commander for Adjustment."

Photo almost looks like a smear of something on the lens.

[Joe Holt]

Bob,

I really appreciate your taking the time to write such an informative reply. I too believe I actually have several things going on at once. I do believe that I was experiencing lens refraction as you described it and I noticed that the problem was "fixed" yesterday when I set the camera to manual and controlled my iris with the ND filter trying to keep the iris from clamping down. The images from yesterday look more like back focus which brings me to Don's reply.

Don,

You may have hit on an answer to my problem. As I said before, we have three identical XL2's with the exact same lens. Last Fall it had come time to send the cameras in for some overdue service and repairs. One had body components that needed repair and another had an image stabilization problem with its lens. So clever me, I swapped lenses so I could send in one camera and lens that needed repair and could keep a working camera to shoot with. If the lenses are matched to the cameras, then I think that could explain why they both show a similar degree of back focus softness. I will swap the lenses back and see if that helps clear things up.

Again, Thanks again both of you for the insights.

Bob, you may not remember me but I remember you from way back when a group of us were chasing the illustrious "Homemade" 35MM adapters. Remember the Agus 35? I haven't been back here since then. The forum sure has gotten bigger.

[Bob Hart]

Good to see someone remembers "the old days".

The AGUS35 and its descendents along with the benchmark P+S products, so soon the featherdusters along with HDCAM based 2/3" Cinealta. I used to joke about the future with street urchins hauling discarded Cinealtas around clattering on the pavement by the cables as drag toys. I no longer offer that levity as the cameras are appearing on eBay like unwanted pets much sooner than I dreamt.


Alas, like me it, AGUS35 has become history back, that a current generation weaned on the Canon 7D probably does not even know about.

Agus Casse himself? My guess is that being the resourceful person he seemed to be, likely as not, he may be driving a RED Scarlett these days. I last heard from him about four years or so back when I was thinking about a small documentary on the topic.

As for groundglass 35mm relay, that has pretty much had its day but medium format relay or 70mm remains very much valid, albeit difficult to implement as it means back to the drawing board and expense.

I managed to get the Letus Extreme up to the real-world performance of the Sony EX1 and the Silicon Imaging SI2K and perhaps do a little better if pure blue and red colours are not mixed highlights in the same image. "Apparent" dynamic range of the cameras appears to be improved. This may however be a smoke and mirrors thing.

Dennis Woods was able to do the same with his Cinevate varifocal relay for the SI2K for his own Brevis adaptor. I don't know if the other adaptor makers persisted so far. The Canon 7D shut that gate fairly smartly despite its own drawbacks.

At 2K, the interactive elements of the system have to be so micromanaged that your reactive creativity is pretty much stifled unless you train up and remain instinctual with it. With fast lenses capable of covering as large a groundglass area as one can get, the choices become limited.

However, there were still three films at Sundance which were originated with groundglass 35mm adaptors.

The wall is the five micron ideal for groundglass texture. The only way forward for detail and sharpness is larger and larger groundglass screens. The lens choices for plate camera format are really abysmal and the hardware, huge and unwieldy.

That did not stop the Coatwolf guys from doing a custom camera for their indie movie "Bellflower" and doing weird dangerous things like sitting out the window of their character car with the "camera" in one hand and the laptop computer recorder in the other.

That is not to say somebody will not do a large format groundglass again for a unique or niche indie project. Like as not, there will be a RED Scarlett on the rear end but I suspect whoever does it will be fairly quiet about it.

Groundglass relayed imaging can still make a well lit and shot piece look more filmic straight out of the camera than the RED and Alexa until the images from those are post-processed.

I cause webmaster Chris Hurd some grief every now and again by enlivening the original thread every now and then. It must surely be a waste of server space by now.

[Joe Holt]

Hey all! I just wanted to give an update. We had a baseball game today. It was another overcast day with lots of diffused lighting but even so, I controlled the iris with the ND filter and noticed that the strange partially soft spots did not appear today. After shooting the game, I had a few free moments to swap lenses back to their original cameras. ( I forgot to do it before the game) I noticed that the overall sharpness of the camera was greatly improved with it's original lens. My guess is I had two compounding problems; Lens refraction from shooting into the sun with the iris clamped down and a soft back focus because of the lenses being swapped around.

Thanks again for the insights. I would never have figured it out on my own.