 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| PhotoKB HomeDiscussion Groups Digital Photography Digital PhotoDSLR CamerasZLR CamerasPoint & Shoot CamerasFilm Photography 35 mmLarge FormatMedium formatDarkroomFilm and LabsOther EquipmentPhoto Technique Nature PhotographyPeople PhotographyTechnique GeneralGeneral Photo Topics General TopicsAustralian PhotographyUK PhotographyDirectoryPhoto Clubs |
Photo Forum / Digital Photography / DSLR Cameras / December 2005Glitch with Canon 300D?
I've been taking a few 'bulb' pictures recently, and on one batch noticed a slight lightened colour cast down the right hand side 10% of the picture, similar to how you might with film where a bit of light has leaked in. I originally put it down to some light entering the lens from a source I hadn't seen in the dark, but took some more today and got the same thing. Any ideas what this could be? I've not noticed any leakage of light on settings other than bulb before. Is my camera/lens bollixed? Any suggestions gratefully received. || I've been taking a few 'bulb' pictures recently, and on one || batch noticed a slight lightened colour cast down the right [quoted text clipped - 5 lines] || leakage of light on settings other than bulb before. Is my || camera/lens bollixed? Any suggestions gratefully received. Did you cover the viewfinder/eye peice? That is often the source of stray light.  Signature"Weak and fearful people deny, and hide from, the horrors of the world, believing that the pretense of a benign world will make it so. This self-deception ultimately creates more horror." -- Machiavelli > || I've been taking a few 'bulb' pictures recently, and on one > || batch noticed a slight lightened colour cast down the right [quoted text clipped - 8 lines] > Did you cover the viewfinder/eye peice? That is often the > source of stray light. No I didn't, but I didn't think there was any light coming in from behind. Its possible there was however, so I'll try again and take your advice and see if it makes any difference. Thanks for incredibly quick response! >No I didn't, but I didn't think there was any light coming in from behind. >Its possible there was however, so I'll try again and take your advice and >see if it makes any difference. Thanks for incredibly quick response! Quite a bit of light can come in through the viewfinder. Outside in bright daylight, I have seen f-stop and shutter speed figures on the top LCD of my cameras that showed a considerable amount of light, only to realize that the lens cap was on. For example, in Av mode at f/8, the shutter speed might read 1/4. Cover up the viewfinder with my finger, and it goes to 30s. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< > >No I didn't, but I didn't think there was any light coming in from behind. > >Its possible there was however, so I'll try again and take your advice and [quoted text clipped - 6 lines] > shutter speed might read 1/4. Cover up the viewfinder with my finger, > and it goes to 30s. Wow, I'm going to check that out. I should be putting the cover on for my long night exposures. Greg >Wow, I'm going to check that out. I should be putting the cover on for my >long night exposures. Of course, there actually has to be a light source behind the camera to have a problem! OK, now I just did an experiment and realized something. I just shone (is that a word?) my 2M candlepower flashlight into the viewfinder of my 20D, in AV mode, with lens cap on, and snapped a picture. The camera metered for full exposure, but the resulting image was extremely dark, so I guess it affects metering much more than it does the actual exposure. That makes sense, when you consider the fact that the mirror goes up against the prism area during the exposure. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< > >Wow, I'm going to check that out. I should be putting the cover on for my > >long night exposures. > > Of course, there actually has to be a light source behind the camera to > have a problem! Yeah, after Santa Anas blow the smog out I've been taking night shots of downtown LA 12 miles to the south of me. From my back patio I have my neighbors patios lights to contend with Greg >> >No I didn't, but I didn't think there was any light coming in from >behind. [quoted text clipped - 8 lines] >> shutter speed might read 1/4. Cover up the viewfinder with my finger, >> and it goes to 30s. >Wow, I'm going to check that out. I should be putting the cover on for my >long night exposures. My 300D came with a viewfinder cover. It is a rubber bit with some groves on the side meant to be threaded onto the carry strap. Works just fine. ---- Paul J. Gans >>>>No I didn't, but I didn't think there was any light coming in from >> [quoted text clipped - 19 lines] > with some groves on the side meant to be threaded onto > the carry strap. Works just fine. Yeah, I know, mine is on the strap. Just basically forgot about it. Greg Signature"Destroy your safe and happy lives before it is too late The battles we fought were long and hard Just not to be consumed by rock and roll" - The Mekons >>No I didn't, but I didn't think there was any light coming in from behind. >>Its possible there was however, so I'll try again and take your advice and [quoted text clipped - 6 lines] > shutter speed might read 1/4. Cover up the viewfinder with my finger, > and it goes to 30s. Great. But since when did this become an issue that can affect only a _portion_ of the picture? Light does indeed enter through the viewfinder, which can screw up the _metering_ (thus affecting the entire picture), but it doesn't normally reach the sensor (or the film). The OP states that only a portion of the image was affected, which means that it has nothing to do with the viewfinder. -- Best regards, Andrey Tarasevich > Did you cover the viewfinder/eye peice? That is often the > source of stray light. It would never reach the sensor with the mirror up. SignatureStacey > I've been taking a few 'bulb' pictures recently, and on one batch noticed a > slight lightened colour cast down the right hand side 10% of the picture, > similar to how you might with film where a bit of light has leaked in. www.google.com: amplifier glow >www.google.com: amplifier glow On my Canon 10D, I see that in the lower right edge on some long images. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< > >www.google.com: amplifier glow > > On my Canon 10D, I see that in the lower right edge on some long images. The AG on my 10D shows up on long exposures as a patch of bright that extends from the right edge to about ~15% across the image towards the left. It dribbles away, not an abrupt transition. The OP's description is consistent with this, but of course it is possible "real light" is worming it's way in somehow. A weird lens flare? Simple experiment: wrap the camera in some towels, put it into a dark closet (preferably at night), and take a picture of the blackness. >> >www.google.com: amplifier glow >> [quoted text clipped - 8 lines] > Simple experiment: wrap the camera in some towels, put it into a dark > closet (preferably at night), and take a picture of the blackness. Although I haven't yet tried testing it to see if it was light leakage from through the viewfinder, I'm pretty confident that its AG, as it matches your description of it. Its easily cropped out, but to ensure it all goes, it means losing about 20% of the width of the picture. > Although I haven't yet tried testing it to see if it was light leakage from > through the viewfinder, I'm pretty confident that its AG, as it matches your > description of it. Its easily cropped out, but to ensure it all goes, it > means losing about 20% of the width of the picture. No need to crop: just subtract a dark frame from the image. Read around: www.google.com: dark frame This will also remove hot pixels from the image, and even some residual "fixed pattern noise". This dark-frame subtraction has to be done with the raw camera data. The higher-end PhotoSlop code can probably do it, but you can download various astronomical image processing tools for free. Alternatively: my 1DMk2 doesn't suffer from the problem to anywhere as near a degree as the 10D. If the 20D/350D is the same: buy a new camera. It's Christmas. And it's what Canon wants you to do anyways ;-) >Although I haven't yet tried testing it to see if it was light leakage from >through the viewfinder, I'm pretty confident that its AG, as it matches your >description of it. Its easily cropped out, but to ensure it all goes, it >means losing about 20% of the width of the picture. If you take an image immediately afterward with the same ISO and exposure time, with the lens cap on and the viewfinder cover, you have the necessary data to subtract it. I don't know how well software can take advantage of it; for best results, the subtraction should be done to the RAW data, and I don't know if there are any programs that will do that and still do a quality RAW conversion. The 20D has this as a feature; it subtracts the black frame from the image before writing the RAW file (if you enable the feature, and it only works with 1 second or longer). Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< > If you take an image immediately afterward with the same ISO and > exposure time, with the lens cap on and the viewfinder cover, you have > the necessary data to subtract it. I know the 20D has dark frame substraction (toggleable via custom functions), doesn't the 300D? -Wolfgang > > If you take an image immediately afterward with the same ISO and > > exposure time, with the lens cap on and the viewfinder cover, you have > > the necessary data to subtract it. > > I know the 20D has dark frame substraction (toggleable via custom > functions), doesn't the 300D? The 10D doesn't have it, so it's unlikely the 300D does either (but only an owner can definitely say). The 20D/etc implementation of dark frame subtraction leaves a lot to be desired though. As far as I can tell, it collects one (1) dark and subtracts that. While this will removes any biases, it does add noise. Better would be for the camera to gather 10 or more darks, average them, and then subtract that from images. A convenient UI for this would be something like the "manual white balance" stuff: pick and choose from a set of already captured darks. For most uses, though, this is probably not an issue: http://www.lrgb.com/20dadark.html a page that even includes a 300D dark frame, amplifiers aglow. > > If you take an image immediately afterward with the same ISO and > > exposure time, with the lens cap on and the viewfinder cover, you have > > the necessary data to subtract it. > > I know the 20D has dark frame substraction (toggleable via custom > functions), doesn't the 300D? The 300D, no, the 350D, yes, but only for longer exposures, bulb only I believe, or ISO1600. Greg >> If you take an image immediately afterward with the same ISO and >> exposure time, with the lens cap on and the viewfinder cover, you have >> the necessary data to subtract it. >I know the 20D has dark frame substraction (toggleable via custom >functions), doesn't the 300D? I never heard of it having that feature. I wish it were available on the 20D on shorter exposures as well; some of the pattern noise other than hot pixels, in short exposures, are similar frame to frame. Vertical banding is repeatable; horizontal banding is unique per frame. Of course, it would be nice if the black frame had a filter run on it to remove the pixel-frequency noise. Anything that isn't a line, a glob, or a streak should be filtered away. Two black frames could verify what is repeatable and what isn't even further. I wouldn't mind losing some burst speed for an optional higher quality mode. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< [dark frame substraction] > Of course, it would be nice if the black > frame had a filter run on it to remove the pixel-frequency noise. > Anything that isn't a line, a glob, or a streak should be filtered away. Thanks, but I prefer to do my image degradation later myself. > Two black frames could verify what is repeatable and what isn't even > further. I wouldn't mind losing some burst speed for an optional higher > quality mode. Go ask Canon. There's the 20Da, maybe there'll be a 20Db for you. -Wolfgang >[dark frame substraction] >> Of course, it would be nice if the black >> frame had a filter run on it to remove the pixel-frequency noise. >> Anything that isn't a line, a glob, or a streak should be filtered away. >Thanks, but I prefer to do my image degradation later myself. What degradation? My suggestion was about removing sensor artifacts that are *repeatable* and are clearly *NOT* signal. The filtering was to remove the random sensor noise from the blackframe, because subtracting it *ADDS* random noise to the image. Instead of filtering, 4 black frames could be averaged together, etc. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.