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Nickagain Feb 11, 2004 10:31 PM

Wanted. C740/C750 owner for noise test.
I have an Oly C750. Apart from the normal levels of "salt and peeper" noise on dark shots/ long exposures, it gets "hot pixels" These look like stars. The best way to get this is to take a lens cap shot at around 10 seconds.

I first noticed it when I took a night shot of stars, and saw a lot more "stars" than should have been there!

I can get rid of a lot of it by image manipulation. But it is still annoying and interesting.

I have had somebocy send me a lenscap shot from a Fuji S602 (3Mpi). It has _none_ of this at all.

I would like to see if it's just my camera, or whether, it's the model.

I would also like to see if the 3MPi C740 has less of this problem.

I guess I would also like to see if other makes with 4MPi sensors have the same problem, but that's the next step.

If oly are not up to scratch, they need to look at this IMO.

Appreciate any help.

Norm in Fujino Feb 12, 2004 2:20 AM

What ISO are you shooting your lens cap at?

Nickagain Feb 12, 2004 6:08 AM


Originally Posted by Norm in Fujino
What ISO are you shooting your lens cap at?

It doesn't matter. Even at ISo 50 it has these "stars"

Do you have either a C750 or 740, so I can see if other cameras have the same rpoblem?

Nickagain Feb 12, 2004 6:28 AM

>What ISO are you shooting your lens cap at?

OK. Here is a shot from somebody else's C750, actually finding out about _another problem (flaring in the TLHC) with them........

.......sorry........No there's not. I can't see how to attach an image. \OK. I am no longer interested in C750s.

Anyway, the other guy's had the same "starlike" noise problems.

C740 is what I am looking for now.

Please. There is so much muttering about oly c750 cameras and hot pixels, I would like to see the truth.[/img]

jayp Feb 12, 2004 8:10 AM

Try this....
In the cam menu choose the "pixel mapping" function and run it. This is supposed to eliminate any "dead pixels" which are causing this problem.

Norm in Fujino Feb 12, 2004 9:05 AM

I took a couple of lenscap photos, one on the automatic (night scene) mode, and the other on manual, 10 seconds, F4 or so.

The automatic mode produced a photo of only about 99k, and I couldn't discern any "stars" in it at all. The manual mode shot was 809k (go figure), and did show some stars, but not so many that they bothered me (how many is too many?). At 1:3 enlargement, I couldn't see any; at 1:2, I could see some, but not brightly. At 1:1, several more showed up, but again, not so many as to be disconcerting. As I increased enlargement, I was able to see them better, but I don't know how significant that is, since I'm not one to blow up photos that large, anyway.

Since the photo is so big, I don't feel like wasting space by uploading it to my website, but if you want to see it, I'll e-mail it to you. Let me know your address if you'd like it.

PS: I haven't done any pixel mapping.

Later update Okay, I just tried pixel mapping, but the photograph I took afterwards looks just about the same (still some "stars" at high magnification).
What? Me Worry?

jkusmier Feb 12, 2004 2:06 PM

Here's a link to one C750 owner's lenscap test results:

EXIF: 16s, ISO 200, F3.2, NR off.

I've seen other results, and performed the same test on my own C750. Enable Noise Reduction and try it again - you'll get a perfectly black picture.

jkusmier Feb 12, 2004 2:08 PM

Just curious, why aren't you using NR on your long exposure shots?

Norm in Fujino Feb 12, 2004 3:54 PM


Here's a link to one C750 owner's lenscap test results:
This one must've been shot at HQ (based on file size). It has noticeable stars at 1:3 mag, while my SHQ shots don't at all. Just now I tried shooting at HQ, and while a couple of stars were barely noticeable at 1:3, they weren't nearly so noticeable as the shot posted above.

jkusmier Feb 12, 2004 4:40 PM

No way to know - he could have taken the pic in TIFF, then converted before posting (I didn't check for EXIF info, but I doubt any is there). I suppose high compression rates could make noise appear more noticeable...

Anyway, this is all academic. Enable NR - it will completely eliminate hot pixels. It's been my experience that a SUBSTANTIAL NUMBER of the complaints made about the C-750 come from users who haven't even read the manual or learned about the camera's features.

As regards noise in general, I personally have a very low tolerance for it, but haven't noticed any noise in the C-750 at ISO 50. It's barely noticeable at ISO 100. Acceptable at ISO 200, though given my aforementioned intolerance of noise, I rarely use ISO 200. Objectionable at ISO 400, which I never use. That said, image noise is inevitable in consumer digicams. Want noiseless pics at ISO 800? Get ready to shell out the $ for a dSLR. I've seen elevated noise at ISO 400 in every type 1/1.8 and 1/2.5 ccd I've looked at. The noise levels in the C-750's 1/2.5 is average. Think this is bad? Better stick to film, because you'll lose sleep over the noise produced by the 8Mp 2/3 type ccd's found in the new Sony's, Canons and Olys. Was hoping manufacturers were going to start making consumer digicams w/ low-noise 4/3 and APS sized sensors, but instead they're trying to cram as many pixels as possible into smallish sensors. Sadly, most consumers are under the simplistic (and mistaken) impression that more pixels = better image quality. Sure, 6 Mp are better than 4 - but not at the expense of reduced dynamic range and higher image noise.

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