My rebel XT/Sigma lens - problem? opinions/help please.

Stustaff

Why is this image so bad, its sooo noisy!? Using a Rebel xt/350D with the Sigma DC 18-200

Cam info is
Shutter speed 1/1000 sec
Exposure program Manual
F-Stop f/6.3
Arpetyre f/6.3
ISO 200
focal length 200.00
No flash
Metering mode Pattern

Tommyboy

Got me. It's not super-cropped is it? My photos (same camera) don't look like this at 1600 ISO. Double check the ISO. If the problem recurs reliably, I would guess an issue with the image sensor?

marlof

Is this straight out of camera? Or is this after some adjustments compensating for underexposure? And is this a "through the air" shot, or did you have to shoot through a glass window?

Stustaff

No Glass No crop! The Raw file looks like this, just done a basic convert to jpeg

BenA2

Stustaff wrote:

No Glass No crop! The Raw file looks like this, just done a basic convert to jpeg

If all that's true, you may really have a problem. Are you getting the same results on other images? If so, I think you're going to want to have your camera looked at. It shouldn't have anything to do with the lens.

If it's only this image... Was it particularly hot when you took it? Heat increases sensor noise. But, even if it was 100F outside, this is still excessive for ISO 200.

ziggy53

I'm not seeing distinct shadows. Was it overcast?

ziggy53

ESiggins

wild stab here, but is it possible this was caused by over-sharpening by in-camera software, or accidental exposure compensation? (the manual for my D70 lead me to belive that exposure comp vasicaly does the same thing as increasing or lowering ISo)

Stustaff

not hot at all quite cool!

Ziggy yeh pretty overcast day.
Esiggins it was a RAW from the camera so no sharpening!

Ihave number of images like this all at 200mm. other shots are fine at shorter focal length.

weird?

photogmomma

I don't know anything about that lens, but the first lens I got with my 10D was a Sigma that was specifically NOT digital. (I bought my package from some very disreputable NY based camera ripoff company.) I brought the camera and the lens into a local camera shop and compared it with a similar Canon lens and it was night and day!

But the only thing is - my pictures didn't look like this. They were just really soft.... I'm just not sure if a lens can cause this kind of grain. But it's definitely worth checking out and comparing that lens to a Canon lens - and making sure that's specifically made for a digital camera.

Good luck. Having a lens that doesn't do what you want really sucks!

Stustaff

photogmomma wrote:

I don't know anything about that lens, but the first lens I got with my 10D was a Sigma that was specifically NOT digital. (I bought my package from some very disreputable NY based camera ripoff company.) I brought the camera and the lens into a local camera shop and compared it with a similar Canon lens and it was night and day!

But the only thing is - my pictures didn't look like this. They were just really soft.... I'm just not sure if a lens can cause this kind of grain. But it's definitely worth checking out and comparing that lens to a Canon lens - and making sure that's specifically made for a digital camera.

Good luck. Having a lens that doesn't do what you want really sucks!

Thanks but it is a Sigma 'DC' lens that means it is specifically designed to work with digital SLR's ONLY.
I really dont see why its doing this????

Cameron

Stustaff wrote:

No Glass No crop! The Raw file looks like this, just done a basic convert to jpeg

What did you use to do the RAW conversion? Are you certain the program you used didn't automatically boost the exposure on an otherwise underexposed image? I'd be curious to check out the original RAW file...

Stustaff

When I viewed the RAW untouched in Adobe Camera RAW it wa s as it appears now.

It really is like that right out of the camera!

marlof

Stustaff wrote:

When I viewed the RAW untouched in Adobe Camera RAW it wa s as it appears now.

It really is like that right out of the camera!

Adobe Camera Raw by default applies some auto adjustments to your RAW files. Go in ACR, and set everything to zero (exposure, shadow compensation etc.) and see if that still makes your picture look that way.

BigAl

For overcast conditions, 1/1000s @ F6.3 seems way too fast for ISO 200. I would expect shutter speeds like that at ISO 800 or even ISO 1600.

I've been trying to find a pic that will satisfy the criteria, and this is the only one I could find at F6.3 under overcast conditions. (t=1/200s, ISO 100 taken at 1424). Bumping this up to ISO 200 would give me roughly t=1/400s

marlof

BigAl wrote:

For overcast conditions, 1/1000s @ F6.3 seems way too fast for ISO 200.

That's why I don't rule out underexposure, which ACR automagically (exposure, shadows and brightness sliders) tries to compensate for. Turning off Auto, and setting these sliders to default should show if that's what's happening.

SpeshulEd

I'm guessing ACR bumped up the exposure and made the image noisey.

here's a really bad example...shot this at iso100, 30s, f/5.6


It needed to be exposed a lot longer...ACR tried to fix it. I think it was worse, but I tried to get rid of some of the noise.

ziggy53

Stustaff wrote:

...
Ziggy yeh pretty overcast day.
...

There's your answer! An overcast day indicates an Exposure Value of 12 or 13.

A proper exposure in those conditions should have been more like (at ISO 200 and f6.3) 1/200th or 1/250th, or around 2 - 2 1/2 stops more duration. A contrast increase explains the additional graininess.

The coarse grain then is the result of strong underexposure, with extremely low contrast, with subsequent compensation by software.

Different RAW processing through different software might produce improved results.

Why the camera chose that exposure is another mystery?

ziggy53

Windwalker

Aperture Ring
I have had a terrible time with my Sigma 70-200 F2.8 lens until today. My pictures were turning out much more grainy the yours. I thought something was wrong with the lens.

Then I noticed that the shots my wife took were much better then mine, sharper and with less grain. The difference was that I had set the camera (*ist DS) to automatic along with the lens when giving it to her. Then I noticed my F stop set in my photos were all F2.8 and the shutter speed very fast (F2.8 @ 1/2000), as apposed to her shots that had more believable settings (F8 @ 1/650)

I took some test shots today with my lens on and off the auto setting of the aperture ring of the lens and had much better results on the auto setting then using the aperture ring on the lens.

Here is what I think is happening (subject to conformation from Pentax). The camera is unable to read the aperture from the lens. It sets the default as F2.8 and adjusts the shutter speed accordingly. The sensor has insufficient light to record a usable image and so “pushes” the ISO speed of the exposure until it has a usable image. This is the cause of the grain.

When I set the lens to auto (“A”) and use the aperture adjustment in the camera I don’t have this problem. The camera sets the aperture correctly and the exposure is correct. If I want to adjust the aperture I should use the electronic setting letting the camera set the lens.

I am checking with Pentax to see if the camera does in fact do it this way, but it fits all of the criteria. As an old film photographer I am in the habit of using the aperture ring instead of the electronic setting in the camera. Might you be doing the same?

Stustaff

YOU could be onto something here windwalker!

I was in AV mode and went to 200mm and then altered the arpeture to 6.3 which is as open as it will go at that zoom.

I will have to have a play and see.

It was puzzling because I have had other shots at 200mm that are fine.

Ziggy your right it doesnt add up it looks too fast doesnt it!

But should I be contacting Cannon/Sigma because the combination really shouldnt cause sucha problem should it?

Windwalker

Aperture
From Sigma;

You MUST be in auto or wide open, but they wouldn't (or couldn't) tell me why. Still waiting to hear from Pentax. It takes a few days via email.

ziggy53

Stustaff wrote:

YOU could be onto something here windwalker!

I was in AV mode and went to 200mm and then altered the arpeture to 6.3 which is as open as it will go at that zoom.

I will have to have a play and see.

It was puzzling because I have had other shots at 200mm that are fine.

Ziggy your right it doesnt add up it looks too fast doesnt it!

But should I be contacting Cannon/Sigma because the combination really shouldnt cause sucha problem should it?

I suspect that you and Windwalker are having two similar results, but for different reasons.

Continue to test your camera to see if you can duplicate the exposure error consistantly. Many things could have caused this type of error that are not the result of a defective camera.

A strong light from behind or to the sides can (potentally) casue light to come in the camera through the viewfinder, altering the exposure. I am not saying that is what happened here, but there are many possibilities to explore.

ziggy53

ziggy53

Windwalker wrote:

From Sigma;

You MUST be in auto or wide open, but they wouldn't (or couldn't) tell me why. Still waiting to hear from Pentax. It takes a few days via email.

That is curious. Which lens specifically?

In the mean time, I would trust the response from Sigma which seems to correspond with your own observation.

ziggy53

Windwalker

ziggy53 wrote:

That is curious. Which lens specifically?

In the mean time, I would trust the response from Sigma which seems to correspond with your own observation.

ziggy53

Sigma 70-200 F2.8 APO DG EX

The emails I got back from them didn’t seem to be knowledgeable, just repeating the party line, i.e. I was corresponding with a “technician” , not someone who understood the design of the lens. I’m still waiting to hear back from Pentax, who, if they follow their normal timeline, should get back to me by next week. To be fair, if I needed immediate information I would just call and sit on hold for 5 to 10 minutes.

ziggy53

Windwalker wrote:

Sigma 70-200 F2.8 APO DG EX

The emails I got back from them didn’t seem to be knowledgeable, just repeating the party line, i.e. I was corresponding with a “technician” , not someone who understood the design of the lens. I’m still waiting to hear back from Pentax, who, if they follow their normal timeline, should get back to me by next week. To be fair, if I needed immediate information I would just call and sit on hold for 5 to 10 minutes.

That's a pretty current lens, so I guess I'm surprised that it requires "Auto" mode or wide open for proper operation. That is disappointing (I feel your pain.) There may be something goofy in how the lens "communicates" with the body that requires the Auto mode for full integration.

I had two copies of the EOS mount of the same lens, and there was no aperture ring or auto mode switch, so I don't have experience that way, and my experience with Pentax only relates to manual focus M42 and PK mount lenses and cameras. Hopefully someone will chime in, or you might start a new thread, lest we hijak this one.

ziggy53

Stustaff

Mine is a current lens too! that doesnt seem to mean much, taken some more shots and got same effect basically in Av mode if I go to 200mm then open lens to 6.3 this is the shot I get, It appears as if the camera is allowing/giving to fast a shutter speed and then trying to save the shot!

the problem doesnt of course occur in any other mode!

BigAl

Are the numbers you gave with your first pic from the EXIF or memory? I have a Bigma, and at the widest aperture it tells the camera 5.6 and not 6.3 so that the autofocus will work. I'd imagine the 18-200 would do the same, so if you're getting 6.3 from EXIF and you had it on the widest aperture, something is fishy.

Stustaff

Yeh thats from The Exif Bigal I think the camera is miscomunicating with the lens!?

Im going to do a test today and see if I can work it out.

kygarden

I have the Nikon version of this Sigma 18-200 lens and I've never seen anything like that happen to me (using D200). I know that doesn't help you, but at least you know someone else (me) is using the same lens and doesn't have that problem.

These were at 200mm with the Sigma 18-200. Different lighting conditions than your photo though...but if it helps...

ziggy53

Stustaff wrote:

Mine is a current lens too! that doesnt seem to mean much, taken some more shots and got same effect basically in Av mode if I go to 200mm then open lens to 6.3 this is the shot I get, It appears as if the camera is allowing/giving to fast a shutter speed and then trying to save the shot!

the problem doesnt of course occur in any other mode!

I agree that this sounds like a repeatable and legitimate problem, probably originating from the lens. If Sigma can't explain it, then I believe they should replace it.

I did find this very similar experience to yours:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00CkrC

ziggy53