grainy photos

strictlypentax · 06-02-2007, 05:38 AM

I posted this in the welcome section, but thought I might need to put it some where else as well.

Hello everyone. I was told by someone in another forum that I may get some help here. Let me introduce myself briefly. My name is Misty and I have been shooting for about a year now. I have learned a lot, but still have a whole lot more to learn.

My most current problem is with grain. I currently purchased the FA 50mm 1.4, and haven't been able to shoot with it without getting grain. Now I did some experimenting and found that when I shoot with my strobes, I'm okay. Shooting in low light situations is my problem. I bought this lens JUST to be able to shoot in low light, and it hasn't done the job I expected of it.

Also, I am getting purple crosses on my photos. I have NEVER had this happen before. Anyone know what's going on?

I have been told by some on another forum that they think I am underexposed, and the fact that I didn't CWB is a problem. Now, I don't understand how I can better expose when I was already @ f1.7. The person that made that comment didn't explain to me how I can compensate for the 2 stop underexposure. As I said, I have a lot to learn, so I just really don't understand this.

I know this is the welcome section, but I sure hope someone will help me anyway.

Thank you everyone!

Oh, btw, no flash. I am shooting some place TODAY that is low light and doesn't allow a flash. That is what I bought this lens for. I have had it for a few days now, and still can't figure out how to get rid of the grain.

Dave Lee · 06-02-2007, 06:15 AM

First of all, don't let a little bit of grain(noise) bother you. Sure, when you zoom in to 100% on the screen it looks terrible, but are you going to print it at that size? You will probably find that it isn't so bad on your final image.

As far as the underexposure, adjust your exposure compensation up 1 ev and see how that works. I don't know how to do that on your camera, so I can't tell you exactly how to do it. You will have to experiment to see how much compensation you will need in different situations.

Good luck,

Dave

Edit: Also, if you are shooting in low light situations, the higher iso required is going to give you more noise. There isn't much you can do about that. Again, on your final image, it's probably not going to look that bad. There are also software options to remove the noise: Noise Ninja, NeatImage, etc.

strictlypentax · 06-02-2007, 06:18 AM

thanks Dave,

Actually my camera only lets me expose 1/2 or 1/3 in ev compensation, and it says that when shooting manual-which I do-it won't work.

Dave Lee · 06-02-2007, 06:23 AM

If you are shooting in manual, just bump the shutter speed down until you get an exposure you are happy with.

strictlypentax · 06-02-2007, 06:41 AM

Well, I knew to do that, but someone else had told me I needed a faster shutter speed than what I am using! They didn't say that would fix the exposure, just said I needed to shoot @ a faster speed. Man, I am sure not getting this!

Thanks for talking this out with me Dave. I appreciate some input.

strictlypentax · 06-02-2007, 06:47 AM

Also, what about that purple cross??!!!

thazooo · 06-02-2007, 07:20 AM

The purple cross is probably a stuck pixel, These can come and go, if it stays and remains in the same spot you've got 2 choices. Clone it out or send your unit back to Pentax for a Pixel mapping to remove the stuck one.
If your brightening an under exposed image, this will cause an increase in noise. It's what happens using digi. Using the exif data, you might try shooting a similar scene at 1/60 or 1/45 @ f1.7 and see if your results are more pleasing. You can also raise your iso to 400 and not notice any increase in noise over iso 200.

*egordon99* · 06-02-2007, 07:21 AM

How did you meter to get 1/90s, f/1.7, ISO200? Or did you just pick those out of the air? That seems like it would be underexposed by quite a bit in a low light situation. Perhaps Photoshop (or whatever you used to convert the RAW file) automatically boosted the exposure for you, which would of course result in grain/noise.

I don't understand how I can better expose when I was already @ f1.7

This comment leads me to believe you really don't understand how the three exposure parameters work. Pick up a copy of Bryan Peterson's "Understanding Exposure". It's a quick read and would probably help you understand this problem. In a nutshell, to let more light hit the sensor, you could have used a slower shutter speed, or increased the ISO. I'm regularly at ISO800 with my FA 50mm in low-light (and at f/2.0 or f/1.4) to keep the shutter speeds up.

The purple cross is a hot pixel, any competent RAW converter can remove them, and you shouldn't see them when you convert to a JPG anyway.

strictlypentax · 06-02-2007, 07:43 AM

I used the on camera meter to get that exposure. I metered with multi-segment, and that particular shot is SOOC JPEG.

You're right in a way that I don't understand how they work. Like I said, I do know that a slower shutter speed, higher ISO, and lower aperature will allow more light, but I was told I should be shooting @ a higher shutter speed. I can posibly acomplish this if I bump up the ISO, but again with the grain. I thought the grain was so bad @ 200, that I didn't even TRY anything past 400.

I do not claim to be at a professional level, but I am working to get there. I do have that book mentioned, and have tried very hard to read it. I am still having difficulty understanding it, but I intend to go back to it next week while my kids are @ their grandmothers. Because my mind just can't wrap around this, I need COMPLETE SILENCE in order to soak it in (of course even then it may not soak in).

Thank you all for your replies.

raz · 06-02-2007, 07:49 AM

if your subject is not moving you can shoot at shutter speed of 1/45 not 1/90 , and so you will double the light coming into the camera. Preferable with a tripod.

And the best thing to do, in my opinion, use the Av mode of your camera, set the aperture to 1.7, and let the camera do the rest, it will pick the right shutter speed. And you can also set your iso at 400 safely I think, with my k100d I can shoot images with no grain even at ISO 800 indoors.

strictlypentax · 06-02-2007, 08:38 AM

Thanks for the suggestions. Yes, my subjects will be moving, so I do need a good shutter speed.

raz · 06-02-2007, 09:07 AM

oh well, if your subject is moving, you will need a fast shutter speed as well ...so you don't have to many options, just increase the ISO, make the room lighter, or use the F 1.4 instead of 1.7

davemdsn · 06-02-2007, 10:07 AM

If you are getting noise at 200 and 400 iso then you are most deffinitely underexposing. I used to have the *istD, which had the same sensor as the DL, and at 200 a correctly exposed image had no noise/grain whatsoever. Even with film, correcting for an underexposed image would cause the image to be grainy.

The meter in you camera is trained to make things middle gray. If you are looking for bright snappy people photos you are going to want to set it to overexpo0se by about a stop.

Your camera works in 1/2 or 1/3 stops of exposure compensation in auto modes. Note that those are steps, not totals. It will do one to two full stops of exposure compensation.

Keep bringing you questions here and you will get good advice. More experience in this forum than I have seen in most others.

Oh, and shoot RAW! Get a decent RAW converter that will get rid of those stuck/hot pixels for you. I get them from time to time but never have to worry about them because my apps take care of them automatically. RAW will also give you a LOT more flexibility in exposure correction. Once you go RAW, that's what you'll..... (searching for a synonym for want that rhymes with raw)....

strictlypentax · 06-03-2007, 09:35 AM

Thanks Dave. I do shoot RAW. I'm still trying to get ahold of this. I will be re-reading Understanding Exposure next week. The only thing is my model will be gone for two weeks, so I will have some difficulty getting some good practice in. My husband tries to help, but I'm embarassed to post anything I get of him as he always looks like he is mad @ the world when I take his picture!

You have all been very nice to post responses. I hope to be able to stay in this forum for a while. Thank you.

Misty

*LeoTaylor* · 06-03-2007, 03:42 PM

I too am confused by the purple square with the plus sign in the first photo.

To me a hot pixel would be a white dot, only one pixel in size. Since this square covers many pixels I assume it is added by a computer to mark the location of a hot pixel. Who adds it? Is the camera adding the symbol (I dread to think so). Is the software Misty is using to process the photo adding the square? Can this "feature" be turned off?