turning ISO 1600 into 3200, how to?

I've read that the 350D can simulate ISO3200 by underexpose ISO1600 in 1 stop. My questions is how can we do it? Cand anyone tell me in a step by step "guide"?

Imagine I'm in M mode I choose 1/125 and then 4.5 and now how can I select the underexposure value? What keys?

What do I need to do afterwards? I read that shooring in RAW mode we need to correct the underexposure of the photo to 0, correct?

Thanks a lot

Hi. Check this post out if you haven't seen it.
http://forums.dpreview.com/forums/read.asp?forum=1031&message=17540058

first of all, no you cant have iso 3200 by underexposing by one spot. there are many many problems with that. One is underexposed images suffer from much higher noise to signal ratio, and simply doing a gamma correction would give you so much noise. test it yourself by shooting an image at iso 800, with correct exposure, and then lower the iso to 400, but use the same exposure parameters and then lighten it up. Second is that your highlights carry approximately half of your tones, so by underexposing, you are cramping your histogram, and loose many of the tones.

However, if you were to do it under manual setting, in the buttom of your view finder you see a line from -2----1---0---+1---+2. Set your shutter speed aperture combination such that its on (-1). in any of the creative modes, there is a button on the back of the 30 which is exposure compensation, and you hold it down and turn the weel, and it sets tha arrow fo the exposure to anywhere between -2 to +2. If you hazzard this technique, I strongly suggest that you shoot in raw, and have a good noise reduction software.

In Manual mode the exposure is made automatically by adjusting the shutter speed? Thats the only way I see the exposure setting moving from -2 to +2 in 350D.

That means we cannot set the shutter speed, exposure value and depth of field with our own settings or am I doing something wrong?

Sorry if I'm writting "stupid" things, I'm just giving the first steps on photography.

By the way what good noise program are you talking about? Any suggestions? Whats the best one?

VladDrakul said:

By the way what good noise program are you talking about? Any
suggestions? Whats the best one?

Click to expand...

I personally like Noiseware. There's a free ("community") version, or you can purchase to get batch and Photoshop plug-in capabilities:

http://www.imagenomic.com/

And for what it's worth, I've had very good results often with the technique you've asked about. I've had to shoot RAW, underexposing by two full stops, at ISO 1600. Usually these shots in dark settings don't need to be brought up to "0" exposure in RAW conversion, since they're already occurring in dark settings. Noiseware helps a ton, then it just takes a little more tweaking here and there in post than usual. It's not technically "ISO 3200" or "ISO 6400", but the results often turn out far better than I expect, and it's a lot better than missing a shot entirely or getting something super blurry.

I haven't bothered to sharpen this for the resize for posting here, but this was with a Sigma APO 70-300, ISO1600, f/5.6 @1/200 (underexposed by 2 full stops), then processed quickly as described above. Camera/lens were at their limits, but I got the shot. The green stuff is the leaves I was shooting through, and I personally like the effect:

hope this makes sense..

first, to do this, you must shoot RAW.

2- set to ISO1600. if your exposure should be 1/125@f/4.0 (example), set to that (M mode)

3- change your exposure settings by either slowing the shutter to 1/60 OR aperture to f/5.6.
4- take the shot.
5- the resulting shot will be underexposed by 1 stop.

6- in your RAW conveersion program, on the exposure slider, set to "+1 stop".. this has the effect of bringing the exposure levels up to what they would have been at ISO 3200. the resulting image will have more 'noise' than it would at ISO1600, exposed as metered. what you are doing is the digital equivalent of 'push processing' in the old film days.. forcing your film to behave the way it would if it were one stop faster.

7- if you have noise reduction software - NeatImage, Noise Ninja, etc. apply it to your image.
8- enjoy your image!

note- you really are only doing this in a situation where 'getting something' is more important than 'getting the perfect shot' - and you need to be accepting of the resulting faults.

Cheers,
S.
--

• How deep does the Rabbit Hole go? *

Free the Images
My XT IS Full Frame -- APS-C/FF of course!

ScottyNV said:

3- change your exposure settings by either slowing the shutter to
1/60 OR aperture to f/5.6.

Click to expand...

Think you meant set the shutter speed to 1/250 not 1/60, since setiing to 1/60 (when the camera wants 1/125) would result in "over-exposing" by 1 stop.

--
Good Day,
Roonal

'Money doesn't buy happiness, but it makes for an extravagant depression' by golf tournament sportscaster

just to reiterate a point made earlier - where this technique causes problems is with noise - noise affects dark areas and details. So, the closer you can get to filling the frame with the subject (making a huge assumption that your subject isn't the dark aspect of the image - i.e. a black panther or black cat or whatever), the better this technique will work. The more cropping you need to do the more pronounced the degradation of detail due to noise will be.

So, for instance, close up shots this technique can work quite well. But for something like low-light sports where you often have to crop the technique does not work so well.

It's like any other tool in your bag - you just have to understand it's abilities and limitations - as long as you use it withing it's limitations it can get you a shot you would otherwise miss. But it won't take the place of having a faster lens or ISO 3200 from a higher end camera (and yes I realize the 20d/30d do something similar to achieve ISO 3200 - it's just the results tend to be much better)

in manual mode you hold down the exposure compensation button on the back of the camera, while turning the dial to change your aperture size. Take a look at your manual for the basic functioning.

I use neat image noise reduction. it is excellent, and free, although I bought it, becuase the freeware version looses your exif information, does not do batch, and does not work as a plug in, and does not work on 16 bit images. but I doubt any of that is going to be of consequence to you at this point.

You will see some "posterization" of the image, as you try to expand your histogram. that means the transition between different levels of gray will not be as smooth. again remember to shoot raw. of course tripod is also an excellent alternative, though I understand not always practical.

as I said I'm new to photography, so I've still not understood entirely this tecnique because I can't seem to set the underexposure setting (meaning the bar on the -2... 0 .....+2) to what I desire. This is bringing some confusion to my head.

I set up the photos to RAW, also ISO1600.

In M mode I set the camera to 1/125 and then to 4.0. Now depending what I'm focussing, dark or lighter subjects the underexposure bar on the -2... 0 ....+2 wanders freely....

what I do next?

vlad. you really need to read the manual. On the M mode, you dont set the exposure compensation, but rather the exposure level by altering your f stop and your shutter speed. Have your f stop to as low of a number as it goes. then change your shutter speed so that the arrow is on -1. as you use faster shutter speeds, the arrow will move in negative direction and slower shutter speed, will make the arrow move in the positive direction in M mode.

--

• How deep does the Rabbit Hole go? *

Free the Images
My XT IS Full Frame -- APS-C/FF of course!

LIke "understanding exposure' by Brian Peterson. He's not able to understand any of the basics you guys are trying to explain...

--
http://www.pbase.com/mariush

VladDrakul said:

I set up the photos to RAW, also ISO1600.
In M mode I set the camera to 1/125 and then to 4.0. Now depending
what I'm focussing, dark or lighter subjects the underexposure bar
on the -2... 0 ....+2 wanders freely....

what I do next?

Click to expand...

1) DON'T MOVE THE CAMERA - pick ONE subject or scene to focus one.

2) For the subject you are focused on, the meter (the -2...0...+2 bar) will tell you how far under or over-exposed you are based on your CURRENT camera settings (1/125 and f4.0 and ISO 1600)

3a) Now EITHER turn the jog wheel to increase or decrease the shutter speed until the indicator on the -2...0...+2 bar is at -1

3b) OR press the "Av+ -" button while at the SAME TIME turning the jog wheel to increase or decrease the aperture setting until the indicator on the
-2...0...+2 bar is at -1

------------------------------------------------------------------------------------------

Alternate Technigue:

1) Set camera to Tv Mode

2) Set shutter speed to 1/125

3) Press the "AV+ -" button and at the SAME TIME turn the jog wheel til the indicator on the -2...0...+2 bar is at -1

Now NO MATTER WHAT you point the camera at, light or dark (within reason of course - limited only by the smallest/largest aperture of the lens you're using), the camera will select an aperture such that the image will be 1 stop under-exposed.

GOOD LUCK!

--
Good Day,
Roonal

'Money doesn't buy happiness, but it makes for an extravagant depression' by golf tournament sportscaster

Well you don't HAVE to shoot in RAW. I've heard (and had myself) some pretty good results just using photoshop.

To do this, open the file in photoshop, create a duplicate layer, and set the blending mode for that layer to "screen". You can adjust the opacity, but I think I read that one "screen" = +1EV (so if you set 33% opacity you'd get +1/3EV, etc.)

but you will get a MUCH better result by shooting in RAW and doing the exposure addition (push) at the beginning of the process.

S.
--

• How deep does the Rabbit Hole go? *

Free the Images
My XT IS Full Frame -- APS-C/FF of course!

VladDrakul said:

as I said I'm new to photography, so I've still not understood
entirely this tecnique because I can't seem to set the
underexposure setting (meaning the bar on the -2... 0 .....+2) to
what I desire. This is bringing some confusion to my head.

I set up the photos to RAW, also ISO1600.
In M mode I set the camera to 1/125 and then to 4.0. Now depending
what I'm focussing, dark or lighter subjects the underexposure bar
on the -2... 0 ....+2 wanders freely....

what I do next?

Click to expand...

I think the technique is easiest and makes the most sense in Av mode. You're probably trying this since the aperture can't open any further anyway, and you can't bump the ISO more directly.

Set RAW & ISO1600.

In Av mode, dial aperture wide open. Press and hold the exposure compensation button while dialing it to -1 (or -2 or whatever). The camera will automatically select the shutter speed to result in an underexposure by however many stops you've told it to.

Trying to do this in M mode would be a major nightmare, as you're assumably in relative darkness and / or having some weird and varying low-light conditions, and probably a moving subject, too. Use Av so that once aperture is set, shutter speed is the only variable, and the camera adjusts it for you.

If you trust the camera to tell you what the degree of underexposure is, trust it to just set the resulting shutter speed for you, too. If you're in M and using the meter, it's the shutter speed you'll dial in by hand on your own anyway.

Sooooo.... Use Av mode, open aperture all the way, dial in the negative exposure compensation, set ISO1600, and shoot RAW. If this doesn't make sense, there are other basic / normal things with the camera to learn how to use before trying to fudge around the camera's limits.