HDR stops help ....

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kamikazi929

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Bryan
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"With HDR's you usually want one image at the recommended exposure, one image under exposed by 2 stops and one image overexposed by 2 stops"
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When taking my HDR's (im very new to this), I usally get my settings when the camera is in auto, jot them down, and then switch to manual, and put them in. Say for example my shutter speed is 1/250, then I take the first photo, adjust the shutter speed to say 1/500 and take the next, then I will adjust to 1/125 of a sec.

This may vary sometimes depending on what im shooting...

But being a total newbie to this, can someone explain , and dumb it down a bit for me :-p what is meant by "one image under exposed by 2 stops and one image overexposed by 2 stops"..

I thought "stops" was related to aperture size?

Thanks all :)
 
You are correct. "Stops" can refer to the aperture, we talk about 'f stops' and 'stopping down'.

However, in a broader context the word can refer to the total amount of light entering the camera and this depends on the size of the hole the light is coming through (ie aperture) and the length of time the light comes through that hole - the shutter speed.

In your example changing from a shutter speed of 1/250 to 1/500 (while keeping the aperture constant) is halving the total amount light getting into the camera. So a photo at 1/500 will be 1 stop under exposed compared to the shot at 1/250. Similarly using a shutter speed of 1/125, at the same aperture, will be 1 stop over exposed.

Hope this helps

Dave
 
As Tringa says, think of stops as just the amount of light used to create the image. You can get one more stop by opening the aperture one stop (e.g Going from F/5.6 to F/4) or by bumping the iso up one stop (e.g going from 800 to 1600) or by changing the shutter speed exactly as you have done in your example.

It's most common in HDR to vary the shutter speed to give you your, normal exposure, your underexposed images and your overexposed images. This is to try to keep the images as consistent as possible. If you varied the aperture, you might change depth of field and the images wouldn't blend well. If you varied ISO, you'll introduce varying noise between the images.

So you're basically doing it exactly right, or at least the conventional way.
 
All the above is good advice, and quite correct.
In your question you ask about over and under exposing by 2 stops.
In order to use -2, 0, and +2 you will need to use (if the correct exposure is 1/250th)
1/1000th (-2), 1/250th (correct exposure), and 1/60th (+2).
Hope this helps, and doesn't confuse.
 
thanks all for the answers, that clears my confusion :- )

now i can start on taking HDRs using the 'proper' recommended stops. Although I realise this can vary depending on what scene your shooting.

I swear sometimes its the basic fundamentals which confuse me. Never been one for numbers haha
 
What camera do you have Bryan?

It may be that the camera will do the +2, 0, -2 exposures (or other ranges) for you via Auto exposure Bracketing (AEB).

Apologies if you already know this.

Dave
 
i have a nikon d3100 which sadly doesnt have AEB. hoping to upgrade in the next few months to a d5100 which does.
 
If it's a static subject (eg. building interior).. keep taking the shots halving the shutter speed until reviewing the shot in the lcd shows it just about all black, then back to where you started and doubling the shutter speed until it's just about all blown. Then you've captured the entire dynamic range of the scene.. but it will require a very solid tripod, locked down tight and a very steady hand. The results are worth it.
 
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