In taking an HDR photo, why do you want 1, 2 or 3 F stop setting? Is one better than the other?

[bravio]

When taking HDR, what advantage does different F stop values offer. I seem to be able to set values and the results look the same.  When do I use a value of 1 vs a value of 3?

[Underachiever]

Why are you doing an HDR shot? Are you doing it to create "an effect", or are you doing it to solve a lighting issue? This is a question that you need to think through. The whole idea behind HDR is to be able to expand the capability of your digital camera.

Your eyes can easily adjust the equivalent of 11 f stops. You can see a coin lying in a deeply shadowed corner as well as the sun coming through a window without much problem. Your camera can handle one or the other. It is capable of about a 7 f stop range.  So, if your intent is to capture that image of the coin and correctly expose for the window, you would use High Dynamic Range (HDR) to do it. You would probably shoot - f2 + f2 from your main exposure setting. Effectively exposing the shadow detail by overexposure, and exposing the window highlight by underexposing. When you merge the 3 shots together, you have an image that is 11 f stops wide. I use 2 stops and the software I use seems to like the 2 stop criteria best.  One stop will expand your exposure range to 9, so like bracketing, it's subjective to what you like. 

[bravio]

Thanks for the good info.  I like the possiblity of making the shot as close to normal eyes as possible.  I do understand the concept that one shot under exposes and one over exposes. Like you, it seems that F2 seems to be the one I use most.  I just wondered with the question if there was a better reason to use 3 or 1.  I have found that 3 and 1 makes such little difference when processed. 

Once again, thanks for the comment.

[Skirball · Accepted solution]

The idea is to expand the dynamic range of your camera.  The wider you make your steps the larger range you can cover.  However, if you make the steps too great then the software will have difficulties stacking the images.  Just like when you stitch a panorama from multiple shots you make sure that there is plenty of overlap between the two.  2 eV (stops) has just settled on a common step to use:  it works well for the programs, and it gives you decent range with minimal shots.  I don't think that there's anything more to it than that.

As far as not seeing a difference with 3 stop increments:  Most modern cameras - by Canon 😞  - are getting around 11 - 12 stops of DR (at ISO 100).  Shooting a 3 shot HDR with 3 stop increments gives you around 18 stops of DR.  That's a lot.  Chances are the scenes that you're shooting don't have that much DR, hence you're not seeing much of a difference.

[knessr]

When taking HDR photos, use the same f-stop so that you have the same depth-of-field in all of your shots. Just vary your shutter speed and shoot off of a tripod.

[Underachiever]

Absolutely right!

[bravio]

Look at the sky and your eye will contract because there is much light. Look at the local brush and trees and they would be dark if we meter on the sky. If we meter on the trees then the sky will blow out. What HDR does is meld the three together so we can see clouds in the sky and leaves on the trees. It is closer to what our eyes do when we focus on clouds or trees. HDR needs not have too far a dynamic range to make the final photo seem strange. 2 or 3 stops are all one needs.