Exposure

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[duncan22]

Hi,,
Am completely new at HDR, whats the best  f setting to go for if taking landscape pictures. I always assumed the highest setting would be best ie.f22 but using a remote control and tripod my final HDR photos using photomatix are not that sharp. Using a Canon 400D.standard 18-55mm canon IS lens. Any comments would be helpful.

Thanks.

[ravenhawk82]

Two things. First, turn off IS while it's on the tripod. Sometimes, it can try to correct for small vibrations that aren't there if it's perfectly still, leading to blur. Second, try shooting at f/11-16. At 22, you'll have a lot of diffraction, causing lack of sharpness. The only time I use f/22 is when I'm taking pictures of fireworks.
My recommendation is to try different f/stops in the 11-16 area and see which one yields the most sharpness, if you're really concerned. All lenses have a "sweet spot".

[duncan22]

ravenhawk82,
Thanks for your reply will certainly try what you suggest !

[DAVE RHUBERG]

Focusing in front of your intended target will give you greater depth on a  distant composition.  Use an online computer like DOFMaster, and decide what you need sharp (from 10' to infinity), and you may focus a 24mm at 1000'@F16, everything from 5' to infinity will be sharp enough to cover you from 10' out.
Lower focal lengths and further targets help.

[bittermonk]

When I auto bracket (with a Canon 5D MkII ), I use the AV mode, rather than manually select the "normal" exposure point.  This takes the guesswork out of the equation.  I have also noticed that when doing so, the camera almost always chooses f./7.1.  I would agree that distance shots are not at their sharpest at 7.1.  I'm not sure how to compensate for this.

[jessea]

1/About diffraction:
the radius of the image of a ray coming through the lens is : r=1.22*L*O where L is the color wave length,O the aperture.
If you do not want diffraction visible,you have to have r<the width photosite (because of the lowpass filter,we can choose that the radius is small enough instead of the diameter:the diffraction spot will be as large as 2 photosites)
In your case,the CANON 400 D has a photosite size of 5.7 micrometer,so for the red(L= 0.8 micrometers),you have:O<5.7/(1.22*0.=5.8 and for the blue(L=0.4 micrometers),you have:O<5.7/(1.22*0.4)=11.7
So,in order to be on the safe side,you shouldn't go beyond 5.6,diffraction wise
2/I concur totally with the advice telling you to disable IS while mounted on a tripod.I suppose that you do so in order to get exactly the same picture but with different exposures and it's easier to process
3/If you have something interesting in a near distance,you might consider taking at least 2 pictures with different focusing distances in order to merge them later on with a specific software.In this case,a depth of field compuing software is handy(mine is in my pocket pc).But remember that depth of field depends also on the size you are willing to print and the distance you are willing to look at the print (these 2 last parameters are often fixed in this kind of software,so,I decided I had to generalize it and to add a new feature: if I want everything sharp from here to infinity,how many pictures do I have to take and at which focusing distances)
4/I am in the process of making pseudo hdr landscape(pseudo because I didn't know about hdr a while ago):my way of doing it is to make an horizontal sweep,taking pictures with much ground and no much sky,then,I sweep back,taking pictures with much sky and no much ground.So,exposure is adapted to the sky,for one sweep and to the ground for the other sweep,and,of course,they overlap.To get true hdr landscapes I will have to add more pictures,with exposures really apart from the adapted one what I intend to do...one day.

[DAVE RHUBERG]

That may be technically true, but impractical as advice.   The diffraction limit of f/5.6 is safe, but only in that diffraction is the one variable that will not be a defect in your picture.  Many other variables can limit absolute resolution, particularly the large amount of picture that will be out of DOF at f/5.6.
For the right picture, yes, use optimal focal ratio.  But what if the lens is best at f/8 or f/11?  The camera is best at f/5.6, but you have a long foreground that needs some detail?   Take pictures, and witness the diffraction, and make an educated decision.
For landscape HDR, I usually use something between F/11 and F/16 for greater DOF, using Hyperfocal Distance focus point.
My D90 is best at F/8, my D70 at f/11, and my pictures at the f-stop I choose, without being afraid of one shortcoming.  My pictures have LOTS of shortcomings.
But an excellent quotation of optical formulae without a doubt.

[jessea]

If you know for a fact that your lens is best at 11,for example,this means that that lens at 11 WITH DIFFRACTION is better than that lens at 5.6 WITHOUT DIFFRACTION,so,go for it.
Using large apertures has a big drawback:DOF(it's good to have values in mind before shooting or a pocket PC which has this thing available),but some advantages:your shutter speed is high and you have less risks of getting something fuzzy,because your subject moves(because of the wind or whatever) and if you have dust on the sensor,it's less visible.Note:the old rule of thumb of setting the shutter speed at the focal length inverse for a full frame is FAR FROM SAFE when you have a subject who moves,even gently.
I would advise to take many more shots than really needed,with different settings(different focusing distances,different apertures and different exposure times in case of HDR),specially if this is a place where you can't go often and to allow you some time for post processing the pictures.