Focus and Exposure Bracketing

[FrankMi]

My Canon SX50 can do Exposure Bracketing and (short stack) Focus Bracketing but not at the same time.

If I had a scene that was both high dynamic range and required more DoF than my f-stop provides, I could get both the short focus stack and the bracketed exposure sets of images but if I am going to combine them into a single image, I could only benefit from one kind of automated bracketing.

I would either need to manually focus close, then mid range, then distant and take Bracketed Exposures at each focus point, OR, shoot Focus Bracketing at -2EV, 0EV, and 2EV. Either way, I would end up with nine images to be combined.

I have two questions for those of you that have played with this scenario. During shooting, are we better to use the camera's automated Exposure Bracketing OR Focus Bracketing and manually set the alternative to get the 9 source images?

The second question concerns post processing. Are we better to do the focus stacking first for each of the three sets of exposure values, then blend the three merged focus stacked images, OR would we be better to merge the three matching exposures first, one set for each focal point, then focus stack the resultant three exposure stacked images?

Perhaps it doesn't make any difference, but then again, there may be different results depending upon the sequence used.

I have tried it both ways (more commonly in producing a panorama than a focus stack) but not in a scientific controlled process so I've not been able to realistically compare the results. If no one else has, I guess I'll need to take the time to do a through test to find out.

Perhaps some of you have thoughts about the process or results that I haven't considered and should take into account for the testing.

[DanK]

I do focus stacking often and exposure bracketing fairly often, but I have never had this dilemma.

It seems to me that it should make no difference what which bracketing you do automatically. What should matter is that you have the right settings--the right exposures and focus points. Whether you get them automatically or manually shouldn't make any difference.

As for the order in postprocessing: that might matter, and I can see arguments for either order. It's possible that there is some relevant information on the websites of relevant specialty software, such as Zerene or Helicon.

[mrinmoyvk]

I could not get the scenario where focus bracketing is required. I am guessing focus bracketing is something like 3 images where foreground is in focus, middle is in focus and background is in focus. If I am not wrong, you might need to check this below thread about hyper focus distance.

Hyperfocal Distance

If you are referring to something other than the above thread, then please explain in more detail about when would you require focus bracketing. This would help me understand the concept better.

[Mike Buckley]

please explain in more detail about when would you require focus bracketing.

There are certain situations (scenes) when the lens being used does not allow you to have everything within the frame in focus. One common example is when a landscape scene includes an object very near the camera and a mountain or horizon that is miles away. Another common example is when close-up or macro photography is being done. In that situation, even though the distance from front to rear of the scene may be a few inches or centimeters, it may not be possible for everything in the frame to be in focus.

One workaround is to move the camera farther away from the scene and to crop the image. The drawback of doing so is that the maximum print size is reduced.

One solution is to use a perspective control lens. The drawback of doing so is that the cost of that type of lens is relatively expensive. Also, many camera bodies prevent the full functionality of a perspective control lens, which requires spending even more money on a camera that does allow full functionality.

The other solution, of course, is to use focus stacking.

[mrinmoyvk]

There are certain situations (scenes) when the lens being used does not allow you to have everything within the frame in focus. One common example is when a landscape scene includes an object very near the camera and a mountain or horizon that is miles away.

Is this something different that choosing a hyper focal distance? Sorry but I am no very clear about the discussions going under hyper focal distance thread, so thought that what you are referring to is the same thing discussed in thread.
About macro, I agree what you are saying (Just read about that on http://en.wikipedia.org/wiki/Focus_stacking).

[ajohnw]

Given this problem I suspect I would focus stack 3 times at 3 different exposure levels as bridge camera sensors are a little limited compared with dslr's so the exposure bracketing will be required more often that it would be on one of those.

Seeing mention of hyperfocal distances there are 2 other methods mentioned here

Depth of field 2/3 behind and 1/3 in front???

The one I mention needs the actual focal length of the lens - not the full frame equivalent. The link explains and shows what the resolution means in practice. This is probably the basis of the infamous F64 club and explains why well. It maximises sharpness on the sensor/film according to detail in the shot and disregards final print size. The framing method is more suitable for the use Bill puts it to, I keep meaning to sort out the maths behind that as they don't seem to be about on the web. Pity really.

When looking around in this area - DOF there are some contradictions. This is basically down to the fact that they are all approximations so in practice they need fiddle factors adding. Diffraction is mentioned but in real terms the best circle of confusion the lens used can produce is the ruling factor. This is why Colin for instance has said diffraction what is that, here is a shot at F22. In practice the detail level in the subject matters as well.

John
-

[Mike Buckley]

Is this something different that choosing a hyper focal distance?

Yes. It's different because choosing the hyperfocal distance doesn't always render everything in focus. The solution being discussed in this thread is viable when choosing the hyperfocal distance isn't a solution.

[DanK]

Is this something different that choosing a hyper focal distance?

To elaborate on Mike's answer: sometimes, you can't close the aperture enough to get the DOF you need, or you may want to avoid extreme apertures in order to avoid diffraction. This is very common in macro work, where DOF is razor-thin even at fairly small apertures. The solution is to stack multiple images focused at slightly different points. You can do this in Photoshop or with specialized software, such as Zerene or Helicon.

I use focus stacking often in macro work for that reason. I rarely use it in landscape work, in part because I can often get enough DOF without it, and in part because if things move (leaves on trees, for example), focus stacks don't work well.

[FrankMi]

I do focus stacking often and exposure bracketing fairly often, but I have never had this dilemma.

It seems to me that it should make no difference what which bracketing you do automatically. What should matter is that you have the right settings--the right exposures and focus points. Whether you get them automatically or manually shouldn't make any difference.

As for the order in postprocessing: that might matter, and I can see arguments for either order. It's possible that there is some relevant information on the websites of relevant specialty software, such as Zerene or Helicon.

I tend to agree with you about the shooting side. As exposure is usually fixed in increments of EV values and focus points can be quite variable, I would think that the focus points would be better done manually and once chosen, let the automated Exposure Bracketing deal with exposure.

On the post processing side, I'll see if the processing order is mentioned on any of the focus stacking software sites like Helicon Focus and Zerene Stacker. Good thought Dan. Thank you for that suggestion!

[FrankMi]

I could not get the scenario where focus bracketing is required. I am guessing focus bracketing is something like 3 images where foreground is in focus, middle is in focus and background is in focus. If I am not wrong, you might need to check this below thread about hyper focus distance.

Hyperfocal Distance

If you are referring to something other than the above thread, then please explain in more detail about when would you require focus bracketing. This would help me understand the concept better.

Hi Mrinmoyvk, I believe that Mike, John, and Dan has explained this fairly well in their replys so perhaps I could offer some examples that will help clarify what I am trying to accomplish.

Although it is common to use focus stacking when doing macro work, it actually applies all the way up to landscapes and, under the right circumstances, any image between the two extremes.

What I am trying to do is determine whether it is better in post processing to do the focus stacking first, then blend the multiple exposure images OR is it better to blend the multiple exposure images from each focus set first, then stack the exposure adjusted focus stack images.

Here is an example of using focus stacking in a landscape scenario. http://www.youtube.com/watch?v=IMiKUnVAFks

This is one possible process for handling the merging of multiple exposure images. HDR processing is another option for this part of the process but with either method, final post processing needs to be done in a product that supports masks and layers. You may want to stop viewing this video at 12 1/2 minutes as after that point the presenter is discussing selling his training videos. http://www.youtube.com/watch?v=EATSiMmrTiU

So, is there a preference for stacking first, then merging or merging first then stacking when both are being used with the same image?

[ajohnw]

The way I read your post the camera itself can dof "stack" and generate HDR images but not both. To me if you want to use the camera to do part of this using it's dof "stack" would be the sensible option. It usually the most complex operation as it can involve both scaling and alignment so if it does it well let it. Taking bracketed shots the same way should make hdr easy. I would look at the various Enfuse based pieces of software for that. It doesn't use tone mapping so produces realistic results.

Watching the crook who did the HDR video GIMP can do that sort of thing but you would need to pay attention to the colours you want before HDR stacking in it. The missing part where he works destructively could be avoided by moving the light shot to the top with a fully transparent mask and then painting opacity and adjusting the whole layers opacity.to suit.

Gimp could also do the focus stack manually in the same way but I would use an Enfuse based application. There is a windows version about and also an LR plugin.

John
-

[FrankMi]

The way I read your post the camera itself can dof "stack" and generate HDR images but not both. To me if you want to use the camera to do part of this using it's dof "stack" would be the sensible option. It usually the most complex operation as it can involve both scaling and alignment so if it does it well let it. Taking bracketed shots the same way should make hdr easy. I would look at the various Enfuse based pieces of software for that. It doesn't use tone mapping so produces realistic results.

Watching the crook who did the HDR video GIMP can do that sort of thing but you would need to pay attention to the colours you want before HDR stacking in it. The missing part where he works destructively could be avoided by moving the light shot to the top with a fully transparent mask and then painting opacity and adjusting the whole layers opacity.to suit.

Gimp could also do the focus stack manually in the same way but I would use an Enfuse based application. There is a windows version about and also an LR plugin.

John
-

Hi John, your comments are appreciated! Although the Canon SX-50 can do both Exposure Bracketing and Focus Bracketing (not at the same time), it doesn't merge the HDR or focus stack images in-camera. I merge or stack the images in Photoshop CS5 as that is what I have to work with.