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Author Topic: STACKING images  (Read 5307 times)
Snook
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« on: February 02, 2009, 11:37:56 AM »
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Hey guys I have reading on stacking and am wondering a couple of things..?
First, I am not quite clear as to why they say you can stack several 30 second exposures to get a 3 minute exposure? If you do 30 second exposure, Won't they all look the same? Or is the trick doing it at the end or beginning of sunset?
If someone could clear that up a little sure would be great.
Also is it absolutely necessary to have a panoramic device of some kind?
Do you guys know of any Good tutorial sites or links that explain things in Detail.
I am not sure how they state shooting 17 images at night is going to give you more depth in the image?
I have been having very little success doing panos so far but and pretty amatuer at it..:+}

I tried to do some panos of a sunset the other day and the sky just was impossible to line up as I was shooting from sunset back torwards opposite of sunset. Had a gradient of purple that was beautful but they just would not line up.
I have seen in a couple places where they say it is best to shoot vertical also, which is where I have made several mistakes as I was shooting horizontally.

In any case I know there a alot of great photographers in here that know a lot about stitching, even in studio I have seen some guys showing stictched images in studio..

Thanks for any help as I like getting my hands in all kind of photography and experimentation....

Snook

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Hoang
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« Reply #1 on: February 02, 2009, 02:47:11 PM »
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Hi, Snook. While I do not do stacking to increase exposure length, but I occasionally use it to reduce noise (and in effect increase usable dynamic range/depth). Because of the nature of noise (it's randomness), mean stacking will average out the random outliers (noise) and retain the common aspects of each frame (the actual subject).

For panoramas, I do not use a panorama head, only a ballhead that can pan. It is helpful to shoot vertically and to overlap by about 1/3 for each image. If you do that, most panorama programs should be able to stitch your images together. How much did you overlap?

Here is a large 62 megapixel panorama I made using only a 20D, Sigma 70-200 f/2.8, and Bogen 488RC2 ballhead / 3021bpro legs.


canon 20d . sigma 70-200 f/2.8 . 70mm
iso 100 . f/8.0 . 1/500s

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Dustbak
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« Reply #2 on: February 02, 2009, 02:53:10 PM »
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There are devices that follow the movement of the solar system. I forgot the name of it for the moment. I once saw the work of someone that makes really long exposures in the desert that used a system like that. That way the stars etc. didn't become the well-known radial stripes. Search on equatorial mounts & systems for instance and you will find some of the necessary stuff.

I stitch outside as well as in the studio. Trick is to try to be as precise as possible. Sturdy tripod, rotate around the nodal point, etc..

I sometimes stack for exposure, to get more DoF. This is a PITA. I have tried to get the blending/stacking automatically with CS4 but that is horrible, it turns out to be manual labor most of the time. Apparently Helicon Focus is better but I have never tried that.
« Last Edit: February 03, 2009, 06:43:53 AM by Dustbak » Logged
E_Edwards
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« Reply #3 on: February 02, 2009, 03:53:51 PM »
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Quote from: Dustbak
I have tried to get the blending/stacking automatically with CS4 but that is horrible, it turns out to be manual labor most of the time. Apparently Helicon Focus is better but I have never tried that.


Dustbak,

Helicon Focus is certainly better than CS4 but doesn't always give you the accuracy and reliability that you need for fast turn around, so in the end, like you, hard labour is what I do, which really is not that hard, not when you do it regularly.

Edward
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cmi
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« Reply #4 on: February 02, 2009, 03:57:22 PM »
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Hi Snook, I have never for myself stacked exposures to increase exposure TIME. But theoretically thats possible. During a single exposures, brightness values in a pixel add up, nothing new here. So if you have 2x 30s Exposures, you can combine them to a single 1min exposure by ADDING the pixelvalues. In Photoshop you could put the 2 exposures in 2 layers, and set the mode of the above layer to "Linear Burn (Add). But on the other hand, the faster way would be to just use the bulb mode of your camera, a stopwatch, and a remote control.

best regards

Christian
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Snook
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« Reply #5 on: February 02, 2009, 05:36:46 PM »
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Quote from: cmi
Hi Snook, I have never for myself stacked exposures to increase exposure TIME. But theoretically thats possible. During a single exposures, brightness values in a pixel add up, nothing new here. So if you have 2x 30s Exposures, you can combine them to a single 1min exposure by ADDING the pixelvalues. In Photoshop you could put the 2 exposures in 2 layers, and set the mode of the above layer to "Linear Burn (Add). But on the other hand, the faster way would be to just use the bulb mode of your camera, a stopwatch, and a remote control.

best regards

Christian


Thanks Cristian for the help..
I just also was wondering how that works..
If I have more than exposure of the same time, let's says 1 shot@ 10 seconds at F11 and another same thing, you mean the image will have luminosity of a 20 second file once merged and with the same quality as a 20 second exposure...?
I just cannot grasp the concept but I am open minded..:+}
Thanks for all the input so far and it would be great to have an explanation as to why this would work...?
Thank you
Snook
« Last Edit: February 02, 2009, 05:37:39 PM by Snook » Logged
carstenw
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« Reply #6 on: February 03, 2009, 04:46:53 AM »
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Quote from: Snook
Thanks Cristian for the help..
I just also was wondering how that works..
If I have more than exposure of the same time, let's says 1 shot@ 10 seconds at F11 and another same thing, you mean the image will have luminosity of a 20 second file once merged and with the same quality as a 20 second exposure...?
I just cannot grasp the concept but I am open minded..:+}

To understand why this works, simply think of multiple exposures with film cameras. If you open the shutter in the same place a second time, then the light continues to accumulate. With digital, you just add it together mathematically, instead of re-exposing a negative a second time. Having said that, I have never heard of anyone doing this?

As far as panoramas go, I use Autopano Pro, which works quite well, and compensates for vignetting and such.

Careful technique is a must, however. In general, you need a panorama head only if you do multirow stitching, and have a part of the scene close to the camera. For example, if you have a bush close to you in the area of the photo which you want to overlap with the next frame, then the act of turning the camera means that you will see the bush from two slightly different angles in the two shots. No panorama program can fix that. A pano head will keep the center of the lens (actually the entrance pupil, I think) stationary, and move the camera behind it, so that both frames have exactly the same view of the bush. You need to find the right offset for each lens and focal length in a zoom, to set it up correctly.

If you want to do multi-row panorams, and will have things close to the camera, you will need a full pano head. If you want to do single-row panoramas (and have things in the scene close to the camera), then you can get by with much less. You just need a rail, something like this, and perhaps an L-bracket: http://reallyrightstuff.com/rrs/Customkiti...c=Pano-Elem-Pkg. Finally, if you want to do panoramas of things far away, any tripod will do, or even hand-held.

Apart from stacking for exposure length and panoramas, there are of course also HDRs, and stacking for resolution, as mentioned above.
« Last Edit: February 03, 2009, 04:50:05 AM by carstenw » Logged

cmi
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« Reply #7 on: February 03, 2009, 10:26:29 AM »
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Quote from: Snook
...
If I have more than exposure of the same time, let's says 1 shot@ 10 seconds at F11 and another same thing, you mean the image will have luminosity of a 20 second file once merged and with the same quality as a 20 second exposure...?
...

Yes.

Also, carstenw explained it quite nicely. If there is a specific fact/thing you dont understand, explain it so we can be more specific... also, why do you want to add up exposure times like this? What specifically do you want to achieve? (I ask that, because for common tasks it is very uncommon to stack images to extend exposure time. Normally you dont want to extend exposure time, but eg get rid of noise / extend dynamic range.)

Christian
« Last Edit: February 03, 2009, 10:30:21 AM by cmi » Logged
Snook
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« Reply #8 on: February 26, 2009, 09:23:46 AM »
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Hey guys looking to find some help on shooting for stacking.
I have a question and was wondering if anybody could help.
HOW do you place your self to shoot an area for stacking for a higher res image.
If I am shooting from a low angle for example inside a church and have the lens maxed out how to a start to take images so that they can be stcked and work properly.
Hard to explain but if I have this image which I will post below, Shot with a canon 1DsMII and a 24-105 IS at almost 24mm.. where would I align the images to shoot in or der stack???
Would I use a tighter lens and shoot sections of the wall on the otherside?
After seeing the image how would you approach this image to shoot it stack so that i use just sections and put them through photomatix or some other stacking program?

Thanks for any help on opening my eyes to this method.
Snook
[attachment=11771:_F6J7662.jpg]


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jjlphoto
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« Reply #9 on: February 26, 2009, 10:19:09 AM »
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Doing an interior such as your would require a pano head that rotates on your lens'es nodal point. Otherwise you will get parallax errors. Simple pano assembly can be done hand held, but only on scenery where things are far away.
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Thanks, John Luke

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« Reply #10 on: February 26, 2009, 10:20:54 AM »
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Quote from: cmi
....So if you have 2x 30s Exposures, you can combine them to a single 1min exposure by ADDING the pixelvalues. In Photoshop you could put the 2 exposures in 2 layers, and set the mode of the above layer to "Linear Burn (Add)....

I do not think that is possible. All you have are several underexposed files. And underexposed shadows are underexposed shadows, period.
« Last Edit: February 26, 2009, 10:22:01 AM by jjlphoto » Logged

Thanks, John Luke

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Snook
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« Reply #11 on: February 26, 2009, 10:34:35 AM »
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Quote from: jjlphoto
I do not think that is possible. All you have are several underexposed files. And underexposed shadows are underexposed shadows, period.

Yeh but my question is where or how do I chose sections to photograph for a stitched picture.
Sorry this maybe needed in another thread as this one was stacking and now I am talking about stitching...

Not to start another thread maybe someone can answer in this one.
How would you approach the above image for shooting it stitched???
Thanks
Snook
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Luis Argerich
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« Reply #12 on: February 26, 2009, 10:35:49 AM »
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About Stacking

Yes the exposure time is increased and noise is reduced, this is used intensively in astrophotography because in a very long exposure the stars will leave trails so if you want a 10 minutes exposure without trails you have to take as many shots as needed in the exposure time you can allow to avoid trails. For example 60 1 second exposures will equal a 1 minute exposure but without the trails.
The software does the aligning needed since things move from exposure to exposure.
Good and free for this are DeepSkyStacker, Registack and Iris.

Max Lyons the author of PtAssembler has also a nice stacking program available on his website.

If things do not move you can stack in Gimp or Photoshop calculating the transparency of each later as 1/N

Example for 5 layers the transparencies are

Layer 5 1/5 = 20%
Layer 4 1/4 = 25%
Layer 3 1/3 = 33%
Layer 2 1/2 = 50%
Layer 1 1/1 = 100%

Layer 1 is at the bottom of your stack

Noise is reduced/eliminated because noise is random in each image so it disappears as it will not happen in the same place in every picture.

Another side effect is that with enough exposures moving objects also disappear, same as in a long exposure.

If focus and/or exposure is different in each shot you should use Tufuse.
If only the exposure is different then either Tufuse or Enfuse will work.
If only the focus changed then CombineZM, tufuse or HeliconFocus will do the stack.

About Panoramas

I think PtAssembler, Hugin and PtGUI are the best softwares you can use, I use the 3 of them and they are great.

Luigi


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Snook
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« Reply #13 on: February 26, 2009, 11:12:24 AM »
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Luigi maybe you could also answer my second questions about stitching??
Would appreciate it.
Maybe I sjould repost to another thread about sticthcing...:+]
Snook
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Jack Flesher
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« Reply #14 on: February 26, 2009, 11:29:38 AM »
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To stitch the first concern is that all the images look similar before assembling.

1) Capture all at the same WB, exposure, etcetera being sure to allow at least a 1/3rd overlap at the seams.  Ideally camera is level and pivots around the lens nodal point so as to eliminate parallax errors. This is where a dedicated panning head like those offered by RRS come in handy.  (Google for more details on how to set up your camera for parallax free pivots.)

2) Next, process them in your raw converter to exactly the same output settings, removing lens aberrations if available.  

3) Pull them into your assembly program -- I prefer the adjustability/edibility Autopano Pro, but CS4 works very well with many images.

4) Render the pano, then bring it back into your image editor for final output editing as needed.

5) You done

Here is a recent stitch done per the above steps:



And a detail grab from that image:



Cheers,
« Last Edit: February 26, 2009, 11:32:13 AM by Jack Flesher » Logged

Luis Argerich
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« Reply #15 on: February 26, 2009, 11:34:32 AM »
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Not sure if I understand what your second question is... Maybe you can repost in a more clear way? I'd try to answer if I can.

Quote from: Snook
Luigi maybe you could also answer my second questions about stitching??
Would appreciate it.
Maybe I sjould repost to another thread about sticthcing...:+]
Snook
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elf
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« Reply #16 on: February 26, 2009, 11:40:05 AM »
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Quote from: Snook
Yeh but my question is where or how do I chose sections to photograph for a stitched picture.
Sorry this maybe needed in another thread as this one was stacking and now I am talking about stitching...

Not to start another thread maybe someone can answer in this one.
How would you approach the above image for shooting it stitched???
Thanks
Snook

1. Use exposure bracketing. Set for shadows, mid, and highlights.
2. Decide how much detail you want in the final image.  Select the lens focal length by this. Longer focal length means more detail. Shorter focal length means fewer frames and less megapixels as well.
3. Decide FOV for final image. Use this to calculate how many horizontal and vertical frames to shoot.
4. Decide on DOF. Use this to determine if you need to use focus stacking to achieve the DOF required.
5. For architectural interiors it's better to use a good spherical pano head, but not absolutely necessary.  I'd practice handheld panos in a more forgiving place first.
6. Shoot each frame with exposure bracketing and focus stacking before moving to the next.
7. Dump all of the images into previously mentioned PTAssembler and TuFuse and wait for your final image to be generated
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Snook
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« Reply #17 on: February 26, 2009, 01:01:46 PM »
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Guys I think there is some confusion here which I started..:+]
My first post was about stacking and I accidentally asked another question which is about stitching in order not to start another thread.
But let me re phrase here...:+}

Look at the image above that I posted of a castle I shot last week.
My question is.
How would a shoot that same seen with the same lens and camera to make it a stitched photograph.
HOW should or would I position the camera/me/lens/ etc in order to have done it as a stitched images.
Would I zoom into sections of the wall and how exactly and shoot overlapping 1/3.
Take in to consideration I was maxed out at 24mm on my zoom.
I am using this canon as an example but how would you do it with any lens/camera.
What is the objected  to zoom out slightly to overlap by 1/3? Or zoom in to areas and shoot more frames?? too get more detail in each frame.
How does that work exacly? I understand a little ore if it is a Landscape far away, but how would you approach it with an image like `i posted??
Hope that is a little clearer.
I am not taling about stacking anymore and I know what stitching is, but how do you set out to do it specially on an image like I posted that is already maxed out at 24mm and a 6 second exposure??

Also a kind of part 2 is if I do not have a pano head how do I postion my sef for every frame to keep the lens as much on axis as possible and how is this done when you need to shoot the first part of the pano then the second and then third etc.. etc..
If the lens stays on axis how does it do so and you have to turn the camera slightly to "see" each part of the pano?
Are you tilting the camera and keeping lens on the same axis?

Thanks for any further information if this makes more sense now

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elf
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« Reply #18 on: February 26, 2009, 01:55:34 PM »
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Quote from: Snook
Guys I think there is some confusion here which I started..:+]
My first post was about stacking and I accidentally asked another question which is about stitching in order not to start another thread.
But let me re phrase here...:+}

Look at the image above that I posted of a castle I shot last week.
My question is.
How would a shoot that same seen with the same lens and camera to make it a stitched photograph.
HOW should or would I position the camera/me/lens/ etc in order to have done it as a stitched images.
Would I zoom into sections of the wall and how exactly and shoot overlapping 1/3.
Take in to consideration I was maxed out at 24mm on my zoom.
I am using this canon as an example but how would you do it with any lens/camera.
What is the objected  to zoom out slightly to overlap by 1/3? Or zoom in to areas and shoot more frames?? too get more detail in each frame.
How does that work exacly? I understand a little ore if it is a Landscape far away, but how would you approach it with an image like `i posted??
Hope that is a little clearer.
I am not taling about stacking anymore and I know what stitching is, but how do you set out to do it specially on an image like I posted that is already maxed out at 24mm and a 6 second exposure??

Also a kind of part 2 is if I do not have a pano head how do I postion my sef for every frame to keep the lens as much on axis as possible and how is this done when you need to shoot the first part of the pano then the second and then third etc.. etc..
If the lens stays on axis how does it do so and you have to turn the camera slightly to "see" each part of the pano?
Are you tilting the camera and keeping lens on the same axis?

Thanks for any further information if this makes more sense now

You will get exactly (well nearly) the same image with any focal length lens when you cover the same FOV. Longer focal lengths will have more detail and require more frames to cover the FOV. It's your decision to make, there is no right or wrong. Normally you'll shoot the entire pano with the same focal length but this is not strictly required.  

Shooting panos handheld takes a bit of practice. You need to rotate the camera around the entrance pupil of the lens.  It takes lots of practice to get good at it or did I already say it takes practice

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carstenw
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« Reply #19 on: February 26, 2009, 03:07:38 PM »
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Quote from: Snook
Guys I think there is some confusion here which I started..:+]
My first post was about stacking and I accidentally asked another question which is about stitching in order not to start another thread.

It is not clear to me if you want to stitch to get greater coverage, or if you want the same coverage at higher resolution. If you want greater coverage, the same focal length will work. If you want the same coverage with greater resolution, choose a narrower lens, like perhaps a 35mm or a 50mm. In either case, choose a lens with the lowest possible distortion, since otherwise you lose resolution when the software corrects the distortion before stitching.

Either way, the best way is with a pano head. Some pano heads have balls in the pivots which "click" at specific angles (12 degrees, 15 degrees, ...). You must learn how many clicks to turn between pictures, for the lens that you are using, so that you get about 30% overlap (horizontally and vertically!) between frames, as Jack said. If there are no clicks (detents), then you probably have a scale for the angle. Same principle.

If you don't have a pano head, and want to try by hand, then imagine that a point about halfway along the length of the lens, but *on* the central optical axis, is the pivot point, and try to rotate yourself and the camera around that point. This is *really* hard! You could practice in the studio with a couple of objects behind each other, and just look through the viewfinder while pivoting, making sure that the objects always stay behind each other. Try 2x1 (row x column) horizontal, 3x1 with portrait orientation, and stitch with your chosen software. Then try 2x2 horiz., 3x2 vert. and so on. I would not do larger than that by hand. It gets unmanageable pretty fast. However, with the 24mm and 3x2 portrait mode, you should have a very wide coverage, so maybe you don't ever need more. You should get the hang of it pretty quickly. Just make sure to position the images in PS or Autopano Pro and check how much they overlap.

I think only practice will make it easy to do. I have done some experimental 100-shot panoramas (on a tripod but with a normal ballhead), and still managed to miss parts of the scene. Swinging over the scene several times while looking through the finder might help to visualize the passes. Start with a spot in the middle that you can always find again, and use that to choose your rows and columns. In each frame, before you move on, check where you are, and then choose where you want your next edge-of-frame to be, then move. If you lose track of where you were, you can always return to the start position and work it out again.

Two things to be careful of: if you are going for very wide coverage, your rows will most likely converge at the ends, since you are essentially covering a part of a circle. If you don't take care to cover the corners, you might have to crop a lot off the vertical and horizontal edges, towards the center of the edges. So shoot extra to cover the corners. The second thing is to always watch your horizon. It is too easy to start slanting.

The last thing is that the software requires some practice too, so make you sure push some tricky panoramas through on your own time before moving on to selling them  Correcting verticals, matching difficult areas with little detail, and other problems will arise.

I hope that helps. This is what I have done, but I am no pro. I have just fooled around with it privately. If everything doesn't make sense the first time, then just work through a few panoramas and things should fall into place.

Here is an example I did hand-held, with an M8 and 50 Lux ASPH, by shooting wildly  36 shots, and I had some problems with coverage towards the edges due to poor planning, so I had to crop. I ignored correcting verticals for this shot. The lens was wide open, so the image has an unusally shallow depth of field for that wide coverage. Two quick shots covered the girl, and then I shot around to get the rest.


« Last Edit: February 26, 2009, 03:11:52 PM by carstenw » Logged

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