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stacker:docs:tutorials:tutorial002 [2012/10/04 05:54] rjlittlefield [Summary: Use either method but be sure to check framing] |
stacker:docs:tutorials:tutorial002 [2012/10/04 20:53] rjlittlefield |
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| **Figure 3. Front and rear frames, focusing by turning the lens ring** | **Figure 3. Front and rear frames, focusing by turning the lens ring** | ||
| - | Notice that the rear frame covers a much larger area than the front frame. It also has quite different perspective. That’s because when we turn the big ring on the outside of the lens, things move inside the lens in such a way that it effectively moves forward and backward quite a bit. | + | Notice that the rear frame covers a much larger area than the front frame. |
| - | You might anticipate that this change in perspective and magnification would cause problems for the stacking software. But actually it works fine, as long as the DOF per frame is pretty shallow and you provide enough input frames for the software to “understand” the stack. The image in Figure 1 is exactly what gets produced from a stack of 28 frames that start and end with what’s shown in Figure 3. | + | It also has quite different perspective. That’s because with this lens, when we turn the big ring on the outside of the lens things move inside the lens in such a way that it effectively moves forward and backward quite a bit. With other lenses, especially models that don't change length as you change focus, the change in perspective may be much less than we see here. |
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| + | You might anticipate that changes in perspective and magnification would cause problems for the stacking software. But actually it works fine, as long as the DOF per frame is pretty shallow and you provide enough input frames for the software to “understand” the stack. The image in Figure 1 is exactly what gets produced from a stack of 28 frames that start and end with what’s shown in Figure 3. | ||
| The reason this works is that Zerene Stacker can figure out by looking at the images how they should line up. This allows it to automatically correct for typical variations in scale and position that are caused by refocusing. | The reason this works is that Zerene Stacker can figure out by looking at the images how they should line up. This allows it to automatically correct for typical variations in scale and position that are caused by refocusing. | ||
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| + | In this example, we turned the lens ring by hand. However, with many cameras and lenses it's easy to tether the camera to a computer and let software control the auto-focus motor inside the lens to step focus. This is described in other tutorials. Using the motor usually provides more precise stepping than doing it by hand. | ||
| ===== Method #2 — Focusing by Moving the Camera or Subject ===== | ===== Method #2 — Focusing by Moving the Camera or Subject ===== | ||
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| {{:stacker:docs:tutorials:tutorial002:image008.jpg}} \\ | {{:stacker:docs:tutorials:tutorial002:image008.jpg}} \\ | ||
| **Figure 6. Output image from method #2** | **Figure 6. Output image from method #2** | ||
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| + | When focusing by rail, there will be changes in magnification and perspective with all lenses. Changes in magnification can be completely corrected by Zerene Stacker, but changes in perspective result in apparent movement that may give artifacts in the result. See [[:stacker:docs:troubleshooting:ringversusrail|HERE]] for more discussion on this point. For critical work, it's better to focus by ring and to choose a lens model that does not change length as it focuses. | ||
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| ====== Summary: Use either method but be sure to check framing ====== | ====== Summary: Use either method but be sure to check framing ====== | ||
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| It is surprisingly easy to go wrong on point 2. This is because the final image contains only areas of the subject that are seen in __all__ of the source images. It is easy to accidentally frame too tightly at either the front or rear of the stack, so that portions of your subject get cut off in the stacked result. | It is surprisingly easy to go wrong on point 2. This is because the final image contains only areas of the subject that are seen in __all__ of the source images. It is easy to accidentally frame too tightly at either the front or rear of the stack, so that portions of your subject get cut off in the stacked result. | ||
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| Go back for a moment and consider the output shown in Figure 6 versus the front and back frames of the stack shown in Figure 5. Notice in Figure 5 that the front frame covers a larger area than the rear frame does. Areas around the edge of the front frame are not included in the rear frame, so they can’t be included in the final output either. When you focus using method #2, the rear frame covers a smaller area. So in this case, you need to be sure that everything you care about is included when you’re focused at the __rear__ of the stack. | Go back for a moment and consider the output shown in Figure 6 versus the front and back frames of the stack shown in Figure 5. Notice in Figure 5 that the front frame covers a larger area than the rear frame does. Areas around the edge of the front frame are not included in the rear frame, so they can’t be included in the final output either. When you focus using method #2, the rear frame covers a smaller area. So in this case, you need to be sure that everything you care about is included when you’re focused at the __rear__ of the stack. | ||
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| If you’re like us, then probably you’ll find it difficult to keep straight whether to pay attention to the front or the rear, based on the focusing method that you happen to be using at the moment. So we have a simple recommendation: don’t try to do that. Instead, just keep in mind that one end of the stack will cover a smaller area than the other end. Check the framing at both ends, and be sure that everything you care about is visible inside a comfortable border. | If you’re like us, then probably you’ll find it difficult to keep straight whether to pay attention to the front or the rear, based on the focusing method that you happen to be using at the moment. So we have a simple recommendation: don’t try to do that. Instead, just keep in mind that one end of the stack will cover a smaller area than the other end. Check the framing at both ends, and be sure that everything you care about is visible inside a comfortable border. | ||
| - | **Summary: for small subjects step focus however you like, but be sure to check framing at both ends of the stack.** | + | **Summary: Be sure to check framing at both ends of the stack. Focus by adjusting the lens ring if you can make fine enough steps. ** |