08-05-2013, 10:03 AM
(This post was last modified: 08-05-2013, 11:35 AM by Brightcolours.)
You will HAVE to change the focal length. Else it will not work.
This is why: the perspective changes with your distance. Test this with the table. If you look at the corner of a table at say 2 meters distance, and then look at the same corner with just 20cm distance, the angles will have increased.
I do not know what exactly the formula will be, for changing the focal length to keep the angles the same when you change your distance. But I think it is probably more simple than you think:
Most probably the only thing you have to do is... NOT change the distance to your subject(s). Only zoom in on the pencil by increasing focal length. This will keep the perspective correct, and will give you what you need.
To keep the DOF similar, use the same diameters of aperture. So, lets say you are shooting the table with a 50mm normal prime, at f4. The aperture size will be: 50 / 4 = 12.5mm. And suppose you shoot the pencil with a 200mm lens. Then use a 12.5mm aperture too (for similar DOF). The f-value you need to set will be: 200 / 12.5 = f16.
So, to recap: Do NOT tilt/shift/move the camera in any way between shots. Keep the height the same too. Only change focal length to get the desired magnification. Use the same aperture size to keep DOF similar.
Quick and dirty example (handheld, no DOF correction) with 18mm (APS-C), then zoomed in to 50mm, then combined:
![[Image: gallery_10230_63_30519.jpg]](https://forum.photozone.de/uploads/gallery/album_63/gallery_10230_63_30519.jpg)
I do realize that this method is nor perfect either, as you might look on top of a small subject, but when it would be bigger you would look upto it. I will have to rake my brain a bit more over this.
Maybe this solves that problem: Note where in the frame the subject rests in the table (the height of the frame). When zooming in, keep that height of that point the same (by lowering the tripod, not the camera angle).
Good luck with your experiments, and your thoughts on my thoughts are welcome.
This is why: the perspective changes with your distance. Test this with the table. If you look at the corner of a table at say 2 meters distance, and then look at the same corner with just 20cm distance, the angles will have increased.
I do not know what exactly the formula will be, for changing the focal length to keep the angles the same when you change your distance. But I think it is probably more simple than you think:
Most probably the only thing you have to do is... NOT change the distance to your subject(s). Only zoom in on the pencil by increasing focal length. This will keep the perspective correct, and will give you what you need.
To keep the DOF similar, use the same diameters of aperture. So, lets say you are shooting the table with a 50mm normal prime, at f4. The aperture size will be: 50 / 4 = 12.5mm. And suppose you shoot the pencil with a 200mm lens. Then use a 12.5mm aperture too (for similar DOF). The f-value you need to set will be: 200 / 12.5 = f16.
So, to recap: Do NOT tilt/shift/move the camera in any way between shots. Keep the height the same too. Only change focal length to get the desired magnification. Use the same aperture size to keep DOF similar.
Quick and dirty example (handheld, no DOF correction) with 18mm (APS-C), then zoomed in to 50mm, then combined:
I do realize that this method is nor perfect either, as you might look on top of a small subject, but when it would be bigger you would look upto it. I will have to rake my brain a bit more over this.
Maybe this solves that problem: Note where in the frame the subject rests in the table (the height of the frame). When zooming in, keep that height of that point the same (by lowering the tripod, not the camera angle).
Good luck with your experiments, and your thoughts on my thoughts are welcome.