Focus Rail for Macro Photography: As I understand it, focus is achieved by moving the camera relative to the subject. Tho the movements are small, my question is, does not the...

srg

As I understand it, focus is achieved by moving the camera relative to the subject. Tho the movements are small, my question is, does not the perspective vary from one position to another? Let's say I am photo stacking a screw or a nail on a diagonal with the front, or top of the screw being much closer to the camera than the farther away point. Do you get my point?

Leitz Loc: Solms

srg wrote:

As I understand it, focus is achieved by moving the camera relative to the subject. Tho the movements are small, my question is, does not the perspective vary from one position to another? Let's say I am photo stacking a screw or a nail on a diagonal with the front, or top of the screw being much closer to the camera than the farther away point. Do you get my point?

Are you talking about "photo" stacking or "focus" stacking? (They are not the same thing.)

Wallen Loc: Middle Earth

srg wrote:

As I understand it, focus is achieved by moving the camera relative to the subject. Tho the movements are small, my question is, does not the perspective vary from one position to another? Let's say I am photo stacking a screw or a nail on a diagonal with the front, or top of the screw being much closer to the camera than the farther away point. Do you get my point?

Yes it definitely does.
At macro level, adjustment can be so small it can be negligible.
It also depends on the lens. The more distortions it has the bigger the changes will be.

https://www.uglyhedgehog.com/t-676863-1.html#11804314

User ID

srg wrote:

As I understand it, focus is achieved by moving the camera relative to the subject. Tho the movements are small, my question is, does not the perspective vary from one position to another? Let's say I am photo stacking a screw or a nail on a diagonal with the front, or top of the screw being much closer to the camera than the farther away point. Do you get my point?

No I don’t get any point at all from that description of your set up. There will BE NO foreshortening or “perspective” (bad term) to worry about. Somehow you’ve invented a new thing to worry yourself.

Essentially you disable foreshortening, you banish it, by using the focus rail. “Perspective” means a viewpoint, and acoarst your image will still show the angle of the viewpoint ... but without foreshortening, cuz the lens to subject distance is constant.

The images get stacked using only the in-focus portion of each exposure. The in-focus portion of the subject is always the exact same distance from the lens. Magnification remains constant. Thus no foreshortening at all along the lens axis. Focus rail travel parallels the lens axis.

User ID

Leitz wrote:

Are you talking about "photo" stacking or "focus" stacking? (They are not the same thing.)

In this case both mean the same thing. No need to ask which method, cuz it’s really both: focusing rail plus stacking.

BebuLamar

User ID wrote:

No I don’t get any point at all from that descript... (show quote)

Good point! The perpecstive is none so it would look like an image taken at extremely long distance.

Canisdirus

If you mean the camera moves ever so slightly toward or away (depending on where you start your focus point)...yes it does change.
There is a very gradual cropping effect over the course of multiple images captured.

cactuspic Loc: Dallas, TX

When your use a rail, you will get distortion due to the fact the position of the lens is changing in relation to the subject. The amount of distortion will change depending upon the depth of the subject and the magnification. The distortion is shown in a tutorial for the stacking software Zerene Stacker at: https://www.zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail. There is also distortion due to focus breathing and changes in lens extension, when turning the focus ring, although the level of distortion tends to be less than than when using a rail, as also noted in the tutorial. The only way to avoid these distortions is to use a bellows and only move the back standard, thereby keeping the same image circle for all of the slices.

SuperflyTNT Loc: Manassas VA

I use the in camera stacking with my Z7 and as the focus advances there is a slight difference in perspective. It’s not noticeable from shot to shot, but in a stack of 200 images you can see it between the first and last. The stacking software is very good at aligning and adjusting for the differences,

srg

Thanks for the thoughtful and informative replies. I will follow the links to learn more.

one_eyed_pete Loc: Colonie NY

cactuspic wrote:

When your use a rail, you will get distortion due ... (show quote)

Thanks for posting the link which provides an easily understood answer with evidence to back up the conclusions rather than conjecture.

fetzler Loc: North West PA

See the following earlier discussion on when to use rails and when not to.

https://www.uglyhedgehog.com/t-352889-1.html

1. If you are shooting landscapes turn the focus ring manually for focus stacking.

2. macros up to 1:1 use focus ring and automatic focus using Helicon remote or similar program. Some cameras have this built in.

3. for macros > 1:1 us a rail.

Each method involves some perspective or magnification changes. Focus stacking software takes care of image alignment.

Picture Taker Loc: Michigan Thumb

I have used the rail with micro for ever (since the 1940s). You can find a rail system between $20 and $30 if you look around. I still use the old one but a few months back got a new one on line for $25.00 and it is as good as my old one.

You don't need anything fancy. I set my camera on manual focusing adjust to the object and then go in and out on the track.

lowkick Loc: Connecticut

The images get stacked using only the in-focus portion of each exposure. The in-focus portion of the subject is always the exact same distance from the lens. Magnification remains constant. Thus no foreshortening at all along the lens axis. Focus rail travel parallels the lens axis.[/quote]

I understand and agree with your explanation, but using a focus rail has to cause a distortion, however slight, of the size of objects from front to back. With the focus never being changed, and starting from the front of the subject, every time you move the rail forward, regardless of how slightly, the next portion of the subject has to show larger than it is in relation to the portion photographed before it. Perhaps the size difference is negligible, even almost imperceptible, but it has to be there.

cactuspic Loc: Dallas, TX

The size difference between two successive slices in a stack is usually small. However, depending on the depth of the stack, the size difference between the first and the last slice may be significant. You will particularly notice it when you see details in the final slice that are omitted from the final composite. The reason this happens is that details (or the out of focus areas area taken up by those details) that are not in all the slices will be omitted from the final composite by most stacking software.