What changes during focusing, perspective or magnification?

[milosh]

OK, here's what's happening:

Two days ago during sunrise, I wanted to take a shot of this old dried tree with a nice white flower as a foreground point of interest, but I was in a hurry and didn't have time to set up my tripod.

Now, the problem was that I wanted both the tree and the flower in focus, and the flower was maybe half a meter away from the lens, while the tree was much further away (maybe 20 meters). There wasn't much light available and I wanted to shoot at f8, so there wasn't any chance both of them would be in focus within a single shot. So, I figured I'll have to do focus-stacking in pp-ing.

I set my camera to Aperture priority mode, f8, lens zoomed to 25mm (18-105mm lens), I got down and framed it, and begun shooting.. I tried to keep the same frame on both photos by keeping my hands in the same position and only twisting my wrist to focus, first on the tree and then on the flower.

Now, after taking the first shot (where the tree is in focus), and tilting my camera down a bit to focus on the flower, while it was focusing on the flower I saw a strange effect (in the viewfinder), like the tree is moving away a bit (just like if I zoomed out a bit). Then I repositioned the camera and took the second shot. The flower is in focus on the second photo, but perspective has changed, it's like every element is a bit further away (zoomed out). I swear I didn't change position of my camera and I didn't touch the zoom ring between the shots. The whole effect was done in lens while focusing (I was witnessing it through the viewfinder).

I tried to stack these two photos in PS with no success, it aligns the layers nicely but the effect is still visible on the flower.

This is probably some well known fact, but it's new for me, I never encountered this before.

After all of this, a question comes to my mind, how does one do focus stacking then??

Here are the two photos so you can see what I'm talking about, these are sooc, they were only resized for the web.

Edit: Ok, found a way to do it using the actual stack command instead of only aligning layers, and it does a great job masking the flower. But, I'm still wondering what it is and will it make some shots impossible to process?

[OsmosisStudios]

It's called focus breathing, and it's common with internal focusing lenses.

It's affecting magnification. What is happening is that, as you're changing focus, youre changing the location of the elements in the lens and, while it's not actually affecting focal length, it's affecting how the lens bends the light.

The best lenses dont do this, or do dont it as much. Its very controlled in cinema lenses because if you're doing focus-pulls in motion picture, you dont want things changing dramatically within the frame. That being said, some people have taken advantage of it for specific effects. If you wanna have some fun, check out the "Vertigo Effect", which is a cinema technique that has the camera moving backwards on a dolly while the operator zooms the lens in: the subject stays the same size, but the FoV changes. Its almost impossible to do with a lens that focus breathes because, as you move and zoom, you also have to adjust focus. If you're trying to keep things consistent, you cant have changes.

Unfortunately there isn't much you can do in this case but try hyperfocal focusing.

[milosh]

Thank you very much, this was a very informative reply! I'm gonna take a look into that vertigo effect, it sounds interesting. Even focusing on hyperfocal distance wouldn't help this situation, since the flower is so close to the lens. I was there again today and I found a similar composition, decided on the focal length I'm gonna use, and I'm gonna be there tomorrow morning before sunrise to set up everything. Btw, the focus stack option in PS is really good.

Thanks once again!

[OsmosisStudios]

This is the textbook example. Scorcese did it right:

[milosh]

Oh yeah, now I know I've seen it before. Looks weird!

[SwissJon]

My lens main zoom lens, Nikkor 16-85, breaths noticeably when it's hunting for a focal point. I found that the 35mm prime I have does it much less. Maybe it's time for a prime?

Looking at the two photos you posted Milosh, the first has a noticeable difference in exposure to the second.. I know this is done by altering the speed of the exposure and not the aperture, and shouldn't make any difference, but if you can lock your exposure separately to your focus on your camera, maybe it'll help?

I'm going to have to try focus stacking with my Lensbaby.. See if I can make the photos any more wierd! :-)

[milosh]

Originally Posted by SwissJon

Looking at the two photos you posted Milosh, the first has a noticeable difference in exposure to the second.. I know this is done by altering the speed of the exposure and not the aperture, and shouldn't make any difference, but if you can lock your exposure separately to your focus on your camera, maybe it'll help?

Yeah, the exposure is different, not sure why it did it, they were taken seconds apart and the scene is the same. It probably adjusted the exposure for the grass and didn't quite get it back when I pointed it up again. This morning I used matrix metering and manual mode, so exposure will be the same.

Edit: my camera is set to lock only focus when shutter is half pressed, and an additional programmable button is set to lock exposure, I just didn't use it.