Focus-stacking halos

[John Mitchell]

I've been experimenting with focus-stacking (closeups of plants), and I'm noticing halos in high-contrast areas such as around the tips of leaves. Most of the halos are very thin and only visible at 100%, but they make the images unsuitable for Alamy. Any advice on how to avoid halos when doing focus-stacking?

[Bryan]

Can't give you a proper answer John, but here are a few ideas.  Of course the degree of magnification changes as you alter the focus and this is normally only apparent in close ups. Maybe try shots whose focal planes are closer together, but it might also be down to the software that you are using.  I've not noticed this problem, but I haven't done much macro photography. Hopefully someone who knows what they are talking about can provide an answer !

[John Mitchell]

23 minutes ago, Bryan said:

Can't give you a proper answer John, but here are a few ideas.  Of course the degree of magnification changes as you alter the focus and this is normally only apparent in close ups. Maybe try shots whose focal planes are closer together, but it might also be down to the software that you are using.  I've not noticed this problem, but I haven't done much macro photography. Hopefully someone who knows what they are talking about can provide an answer !

 

Thanks for the suggestions. I've only been doing closeups (not macro) so far -- e.g. trying to get more than one part of a shrub in focus. The rain has stopped for a few minutes today, so I'm going to venture outside to do some more experimenting. It could very well be the software. I'm using a free program called CombineZP. It gets decent reviews, but I'm probably asking too much from it. I should try some other programs as well. Sometimes there are downsides to being parsimonious. 😉

[M.Chapman]

As the camera or lens moves closer to the subject (to focus on the farthest parts of the subject) nearer parts (which are now out of focus) may obscure more of the distant parts of the subject. For an extreme example, hold your thumb up in front of the centre of your computer screen (displaying a page of text) about halfway between the screen and your eye. Now watch what happens to the amount of computer screen that's visible as you move your eye closer to the screen whilst keeping your thumb still. More and more of the screen is obscured by the out of focus thumb which will cause ghosting. Now hold your thumb towards one edge of the screen and try again, and you'll see the opposite happens (more of the computer screen becomes visible). Ghosting can be avoided in this case as the background parts that are coming into focus aren't obscured. It's all down to the change in perspective.

 

So how to minimise the problem?

Choose subjects with have nearer edges that lie towards the edge of the frame (i.e. concave subjects)?

Choose convex subjects with soft curved edges (e.g. the surface of an orange)?

Use a longer focal length lens so the change in perspective is reduced?

Keep the lens fixed and move the camera / sensor?

 

Software can only do so much.

 

Mark

Edited February 19, 2021 by M.Chapman

[John Mitchell]

51 minutes ago, M.Chapman said:

As the camera or lens moves closer to the subject (to focus on the farthest parts of the subject) nearer parts (which are now out of focus) may obscure more of the distant parts of the subject. For an extreme example, hold your thumb up in front of the centre of your computer screen (displaying a page of text) about halfway between the screen and your eye. Now watch what happens to the amount of computer screen that's visible as you move your eye closer to the screen whilst keeping your thumb still. More and more of the screen is obscured by the out of focus thumb which will cause ghosting. Now hold your thumb towards one edge of the screen and try again, and you'll see the opposite happens (more of the computer screen becomes visible). Ghosting can be avoided in this case as the background parts that are coming into focus aren't obscured. It's all down to the change in perspective.

 

So how to minimise the problem?

Choose subjects with have nearer edges that lie towards the edge of the frame (i.e. concave subjects)?

Choose convex subjects with soft curved edges (e.g. the surface of an orange)?

Use a longer focal length lens so the change in perspective is reduced?

Keep the lens fixed and move the camera / sensor?

 

Software can only do so much.

 

Mark

 

 

Thanks. I haven't been moving the camera (on a tripod) or changing the focal length of the zoom lens that I've been using. I just move the focus point (flexible spot focus)  -- i.e. I  leave the camera and lens stationary without any change in the framing of the subject. Typically, I take only three images focused at near, middle distance, and on the farthest area that I want in focus. The results are fine except for the halos. CombineZP isn't good with edges, though, so I have to crop somewhat.

Edited February 19, 2021 by John Mitchell

[M.Chapman]

30 minutes ago, John Mitchell said:

 

 

Thanks. I haven't been moving the camera (on a tripod) or changing the focal length of the zoom lens that I've been using. I just move the focus point (flexible spot focus)  -- i.e. I  leave the camera and lens stationary without any change in the framing of the subject. Typically, I take only three images focused at near, middle distance, and on the farthest area that I want in focus. The results are fine except for the halos. CombineZP isn't good with edges, though, so I have to crop somewhat.

 

The lens will be moving when it focuses. It maybe internal an internal element, but it will move. When I said use a longer focal length, I meant use the same longer focal length for all shots. Sorry if that wasn't clear. There's no ideal solution though as any change in magification risks halos too. Let's hope there are some macro focus stacking experts who can give more experienced advice. Reducing the aperture may also help.

 

There's other info here.

 

https://www.heliconsoft.com/helicon-focus-main-parameters/

 

Mark

Edited February 19, 2021 by M.Chapman

[Bill Brooks]

My experience is, with the camera on a tripod, that halos are due to mainly slight subject movement between shots.

 

I use photoshop. Load all shots as layers in one file. Select all layers and auto align layers. Photoshop will make each layer slightly smaller to compensate for the telephoto effect when your layers have different focus points. A 100MM lens at 1:1 is actually a 200mm lens. At infinity only, it is a 100MM lens. Size of subject changes as you focus. Can cause halos.

 

Crop your aligned image to the smallest layer.

 

Focus stack the set of aligned images.

 

You should have a mainly focus stacked sharp image with some halos.

 

Select all aligned/stacked layers and duplicate them so you have a second set of aligned/stacked layers above the first set of aligned/stacked layers in the same file.

 

Remove all image masks from the top second set

 

With the bottom image set showing only, look for halos at 100%.

 

Go to the top set of images and turn each layer off and on individually until the halo disappears in the bottom set. You have found the layer in the top set that can cover up that particular halo.

 

Select the cover up layer in the top set, make a layer mask and fill it with black. The halo will reappear. Paint white on the cover up layer mask and watch your halo disappear.

 

Proceed to the next halo, find the cover up layer for that halo and do it again.

 

Delete any layers in top cover up set that have not been used. Flatten image using bottom image set and any cover up layers

 

Here is a an image using the technique. Used a wide shooting aperture to keep the confusing background out of focus. This required a lot of shots to get the depth of field on the flower without bringing the background into focus.

 

[John Richmond]

Like Bill I also use Photoshop for the alignment and photo stacking of images loaded as layers.  I do see some halos - but they're invariably caused by slight, often minute, subject movement.  I don't go to the lengths he does to eliminate them - mostly because I'm no expert on Photoshop.  Instead I try and eliminate halos at source by only shooting in absolutely still conditions, either inside in my little home studio, or outside when it's dead calm.  Even then it can take more than one set of stacks to get a usable final image.  

 

One advantage is that I now use Olympus OM-D cameras with built in focus bracketing and their excellent 60mm macro lens.  Depending on lighting conditions a single stack of say 7 - 10 images can take less than a second and involves no camera movement other than the slight focus shift between each shot.  Using a focusing rail, as I did pre Olympus, was both considerably slower and far more prone to accidental equipment movement.

 

I'm happy with my results:

 

 

 

[John Mitchell]

Wow! Lovely pics by you experts. All this is above my current paygrade, but thanks very much for the detailed replies. I now have a feeling that the halos I'm seeing might (?) have been due -- in part at least -- to slight movement of the plants between shots. It wasn't a totally windless day. I guess I need to get up earlier in the morning and try again.