Robin Wong and Focus Stacking

[Ken Croft]

I have been following a thread here on focus stacking so I thought I would try it out on my OM1 and E-M1ii, and find out more about it. After viewing a load of videos and in particular trying to get an understanding of the actual meaning and effect of focus differential, I thought I had as good an understanding as I was ever going to get. I appreciate that distance and aperture all are involved. But then I found a video by Robin Wong that made me wonder if I didn't understand at all. Now I hope this is not a "hate crime" but I cannot really enjoy the manner of presentation nor his voice, but he usually has something to say that I can appreciate.

At one point he took a focus-stacked image of a watch face, wanting all in the image to be in focus. He used the 60mm macro set at ISO 200, f5 and 1/30 and he set 15 frames at a focus diff of 1. He explained that an FD of 1 will give a very narrow focus plane. He did the stack and showed that only the area where he had focussed was sharp and the rest of the image was totally blurred. He then set an FD of 10, made the stack and then showed the whole image was in focus. I was befuddled by this.

This result is contrary to everything I thought that I had discovered about focus stacking. Even my own tests using a slanting rule as a target found the total opposite of his result. Small FD ie 1 gave all in focus and high FD ie 10 gave extremes of the image out of focus.

Can anyone explain, or is it simply that the answer is that Robin is Wrong?

Ken C

 

[Joe Lynch]

It depends on how much of the distance is spanned by your choice of FD and number of frames. I don't do a lot of focus stacking but the example you cited makes perfect sense to me--the step size was very small and the number of frames didn't span the watch depth. When he increased the FD, the watch depth got spanned before the frame count ended.

I DO know a lot about making videos and I greatly appreciate Robin's efforts and final results because I know personally how difficult and time consuming it is to produce a fine video with good lighting and sound and presentation along with good technical content. I love his work.

 

[mikero]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

 

[Mark Ransom]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

Seems like your choice of aperture would play a part too, by determining how much of each slice is in the DOF.

Makes sense. Why would they give you a setting to change, if a single number provided the best results in all circumstances?

 

[Joe Lynch]

... Why would they give you a setting to change, if a single number provided the best results in all circumstances?

Because one has to start somewhere, and after that, it's all trial and error anyway, since there is no way currently to tell the camera where to start and where to end and exactly what DOF and number of frames is needed anyway.

 

[David5833]

He used the 60mm macro set at ISO 200, f5 and 1/30 and he set 15 frames at a focus diff of 1. He explained that an FD of 1 will give a very narrow focus plane. He did the stack and showed that only the area where he had focussed was sharp and the rest of the image was totally blurred.

The FD of 1 was too small in that case, the focus moved during the 15 frames such a small total distance that it didn't cover enough of the watch.

He then set an FD of 10, made the stack and then showed the whole image was in focus.

In that situation, the FD of 10 moved the overlapping in-focus areas enough total distance in 15 frames to include the entire watch.

This result is contrary to everything I thought that I had discovered about focus stacking. Even my own tests using a slanting rule as a target found the total opposite of his result. Small FD ie 1 gave all in focus and high FD ie 10 gave extremes of the image out of focus. Can anyone explain, or is it simply that the answer is that Robin is Wrong?

Wong was right...for that situation. For a different combination of parameters (subject size, field of view, camera distance, FD, aperture, and number of frames) the converse might have been true. It can take a lot of trial and error to find the best combination in each situation.

--
https://www.flickr.com/photos/143821723@N06/

 

[mikero]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

Seems like your choice of aperture would play a part too, by determining how much of each slice is in the DOF.

Makes sense. Why would they give you a setting to change, if a single number provided the best results in all circumstances?

As I understand it, not really. The algorithm used takes into account the aperture, subject distance, etc. So if you stop down the lens to get more DOF on a single shot, then the re-focusing steps will be larger for a given focus differential.

But note I said 'in most cases' and not 'in all circumstances'.

Search for Richard Turton. He's done a lot of work on this on this forum.

Mike

 

[gary0319]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

Seems like your choice of aperture would play a part too, by determining how much of each slice is in the DOF.

Makes sense. Why would they give you a setting to change, if a single number provided the best results in all circumstances?

As I understand it, not really. The algorithm used takes into account the aperture, subject distance, etc. So if you stop down the lens to get more DOF on a single shot, then the re-focusing steps will be larger for a given focus differential.

But note I said 'in most cases' and not 'in all circumstances'.

Search for Richard Turton. He's done a lot of work on this on this forum.

Mike

That is not my experience. My cameras don’t do any aperture/focal length/distance calculations. As Joe stated it’s mostly trial and error. I have, through many focus stacked experiments come to a “starting” set of parameters of focal length/ distance to subject/aperture/differential/number of shots that produces a given in focus depth. Once that was known ( by trial and error) I could adjust accordingly ….. and more trial and error.

I have a lot of friends that have sought a “formula” for all of this and all have given up in frustration.

 

[mikero]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

Seems like your choice of aperture would play a part too, by determining how much of each slice is in the DOF.

Makes sense. Why would they give you a setting to change, if a single number provided the best results in all circumstances?

As I understand it, not really. The algorithm used takes into account the aperture, subject distance, etc. So if you stop down the lens to get more DOF on a single shot, then the re-focusing steps will be larger for a given focus differential.

But note I said 'in most cases' and not 'in all circumstances'.

Search for Richard Turton. He's done a lot of work on this on this forum.

Mike

That is not my experience. My cameras don’t do any aperture/focal length/distance calculations. As Joe stated it’s mostly trial and error. I have, through many focus stacked experiments come to a “starting” set of parameters of focal length/ distance to subject/aperture/differential/number of shots that produces a given in focus depth. Once that was known ( by trial and error) I could adjust accordingly ….. and more trial and error.

I have a lot of friends that have sought a “formula” for all of this and all have given up in frustration.

Gary, I don't really agree with you. The fist image below shows a single shot at F4 on the left, and F8 on the right. Unsurprisingly the DOF at F8 is greater.

The second image below is a result of 15 frames stacked in camera, using a focus differential of 3. Again, F4 on the left and F8 on the right.

It seems to me that the F8 stacked shot covers a much greater total distance that than the F4 stacked shot, implying that the lens refocused by larger steps in the F8 case. Or to put it another way, the algorithm used takes into account the lens aperture when considering the refocusing adjustment to make.

Mike




Single frame




15 frames stacked in camera with focus differential of 3

 

[Ken Croft]

It depends on how much of the distance is spanned by your choice of FD and number of frames. I don't do a lot of focus stacking but the example you cited makes perfect sense to me--the step size was very small and the number of frames didn't span the watch depth. When he increased the FD, the watch depth got spanned before the frame count ended.

I DO know a lot about making videos and I greatly appreciate Robin's efforts and final results because I know personally how difficult and time consuming it is to produce a fine video with good lighting and sound and presentation along with good technical content. I love his work.

I now realise that you are absolutely correct as I have repeated Robin Wongs's tests with the same result. When he set the FD to 10 there were probably only a few images that were used in the eventual stack with most of them being totally blurred. It seems that an FD of 1 is only appropriate for very shallow depth in the image.

I am basically back to where I started but with a greater understanding of how much I don't understand! I do understand that it is complicated.

--
Ken C

 

[g7_chord]

...I cannot really enjoy the manner of presentation nor his voice, but he usually has something to say that I can appreciate.

...

Ken C

Just want to say that I like his energy level, his presentation, and voice. A welcome change from most YouTube videos.

 

[Dann-Oh]

I have been following a thread here on focus stacking so I thought I would try it out on my OM1 and E-M1ii, and find out more about it. After viewing a load of videos and in particular trying to get an understanding of the actual meaning and effect of focus differential, I thought I had as good an understanding as I was ever going to get. I appreciate that distance and aperture all are involved. But then I found a video by Robin Wong that made me wonder if I didn't understand at all. Now I hope this is not a "hate crime" but I cannot really enjoy the manner of presentation nor his voice, but he usually has something to say that I can appreciate.

At one point he took a focus-stacked image of a watch face, wanting all in the image to be in focus. He used the 60mm macro set at ISO 200, f5 and 1/30 and he set 15 frames at a focus diff of 1. He explained that an FD of 1 will give a very narrow focus plane. He did the stack and showed that only the area where he had focussed was sharp and the rest of the image was totally blurred. He then set an FD of 10, made the stack and then showed the whole image was in focus. I was befuddled by this.

This result is contrary to everything I thought that I had discovered about focus stacking. Even my own tests using a slanting rule as a target found the total opposite of his result. Small FD ie 1 gave all in focus and high FD ie 10 gave extremes of the image out of focus.

Can anyone explain, or is it simply that the answer is that Robin is Wrong?

Ken C

The FD setting will tell the camera how far to move the focus plane for the next image of the stack. As one who has started down the macro journey, unfortunately its a lot of trial and error.

I did find a document from OM Ambassador Chris McGinnis (see the link below, its a link to the file on my google drive). It really helps with nailing your starting point for macro images and stacks.

Loading…

drive.google.com

 

[MovingH2O]

This thread may be of interest, although of course hardware and firmware may have changed in eight years:

Loading…

www.dpreview.com

 

[gary0319]

You need the depth of field for each slice to overlap. Too small a FD and there is a needless level of overlap. Too large a FD and there will likely be no overlap resulting in out of focus bands in the stacked image.

If you stick to a FD of 3, you won't go far wrong in most cases.

Mike

Seems like your choice of aperture would play a part too, by determining how much of each slice is in the DOF.

Makes sense. Why would they give you a setting to change, if a single number provided the best results in all circumstances?

As I understand it, not really. The algorithm used takes into account the aperture, subject distance, etc. So if you stop down the lens to get more DOF on a single shot, then the re-focusing steps will be larger for a given focus differential.

But note I said 'in most cases' and not 'in all circumstances'.

Search for Richard Turton. He's done a lot of work on this on this forum.

Mike

That is not my experience. My cameras don’t do any aperture/focal length/distance calculations. As Joe stated it’s mostly trial and error. I have, through many focus stacked experiments come to a “starting” set of parameters of focal length/ distance to subject/aperture/differential/number of shots that produces a given in focus depth. Once that was known ( by trial and error) I could adjust accordingly ….. and more trial and error.

I have a lot of friends that have sought a “formula” for all of this and all have given up in frustration.

Gary, I don't really agree with you. The fist image below shows a single shot at F4 on the left, and F8 on the right. Unsurprisingly the DOF at F8 is greater.

The second image below is a result of 15 frames stacked in camera, using a focus differential of 3. Again, F4 on the left and F8 on the right.

It seems to me that the F8 stacked shot covers a much greater total distance that than the F4 stacked shot, implying that the lens refocused by larger steps in the F8 case. Or to put it another way, the algorithm used takes into account the lens aperture when considering the refocusing adjustment to make.

Mike


Single frame


15 frames stacked in camera with focus differential of 3

That's interesting........ which camera

/lens was used. I'm going to a botanical garderns tomorrow and plan on using the OM-1 II to test out the in camera focus stacking,k so I'll keep your example in mind.

Thanks for posting this.

 

[mikero]

Gary, sorry I should have said. I used the OM-1 Mk1 and 90mm macro.

Mike

 

[Steve Balcombe]

[snip]

At one point he took a focus-stacked image of a watch face, wanting all in the image to be in focus. He used the 60mm macro set at ISO 200, f5 and 1/30 and he set 15 frames at a focus diff of 1. He explained that an FD of 1 will give a very narrow focus plane. He did the stack and showed that only the area where he had focussed was sharp and the rest of the image was totally blurred. He then set an FD of 10, made the stack and then showed the whole image was in focus. I was befuddled by this.

I'm not surprised you are confused. I just watched the video and it's the worst explanation I've ever seen.

The depth of field of each frame in the stack is determined by the subject framing and aperture. Nothing new there, but you can often choose settings which give you a fairly narrow depth of field per frame, because the total depth of field will depend on the number of frames - but also on how much the focus is shifted backwards (away from the camera) from frame to frame. You can use a big step (differential), in which case you will need more DoF per frame and your settings will need to allow for this; or you can choose a small step and then you will be fine with less DoF per frame. There are two ways to benefit from a small step - using a larger aperture may result in maximum sharpness; and/or it will allow more overlap between the in-focus areas of each frame, ensuring consistent sharpness from front to back, with no 'banding'.

Unfortunately, the actual amount of focus shift per step is shrouded in mystery. (The only other brand I have extensive experience of - Canon - is just as bad.) You just have to experiment and get used to what works. I've seen it suggested that a differential of 3 often gives good results, and that has been my experience too, so maybe start there and see how you get on.

That may be a little difficult to visualise, but it's the best I can do without examples and diagrams!

(Edit: Robin touches on the subject of sync speeds for flash in electronic shutter mode, but the OM-1 is not mentioned anywhere so presumably the video pre-dates the OM-1, I didn't check. Anyway, the fast readout allows it to be a respectable 1/100.)

--
https://www.flickr.com/photos/stevebalcombe/ or
http://www.flickriver.com/photos/stevebalcombe/popular-interesting/

 

[gary0319]

Gary, sorry I should have said. I used the OM-1 Mk1 and 90mm macro.

Mike

Thanks, tomorrow I'll use the OM1 II with either the 40-150 f/4 or the 12-45 f/4.