Focus stacking with tech cam.

[Pemihan]

How do you guys go about shooting focus stack images with tech cam? Adjust the lens or move the camera?

I have a RRS Focusing Rail with lead screw that can be adjusted in minute increments for super-fine focus but of course you can achieve the same by adjusting focus on the lens. I'm trying to get my head around which is the better solution, so any input would be appreciated.

I have used my XF up until now, but have it up for sale so will use my tech cam from now on. This is the kind of images I'm working on:

 

[Greg Haag]

How do you guys go about shooting focus stack images with tech cam? Adjust the lens or move the camera?

I have a RRS Focusing Rail with lead screw that can be adjusted in minute increments for super-fine focus but of course you can achieve the same by adjusting focus on the lens. I'm trying to get my head around which is the better solution, so any input would be appreciated.

I have used my XF up until now, but have it up for sale so will use my tech cam from now on. This is the kind of images I'm working on:

Peter,
Any manual focus stacking I have done has always been via lens adjustment whether with MF DSLR or Tech camera, but I am new to technical cameras, maybe there is a better way. Thanks for asking, I look forward to seeing what everyone has to say.
Greg

 

[jng]

I've read arguments for doing this both ways, but I do focus stacking by changing focus on the lens itself. I find the macro rail to be useful for positioning the camera. I generally locate the near and far points, and work my way down from near to far in gradual increments by turning the lens helical a few degrees at a time, stopping at wherever I remember the far focus point to be (easier when it's at the lens's hard infinity stop). The process is deliberate to say the least but seems to work as long as one of my assistants doesn't interfere while I'm shooting the stack, which can take several minutes:



This particular setup was with my X1D but I find myself using the Cambo + IQ3100 more frequently these days.

John

EDIT: Presumably by moving the entire rig, magnification remains constant whereas changing focus would alter magnification as one moves down the stack. Intuitively the former would seem to be preferable but software like Helicon Focus seems to handle things pretty well.

 

[mristuccia]

Hi Peter,
I hope you don't mind if a add a question on this subject.
By moving the focusing ring I've noticed that there is also a very small change in the magnification factor. Do the stacking softwares take this into account? What is the loss in terms of resolution if the stacking also implies a different scaling factor for each frame?

 

[darr]

I have tested both ways (years ago) and found it easier to use the focusing rail scale. Set a back point and a front point then slowly creep along and shoot.

 

[pegelli]

I use both methods i.e. macro rail to move the camera without touching the focus and slowly changing focus from one end to the other.

With a macro rail you're changing perspective between the different shots and with changing focus you're changing magnification between shots.
I found that Helicon focus deals equally well with both methods and the differences between the shots of the series.
However I never tested identical situations with both methods to study any potential differences between the two methods.

Pls. note this experience is solely based on 35 mm equipment, I have no experience with MF and/or Tech Cams so YMMV (except for the change in perspective vs. the change in magnification between the methods that is true for every film/sensor format )

 

[Shashin]

I have always done stacking using research microscopes and images would be measured for scale. I have used Helicon Focus and proprietary microscope drivers. Given a blank or out of focus background with thin DoF, shifting the entire camera and lens (or subject if on a stage) works well as magnification does not change at the subject plane. But the neat thing about photography is seeing is believing. If you are getting results that look good, then use that method. Unless you are going to collect data from an image, then changes to magnification are only important if you see distortion or artifacts.

 

[Shashin]

Hi Peter,
I hope you don't mind if a add a question on this subject.
By moving the focusing ring I've noticed that there is also a very small change in the magnification factor. Do the stacking softwares take this into account? What is the loss in terms of resolution if the stacking also implies a different scaling factor for each frame?

There is no perceptual loss of resolution. The different methods can distort or create artifacts in the out of focus background. But stacking can create other artifacts based on the stacking software--Helicon focus with stereoscopes can create edge effects, although I think it has come a long way since I was using that.

 

[Shashin]

This is probably the biggest thing I have stacked (physical size, not image size). This is moving the the camera/lens in relation to the subject.

 

[danlindberg]

Both! I sometimes (not very often) focus stack for landscapes and then my standard procedure is three exposures starting with infinity and then dialing back on the focusring a tad twice.

When I do tabletop then I use a rail. Depending on subject size/distance/form I usually end up with 4-8 exposures.

 

[MGrayson]

I’m a hand-held focus stacker (sort of). Usually, focus on near object, move focus point to distant object, have AF on rear button, so can quickly shoot-AF-shoot. Primitive, but it works.

Matt

 

[dchew]

I've done very little focus stacking. I am looking forward to trying some focus stacks with the Actus. If there are three ways to do this:

1. Keep the sensor in the same place; refocus lens helical (std focus stack)
2. Keep the lens/sensor distance constant; move the whole camera (a focus rail)
3. Move the sensor back and forth; keep the lens in the same place (Actus or other view camera)

Am I correct in thinking the only way to keep perspective constant is #3? Magnification changes, but not perspective...? So, if the stacking software does a reasonable job resizing the images during alignment would the ghostly edges between objects be improved? For example, edges of fern leaves layered on top of each other.

Dave

 

[Shashin]

I've done very little focus stacking. I am looking forward to trying some focus stacks with the Actus. If there are three ways to do this:

1. Keep the sensor in the same place; refocus lens helical (std focus stack)
2. Keep the lens/sensor distance constant; move the whole camera (a focus rail)
3. Move the sensor back and forth; keep the lens in the same place (Actus or other view camera)

Am I correct in thinking the only way to keep perspective constant is #3? Magnification changes, but not perspective...? So, if the stacking software does a reasonable job resizing the images during alignment would the ghostly edges between objects be improved? For example, edges of fern leaves layered on top of each other.

Dave

The short answer is not quite. The following is a longer answer.

What we have not discussed here is the scale. If you take the second method and you are focused on infinity, how far do you have to move the camera/lens to focus on the area 10 feet in front of the camera? If you are focused at 100X, how far do you have to move the lens toward the object to focus closer. In both cases, the situation is impossible. Basically, object to lens distance and lens to image distance are conventions, but those two measures are simple conjugate planes whose relationships hold regardless no matter what is an object or image.

Lets assume a normal view camera lens and not an internal focus lens (IF lenses change focal length to focus, which makes this more complex).

The first and third situation is good for far distances like landscape. Magnification nor perspective is not going to change very much in terms of the distance changing during focus. (Linear perspective is a ratio between camera and object distances and the slight movement in the change in distance through focusing is not going to have any significant change in the ratio.) With extreme magnification, starting around 1:1 and greater, situation two tends to be better than one because moving the lens to focus closer becomes too extreme and at some point impossible. The third situation is actually good for close subjects as moving the image plane to change focus distance requires less travel. But because magnification is still changing, the effective perspective when the stack is combined with not be normal as the near and far slices of the stack will not be at the same magnification (magnification will change their size relative to the ratio given by the camera to object distance). How this actually effects the perception of the image is probably insignificant as the scale of landscapes does not impact the ratio to any degree and with close subjects a viewer has a perspective that is unfamiliar. The most important thing is it "appears" natural.

If you are using a view camera, I completely agree that focusing with the back is universally the best practice, regardless of the scale. I would use that technique until scale becomes so small where I need to move the entire camera to stack (or I have evidence it does not give acceptable results). Focusing from the back simplifies the setup as you don't need an intermediate mechanism to move the camera and can use a fixed mount.

 

[Pemihan]

When using the XF focus stack the lens refocus. That's what I have been using so far and that works for me. So with that in mind I should just continue doing that with my tech cam (pancake). I might try moving the whole rig on a focusing rail and compare the two.
With the XF I'm using the SK80LS and he closest tech lens I have is the SK60XL which is a little to wide but I also have the SK120 Aspheric which might work with a macro adapter. I'll let you know the result when done.

Regarding software I find that Zerene Stacker does a better job than Helicon for the plants project I'm shooting.

 

[drunkenspyder]

I am a lens focuser myself. Zerene Stacker has a a short article on their website that convinced me, though it's by no means exhaustive. And that Phase does an excellent job with their automated focus stacking helps to create a habit. I agree that Helicon Focus, which I prefer over Zerene Stacker, seems to handle both methods well. I don't generally focus stack with my tech camera, but that's because—having been exposed to the precision of the Phase and the adequate convenience on the Nikon—I don't believe I get adequate results shooting just a few frames with arbitrary focus settings manually.

 

[dchew]

When I stack with the Alpa, the HPF rings make it a breeze. F/11, focus every 5 degrees (each major tick mark is 5 degrees). Works with all lenses because the helical pitch is about 0.03mm for all.

Dave

 

[jng]

I've done very little focus stacking. I am looking forward to trying some focus stacks with the Actus. If there are three ways to do this:

1. Keep the sensor in the same place; refocus lens helical (std focus stack)
2. Keep the lens/sensor distance constant; move the whole camera (a focus rail)
3. Move the sensor back and forth; keep the lens in the same place (Actus or other view camera)

Am I correct in thinking the only way to keep perspective constant is #3? Magnification changes, but not perspective...? So, if the stacking software does a reasonable job resizing the images during alignment would the ghostly edges between objects be improved? For example, edges of fern leaves layered on top of each other.

Dave

Ghosting of edges of objects in front of/behind each other has been my biggest challenge. I'll make a note to compare methods 1 and 2 next time (method 3 not possible as I don't have the right setup for this).

John

 

[Pemihan]

Ghosting of edges of objects in front of/behind each other has been my biggest challenge. I'll make a note to compare methods 1 and 2 next time (method 3 not possible as I don't have the right setup for this).

John

I tend to get lots of ghosting with Helicon Focus but almost nothing with Zerene Stacking. YMMV.

 

[jng]

I tend to get lots of ghosting with Helicon Focus but almost nothing with Zerene Stacking. YMMV.

Thanks, Peter. I just may need to give Zerene a try as well...

John

 

[gerald.d]

Ghosting of edges of objects in front of/behind each other has been my biggest challenge. I'll make a note to compare methods 1 and 2 next time (method 3 not possible as I don't have the right setup for this).

John

If what you are describing is what I've come across, I'm not convinced there is any easy solution to this. The impact varies depending on the relative size and distance of the objects, but the simple fact is that you can have a scenario where it is impossible to actually see parts of a background in focus because when you focus on the background, parts of it are blocked by an out of focus part of the foreground.

Here's an example -

Note the texture of the base plate of the movement (upper quarter of the frame)

If you look at the upper right section of the spring, you'll notice that that between the spiral of the spring, the base plate is fuzzy. That's because in the image where the focal plane was on the base plate, the bokeh from the spring completely blocked any visibility of base plate. It doesn't matter which method you use, because there simply is no data in any file of the base plate beneath the spring in focus.

I can't see any way to circumvent this other than a lot of editing in post.

Kind regards,


Gerald.