nonlinearity of an Olympus focus block

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NikonUser
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nonlinearity of an Olympus focus block

Post by NikonUser »

Currently working on the genitalia of micromoths as an aid to species identification.
Using a FF Nikon I rarely have to use a 10x objective, at 10x any dirt on the sensor does not show in the final image.
For this tiny micro, a Stigmella sp., I used a MPlan 40x LWD.

When looking at the 49 frames I could see the image had moved between frames. There is a tiny spot on the sensor the position of which is recorded on each frame. The scatter of these dots in the final stack shows the nonlinearity of this Olympus BH2/BHS focus block.

Kudos to Rik and Zerene Stacker for automatically aligning the 49 genitalia slices to give one useful stack.
Image
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
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ChrisR
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Post by ChrisR »

Mine would be more linear, as a result of magnification changes.
I might be in interesting to try a stack with an elastic band or two to take up slack.
Chris R

NikonUser
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Post by NikonUser »

Thanks Chris.
Not sure if there is any slack. The setup is a 'complete' BH2/BHS stand except that the overhanging arm for the objectives being cut off.
Camera and objective mounted vertically, not attached to microscope and not moved. Specimen is a slide-mount and is on the microscope stage. I move the stage using the built-in focus block.
The stage is quite heavy, complete except for a substage condenser - which I could add to give the stage more weight.
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

ChrisR
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Post by ChrisR »

So about what, 2 turns sf the knob?
I agree, it looks a bit odd!
I suppose if you were using flash and the camera were swinging about, it would expose wherever it happened to be but you'd still get a sharp image. That sounds unlikely though, you'd have noticed the wobble before now!
Chris R

rjlittlefield
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Post by rjlittlefield »

The pattern of dots looks to me more like random jitter, as opposed to some sort of smooth non-linearity like the corkscrew patterns that we often see with rails.

One quick way to tease that out is to process the stack, then use File > Save Other > Save Registration Parameters to write a tab-separated values file that can be pulled into Excel for graphing. Plotting XOffset versus YOffset as a scattergram with connecting lines will reproduce the pattern of dots that we see in the PMax image, and the connecting lines will indicate the sequencing.

If the plot looks like a random hairball, as I expect, than it might help to introduce some off-axis loading of any moving parts like the stage, to keep them firmly engaged at all times on the same sides of the guide rails.

Sometimes parts that aren't supposed to be moving actually are, like the camera on its bayonet adapter or the objective or turret in their respective mounts. If that's the cause, then loading those things can help too.

My rig with camera on salvaged focus block has problems like this in some stacks but not in others. For the moment I'm assuming that it's a difference in off-axis loading depending on orientation, but it could also be a matter of one part of the travel versus another.

In any case, the moving around probably doesn't matter much for what NikonUser is doing. Subjects like this tend to play well with computational alignment, as illustrated by the clear result here.

--Rik

NikonUser
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Post by NikonUser »

Chris - just 1 turn of the dial, 50slices @ 4µ

Rik: Random jitter seems correct. I reshot the slide with the same settings but did not change the focus between exposures. Thus, the focus block was not touched.
I simply took 50 shots with mirror up using a remote cable to fire the shutter (D810 has a physical cable connection, I like the D90 which has a true un-attached remote).
My D810 has quite a few tiny spots on the sensor all of which produced clusters of 50 dots.
As the scope and focus block were not moved my interpretation is the 'jitter' is occurring in-camera; likely a bit of extra jitter frrom the focus block when it is used.

But as you mentioned, not a practical problem as Zerene takes care of it.
Image
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

NikonUser
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Joined: Thu Sep 04, 2008 2:03 am
Location: southern New Brunswick, Canada

Post by NikonUser »

Full frame showing multiple clusters of 50 dots/cluster
Image
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

rjlittlefield
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Post by rjlittlefield »

NikonUser wrote:I reshot the slide with the same settings but did not change the focus between exposures.
That's a powerful test: nothing is supposed to be moving, but obviously something is.

I've gotten surprised by that sort of thing several times. Probably the most confusing one eventually turned out to be a few microns movement in the bayonet mount at the front of an Olympus bellows, where it was effectively causing the objective to move around over the subject every time the camera took a picture. I put a few drops of gel superglue around the outside of the bayonet joint, and suddenly things got stable. (Gel superglue so it wouldn't wick into the joint and would be easy to break loose for some reason.)

In your case, I'd place a modest bet on mirror/shutter shock propagating down through the microscope frame to slightly shift the stage with respect to the frame, or maybe even the slide with respect to the stage.

It would be interesting to know if off-axis loading the stage with a rubber band would make the jitter go away.

--Rik

Chris S.
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Post by Chris S. »

NU,

I used to get dots in patterns like that with my Nikon bodies. Yes, loading with surgical tubing did help. But much more helpful and elegant was a homemade camera clamp (documented here):

The blue lines depict axes available for adjustment. For such a simple clamp, the opportunities for adjustment are considerable:

Image

I found that Nikon bayonets can permit a little rotation around the lens; to a smaller but significant degree, they also permit some sideways and verticle sway or jiggle. The clamp solved all of this, and also let me make repeatable any influence of camera sag due to gravity. This clamp adds enough stability, repeatability, and predictability to my macro rig that I wouldn't consider shooting without it.

As it's likely that other camera brands also have play in their bayonets, and because this approach is adjustable for any camera, I've wondered why more photographers haven't adopted it.

--Chris S.

Lou Jost
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Post by Lou Jost »

This is one of the biggest advantages oif a mirrorless camera. Alternatively you can make your D90 "mirrorless" by taking a long exposure and, while the mirror is up, tape it there. The camera still works normally and you use live view for working. You still have shutter bounce but this is much less than the mirror shock.

I've done this with the D90. One problem is the D90 live view is not made to be kept turned on for a long time, and may overheat.
Last edited by Lou Jost on Thu Nov 07, 2019 8:58 am, edited 1 time in total.

mawyatt
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Post by mawyatt »

Chris,

That is a elegant solution to the Nikon F mount problem. I have some F mount adapters that you can see and feel the movement. At one point I had thought of super gluing a F mount to 52mm adapter to the camera :shock:

I can't use solution as you've shown because the clamp protrusions below the camera/lens mount ARCA plate would interfere with the THK rails I use. However I think I can use your concept and use a small (100mm) ARCA plate attached to the camera base and to the bottom of the long ARCA plate that supports the lens assembly. The two ARCA clamps would then be bolted together with a long photo 1/4-20 bolt and nut. May need some spacers between the plates.

Just tried this out, although I don't have the proper 100mm ARCA plate, so used a longer plate and it works. Now need to order some 100mm ARCA plates.

Thanks for the concept.

Best,

Image

Image
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NikonUser
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Post by NikonUser »

Thanks for all the feedback

Rik wrote "I'd place a modest bet on mirror/shutter shock propagating down through the microscope frame to slightly shift the stage with respect to the frame, or maybe even the slide with respect to the stage."
The camera is on a separate stand, on same heavy table as the scope but no contact; the BH2/BHS is quite a heavy microscope.

Chris: Followed your idea and solidly clamped the camera to the upright stand, so now both camera and bellows are 'locked down'.

Still got some jitter, but now seems to be linear !

I can live with it as Zerene can handle such problems.
Following image enlarged

Image
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives

rjlittlefield
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Post by rjlittlefield »

Super, thanks for the follow-up!

--Rik

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