Focusing rail: What do you use?

lauriek · Post by **lauriek** » Thu May 05, 2011 11:46 am

I understand completely Rik but you have to admit

Here is the base.

followed by a picture of an Owl, that _is_ funny!

(especially followed by a Canada goose stand and a gopher ball head!)

rjlittlefield · Post by **rjlittlefield** » Thu May 05, 2011 12:22 pm

No disagreement on that! In fact I burst out laughing aloud when I saw it -- my family wondered what I had stumbled onto this time. Then I thought perhaps we were the victims of an elaborate practical joke. I still haven't completely ruled out that possibility!

--Rik

Craig Gerard · Post by **Craig Gerard** » Thu May 05, 2011 5:51 pm

That thread is a classic, especially if you read the commentary for each image.....

I still burst out laughing whenever I read it and Tesselator's comments.

http://www.photomacrography.net/forum/v ... c&start=15

Craig

yeatzee · Post by **yeatzee** » Thu May 05, 2011 6:19 pm

Ok back to the topic

How do you know what increments to use for each stack? Also how do I know how much each little tick on the micrometer represents?

Craig Gerard · Post by **Craig Gerard** » Thu May 05, 2011 6:44 pm

Some information regarding micrometers and increments.
http://www.photomacrography.net/forum/v ... php?t=4571

Craig

elf · Post by **elf** » Thu May 05, 2011 8:37 pm

yeatzee wrote:Ok back to the topic

How do you know what increments to use for each stack? Also how do I know how much each little tick on the micrometer represents?

You need to calculate the DOF for your lens and bellows extension

p.s. Or you could try one of the spreadsheets or other threads explaining how:
http://www.photomacrography.net/forum/v ... php?t=8054
http://www.photomacrography.net/forum/v ... php?t=8663
http://www.photomacrography.net/forum/v ... php?t=9056

yeatzee · Post by **yeatzee** » Thu May 05, 2011 11:37 pm

on the 1" starret micrometer

I used 2 "tick" increments between each shot for this one:

http://photomacrography.net/forum/viewt ... 2&start=15

rjlittlefield · Post by **rjlittlefield** » Thu May 05, 2011 11:58 pm

The increment appears to be 0.001 . There should be 25 increments per rotation, each rotation moving the spindle by one small division on the linear scale. Each small division on the linear scale is 1/4 of 0.1, hence 0.025 . Your increments were 0.002", roughly 0.05 mm.

Your magnification was around 4.8 (=135/28, for the lens combo), and your effective f-number was then about f/23 (=4*(4.8+1), f_r*(m+1) ). Using standard formulas and a Circle of Confusion value = 0.030 mm, the calculated DOF is then 2*C*f_r*(m+1)/m^2 = 0.06 mm.

Sounds to me like you were pretty much dead on -- small enough, not too small.

--Rik

yeatzee · Post by **yeatzee** » Sat May 07, 2011 6:20 pm

rjlittlefield wrote:The increment appears to be 0.001 . There should be 25 increments per rotation, each rotation moving the spindle by one small division on the linear scale. Each small division on the linear scale is 1/4 of 0.1, hence 0.025 . Your increments were 0.002", roughly 0.05 mm.

Your magnification was around 4.8 (=135/28, for the lens combo), and your effective f-number was then about f/23 (=4*(4.8+1), f_r*(m+1) ). Using standard formulas and a Circle of Confusion value = 0.030 mm, the calculated DOF is then 2*C*f_r*(m+1)/m^2 = 0.06 mm.

Sounds to me like you were pretty much dead on -- small enough, not too small.

--Rik

Awesome, thanks!

yeatzee · Post by **yeatzee** » Sun May 08, 2011 4:02 pm

Wait when you say it looks like .001 increments do you mean .001 mm or .001"? The latter right?

If I needed to use 2 increments between each shot for that, how high of a magnification can I manage? Im not even at a high magnification yet and im already running out of precision movements? I thought I'd be spinning and spinning the micrometer to get to the focus I wanted between shots

edit: I realize I am failing at putting my thoughts into sentences.... I don't know how to say what im thinking

rjlittlefield · Post by **rjlittlefield** » Sun May 08, 2011 5:24 pm

when you say it looks like .001 increments do you mean .001 mm or .001"? The latter right?

Yes, 0.001" per increment. 0.0254 mm = 25.4 µm (microns).

I don't know how to say what im thinking

My guess would be that it's something like "Good grief what am I getting myself into?! "

Well, basically what you're getting yourself into is microscopy without the microscope.

When you shoot something with a DSLR at 10X, it's roughly the same as looking through a 100X microscope. The DOF as far less than paper-thin, as it's easy to appreciate by looking at a piece of paper at 100X and observing that you have to crank the fine focus knob up and down to catch the top and bottom surfaces. In fact the DOF of a typical 10X objective is around 15 microns = 0.015 mm = 0.0006", about 3/5 of one increment on your micrometer, and about 1/5 the thickness of a piece of paper.

At 20X the problem is worse, with DOF around 5 microns = 0.005 mm = 0.0002", about 1/5 of one increment on your micrometer. Probably that's around the practical limit of your micrometer, and you'll find it touchy and annoying. At least I always did, since that's also the limit of the screw table that I used for many years.

For convenient operation at high magnification, people use microscope focus blocks, which (no surprise!) are designed to make the kind of small movements that are required when looking through microscope objectives. The StackShot rail -- a "simple" screw driven by a stepper motor -- can also work fairly conveniently down to around 1 micron (1 µm = 0.001 mm), due solely to the small angular increments that its motor can move reliably.

I wish I could instantly make you comfortable working in this regime, but I have no idea how to do that. It'll come in time, honest.

--Rik

ChrisR · Post by **ChrisR** » Sun May 08, 2011 6:07 pm

I found it a big help to tape a Loupe over the micrometer, which makes it much easier to do fractions of a tick mark.
And I do too many steps on purpose, if they're tricky to set. That way I'm less ikely to miss, and get a fuzzy band.

NB there's likely to be some "play" in the screw, so if you overshoot, back off more than necessary, and wind up to the point you wanted from the same direction as the other steps.

SONYNUT · Post by **SONYNUT** » Sun May 08, 2011 6:17 pm

or this........
http://www.photomacrography.net/forum/v ... highlight=

yeatzee · Post by **yeatzee** » Sun May 08, 2011 7:23 pm

SONYNUT wrote:or this........
http://www.photomacrography.net/forum/v ... highlight=

Could you elaborate more on this? Looks interesting!

SONYNUT · Post by **SONYNUT** » Sun May 08, 2011 8:50 pm

take out the screw out of the end of your micrometer and pop on the washer..makes it easier to eyeball positions..i made a 24 16 12 8 6 position /hole..washers..

you can do it with a printed out sticker or something too..I use the 24 position indexer on my mill to drill the holes