Nikon Objective is in.

abpho · Post by **abpho** » Thu Sep 15, 2011 3:03 pm

I just got my first Nikon objective. Love it. Great quality. Colour looks more natural. Crazy magnification. Just not sure what type it is. But I do want more.

Just some quick samples. Almost no post work done. The stacks came out very clean.

Grasshopper mouth parts - 46 images.

Grasshopper third ocelli - 55 images.

Questions:
1) I have the bellows setup to give me a distance of 150mm from the base of the objective to the sensor film plane. Do these lenses work with other lengths to give different magnification rates? If so, what range should I stick with?

2) How do you figure out what nominal aperture the lens has? I know that a larger N.A. means more light. And sharper. Is that because of less diffraction due to a larger aperture?

3) How can I tell exactly what lens I have? It does not state which PLAN it is. Only that is it a PLAN.

CheerS!

Craig Gerard · Post by **Craig Gerard** » Thu Sep 15, 2011 4:28 pm

Ab,

Good result!

You have the objective set at the correct distance from the sensor; but could move in either direction, to some extent; for example 8X to 12X. This is open to debate, not sure of the current consensus.

Assuming this is the $24.00 bargain; the objective you have is a Nikon CF 10X 160/- M Plan with a numerical aperture of 0.25 originally used with the Nikon Labophot microscope.

Your second question requires a more detailed response and hopefully someone will elaborate further; in brief, yes, yes and yes

Craig

seta666 · Post by **seta666** » Thu Sep 15, 2011 4:32 pm

1-The objectives marked as 160/- need 150mm extension from sensor, the ones marked 210/- need 200mm extension. You do not say what lens you have got

2-Normally for effective aperture you divide Mag/NA*2 (correct me if I am wrong)
So for a 10/0.25 that would be 10/0.5=f20
Nominal aperture is eF/mag+1 so 20/11 =f1.8 (once again correct me if I am wrong)

3-your lens has to have some markings on it, like 10/0.25 210/- maybe they are earased by use so a picture of the lens may help identify it

regards
Javier

lauriek · Post by **lauriek** » Thu Sep 15, 2011 5:20 pm

You missed a couple of slices from the front of the stack on the first one - easy to do at this magnification. I try to ensure I shoot from everything _just_ oof at the front to ensure I get the frontmost detail in focus.

I use my 10x/0.30 160 N objective from minimum to maximum bellows extension, it's all good - I shoot 4/3 sensor which might make a difference... The higher NA/mag objectives like the 40x/0.50 cannot be used away from their optimal extension without introducing awful aberrations in my experience. It's worth getting a measure out to get it as close as you possibly can!

abpho · Post by **abpho** » Thu Sep 15, 2011 7:00 pm

Thanks Craig, Seta666, Lauriek.

Lauriek; I know about the missed portion in the first picture. This was just a quickie. What do you mean by getting a measure out?

Here is the lens. I should have included it earlier.

Thanks again.

abpho · Post by **abpho** » Thu Sep 15, 2011 10:22 pm

Based on what Seta666 gave me and what Rik mentioned in another thread, I have the following formulas to calculate the effective (eF), nominal apertures (n), and the increment required (step size) to move the camera up for a seamless stack.

SS = 2cn(m+1)/(m*m)
eF = n(m+1)
eF = m/(NA*2)

SS = step size
c = circle of confusion

0.030 for the Canon 5D2
0.019 for the Canon 7D
I got these values from DOFMaster

n = nominal aperture
m = magnification
1 = a lonely number
NA = numerical aperture from an objective lens.

Here is my math pertaining to the Nikon CF 10x 0.25 160/- M Plan objective I just got.

eF = m/(NA*2) = 10/(0.25*2) = f/20
I read that I should keep this below f/22. Not something I can control with my objective, but with my other macro lenses I can.

Then:
eF = n(m+1) -> n = eF/(m+1) = 20/(10+1) = f/1.8

Therefore this 10x objective lens has a nominal aperture of f/1.8. Then taking the formula for step size I can figure out how much to increment my micrometer for a seamless image.

SS = 2cn(m+1)/(m*m) = 2(0.03)(1.

(10+1)/(10x10) = 0.01188mm

I converted this into thou because my scale is calibrated in thou. 25.4 mm = 1 inch. 0.0254 mm = 0.001 inch.
0.01188/0.001/25.4 = 0.47 thou

According to this number I needed to increment my micrometer by roughly half a thou. Which is doable. I can easily dial in between the tick marks. But I originally incremented the unit by 1 thou and the pictures posted above turned out great. Why?

For the people that are using the Nikon M Plan 20x 0.4 ELWD 210/-, what step size are you using for your stacks? I think I won't be able to use this lens with my current rig. I need to be able to dial in smaller increments.

ChrisR · Post by **ChrisR** » Fri Sep 16, 2011 2:15 am

I originally incremented the unit by 1 thou and the pictures posted above turned out great. Why?

Lots of factors come in to it. Look around the Nikon MicroscopyU sites for resolution (depends on NA) and the size of your pixels (which are much smaller than the C of C you quote) - see the Cambridge in colour site about diffraction.. ( Sorry I can't find links quickly, I'm on a really slow connection, but if your search tthe forum you should find them soon)

Then consider - if you're going to shrink the image down by a factor of five or so to show it on a monitor you're throwing a lot of resolution away IF everything was perfect, which it wouldn't have been! Upshot is that it's best to do some careful tests on some really fine detail then pixel-peep, then see what you can actually see at the size you're going to use.
The sums just aren't a perfect guide.
When you DO come to a conclusion, diffuse the light differently and you'll get a different result!

Using a really good 10x NA0.25 objective, I expect you'd find that you'd need to go shorter than half a thou (12 microns) to scrape the last of possible resolution, though in practice you may well not see it.

Try with the smallest steps you can manage, which would probably be one or two tenths of a thou. Say that's 4 microns. Then try a stack using every frame, then another using every second, then every third etc. You may be surprised how much or little it matters, depending on your final size.

You may find your Canon in-camera JPG converter makes a bit of a mess of some fine details near pixel level too, try converting from RAW with minimum compression.

Craig Gerard · Post by **Craig Gerard** » Fri Sep 16, 2011 2:25 am

http://www.cambridgeincolour.com/tutori ... graphy.htm

rjlittlefield · Post by **rjlittlefield** » Fri Sep 16, 2011 10:12 am

I like ChrisR's discussion and summary: the sums just aren't a perfect guide. The standard formulas are only approximations and the CoC values are rules of thumb. The amount of blur that is acceptable or even detectable depends heavily on how the image is displayed, and it also changes somewhat depending on subject, lighting, and viewer criteria.

In my experience, the standard calculations are about right for critical pixel-peeping. What I mean by "about right for critical pixel-peeping" is that if I compute a required step size X, shoot test stacks, and compare the results by viewing actual pixels and flashing A/B/A/B in place, then I can definitely see improvement from step size 2X to X, but not from X to X/2. That said, the result at 2X will typically look fine if I view it in isolation, and maybe even if I compare 2X and X side by side instead of flashing in place.

The experiment that ChrisR suggests is one of my favorites too: shoot a stack with very fine steps, then process it with various skip-factors to see what makes a good tradeoff for what you're doing.

--Rik

Chris S. · Post by **Chris S.** » Fri Sep 16, 2011 12:40 pm

abpho wrote:For the people that are using the Nikon M Plan 20x 0.4 ELWD 210/-, what step size are you using for your stacks?

My starting point for the 20x ELWD on a Nikon D200 is 2.9 microns. As others have said, the needed increment varies. With a new subject or lighting approach, I often shoot a quick partial stack at my "starting point" for the lens and adjust from there.

A $24 10x capable of delivering what you demonstrated is a great bargain! I have a similar lens, thought it is explicitly labeled "M Plan," and is for a 210mm tube. Since I have several choices at 10x, I haven't shot with it much, but my starting point would be 8.2 microns.

Cheers,

--Chris

abpho · Post by **abpho** » Fri Sep 16, 2011 1:49 pm

25.4 microns (µm) I can do easily. With 12.7 µm if I go in between tick marks.

I have an idea to allow me to use smaller increments on my current micrometer. But I wonder what the accuracy (tolerances) of the hardware is. I want to increase the resolution by 4x. That should give me 6.35 µm. Or, 3.18 µm between tick marks again.

lauriek · Post by **lauriek** » Fri Sep 16, 2011 1:55 pm

Lauriek; I know about the missed portion in the first picture. This was just a quickie. What do you mean by getting a measure out?

I meant for the higher magnification objectives (e.g. 40x/0.50) you need to get the extension set to exactly the right distance so get your measure (ruler) out and make sure it's exactly 200mm/150mm/whatever it's supposed to be!

rjlittlefield · Post by **rjlittlefield** » Fri Sep 16, 2011 2:00 pm

My first stacks with 20X NA 0.4 were using a manual screw drive at 0.1" pitch with 0.001" tick marks. Turning carefully at 5 increments per tick, 0.0002" = 5 µm average, the results were gratifying though certainly not perfect. See HERE and HERE.

--Rik