Determining number of shots for a stack?

[bvalente]

okay fair enough. I was really aiming for an image that is well executed by this community's standards, but I realize it wasn't helpful in diagnosing. My pincer fell apart so I will retry and change only one thing at a time

Cheers

Brian

[Charles Krebs]

Brian,

Chiming in a little late here...

All good advice. You don't need to be a mathematician, but you should figure out what the increments are on your micrometer scale. Of course, if you work it out by actual testing, I suppose it really doesn't matter. But sometimes it's nice to look at calculations to come up with a reasonable starting point, and then you'll need to know how much you are actually moving things.

Elf's spreadsheet is very cool, and is the only one I've seen that covers his working method. It's necessary for the way he works, but his technique of focusing with the rear bellows standard is somewhat "specialized".

I have a few calculations that I find useful and put them in a spreadsheet form as well (they have nearly all been brought up in this thread already). It was not for "public consumption" since things were set down pretty randomly for my own purposes, but I added a few notes and re-arranged things so others may find it to be of some use. There's a large number of exceptions, caveats, and footnotes that could/should be added (pupillary magnification factors, circle of confusion selection and such) but with that understanding I think you can get some decent starting points here:
http://krebsmicro.com/DOF3.xls

(The upper sections relate to microscope objectives. The sections below the "black bar" are more universal for bellow use with lenses marked in "f-stops")

[rjlittlefield]

I was really aiming for an image that is well executed by this community's standards, but I realize it wasn't helpful in diagnosing.

The image is well executed. The full size version easily passes one of my standard tests for sharpness: make a copy, shrink to 50%, expand by 200%, and compare to the original. If there's little or no difference, it was fuzzy; if there's an obvious difference, it was sharp. It's sharp. And the subject and composition are interesting. Good job!

That said, I confess that my first thought was a lot like ChrisR's. Sometimes you have to change two things at once, but then it gets difficult to tell what mattered. Based on my own experience, and considering the conditions of your first image (shot with flash; center clean; high magnification and lens with its wrong face forward), I'd be inclined to bet on the lens change. I wouldn't be inclined to bet much, though, having been wrong way too many times.

By the way, according to the literature I have, the Luminar 40 mm is designed to be used front forward at magnifications greater than life size. ("Maximum performance" at 5:1; "good performance" from 4:1 to 16:1".) So in switching to that lens, you not only used different glass but also took care of the "wrong face forward" problem.

--Rik

[AndrewC]

Best thing for damping is probably sorbothane.

Andrew

[bvalente]

Thanks Rik and Andrew - feedback much appreciated!

Andrew it's interesting you mentioned this because I addressed my vibration through some sorbothane feet on my main board. I'll have to post a pic of my setup as soon as it's in some semblance of shape.



Cheers

Brian

[bvalente]

I was talking about putting together a spreadsheet, but this little web page calculator from AndrewC seems to get close to what I was envisioning:

http://tirpor.com/macro/macro_DOF.htm

I only hope you will finish up the microscope objectives portion!

Cheers

Brian

[AndrewC]

I was talking about putting together a spreadsheet, but this little web page calculator from AndrewC seems to get close to what I was envisioning:

http://tirpor.com/macro/macro_DOF.htm

I only hope you will finish up the microscope objectives portion!

Cheers

Brian

Will do To be honest I put it together to teach myself a bit of Javascript programming but if it is useful I'll finish it off.

As I'm sure our erudite optical experts will point out - any of these calculations make a lot of assumptions and approximate real behaviour but they do give you a good starting point.

rgds, Andrew

[bvalente]

A good starting point is all I can ask!


Cheers

Brian

[Charles Krebs]

Brian,

A good starting point is all I can ask!

Try this and see if it answers some of your your questions.

[AndrewC]

Brian,

A good starting point is all I can ask!

Try this and see if it answers some of your your questions.

Which is basically what is on my web calculator which shouldn't be a surprise as we are using the same equations ... from the MicroscopyU page http://www.microscopyu.com/articles/for ... depth.html

Though of course one could go into a long discussion about using the CofC or double pixel pitch in the objective calculations I might code that in as an option sometime ....

[AndrewC]

I was talking about putting together a spreadsheet, but this little web page calculator from AndrewC seems to get close to what I was envisioning:

http://tirpor.com/macro/macro_DOF.htm

I only hope you will finish up the microscope objectives portion!

Cheers

Brian

.... done

[bvalente]

Thanks guys

Both look like great tools. Andrew your page has already proven useful to me and operates on a level I can easily understand. Well, almost.

I don't know all the details, but I do know reversing the lens is generally preferable. Is it possible to include an option to choose reverse or non-reversing of the lens?

Also I hope you add 40mm to the enlarge lens list!


Charlie your spreadsheet is more comprehensive. It will take a bit of time for me to ingest but will be helpful as I use more of my various cameras, objectives, etc. I may try putting on a slightly more user-friendly veneer to the basic calculation engine you have. I am a sucker for pull-down menus and plain english


Cheers

Brian

[Charles Krebs]

Andrew,

Which is basically what is on my web calculator

I see it's there now, wasn't earlier when I posted!

[AndrewC]

....

I don't know all the details, but I do know reversing the lens is generally preferable. Is it possible to include an option to choose reverse or non-reversing of the lens?

Also I hope you add 40mm to the enlarge lens list!

.....

Done. Some time I might make it a field you can just type a number into but then you need to add lots of other code to catch errors plus it opens up some other issues to do with web security I don't want to be hassled with

For the calculations it doesn't matter if the lens is reversed or not, so long as it is a simple symmetric lens. I'll add a picture sometime soon showing where you need to measure to for the extension - basically it is the shoulder of the enlarger screw mount, so if you are using the lens reversed it seems as if you are measuring to the front of the lens facing the subject.

[lauriek]

For the calculations it doesn't matter if the lens is reversed or not, so long as it is a simple symmetric lens.

This comes up quite often. How would one know if a lens is a simple symmetric lens or not, examine the apparent aperture size from both sides?