Medicago intertexta - the Calvary Medick

Franz Neidl · Post by **Franz Neidl** » Fri May 29, 2009 6:22 am

This time I did not succeed in making a good stack. Nevertheless I want to show you Medicago intertexta, the Calvary Clover or Calvary medick.

Franz

Harold Gough · Post by **Harold Gough** » Fri May 29, 2009 8:36 am

A crown of thorns! These medics are fun!

Harold

Franz Neidl · Post by **Franz Neidl** » Fri May 29, 2009 2:18 pm

I thought it could be useful to add also the lateral view of the fruits from Medicago intertexta.

Franz

Franz Neidl · Post by **Franz Neidl** » Sat May 30, 2009 1:19 am

This morning I succeeded in making a better stack.
with Zerene, 3 pictures.

Franz

rjlittlefield · Post by **rjlittlefield** » Sat May 30, 2009 1:31 am

Very nice! So, was the problem that the scale option was unchecked, or was the default of 5% not enough to handle this stack? Or was the problem something else?

By the way, how big is this thing?

--Rik

Franz Neidl · Post by **Franz Neidl** » Sat May 30, 2009 2:05 am

Hallo Rik,

the scale option is now on 15 and the program works fine! This was the problem. (I have to admitt that I dont know the function of the "scale option". As you see I have to learn a lot in my old days).

A fruit of Medicago intertexta is about 1 cm wide.

Franz

rjlittlefield · Post by **rjlittlefield** » Sat May 30, 2009 8:03 am

Franz, thanks for the additional information.

Every stacking package has some way to correct for changes in image size as you change focus. This is very important in macro work, where the image size will change visibly from frame to frame.

Most packages also have a limit of some sort, to keep the software from occasionally giving crazy results.

In ZS, the default limit for scale change is currently 5% from frame to frame. This is safe with most stacks, which have 2% or less. But your stack here had more than 5% change, due to a larger than usual focus step and a fairly short lens. That made it run into the limit, and the result was bad alignment.

DOF for a 1 cm object is only around 1 mm even when stopped down to where diffraction blur is becoming visible. It is even shallower for wider apertures. So more than 3 frames are needed to get best results for the front half of a 1 cm sphere. If we looked close ("pixel-peeping"), we would probably see some bands of blur in the stacked image. At the resolution shown here, the image looks great.

--Rik