G. Sirri – INFN BO 1LNGS 25 May 2005

Test of a dry objective with correction collar

Dry objectives having an high numerical aperture give aberration when imaging through coverslips that deviate from design thickness and refractive index.

To prevent artifacts, many objectives are equipped with correction collars that help compensate for coverslip thickness variations.

By means of the Cover Glass Correction slider the position of a movable lens group is adjusted inside the objective.

In this way, it is possible to observe the specimen through variable glass thickness from 0 to 2 mm.

This can be useful in emulsion scanning because the thickness of the intermediate medium between the front lens and the object plane ranges from 0 (when we scan the top) to about 0.3 mm (bottom).

Note that when the collar is adjusted, focus tends to shift and the magnification can slightly change.

G. Sirri for the Bologna group

G. Sirri – INFN BO 2LNGS 25 May 2005

Characteristics of the objective

This type of objective can be found normally in the market (from Leica, Nikon, Olympus or Zeiss) and are largely used by biologists.

We have used for this test the

ZEISS LD Achroplan (code 440864)magnification: 40x numerical aperture: 0.60working distance: 1.8 mmcorrection range: 0-2 mm

We installed this objective in our prototypal microscope equipped with Zeiss tube lens and our custom CMOS camera.

The Field of View is about 395x310 µm²

The micron/pixel ratio is 0.310 µm (top) and 0.305 (bottom).

G. Sirri – INFN BO 3LNGS 25 May 2005

Test conditions

In our case the usage of this objective requires a continuum collar rotation synchronously with the movement of the vertical stage.

However, we used only 2 correction positions d~0 for the top and d~0.25 for the bottom.

1.6 cm² has been scanned in the plates 34,35,36,37,38,39 of the reference brick (CERN June 2004, Brick 5 without lead) and one-by-one compared with the same measurements with the standard oil objective in the standard microscope.

20 levels (4 inactive) for view were grabbed.

The minimum area of the clusters was 3 pixels.

Since we do not have any automatic rotating system, we scanned all the fragments of the top and then of the bottom. After the merging the two raw data files into one as in an ordinary acquisition, we analyze the data with FEDRA.

G. Sirri – INFN BO 4LNGS 25 May 2005

Grains analysis

z0

eZLevel-to-level distance ~ 0.5 µm

Vertical clusters chains obtained using the libEGA of FEDRA

z

DRY OIL

Clu

ster

are

a (

pix

els

)

Clu

ster

are

a (

pix

els

)

cluster-to-grain_center vertical distance (µm) cluster-to-grain_center vertical distance (µm)

ggrains

cluster

G. Sirri – INFN BO 5LNGS 25 May 2005

Base Tracks (pl35, 1.6 cm²)QUALITY CUT

SIGNAL

BACKGROUND

G. Sirri – INFN BO 6LNGS 25 May 2005

Base Tracks (pl34, 1.6 cm², chi_puls cut)

Slope X

Slo

pe Y

After the quality cut

DRY: ~ 110 tracks/mm²

OIL: ~ 92 tracks/mm²

G. Sirri – INFN BO 7LNGS 25 May 2005

Base Tracks [microtracks – base tracks agreement]

Plate 35

(0.0 , 0.0)

σ = 6 mrad

DRY

OIL

Plate 35

(0.4 , 0.0)

σ = 23 mrad

Plate 35

(0.0 , 0.0)

σ = 9 mrad

Plate 35

(0.4 , 0.0)

σ = 21 mrad

4.8 cm² 4.8 cm²

1.6 cm² 1.6 cm²

G. Sirri – INFN BO 8LNGS 25 May 2005

Volume Tracks (6 plates – no holes – 1.6 cm²)

G. Sirri – INFN BO 9LNGS 25 May 2005

Volume tracks : angular residuals

Linear fits:

DRY

OIL

G. Sirri – INFN BO 10LNGS 25 May 2005

Volume tracks : position residuals

DRY

OIL

G. Sirri – INFN BO 11LNGS 25 May 2005

Volume Tracks : efficiencies

DRY

OIL

G. Sirri – INFN BO 12LNGS 25 May 2005

Conclusions

These are preliminary results because the on-line parameters were not well tuned.

However, the use of this technique seems to give results comparable to our oil results on the same conditions.