User`s guide

SECTION 2.0

THEORY OF OPERATION

2.1 PURPOSE OF THE MODEL PFE-1

Two of the most serious limitations to doing photometry with the small format CCD cameras

are small field sizes and lack of a convenient way to insert photometric filters into the light

path. The PFE-1 provides an off-the-shelf solution to both these problems.

The TC-211 CCD chip used in the SBIG ST-4 and Lynxx PC series cameras has an

array of 165 pixels by 192 pixels. The chip is only about 1/10th inch square and therefore

offers a very small field-of-view. Finding and centering an object can be difficult without

some sort of pre-viewer. Off-axis guiders do not provide full-field views and are of limited

use. However, the eyepiece of the PFE-1 provides a full field view (approximately 0.4° with

an 8" f/10) and an illuminated reticle which exactly defines the CCD detector field of view.

Locating and centering an object with the PFE-1 is as simple as looking through the

eyepiece, positioning the telescope, and opening the flip-mirror.

Because of the limited field size, to properly perform differential photometry a separate

image is often required for both the check and comparison stars. To effectively double the

field-of-view, Optec offers the 0.5X telecompressor (stock no. 17610) mounted in a

removable 1¼" telescope coupler. This option can be used with light cones of f/10 or higher

without vignetting when using cameras having CCD's no larger than about 3.3mm by 2.4mm

size.

For planetary imaging, a 3x tele-extender (stock no. 17611) triples the effective focal length

of the telescope system. A well corrected negative achromat is used in the tele-extender for

unparalled planetary images.

The other important issue for any photometric use of a CCD is filters. The PFE-1 has a filter

port directly behind the flip-mirror which allows the use of ½" diameter photometric filters.

The standard PFE-1 requires the filters to be mounted in 2-position filter sliders (stock no.

17050). The automated version PFE-1A includes a stepper motor and can use the 6-position

filter sliders which are controlled by the SSPCARD and computer. See Section 9.0 for full

details of the automated option.

Johnson, Strömgren, Wing, and Hß filters are available in ½" diameter sizes directly from

Optec. Refer to Sections 5.0 through 8.0 for additional information on our filter

specifications for photometry.