Tele Vue NP127is - Manual (Page 7)

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4.1 Adjustable Position End Ring
The tilt of the End Ring to the optical axis can be changed to compensate for any tilt errors you may see in
your photography. The telescope is aligned with the End Ring locked firmly against the end of the draw
tube. In this way you are always assured of a reference point to return to if necessary.
To determine which way to tilt the End Ring, it is necessary to focus on the part of the image that comes
to focus first when racking out the focuser from its “in” position. That will permit adjusting, or “jacking,”
the End Ring “out” to match that focus point in the field.
You will need to remove your camera equipment, including the Imaging System Adapter to adjust the
tilt of the End Ring . Slightly loosen the three Jamb Screws located on the face of the End Ring with the
appropriate Allen key. Then, “jack” the End Ring to the desired position using the appropriate Allen key
Jack Screws. Tighten the Jamb Screws against the End Ring and reinstall your camera. Some trial and
error imaging will be necessary, so it is best to carry out any necessary adjustment during an imaging
session.
4.2 Prime Focus
Prime focus photography involves attaching a camera, without its lens, to the telescope. In this method
the telescope becomes the camera’s lens. In the case of the NP127is, it is a 660mm focal length, f/5.2
telephoto. It is the focal length of the telescope in combination with the diagonal dimension of the CCD
chip or film frame that will determine the amount of field your photograph will cover. The shorter the focal
length or larger the diagonal dimension, the greater the field that will be recorded.
The parts necessary for Prime Focus photography are: camera with T-ring, appropriate T-ring adapter,
Extension Spacers, Imaging System adapter, telescope.
To obtain the best edge sharpness with CCD chips 30mm or larger, use the Large Field Corrector
(LCL-1069) in the configuration listed on page 6.
The recommendations in the chart and diagrams are specifically for SLR (digital or film), Apogee and
SBIG STL series cameras. If you have a different camera, you will need to determine the spacing necessary
to achieve reference distance from the seat of the Large Field Corrector to the CCD chip. These spacers
will be added between the seat of the Large Field Corrector and the face of your camera. Check the Tele
Vue website for on-going camera updates.
To start, you need to know the distance from the chip to the faceplate of the camera. This should
be specified in the camera’s documentation; call your camera’s manufacturer if it is not. The equation is
simply 2.6” — Chip to faceplate distance = additional spacer length required. There is enough tolerance
in this value that using threaded Imaging System extension tubes along with 0.040” and 0.080” spacers
to bring you as close as possible will work fine.
4.2a) To gain more field with chips APS size and smaller, use the 0.8x Reducer (NPR-1073). While the
reducer can be used with larger formats, noticeable vignetting will occur. The standard technique of “flat
fielding” should compensate. The arrangement of parts necessary for Prime Focus photography with the
0.8x Reducer is: camera with T-ring, appropriate T-ring adapter, NPR-1073, Extension Spacers to mini-
mize draw tube out-travel, Imaging System adapter, telescope. The equation to figure the proper spacing
between the 0.8X Reducer and the CCD chip is: 2.44” — Chip to faceplate distance = additional spacer
length required.
4.2b) To gain more magnification, the 2x (PMT-2200) and 4x (PMT-4201) Powermates are recommended
for best performance. Start by inserting the 2” Accessory Adapter into the end of the focuser. (Since increas-
ing the magnification will reduce the field, the large opening provided by the Imaging System Adapter is
of no benefit.) The arrangement of parts necessary is: camera with a T-ring attached, Powermate with cor-
responding T-ring adapter (PTR-2200 or PTR-4201) attached, 3.5” Extension Tube (X3C-0009), telescope.
There are certainly a variety of ways of setting up the Tele Vue-NP127is for photography!