Tele Vue NP101is - Manual (Page 9)

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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 NP101is, it is a 540mm focal length, f/5.4
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: SLR/DSLR camera body with T-ring, appropriate
T-ring adapter, Extension Spacers, Large Field Corrector (if necessary), Imaging System adapter, telescope.
To obtain the best edge sharpness with 35mm or larger formats, use the Large Field Corrector
(LCL-1069) in the configurations listed below.
The recommendations in the chart and diagrams are specifically for SLR (digital or film) and the Apogee
and SBIG STL series cameras. If you have a different CCD camera with a 35mm or larger format, you will
need to determine the spacer necessary to achieve the optimal distance from the shoulder of the Large Field
Corrector to the CCD chip. 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. Simply subtract
“chip to faceplate” distance from 2.75” to get the spacing required from the Large Field Corrector to your
faceplate, for up to 35mm formats. For larger formats, such as 53mm diagonal, use 2.67” instead of
2.75. Use threaded Imaging System components to bring you as close as possible.
Since there are tolerances in all manufactured parts, it may be necessary to vary the spacing slightly
from the nominally calculated value. Should your star images in the four corners look slightly elongated,
try using the next smallest increment of threaded spacer with either the 0.040” (TLF-0040), 0.080” (TLG-
0080), or both in between the threaded spacers to fine tune the image.
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 such as 35mm, noticeable vignetting will occur. The standard
technique of “flat fielding” can compensate but requires significant image “stretching.” 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 minimize draw tube out-travel, Imaging System adapter,
telescope.
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-NP101is for photography!