How to use an optical pole finder?

The pole finder is an accessory for equatorial mounts that allows you to quickly set the mount’s polar axis. When the polar axis is precisely set, an equatorial mount allows you to track an object while rotating along only one axis (right ascension). If the polar axis is not set accurately, the object will gradually “drift” in the field of view and additional correction will be required along two axes at once. Accurate polar axis alignment is especially important for long exposure photography. There are various ways to set the polar axis (drift method, auto-targeting system, electronic pole finders, etc.), however, in my opinion, the optical pole finder is still a simple and fast option, especially for small mounts -trackers, and also if it is not possible to carry a laptop or microcomputer with you.
The optical pole finder is a small lens telescope that consists of a lens, an eyepiece and a special reticle located in the field diaphragm of the eyepiece. The pole finder is designed to simultaneously show Polaris and the reticle clearly in the eyepiece. To adjust the sharpness of the reticle, simply rotate the eyepiece around its axis. The pole finder can also be equipped with a reticle illumination. The image in the finder is upside down, this is normal and has already been taken into account.

The pole finder can be screwed directly into the polar axis of the telescope (for example, with Sky-Watcher EQ5 mounts), or screwed to the side of the body (Sky-Watcher AZ-EQ5). For some mounts it is installed initially (Sky-Watcher HEQ5), for some it is already built into the design and non-removable (Sky-Watcher Star Adventurer), for some it must be purchased separately (Sky-Watcher EQ3-2) and installed independently.

When purchasing a pole finder, carefully read its description and, if necessary, check with the seller whether it is compatible with your mount. Before installing the pole finder, be sure to read the instruction manual.

Yes, a pole finder can be attached to almost any equatorial mount. And even to an alt-azimuth mount, if it can be used in equatorial mode.

Sky-Watcher AZ-GTi
Sky-Watcher AZ-GTi

The reticle in polar finders comes in two types – with constellations and the North Star mark, or with constellations and a “dial”.

My approximate algorithm for using a pole finder.
1. Assemble the mount, the polar axis should be directed as accurately as possible to the north (towards the North Star). It is advisable to install the tripod using the built-in bubble level. Not installing counterweights and a telescope yet. Check that the protective cover from the finder shaft has been removed from the upper part of the mount, and that the counterweight axis or declination axis does not cover the finder lens.
2. Adjust the tilt of the polar axis and the azimuth position of the mount so that the polar finder shows the North Star. For a quick preliminary search, you can use a green laser pointer by shining the finder from the side of the eyepiece into the sky so that the beam approximately hits the North Star. Then remove the laser, look into the pole finder, and catch the North Star.
3. Next, it is necessary to drive the Polar Star onto the outer circle, since it is not located exactly at the North Pole of the world, but at a small angular distance from it, and also rotates around it during the day.

If you are using an old type finder (with the Big Dipper and Cassiopeia on the reticle), then by loosening the mount’s right ascension (R.A.) axis, rotate the polar axis together with the pole finder so that the appearance of the constellations in the sky coincides with what is visible in the finderscope. That is, if Cassiopeia is in the sky at 12 o’clock (above), then in the finder it should also be at the top.

To find the position of the polar star using the SynScanInit application (for Android). Turn on the GPS in the smartphone, launch the application, wait until the coordinates of the observation location appear in the application.

Then press the GOTO POLARIS VIEW button, specify NORTH for the northern hemisphere, and SOUTH for the southern hemisphere:

To select the finder reticle type, press CHANGE RETICLE:

By adjusting the tilt of the polar axis and its position in azimuth and latitude, we ensure that the Polar Star falls into the circle with the inscription POLARIS. If nothing is visible through the finder, illuminate the finder shaft with a dim flashlight.

Owners of a polar finder with a “dial” can also use the SynScan Pro application, the position of the North Star is located in the Main Menu > Useful > Advanced > Pole Finder. Here the setting is similar – we rotate the mount along the right ascension (R.A.) axis so that one of the numbers 0, 3, 6 or 9 is at the top, bottom or side, and drive the North Star to the place where it is in the application. For example, in the image below and above, the North Star is “at 8 o’clock” – we drive it there. Even if the “nine” in the pole finder is at the bottom, the North Star should still be on the left, with a rotation of 240 degrees relative to the top point.

4. After this, install the equipment on the mount (counterweight, telescope, camera), balance it, and then once again check the position of the North Star in the finder. If everything is in order, then we begin observing or filming.

The polar axis adjustment must be done each time the telescope is assembled.

You can forget it, it’s not needed.

The optical pole finder must be shipped from the factory aligned, that is, the optical axis of the finder and the center of the reticle must coincide. I recommend that you definitely test it before using it. It’s very easy to do. After the Polar Star is on the circle, turn the mount along the right ascension axis and see if the Polaris has escaped from the circle. If not, then everything is fine with the finder alignment. If it runs away, then you need to try to adjust it.

There are three hexagon screws near the eyepiece. They adjust the position of the reticle in the eyepiece. Rotate these screws VERY carefully and alternately so that the mesh does not fall out of its seat. The finderscope test and alignment can also be performed on a distant ground object by adjusting the latitudinal tilt of the mount so that the finderscope is nearly horizontal.
In addition, it sometimes happens that the polar finder can be installed in a mount with a slight misalignment relative to the polar axis of the mount itself. One of the reasons I’ve encountered is that there is too much play between the threads on the mount and the threads on the finder. In total, the finder was screwed in skewed. What helped was winding a thick thread onto the thread of the finder and then screwing it into the mount. Instead of thread, you can try fum thread to seal the connection of water pipes.

Another possible problem is that the reticle is clearly visible through the eyepiece, but the stars are blurry. In this case, you need to slightly loosen the ring on the lens tube, twist the tube while looking at a distant object, then tighten the ring.

If it is difficult and inconvenient to install the polar axis, you can buy an angular viewfinder for the camera and make a mount for the polar finder eyepiece, or look for a ready-made option like this:

1 thought on “How to use an optical pole finder?”

  1. Спасибо, всё понятно! Использую SynScan Pro для точного наведения.

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