When to Align the Finder
Your finder is a precision instrument that is removable, and can be precisely moved in two directions. All this ability to move means you can’t expect it to remain rigidly pointed in the desired direction forever. You will need to align your finder
- When you first assemble your telescope; and
- Any time you remove the finder from the telescope; and
- After any shocks or jolts to the telescope or finder; and
- With some telescopes, if the telescope or finder are rotated; and
- At various other times.
The other consideration on when to align your finder is that it’s better to do it in daylight, if possible, or at least not in the dead of night. You’ll be better able to see what you are doing, and you won’t be cutting into your precious observing time. Finders with cross-hairs can be aligned in daylight. “Red dot” finders must be aligned when it is dark enough to see the dot against the sky, but this can often be dusk rather than full darkness.
The details of how to adjust your finder will vary with the specific model, but the general approach you will follow is as follows:
Point your telescope at an easy-to-find, non-moving object as far away as possible.
- If you are aligning a cross-hair finder in daylight, use a distant tower, chimney, telephone pole, etc.
- Avoid moving objects such as trees swaying in the breeze.
- If you are aligning at night, use the North Star if at all possible — it doesn’t move.
- As a last resort, use a bright star, but be prepared to have to repeat the next steps several times to accommodate the star’s motion.The advantage of using a piece of a distant building or other object on the ground is that you can find it by “walking the scope” along the horizon and up the side of the building or object.
Adjusting a Unit-Power Finder
Unit-power finders are generally very easy to adjust. Most have simple dials for up/down and left-right. Some use a 3-point adjustment system or require tools. On every unit I’m familiar with, adjustment can be done with one hand, by adjusting one knob or screw at a time, so there are no complex motions to master.
Here are a few examples:
This Stellarvue “red dot” finder has simple knobs for adjusting the up/down and left/right location of the red dot. The brightness control is also visible here, underneath the front window on the right in this photo.
Most other small red-dot finders have similar controls.
The Telrad finder’s adjustments are slightly different. There are three adjustment knobs, each moving the reticule toward or away from the centre of an imaginary triangle. The directions of movement are up/down, up-left/down-right, and up-right/down-left.
While it may take you one or two minutes to become used to these directions, I find the Telrad quickly becomes the easiest of the unit-power finders to align. The large, well-spaced knobs produce a predictable and smooth motion of the large concentric-rings reticle, making fine-tuning so easy that I always touch up the alignment before every observing session.
Adjusting a Magnifying Finder
Adjusting a magnifying finder scope is similar in principle, but the actual technique is slightly different because of the way most finder scopes are mounted. Finder scopes are usually mounted in a single or double set of rings which are, themselves, mounted to the main telescope. The telescope-to-rings mount is fixed and non-adjustable; what you adjust is the system that holds the finder scope inside the rings.
To be steady yet adjustable, the finder scope must be held by pressure at two different points along its length. Most do this by using two separate rings, each of which has 3 screws that press against, and support, the finder scope.
On some smaller finders, a single ring with 3 screws is used at one point, while another point on the tube is held by pressure from a rubber grommet in a close-fitting tube. The result is that your finder scope will likely have either 3 or 6 adjustment screws. Both systems work well, but I find the 6-screw system adjusts more smoothly and holds its alignment better, and I prefer it.
The finder should be securely mounted on your telescope (this one is removed to facilitate the photo). Locate the 3 or 6 adjustment screws on your finder scope and tighten them all just snugly (holding without any “flop”, but not so tight they deform the screws or the finder scope). On first setup, try to tighten them in such a way that the finder scope is roughly centred in the ring system — with each of the screws screwed in about the same distance.
Adjusting is done using only 3 screws. On a 3-screw system, just use the existing screws. On a 6-screw system such as the one shown here, do the fine adjustment with just one set of 3 screws — front or rear, it doesn’t matter. Ignore the other set after making sure they are snug.
To move the finder a small controlled distance, you will need two hands. Hold two adjusting screws, one in each hand’s thumb and forefinger. While looking through the finder, smoothly and gently loosen one screw a small amount and tighten the other screw at the same time, so the combination remains snug. You will see the view in the finder shift slightly. Note the direction of shift and continue, reverse, or pick a different pair of adjustment screws, and continue until you have the target centred. Because you have adjusted two screws all along, the screws should still be snug when you have the finder perfectly pointed, so no final tightening will be needed.