Comparing magnifications

The Milky Way is in its full glory during the summer months. So when you find yourself observing along that region, be sure to enjoy the larger picture at low power by using a wide-field eyepiece. Do that before homing in on a single object with higher magnification. Other than a different — but equally stunning — view, deep-sky objects will be less spread out, so they’ll look a bit brighter. Additionally, if you include a sketch of the broader area, it presents a great way to compare views using different magnifications.

As an example, let’s take a look at the magnitude 9.2 open cluster NGC 6704 in the constellation Scutum the Shield. It lies within the large dark nebula complex Barnard 111 that drops down from the Great Rift in Cygnus the Swan into the northern section of the Scutum Star Cloud.

I viewed it through a 4-inch telescope with an eyepiece that gave a fairly low magnification of 26x. The 6′-wide cluster then appeared as a faint smudge a bit more than 1° north of the Wild Duck Cluster (M11) and 1° east-southeast of the magnitude 4.2 star Beta (β) Scuti.

A strand of five 8th- to 9th-magnitude suns curves 12′ north of NGC 6704. Another chain of five stars northeast of the cluster extends 36′ in a northeast to southwest orientation, with the brightest member shining at magnitude 7.4. Several starless areas that indicate the presence of dark nebulae are noticeable.

As you spend time sketching this region, your eyes will become more attuned to the soft glow of the stars that surround the patches of dust clouds, making both viewable. The dark nebula complex consists of several smaller Barnard objects. B110, one of the darkest lobes, lies just east of Beta Scuti.

If you use the standard technique I’ve described many times in previous columns (graphite on white paper), you will produce a negative image.

This means the patches of diffuse star glow will appear dark on your paper. In fact, the brighter the glow, the darker you must draw it.

Use a soft, clean blending stump loaded with graphite to render the illumination. To prevent graphite from building up on the tip of your blending stump, rub it against a block of sandpaper several times during your observation so it remains clean and soft.

Once your wide-field sketch is complete, swap out your eyepiece, increase the magnification, and take a closer look. At a power of 125x (which I got by using an 8mm eyepiece), the entire cluster resembles a lopsided heart (upside down if your eyepiece orientation places north up) with a thick, dark ring surrounding it.

When you first compare sketches of the same area at various magnifications, the differences between them may surprise you. You’ll have to decide which one you like best. Or, if you have a bit more time, toss in a third sketch at an in-between magnification.

Try this technique, and you might find yourself making several sketches of the same area to add to your observing log. Better yet, share them with your astronomy friends!