Backyard Voyager
Antares 7 x 50mm and 12 x 80mm Right Angle Correct Image Finders
by Eric Jamison
I recently was looking to replace my old 8 x 50mm right angle correct image finder, which had become worn out after years of service. One finder that caught my eye was the Antares 7 x 50mm finder which is available from Astronomics.
Antares 7 x 50mm Right Angle Correct Image Finder
I first began using a 8 x 50mm right angle correct image finder back in 1980 when I owned a C8 . Correct image finders use an Amici prism diagonal that provide images that are right side up and non-reversed, which made it easier for me to locate deep-sky objects rather than finders that provide images that are upside down and reversed.
When considering which brand of finder to buy there were a number of features I was looking for. This included: the finder being made of aluminum and available in white color; the achromatic lenses being fully multicoated; an Amici prism diagonal that uses 1.25" eyepieces that are removable; and a finder that was not be too heavy.
The Antares 7 x 50mm provided all of these features and at a price of $84.95 (as of fall 2005) was less expensive than some other finders on the market. The finder has a fully multicoated achromatic doublet that provides a limiting magnitude of 11, and a field of view is 6.3 degrees wide. The eye relief is 15mm and the eyepiece has a roll-down rubber eyecup for those who wear eyeglasses. The lens shade on the finder has internal grooving that cuts down on light scatter and increases contrast, as well as reduce dew formation. The finder weighs 18.4 ounces, without a finder bracket.
Closeup of the Antares Eyepiece
To reach focus you loosen the set screw on the side of the prism diagonal and slide the eyepiece in and out until the image is sharp, then tighten the set screw. The eyepiece does have a diopter ring that can be used to fine-tune the focus. Also the eyepiece can be rotated so that the cross hairs match the telescopes' optical axis.
Intial impressions from testing the finder during the day were favorable. For example nearby trees appeared sharp and showed good contrast. Under the night sky the same was true for deep-sky objects and the Moon. One nice feature is that the cross hairs are wide enough to be easily visible, something I have not always seen in finders from other manufacturers. Star images were sharp out to around 75% ~ 80% of the field of view before they began to show some distortion, similar to performance I have noted in other finders.
Antares 12 x 80mm Right Angle Correct Image Finder
I decided to purchase an Antares 12 x 80mm Right Angle Correct Image Finder to use with my TMB 175mm refractor to help locate faint deep-sky objects. It's features are the same as the 7 x 50mm finder, except that its' field of view is 4.33 degrees wide, and it is larger and weighs 44.5 ounces. Depending upon which telescope you plan to use this finder on you may need to add an additional counterweight. The price of the 12 x 80mm finder as of fall 2005 was $184.95.
The limiting magnitude of the 12 x 80mm finder is 12, and the added light grasp and resolution of this finder makes it easier to see fainter deep-sky objects that are more difficult to see in the 7 x 50mm finder. It shows also more detail in the brighter deep-sky objects. For example, while M31 is visible in the 7 x 50mm finder it begins to show some of its structure in the 12 x 80mm finder, such as a dust lane.
Overall I have been very impressed by how well these finders perform. The quality is quite good, and they are less expensive than some other finders on the market are. Besides being available in white, they are available also in blue and black colors. Highly recommended.