FOV Update..Binoculars

FOV Binoculars

If you have a pair of binoculars some manufacturers will indicate the field of view by marking somewhere on the frame..xxx@1000 feet..if it is marked 235@1000 it means if you looked at a 235 foot ruler 1000 feet away it would stretch completely across your field of view.

Author and Astronomer Phil Harrington in his book 'Touring the Universe Through Binoculars' has a formula to determine the FOV in degrees based on that manufacturers mark. Divide the xxx value by 52.5...my 10x50 were marked 235@1000 so 235/52.5 = 4.51 degrees...

To test the formula I went out last night and found a pair of stars, Mizar and Alioth inthe handle of the Big Dipper, that are approximately 4.5 degrees apart. There was a star on each side of the field just as predicted..

Now I can star hop using my binoculars...

BTW I the used ECUlite4 star chart program to find a pair of stars 4.5 degrees apart for the test. It has a feature that can measure angular distances between stars on the chart.

Phil Harringtons book 'Touring the Universe Through Binoculars' has an excellent chapter on binoculars and how to choose a pair.

Ok Lets get out there...The mosquitoes are waiting...

True Field of View

True Field of View

An astronomer not only has to be familiar with the night sky but he also must know his telescope inside and out before he can explore the unknown (at least to him) regions of outer space. One critical characteristic of the telescope that must be determined is its true field of view (FOV), the area of the sky that you see when looking through the eyepiece.

Once you know how big of piece of the sky you’re seeing through an eyepiece, you can plot your course through the stars using a star chart.

To measure the FOV of your eyepiece, find a star located near the celestial equator. You can usually display this line on a star chart program, or locate it on a printed star chart. Use it to help you pick a star. We will take advantage of the fact that a star located on the celestial equator drifts about 1 degree every 4 minutes as the night goes on.

Center the star in the eyepiece and turn off the clock drive. Record the time it takes the star to drift to the edge. If the star takes 2 minutes to drift to the edge, the distance from the center of the eyepiece to the edge is ½ degree or the distance across the whole field of view is 1 degree. Simple, eh?

For my 6-inch f/8 newtonian, the star took 2 minutes 52 seconds to drift from the center to the edge of my 1 inch eyepiece. That’s almost 3 minutes or ¾ of a degree. So the true field of view is 1 ½ degrees. Using the same method I found that my finder-scope has a FOV of 5.25 degrees. I am ready to start plotting star hops on my star charts

Now I can set up my star chart program to create finder circles to match my finders FOV and my eyepieces FOV. Above is a star hopping chart to find M13 in Hercules. I use the freeware program Cartes du Ciel to make my star charts. I have one for each Messier object.

Updated Jupiter-Neptune finder chart July 13,2009

Here is an updated chart..Since Jupiter is moving so fast it may best to use u Capricorn as a reference.

Good Luck,

Brian C

Neptune Finder Chart for July 2009

Back by popular demand is a finder chart for Neptune. It is really easy to find this time as Jupiter is a great jumping off spot for star hopping. The fields are 1 degree, a typical FOV for low power eyepieces. As time goes on Jupiter will change its position among the stars but Neptune should stay there for while so note the star field around it.

Good luck and happy hunting

Brian C

Three the easy way M31 M32 M110

It was a clear cool nite at the observatory tonite. We were able to stay out until 11:00 PM until the dew rolled in. The deep sky team got together tonite to try their hand at locating M31. Thanks to the pictures in all the text books and magazines it is easy for the inexperienced stargazer to miss the Andromeda gallery. They're expecting to see this huge galaxy with spiral arms. Not the little fuzz ball that appears in the eyepiece of their 6 inch reflector.
The team used the star charts they prepared to hop to M31, but tonite it was an easy naked eye object. Once centered on the fuzz ball that is the core the Andromeda galaxy, you could notice a fuzzy star near the edge of the eyepiece. The chart identified this as M32. That meant M110 should be just outside the field of view on the other side of the eyepiece but it was hard to see. All claimed they could pick it out of the gray background in the eyepiece but I think for some it was wishful thinking. We'll break out the 10 inch next time we're out.

BrianC

Finding Neptune

Well it was a nice clear week in Tichigan and it gave us the opportunity to exploring the solar system. Armed with pair of 10x50 Binoculars we set out to find Neptune. The hardest part was finding a decent set of finder charts. Finally we found a program called Cartes du Ciel ( a free program ) that generated awsome star chart. It was kind of tough recognizing the constellation of Capricorn. It was low and in the haze at 9:30 PM. But once we found the stars Deneb Algeti and Nashira it was easy to see Neptune as a small blue star in the middle of a equilateral triangle just west of 42 Cap. If you didn't know where to look you'ld miss it. Even with the 6 inch and 10 inch newtonians we couldn't see much more than a pinpoint of light.

We''ll try to figure out how to post the charts.

K9WIS.
Auf 24, 2008