From eyes, to finder-scope, to eyepiece

[CarlJoseph (Carl)]

Hi all,

I'm having a little trouble figuring out "distances" when moving about the sky. Hoping for some tips and guidance from the good folks here.

I didn't have too much trouble matching what I saw on the screen (Stellarium) with what I saw naked eye. Constellations and the like were mostly fine.

After aligning my scope to roughly the right spot, getting the target in the finder scope was sometimes problematic. You see so many extra "things" in the finder scope and I tended to get quite lost. I have a 6x30 finder scope.

Are there any "tricks" or things that I can do to help? For example, people talk about "degrees" or "arc seconds" between objects. How do I relate these to what I see in my scope or naked eye?

Some of the targets I couldn't catch were:

NGC 4755 (The Jewel Box)
I think I managed to find this but am not certain yet. What I could figure out was how far away from β Crux I should move my finder scope to locate the area. I wasn't even sure it was β Crux I was looking at in my scope because of all the other stars that appear when looking through it.

NGC 253 (Sculptor galaxy)
I had no luck finding this at all. Perhaps it's beyond a basic 4.5" reflector? I found the Sculptor constellation and ɑ Sculptor. I then drew a line down to β Centaur. Half way between somewhere should be the Sculptor Galaxy. No luck. The moon was up so perhaps this was part of the problem. :-(

NGC 5139 (Omega Centauri, Globular Cluster)
Perhaps I didn't stay out long enough for it to be high enough in the sky, but even finding the vague location was problematic.

What I DID see:

47 TUC
After a bit of work on this a few nights ago, I managed to find it again really easily. I can't resolve any of the stars and it just looks like a bit of a blur in the middle, but I definitely know it's it.

Orion Nebula
I've been exploring this for a little while now. Every time I can make out more detail and see more of the nebulous gas. I can now easily make out the trapezium although it isn't all that easy in my scope.

So, any tips for a beginner about making the leap from naked eye to the finder scope and knowing what I'm actually looking at?

Thanks,
Af.

[Roobi]

I like you as a beginner am having a little trouble also. I have a 5.12" reflector and actually posted in general chat about not being able to find the sombrero galaxy 2 secs ago. I wonder if these galaxy's are out of reach for us with our beginner scopes. The red dot finder is fantastic for locating, i have a fixed finder scope with the red dot and it definatly helps a bunch. I also get pretty confused going from stelarium to scope and trying to navigate my way around. it seems to be just slightly different. especially when using a 10mm and having to flip everything in my brain to match stellarium to what im seeing. I'm sure this is something we'll just eventually get better at doing.
Clear skies to you.

Roobi

[astro744]

Try the following all with your arm extended as far as possible (arms length).

Fingers spread as much as possible gives you a span of approx. 20 degrees.

Fist clenched gives a span of approx. 10 degrees.

The width of your fingernail at arms length is approx. 1 degree.

The Moon is 1/2 degree.


To work out what your telescope shows use either one of the following formulae:

True Field of View (TFOV) = Apparent Field of View (AFOV) divided by magnification.

OR. TFOV = Field stop diamater (FSD) of eyepiece x 57.3/focal length of telescope. This is more accurate but you need the field stop diameter available from most manufacturers or measured if you can see the field stop at the bottom of the eyepiece.

Don't worry about the accuracy too much and use the first formula as a guide and simple calculation.

eg. telescope = 114mm f7.9, f.l. = 900mm

A 32mm eyepiece will give a magnification of 900/32 = 28x
A 32mm (1.25") eyepiece generally has a AFOV of 50degree.
Therefore TFOV = 50/28 = 1.8degree.

OR. A 32mm eyepiece generally has a FSD of 27mm. Therefore TFOV = 27 x 57.3/900 = 1.7degree.

Eyepiece distortion can mean the figures are slightly different but either formula will give you a guide to the TFOV you are seeing.

A red dot finder is a good idea and if you get the Telrad you also get 0.5, 2 & 4 degree red circles as you look throough the Telrad which helps in seeing TFOV against the sky.

[mental4astro (Alexander)]

Hi afro boy,

Finding stuff in the sky isn't always easy. I've been doing this for more than 25 years, and somethings will always challenge.

A 6X30 finder is no doppie instrument. From a dark site it can reveal galaxies like M 83, the Sombrero and Centuraus A. No pissy thing.

I came up with a little device you too can make, that's helped me imeasurably, and takes alot of the guess work out. Here's the IIS link to it:

http://www.iceinspace.com.au/forum/s...ad.php?t=53378

I routinely use it now, both from home and dark sites. So easy and cheap to make.

Binoculars also help to recie a spot and from home they are invaluble as they reveal stars otherwise washed out by light pollution.

[floyd_2 (Dean)]

Another thing that you could consider is a set of printed sky charts. There are a lot of decent ones around, and you can have them at the scope (along with your red torch) while you're navigating the sky. I have the following ones:

1. Sky Atlas 2000.0 Field Edition (comes as a set of individual charts)
2. Herald Bobroff Astro Atlas (excellent - big and spiral bound)
3. The Edmund mag 6 star atlas (now given away - but an excellent beginners set of maps that only goes to Mag 6)

A printed star atlas and a red torch would be a great investment for you. A star atlas allows you to keep your dark adaption whilst navigating the sky from a map, and also means that you don't have to keep going back to the computer screen to compare the sky to a computer map (in the process ruining your dark adaption).

Dean

[Roobi]

"I came up with a little device you too can make, that's helped me imeasurably, and takes alot of the guess work out. Here's the IIS link to it:

http://www.iceinspace.com.au/forum/s...ad.php?t=53378"

Brilliant mate. Such a simple idea but so effective. cant wait to try this out.

[CarlJoseph (Carl)]

Wow! Thanks so much for all the advice and ideas. It's cloudy out today but hopefully it will clear up in a couple days so I can give these things a shot.

The handspan/degrees thing is really useful and so is the transparent circle for printed maps too. Am going to give them both a shot as soon as I can and report back.

So, is the Sculptor Galaxy out of reach for a basic 4.5"?

Cheers,
Af.

[barx1963 (Malcolm)]

Afro
NGC 253 is fairly low and hard to catch with any moon. You may get it at the next new moon.
Omega Cent is visible to naked eye if LP is moderate. From Hadar (Beta Centauri) which is the Pointer closest to Crux, move north, which is left at this time of year to the next brightish star, that is Epsilon Centauri, then keep moving in that direction about 2/3 of the distance between Beta and Epsilon and check in your finder, should be a fuzzy patch. It doesn't get very high until after midnight, I was observing it at 1am this morning. It is not at its best until March or you have to wait until 3 or 4 am. Well worth the wait though! As I said you should be able to pick it up naked eye if your skies are moderately dark.
Jewell bos is leterally next door to Mimosa (Beta Crucis) Should be seen in the same finder field as a fuzzy patch. In your scope you should see a triangular shape with a reddy star in the middle and a hint of other stars in background. It is fairly small. It should be high enough at 11pm to see clearly even with a bright moon.

[CarlJoseph (Carl)]

Thanks again for the tips.

I have an electronic angle finder (I use it for my woodworking). I'm wondering if in the meantime this would be useful on a scope?

If I put it on top of my scope and set the angle to the correct altitude, then it would just be a matter of moving the Azimuth (horizontal) back and forth a little until I find the right spot.

Would this work?

Cheers,
Af.

[barx1963 (Malcolm)]

I have seen this done with a moveable ring for azimuth and the electronic spirit level. then simply point to a star with known coordinate and turn the ring so is reads correctly. Of course you have to convert RA and Dec to Alt/Az for your location and time, Stellarium can do this and I beleive there is an iPhone app available as well.

[richardda1st (Richard)]

When using Stellarium you can flip the screen image left to right and top to bottom. Do this when you zoom in and compare to your scope's view.

Also Stellarium and most others will show you circles to match your eye piece view, to show you what is actually in your view. But you first have to download & install the ocular plug-ins from Stellarium, other plug-ins also available.
Barrykjerdes a member here on ISS can help you out with Stellarium (hope Barry dosn't mind me mentioning him)

I made my self an azimuth scale for my dob and fitted a digital inclinometer to my scope for altitude. So long as I have the altitude & azimuth details I can point my scope to any target. There is a few threads in ISS to help you. If you are interested and require any help just let me know.

Cheers
Richard