Finderscopes - chasing stars!

[SilverAstro]

Or, if you are feeling experimental on a cloudy day and want to save some pennies there are lots of plans on the interweb to make your own zero-power finder like the Telrad and Rigel.

This one is especially ingenious : http://www.sff.net/people/j.oltion/35mm_Finder.htm

and another neat design (that also well illustrates the principle) http://www.geocities.jp/toshimi_taki/aiming_device/aiming_device.htm ,  his site is worh exploring, includes a nice printable star chart http://www.geocities.jp/toshimi_taki/

[Astro Imp]

44 minutes ago, Stu said:

This is what you need, a Telrad or a Rigel finder.

https://www.firstlightoptics.com/finders/telrad-finder-astronomy.html

https://www.firstlightoptics.com/finders/rigel-quikfinder-compact-reflex-sight.html

x1 mag, and present a set of circles of known radius i.e. 4,2 and 1 degree on the Telrad so you get a clear idea of scale when you star hop. Get everything aligned, then centre the star in the Telrad and it should be pretty close in the RACI.

As I said earlier, although the Telrad is a great piece of kit it won't fit on the S/W 200 truss tube.

[kilix]

it seems to me, that you should start looking along the main scope barrel as a first step. There should be no guesswork, if you are aligned +-5° by eyeing the barrel, then looking in the finder should reveal a starfield with multiple stars, but one of them is clearly brighter than the others.
If that's not the case, check your finderscope alignment.

Maybe this is another case where the see-through finder is in an advantage. By looking through it with one eye and looking at the sky with the other eye, you become accustomed to the view, which you see by looking along the tube. Then it is easier and more natural to eyeball the scope more accurately. Mk1 eyeball is a nice finder too

I dunno, I am really a green observer too with less than 100hours under the sky, maybe I am not the right one to give advice on the forum, but aligning the GoTo is one of the easier tasks when starting the observing session.

1. Make sure you know some constellations in the sky

2. make sure you can spot more famous stars easily (like Aldebaran, Capella, Rigel, Mizar, Betelgeuse, Polaris, Procyon, Pollux, Castor Vega, Deneb... at least few of those)

3. eyeball the scope to one of the stars (1st star preferably Polaris), move the tube roughly with hands, don't bother with keypad at this point

4. Now take the keypad and align the finderscope cross with the selected star, if you can not spot a remarkably brighter star in the finderscope, move the scope around in circles till you find it

5. Align the star in the middle of the telescope eyepiece, if not sure, defocus the telescope, so you have big circle instead of a spot, easier to tell if the big circle is in the middle of the EP.

5. use higher power EP to refine the centering more accurately

6. confirm 1st star on the keypad and repeat steps 4-6 for the second star.

[Moonshane]

I don't use goto but here's my take on finding stuff

 

[JOC]

killix looking along the barrel is something I haven't yet tried, but it does make sense as something else to try.

Star identities - making rapid progress from zero before Christmas.  Now at

Aldebaran - yes, Capella - not yet, Rigel - yes, Mizar - not yet, Betelgeuse - yes, Polaris - yes - at the end of the plough, Procyon - no, Pollux - yes, Castor - Yes, Vega - yes, but it's always hidden behind my hedge where I can't use it, Deneb - not yet.  Added Sirius last night

[SilverAstro]

23 minutes ago, JOC said:

 Mizar - not yet, 

Polaris - yes - at the end of the plough,

good progress there, exciting and fun isnt it !

I dont wish to appear pedantic (again!) but polaris wasnt there the last time I looked

Mizar is well worth finding with lovely Alcor next to it.

[JOC]

Polaris - i thought you found the two stars at end of the bowl of the plough and followed through in a more or less straight line and the next decent bright star was Polaris, i.e.at the end of the plough and yes, keep going - a note I didn't think I needed to add.  Is that not correct?

[Moonshane]

[SilverAstro]

The only reason I raised it is that I seem to remember reading that you were having trouble with too many stars in your finder and not being able to find it, thought this might have been the reason. Not at the end of the plough,  at the end of the line from the pointers, IN ursa minor the little bear.

No worries, as long as you are looking in the right place that's ok.

[JOC]

Moonshane, that's it, that's what I do :-)

So I need to learn the names Merak and Dubhe, that's this weeks cloudy night task.  Remember them and get them the right way around :-)

[JOC]

SilverAstro, you remember right :-)  I tried again last night.  There do still seem to be a lot of stars that suddenly appear in the magnified finderscope, but last night I followed the instruction to pick the brightest and got on a lot better. :-)  Ursa minor would a good confirmatory pointer, but she is stuck behind a large willow tree!!

[SilverAstro]

It is actually quite a deceptively long way from the plough ( especially thro' a 'scope !) not as is often shown in diagrams !!

You have it eyeballed unaided, along with the tail of the little bear,  ok ?

[SilverAstro]

1 minute ago, JOC said:

Ursa minor would a good confirmatory pointer, but she is stuck behind a large willow tree!!

UuuuErrr, that doesnt sound too good !

 

[SilverAstro]

This is where we all get at xporpises cos typing isnt good !

Polaris is part of U. Min - at the end of its tail - so if that is all behind a willow we are in trouble

On top of which, diagrams always show the two pointers pointing straight at polaris but they dont in real life, it is a bit off the line.

[John]

Thats one advantage of the zero power, illuminated reticule finders (eg: Telrage, Rigel etc), you use the stars you can see with your naked eye. Not so good if you observe from a heavily light polluted area and can't see many stars though. In those circumstances an optical finder can help by showing enough stars to "hop" by.

Personally I find having both the illuminated reticule finder and an optical one on the scope the best solution.

A good hard copy star atlas helps a lot as well !

[Charic]

On 1/7/2017 at 13:13, JOC said:

If I go clay pigeon shooting I can keep two eyes open

I have a much easier telescope to setup, but when using my straight though  9x50 your method of both eyes open is exactly spot on.
Whatever method you choose, it gets easier with practice.

[Dave In Vermont]

Everyone should have and know the trick of using the two "Pointer Stars" in Ursa Major - Merak & Dubhe. 

 

 

Simply line these up as shown. The brightest star they point to is Polaris, magnitude 1.99.

Hope this can help someone out there -

Dave

[kilix]

7 hours ago, JOC said:

killix looking along the barrel is something I haven't yet tried, but it does make sense as something else to try.

Star identities - making rapid progress from zero before Christmas.  Now at

Aldebaran - yes, Capella - not yet, Rigel - yes, Mizar - not yet, Betelgeuse - yes, Polaris - yes - at the end of the plough, Procyon - no, Pollux - yes, Castor - Yes, Vega - yes, but it's always hidden behind my hedge where I can't use it, Deneb - not yet.  Added Sirius last night

It's not a definite must-know-star list Don't take it so seriously. That's the list of stars, which help me with navigation on the night sky. Do it your own way, learn the stars you like, or those, which you see most easily at a given time of the year.

What I did, was learning the constellations and remembering the name of atleast one star from each constellation. That helps a lot when starting your observing session and aligning GoTo, because you immediately know, which stars you want to use when aligning GoTo. You pick 2 of the brightest stars you know by name (preferably Polaris is one of them).

Then, in time, you learn more than one star per constellation. You get to know double stars, carbon stars, or variables by name. Planisphere is a very good tool for learning. And dirt-cheap too!

And then, in time, people start to give you weird looks, when you point at the night sky and shout: "THERE'S ALKAID!"

[Stu]

On 21/01/2017 at 13:41, Astro Imp said:

As I said earlier, although the Telrad is a great piece of kit it won't fit on the S/W 200 truss tube.

Fair enough, but a Rigel will which is why I suggested both options....

[dannybgoode]

8 hours ago, JOC said:

killix looking along the barrel is something I haven't yet tried, but it does make sense as something else to try.

Star identities - making rapid progress from zero before Christmas.  Now at

Aldebaran - yes, Capella - not yet, Rigel - yes, Mizar - not yet, Betelgeuse - yes, Polaris - yes - at the end of the plough, Procyon - no, Pollux - yes, Castor - Yes, Vega - yes, but it's always hidden behind my hedge where I can't use it, Deneb - not yet.  Added Sirius last night

Deneb is easy-its the bright start above the hedge where Vega is and to the left a little! That's assuming your hedge isn't hiding both of them. 

Someone about 100 years ago selfishly built a row of houses behind mine not considering that someone might want to do astronomy from my garden and that blocks Vega but I can see Deneb for a good while.

 

[JOC]

Thanks everyone. 

Deneb - I've checked on stellarium and it looks a good bit higher than Vega and, as you note to the left.  However, looking at the map so are Cygnus and one called Rukh - however those two seem to be part of Cygnus.  I think the best thing to try is when I feed the sheep the next starry night when am 150m away from my naughty hedge I'll see if I can work out Cygnus - maybe take Stellarium over on the phone - that big cross shape looks like it might be fairly distinctive - then if I can find it the top star will be Deneb and looking at it relative to Vega could well be beyond the hedge trap. 

Polaris - Ursa Minor is indeed mainly behind the willow tree at the telescope location, but I think the long 'tail' pokes out of the top and if so then I am seeing Polaris on the end.  The star I think is Polaris as I find it from Ursa Major is def. not in ruler straight line from the pointing stars, but is 'close enough for Government work' (I can say that I used to be a Civil Servant LOL).  IIRC as I look at the sky I think it is a little to the left of where that ruler straight line would be and a reasonable distance away.  It does sound as though I need to confirm this though and I think this is another thing I can do whilst feeding the sheep and I am away from the hedge.

All in all it sounds like I should be making more use of a planetarium than I am and to be honest I don't know why I haven't done so - I think it is the lure of having the telescope to look through and I forget that I have the mobile phone with Stellarium and things like Google sky on them.  I like finding and looking at things, but I guess I'd get much more out of it if I knew what I was looking at!! 

[SilverAstro]

3 hours ago, JOC said:

 Polaris - Ursa Minor is indeed mainly behind the willow tree at the telescope location, but I think the long 'tail' pokes out of the top and if so then I am seeing Polaris on the end.

is def. not in ruler straight line from the pointing stars, but is 'close enough for Government work' 

  It does sound as though I need to confirm this though and I think

yes, if yoiu can see its tail, you got it !

def not in line, as I mentioned earlier,,  everyone draws it straight ( Dave has done it now as well ), when I was young I used to think it was me or my eyes that were bent cos no one ever said !

your description sounds good confirmation to me

Yes all's well, good to go   sorry if I woried you, but with so many stars and even more in finders I thort I'd check that you were not off on a goose somewhere

Enjoy.

 

[westmarch]

On 07/01/2017 at 13:32, Nyctimene said:

In my experience, it's best to use a finderscope together with a Red Dot finder or a Telrad/Rigel.  The RDF gets you roughly to the star field, then you switch to the RACI finder, after that to the main scope with the lowest magnification. Always align the three devices carefully, when starting your session.

Even after more than forty years of observing I still use the technique described in the sticky "Collimation and Star Hopping" by moonshane at the top of this subforum - I use a cutout template, showing exactly the true field of view of my finderscope. You'll have to match the template to your star map's scale ( shown e.g. on the inner side of the front cover page of the Pocket Sky Atlas). You then can start, on the map,at a reasonably bright star, make yourself familiar with the star patterns in the field (conspicuous triangles, close paired stars, trapeziums etc), and then  try to find the stars with your finderscope. It' ll need som training, but works fine afterwards, even in star-crowded regions.

If you don't know the true field of view of your finder, determine it with the star drift technique. Point your finder at a bright star near the celestial equator (+/- 3°), at the moment Mintaka, the western star in Orion's belt. Bring this star just outside the field of view, then stop the drive  and let the star drift through the whole field of the finder, crossing the center as close as possible. Take the time this passage takes in seconds (time seconds), repeat this procedure two times and calculate the mean value. Now divide the transit time in  seconds by four, to get the true field of view in arc minutes (60 arc minutes= 1°). I 'd suggest that you do this again with your main scope and the eyepiece, which gives you the widest field. You then can make the cutouts (with a fine pair of scissors) in the same sheet of paper or semi-transparent plastic sheet. The same can be applied to your bins.

Hope this helps.

Stephan

Hi,

I agree with Stephan.  The FOV of your RACI finderscope is usually given in the specification - my 9x50 finderscope is about 5°. I kept loosing the cutout so I found a key ring that had a circumference that matched my finder FOV and attached it to a holder (amazing what you find in Xmas crackers).  I use it with a sky atlas to star hop.

John

 

[JOC]

Hi John - they say pictures are worth a thousand words.  Yes, I can see how your picture above works - that's clever!

[Astro Imp]

@westmarch that's brilliant, thanks for posting.