Finderscopes - chasing stars!

[JOC]

So, is it something you just get the knack of doing?

Even with the Goto I need to line up on a known star or two.  So I've quickly upgraded to a finderscope with a right angled eyepiece (thanks Santa!), but even so it still seems a bit hit and miss to find a star in an otherwise black sky.  I can align the finderscope to the telescope - that bit is not problematical ,  It's the next bit that seems difficult.  So I point the telescope at what seems the right bit of sky for the star I've decided on using and peer through the finderscope.  The sky is black - do I move L, R, Up or down then when I do suddenly hit a star how do I know its the one I want.  Sometimes I can land on Orion's belt, but even if I chase Betelgeuse I'm never easily 100% certain that I've found it as it always seems further away than I expect.  Currently my best hope is to suddenly spot a moving aircraft in the line of finderscope sight and then take a quick look to see where this moving object is relative to what I want to find, but there is not always a convenient aircraft up there.   Is it just something you get used to doing and does anyone have any tips to make this quicker/easier for me please?  Many thanks

[PeterCPC]

GOTO systems will generally suggest the brightest stars for alignment. You need to familiarise yourself with the constellations I think and I would suggest getting a Planisphere or downloading Stellarium.

Peter

[popeye85]

Are you able to mount both the rdf and finderscope together? Maybe use the rdf to get into the correct bit of sky then fine tune with the finder.

Also finding out what colour your chosen star should be and using that info to confirm you have got the right one.

[JOC]

I've got Stellarium and am using it - in the sky I can see what I need to find, its just the physical process of tracking it down with the finderscope against the black sky which seems difficult and then knowing if I've hit the correct 'bright' star that I was intending to find.

popeye85 rdf?  sounds an interesting theory - more info please?  The colour of star is a good idea.  I found Castor the other night and that seems a useful find as it is was a double star and that is useful confirmation that I'm on the right location - I've started to realise that things like that are worth noting, but again it finding them against the dark sky in the first place that seems awkward. 

[brantuk]

Once the finder and scope are reasonably accurately aligned - point at a planet (usually quite distinctive) and refine the alignment with small adjustments. Then it should be fine for stars - check on Betelgeuse which has a distinctly red'ish hue about it.

[Knighty2112]

As Popeye suggests I normally use my Celestron Starpoiner Pro to roughly aim at the right star, then fine tune to centralise the star in my scope with my 9x50 RACI finderscope. Also, when I use the starsto align my Goto mount up I tend to always use the brightest ones available, which normally mean Vega, Deneb, Sirius, Arcturus, Betelgeuse etc. 

[ronin]

Quote

GOTO systems will generally suggest the brightest stars for alignment. You need to familiarise yourself with the constellations I think and I would suggest getting a Planisphere or downloading Stellarium.

Peter

Not always, the skywatcher criteria seems a bit odd. Once one asked to centre a dim stars in the neck of Leo, it completely ignore Denebola and Regulus. I didn't even know where the star it asked for was. Meades are "better" they try to only use isolated bright stars, but they have a lesser choice. Never did quite understand why Skywatcher have a big list of alignmnet stars as many are almost unknown. Likely someone has said anything Mag 4 or brighter and not realised how many here are.

Part of the problem is even with stellarium on a phone/table byt the time you select search enter the stars and get it displayed time has gone and you may fail alignment. Having met botyh Meade and Skywatcher Meade did  a better, more user friendly perhaps (?) job of the alignment process.

Getting a finder scope that you get along with can be timeconsuming. I have found I like RDF's, others cannot use them. I cannot use a Telrad, many like them. Want to try a laser pointer based one next.

Any finder needs to be well aligned to the main scope and I suspect that like myself many sort of leave them to drift out before making a major readjustment. Likely one of those cases where checking it every time or every other time and just tweeking it back to the centre is a good idea.

[JOC]

I can make the finderscope and the telescope aim at the exact same object - that bit I sussed in the first five minutes of playing.  It the process of waving the finderscope/telescope combination at an otherwise black sky and striking a star with the finderscope that is the problem.  If I go clay pigeon shooting I can keep two eyes open - one looks down the shotgun sight one can see the sky with the approaching target in it - I can therefore know if I'm pointing the shotgun in roughly the right direction to see the clay along the shotgun sight - does that explain the scenario any easier.  It's difficult to crouch behind the straight through finderscope to do the same thing, and impossible now I've got the right angled one (which seems a much easier use once I'm up and going) - Maybe if I can I should deploy both...............use the straight through one for finding calibration stars in the sky with both eyes open, then use the right angled one once I'm up and running and just have the process of aligning both, I could align the second right angled one as the goto will itself have put me very close to a star which even slightly out of alignment would be close to being found in the finderscope.

[Knighty2112]

You could get a laser pen finderscope that would help aim the scope easier. Never tried one, but you would have to be careful no planes or helicopters where about if you did ever use one.

http://www.rothervalleyoptics.co.uk/rother-valley-optics-5mw-green-laser-pointer-with-bracket.html

[alanjgreen]

JOC,

I had this problem when I got my first celestron scope (with free straight through finder) - how to get the star to the center of eyepiece quickly during alignment when it is time critical!

First, i purchased a right angled erect image finder to replace that but still had the exact same issue - how to get the scope to the star in double quick time

Next, I purchased a "Baader Skysurfer V" red dot finder - best money I ever spent - I could get straight to the star (with both eyes open looking through the red dot finder). It seems expensive but it does include the bracket to fix it to the scope (thats worth 25 quid). Its also big 40mm aperture so easy to see through. Its basically a metal gun sight that has been adapted for astronomy!

Baader also do a cheaper "sky surfer III" but you would need to read up on that, I have not used one.

Now, I only use the rdf, straight through finders are gathering dust in a box in the garage.

BUT, as said above (by popeye) if you can mount both a rdf and a 8x finderscope then you have the best of both worlds.

Maybe you can skip some of the redundant purchases along the way

 

Alan

 

[Peter Drew]

I think this is definitely a case where you would benefit from a RDF in addition to your RA optical finder. Once the RDF is aligned and centred on the star you wish to acquire I think you could be confident that the star visible in your optical finder is the one you want. 

[Nyctimene]

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

[JOC]

I'm liking the idea of these red dot finders - that's the RDF acronym - got it now :-).  They don't magnify - yes? and would show me more of the sky that I can see with my eyes.  I've look on some You Tube videos and will do some more research, but they look like a better solution at the moment - many thanks all.

[popeye85]

Do you not have the SW discovery? My one came with a RDF?

[rockystar]

I line the scope up by eye, from the bottom, to get it in a rough ailignment. Then use the finder to narrow the search. If you use the stars in Orion's belt, you should be able fit them all in your finder, so you can be sure you're where you think you are.

[JOC]

rockystar - I'll give that a try - at the moment Orion's belt is indeed my main recognisable point of reference as, yes, they do all fit in the viewfinder...................once I've found them!!   I think a few more nights eyeballing where Polaris is and I'll have that one, and I can find the Plough, Ursa minor and Casseopiea on a good night.  I want to work on Gemini as not only does it have my latest neat find - that double star Castor in it (which is going to be an excellent reference point, but it is also my own star-sign.   However, all those in the viewfinder are on the 'once I've found them through it' basis.  If I continue to have problems these RDF devices appear to achieve what I'm currently struggling with so if necessary I'll have no hesitation is getting one, but for the moment I think my bank balance will prefer that I continue with Santa's gift and see if I can get any quicker with it.  Now where are those aeroplanes......

[kilix]

I found aligning by a see-through finder difficult at first too, was thinking about buying a RACI or RDF, but the more I did it, the more easy it became. I use the both-eyes-open-technique, which is natural and quick. I have to bend my body to crazy angles sometimes, thou, see-through finder is not optimal in this respect. Of course, the first rough alignment is done by looking along the barrel of the telescope, then switching to the finderscope.

I almost always use Polaris as a first alignment star. It is visible all-year-round and there are no other bright stars near it. Nearest star with similar brightness (magnitude 2) is Kochab from Ursa minor, but you cannot mistake Polaris for Kochab, they are too far apart and most probably not in the same FOV of your finder.
I don't know how your GoTo works, but mine - after the first star is found - slews roughly to the second selected star. Then it is not a matter of finding the second star in a finder, one can (most of the time) spot it somewhere in the FOV of the main telescope at the lowest magnification. Again, there is almost no room for error, as the star is brighter then all other stars in the same FOV.

[Astro Imp]

On 07/01/2017 at 14:02, JOC said:

I'm liking the idea of these red dot finders - that's the RDF acronym - got it now :-).  They don't magnify - yes? and would show me more of the sky that I can see with my eyes.  I've look on some You Tube videos and will do some more research, but they look like a better solution at the moment - many thanks all.

If you go down this path don't be tempted by the Telrad, there is insufficient room to mount it on your scope. I'm speaking from experience as I already had a Telrad before buying the same scope as yourself.

Good luck and enjoy.

[N3ptune]

One solution could be to return the 90 degrees finderscope and get a straight through one instead. (It might not be the favourite solution but it's a good one)

With the straight through finder, you can look at the sky with the left eye while looking into the finder with the right eye, now you can aim at whatever you want using the left eye, this is really fast and effective...

--> With a 90 degrees finderscope, I read this the other day:  It's like driving a car forward while looking through the side window.

Sometimes I get into odd positions in order to look thought my ST finder.. but, it's fast and effective. (and inexpensive)

[Dave In Vermont]

When I'm not using a GoTo-mount and I just wish to align my finder-scope with my main telescope, I choose Polaris - as kilix says above. It's simply easy as Polaris doesn't drift around much to compensate for orbit and Earth's sped-up rate.

For aligning purposes, I always start with a low-power eyepiece. Even with a GoTo-mount. This is no problem to me, as I do know my way around the sky - as you'll be doing sooner than you may realize.

Dave & his Cloud-Bank...

[JOC]

Thanks all, I've been trying Polaris as the second star for the goto.  However, I'm starting to reconsider this, as, although I am absolutely clear which one it is - it looks a single star when I look up at it, but when I then look through the finder scope there are about 10 points in the sky anyone of which could be Polaris, but I couldn't work out which it was as there seemed no characteristic that I knew of to check out which particular star it would be.  Betelgeuse burns away golden and 'in me face' and screams "it's me".

[Astro Imp]

2 hours ago, JOC said:

it looks a single star when I look up at it, but when I then look through the finder scope there are about 10 points in the sky anyone of which could be Polaris,

No! If Polaris is in the field it will be by far the brightest.

[dannybgoode]

The nice thing about an RDF (I use the Telrad one) is with a little practice you can use it with both eyes open and kind of swap looking at the target star with the eye not looking through the finder with the one that is.

Makes keeping it in view and tracking it easy.

I am just about to pick up an eyepiece with crosshairs for final centering after getting it thereabouts in the RDF.

[JOC]

AstroImp, then I must have been miles off, which could have been the case as I don't recall a problem previously.  I bet I got star one wrong, i.e. thought I'd got Betelgeuse, but hadn't, s'funny I've been quite successful on other nights.  More practice needed!

[Stu]

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.