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Thoughts On Finderscopes??


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Hi Guys

It occurred to me the other day that, as a non GoTo Ludite, I spend a fair bit of time trying to get lined up on the right bit of the sky. So, why not make it as easy as possible? So, I need (??) a better finderscope for my 16" Dob. What to buy?

I use a Telrad to get me to roughly there or thereabouts, then tend to head to the wide eyepiece and swap to higher power once located. I'm hoping to cut out the wide angle eyepiece swapping in and out part by getting a bigger finderscope to complement the Telrad which isn't going anywhere.

My current finder box contains TS and Skywatcher RACI 30 & 50mm finders. Which I struggle to focus with and don't seem to gather much light. I would love to be able to glimpse brighter DSO through the finder, but obviously need a nice wide FOV for the star hop.

Is bigger better? thoughts?

Paul

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I use a 50mm RACI combined with a Rigel Quikfinder on my 12" dob and find it a very effective combination. I should really add to that using a low power wide angle eyepiece in the scope can also be very useful for nailing the target object.

Some folks do use 60mm-70mm finders with medium to larger dobs but I've got used to my 50mm now and I have a good feel for how it's view correlates with my star atlas, which helps a lot.

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I'm using a combo of a Baader Sky Surfer III (RDF) with the 10x 60 Baader Vario Finder for the 18" Obsession Dob. Works quite well, but,in my eyes, not really superb. The 10x60 is giving a sharp view, but the true field of view (TFOV) is with just 4.1° rather narrow (Baader doesn't mention this in their ads and descriptions, and, at phone request, claimed, not to know!). The 45° Amici prism works fine, but focusing is somewhat awkward (draw tube with setting screws, or front focusing ring), and the reticle eyepiece's illumination is to use only in the lowest setting, when you are looking for DSO's.  A larger TFOV would be fine, but over the years I have learnt to live with the downsides of  the (expensive!) Vario Finder. Whether I would buy it again--?? I'm not sure about this.

Stephan

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Thanks guys

All good advice. So the going bigger option doesn't seem to have many takers (other than Peter - but he thinks that an 8" telescope for each eye is perfectly normal behaviour - a 6" finder scope! How cool is that???!!).

Has anyone tried the 60mm finders. Or, perish the thought, the 80mm Altair Astro version? ???

The Fov issue highlighted by Stephan could be a deal breaker.

Paul

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Recently giving up my EQ6 I have found myself going over old ground as far as finders go. Telrads never appealed to me due to the size but I get on well with my Rigel finder. Basically the same as the telrad all but missing a reticle ring and 1/4 the foot print of a telrad which makes it ideal for fraks.

I have recently picked up another 9x50 raci finder which I am yet too get out with. I say another as I'd had one years ago but really struggled with it compared to a straight through finder. I so like having one eye on the sky while the other explores the x9 view. Sadly I'm not getting any younger and my neck really don't like looking through a standard finder for long so a choice had to be made. I have though over the year become far more efficient at finding things with maps and the Rigel so fingers crossed round two is a better success with the raci finder :undecided:

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59 minutes ago, Paul73 said:

Thanks guys

All good advice. So the going bigger option doesn't seem to have many takers (other than Peter - but he thinks that an 8" telescope for each eye is perfectly normal behaviour - a 6" finder scope! How cool is that???!!).

Has anyone tried the 60mm finders. Or, perish the thought, the 80mm Altair Astro version? ???

The Fov issue highlighted by Stephan could be a deal breaker.

Paul

I tried a 60mm and 80mm TS finder briefly. The edge distortion was vomitworthy making them all but useless!

The SW 80 or 100mm Star Travel would make a good fuzzy finder, or a sweet little Equinox 80ED. 

Mike

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5 hours ago, Paul73 said:

I spend a fair bit of time trying to get lined up on the right bit of the sky

For my straight through finder, I've found the best method for me is to keep both my eyes open, its so intuitive, the target aligns quickly, then onto whatever eyepiece is in the focuser.

5 hours ago, Paul73 said:

I struggle to focus with

Its more obvious during the day on a distant target, when you can see details better but the finder scope themselves  need focusing too, the adjustment is at the objective end!

Apologies if that too basic and I have mis-understood your focusing issue ?

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1 hour ago, Paul73 said:

Thanks guys

All good advice. So the going bigger option doesn't seem to have many takers (other than Peter - but he thinks that an 8" telescope for each eye is perfectly normal behaviour - a 6" finder scope! How cool is that???!!).

Has anyone tried the 60mm finders. Or, perish the thought, the 80mm Altair Astro version? ???

The Fov issue highlighted by Stephan could be a deal breaker.

Paul

I should add that although the 150mm F5 does indeed serve as a finder it has other roles. We use it to demonstrate the difference between high and low power views and also for real time large screen video for white light solar, planetary occultations and transits.   :icon_biggrin:

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To be able to see fainter stars or bright DSO, you need bigger aperture and higher mag; to have wider TFOV, you'll need shorter focal length of finderscope, this two go against each other, you'll need to decide the best compromise for you.

Most finderscopes are f3.8, for 50mm, the focal length is 190mm, 9x means the EP in finderscope is about 21mm, with a simple kellner of about 45° AFOV, you get TFOV about 5°.

If you go up to 80mm finder, say st80 (assuming with erecting diagonal), even with 24mm Pan, you can only get about 4° TFOV for 10.5x mag. You can of course have 2" diagonal and use 31mm Nagler, then you'll have 8x for about 6.4° TFOV, not any wider than your 6x30 finderscope, not to mention the possible balancing issue.

So, it's all about to find the suitable balance of your needs, just like everything else.

BTW, looking through a finderscope carefully, you'll know how a simple Kellner eyepiece works in a f3.8 scope.:smiley:

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I just use a Rigel and the constellations for point and shoot and then have a large TFOV eyepiece in the focuser, for the 15" anyway. The 30ES 82 gives about 1.34 deg in this scope which isn't too bad. A person gets to know the sky pretty well like this.

and...finder scopes mess me up :help:

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Well. This is a first. A "what shall I buy?" thread where the collective recommendation is NOT to spend money!!!

I'll soldier on with the 10x50 and put the non existent money towards a 24mm Panoptic ???

Thanks for all the advice.

Paul

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I built myself a 14x70 finder scope which works very well. It has a 4.4 deg FOV, much like a pair of 15x70 bins (you could build a 15x70 finder out of a cheap pair, I suppose). For me the starting point was a 70mm F/5 scope, a 1.25" 90 deg Amici prism, and an Antares 25mm 70 deg EP. I added cross-hairs and an illumination system later.

C8full3.jpgC8full2.jpg

 

14x70 mm finder w.o. illuminator

IMAG0708.jpgIMAG0707.jpg

Antares 25mm 70deg EP, with reticle added

IMAG0738.jpgIMAG0740.jpg

Illuminator added.

 

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Thanks Micheal

3.5° is what I got with my ED80 and Ethos 21mm. Fine for the bright stuff but, as you say, a bit more Fov would get it bang on.

What 70mm f5 scope did you use? I've dug up these two candidates:

http://www.bresser.de/en/Astronomy/Telescopes/Classic-70-350-Refractor-Telescope.html

https://www.harrisontelescopes.co.uk/acatalog/Celestron_Travel_Scope_70_Telescope.html#SID=1700

Whilst I'm not looking for top notch viewing, a clean image that doesn't anoy me would be nice!

Any thoughts?

Paul

 

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I have a an Altair Astro 60mm finder guider which I use with a 21mm Hyperion eyepiece giving a pretty big 6 degrees FOV, not sure if this is reduced a bit when the RACI prism is used. It's a very lightweight solution and I have actaully been having fun using it on its own as a little richest field scope - it does pick up alot, though some may find the edge distortion annoying. However I have to say that with my old 6x30 straight through finder or my Rigel quickfinder I can pretty much find my targets straight away using the C8, so in reality a larger finder has not been needed, just a nice to have.

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On 31/01/2017 at 20:45, Paul73 said:

All good advice. So the going bigger option doesn't seem to have many takers (other than Peter - but he thinks that an 8" telescope for each eye is perfectly normal behaviour - a 6" finder scope! How cool is that???!!).

Has anyone tried the 60mm finders. Or, perish the thought, the 80mm Altair Astro version? ???

I have tried the 80mm Altair finder with my 12" Dob but after serious evaluation I traded down to a Tele Vue 60 refractor with a Everbrite diagonal and a Panoptic 24mm EP :grin:

It sits beside my Rigel Quikfinder, which I think is the best finder available.

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Have a rummage through your bits and bobs. If you can find a 70mm ED F/6, a 2" Baader Amici prism and a 41mm Panoptic, you can knock yourself up a half-decent RACI with over 10x magnification and TFOV of over 6 degrees. You may need some heating straps to keep the frost off.

:happy11:

tmp_30739-DSC_01091782051850.JPG

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Some reasons why it can be hard to get a scope pointing at the right bit of sky:

1. Sky is too bright (light polluted), so few stars are visible and it's guesswork to point the scope initially at a bit of black. Far easier if you can start by aiming for a naked-eye star and working from there.

2. An inadequate map (too detailed or not detailed enough) so that once you start looking through the finder you can't be sure if you're looking at the star you thought.

3. Inadequately aligned finder. Check it in daytime or with a stationary object at night (Polaris or, *sigh*, distant streetlight).

4. Trying to view objects that are just too faint/difficult for the scope/conditions/observer. Go for things you know you have a real chance of seeing.

5. Failing to match the finder or eyepiece view with the map. Be sure to observe which way stars are drifting in the FOV: they exit at West (like sunset) which is on the RIGHT side of a star map with north at the top.

6. If your finder happens to involve an odd number of mirrors (e.g. 1 but not zero) then everything is left-right inverted compared to your map, which is basically a nightmare (been there and had the headache). A prism (on a right-angled finder) is fine.

Here, for what it's worth, is how I do it:

1. Align finder on Polaris. (I use the stock 50mm that came with my 12" flextube and have used the stock 30/50mm straight-through finders on all the scopes I've owned in the last 17 years).

2. Choose target area, examine naked-eye stars and compare with S&T Pocket Atlas. Point scope at a naked-eye star.

3. Compare magnified view with map. Navigate around star, comparing view with map, until absolutely certain that it's correct, and the map is correctly oriented.

4. Get within shouting distance of the intended target.

5. With a low-power eyepiece in the main scope (I use a TeleVue 32mm plossl) and an appropriately detailed map (I use Great Atlas Of The Sky), navigate to the exact target area.

6. Raise power and wait. After about ten minutes a mag 15 galaxy comes into view. Description composed mentally, then dim red light on and write it down. Choose next target (the nearest thing to the one you just looked at, while you're still familiar with star patterns in that area).

Alternatively keep buying new gear in the hope it might solve any of the problems listed above ;)

 

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