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Paul Muller
super member

Reged: 03/07/12

Loc: Alexandria, VA

What finderscope for big Dobs?
#5298598 - 07/01/12 09:58 PM

I am working on building my 12.5" Telekit and as of yet don't have a finder picked out other than a Telrad. What finderscopes do you typically use for bigger Dobs (meaning 5 feet tall or more)? Is a right angle finder pretty much a given? I'm used to the views a 4" refractor can provide, so I want to make sure the finder is large enough to take advantage of the extra light gathering power of my Dob.

Edit: I've been looking at things like the Stellarvue F50. Does this seem like a good fit for this scope? Or would an 80mm be better to take advantage of the large aperture?

Edited by Paul Muller (07/01/12 10:02 PM)

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David Pavlich
Transmographied

Reged: 05/18/05

Loc: Mandeville, LA USA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298612 - 07/01/12 10:11 PM

My experience with a Newt, or anything with a relatively wide field of view, a Telrad does very well. And for star hopping, they're unmatched. HOWEVER...having said that, I always have a Telrad or Rigel finder teamed up with a simple 9X50 RACI finder like the type Orion sells.

David

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DavidC
Pooh-Bah

Reged: 11/24/05

Loc: Mesa, Arizona

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298618 - 07/01/12 10:15 PM

I use an 80mm with my 13 inch, that makes it easier to find things than a 50mm. If you have an 8 or 10 inch you could get away with a 50mm, that's what I use on my 8 inch. Go with 80mm, you'll like it better.
David

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Paul Muller
super member

Reged: 03/07/12

Loc: Alexandria, VA

Re: What finderscope for big Dobs? new

new

[Re: DavidC]
#5298665 - 07/01/12 10:41 PM

Do you typically mount them on the upper cage, or down on the mirror box? I've seen both in pictures.

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Shane LaPierre
super member

Reged: 04/17/09

Re: What finderscope for big Dobs? new

new

[Re: DavidC]
#5298666 - 07/01/12 10:42 PM

Here's a finder I had on my old 20"

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jrbarnett
Eyepiece Hooligan

Reged: 02/28/06

Loc: Petaluma, CA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298680 - 07/01/12 10:52 PM

I use either a GSO or Orion 50mm RACI with my very tall 16-incher. They are relatively cheap, work reasonably well, and don't weigh too much. As I use DSCs to find most of my targets, the magnified finder is most often used for aligning the DSCs.

- Jim

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Zoomit
sage

Reged: 12/04/06

Loc: Tehachapi, CA

Re: What finderscope for big Dobs? new

new

[Re: jrbarnett]
#5298789 - 07/02/12 12:52 AM

I have a Stellarvue F50 on my 18" and find it big enough, but I survived for a long while with just a Telrad. The F50 is nice, but the alignment rings are easily inferior to the Orion RACI mounting ring. I use a 6x90 Orion RACI on my XT8 and it is so much nicer to use the two orthogonal screws and the retaining o-ring to align it verses the six screws on the F50 rings.

If I were to do it again, I'd just get a Orion 9x50 RACI and invest the savings in a filter or eyepiece.

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rick-SeMI
sage

Reged: 01/08/11

Loc: Michigan - USA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298802 - 07/02/12 01:08 AM

For the 16" DobStuff Kit - I cut a piece of thin plywood into an 'L' shape for the Telrad and
added a Synta foot for either and Orion RDF or 9x50 RACI.
I have grown fond of using the Telrad/9x50 combo.

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John Kuhl
sage

Reged: 11/10/05

Loc: SoCal

Re: What finderscope for big Dobs? new

new

[Re: rick-SeMI]
#5298828 - 07/02/12 01:44 AM

I never use a finder. I have a Telrad on all of my scopes, and if I can't find it with that I put a 31 Nagler in and use the scope as the finder.

Best, John

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Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298910 - 07/02/12 05:04 AM

Quote:

I am working on building my 12.5" Telekit and as of yet don't have a finder picked out other than a Telrad. What finderscopes do you typically use for bigger Dobs (meaning 5 feet tall or more)? Is a right angle finder pretty much a given? I'm used to the views a 4" refractor can provide, so I want to make sure the finder is large enough to take advantage of the extra light gathering power of my Dob.

Edit: I've been looking at things like the Stellarvue F50. Does this seem like a good fit for this scope? Or would an 80mm be better to take advantage of the large aperture?

I have 4 Dobs, a 10 inch F/5, a 12.5 inch F/4.06, a 16 inch F/4.42 and a 25 inch F/5. They are all setup with basically the same finder configuration: A Telrad + a 8 x 50 or 9 x 50 straight-through finder.

The advantage of the straight-through finder is that I am looking in the direction the scope is pointing, it's like aiming a rifle, I can't imagine doing it with a right angle finder... The Telrad and the magnifying finder are side by side so I can move from one to the other with ease. Some complain that they need to bend their neck to use a straight-through finder but that same bend is necessary to use a Telrad...

If the skies are dark, for many objects, the Telrad by itself is sufficient but sometimes I use the magnifying finder so I can starhop more accurately using stars that cannot be seen naked eye. A easy example of this is the double planetary in Gemini, 2371/2. With the Telrad, I can get near it, with the magnifying finder, I can center it.

The purpose of the finder is not to see the object itself but rather to assist in pointing the telescope by showing stars that are not easily visible naked eye. I don't expect to see the object in the finder, only guide stars I use in starhopping.

I do find that the exact locations of the finders are critical, a few inches off and it can be quite uncomfortable and/or awkward. Getting the finders positioned so that moving from the telescope eyepiece to the finders is natural and unencumbered is an important step in making a telescope really "work."

That's how it works for me.

Jon

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Achernar
Postmaster

Reged: 02/25/06

Loc: Mobile, Alabama, USA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5298930 - 07/02/12 05:52 AM

I've been using a 50mm straight through finderscope teamed up with a Telrad on my 10 and 15-inch Dobs. Even with the 15-inch, I can starhop my way quickly and efficiently. An 80mm finder is a good option too, but you will need to take into account the weight of the finderscope(s) to balance the telescope. Ever pound of weight on the UTA must be counterbalanced by several more on the back end of the mirror box.

Taras

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Jarad
Postmaster

Reged: 04/28/03

Loc: Atlanta, GA

Re: What finderscope for big Dobs? new

new

[Re: Achernar]
#5298959 - 07/02/12 06:47 AM

First question - do you plan on using DSC's? If so, a Telrad or Rigel is all you need.

Second, even with a magnifying finder, I find a reflex finder useful. It makes getting close a snap, then you can switch to the finder to get it perfect.

You didn't say your f-ratio. With a moderate to fast 12.5", I think you could get by with just the reflex sight and a good low-power eyepiece. With a long-focus one, you might get some utility out of a magnifying finder. The whole point of the finder is to have a wider FOV than the scope, so you don't want a huge one. An 8x50 should be plenty. An 80mm really becomes more of a secondary wide-field scope than a finder (not that there's anything wrong with a secondary wide-field scope...).

Jarad

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Houdini
professor emeritus

Reged: 07/13/07

Loc: Europe

Re: What finderscope for big Dobs? new

new

[Re: Jarad]
#5298985 - 07/02/12 07:39 AM

Use of a finder is very personal, everybody seems to have different habits.

I've been using a straight-through 15x60 finder on several telescopes for over 20 years now.
I do the global pointing of the telescope by looking through the finder with my right eye, while looking directly at the sky with my left eye. This projects the cross-hairs of the finder on the sky. No need for a Telrad or Red Dot Finder.
When I'm in the right area, the finder is large enough to show most bright objects, and plenty of field stars for star hopping with an atlas like the Uranometria.

Robert

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Paul Muller
super member

Reged: 03/07/12

Loc: Alexandria, VA

Re: What finderscope for big Dobs? new

new

[Re: Houdini]
#5299043 - 07/02/12 08:40 AM

Thanks for all the replies, everyone!

My scope is a 12.5" f/5, so it's medium speed. Based on the replies here, I will probably start off with my Telrad and then see if it makes sense to continue with a dedicated finder.

I do plan on installing DSCs eventually, but not right off the bat. That will mitigate the need for a fancy finder. The big argument in favor of getting one now is that I live in a fairly light polluted area, so it would help me pull in fainter objects that I won't be able to see with my naked eye, thanks to Washington, D.C. clogging up the skies.

That may be the biggest factor in getting a finder - battling skyglow.

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Paul Muller
super member

Reged: 03/07/12

Loc: Alexandria, VA

Re: What finderscope for big Dobs? new

new

[Re: Shane LaPierre]
#5299050 - 07/02/12 08:47 AM

Shane, that's a helluva finder!

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dh1972
member

Reged: 05/11/12

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5299119 - 07/02/12 10:01 AM

I just ordered a 12" Zhummel that comes with an 8X50 finder. While I live in light polluted skies, I am not looking to track down ultra faint fuzzies....only the more brighter ones if you will. With that said, using a low power 82 degree eyepiece and finder, what purpose would the telrad serve me? Does the telrad just help me narrow down a larger field of view....which then goes narrower in the finderscope....which then of course goes narrower in the scope itself? All three serve as a funnel going from larger to smaller I assume.

Edited by dh1972 (07/02/12 10:01 AM)

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Jarad
Postmaster

Reged: 04/28/03

Loc: Atlanta, GA

Re: What finderscope for big Dobs? new

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[Re: dh1972]
#5299157 - 07/02/12 10:24 AM

The point of a telrad is that is a "widest field" finder. You just look through it and you can see where you are pointing. It makes aiming the scope at anything you can see incredibly easy. The only downside to it is that you can only see naked-eye visible stars through it, so you can't do a star-hop on things fainter than that.

The advantage to a magnifying finder is less the magnification and more the light-gathering. They let you star-hop using stars that are not visible to the naked eye. The disadvantage is that the larger the finder is, the narrow its field of view is, which means you may have difficulty getting close enough to see what you want in the finder in the first place.

Personally, I find that for 99% of what I do, the Telrad or Rigel is sufficient to get me close enough that I can navigate from there using a 35 Pan in my 14.5" f4.3 scope. And I find the ease of using the reflex sight outweighs the advantages of a magnifying finder.

At one point, I did have an ST-80 attached to the rocker box of my 18" Starmaster. The Starmaster also had a Telrad, and full GOTO, so I primarily used the ST-80 as a secondary widefield scope. I would go back and forth between it and the main scope on things like M31 and the Veil. But I didn't really use it to find things.

As Robert said, it really comes down to personal preference. With a bit of practice, you will be able to find things with whichever you choose - Telrad, RACI finder, or straight-through finder.

Jarad

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Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: What finderscope for big Dobs? new

new

[Re: Paul Muller]
#5299185 - 07/02/12 10:50 AM

Quote:

Thanks for all the replies, everyone!

My scope is a 12.5" f/5, so it's medium speed. Based on the replies here, I will probably start off with my Telrad and then see if it makes sense to continue with a dedicated finder.

I do plan on installing DSCs eventually, but not right off the bat. That will mitigate the need for a fancy finder. The big argument in favor of getting one now is that I live in a fairly light polluted area, so it would help me pull in fainter objects that I won't be able to see with my naked eye, thanks to Washington, D.C. clogging up the skies.

That may be the biggest factor in getting a finder - battling skyglow.

Paul:

In my experience, Telrads are great if the sky is dark enough that you can see sufficient guide stars naked eye, if you can see the Milky Way, then you might well get by without a magnifying finder.

If I am working from an urban/suburban location where directly overhead I might be looking at magnitude 4.5 stars then a magnifying finder can be very useful as it will show me stars to guide with in most parts of the sky.

Jon

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BigC
Carpal Tunnel

Reged: 09/29/10

Loc: SE Indiana

Re: What finderscope for big Dobs? new

new

[Re: Jarad]
#5299286 - 07/02/12 02:30 PM

Being blessed with moderately dark sky,at least compared to the nearby cities,I often have difficulty picking out the desired alignment star from all those visible in a nice big 8x50 finder so oddly enough the cheap 5x24 finder or red dot finder is a better tool for that first step.Then either the main scope or a bigger finder to close in on the object.

I am considering a seperate battery holder with a couple rechargeable AA cells wired in place of the expensive little coin cell in the RDF.It is too easy to leave the RDF turned on.....

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MitchAlsup
Pooh-Bah

Reged: 08/31/09

Re: What finderscope for big Dobs? new

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[Re: BigC]
#5299310 - 07/02/12 03:41 PM

I use nothing other than a Rigel (telrad equivalent +/-) and a 31mm NT5 as my finder for my 20" DOB.

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