Jeff Morgan
Post Laureate
Reged: 09/28/03
Loc: Prescott, AZ
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Re: What finderscope for big Dobs?
[Re: Paul Muller]
#5299373 - 07/02/12 04:13 PM
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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?
The F50 is a very good finder. I have used it on my 4.7" refractor and 12.5" reflector. The only weaknesses are the nylon screws (which seem to cause the alignment to shift), and the helical focuser grease. The focuser is stiff to turn. However if you use the illuminator, the torque seems to cause the focuser to rotate on its own, shifting focus. Very annoying, probably very fixable once I clear some other items off my "to do" list.
Before I started building my 16", I tested the efficiency of the F50 by seeing how accurately I could star hop with a medium power eyepiece in the main scope. The idea was, how often can I put the target into a small (3/4 degree) field? The answer was, 100% of the time. No challenge at all really, even though the finder shifts as mentioned above.
So while I have used larger (80 mm) finders in the past, I came to the conclusion that as long as the main scope can deliver a true field of 3/4 degree, the F50 was all I needed.
The aforementioned 16" will be equipped with ServoCAT. While I could have opted for just a Telrad, I still want the optical finder in case the technology fails me.
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saleratus
member
Reged: 05/06/09
Loc: Dorset (UK) & Utah
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Re: What finderscope for big Dobs?
[Re: MitchAlsup]
#5299561 - 07/02/12 06:11 PM
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I normally use a Telrad or Laser Finder for my big Dob. Scopestuff sells a wonderful laser pointer mount that goes on a Telrad base, so you can switch the two. This is useful sometimes in dewing conditions as Telrads will fog up.
The nicest finder I've seen is the Baader sold by astro-physics. It includes an amici-type prism so that the stars it it appear as they do on your chart.
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Achernar
Postmaster
Reged: 02/25/06
Loc: Mobile, Alabama, USA
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Re: What finderscope for big Dobs?
[Re: Jon Isaacs]
#5299742 - 07/02/12 08:05 PM
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Precisely why I use a Telrad teamed up with a 50mm finder. If I can see it, I can find it with them, without digital setting circles, which I do use often simply because they allow me to make the most of the relatively few opportunities I get to observe galaxies and nebulae.
Taras
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Paul Muller
super member
Reged: 03/07/12
Loc: Alexandria, VA
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Re: What finderscope for big Dobs?
[Re: Achernar]
#5300825 - 07/03/12 03:27 PM
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It sounds like I need to start off simple and test out combinations of Telrad/finder/eyepiece until I find out what works best for me. But that seems to be par for the course in this hobby - it's tailored to each person's individual tastes!
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saxmaneagle
sage
Reged: 08/21/07
Loc: Saint Francis, MN
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Re: What finderscope for big Dobs?
[Re: Paul Muller]
#5302106 - 07/04/12 11:45 AM
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I use just a Telrad, and 50mm EP in the scope. Been using this combo for years, and have never felt the need to add a finder.
When the sky is not dark enough to see target stars, I use a cheap 10x50 bino to familiarize myself enough with the area before pointing the Telrad.
Using bino's and sky charts are a great way to learn the sky. Often Ill switch from the 10x50 binos, and go to my 20x80 binos, on a tripod, for a long study of the target area.
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Old Rookie
sage
Reged: 09/05/08
Loc: North Central Ohio
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Re: What finderscope for big Dobs?
[Re: saxmaneagle]
#5302212 - 07/04/12 01:02 PM
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I know a lot of guys that have both a telrad and/or a finder. I use both even though I use DSC's most of the time. However, DSC's are mechanical and electrical devices and can fail. In that case, I still have my 18" telescope, 50mm finder and Sky Atlas to find stuff with. That's why I have both. Sometimes, I just find stuff the old fashioned way and go at it with the charts and finder.
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KidOrion
professor emeritus
Reged: 07/07/07
Loc: Carbondale, IL
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Re: What finderscope for big Dobs?
[Re: Old Rookie]
#5302312 - 07/04/12 02:11 PM
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With my 13.1" Dob currently unusable, I'm using a friend's 12.5" Dob, which has only a Telrad bracket. I've gotten much better using only a Telrad (vs. a Telrad/finder combo), but I'm still planning to mount my 11 x 80 RACI finder on the big scope once it's back in working order.
OTOH, our club now has an 8" SCT with only a finder; it's amazing how difficult I've found it going back to equatorial motions and finding with only a finderscope.
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GeneT
Ely Kid
Reged: 11/07/08
Loc: South Texas
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Re: What finderscope for big Dobs?
[Re: David Pavlich]
#5302342 - 07/04/12 02:24 PM
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I always have a Telrad or Rigel finder teamed up with a simple 9X50 RACI finder like the type Orion sells.
I recommend having both a Telrad and optical finder. They complement each other very well. The Telrad gets you close to the object. The optical finder shows you a telescopic view. Use a wide angle eyepiece such as a 31mm Nagler, and it acts like a finder too.
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Jeff Morgan
Post Laureate
Reged: 09/28/03
Loc: Prescott, AZ
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Re: What finderscope for big Dobs?
[Re: Old Rookie]
#5303663 - 07/05/12 11:59 AM
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I know a lot of guys that have both a telrad and/or a finder.
While Telrads and optical finders play well together, I have found that the longer the telescope, the more accurately you can point the tube to a spot. Probably because of less parallax error between the eye and the optical axis. On my 8" refractor it was rather easy to point to within 1 degree of a target star, and pick up from there with the 8 x 50.
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csa/montana
Den Mama
Reged: 05/14/05
Loc: montana
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Re: What finderscope for big Dobs?
[Re: Jon Isaacs]
#5304245 - 07/05/12 07:30 PM
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I also use a Telrad + Antares 8x50 RACI + 5mW laser, on my 16".
I find I use the Telrad the majority of the time.
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Paul Muller
super member
Reged: 03/07/12
Loc: Alexandria, VA
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Re: What finderscope for big Dobs?
[Re: csa/montana]
#5305021 - 07/06/12 08:56 AM
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I'll probably go ahead and order the optional accessory mount for my Telekit, so that I have that in case I want to mount a larger finder on my scope in the future. However, not having used a Telrad before, does it take any getting used to before you can start zipping around the sky with it?
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Jarad
Postmaster
Reged: 04/28/03
Loc: Atlanta, GA
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Re: What finderscope for big Dobs?
[Re: Paul Muller]
#5305220 - 07/06/12 11:22 AM
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I find the Telrad or Rigel to be the easiest to learn to use - the bullseye is where the scope is pointed. Once you get it aligned, you should be off pretty quickly.
Magnifying finders tend to take a bit more to get used to, since you usually have to adjust to either a rotated or reversed field or right angle view. You can still get the hang of it pretty quickly, though.
Jarad
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jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
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Re: What finderscope for big Dobs?
[Re: Jarad]
#5306659 - 07/07/12 12:11 PM
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I'm in the process of refurbing my homebuilt 16.5" f/6.5 Dob. The biggest challenge with this scope has always been pointing it. The widest field of view I get with my 1.25" eyepieces is about 0.4 degrees using my trusty old Meade 20mm RG Erfle. I've experimented with quite a few pointing systems including finders, a Telrad, a laser pointer, and setting circles (homemade azimuth circle with a digital inclinometer). The Telrad is my old favorite, but from my red zone back yard I have a huge problem seeing stars through the illuminated reticle even with is turned way down and fitted with a cover (cycling it barely off to barely on helps). Since adding my laser pointer the Telrad has become redundant and I've taken it off (actually I moved it over to a new home on my homebuilt 10" scope). I have a 60mm finder that proves very useful for finding guide stars that are hiding behind the light pollution. The setting circles are useful when hunting targets like M3 that don't have good guide stars near them. Sooooo, at the moment my big Dob is fitted with setting circles, a 60mm finder, and a laser pointer.
I had my big scope out last night and I'm still not completely happy with pointing it. My laser pointer is generally the easiest and most useful device, the problem is still pointing it accurately. I had a crazy idea this morning I'm going to try. I just ordered a second laser pointer from Orion (they're on sale right now by the way) and I'm going to mount it on my ETX-80. I'm going to try and use the GoTo on my ETX-80 to point the second laser pointer to the right spot in the sky, then guide my 16.5" to that spot using its laser pointer. It's so crazy it just might work. 
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Jarad
Postmaster
Reged: 04/28/03
Loc: Atlanta, GA
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Re: What finderscope for big Dobs?
[Re: jgraham]
#5306803 - 07/07/12 01:44 PM
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Actually, I know a guy who did something similar. He bought a cheap GoTo scope, removed the scope completely, and just mounted a GLP on it. He sets it up a few feet away from his dob, aligns it, has it GoTo whatever he wants to find, then aims the dob at the laser with a Telrad. Actually works quite well.
Jarad
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jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
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Re: What finderscope for big Dobs?
[Re: Jarad]
#5306868 - 07/07/12 02:26 PM
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Good point. I also have a spare DS-2000 mount that I can use with or without a scope. I was thinking about the ETX because it is so compact and having the scope would make it easy to synch the mount. However, there's no reason that I couldn't synch the laser by itself. It is gonna be fun finding out!
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Jeff Morgan
Post Laureate
Reged: 09/28/03
Loc: Prescott, AZ
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Re: What finderscope for big Dobs?
[Re: jgraham]
#5306992 - 07/07/12 04:07 PM
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Quote:
I'm in the process of refurbing my homebuilt 16.5" f/6.5 Dob. The biggest challenge with this scope has always been pointing it. The widest field of view I get with my 1.25" eyepieces is about 0.4 degrees using my trusty old Meade 20mm RG Erfle.
I'm curious as to why you would not want to put a 2" focuser on that scope and use a 2" eyepiece? Equipped that way you would have no trouble doubling that true field, which would make life a lot easier.
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jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
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Re: What finderscope for big Dobs?
[Re: Jeff Morgan]
#5307019 - 07/07/12 04:28 PM
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Heh, heh, when I originally designed the scope (1998) I didn't have any 2" eyepieces. The design (my 24th homebuilt telescope) was driven by simplicity and cost and doesn't really have what you would recognize as a focuser. It simply uses a piece of 1.25" chrome drain pipe passing through a beefed up section of the upper tube assembly. This worked for the eyepieces I had at the time, saved a lot of weight and cost, and helped me squeeze a fully illuminated field out of a relatively small secondary. However, I am looking at a complete redesign of the truss and upper tube assembly that will include a MoonLite 2" dual speed focuser. In the mean time, I still gotta point The Beast. I had it out last night (hotter'n heck even at midnight!) and the view of M3 was just amazing.
Oh yes, and I ran the math and you are correct, I should be able to increase my true field out to just shy of 1 degree using 2" eyepieces that I already have. Now I just gotta rebuild the truss and upper tube assembly to make it happen.
One crisis at a time...
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tejasdragon
sage
Reged: 09/08/11
Loc: Garland, Texas
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Re: What finderscope for big Dobs?
[Re: jgraham]
#5307662 - 07/08/12 01:49 AM
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Just some more food for thought, this is the 4.5" f/8
finder and my old 12.5" f/6 dob. More than one of us
are a little nuts.
Henry
Edited by tejasdragon (07/08/12 01:50 AM)
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izar187
Pooh-Bah
Reged: 09/02/06
Loc: 43N
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Re: What finderscope for big Dobs?
[Re: tejasdragon]
#5307866 - 07/08/12 08:19 AM
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One can also use half of a binocular as a finder. I've used one half of an old pair of garage sale 10x50's on my 13" for many years. In this situation a home brew mount has to be figured out based upon the shape of the half bino. But you get an erect straight through image with adjustable focus for glasses on or off at the finder. I also recommend a unit power finder, like the Telrad. On the 13" I often use both together, and sometimes just one or the other. Straight through powered finders can sometimes allow one to skip the unit finder step, and skip the low power wide field finder eyepiece step as well, and go right to mid or high power observing. Lots of working options are available.
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jgraham
Postmaster
Reged: 12/02/04
Loc: Dayton, Ohio
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Re: What finderscope for big Dobs?
[Re: izar187]
#5308017 - 07/08/12 10:40 AM
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A lot of good ideas. I thought about mounting a spare StarBlast on my 16.5", but I want to try something smaller and simpler first.
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