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Thread: Idea: mini-telrad?

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    Default Idea: mini-telrad?



    One of the challenges of owning a Portaball telescope is that because it lacks clutches, the telescope must stay in balance via "stiction" alone. This means that additional weight at the front of the scope is bad, and requires a lot more ballast in the back, which in turn makes the whole scope heavier and less nimble in its socket. It's for this reason that the standard Portaball delivered by Mag1 uses a modified Rigel Quickfinder that has the battery compartment replaced with a pogo-pin mount that attaches to wiring down the truss and into the sphere, where it can use the primary battery for power. This eliminates a few ounces of weight at the front by eliminating the batteries.

    I use a Telrad right now in my Portaball (instead of the Rigel) and have so far dealt with the big ballast requirements in the back. But recently I've been thinking that it should be possible to create a lightweight Telrad by cutting down a full-size one. Removing the 2x AA batteries would save a lot of weight, and shortening the box would save even more.

    My plan is to buy a new Telrad and start by replacing the standard 2x AA battery holder with a CR2032 coin cell holder, mounted opposite the brightness adjustment knob (out of the way of the light path). I could then cut the end of the Telrad off, saw a section of the middle out, and then glue the end back on with some plastic modeler's cement. A cut-down lid should still fit in the resulting shortened box. The same treatment could be done to the base to allow the standard mount to continue working.

    So before I start hacking up my Telrad, a couple hopefully obvious questions:

    1. Will the Telrad run off of a CR2032? Since it's just an LED being lit, seems like this is a no-brainer (and begs the question as to why this wasn't done originally)

    2. Will the plastic used on a Telrad work with plastic modeler's cement? I believe it's ABS plastic...should I use modeler's cement or ABS pipe glue? Will a butt joint hold stiffly enough? I suppose if it doesn't, I can take some of the leftover plastic and reinforce the joints.
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    Default Re: Idea: mini-telrad?

    Yes it would run off 2032. But would drain it fast. The best would be to have 2 in parallel together. It would be both ++ together and both - - together. The biggest problem I forsee with this mod would be getting the mounting plate correct. Use epoxy.
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    Default Re: Idea: mini-telrad?

    Paul, see this: http://www.astronomyforum.net/member...r-hopping.html

    Gabrielle resized her telrad considerably. Note the batteries are now on the outside.

    Unfortunately, she just left for vacation for a couple of weeks so is not around to ask about it, but it is something to consider.
    Bryan

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    Default Re: Idea: mini-telrad?

    Quote Originally Posted by Wire View Post
    Yes it would run off 2032. But would drain it fast.
    Well a typical CR2032 has ~240mAh capacity. A typical alkaline AA has ~2000mAh capacity (since they're in series you only get one cell's worth of capacity). I'm running my Telrad on AAAs, which typically have ~1000mAh capacity.

    With AAAs I have used the Telrad for over a year for several hours a month and haven't needed to change the batteries. So I suspect a CR2032 will be enough. But if it isn't, I suppose I could use the same type of battery used in my Gemini-2 controller: the CR2354, which has a 600mAh capacity. That would get me at *least* 6 months of runtime without needing to change batteries, possibly longer since the lithium chemistry holds its voltage better than alkaline AAAs.

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    Default Re: Idea: mini-telrad?

    Quote Originally Posted by bladekeeper View Post
    Paul, see this: http://www.astronomyforum.net/member...r-hopping.html

    Gabrielle resized her telrad considerably. Note the batteries are now on the outside.

    Unfortunately, she just left for vacation for a couple of weeks so is not around to ask about it, but it is something to consider.
    Hah! This is exactly what I was planning to do (aside from using a coin-cell battery instead of an external AA/AAA holder). Great minds think alike!
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    Default Re: Idea: mini-telrad?

    As a side note - the (non-rechargeable) lithium AAs are significantly lighter than normal Alkaline AAs (and have more capacity and work better in the cold).
    When I was shooting film with a Nikon f5, which used 8 AAs, this made a big difference to the weight .
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    Default Re: Idea: mini-telrad?

    Hi Paul,

    Can I throw a "monkey in the wrench" here? Have you thought about just attaching a green laser onto the Portaball? They are smaller, lighter, and can handle cold better as they are now "mainstream" items. Careful use and pointing would minimize any aviation interaction/conflict. Just a thought.

    Cheers,
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    Default Re: Idea: mini-telrad?

    Well, in that case, you might consider also a Rigel Quickfinder. Much lighter than a telrad and a smaller footprint. Same functionality. I use both and like them equally as well.
    Bryan

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    Default Re: Idea: mini-telrad?

    Here's a pic of my "Shorty Telrad": IMG3217.jpg

    I used a CR2032. I shortened this Telrad to 6 & 3/8 inches in 2015 and I've used it on and off since then and it has never drained yet! After I acquire the object in my scope, I turn off the switch, as I am ever mindful of draining the battery if I leave it on, which I have occasionally for hours and it still hasn't drained. I can't remember which glue I used, but I have had no problems with it at all. I'm not the best at cutting, so I covered the Telrad with self-stick blue felt to about 1/16th inch thick, which I like better than the black plastic look anyway.

    Looking at it now, I can see where I could have mounted the battery like you suggest, and it would be shorter. Maybe I'll do that for my next "Shorty Telrad". I just happen to have a brand new one still in the box!

    Here is my "Shorty Telrad" on my 4.7" reflector: AZstarparty17.jpg
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    Default Re: Idea: mini-telrad?

    Quote Originally Posted by bladekeeper View Post
    Well, in that case, you might consider also a Rigel Quickfinder. Much lighter than a telrad and a smaller footprint. Same functionality. I use both and like them equally as well.
    The Rigel doesn't have a 4 degree ring, otherwise I'd use one. The 4-2-.5 pattern used by the telrad is the best for star hopping.

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