Posts Made By: Tom Lacovik

How thick should a 2.6" secondary be (if it is even possible to get varying thicknesses). I keep trying to save weight on my Upper Cage, and keep not finding suitable weightsavers. The secondary is just one of many such items. How thin should I consider going (not that it's up to me, rather what the 'good' opticians are putting out). So if someone wants to recommend something good but light for me, I'd be much obliged.

Tom.

Hi All.
I have seriously been considering laser eye surgery for several years. I'm really tired of glasses now and want rid of them. I wonder if any serious observers here have had the procedure done and how it has affected their observing experience, positively or negatively?

Thank you.
Tom L.

In building a 13.1" f4/5 truss dob, the Kreige/Berry book recommends 60% of the primary diameter as the minimum height for the upper cage.

Well that comes out to about 8"... But I would like if possible to shave an inch (or two?) off of that if possible. I don't think I'll have a shrowd, but unless a baffle opposite the focuser is avoidable with an 8" or 9" upper cage height, then why bother with 8" at all?

I mean, if I *HAVE* to add a baffle no matter how tall my cage is up there, then why bother making it 8" and why not just have it be smaller and more compact, nesting better for travel and finally, lighter?

So, how low should I go?

Thanks.
Tom.

I am building a 13.1 Truss Dob. The upper rings are 15" ID and the focuser will be at the bottom ring to maximize the amount of baffling I get from the upper cage structure.

It's nice that a 2 ring structure provides a very strong mounting for your secondary and focuser and for attaching trusses, but I really wish it could complete the all-in-one functionality picture by also providing adequate baffling (whatever that may be).

I say "whatever that may be" because that is really my question. Once or twice I've seen these HUGE figures for cage height to provide true and total baffling which strictly speaking, i'm sure are 'correct'.

I just find a 2 foot cage impractical and not 'minimal' or streamlined in keeping with my design goals (not to mention ugly (in the greek ratio sense) proportionate to a smallish scope like a 12.5 or 13.1"

So what in your experience, is a good compromise? A good call? "enough" cage height so that you don't really need to velco on extra kydex, no matter what the absolute mathematical formula says, what is 'good enough' so that I can keep my cage as small/light as possible and not have to to the velcro on spiel?

Kind of a field-experience, or rule-of-thumb, type question rather than a "Newt says 28.7389" question if you know what I mean.

In short, I need help keeping my cage height down, but also not so low that I MUST use a kydex add on. Is there such a thing?

Thanks for sharing your experience.
Tom.

I would like to say so long to Lee, not farewell. I know you'll drop in every now and then even though you're giving ATMing a rest for now. Anyway, it was inspired work like that which got me to try to take a stab at it myself.

So as I say so long to you Lee, I'll introduce myself to the other ATMers here.

"Hello, My name is Tom. And I'm a scope-a-holic..."

I've posted here a few times, and having made my major design decisions (though lots still left), I've plunged in and decided to make a scope.

Mine will be a string dob, 13.1 Swayze primary, 2.6" Nova Secondary (from an Obsession 15). Carbon Fiber curved vanes, and a 3 piece design which it is my goal to get to collapse and nest into itself for ultracompact transport...

Here is a photojournal so far.... and thank you for any help you may offer... I too hope my efforts will help others like Lee has someday...such is the circle of ATMing I guess.

Tom.

http://www.graphicaindustria.com/atm

Hi. I was looking for some kydex which seems expensive no? Anyway, I went to the plastics store and found this dirt cheap sheet of polyethylene 10 mil black plastic. soft enough to curl and cut with scissors, yet stiff enough to make a cylinder. pebbly on one side, smooth on the other.

It costs like $4 for a 4 foot by 2 foot sheet. He told me glue doesn't stick to it and its nearly the same material used in milk jugs, chosen for its ability to be formed and for it's non-stick nature. He said it's melting point is 300 degrees.

So, can you see any reason NOT to use this...to me it sounds looks and feels EXACTLY like kydex but a fraction of the brand name's cost.

Thoughts?
Tom.

For a thin (1/2"?) secondary 2.6" how much heat (in W) is 'normal'? I'm not sure what temps these correspond to but on my breadboard 2W (3 or 4 resistors in series) is HOT as is 1.5W, whereas 1W is medium and .5W is hardly noticable.

Also do you silicone your resistors to the back of your mirror or to the aluminum wall housing the mirror itself. In short, how much heat is needed (subjective I guess, but how much do YOU need in that case) and how much is too much?

Thanks in advance.
Tom.

p.s. while we're on the subject, same question but for a) telrad and b) eyepiece.

Hi all.

Can someone please tell me what the value or range of the Potentionmeter in a Telrad is? For the craziest of reasons while I was taking it apart to modify, mine popped out with enough force to pop free of the solder, went flying, and now I can't find it. So I'll need to replace it.

Thank you in advance for helping me do that.
TomL

Hi Gang.

Going by the KB book, I and many others feel the recomendations though sound are a bit of an overbuild. That's probably a good strategy as many people will need a little safety provided by slightly over built design to cover up sources of error or slop. Fair enough. I don't want to cut corners either but I want a lighter upper cage without compromising the integrity of the cage.

Here's what I've found: Cutting 1" wide rings (17 OD / 15 ID) with 3/4" struts (9" tall) I have found that putting the minimum in without a focuser board in there just yet... for me (3 vane spider) is 3 struts min, but I feel I can twist the cage set up like that (again no focuser board in there yet, but you get the idea). With 5 struts layed out in an even hex pattern (the focuser board to be the virtual 6th strut) it is so stiff (even without the board) that I feel I could stand on it and definitely can't torque it by hand.

So much so that I was thinking of recutting the rings out of my sheet of 1/4" Baltic Birch Ply instead, and going with 5 struts not 3. I'll probably try it anyway, but if someone has a thought about this or better yet, experience, please share with me. My thinking is that the stiffness is coming from the number of rungs, like a ladder, not from the THICKNESS/WEIGHT of the sides of the ladder. The NUMBER of rungs (struts) is what makes for non-twistable stiffness it would seem.

After all, you ultralighters out there are making foamcore rings, so why not my 1/4" BB idea? Not ultralight, but half the weight of my 1.34 pounds worth of 1/2" BB.

Penny for your thoughts.
TomL

No this isn't a carnival guessing game, rather, I need real info on some weights from someone who has or can weighed it, such as. forgive me for not trusting posted weights on company websites. in the past, from some vendors, i have verified that they are not accurate, sometimes they are including packaging, sometimes rounding down, sometimes just rounding up for shipping weights...but if you have a scale and/or direct knowlege of these things, it would help:

1) a complete astrosystems 2.6" holder, stalk, mounting bolt, hub, top nut all together.

2) an astrosystems 3 vane spider

3) a telrad with base and batteries installed. ready to go. some say 11 ounces some say a pound...

i'll take any of the 3 answers thanks!
TomL