Re: ATM Trying to get rid of tube currents in a Newton telescope

[goffaxe@azstarnet.com (Bob & Valerie Goff)]

If your fan is attached to the back of your cell and blows air in, It Sucks.
Your fan needs to be connected to the cell by a long length of elephant nose
hose
 ( laundry drier hose )  and the air must be sucked through the tube assy
past the mirror and then through the ENH and vented.
When the machine is attatched directly to your telescope it makes the
telescope vibrate and when you turn your quaint little motor off, residual
heat floats back up the tube. And the dumb motor is hot from your having
used it. 
Didn't we engage in this very coversation in about November of 1986?

Bob

Which Bob you ask?

>I thought I would jump in and second Bob's and others opinions.
>I have only built one scope and I incorporated a small muffin fan
>(12vdc-~19scfm) into my mirror cell . The tube is also heavily baffled. Eight
>are installed at approx the same distance apart and are the same annular
>size.(made from 1/8" masonite). I didn't follow Newt or anything. I just used
>the F+d/100 formula and then added a little.
>
>I remember  that several of you warned me about these tube current
>devils that would hang out in my tube but I have yet to be plagued by them. (My
>tube is a piece of 10" sonotube)Images are great and contrast is better than
>other similar instruments.(Mine being 8"f/7)
>
>I run the fan initially to facilitate faster equilibrium of the primary(8" full
>thickness pyrex) but do not have to leave it on after equilibrium is
>reached.Are the tube currents the effects that others see due to a hot piece of
>glass or do they hang out in tight tubes regardless of the primary to outside
>air temp differential? I suspect that alot of "tube currents" are actually poor
>seeing conditions.
>
>I have a few pictures on my TM page(sorry that it is incomplete at this time) I
>simply plug a 1/4"phono plug into the back of the cell( a Berry variant)when I
>want the fan on.
>Check the mirror cell link on  http://user.icx.net/~mfleenor/frames.htm for
>more info on my mirror cell.
>
>Mike
>
>Mike Fleenor
>Knoxville,TN
> http://user.icx.net/~mfleenor/
>Visit Mike's Home Planet
>
>Bob Rubendunst wrote:
>
>> Keep the baffles, but improve the cooling.
>>
>> After adding baffles, tube currents got worse for me. The first thing I did
>> was mount an indoor/outdoor thermometer on my scope: the mirror was often
>> 10 degrees hotter than ambient, and thermal equilibrium never happened.
>>
>> The solution was two fans: a tiny one that sucks air across the back face
>> of the mirror through the mirror cell, and another fan on the exterior that
>> sucks all of the first fan's exhaust, and more, out the back of the tube.
>> Tube currents are gone, and contrast is better with the baffles.
>>
>>  +------------------+
>>  |      mirror      |
>>  +------------------+
>>    X              X
>>  +------+   +-------+
>>  |      |   |       | <- mirror mount board
>>  +------+   +-------+
>>       +-------+
>>       |  fan  |
>>       +-------+
>>
>> +---+------------+---+
>> |   |   F A N    |   | <- outside board w/ collimating screws
>> +---+------------+---+
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