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DIY dewshield tips anyone? What have you used?

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#1 Matt Wallin

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Posted 12 March 2013 - 06:06 PM

As rare as a clear New Moon is around my parts, especially this time of year, I was excited to get out observing last weekend. The dew was absolutely fierce for a few hours, and I was barely able to undew my secondary with some extended downtime using improvisation with a handwarmer pack. My eyepieces and binoculars were another somewhat more manageable problem. My DIY dew heater on my Telrad saved me from being without aiming, barely, I think I might need to bump up the wattage a tad, I have 0.9W going to it, and it was marginally effective on this night, though it has been totally effective on several less soggy nights. I have been toying with making a dewshield for my Z10 for stray light control and contrast enhancement (people's comments on the result for those purposes are very welcome), but now I am really motivated to make one for dew control puposes as well. I am intending to make it ~1.5 x tube diameter, and I would like it to pack flat if possible. Is 1.5 x tube diameter long enough to prevent dewing?Since my optical finder also dewed almost immediately and was useless all night, I had intended to make a shield for it as well using "foamies" craft foam sheets. Any recommendations on materials or slick designs are welcome, I like my DIY stuff to be effective first, but looking good is important to me too. Thanks in advance!

#2 DebrisDisk

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Posted 13 March 2013 - 09:03 AM

For cheap and lightweight I used black drawing paper with a strip of heavier paper as a stiffener on the sky end. It lives wrapped around the scope tube held with a springy kind of cord from Jo Ann Fabrics. Just shift it forward to deploy.
This has lasted years in South West Florida where humidity can effect the trajectory of 7.62mm. It also is a stray light shield.

#3 BarabinoSr

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Posted 13 March 2013 - 10:02 AM

Hi Debris ! I"ve also had some bad dewing nights here in southern Louisiana while using my 8" reflector too. Sometimes we get the gulf moisture coming in from the south off of the Gulf of Mexico. Usually if it is that serious where everything stays wet, I will not observe that evening. To combat that, I sometimes add a short cardboard 6" to 10" extension over the front end of the tube with a couple of moisture absorbing packets of silica gel taped inside.You may find these on ebay I believe since the moisture falls out of the air around you this has helped me keep the optics dry. Your idea of keeping the temperature of your primary mirror warm enough to prevent condensation is a good one, and must be effective even more if you have your scope pointed toward the zenith. It is during that time when the moisture comes straight down into the tube. On occaision even reflectors need dewcaps like refractors do.

#4 Cary

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Posted 13 March 2013 - 11:27 AM

We make our "Farpoint" brand dew sheilds from .040" thick ABS plastic with 2" velcro closures and a foam strip. We reinforce the velcro by sewing it to the plastic. Her's a pic that shows the layout. If you can find a source of ABS in less than full sheets and the velcro by the foot then you can probably make these yourself less than the retail price.

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#5 Pinbout

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Posted 13 March 2013 - 11:34 AM

We make our "Farpoint" brand dew sheilds from .040" thick ABS plastic with 2" velcro closures and a foam strip.



thanks for the tip, I did something similar with some extra kydex laying around for my surplus shed 127f5.5 frac. But I used the smelly contact cement to apply the velcro, I don't think my sears sewing machine would take well going thru the kydex, leather ok but kydex? :grin:

#6 Cary

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Posted 13 March 2013 - 12:58 PM

I would think if your machien is up to leather it will handle the ABS. Just make sure you use a large needle.

#7 herrointment

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Posted 13 March 2013 - 01:05 PM

Anything and everything including Walnut!

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#8 Matt Wallin

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Posted 13 March 2013 - 02:12 PM

Thanks for the replies all. Cary, that is very much along the lines of what I was thinking of, do you add any type of flocking, as the PVC seems a bit shiny? Do you find your design is solid in the event of wind gusts? As for length, are most observers finding that ~1.5x tube diameter is keeping you in the game on most nights?

#9 Canada_LX10

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Posted 13 March 2013 - 02:16 PM

I built my dew shield for my 8" SCT out of a camping mattress pad. It was under $10 and is soft and easy to work with. I used a gray tarp tape to join the edges together. It slips on and I use a velcro strap around it. The pad is about 3/8" thick. You could make several out of one pad. Easy and simple.

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#10 Pinbout

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Posted 13 March 2013 - 02:34 PM

do you add any type of flocking, as the PVC seems a bit shiny?



you could do it with prostar's flocking material which is pretty much kydex with a synthetic suede material on one side.

#11 Trondur

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Posted 14 March 2013 - 01:09 PM

I make mine out of black craft foam sheets (A.C. Moore, etc.) with self-stick black felt from Walmart as flocking. I use wide velcro, as was mentioned above, but staple it on. A neat staple job looks OK, especially if you black out the staples with a Sharpie. I point the velcro overlap down, so it isn't noticable.

#12 jgraham

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Posted 14 March 2013 - 01:24 PM

The dewshield on my SN6 is made from a section of Sonotube water-proofed with vinyl contact "paper" and sprayed on the inside with flat-black paint. It is attached with 6 set screws in inverted screw insets.

The dewshield on the guidescope is made from a thin sheet of black foam rubber from an art store. The material was cut to length, wrapped snuggly around the tube with about 1/2" of overlap, and the seam bonded with hot-melt glue.

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#13 jgraham

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Posted 14 March 2013 - 01:26 PM

The dewshield on my SC8 is fabricated from thin aluminum flashing, cut to length with about a 2" overlap, and joined with two staggered rows of pop rivets. The inside is flocked with black construction paper. The sheild is attached with Velcro tabs.

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#14 Pinbout

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Posted 14 March 2013 - 05:49 PM

I still want a logo on my dew shield...

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#15 Tom McDonald

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Posted 14 March 2013 - 06:27 PM

Anything and everything including Walnut!


:bow: :bow: :bow:

#16 don clement

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Posted 14 March 2013 - 06:41 PM

Here is a DIY dew prevention control circuit to add to your DIY dew shield that automatically keeps the dew shield a small amount above ambient:

http://clementfocuse...ntrol_Print.pdf

Don Clement

#17 Pinbout

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Posted 14 March 2013 - 07:09 PM

i want something like that for the shield on my motorcycle helmet.

#18 don clement

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Posted 14 March 2013 - 08:09 PM

My DIY automatic prevention dew prevention circuit also works on bathroom mirrors to prevent fogging. BTW before I posted my DIY automatic dew prevention circuit in 1999 for amateurs to use, there were no commercially available automatic dew prevention devices available that monitored ambient temperature and the temperature of the optics to control a dew heater.

Don Clement

#19 Gordon Rayner

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Posted 14 March 2013 - 09:07 PM

For smaller scopes, ABS DWV black pipe from Home Depot, Lowe's, etc. has worked for up to 5 inch binoculars, and heavier PVC also worked on many 5 inch Nikon 20 x 120, Model I, the early model. The early Nikons suffered from galvanic corrosion between the aluminum body and the brass sprayshield ( for fishing, with saltwater spray as the electrolyte. )

Saw the tube with two parallel cuts, about 1/2 inch to an inch apart, parallel to the pipe axis. Released molding stresses cause the pipe to contract. Thus, it will grab a range of telescope tube sizes.

The interior can be roughened with sandpaper and/or painted flat black, or install black flocking paper, or velvet.

For uniform external appearance, wipe the ABS DWV outside with MEK, lacquer thinner, etc.

Orient the sawed slot down , away from the sky.

#20 Pinbout

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Posted 14 March 2013 - 11:33 PM

this is the frosted vinyl logo I was thinking about putting on the dew shield. the frosted on black looks like a satin aluminum.

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#21 Matt Wallin

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Posted 15 March 2013 - 06:03 PM

Danny, looks good,what material did you use on your shield? Also, it looks like you have about 2 diameters there for length, I imagine that has been pretty effective, has anyone had dewing problems with slightly shorter ones, say about 1.5 diameters long?

#22 1Old Timer

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Posted 15 March 2013 - 06:23 PM

"DEW" What is DEW? Here in Colorado we have "Mountain Dew". Dew is rarely a problem as our humidity here on the Front Range is seldom above 20%. It does form occasionally, especially on my finders and eyepieces. My scopes are reflectors so primary and secondary mirrors are somewhat protected. The main problem here is not having stable air for good seeing due to the close proximity to the 10-14,000 foot mountains we have. Good seeing comes around 1:00AM when the atmosphere finally settles down over the mountains that are West of me. The cold air in the mountains flows down hill mixing with the warmer air where I am thus making for lots of turbulence. DEW does occur when the humidity is around 20-30%. It's not uncommon for the temp. here to drop 20 or so deg F after sunset, summer or winter.

For eyepieces, I cover the one that I'm using in the focuser with an large old pill container. For the eyepieces I'm not using, I just put a Hothands handwarmer in my eyepiece case thus keeping them warmer than the ambient dewpoint. Works for me. I have occasionally taped one to the main tube opening while I'm waiting for the scope to thermally stabilize.

Maybe this should be posted somewhere else as it doesn't provide much information on setups for dew prevention. Sorry!

#23 Pinbout

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Posted 15 March 2013 - 06:35 PM

kydex, its 12in long, left over stock from a uta I was building. But its overlapping the entire cell so it's really only 7in passed the glass.

#24 txairman

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Posted 17 March 2013 - 08:51 PM

I used craft foam sheet of black color and velcro strips. It made professionally looking dew shields with good flocking and excellent portability. For transporting I just roll them out and pack in the OTA box flat.






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