Re: [APML] Home made Dew Shield?

["Monte Wilson" <montezinho@bigpond.com>]

Clarification! A shield is better than no heater - for sure. But if I had to
choose between a heater or a shield, the shield would always loose.


----- Original Message -----
From: "Lewis V. Bishop" <lewis.bishop@red7consulting.co.uk>
To: <astro-photo@seds.org>
Sent: Wednesday, August 14, 2002 6:47 PM
Subject: RE: [APML] Home made Dew Shield?


Monte,

>I don't have any time for shields. I don't think they work and increase the
>chances of wind buffeting. A gentle and constant heat has worked really
well
>for me. I haven't suffered from dew on any lens, in any situation since.

I had 2 cameras out last night, one with a homemade shield and one without.
The one without dew'd up on a longish exposure whilst the one with didn't so
i think they may work for a limited time...

I found some more hints about making one and eventually sliced up a pringles
packet, lined it with my black acoustic insultation foam (5mm thick) and
covered it in reflective material (not sure if that would help or not)... as
i said, it seemed to work reasonably well.

Lewis.


-----Original Message-----
From: Monte Wilson [mailto:montezinho@bigpond.com]
Sent: Mon 8/12/2002 10:13 PM
To: astro-photo@seds.org
Cc:
Subject: Re: [APML] Home made Dew Shield?

I use resistance wire (also known as Nichromium wire) and an insulating tube
around it. To wrap a lens you will need about 15ohms (around 3 or 4 feet) of
it. The tube is sometimes known as spaghetti, it is made of fibreglass and
has an internal diameter of about 3mm. It comes in 3 foot lengths. I think
electricians use it when they need a heat resistant insulation. The end
result is a length of insulated wire about 3 or 4 feet long that gets warm.
On the ends of this wire connect ordinary wire to run to the battery. It is
hard to solder on to Nichromium wire so you may have to join wires by
twisting them. Don't use resistors, they have poor heat transfer because of
their shape and are far to messy and fiddly to work with. 4 Ohms is a bit
low - it would get way to hot with that.

What I do with camera lenses is coil the wire around the lens and when it is
all on there, get an old sock, cut the end of it and use it to hold the
coiled wire around the lens.

I don't have any time for shields. I don't think they work and increase the
chances of wind buffeting. A gentle and constant heat has worked really well
for me. I haven't suffered from dew on any lens, in any situation since.


----- Original Message -----
From: "Tim Hart" <Tim.Hart@haworth.com>
To: <astro-photo@seds.org>
Sent: Tuesday, August 13, 2002 1:24 AM
Subject: Re: [APML] Home made Dew Shield?


> I'm working on the same project for my Camera.
>
> I've been working on a dew shield using resisters.  But somewhere in the
math I messed up....my first attempt was a bit to HOT at 300F.  For the
second try I intend to lower the voltage and Ohms....live and learn.
Luckily I tested it beforehand!
>
> If anyone can help...here is what I used on the first attempt.
> 24 Amp Hour 12 Volt
> 4 Ohm load
>
> Currently I'm to weather impaired to watch the Perseids :(
>
> >>> lewis.bishop@red7consulting.co.uk 08/12/02 08:48AM >>>
> Hi all,
>
> I was out on Friday attempting to capture some of the Perseids (well why
not since they're here) and suffered from dew on the lens. I searched the
web for hints on making dew shields but only came up with 'insultation'
techniques and also one on hand-warmers...
>
> I tried again on Saturday with 2 hand warmers which appeared to work
better BUT i decided to try and make a home made dew shield to help.
>
> I noticed that many on the web are made from some sort of foam and were
black on the inside and silver (to reflect heat) on the outside. I would
have thought that the heat reflection should have been on the inside??? I
have some computer acoustic insultation (about 5mm thick) - would this suit
or should i look at something like pipe lagging?
>
> If i wrap the lens in the insulation materiel i noticed that looking
though the view lens shows the corners cut off by the 'tube' - is there a
specific amount that should/should not protrude from the lens?
>
> Has anyone any hints specifically for camera lenses rather than
telescopes?
>
> Thanks,
>
> Lewis.
>
>
>
>
>
>
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