Dew on lens

multiweb (Marc) · #1 14-09-2009, 10:49 PM

I have a 68mm (18-35mm) Pentax lens that I would like to use to do widefield. How do you guys keep your lens dry on your DSLRs? Dew shield? Heaters?

DavidU (Dave) · #2 14-09-2009, 11:05 PM

Seen this?
http://www.telescopeplanet.co.uk/Vie...e=PON08J000042

erick (Eric) · #3 14-09-2009, 11:09 PM

By using a 2" or 3" heating strap. I can recommend the Dew-Not straps. With some form of controller, of course. I just built another one for about $30.

jjjnettie (Jeanette) · #4 14-09-2009, 11:11 PM

I just use the hair dryer in between shots, but that Kendrick unit looks like it's the go. I want one.

CoombellKid · #5 15-09-2009, 06:17 AM

Having had the same problem myself. I went the slightly more expensive
way and brought another Thousand Oaks dew controller and dew strap.
I went this way because I have the same system on my dob and it
works beautifully. It has four independant channels so it can be
expanded and used on my 20x80's which I also find needs a bit of dew
control.

That Kendricks unit above looks alright too, probably works out about the
same price as the system I'm using above.

Cheers,CS

dugnsuz (Doug) · #6 15-09-2009, 08:47 AM

I use the Kendrick MicroFirelite Controller and two 3" heater straps (Camera lens and Guidescope) - works well. Approx $150AU for entire setup.
http://www.kendrickastro.com/astro/index.html
Gave up using the hairdryer after I read it tends to blast hot dust onto your multicoated lens surface!!!
Doug

ps...and the irony of me using a hairdryer isn't lost on me either!!!!!

RB (Andrew) · #7 15-09-2009, 08:59 AM

Marc I assume you already have a dew controller so all you need is a 2" or 3" strap like Eric and Doug suggests.
I highly recommend it and that's what I use, along with a hood too.
I never shoot without it because the dew forms so quickly on camera lenses.

[1ponders] (Paul) · #8 15-09-2009, 09:22 AM

3" - 4" Dew strap on the 17-40 works a treat.

However be careful if using a larger one. While needing a dew strap at Duckadang I borrowed on off The h0ughinator, but it was a bit big (meant for a 10" scope

). So I wrapped it around a couple of times and set it going. It was a fairly heavy dew so I set it about 3/4 (lots of glass on the 17-40). I came back later to check only to find dew on it.

Or what I thought was dew.

The moisture was ...on the inside!!!!! I had turned the strap up too high and it had driven all the moisture in the lens onto the coolest surface, the inside of the lens itself, just like a boiling kettle and a window.

Pity I couldn't have vented the lens at the same time and then perfectly sealed it. I wouldn't have had to worry about fungus on the insides after that.

multiweb (Marc) · #9 15-09-2009, 09:24 AM

Thanks all for the tips & links.

RB (Andrew) · #10 15-09-2009, 09:29 AM

Quote:

Originally Posted by [1ponders]

While needing a dew strap at Duckadang I borrowed on off The h0ughinator, but it was a bit big (meant for a 10" scope

). So I wrapped it around a couple of times and set it going.

LOL Paul, the reason Houghy uses a 10" strap on his setup is that he usually has 5 or 6 wide angle lenses/cameras side by side, he simply wraps it around them once.

[1ponders] (Paul) · #11 15-09-2009, 09:35 AM

I thought the size of it for a widefield lens was to scare the cloud cover away over Newcastle via thermal converction.

RB (Andrew) · #12 15-09-2009, 09:41 AM

Quote:

Originally Posted by [1ponders]

I thought the size of it for a widefield lens was to scare the cloud cover away over Newcastle via thermal converction.

Ah yes you're right, I remember him mumbling something about it having a dual purpose.

erick (Eric) · #13 15-09-2009, 09:47 AM

Quote:

Originally Posted by [1ponders]

The moisture was ...on the inside!!!!!

So, what next? Did you throw the lens away?

How did you get the internals dry again?

[1ponders] (Paul) · #14 15-09-2009, 09:50 AM

I turned the heat down Eric. Nothing I could do about moisture on the inside. I haven't seen any evidence of it since under 'normal' dew strap operation.

erick (Eric) · #15 15-09-2009, 09:53 AM

Thanks Paul.

montewilson (Monte) · #16 15-09-2009, 11:36 AM

Hi Marc - Prevention is better than a cure. Dew straps are great, make your own, don't buy one unless you are really rich.

The secret however is to also get an old sock (thick ones are best) and cut a hole in the toe area and put that over the lens after you have attached the heater. You will loose less heat from around the lens body and therefore need less heat to keep the dew off.

Call me for more information.

multiweb (Marc) · #17 15-09-2009, 12:27 PM

will do

leon · #18 15-09-2009, 01:48 PM

Have to agree with that one Dougie.

Leon