Can dew do damage ?

[Ewok]

Hi all.

Just wondering if dew can damage my scope? It was really getting quite damp the other night and I packed up as I didn't want to cause any damage . I haven't got any anti-dew devices as yet - so second question is what would be best to use ? ( as cheap as poss would be nice as I'm skint at the moment )

Thanks for reading and looking forward to any advice.

[Suzpaz]

Not sure if it will damage, but you should turn the scope downwards if you are afraid of moisture. Dunno HOW much it helps, but it helps.

[Horus]

Good newbie question...............

[rowan46]

the first thing you should consider is a dewshield this should extend about 1.5x diameter of your scope. people often make them out of camping mats, the darker the better. don't cover the whole scope its usually only the secondary mirror that gets dewed up and if you cover the whole thing it will take longer to cool down. some people use a hairdryer on a cold setting if things get bad or one of those fans for inflating airbeds but they tend to be noisy at night so there are systems called dewbands which contain a heating element and keep the mirror above the dewpoint. if you are fairly au fait with electrics there are some threads on making home made dewbands in the diy section. As to damaging the scope, dew won't damade your scope but it can leave smears on your glass if it not dried properly. so when you take your scope in it night, wipe the outside with a dry cloth and leave the scope pointing slightly down with the caps off.

[jgs001]

My scopes and kit regularly get very dewed up... How you treat them will determine how they cope. The optics on the scope got cleared of dew 4 times the other night with a hair dryer from a distance on cool, then I left them uncapped pointing down in the garage to allow any dew to clear, when I'd done.

[Jimmy Stix]

This may sound like a dumb question but please bear with me.

Is dew going to be a real problem with a Mak 127? I assume that this will not be as big an issue as with the open tube construction of a reflector. Unlike my birdwatching optics I realise the Mak is not totally sealed and is open to the air when attaching eyepieces etc. and that, as they just sit in there, they are not airtight.

Thanks for you patience.

[acey]

Dew can potentially damage reflector coatings by depositing salts that accelerate erosion of the surface, eventually leading to "pinholing" (little holes that you can see by holding the mirror up to light and looking at the back). My 8-inch mirror developed pinholes after about 5 years, though so small and few that they probably had little effect on the view (and anyway I upgraded).

Simplest prevention is a dewshield (to protect ther secondary), not pointing the scope needlessly up towards the sky (to protect the primary) and not leaving dewed optics sealed.

[rowan46]

"Is dew going to be a real problem with a Mak 127? I assume that this will not be as big an issue as with the open tube construction of a reflector. Unlike my birdwatching optics I realise the Mak is not totally sealed and is open to the air when attaching eyepieces etc. and that, as they just sit in there, they are not airtight."

You won't get any dew on the mirrors but the big corrector lens at the front is very prone to dew, You will need at least a dew shield for a mak or sct

[haitch]

Not that I've suffered 1st hand but I believe putting optics away damp can encourage fungal growth.

[pvaz]

Not that I've suffered 1st hand but I believe putting optics away damp can encourage fungal growth.

Yeah. They only need to be in the dark, on a place with high humidity % and a mild temperature long enough to develop fungus.

If it's an external surface then no harm as you can simply wipe it with a cleaning fluid. For internal optics, such as the inside of an EP, then you either dismantle it or send it for maintenance.

[Ewok]

Cheers for the advice guys, I will look into making a dewshield asap.

[haitch]

One of the worst times for condensation forming is when you bring cold gear back into the house with its warm moist air hitting the cold equipment.

I like to close my tube up and shut my EPs in the case when outside in the cold air as long as there is no dew on them already. That way they are full of, and surrounded by much drier air. Cold air can hold very little moisture and, once it warms back up to indoor temperatures, there is no chance of any moisture condensing out.

[haitch]

"Is dew going to be a real problem with a Mak 127? I assume that this will not be as big an issue as with the open tube construction of a reflector. Unlike my birdwatching optics I realise the Mak is not totally sealed and is open to the air when attaching eyepieces etc. and that, as they just sit in there, they are not airtight."

You won't get any dew on the mirrors but the big corrector lens at the front is very prone to dew, You will need at least a dew shield for a mak or sct

When you say it is less likely to be an issue than with a reflector do you mean due to the moisture getting inside?

If you have dew the issue is less with sealed optics as you only have to worry about the moisture on the outside. However, a design like a Mak is more likely to suffer from dew in the first place because more air will circulate around the external optics and once the corrector plate falls below ambient temperature (which it will quite easily when pointed at the sky as it radiates energy out towards the void of space) dew will form quite readily.

Truss tube reflectors are a different matter though!

[RikM]

I had more dew problems on the front corrector of my Skymax 127 MAK than with the secondary mirror on my reflector. I made some simple dew shields from a black ASDA foam camping mat (£1.50) and these work a treat. Make sure you make them long enough though. I used sticky vercro pads to hold them together.

Rik

[RikM]

Here's a quick pic of the first foam and electrical tape version.

Rik

[Jimmy Stix]

Cheers for the advice guys, I will look into making a dewshield asap.

And thanks for the help from me too guys. I did rather hijack Ewok's thread (sorry Ewok!) but it was kinda on the same lines.

I shall have a go at making my own dew shield while I wait for a clear night.