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Correct procedure for bringing scope in from the Cold

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I've noticed my SCT front objective lens has some minor staining on the inside of the front objective lens. I don't know what effect this will be having on my viewing experience? I suspect it has occurred when dew has formed or perhaps condensation when the scope has been brought back inside the warm house. In any case I don't want the problem to get worse.

What is the correct procedure for bringing a scope back inside?

Should I cover the front lens and the eyepiece holder while still outside? Or should I bring the scope in first and let it warm up before putting the covers on? Or perhaps I should just cover the front lens but leave the eyepiece holder open to allow warm air to get inside?

I really don't know what I should be doing?

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Unless the staining is very opaque, it will probably not have much of an effect when you are observing. I read some where that the best thing to do if your scope is covered in dew is to leave all the lens caps off (including EPs) when you bring it inside. Wipe the outs of the scope down with a towel and then dry off any condensation on lenses/corrector plates etc withe a hair drier.

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I cap my scopes before bringing them in then leave them capped while any condensation that has formed slowly dissipates. Keeping the caps on seems to preserve a slightly colder pocket of air in the tube around the optics so the warming up process is a little more gradual.

I tend not to speed up evaporation using a hair dryer or similar as I fancy that a gradual warming / evaporation minimises the chance of traces being left on the optics.

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Minor staining usually does not deter your viewing experience. You might be able to measure them with a camera side by side, but you shouldn't worry too much. The mirrors usually have to be really stained for it to affect in a large degree.

Theoretically you'd want to make the temperature shift slow. That's why I box up my telescope outside and let it sit in the box inside with just a tiny opening, this means any temperature change inside the box will come on slower.

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So we have votes for leaving the caps off.. and for putting them on! I was hoping for a clear cut answer. lol

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I honestly dont think it matters unless you put them on top of a radiator.

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Pick it up, hold firmly and carry it in carefully without dropping.

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The staining has no effect and is going to happen no matter what you do. If the optics are sealed air-tight then they shouldn't mist up when moved indoors, but in general they won't be air-tight. The tightness of caps can vary depending on the temperature of the scope - they can get looser if it's very cold (because of the differential expansion/contraction of metal and plastic). Reflectors with an exposed primary at the bottom of the tube are never air-tight.

My 8" Orion dob had a solid tube and baseplate covering the primary at the bottom. I used to cap it at the end of session and keep capped, but I discovered that moisture sometimes formed and stayed trapped inside (seen when I uncapped next day). With my 12" flextube I transport it capped but remove the caps when I bring it indoors and let the moisture evaporate overnight. Needless to say, the mirror is covered in stains - but I only see them when I look down the tube, they have no effect on what I see through the eyepiece.

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The kitchen in my old house used to open out onto the patio where i could observe from. Luckily there was an inner door from my kitchen to lounge.

I would open the kitchen door and let all the heat out then bring the scope into kitchen for an hour or so whilst keeping my lounge door shut. Then whip the kitchen/patio door shut and the let scope slowly come up to temperature before bringing into the lounge.

if you have a conservatory or kitchen setup similar to this that's great. But in another property i had no such option so i put a small lean-to with door outside and put the scope in there before bringing it into the house.

All with caps and eyepieces off.

I hate bringing my equipment from the cold into a baking hot house and have always taken whatever measures i can to reduce the impact of doing so. Its simply not good for optics or electronics.

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I cap my scopes before bringing them in then leave them capped while any condensation that has formed slowly dissipates. Keeping the caps on seems to preserve a slightly colder pocket of air in the tube around the optics so the warming up process is a little more gradual.

I tend not to speed up evaporation using a hair dryer or similar as I fancy that a gradual warming / evaporation minimises the chance of traces being left on the optics.

Same here, caps om outside....bring it in let it dry gradually..

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I'm fortunate that I keep my scope in the unheated garage so there is not too much temperature differential, nevertheless I leave my scope with all caps off in an elevated position, mirror at high point 'til morning. Haven't so far noticed a problem.

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It's actually not the mirror, but the inside of the front objective lens. It looks a little like faint dew, but it doesn't go away when the scope is warmed up! I've only had this scope a couple of months, so I'm quite keen to keep it in good condition. The 'stains' may have developed early on before I was using a dew heater strip, I didn't realise how bad these scopes dew up! Mostly I have been putting the caps on before bringing it back inside.

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I would pressume that you use a dew shield whilst in use?

I take my C8 back in the house capped, but I leave it in an unheated room overnight (by which time the house has cooled anyhow). So for a while I set it back up on the tripod (fork mount) take the lid off and point the tube down a bit and allow the corrector plate to gradually de-mist. I never leave the drawtube uncapped after the diagonal has been removed.

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I always cap my scopes and then put them in a dry box before I bring the box back into the warm house. This allow the scope to warm slowly. Since the scope and the air surrounding it is at the same tempature, I don't get condensation on any part of the scope.

The moisture absorber in the box will take care of dew that has formed during the observing session.

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I would pressume that you use a dew shield whilst in use?

I've been using a Dew heater strap, but even that on full power hasn't been enough recently. I've recently bought a dew shield to add to the mix.

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I arrange my mct so the meniscus is pointing down with my dew shield on. I leave the cap off (it has a habit of falling off when pointed down, on wood floors thats a nasty sound 2 hours after going to bed :D). Using the dust cap for the back of the scope I tape a silica gel pack in to the dust cap and seal the scope with it. I'm not worried about it going in to the scope as the baffle is only 21mm. The gel pack goes into a 50 degree oven when I'm observing to ensure it's dry.

With compound telescopes I think the important thing is to get them sealed somehow and the inside exposed to some desiccant, like Keith's dry box or by getting a desiccant cap.

I'm not sure where your staining is coming from but it's entirely possible that you have some moisture inside that you can't get rid of by warming it up alone. Metal is a better conductor than glass so even if you warm it (keeping it in centrally heated room) the glass will probably be at a lower temperature than the metal and condensation may appear on the interior if there is moisture inside the scope. Try a dessicant cap as this will absorb the moisture and prevent it from recirculating inside your scope.

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I only bring my scope inside the house when doing repairs or modifications. I store my scope in an unheated garage. Since the garage is usually close to the outside temp, the cool down is a lot quicker. It also allows the mirrors to defog without staining by letting it stabilize slower when I'm done using it.

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I've not got a garage, so have to bring everything into the front room (at the moment - I've been told this practice must change :)). Kitchen is hotter so tend not to leave stuff there, especially when it first comes in. I've tried bringing my fracs and sct in capped and uncapped. Doesn't seem to make any difference with my fracs, but I've got a feeling its best to bring the sct in capped. I usually just dry off the body and place it in its box, with some silica packs, and leave the box open. Despite using a dewshield, I've manged to still get some tiny dew spots on the corrector plate but makes absolutely no difference to the views. Thinking of some heated straps next.

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Interesting that you choose to store the scope in the garage. I have a garage, but have been storing the tube in the house (I leave the mount in the garage). My theory was that a cold and damp environment with more fluctuations in temperature (at least relative to inside the house) would be a bad place to store optics. Is it better to store the scope in the garage? Obviously the cool down will be quick, and the scope will be subject to less sudden changes in temperature.

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My C9.25 has similar marks on the inside of the corrector plate. I leave it stored outside in a case in my observatory shed and recently I have put on a home made dessicant cap. Next to that I store my dob tube in a scope bag. My theory is with the extra protection from the bag/case the moisture doesn't get to the scope but they remain at ambient temperature for instant use.

I have a dew strap that really works well with the C9.25 and whilst it is on the internal marks seem to disappear. I leave the eyepiece case outside too,but the electronics come inside.

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I have a dew strap that really works well with the C9.25 and whilst it is on the internal marks seem to disappear. I leave the eyepiece case outside too,but the electronics come inside.

Quick question about your dew strap. Do you run it around the plastic end cap and over the dovetail bar? Or do you run it around the metal tube pushed up against the plastic end part and underneath the dove tail bar?

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I run it around the black end part where the corrector is and over the dovetail bar. The fact that it goes around the dovetail bar does not affect it`s performance too much.

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Found this:

7) When you wish to come in from a night of observing and dew or frost HAS FORMED on your lens, DON'T COVER UP THE FRONT LENS! However, ALWAYS plug up the eyepiece holder so that moisture cannot condense INSIDE the telescope! Editor's Note: A 35mm film canister works beautifully for this purpose.

From here: http://www.optcorp.com/product.aspx?pid=1959

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