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Skiba
member
Reged: 11/16/07
Posts: 16
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DEW! 
I've had my 9 1/4 SCT for a year now. Every photo session I've done so far ends in the corrector plate being covered in dew. I can propably keep the plate dew-free for about an hour or so, depending on the weather. This doesnt give me much time to shoot with clear optics.
I'm using a dew shield (commercial one) and Dewbuster with a homemade heater strip. I've tried different setting on the dewbuster. Last night I had it on full power, but still didn't keep the plate clean.
Is there something I'm missing, any tips & trick that might help??
As a result of continuously dewing up, the corrector plate has accumulated a thin layer of dust and other particles.
I know you shouldn't clean the plate unless absolutely necessery, but then again, I dont know where to draw the line. When does it start to effect the scopes performance?
If I were to clean it, what is the best way to do it without removing the corrector plate?
In the picture you can see the dirt layer only around the flash, but it covers the whole plate. Is it in "normal condition"?
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rmollise
Carpal Tunnel
Reged: 07/06/07
Posts: 1660
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Quote:
Is there something I'm missing, any tips & trick that might help??
As a result of continuously dewing up, the corrector plate has accumulated a thin layer of dust and other particles.
I know you shouldn't clean the plate unless absolutely necessery, but then again, I dont know where to draw the line. When does it start to effect the scopes performance?
If I were to clean it, what is the best way to do it without removing the corrector plate?
In the picture you can see the dirt layer only around the flash, but it covers the whole plate. Is it in "normal condition"?
Missing? Mus' be, since I never have this problem down here on the Gulf Coast where dew is a fact of life.
--Make sure you are using a good, strong battery.
--Place the heater strip BEHIND the corrector assembly directly on the tube.
--The temperature sensor should be INSIDE the dewshield, but not touching it.
The above allows me to remain dew free and never turn up past about 10 degrees.
As for cleaning? It's impossible to tell from your image. In oblique and/or strong light any corrector will look horrible. If you are not sure it needs cleanin'...DON'T.
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Uncle Rod
Watch for Rod's New Book:
Choosing and Using a New CAT--coming in December!
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dave b
Carpal Tunnel
Reged: 05/10/05
Posts: 2460
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make sure your heating strip is insulated from the night sky. you dont want to be wasting heat trying to heat the entire universe.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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Joe Bergeron
Vendor - Space Art
Reged: 11/10/03
Posts: 845
Loc: Upstate NY
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Quote:
make sure your heating strip is insulated from the night sky. you dont want to be wasting heat trying to heat the entire universe.
That's for sure. Global warming is bad enough; we don't want to be responsible for universal warming too.
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Seven telescopes of a diverse nature.
Multiple chums glittering in the sky. New friends await.
My Web Site
English Lessons for Amateur Astronomers
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SanDiegoPaul
professor emeritus
Reged: 07/22/05
Posts: 622
Loc: San Diego
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How warm does your home made strip get? Is it very noticeably warm when you hold it in your hand off the scope?
My first thought is that you aren't heating the corrector enough.
As for cleaning, don't worry about that yet. There's nothing on the picture you attatched to indicate a big issue. And once you keep the plate dry, it will become less of an issue for ya.
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Meade 10" Lx200-R with Moonlight SCT Focuser
Mitty Evolution Wedge
AT-80 Guide Scope
SBIG ST402ME CCD Imager
Canon Digital Rebel DSLR
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Please visit my gallery!
http://www.pbase.com/sandiegopaul/
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Skiba
member
Reged: 11/16/07
Posts: 16
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I'm using a 18ah battery which also powers the mount.
I think it should be enough.
The strips do get warm, thats not the problem. The insulation might be somewhat poor, but should do the job. I mean it will just drain the battery faster, but the temperature sensor keeps it at the right level.
I built the strip from one of those plastic strips that you hang over your door to stop flies getting in.(don't know the english word). I used duct tape to put the resistor ladder and plastic strip together.
Not sure what rmollise meant by keeping the temperature sensor inside the dew shield. Atleast in the Dewbuster one sensor hangs beside the telescope to measure the air temp. and one is under the heater strip.
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Midnight Dan
professor emeritus
Reged: 01/23/08
Posts: 619
Loc: Brockport, NY
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It is difficult to tell by the photo for sure, but it looks to me like there's more of a film on the corrector plate. If there are just dust particles, you can have quite a few and not affect viewing much. But a film like that can do two things: it can cause soft images, AND it can encourage further dewing by providing nucleation sites for additional condensation.
You're right to avoid cleaning as much as possible, but if it were my scope and it looked like that when there's no condensation on it, I would clean it. There are some very good instructions for careful cleaning and making your own solution on Dr. Clay's site at Arkasas Sky Observatory:
Arksky Cleaning System
I've used it and it works great.
Hopefully, that will reduce dewing issues. However, I would have thought that the dew heaters would do the job. Can you provide a photo of how you have it mounted? Also, do you start the heaters up at the beginning of your session rather than after you start seeing dew?
One more question. If you have homemade strips, are they made from individual resistors? If so, are you mounting the heat sensor under one of those resistors, or in between them? With resistors, you have a bunch of point-sources for heat and each one will be hotter than the spread-out heat of a commercial strip. So if you mount the sensor under or very near to a resistor, you'll sense too much heat too quickly and the Dewbuster will throttle it back too much.
-Dan
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Scopes: Celestron NexStar 8, Orion EON 72mm ED/APO on Astroview mount (EQ3)
Eyepieces: Celestron 40mm, 25mm, Baader Hyperion 13mm, 8mm, 5mm
Other: Telrad, 2x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller
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Skiba
member
Reged: 11/16/07
Posts: 16
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Yes, theres a film AND dust particles. It's like permanent dew, and it gets much worse when you take the scope outside for a few hours.
Here's some more pics of the corrector plate. It's really hard to take a picture of the layer, but you can see it clearly with a flash light. There's also one pic of the heater strip
I always start the heater when I take the dust cover off, sometimes even before that.
I'm using individual resistors and the heat sensor is between them. The gap isn't big between the resistors, the sensor barely fits in between them.
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rmollise
Carpal Tunnel
Reged: 07/06/07
Posts: 1660
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Quote:
I'm using a 18ah battery which also powers the mount.
I think it should be enough.
The strips do get warm, thats not the problem. The insulation might be somewhat poor, but should do the job. I mean it will just drain the battery faster, but the temperature sensor keeps it at the right level.
I built the strip from one of those plastic strips that you hang over your door to stop flies getting in.(don't know the english word). I used duct tape to put the resistor ladder and plastic strip together.
Not sure what rmollise meant by keeping the temperature sensor inside the dew shield. Atleast in the Dewbuster one sensor hangs beside the telescope to measure the air temp. and one is under the heater strip.
What I mean is put the air temp sensor INSIDE the dew shield. Since it sounds like you are using a home-brew heater strip, I am guessing that is where your trouble lies. I'd try a Dew-Not strip: cheap and effective.
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Uncle Rod
Watch for Rod's New Book:
Choosing and Using a New CAT--coming in December!
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Quote:
Yes, theres a film AND dust particles. It's like permanent dew, and it gets much worse when you take the scope outside for a few hours.
Here's some more pics of the corrector plate. It's really hard to take a picture of the layer, but you can see it clearly with a flash light. There's also one pic of the heater strip
I always start the heater when I take the dust cover off, sometimes even before that.
I'm using individual resistors and the heat sensor is between them. The gap isn't big between the resistors, the sensor barely fits in between them.
Hmmm this is quite perculiar.
I have been using a 8" SCT from meade for about 4 years and havent cleaned it even once in over 2 years.
My corrector plate has like a thick layer of dust on it, and about 4 finger prints. Still, my scope rarely dews up and i dont use a dew shield nor a dew heater when at home.
IF you are observing from an area that is not surrounded then you will probably get a lot more dew than i do. I guess im the odd man out, since i observe from my backyard. I am surrounded by a forest of trees to the north east and west, and to the south is my house.
I guess my backyard acts like a natural dew shield, as the trees are all blocking the moisture from hitting my area. But, this is also really bad since I am very limited in what i can see to the north east and even west.
After all this time not cleaning my scope, it definitely has dewed up a few times but only when its been really bad. Most of the time though it doesn't.
I dont understand what that film is on the front of your corrector. Is that just the coating looking like that? When i take a pic of my scope it looks like:
Note the obscene amount of dust and the 4 fingerprints? Yea...these are all over a year old...and yet i dont see any difference in quality of image. I STILL even yesterday with this much gunk on the corrector got a perfect view of dumbell, ring, lagoon, trifid nebulas, jupiter, basically all of my usual targets. They all come out crisp with pin point stars. The only target that i am unsure of is Andromeda galaxy, since its kinda blurry without detail.
Note how my corrector plate does not have this strange FILM that yours does. Could it be pollen that got stuck to your corrector?
Here is a pic taken right after i took these up here...but notice how much less dust you can see. Its ALL about how the light is hitting the corrector...and im pretty sure any corrector plate except a brand new or just cleaned one will show some sign of dust or irregularities. It doesnt affect anything.
Note, i did not clean my telescope optics or eyepiece optics in over 2 years, so all pics here are of the same corrector plate taken about a month ago at my house.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Midnight Dan
professor emeritus
Reged: 01/23/08
Posts: 619
Loc: Brockport, NY
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Uncle Rod:
I don't understand your advice to put the air temp sensor inside the dew shield. I have the DewBuster as well. The instructions say that the air temperature sensor should be out in the air outside of the scope and not touching the scope. The heat sensor should be clipped onto the dew strip so that it is underneath the strip and measures the temperature of the scope body.
Is there something I'm missing here?
-Dan
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Scopes: Celestron NexStar 8, Orion EON 72mm ED/APO on Astroview mount (EQ3)
Eyepieces: Celestron 40mm, 25mm, Baader Hyperion 13mm, 8mm, 5mm
Other: Telrad, 2x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller
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rmollise
Carpal Tunnel
Reged: 07/06/07
Posts: 1660
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Quote:
Uncle Rod:
I don't understand your advice to put the air temp sensor inside the dew shield. I have the DewBuster as well. The instructions say that the air temperature sensor should be out in the air outside of the scope and not touching the scope. The heat sensor should be clipped onto the dew strip so that it is underneath the strip and measures the temperature of the scope body.
Is there something I'm missing here?
-Dan
All I can tell you, Dan, is that this is what I have done since I used the first DewBuster prototype Ron Keating (DewBuster) delivered to me and no dewey correctors do I have. I am pretty sure that that is what Ron initially advised me to do. Anyhoo, it works for me.
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Uncle Rod
Watch for Rod's New Book:
Choosing and Using a New CAT--coming in December!
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mikiek
scholastic sledgehammer
Reged: 10/10/07
Posts: 925
Loc: SE Texas
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I had a film similar to what you describe. You could see it in the daylight all over the corrector. After a few hours at night it was really more visible. I think it tended to attract condensation - even with a full blown dew system. Not sure what it was, but I felt it was definately affecting the view. It was very frustrating trying to get it cleaned up. I used several different products (most mentioned on this site) but for the most part it just smeared it around on the glass. I could see what almost looked like an oily sheen to what ever it was that just moved around the plate as I wiped.
One day I finally said to heck with it. I pointed the corrector somewhat downwards and sprayed down the entire plate with Windex (original version, no scent or additives). Then I went through almost a roll of paper towels - on towel, one wipe - and gently wiped it up. I had to go through that routine 3 times but it finally came up.
Now, did I do damage to the corrector? Visually it doesn't appear so. Microscopically? Maybe. I just went with the lesser of 2 evils. The film was having an adverse effect on my views. Maybe that much cleaning might affect things as well, but maybe not. I don't notice any damage, and the view is certainly better.
BTW - since the film is gone I get little or no condensation on the plate.
Just as a disclaimer - most folks on this site would NOT recommend doing what I did. It was a decision I made knowing full well that I could do damage to the plate. Fortunately, it worked out in my case.
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___________________________________________________________
May there always be starlight on the path - R.Burnham
___________________________________________________________
Celestron CPC 1100
Radian 3mm, 5mm, 8mm, 12mm
Panoptic 22mm, 27mm, 35mm(the brick), 41mm (the cinder block)
Nagler 3-6 zoom, T4 17mm
Ethos 13mm
Everbrite Diagonal 2", Powermate 2X
FeatherTouch Crayford, Microfocuser
Telrad Finder, SV 9x50 RACI
Kendrick Dew System
TV NP-101(riding the CPC)
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bierbelly
Postmaster
Reged: 01/23/04
Posts: 5434
Loc: Sterling, VA
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shhhhh...don't tell anyone else...RainEx.
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12" DSH
8" f/4 Vega MakNewt
6" MN66
TV85
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Skiba
member
Reged: 11/16/07
Posts: 16
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I think I'll just clean the corrector plate too.
Based on your experience and others here, the dew problem seems to be caused by the film.
I got some isopropyl alcohol today. Our local farmacy didn't have distilled water, and said it would have to be ordered --> double the price.
I'm not sure what caused the film, maybe condensation...
Do you bring your scope inside after use and does that cause
condensation?
I live up north and this happens every time I use the scope and bring it back inside. I know condensation isn't that big of a deal if you just let it dry out, but....If leave the dust cover on, it might take 1½ days to dry out(don't know if thats a bad thing), and if I leave the cover off it's a dust magnet inside the house.
Is it ok if I just leave the dust cover on and let it dry out slowly or is there a better way to deal with condensation?
Edited by Skiba (09/02/08 05:28 PM)
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Anyone care to tell us what this film layer on his scope is?
In all my years of observing all over the humidity of the northeastern united states, I have never seen any scopes with that kind of film on it...especially one that is hard to clean off.
Look at my scope....its from late 2002, only been cleaned 1 time ever, and I have had a hard time seeing all that dust and fingerprints affecting my view. If you have some kind of hard to clean off film on your corrector, then maybe the view can surely be degraded.
Any idea what that film could be? pollen maybe?
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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mikiek
scholastic sledgehammer
Reged: 10/10/07
Posts: 925
Loc: SE Texas
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The scope stays in the garage - cap on and covered. When it used to get dewed up I would point the corrector down and leave it uncovered overnight.
I hope your film is easier to get off than mine was. In my case Isopropyl didn't work. Check your label as there are different percentages of concentration. It's usually already diluted with water.
A couple of things to do before and during
1. Using some sort of blower (a camera lens blower works) make sure you get off as much loose dust as possible. That's what really scratches up the coatings. If there's a lot of dust that won't come off try lifting it off with a wipe. You DO NOT want to rub that stuff around on the glass.
2. Make real sure whatever you're using to wipe with has no additives. I was using cotton make-up remover pads at first but I swear I think there was something in them.
3. Do not spare your wipes. One pad/cotton ball/paper towel - one wipe. Start at the secondary and wipe to the outside rolling your wipe upwards as you get to the outside.
4. Do not use the side of the wipe that your fingers come in contact with. Whatever solvent you're using will take the oil off your fingers and it will go to the wipe.
5. Move the wipe VERY slowy. Make sure there is no residue left on the glass. The reason I like paper towels (folded into a quarter) is that you can dampen the leading end with your solvent and leave the trailing end dry so that it can absorb what ever solvent is left.
6. Be patient. It could take more than 1 cleaning to really get the stuff off.
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___________________________________________________________
May there always be starlight on the path - R.Burnham
___________________________________________________________
Celestron CPC 1100
Radian 3mm, 5mm, 8mm, 12mm
Panoptic 22mm, 27mm, 35mm(the brick), 41mm (the cinder block)
Nagler 3-6 zoom, T4 17mm
Ethos 13mm
Everbrite Diagonal 2", Powermate 2X
FeatherTouch Crayford, Microfocuser
Telrad Finder, SV 9x50 RACI
Kendrick Dew System
TV NP-101(riding the CPC)
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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One thing to note....
As doctor clay sherrod has said before, you do not need to blow dust off with a blower bulb if you have a good, clean, brush.
If you get the 40 dollar doc clays complete cleaning kit, you'll notice it does not come with blower bulb. Why is this? because you can successfully get all of the dust off the corrector just brushing with the brush, and then no need to use compressed air.
http://www.weasner.com/etx/reviews/2004/images/lens-cleaning4.jpg
Here is a picture of it, if you haven't seen it. So, you dont need to get both blower bulb and camel hair or synthetic brush...since you are basically repeating a process two times.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Midnight Dan
professor emeritus
Reged: 01/23/08
Posts: 619
Loc: Brockport, NY
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Quote:
Is it ok if I just leave the dust cover on and let it dry out slowly or is there a better way to deal with condensation?
I live in the NE too and have terrible dew problems. First thing, once you have cleaned it, your dew heaters should keep dew off of the corrector while you're outdoors. So you should have less problems with it being wet when you bring it in.
But before coming in, put the corrector cap on. If there is any other moisture obvious on the scope body, wipe it off as best you can with a towel. Taking a towel with you should become part of your routine.
When you get it into the house, the cold scope body may condense more moisture if your home air is humid. DON'T take off the corrector cap so you won't expose it to humid indoor air at this point. Give it some time to warm up and wipe down the outside again if needed.
Once the scope is reasonably warmed up (maybe a half hour), then take the corrector cap off. There may be a bit of condensation inside but it should be minimal. Let the condensation evaporate before putting the cap back on.
Taking it outside on a cold night is a different procedure. You want to take it out a good 30-60 minutes ahead of time for the cool-down period. When you first take it out, remove the corrector cap momentarily to allow your home's humid air to escape. Now when you put it back on, you'll be trapping the more dry cold air inside so when the scope cools off there should not be any condensation on the corrector.
-Dan
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Scopes: Celestron NexStar 8, Orion EON 72mm ED/APO on Astroview mount (EQ3)
Eyepieces: Celestron 40mm, 25mm, Baader Hyperion 13mm, 8mm, 5mm
Other: Telrad, 2x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller
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mikiek
scholastic sledgehammer
Reged: 10/10/07
Posts: 925
Loc: SE Texas
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I would never recommend compressed air of any type. But I do have a problem with using a brush. If the brush can lift the particles off then great. If the brush is 'sweeping' the particles across the glass that's a problem.
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___________________________________________________________
May there always be starlight on the path - R.Burnham
___________________________________________________________
Celestron CPC 1100
Radian 3mm, 5mm, 8mm, 12mm
Panoptic 22mm, 27mm, 35mm(the brick), 41mm (the cinder block)
Nagler 3-6 zoom, T4 17mm
Ethos 13mm
Everbrite Diagonal 2", Powermate 2X
FeatherTouch Crayford, Microfocuser
Telrad Finder, SV 9x50 RACI
Kendrick Dew System
TV NP-101(riding the CPC)
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