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Dessicant eyepiece caps

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#1 BillHarris

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Posted 11 August 2019 - 09:49 PM

Probably the best thing you can do for keeping the optics of your Questar in good condition is to keep the interior of the tube as dry as possible. The temperature changes from taking it outside and back inside can cause humidity to humidity to enter the tube assembly. I have ordered a cap that fits in the eyepiece holder that contains pacs of silica gel that absorb moisture and indicate when they have reached capacity. These are the Farpoint brand, which are available from a number of distributors for about $40. When not in use, store the scope with the dessicant cap in place to absorb moisture. I believe this may help the service life of BB coatings, too.

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#2 Jim Waters

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Posted 11 August 2019 - 10:03 PM

When they reach capacity I put them in the oven at 150F for 2 hours to recharge them.


Edited by Jim Waters, 11 August 2019 - 10:03 PM.


#3 RobertPettengill

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Posted 11 August 2019 - 10:13 PM

An old Kodak 35 mm plastic film canister fits snugly in the Questar 1.25” eyepiece diopter tube. Just drill some holes in the bottom and put a desiccant pack inside. An eyepiece cap will cover the holes and keep it fresh, if needed.

;rob

#4 BillHarris

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Posted 11 August 2019 - 10:20 PM

Jim--

The Farpoint dessicant packs are made of plastic. Will they withstand the heat?


Rob--

So they will. I'd forgotten about that size match!

#5 Jim Waters

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Posted 11 August 2019 - 10:27 PM

An old Kodak 35 mm plastic film canister fits snugly in the Questar 1.25” eyepiece diopter tube. Just drill some holes in the bottom and put a desiccant pack inside. An eyepiece cap will cover the holes and keep it fresh, if needed.

;rob

Great idea Rob.



#6 Jim Waters

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Posted 11 August 2019 - 10:28 PM

Jim--

The Farpoint dessicant packs are made of plastic. Will they withstand the heat?


Rob--

So they will. I'd forgotten about that size match!

The ones I had did.  Put some aluminum foil on a cookie sheet and try one to be sure.  Check their web site on how to recharge them.


Edited by Jim Waters, 11 August 2019 - 10:29 PM.

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#7 JamesMStephens

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Posted 11 August 2019 - 10:30 PM

I've heated the desiccant packs in the toaster oven and they take it fine, provided you take care.  That said, I really wonder if these desiccant caps do anything.  One design flaw (I think) is the position of the O-ring.  The groove shouldn't be at the end of the cap, but displaced inwards a little bit so that you would have to push it in and get a good seal.


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#8 Jim Waters

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Posted 11 August 2019 - 10:34 PM

One design flaw (I think) is the position of the O-ring.  The groove shouldn't be at the end of the cap, but displaced inwards a little bit so that you would have to push it in and get a good seal.

Now that JamesMStephens mentions it, he's right.  To get a good seal the o-ring needs to be inward.



#9 Optics Patent

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Posted 11 August 2019 - 10:46 PM

This raises the question: where does the barrel interior have the greatest air exchange when an eyepiece is in place?

I suspect around the corrector.

The effective thing about this approach is that it protects the optics without the rapid depletion that a packet in the traditional and leaky case will experience. Of course if you have it in a sealed Pelican case then the eyepiece trick is unnecessary.

#10 Jim Waters

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Posted 11 August 2019 - 11:26 PM

I put 3 to 4 large 2"x2" in my eyepiece Pelican Case.



#11 BillHarris

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Posted 12 August 2019 - 02:49 AM

Living here in the Deep South, humidity amd moisture is generally a problem. A normal situation is dew dripping from the tube. Or the tube frosting over. I would suspect that the majority of the air exchange would be in the control box (while the scope is in use). And especially with the axial port uncovered during photography. And the humidity would diffuse forward to the tube interior.

Back in the day, I used a lot of indicating silica gel with my scope. Especially with deep-sky astrophotog. High humidity in the Pelican camera box could fog the hypersensitized film. So I made a number of pouches out of fine mosquito netting and put one with recharged silica gel in the camera box at the end of the session. And in the eyepiece cases. And I actively dehumidified the scope interior the next day.

It's been a battle.

#12 Loren Gibson

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Posted 12 August 2019 - 06:53 AM

I've been reluctant to re-heat silica gel in the "plastic" (or whatever material it is, it has to allow moisture through the material) pouches in an oven. I've been disposing and replacing them. Here's what I currently use:

 

https://www.amazon.c...e?ie=UTF8&psc=1

 

They have indicator beads to indicate their condition. I put two of them at a time into the 1.25" desiccant plugs, and 3 or 4 of them into the 2" plugs.

 

Loren



#13 RobertPettengill

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Posted 12 August 2019 - 07:18 AM

The plastic desiccant bags definitely will melt in a microwave. You can find them in paper bags on Amazon.
Microwave drying is much faster. Even with paper you need to let the bags cool between a few 30-60” high heat sessions or the paper will scorch.

You can also buy small cotton bags and fill these with desiccant. Cotton holds up well to the microwave and hot desiccant.

I use an airtight Pelican case, so I only put these in place of the eyepiece when warming up to room temp. If I didn’t open the back Port for photography I probably wouldn’t bother with this unless the scope was getting soaked in high humidity.

Edited by RobertPettengill, 12 August 2019 - 07:19 AM.


#14 munirocks

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Posted 12 August 2019 - 07:39 AM

I started populating my scopes and eyepiece cases with colour-changing dessicant last week. The ones in the eyepiece case only took about three days for the orange dessicant to turn green. The ones in the scope have darkened more slowly, but darkened nonetheless. The depeletion rate is much faster than I though would happen. I'm still trying to figure out if the depletion rate will slow down after an initial drying out period, or if I'm just in a humid environment and will need bigger bags and frequent recharging on an ongoing basis.



#15 LKSM12

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Posted 14 August 2019 - 02:05 PM

I use the old 35 mm film canisters with one of the little packs of silica gel in there. However I razor blade the bottom of the canister out only leaving about 2 mm around the circumference. Then I took some 3M contact cement brushed it on there and then set it on some window screen material let it dry cut it out with a scissor around the canister and that gives me much better airflow then simply drilling holes because the screen is the full bottom of the film canister now. When you replace the silica packs you have to make sure that the film canister is setting on the screen on a flat surface so you don't push the silica gel out through the bottom.

#16 Optics Patent

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Posted 14 August 2019 - 09:25 PM

It occurs to me that these are great for scopes that are out on display.

I’d be tempted to ask Vernonscope for some finished Brandon barrels. Might make an interesting group buy.
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#17 davidmcgo

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Posted 15 August 2019 - 10:53 AM

Farpoint has a nice 1.25" dessicant cap:

 

https://farpointastr...-desiccant-cap/

 

On the small Questar, these would probably work well and look nicer than the now getting hard to find film cans. 

 

I have a 2" cap on my Astro Physics 130 f8 EDT and with the volume of that tube, I'm kind of skeptical on the cap holding enough dessicant to do much.

 

Dave



#18 Optics Patent

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Posted 15 August 2019 - 11:47 AM

I'm kind of skeptical on the cap holding enough dessicant to do much.

Yes, but consider that the volume in the barrel is not much more than 10% the volume of a compact Questar case, and better sealed. 

With indicating desiccants at least one know whether it needs to be replenished. 

 

I'd note that when I fill my own giant "tea bags" there are crumbs at the bottom of the container, and I'd want to have something of a fabric filter to contain the fines and keep them out of the control box.


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#19 BillHarris

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Posted 18 August 2019 - 01:07 PM

I found this at a Pelican dealer.  Not a bad idea to keep the case interior dry.

 

https://www.thecases.../peli-desiccant

 

 

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#20 Loren Gibson

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Posted 18 August 2019 - 02:46 PM

Bill, that is exactly what I use in my Q. case. You can also get them from Amazon.

 

 

 

Loren


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