Using Ha filters in near freezing temperatures?

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RKBerta
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Using Ha filters in near freezing temperatures?

Post by RKBerta »

Here in Michigan, US we are heading into Winter. I am curious what precautions are appropriate for Ha filters when used in cold weather which is near or below freezing.
I remember seeing a note that the filters should be allowed to gradually adapt to the temperature both when going out of a house for use as well as when bringing them back in. It was suggested to temporarily store it in a area like an unheated garage in both cases to minimize shock to the filters. That would allow gradual adaption instead of going from warm house to freezing temperatures and vice versa.
I suspect that the proper care would be based on the type of filters. I have both a Lunt 60 Ha scope as well as a Coronado 60 Ha external etalon used with a normal telescope to adapt for Ha plus the matched blocking filters for both. I also have a Day Star Quark Chromosphere model. That one may be more tricky since it uses a heated element to bring to optimum band. I have avoided use of the equipment when the weather gets uncomfortably cold but am curious if it is a big issue safety wise for the equipment or won't allow the equipment to work at design optimum.


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Re: Using Ha filters in near freezing temperatures?

Post by DeepSolar64 »

I have two Coronado tilt tuned scopes. When taking them out of the warm house I let them gradually cool down before uncapping the blocking filter and front etalon to observe in the winter. I cap them securely before going back in. I do the same in the hot days of summer. I leave them capped coming out from the air conditioned house and let them adjust to the warm air before uncapping them and observing. and then securely cap them before going back inside. So far I have had no issues yet.

The fall and the spring are the easiest. The temperatures between inside and outside are not so different so often one can go straight to observing.

James


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Re: Using Ha filters in near freezing temperatures?

Post by Rusted »

I carry my Lunt BF1200S and ZWO camera back and forth in small, plastic, food containers with snap-on lids.
They travel in a pocket of my laptop case so are not warmed up too quickly on returning indoor to a cool room.

The straight-through BF was already clouded on the blue filter after less than a year.
After removal, it responded to a moist, lens cleaning tissue and de-ionized water. Finished off in a dry Kleenex.

The PST etalon remains in place on the telescope. Being air-gapped I have presumed it immune to temperature.
Oil-gapped etalons and filters are considered vulnerable according to Lunt.

The ergonomics of removing the entire filter train would require a long, sealed, storage tube. The motor focusing protrudes.
Plus the difficulty of adding balance weights to the rear of the main tube and removal on the next imaging session.

The worst part of winter is dewing of the full aperture, D-ERF and 6" objective.
I use a hairdrier and heat bands but can lose a whole morning to dew after a frost.
I remove the D-ERF to speed things up but fear dropping it while working from a stepladder.
Turning the telescope sideways to the sun, over lunch, allows some warmth to soak into the main tube through the observation slit.

I fear I shall have to cut a large hole behind the objective. To allow the blast from the hair drier to reach the back of the dewed objective.
This means completely dismantling the scope [including the baffles] to avoid metal [galvanized steel] swarf ever reaching the optics.

Always a major effort with larger refractors on a raised mounting.
I have to use a block and tackle, perch on a stepladder and take great care of the swinging counterweights.
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P1460744 ha filter train rsz 800.JPG
P1460744 ha filter train rsz 800.JPG (66.41 KiB) Viewed 466 times


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Re: Using Ha filters in near freezing temperatures?

Post by marktownley »

I would recommend getting a Lunt blocking filter heater if you plan to observe in the cold regularly.


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Re: Using Ha filters in near freezing temperatures?

Post by MapleRidge »

Hi RK...

I am east of you in S. Ontario and experience similar winter temps.

In my opinion, the greatest risk is taking cold optics into a warm room where condensation will form on both the interior and exterior of the tube and optics. If you cap the scope and/or put it in a case then the moisture lingers longer.

In my case the scopes (solar and night use) are all permanently mounted in unheated observatories. I leave them out 365 days a year...the interior remains near air temp so it avoids big temperature swings when opening up and cools slowly as the day turns to night. I let a dew heater run on low on the telescope objectives, but the etalons (pressure tuned and tilt tuned Lunts + a PST) and blockers (Ha+ CaK) have never had an issue. I keep the Daystar filters in a ziplock bag with desiccant to help extend the life of the blockers/trimmers which degrade over time.

The only times I get much in the way of condensation is when the winter temps take a wild swing from bitter cold to above zero as a warm front moves in and we go form -20C to +5C or more in a few hours. This usually happens a couple of times each winter but has not caused me any issues.

If you have to take equipment inside I would suggest keeping it in an unheated garage or similar location to avoid the temperature swings and condensation). Leave the caps off until the moisture clears.

Just my experiences...best of luck finding a solution for your own situation.

Brian


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Re: Using Ha filters in near freezing temperatures?

Post by EGRAY_OBSERVATORY »

Hi Bob, in addition to that which Brian has said, in both my observatories I've installed de-humidifiers which do the business of very quickly drying and keeping dry the gear.
Around 40% humidity or lower works well, with the only snag during the winter-months of having to keep the internal air temperature above 5-degsC, as otherwise the water extracted by the refrigerant and Peltier Heat Pump de-humidifiers will very likely freeze within the coils and damage the units.

Not a problem as near to both are small thermostat-controlled oil-filled radiators with thermometers to monitor each observatory.

Only really useful for relatively sealed spaces though...

Terry


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Re: Using Ha filters in near freezing temperatures?

Post by RKBerta »

Thanks all for the suggestions. I don't have any problems with regular scopes and cameras...my concern is with the Ha filters and blocking filters. I do very gradual temperature changes to avoid shocking the gear. I also have dehumidifiers and smaller packets of moisture absorbents that goes in cases that are regenerated every couple of months. I found that if you place gear inside of plastic bags that are sealed while outside, and than come into the warmer area, the condensation will be on the outside of the plastic bag and not on the equipment. Once the temperatures stabilize the gear can be brought out of the plastic bag. I also like going from outside to an intermediate location such as an unheated garage. Later when it stabilizes there I than bring into the house.


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Re: Using Ha filters in near freezing temperatures?

Post by rigel123 »

My suggestion is the same as Mark's, either get the BF heater from Lunt or use dew heating straps around the blocking filter as you can lose contrast of your image as the BF gets colder. I have had my tilt tune Lunt 60mm for nearly 10 years without issues although I’ll admit to not going out much with it when temps are much below freezing, not that I’m too worried about the scope, I just hate frozen fingers!


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