2 replies to this topic

[Scruffy-the-janitor]

Hey all,

 

Brand new here, but long time lurker,  So sorry if formatting is wonky.  I've had my Lunt LS80 about a month now. One thing I noticed as the weather changed that was not advertised, I feel, was how the blocking filter is effected by the temperature. One perk over the Quark I thought while buying is that it didn't need time to reach temperature like the Quark did. But as it got colder and colder I noticed my views becoming more and more soft. (yes I equalized the pressure in the tuner). I didn't know why  this was happening at first until I thought MAYBE temperature did effect the scope like the quark. So a quick google shows that there were some threads here about cold making poor conditions. I'm just making a new post (especially with winter looming) because I think this may be important for someone to find when deciding on what to buy as well as trouble shooting. Nothing like this showed up when I was comparing the two before I bought. I still would have went with the Lunt but it would have been nice to know to reduce trouble shooting. Granted I'm still a novice at imaging but here are two images from two consecutive days on Nov 10 and 11. First day was about 35°F/02°C and I took my Lunt out of my cold garage when I set up. The second image is after I kept my scope in my house all night to warm up and the ambient temp outside was ~42°F/5°C. I noticed a big improvement with the temperature change and the views got softer as the scope cooled. Still working out a way to keep it warm, modified dew heater, wrapping the outside of the blocking filter in hand warmers etc etc. Any ideas would be appreciated.

 

 

 

Edited by Scruffy-the-janitor, 17 November 2018 - 03:37 PM.

[George9]

For a blocking filter, I use a 3" dew heater attached directly to a 9v or a 12v lithium battery.

 

As noted in the other thread, in my LS80 DSII, at 50F I can detect a difference, at 40F I notice a difference, at 30F the difference is big enough to be disappointing, and at 20F it is a very poor view. With the above heater, the scope stays like warm weather down to 10F that I have tested.

 

All H-alpha filters have limits on temperature and altitude. The old DayStar T-scanner was notorious for a narrow temperature range. My two old 60mm pre-Meade Coronado filters both had limits. One was poor above 90F and below 25F. The other was poor below 30F but good to at least 100F. I had conversations with David Lunt about them, who insisted the etalon was not sensitive to temperature and he was right. It was the blocking filter, in retrospect.

 

There are one or two reports of Quarks hitting their upper temperature limit in a very hot environment, but that seems very rare (and perhaps a false report?). My Quark seems fine 25F to 100F that I have tested.

 

In cold weather, given the choice of the Lunt 80 DSII with a heater or a Quark on a 70mm or 92mm refractor, I use the Lunt. The DS always wins in contrast, and it doesn't have to heat up. On a 130mm or 155mm, that's a different story; the answer there is to use both the Quark and the Lunt.

 

George

[BYoesle]

The effect of cold temperatures is to reduce the spacing of the reflective elements of both air and solid spaced etalons and decrease the CWL in to the blue wing. Colder temperatures also increase the air density for air spaced etalons, which increases the refractive index of the air spacer and would shift the CWL to the red wing. Dielectric layers of the blocking filter likely are similarly affected by the change of temperatures similar to a solid spaced etalon. The magnitude of these changes is usually disproportional between pressure, temperature, and air density.

 

Even small changes in gap spacing (aka "richview" tuning, or temp. tuning of mica etalons) or refractive index are noticeable. Of course pressure changes the air density and therefore the gap refractive index, which is how most of the Lunt internal etalons are tuned.

 

Keeping both the etalon and blocking filter relatively near their standard operating temperatures should therefore help stabilize etalon/blocking filter performance.

Edited by BYoesle, 18 November 2018 - 01:25 PM.