Pressure tuned Lunt and temperature

[wkyee]

I had my LS60 upgraded from tilt-tuned to pressure tuned about 2 months ago. When I got it back, I was disappointed with the view - almost all the contrast was gone, and I couldn't see filaments. I contacted Lunt, they suggested that I change the o-rings, which they sent me. I have still not installed them. Today, I went out today and got spectacular views. The only difference is the temperature, which is not 40-50 degrees F. Before, I was observing at 10 - 20 degrees. The Lunt folk insist that the scopes are not temperature sensitive. My observations suggest otherwise.

Or maybe the scope needs to be "broken in" somehow?

What are other people's experience?

[Cschur]

Sounds like an experience I have from time to time in cold weather. What I did find out was several things. I have a PT Lunt LS100 and gotten pretty familiar with the idiosyncrasies of the PT. Yes as the tuner warms in the sun (its black remember) the tuning will need to be readjusted. You can tell if you need to "burp" the tuner when you screw it all the way in and it still doesnt give you the darkest image with a disk full of details. IF so, then unscrew it all the way, and just before it comes off, mark it with a sharpie or tape so you can get the right spot started again. then put it back on and tune to about 1/4 to 1/2 inch from bottoming out for darkest solar image. It should get lighter if you keep tuning in, as it passes the band center. Thats how you tell its been pressure compensated.

Hope this helps!

Chris

[solarchat]

Willie.
The pressure tuned Lunt's arent temp sensitive per se, but they are extremely pressure sensitive, that's the design of the pressure tuner. Of course, air pressure is directly related to temperature so the tuning will be vastly different as the temperature changes with the pressure tuned model.

If you didn't do this yet, you are supposed to take off the pressure tuner all the way before each observing session to let the ambient pressure into the etalon chamber, then put it back on and screw it down until the prominences are the brightest and the contrast the best on the surface. This is tuned.

As the temperature changes throughout the day you will have to change the tuning. Sometimes taking it all the way off and retuning it again is in order throughout the day. If it does not hold the setting you tune it at without a major temp change then the o-rings are not holding the air and should be replaced. Replace the old rings with the new ones, grease them up liberally with the supplied package of grease and then screw the tuner back on.

[Gert]

Hi All,

What was said before is all correct. Let me add that temperature affects pressure tuned etalon performance in many ways. The metal housing of the etalon and the quartz spacer change length, the refractive index of the air changes, and of course the pressure of the confined air in the pressure chamber. All these effects may track differently with respect to wavelength. I've once pulled some dependencies together into a spread sheet. More for my own education and not very pretty for public consumption.
But if you want you can pick it up here.
http://drgert.dyndns.ws:8000/download/e ... ure_v4.xls

Clear Skies,
Gert.

[Peter Williams]

I purchased a secondhand Lunt LS60THa a few weeks ago now.
It has the internal pressure tuner and I also have the add on front double-stack unit.
What I've noticed is that the most contrast and best surface details seem to occur at about the point the pressure tuning knob is about to fall off.
It seems to be at its best with no pressure, or very little pressure.
Does that seem like a problem?

[wkyee]

I did all the steps discussed above. None made any difference, but the warmer it got outside, the better and easier it functioned.

Peter - when it was really cold I had the same effect. The best tuning was with the tuner almost falling off.

[Peter Williams]

Thanks for the info Willie,
it's the end of Summer and beginning of Autumn here, plenty of sun and warm wind still, typical air temps here are in the mid 20 to low 30 C range when I've been observing. The scope seems to retain tuning well and doesn't change much over time as it sits out in the sun for hours.
I think I'm getting better at tuning it, on the weekend I got the most even illumination and detail I have managed so far.

[swisswalter]

Hi Willie

I found that my LUNT 100 needs aclimatisation in order to show a good contrast . So I place it outside in the sun for al leas 30 minutes prior to the session

[wkyee]

Out again today. Temperature warmer, view even better. If this is not temperature related, I will eat my shoe.

OTOH, I would be glad to wait 8 more months until i got to test the cold weather end of its performance again.

[Rybak]

Hi
Last year I used my PT Lunt LS100THa at temperatures from plus 30 C to minus 20 C and there were no problems with tuning, but I often had to take off the tuner and then screw it in.
But I had problems with Coronado SM II 90. In order to tune it at 0 C I had to move stop pin for 4 positions, at minus 10 C - for 8 position, and at minus 20 I also could not tune, but did not move that pin any more because I was afraid to break etalon.

[wkyee]

I discussed this issue with Rikki from Lunt at NEAF. She said that what I was getting was due to something pinched in the blocking filter, and they will fix it if I just send the BF back to them.

I just need to find a week when I can do without the scope. Here in the NE USA, that shouldn't be hard.

[axlefoley]

Hi

But I had problems with Coronado SM II 90. In order to tune it at 0 C I had to move stop pin for 4 positions, at minus 10 C - for 8 position, and at minus 20 I also could not tune, but did not move that pin any more because I was afraid to break etalon.

After your suggestion Aleksey I moved the pin in mine but only 1 hole, in saying that we have temperatures around 28c to 38c all year round compared to your cold climate.

[Merlin66]

Alexsey,
I thought the SMII series had both the T-max tilt option and the "Rich-view" tuning....why would you use the Pin adjustment in preference to the tilt tuning???

[axlefoley]

Ken I had mine hard up against the pin and was not quite in focus so with Alekseys advise I moved the pin 1 hole and fixed the problem.

[swisswalter]

Alexsey,
I thought the SMII series had both the T-max tilt option and the "Rich-view" tuning....why would you use the Pin adjustment in preference to the tilt tuning???

Hi Ken

with the tilt unit you get the gost out of the FOV and with the rich-view unit you optimise constrast and flattness

[ForrestLockhart]

I received my Lunt 60PT last December and couldn't wait to try it out. So out in my 38 degree Northern California yard I went. Not a good first light experience.
My PST did a better job out in the cold. My buddy's Lunt 60 tilt-tuned scope provided better views too, and as a result my wife says I got grumpy. But I've come to understand my scope now and I've found that, whatever the reason, setting it up out in the Sun for 20 minutes or so in cool weather provided me the solar views I had initially hoped for. Now that the days are in the 60's or higher, I can just bring it out and experience great detail as soon as I insert an eyepiece.
I am, once again, a happy man. I wonder how much better view I could get with a new Lunt 100PT? Hmmm....
Forrest
ps - Per Rikki, I always reset the pressure tuner before every observing session.

[GUS]

I observe at an elevation of 1050 meters and at temperatures between -5 to 30 degrees with the Ls 60 PT and do not notice much variation due to temperature. In that temperature range the PT tuner is almost completely all the way in with no threads showing,with no detail (apart from sunspots) showing till i am almost three quarters of the way in. The only trouble i have is with the stiffness of the tuner,which has been tight since day one.It was to the point were i had to hold onto the mount(vixen porta) to stop the scope from mowing. I recently put some extra grease on it and it seems to be a lot better now.

[Rybak]

Alexsey,
I thought the SMII series had both the T-max tilt option and the "Rich-view" tuning....why would you use the Pin adjustment in preference to the tilt tuning???

Hi Ken

with the tilt unit you get the gost out of the FOV and with the rich-view unit you optimise constrast and flattness

Hi All

Both the tilt and RV-Tuner may optimise contrast and flattness. Of course i used pin adjustment at minus temperature only after all other unsuccessful attempts.