Temperature Compensation

Notes on Temperature Compensation:

1.The Temperature Compensation Wizard is designed to collect position vs temp data during the night. Most focuser drivers allow the user to enter the slope of the best fit line for TC purposes which can be calculated using Excel.

I was never able to achieve a statistically significant correlation between temp & position with my focuser that contains the temperature sensor installed in the control box along with the electronics.

I am currently using a focuser with an external temperature probe which is placed near the primary of my 16” f4.5 Newtonian. I find that within any one night, I have good statistical correlation but poor correlation night to night with similar slopes and data spread around the regression line which is probably due to environmental differences. In other words, I can not use data from multiple nights to built a single TC model. The slopes are close but the line can be shifted up or down from night to night. With that, I currently focus at the start of the night, enable TC then refocus every 2-3 hours which is an improvement over every 1 hour without TC.

Steve Brady

2.In my attempts at Temperature Compensating Focusing (TCF), I have resorted to burying the Temp Probe in styrofoam (except the metal-to-metal contact against the scope near the rear doublet). This helped reduce but not eliminate the non-linearity.

( http://tech.groups.yahoo.com/group/FMaxUG/message/7779 ).

3.Mini controller from Moonlite contains a temperature probe. I have been known to take the controller's plastic box apart, cut/drill holes in it to improve ventilation (faster temperature tracking that way), and then tape that controller box to the rear casting of my SCT...to track the temperature of the scope. Seems to work ok, but keep in mind that the temp. sensor is next to electronics that generate heat. After you power up the focuser the temperature readings will not stabilize until about 15 minutes have passed...and that's important if you want to do a decent job of temperature compensation.

Tom Krajci

Cloudcroft, New Mexico

http://picasaweb.google.com/tom.krajci
Center for Backyard Astrophysics (CBA)

http://cbastro.org/ CBA New Mexico

American Association of Variable Star

Observers (AAVSO): KTC http://www.aavso.org/

( http://tech.groups.yahoo.com/group/FMaxUG/message/7762 )

4.We recently completed some work verifying how temperature compensation works with a classic C14 at our local club observatory. There is no question the relationship between temperature and focal position shift is linear.

As proof, I've just uploaded plots at f/11 and f/6 taken with the C14 on a Paramount ME, Optec IFW, TCF-S focuser, Pyxis rotator and ST-9 camera. The FocusMax (v3.4.40) Temp.Comp.Data learn wizard was used to obtain all data. The two plots can be found in the files section under a new folder labeled "Temperature Compensation."

"http://tech.groups.yahoo.com/group/FMaxUG/files/Temperature%20Compensation/"

The results and corresponding Temperature Coefficient values are shown on the plots as well. These TC values relate to the 2.2 micron step size of the TCF-S focuser. In strictly linear terms we found that the C14 focus at f/11 moves nearly 0.4mm per degree C. The same scope at f/6 (using the Optec NGW 0.5X telecompressor) was only about 0.27mm per degree C.

You are most certainly correct saying that temperature compensation can and does work. We have thousands of customers using the TCF-S and temperature compensation. The key is to perform the due diligence to determine the Temperature Coefficient for your specific optical system as you have done.

Very best,

Jeff.

Jeff Dickerman

Optec, Inc.

(http://tech.groups.yahoo.com/group/FMaxUG/message/4933 )