Hi Gary,
I did not observe such a behaviour.
Here are some compacted data which show that temperature compensation in SGP calculates what it is supposed to:
FSQ 106N
Canon EOS 600D, modified
External temperature sensor at the scope.
November 10th, 2017, 23:15 Uhr: TempComp enabled in SGP (temperature coefficient -8 steps/K, corresponding to -53 µm/k).
AutoFocus setting: AF at start of sequence and at temperature change by 1 K
Auto Focus.
Autofokus step size 25, 8 s, 2x2
Time, Focus position, HFR, Number of stars
23:48:33, 25013, 7,01, 12
23:48:52, 24988, 5,81, 21
23:49:11, 24963, 4,58, 26
23:49:29, 24938, 3,38, 51
23:49:48, 24913, 2,77, 71
23:50:07, 24888, 2,64, 75
23:50:26, 24863, 3,41, 46
23:50:44, 24838, 4,46, 26
23:51:03, 24813, 5,75, 19
[New auto focus method calculated focus at: 24901
Old auto focus method calculated focus at: 24888]
Result: New focus position is at 24888 (16,91 °C)
23:51:26 validation frame, HFR 2,01, 97 stars
Acquisition of 5 images with temperature compensation enabled in SGP:
HFR, Number of stars, Focus position and Temperature are saved with Image History. HFR und Number of stars are not saved in the FITS header.
23:52:27, Exposing for 300 seconds… 20171110_0001.fit: FOCPOS 24888, FOCTEMP 17,67; HFR 4,12, 217 stars
23:57:40, Temperature compensation: Adjusting for 0,7 degrees (end: 17,7; start: 16,9; coefficient: -8) for 5,8 steps…
00:01:41, Exposing for 300 seconds… 20171110_0002.fit: FOCPOS 24894, FOCTEMP 17,52; HFR 5,22, 178 stars
00:06:55, Temperature compensation: Adjusting for -0,2 degrees (end: 17,5; start: 17,7; coefficient: -8) for -1,4 steps…
00:09:06, Exposing for 300 seconds… 20171110_0003.fit: FOCPOS 24893, FOCTEMP 17,04; HFR 4,44, 178 stars
00:14:21, Temperature compensation: Adjusting for -0,5 degrees (end: 17,0; start: 17,5; coefficient: -8) for -3,6 steps…
00:15:31, Exposing for 300 seconds… 20171110_0004.fit: FOCPOS 24889, FOCTEMP 17,01; HFR 4,49, 154 stars
00:20:46, Temperature compensation: Adjusting for 0,0 degrees (end: 17,0; start: 17,0; coefficient: -8) for 0,1 steps…
00:21:32, Exposing for 300 seconds… 20171110_0005.fit: FOCPOS 24889, FOCTEMP 18,19; HFR 3,94, 164 stars
00:26:48, Temperature compensation: Adjusting for 1,2 degrees (end: 18,3; start: 17,0; coefficient: -8) for 9,8 steps…
00:26:48 Auto focus required (temperature change trigger). Last temp: 16,95; Current temp: 18,27
Autofocus step size 25, 8 s, 2x2
Time, Focus position, HFR, Number of stars
00:26:52, 24989, 4,73, 6
00:27:10, 24964, 3,89, 7
00:27:29, 24939, 2,99, 6
00:27:48, 24914, 2,67, 4
00:28:07, 24889, 2,72, 10
00:28:25, 24864, 3,57, 8
00:28:44, 24839, 4,92, 8
00:29:03, 24814, 6,26, 8
00:29:22, 24789, 7,88, 6
[New auto focus method calculated focus at: 24898
Old auto focus method calculated focus at: 24902]
Result: New focus position is at 24902 (18,50 °C)
00:29:43, validation frame, HFR 3,75, 24 stars
The order of decreasing sharpness of the images was:
0005 > 0001, 0004, 0003 > 0002
These results were poor.
My interpretation of these results is:
Temperature compensation in SGP (between frames) was working basically as expected. The corrections were calculated and executed correctly according to the equation:
fp(T) = fp(T0) + c * (T - T0)
(fp: focus position, T: temperature, T0: temperature of last AF run)
T T-T0 dfp dfp fp
abs rel
16.91 0.00 0 0 24888
17.67 0.76 +6 +6 24894
17.52 0.61 +5 -1 24893
17.04 0.13 +1 -4 24889
17.01 0.10 +1 0 24889
18.19 1.28 +10 +10 24899
(dfp abs. values relate to fp(T0), dfp rel. data relate to the actual fp, i.e.:
fp(T) = fp(T0) + dfp abs and
fp(T[n]) = fp(T[n-1]) + dfp rel
SGP outputs the dfp rel data to the logfile - so in my case all these values are correct.)
So my summary is: SGP does it right The representation of the operations in the logfile is somewhat strange.
I had a very good correlation of temperature and focus position in 3 nights before, when wind was completely absent, see Proposal of a "Quadratic Fit" Auto Focus evaluation method - Auto Focus - Main Sequence Software.
In the night of 10. Novemerb 2017 (data above) the observing conditions were especially poor: strong warm wind with some dust caused an increase of temperature during the night, poor transparancy. During the last focus run even the gude star was lost. So it was not surprising to me that my focus results were not satisfactory. However, I’m sure that this was mainly for one reasons: Temperature measurement at the scope was strongly affected by the unequal strong wind, and false corrections resulted from poor temperature measurements . What I learned from that experience is: It is indispensable to protect the temperature sensor from wind. This is a point that chasmiller46 and pscammp already pointed out in another thread:
Question for users of temperature compensating focusers - #3 by chasmiller46 - General - Main Sequence Software and Question for users of temperature compensating focusers - #5 by pscammp - General - Main Sequence Software
For temperature compensation we want to measure the temperature change of the scope (in the case of an refractor it is mainly the temperature of the objective), not of the sometimes (especially when wind blows) readily changing temperature of the air. The temperature of the scope is always changing slowly, its mass has to be warmed up / cooled down. So it might be advisable to apply thermally conductive paste between sensor and scope, and cover the sensor with thermally insulating material in order to avoid the influence of wind. I hope these hints will be of help.
Bernd
p.s.: I still wonder whether my questions Unanswered questions: AF methods "weighted average" / "best fit" - Auto Focus - Main Sequence Software will be answered by the developers some day.