hello,

last night , i have found a strange behaviour with filter offset.
i have done the focus with focusmax before starting the session with @focus2 and compensation t°.
also, i have unchecked the focus on the target list.
at the beginning of the session, the first exposure was ok.ccda have done the offset of the ha filter.
21:05:12 Light Frames
21:05:13 Starting Focuser Temperature: 1.6
21:05:13 Starting Focuser Position: 4521
21:05:13 Temperature Compensation Slope: -23
21:08:36 Light Series 1: 18 light frame(s), binned 1x1, Halpha filter, 1200 seconds.
21:08:36 Guide exposure is 2.8 sec.
21:08:40 Focuser moved by -402 to 4119
21:10:54 Exposing...
21:32:27 D:\astro\st8\st8 pictures\11 24 07\071124_NGC7538\Halpha66W_NGC7538_00001.fit

but at the second exposure,ccda have done the offset of the clear filter on the ha filter.?
so, all my exposure after the first is out of focus...
21:32:27 D:\astro\st8\st8 pictures\11 24 07\071124_NGC7538\Halpha66W_NGC7538_00001.fit
21:32:30 Focuser temperature: 1.4
21:32:32 Focuser position was: 4119
21:32:38 Focuser moved by 404 to 4523
21:32:38 Focuser position is compensated to: 4523

after this ,the t° compensation work normally but with the wrong offset.

you probably said to me why i have done this,why i don't do the focus with @focus?it's just because i don't have the same result with focusmax and @focus2 on the same star, at the same time...focusmax do a best job,sometimes i have a difference of 100 steps with the tcfs(my critical focus zone is 40 steps),i have tried severals adjustments with @focus without sucess.focusmax is more accurate...

see the log below.
thank you for your help
michael

ccdap20071124_210509.log (31 KB, 69 downloads)

Michael,

Since you are using the clear filter for focusing, try setting your offsets relative to the clear filter, not the red filter.

Let me know how that works.

hello john,

update,
i have done the offsets relative to the clear filter with the same result.you can see it in the first log at 1:05

the second log is a session with a focus with Ha filter,and i don't used the option to use the clear filter for the focus on the focus settings.the mistake don't appeared in this session...
regards

michael

ccdap20071128_003930.log (19 KB, 67 downloads)

second log

ccdap20071128_203105.log (31 KB, 62 downloads)

Michael,

I have been reviewing your logs for a while. You have the Ha focus offset in CCDAP set at -380. At 00:48:05, the focus position using the clear filter is 4390. At 20:39:21, the focus position using the Ha filter is 4285. These data are right after focus and before any offsets are set by CCDAP. Thus the Ha focus offset relative to the clear should be 4285 - 4390 or -105.

I suggest the following:
1. Before any run, focus using the clear filter. You can use the Focus Now button on the focus page of CCDAP.
2. Verify your focus offset. Take at least 7 focus measurements with each filter. Discard the highest and lowest and average the remaining 5. Compute your offset from these using the clear filter as reference.

All that having been set, there is no substitute for focusing at the start of each series when using different filters.

BTW, with your Optec focuser, make sure its native temperature compensation is not enabled. That may be the source of the FocusMax hangs.

Hi Michael,

One additional thing I would call attention to is that many systems, due to multiple equipment in the optical train, do not have a linear temperature/expansion relationship. In the days before CCDAutopilot (I'm going way back to before CCDAP1 :-)) ), I used temperature compensated focusing to help get through the night, but never could get the focusing to be just right. So I collected data for a couple of nights and plotted the actual focus position and compared it to a straight line. That's when I found the non-linear relationship (at least with my setup at the time). Now with the ease of refocusing the equipment every X min. and after each filter change, being in focus is one thing I don't worry about anymore.

And just one other heads up, if you are using any Kendrick dew heaters, don't power them from the same supply as your Optec as the switching nature of the Kendrick controller can make the Optec focuser misread and move to the wrong position ( I had that happen to me and sent the data to Kendrick to show them what was happening)

hi john, hi frank
thank you for yours replies.
i have made a big mistake,sorry, i have posted the wrong logs... the goods logs is below.
in the first log below "190432", i have a skystar failed, but the problem is not here.
if i consider the focus position is good at :

20:32:38 Starting Focuser Position: 4968

focuser was moved to halpha position:

20:32:42 Focuser moved by -380 to 4588

and exposing:

20:56:25 D:\astro\st8\st8 pictures\11 27 07\071127_NGC7538\Halpha66W_NGC7538_00001.fit
20:56:29 Focuser temperature: 4.5
20:56:30 Focuser position was: 4588

and there is the mistake:

20:56:36 Focuser moved by 392 to 4980
20:56:36 Focuser position is compensated to: 4980

why 392?
next exposure:
21:18:30 D:\astro\st8\st8 pictures\11 27 07\071127_NGC7538\Halpha66W_NGC7538_00002.fit
21:18:33 Focuser temperature: 4.0
21:18:34 Focuser position was: 4980
21:18:38 Focuser moved by 11 to 4991
21:18:39 Focuser position is compensated to: 4991

t°compensation work at this time.
this behaviour was produced when i check the option "focus with" clear filter.
i have unchecked this for the second log "203105",so i have done the focus with the halpha filter, and it's work.
if the weather is good, i'll try to reproduce the mistake.

for the offsets, i have done it with severals focus measurements for a couple of nights, i can do it again , to ckeck it another time, but i don't think there is a problem.
for the t° compensation , it is not enabled in the tcfs, i'm on manual mode on the handpad.larry weber suppose that is an hardware problem...i'll try soon with an another computer,wait and see..

frank, thank you for your tips,it's very interesting, i'm very interessed by your data or an article about the non linear relationship ;-) i don't know it.
in my case with @focus2 the focus sequence is too long,if i can use focusmax, it's a good deal,but i can't at this time .
i have a good result with t° compensation with my setup.sometimes i check the focus at the end of the night (with a new focus on a star at the meridian),and i can compare with the focus and t° compensation, the result is good,this is never outside the critical focus zone (about 10/20 steps).but the C9.25 is more stable than the other telescope that i can used.for the dew heaters,it's interesting,strange behaviour!, i 'm using an home made dewheater, and i don't see this trouble,but i check it as soon as is possible,may be an issue.

thank you very much

log below with the offsets error.

ccdap20071127_190432.log (14 KB, 58 downloads)

good log with ha focus

ccdap20071128_203105.log (31 KB, 52 downloads)

Michel,

I can't do anything with the logs you supplied. In order to investigate your issue, I need two logs with successful focusing. Your 190432 log did not have a successful focusing so I am unable to compare it to your 203105 log.

Please post two logs, one with clear filter focusing and one with Halpha filter focusing and make sure both achieve focus.