Are large slews associated with EFFTIME discrepancies across tiles

[geordie666]

In Issue #226 we started tracking the relationship between large slews and strong EFFTIME patterns across petals. As one example of the pattern, from that issue:

I'm leaving this issue open so we can track if there are other cases, and discuss how better to distinguish/diagnose them.

[forero]

I think this is a similar example of a strong EFFTIME pattern across petals after a large slew. This is tile 1951 observed on 20241109

[geordie666]

Anand reported yet another case of the large-slew-effect here:

https://desisurvey.slack.com/archives/C01HNN87Y7J/p1732126974253839

for tile 23487:

[LNapolitano]

Adding another example from 20241204, Tile 9731

[schlafly]

6026 is another example here, following a long slew from a high airmass test tile at dec = -38. I will mark it unsure temporarily but we need to decide if we want to keep it or remove it.

[daqiii]

Do you have the exposure number for this? What you are saying is that after a long slew we have reduced efficiency (EFFTIME or technically less light down the fiber) for some but not all petals? And it is always petal1 independent of the slew? Thanks Klaus From: Eddie Schlafly ***@***.***> Date: Friday, December 20, 2024 at 11:29 AM To: desihub/desisurveyops ***@***.***> Cc: Subscribed ***@***.***> Subject: Re: [desihub/desisurveyops] Are large slews associated with EFFTIME discrepancies across tiles (Issue #247) image. png (view on web) 6026 is another example here, following a long slew from a high airmass test tile at dec = -38. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed image.png (view on web)<https://urldefense.com/v3/__https:/github.com/user-attachments/assets/ca9a538f-948b-4d08-ae68-ded54caa1170__;!!KGKeukY!3NHkzZAQFdgbd2fXo3cjBgwQAxyPb1xkWwrQitoF927Pwsm8-1zakl21kpd1_5QKhAsbM4ho2MGekaYySSq-oA745A$> 6026 is another example here, following a long slew from a high airmass test tile at dec = -38. — Reply to this email directly, view it on GitHub<https://urldefense.com/v3/__https:/github.com/desihub/desisurveyops/issues/247*issuecomment-2557323698__;Iw!!KGKeukY!3NHkzZAQFdgbd2fXo3cjBgwQAxyPb1xkWwrQitoF927Pwsm8-1zakl21kpd1_5QKhAsbM4ho2MGekaYySSpAiUQ2Jg$>, or unsubscribe<https://urldefense.com/v3/__https:/github.com/notifications/unsubscribe-auth/ABQ5P63UJGDVX7S4D4Q4WYT2GRAX7AVCNFSM6AAAAABRMPVVF2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNJXGMZDGNRZHA__;!!KGKeukY!3NHkzZAQFdgbd2fXo3cjBgwQAxyPb1xkWwrQitoF927Pwsm8-1zakl21kpd1_5QKhAsbM4ho2MGekaYySSqHA8c0wQ$>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[schlafly]

This is another example of the same kind of situation we've seen for a while; you can see a selection of other cases earlier in the github ticket thread. We don't understand it well. In this case it was expid 269082. It's not always petal 1; often it looks to me like a gradient across the focal plane (in this case, less light in P123, more in P678). But it is not terribly clear cut.

[daqiii]

Interesting – 269082 is the first exposure after a Loops sequence - this is the one we run during the caravan.. Unfortunately, this ran at the -38 dec position. Would have saved us 3-4 minute slew time if we had moved to the new field during this time. But that’s besides your point. This is the FOCUS plot for this time: ***@***.*** 269082 started at ~3:14 We got a first update in focus position at 3:15 but that’s just the change from the look up table due to the new pointing position. The first autofocus update doesn’t happen until 3:19 and the focus was changed at 3:23 The exposure was split at 3:33 but unfortunately the split failed (I assume because of an offset violation but I haven’t verified this yet with the logs.) So about half of 269082 was taken with the system out of focus by about 100 microns Is that enough to explain your drop in efficiency? One take away for me is that we should be running the focus loop and not just the sky loop during the caravan time to keep auto focus locked in better (again, I think it was a coincidence that the long slew happened after the caravan.) Cheers, Klaus From: Eddie Schlafly ***@***.***> Date: Friday, December 20, 2024 at 12:02 PM To: desihub/desisurveyops ***@***.***> Cc: Honscheid, Klaus ***@***.***>, Comment ***@***.***> Subject: Re: [desihub/desisurveyops] Are large slews associated with EFFTIME discrepancies across tiles (Issue #247) This is another example of the same kind of situation we've seen for a while; you can see a selection of other cases earlier in the github ticket thread. We don't understand it well. In this case it was expid 269082. It's not always petal 1; This is another example of the same kind of situation we've seen for a while; you can see a selection of other cases earlier in the github ticket thread. We don't understand it well. In this case it was expid 269082. It's not always petal 1; often it looks to me like a gradient across the focal plane (in this case, less light in P123, more in P678). But it is not terribly clear cut. — Reply to this email directly, view it on GitHub<https://urldefense.com/v3/__https:/github.com/desihub/desisurveyops/issues/247*issuecomment-2557392713__;Iw!!KGKeukY!2FQQY25rHM_KftpIW9hUIUmHn7_2koXMyhWwjwpO-IR1tm2FbfCrJib7ckP35L0D5nxQBezDGtjV0X0a9_Z8JdTW_Q$>, or unsubscribe<https://urldefense.com/v3/__https:/github.com/notifications/unsubscribe-auth/ABQ5P65YQJAT5BDKHKUFOS32GRES3AVCNFSM6AAAAABRMPVVF2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNJXGM4TENZRGM__;!!KGKeukY!2FQQY25rHM_KftpIW9hUIUmHn7_2koXMyhWwjwpO-IR1tm2FbfCrJib7ckP35L0D5nxQBezDGtjV0X0a9_ZgoZowfw$>. You are receiving this because you commented.Message ID: ***@***.***>