I'm using kstars/ekos with a 5D Mark III and experienced problems when it was time to capture flat frames.
The 5D mark III is part of the canon DSLRs where the bulb mode is separated from manual mode on the dial.
I've try to make some test to clarify things, here is what I've noticed :
Dial : M mode ->
Force BULB : ON -> the exposure setting in ekos has no effect and doesn't seem to affect the exposure set on the DSLR. The exposure time selected on the DSLR is used.
Force BULB : OFF -> the exposure setting in ekos works as expected and modify the DSLR exposure time. But if you set an exposure time > 30s, the exposure is not set on the DSLR and it uses his currently set exposure.
Dial : BULB mode ->
Force BULB doesn't seems to has any effect (seems logical because it's already forced on the DSLR) but the exposure time is limited to 0.001 (1/1000) so it can be a problem to capture flat frame for high ISO
If anyone has more infos on the worlkflow/configurations and pratices to use with this kind of canon camera with separated M/BULB mode, I'll be really happy to learn about
In manual mode set Force Bulb to OFF. Use this combination for exposures of <1s.
In bulb mode set Force Bulb to ON. Use it for exposures of 1s or more.
You CAN use the manual/bulf off combination for exposures of up to 30s though. In this case you'll be limited to the camera's pre-defined exposure times.
How about we come up with a simple table and add it to the driver documentation? is this canon specific as well? So the table includes the modes (Bulb / Manual), and the FORce BLOB setting, and what exposures they can take .. I think that would clarify it for the end-users.
"Official guidance" would be helpful for sure. If I recall correctly the problem was cameras with separate "B" mode behave differently compared to all others. So we might end up with two tables. I don't remember what exactly the difference was but what I remember is it was pivotal and did cause trouble under certain circumstances. I'll check this out after the weekend.
I'm afraid this is going to be a lengthy posting as the issue can be complex.
Ekos has two destinct methods of taking an exposure.
The first one utilizes the camera's internal list of predefined exposure times (exposure widget: shutterspeed). In this mode, when an exposure is triggered, Ekos compares the desired exposure time to the shutter speeds offered by the camera. If it finds an exact match, it fires the shot. If it does not find an exact match, it selects the closest one (if considered close enough, otherwise Ekos will fall back to "B" mode which does not work with these cameras) and fires the shot. For example my 5D Mk2 does not offer 1/100s. When a 0.01s exposure is requested, Ekos triggers a 1/90s exposure. The fits header will show EXPTIME 0.0111111s in this case.
The second method utilizes the camera's bulb mode (bulb widget: eosremoterelease). In this mode Ekos opens the shutter, starts a countdown, and as soon as zero has been reached, it closes the shutter.
The "FORCE BULB" setting tells Ekos whether to look for camera internal shutter speeds first, or use bulb mode right away.
Generally, bulb mode works well for all exposure times except short ones and manual mode works perfectly for all shutter speeds that are predefined in the camera. Since very short exposures can't be produced precise enough in B-mode, it is a good idea to use bulb mode for exposures of 1s or more, and manual mode for exposures of less than 1s.
Unfortunately, cameras like the Canon 5D and 6D have a separate "B"-mode (selectable via main dial) whereas for most other Canon cameras "B" is just one of many shutter speeds within "M" mode. What it means is Ekos cannot toggle between "M" and "B" with cameras like the 5D and 6D. What's more, Ekos reads the list of available shutter speeds from the camera at startup, when the initial connection is made. If the 5D/6D's main dial is set to "B" at that time though, the list contains "bulb" only. In order for Ekos to obtain the full list of available shutter speeds, the camera must be set to "M" when the connection is made. (figured this out today, needs confirmation)
The table contains two useful combinations only:
Force Bulb ON / B-mode for exposures of 1s or more
Force Bulb OFF / M-mode for exposures of <1s.
( Yes, the latter combination will work up to 30s but I can't see why a 10s exposure should not be taken in bulb mode.)
I don't know whether this is purely Canon specific.
When other combinations are tried, all sort of nonsense can happen. The results depend upon two things: 1. the exposure time set in Ekos and 2. the shutter speed that is set in the camera's sub-dial. For example, if
1. the Camera is set to M-mode but
2. Force Bulb is ON,
3. the exposure time selected in Ekos is 1s and
4. the shutter speed in the camera's sub-dial is set to 1/10s
you'll end up with 3 exposures of 1/10s each (the camera keeps firing 1/10s shots for as long as ekos runs its count down), the first two triggering error messages and the last one being displayed in FITSview.
So, for the time being, my advice to "B"-mode camera owners would be this: First of all make sure the camera's main dial is set to "M" when Ekos is started. Secondly, for exposures of 1s or more, use the "Force Bulb = ON" / "B"-mode combination and for exposures of less than 1s use "Force Bulb = OFF" / "M"-mode.
Taking flats requires particular attention. Users can set an ADU level and Ekos will try to get there by taking test shots and adjusting exposure times until the desired ADU level is reached within a certain tolerance that can be set by the user, too. Some flat boxes feature a (too) bright light source which in turn requires rather short exposure times in order to achieve a suited ADU level. So the "B"-mode camera user might want to set the main dial to "M" and switch "Force Bulb" OFF. Let's assume the target ADU level is set to 30.000, tolerance is set to 1000. Ekos takes a 1/10s shot which delivers 2400 ADUs. The next shot is taken at 1s which delivers 24000 ADUs. Now, in order to get to 30.000, the exposure time would have to be increased by 25% (to 1.25s). However, the camera does not offer a shutter speed of 1.25s. The two neighbouring shutter speeds (1s and 1.5s) cannot deliver the targeted ADU level within the given tolerance. This attempt to take flats will fail. With other cameras, Ekos would automatically switch over to B mode, start a 1.25s countdown and succeed. B-mode cameras require the user to manually intervene. Two possibilities:
1) Increase tolerance, in this case to 7000, for instance. The 1s shot will be good enough, 1s be used for all flat frames.
2) Set camera to B, set Force Bulb to ON, set exposure to 1.25 and start again. (never tried, but should work IMO)
Longer term, I strongly feel we could (and should!) get rid of the "Force Bulb" thing altogether. That would require some additional work though.
P.S.: Anthony, here is one possible explanation as to why a "Force Bulb = OFF" / "B"-mode combination might have worked. If the camera was set to B already when Ekos was started, the list of available shutter speeds comprised "bulb" only. When Ekos requested a 120s exposure, it was unable to find a matching value in the list and as a result fell back to "B"-mode. Normally, this fallback would have caused a failure but in this particular case (since the camera was set to "B" and Force Bulb was now set to ON which is a recommended combination) Ekos would open the shutter, count down 120s and close the shutter.
Wouldn't the best (most user friendly) way be to check the exif of the returned image for exposure data, see if that more or less matches what you wanted as exposure time and logged a WARN message to the user alerting him to set the mode to B?
I just started with this stuff and was merrily taking 300s exposures along with 30s ones and just wondered why my 300s were much darker.