Hi Doug/Colin Returning to this problem - is it possible, as Colin suggested back in Aug, that the homing sensor is slightly offset with this particular FW? As An FW8G I would not think this to be an issue because otherwise the mechanical indexer would miss and not rest in its slot. More puzzling is why any misalignment does not show up in flats.
Martin, I thought we had seen one flat that was slightly problematic. Am wondering if there is enough of a tolerance in the holes where the filter wheel body that bolts onto the camera part that the entire fw body could be shifted to the left a bit? In other words, if there is a 1-2mm amount that the FW body could be moved sideways relative to the camera body. This would shift the carousel centre over, and maybe give a mm or so on the filter slots. This idea is not yet vetted by the team here, and the tolerances in manufacturing are so tight this should not really be possible. But I throw it out there anyway.
You’re right, there isnt any room for maneuver there. I have been unsuccessful in being able to flat this out but the entire camera has been apart on this trip to try and resolve this. All of the washers have been replaced (the ones you brought to AIC), every filter has been examined for coating failure, the primary baffl`e has been removed etc so over the next 2 nights all new flats will be taken, but last night when I was adjusting the position of the pick off mirror I could clearly see the shading. Here is the pic showing the alignment of the FW in relation to the sensor.
When you operate the wheel you should hear a "clunk clunk clunk" sound as it moves from detent to detent. The wheel should stop moving simultaneously with the last clunk. If you watch the wheel operate, does that happen correctly?
I can certainly hear the clunking, but whether the carrousel actually stops moving after the final clunk is something I can observe when I remove the camera tomorrow to see if the blank filter cell is also mechanically aligned as the lum filter shown in the image.
Gents I have sent you a video containing flats taken through 6 filters. You can see the vignetting shifting about as the filter wheel rotates. This could potentially explain why I cannot flat field it out if it is this inconsistent. It is not supposed to do this of course given the design. On the contrary it is supposed to make your flats more consistent. I have now uploaded two videos showing FW rotation for comment (the same Google Drive Link I sent you)There is no slack that I can detect when the wheel drops into the indent and the 2 screws holding the wheel are tight. Martin
I don't have the video. How did you send it? Also Tim has pointed out that your photo wasn't taken square on to the camera, which will tend to make the filter look off center.
I dont know yet. Tonight will tell as I take the first batch of flats and actually image then calibrate. The change in position of the vignetting in the video was also normal do you think?
I do have a theory. The filters are not a snug fit but I do try to sit them centrally in the holder. Quite often though, especially before when the chain was hitting the top of the fixing screw, the filter would move to one side of its holder, hence the gap on the opposite side can easily be 1mm-1.5mm or so. Hence the variation in vignetting could be down to the fact that the filters are simply not central. This however, should flat out quite normally.
‘No... but it's impossible to know what is going on from that.” but the only thing that is moving while taking flats is the FW, tracking on the telescope is turned off. So perhaps that is quite telling. Got clouded out last might so could not test further.
I'm sure you're very familiar with the difficulty of diagnosing things remotely. More so when someone else is running the tests, because it's hard to know exactly what he was doing. It certainly sounds like there was a filter wheel issue. But when examined directly it was working correctly. Perhaps something was rubbing/interfering with the motion?
I certainly do! the only thing that is on top the FW is the cover of course and when the Fw is moving during normal ops I cannot hear anything unusual and I have had the whole thing apart so no rogue washers etc
It's a shame you got clouded out... it's possible that you did something that cleared the problem - e.g. rogue washer that fell out when you detached the camera, that sort of thing.
