Doug I am having some sort of problem with the FW8G whereby I am taking flats at the PA of the camera, and on the corresponding side of the mount where the lights were taken and I have remeasured the linearity of the STXL11002 to see if that had changed somehow. However, all of the light frames, regardless of filter are showing the edge of the filter holder in the top left of the image with red being the worst. But the flats are not correcting this. I have not seen this problem before. I can confirm that the scope is not obstructed when taking the lights, so its not that. Any suggestions as to how I can resolve this? thanks martin
Hi Martin, Can you confirm I'm understanding this properly? a) A light frame shot through a filter such as Red is showing the edge of the filter holder. b) Are the corresponding flats (eg Red) showing the edge of the filter holder? Am wondering if the home position sensor is slightly offset from the normal position (loose screw on the optical sensor). Could you post a sample FITS of the red filter flat? Are you doing sky flats (scope pointing up) or panel flats (scope horizontal)?
Hi Colin a) yes, I believe it is the edge of the filter holder, strong in the top left, but weak in the lower right. b. Annoyingly, no. If it did I think I would be able to flatfield it out, but the flats do not show it and therefore do not remove it. Yes, doing sky flats using CCDAutopilot which calculates the null point automatically. I took fresh flats last night having remeasured the linearity of the camera, and took it at the PA of the target, still the same. I have your email address I think so I will send the FITS via wetransfer. too large to post here. cheers Martin
Hi Martin - got the images. Using Analyze... Pixel Math... I divided the one by the other, and got this: If you look at the bottom of the image, there is a fairly big donut that shifts. By the size of the donut, am thinking it is on a filter. The smaller donuts don't shift, and those are likely on the front of the chamber window. If you blink between the two flats, you can see a shift going on in the position of the image circle on the chip. Am going to think about this a bit. Until I get my morning coffee, am thinking possibilities might include (feel free to rule out): - some kind of mechanical flexing going on with the way the camera+FW is attached to the scope. -- The null point is going to move a bit, so wondering if its camera orientation (camera vs gravity tugging down) - I don't think its the filter carousel flopping around - that's pretty unlikely - the bearing/spring positioner that puts the carousel in position should be doing its job or it would be obvious Am thinking about how to troubleshoot. Is this one down in Australia?
Hi Colin - not following. I think you need to see a light frame to see the issue I am having. I will send that and when you get it take a look top left and lower right. FWIW - The configuration I have on this scope has been sound for a very good while now, and I have not seen this issue before i.e Flat fields not matching the optical noise in the image. this is the scope in Chile.
Colin - just sent you two red frames, one raw, the other calibrated. Here is the other puzzling thing, while the shadowing is present in LRB images, its almost non-existent in the green. I will send you one.
Thanks Martin - I got the files. Agree, the green looks near-perfect. I'm puzzled. It's not obvious (to me) why this is happening. Let me ponder this some more.
Martin, That's really unusual. Can you pop the lid off the filter wheel and run it through some different slots? Maybe it's binding somewhere and you can see it happen - check for obstructions etc. There is a mechanical indexer so it will be very obvious if it doesn't land in the right place. Doug
I think we have resolved this but I am waiting to get some new flats and light frames on the same target to confirm. If this proves to be the case, this is something I have flagged to you before. To recap, the washers you provide are too small to securely reach the edge of a 50mm filter. On top of this, the FW chain catches the top of the screws that secure the shoulder piece/washer in place. So having removed the FW cover we found that over time, the chain has caused some movement of the shoulder/washer to the point that nearly all of the filters are no longer secured in place by a washer. So what I have been seeing is not the edge of the filter holder, but the edge of the filter itself and this clearly explains why I cannot duplicate it in flat, because the filters are moving around. Martin
Furthermore, the support guys in Chile have confirmed that other STXL cameras in the same observatory have the same issue of the chain catching the top of the screws.
Martin, Thank you for the feedback. We'll review the filter wheel design and see what we can do to mitigate this. Doug
Hi Martin, I'm in the process of investigating the filter clearance, and had a few questions for you: 1) Do you know the brand/part number/thickness/diameter of the filters you are using? 2a) Is the top of the pinion gear on the motor flush with the top of the motor shaft? There are 2 set screws holding this gear in place. If I loosen these set screws and lower the pinion gear, the chain does rub on the filter retaining screws. 2b) The pinion gear should be oreiented gears up, set screws down towards motor. Can you confirm that it is not upside down? It will rub if it is. 3) Would it be possible for you to take a side shot picture of the chain showing the height gap to the filter screws? I would like to compare to another unit. 4) Are you using the filter retainer o-rings? Are the retainer washers installed with the groove side down? Thanks! Colin W
Hi Colin apologies for the dreadfully slow reply. 1. Filters are Astrodon Gen II LRGB and Ha/SII/OIII NB filters. They are 3mm thick with a diameter of 49.7mm (taken from Astrodon website) 2a/2b - sorry, the camera is remote in Chile. It has been off 3 times now to investigate this issue (which has now returned) and with a commensurate level of new dust motes. 3. As above 4. I was, but the support staff at the site have now cut larger washers....but as I said above, it appears the problem has returned. I will go to the site in a few weeks, but that is the best I can do for answers for now. regards Martin
Hi Colin can you please post a photo of the filter o-rings and washers showing the groove side that are currently used for the STXL-FW8G. Want to make sure I have the right items. thanks Martin
Hi Martin, I have attached 2 images showing how the O-Rings and Washers are oriented. Please keep us updated! Kindly, Colin
Well that is interesting. I do not have anything like that in this particular camera. Doug - can you please bring 2 complete sets for an FW8G to AIC? I will purchase them from you at the conference. Thanks Martin
To be clear... what part(s) are you missing? They would definitely have been shipped with your wheels.
I dont have any of those O-rings and my washers are all a tan-coloured flat nylon - and I dont have any washers that have a groove in them. I have 3 FW8G filter wheels so in fact please bring along 3 sets. That ok?
I'll check with our fulfillment people. They can probably put a package in when they ship the booth down. (I don't carry commercial goods over the border - major hassles ensue.)
