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Here my latest capture and I seem to have 2 major issues. My flattener seems to not be at the correct backfocus, but i am staring myself blind figuring out which way it should be adjusted. I also seem to have gotten more and more pinched optics probably due to the cold nights. I did try to adjust this a while ago by adjusting the correct screws but somehow it has gotten worse. if anyone has a good guide for the ZS73 on how to fix this would be much appreciated https://www.astrobin.com/i3y5mi/ |
1.91
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Hi Sean! If you suspect picnhed optics due to OTA contraction, you could try shooting an artificial star indoors, at a room temperature, to see if the defect is gone. If you don't have an artificial star, you could just open a very tiny whole in an aluminum foil with a pin and then put it over a flashlight. |
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11.01
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| From a back focus point of view, I guess we'd need to know what you have in the optical path and how you have tried to achieve the 56,8mm back focus distance |
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3.15
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Andy Wray: Hi Andy, Here is the full layout of the setup Zenithstar 73 Setup mm 6.50mm ZWO ASI183MM Pro Backfocus 20.00mm EFW 8x1.25" 2.25mm Connector M42M>M54M 18.00mm Falcon Rotator 8.25mm Connector M54M>M48F 56.80mm Backfocus 1.00mm Filter thickness 57.13mm Backfocus + 1/3 Filter thickness 2.13mm Flat73R adjustment Have it set now at the 2.1mm on the FLAT73R but I see some weird star shapes still |
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Sean van Drogen: That's quite difficult to follow: can you post a photo of your set-up? |
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3.15
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Andy Wray:Sean van Drogen: Yeah the table from my excel got quite garbled there   |
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| I added up your various distances: 6.5mm for the camera, 10.5mm for the couple of connectors, 18mm for the rotator and 20mm for the filter wheel and got 55mm in total. You then are allowing 0.33mm for the filters takes you to 55.33mm (although most filters are more than 1mm thick, so I would probably say .66mm extra). If we did say 55.66mm, then I would have set the flattener to more like 1.1mm to achieve the 56.8mm back focus. I don't have anything like your setup, so please take this with a pinch of salt, but maybe worth a try. |
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11.01
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Errm, just looked at your photo and the flattener is totally screwed in and not set to anywhere near 1 or 2mm. I was expecting to see it looking like below, but set at between 1 and 2mm: |
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1.91
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By the way, in my experience, the actual width of the elements seldom matches the official specs. There's always small deviation due to interface unevenness. These may add up to a milimeter or two, if not more. So, I use a set of calipers and measure actual distance as I add each element. D |
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David Nozadze: Yes indeed all the measurements where done with a calliper the specs for most things were correct the connectors were both 0.25 out CS Sean |
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Andy Wray: Ah that would be massive user error I just measured distance between the silver ring and front. Never saw that it had an actual measure on it itself. And I have been using it for almost a year like this |
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11.01
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| I'm not sure whether you use the black bit or the silver bit to select the spacing, so probably worth checking their manuals before setting it, but hopefully that will help. |
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Hi, I fell into the same backfocus trap. Expected backfocus is 67.7mm: New Adjustable Flat73 for Z73 - William Optics So just forget about the 55mm - that's for the scope without the flattener. Unfortunately bad weather currently keeps me from verifying that my setting is now correct. As soon as I can test, I'll report my experience. Good Luck and clear skies Wolfgang |
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Just realized you're using Flat73R which has a backfocus of 56.8mm: Adjustable reducer flattener Flat73R for Z73 - William Optics Best regards Wolfgang |
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11.01
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Found this on the WO website: adjust the black bit to about 1.1mm and then lock in place with the silver bit is where I would start. |
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Hi, Have just been through backfocus hell on my Stellarvue and as noted the optics will vary no matter what is published. Each chunk of glass is different. It might be helpful to see some PI or CCDInspector images... need to make sure off the bat you have no tilt. AND, to have some objective baseline. Then what I did was add 1mm between the flattener and the camera and compare the results in PI or CCDInspector... if better, yea! perhaps more of the same... if worse back in the other direction... you can get thinner spacers for fine tuning Spacers on the telescope side of the flattener make little difference as you will be focusing anyhow on that side... so it goes in and out.. Insights born of painful experience and a lot of help from smart folk... More pictures! I am stuck in rainy skys for once in California..... JY OOOOps, I see you have adjustments built in... should be a piece of cake... wish I had that flattener.... |
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11.01
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OOOOps, I see you have adjustments built in... should be a piece of cake... wish I had that flattener.... I went through the same hell as you with my fixed coma corrector, but it was worth it in the end. |
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3.15
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Andy Wray: So used the markers on the flattener to set it to around 2.1mm. Which resulted in a measured GAP of 2,6mm with caliper. So think that might explain it. Will have to wait for another clear night, but being half a centimeter out might explain a few things. |
