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EdgeHD 8" and star issues saga

souls33k3r
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souls33k3r

souls33k3r

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Good day to all,

Hope everyone had a good night of imaging. It was supposed to be high clouds but to the naked eye i couldn't really see much or any at all. I did keep an eye on stars and see how much they twinkle but they didn't so something must be right. A bit later on in the evening i think when Venus was quite low in the horizon, it started to show up a little hazy.

It was a night for me to test a few things with my scope before i can commission it for active service. So i've had this EdgeHD 8" scope for quite a while now, always used it with a reducer because for some reason imaging using an F/10 native scope in Bortle 8 skies is not an idea i was to toil with and i have never really used it for more than a very handful of times per year since I have had it. Last time i used this scope (September 2018 because I have since had faster refractors in between to play with) the stars in one of the corners were slightly elongated. But then this is something I have already seen with this scope (a thread that i started in June 2017) and never got to the bottom of it. I even asked vendors but it was either put down to spacing or tilt issues. I guess this is the reason why i never really did any justice with this scope.

Anyway, this is just a quick report of my saga, something to look back at if needs be, maybe warn others, maybe it might be useful for someone else with the same setup. A few nights ago i slapped on the lakeside focuser on the stock focuser hoping to automate the focusing setup but it all went pear shaped. I was unable to find HFR any lower than 3.8 when focusing manually, getting HFR of 8 - 10 when running autofocus routine. Nothing made sense and i started another thread where i was suggested to look at the external focuser (i promise this is all relevant). So before i splashed out another £500 worth of an external focuser, i really wanted to test a few more things, one of which was "Could it really be the focuser playing up and causing the bloated stars and autofocus issues". Night before last with the ever so awesome help of @angryowl, i collimated my EdgeHD using his artificial star. I did not want to waste any valuable time on a clear night, in the dark and cold so setup the scope inside while it was cloudy, added a million spacers to come in focus of the artificial star which was placed outside. Turns out, my scope held it's collimation fairly well over the years. I remember a few years my stars in the middle when out of focus looked good enough donut but around the edges they seemed like they were out of collimation because each corner stars had the thinner part of the donut pointing towards the middle (if that makes sense). I did pose a question whether this was normal and i was told that as long as my middle star when out of focus was round, i should be collimated so left at that. Anyway, with the artificial star, i knew my scope was collimated.

Taking full advantage of last night, i took off the autofocuser, slapped the stock focus knob back on, set up my gear with the reducer and polar aligned. Slewed towards arcturus just to verify the collimation and i can tell that scope is collimated. It is when i started to rack the focuser the other way around, i started to notice the same weird donut patterns around the corners. Again thinking this is normal (so i was told). Took a 30 seconds Lum exposure when in focus and noticed the stars in the middle (good pinpoint), top right (ok but slightly elongated), bottom right (again ok but slightly elongated) were ok but the stars in the bottom left and top left were streaks! some were even comet like stars. I decided to spend some time thinking and started to see an outward pattern. I was too close to the sensor. I took off the camera, fw, oag and reducer (it all comes off as one unit), took the caliper out and started to measure my distance. I should be at 106mm, i was at 111mm. So the reference diagram that tells me i'm too close was a duff (Yet again. I had the same issue when i was getting my backfocus right for Esprit 100). So now that i am at the correct spacing, slapped everything back on, took test exposure, seeing the same pattern of streaks in the top and bottom left hand corner. At this point i called @angryowlbecause when frustration kicks in, two heads and especially with one being sane is better than one. So started to experiment. Took 300sec of Ha on M81, stars looked better but still comet shaped.

At this point @angryowl suggested i take off the reducer and try at native focal length. So added a few spacers in and took 30 sec Lum and 300sec Ha. My stars are so much better now! (maybe a hint of focus issue, maybe back focus but GOOD!!!) Ok now as much relieved i was, i soon realised that it is the reducer that has been causing me this issue all along. The weird star shapes in the corners, the auto focuser not being able to do its thing, it all adds up. THE REDUCER has been the culprit. While i was wiping my tears in knowing that i now might ALSO need a new reducer (these bad boys cost around £350) along with the external focuser which i'm now looking at another spend of around £1000, @angryowl suggested that i see if i can shake the reducer and see if i can hear any rattling. i could, not sure if this was normal but was told that it shouldn't be. This is when i remembered watching a video from astronomyshed about a pinched optics scope, Dion takes the cell out of the tube and shakes the tube, hears the rattling of the lens and suggests to tighten the retaining ring enough that the rattling disappears. I noticed that the reducer had a retaining ring and it was a few turns loose. Tightened it up, rattling went away, went back outside and slapped the reducer back on. Took test exposures and my stars are now looking so so soooooo much better. Might still need a few tweaks but this i can most certainly live and work with. I am so glad this is now the end of this saga. Maybe next time when i'm out, i will try the lakeside focuser once again on the stock focuser.

I really cannot thank @angryowl enough for staying up until 2:30am last night looking at these issues with me and helping me all the way. He really is a Godsend. Sorry about the long post but it all had to be said.

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souls33k3r

souls33k3r

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3 minutes ago, MarkAR said:

:hello2::hello2:Well done on finding the culprit. Hope you get some awesome images now.

Cheers buddy. I really couldn't have done this without the sane headed mate of mine. The issue is that I have to set p and tear down each session and these issues could be very easily resolved if I had a permanent setup of some sort, but because I don't, one tends to rush in to the sessions. I didn't want that but then time was ticking as well. 

I really can not wait to put this scope through its paces. 

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souls33k3r

souls33k3r

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5 minutes ago, Timebandit said:

 

 

As they say Two heads are better than one, you have a good mate their. Happy you got to the bottom of the problem👍

 

 

 

Indeed mate. He has helped me countless number of times. He really is the opposite version of me which is why we bounce each other off so well. He's very analytical where as I'm very, let's wing it and say a prayer lol. 

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MattJenko

MattJenko

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This hobby is such a mix of the insanely fine-grained technical and the crude! Identifying a persistent imaging issue with a shake :). Glad you nailed this without recourse to opening the wallet. A success for persistence.

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souls33k3r

souls33k3r

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33 minutes ago, MattJenko said:

This hobby is such a mix of the insanely fine-grained technical and the crude! Identifying a persistent imaging issue with a shake :). Glad you nailed this without recourse to opening the wallet. A success for persistence.

Cheers mate.

And this is exactly why we lot start pulling our hair out. The issues that we encounter mostly have insane fixes. You throw money at this hobby but it will throw a tantrum when you're least expecting and then we question our sanity and ask ourselves "why the hell did I ever choose this hobby", the answer is then quickly given by yourself again when things start to behave properly :)

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souls33k3r

souls33k3r

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On 22/04/2020 at 16:53, Louis D said:

Amazing what a tiny bit of misalignment in optics can make in an image.

I agree mate. Looking back at it now, I'm not surprised because since then I've been looking in to making sure this never happens again. Seems like everyone who has ever owned this reducer has been frustrated and just reverted back to the F/10 scope. 

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Shimrod

Shimrod

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20 minutes ago, souls33k3r said:

I agree mate. Looking back at it now, I'm not surprised because since then I've been looking in to making sure this never happens again. Seems like everyone who has ever owned this reducer has been frustrated and just reverted back to the F/10 scope. 

 

Mine fell apart in my hands when I removed it from the OTA - the retaining ring had worked loose enough when undoing to that the elements all fell out. Fortunately I was indoors and I was able to catch everything and retain the right sequence. I now have some trapped dust between elements so it has to come apart again to get cleaned. It's a bit disappointing on quality for something that costs £350.

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souls33k3r

souls33k3r

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1 hour ago, Shimrod said:

 

Mine fell apart in my hands when I removed it from the OTA - the retaining ring had worked loose enough when undoing to that the elements all fell out. Fortunately I was indoors and I was able to catch everything and retain the right sequence. I now have some trapped dust between elements so it has to come apart again to get cleaned. It's a bit disappointing on quality for something that costs £350.

Ouch!!! That's nearly a scare story right there. I'm not even sure how these things would unscrew themselves when you clearly are never going to touch that bit of the body. It's scary that it happens and will continue to happen. We just need to ensure that it's tight enough pretty much all the time. 

Also got me thinking, how tight it needs to be because clearly when the retaining ring was loose, my stara were all over the place, I've tightened it now and can still see eggy stars but I can live with that (as compared to what I had to work with previously). But you're right, it's not cheap to replace. Not sure if vendors have picked up on this issue and have relayed it back to Celestron? 

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