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Author Topic: PHD (1 and 2) perfect straight line, but star trails for some objects  (Read 8125 times)

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Offline rofus

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Last and final report for this topic :)

After some more tests in different parts of the sky, I can confirm that fixing the primary mirror moving inside its cell, fixed any tracking problem and fixed as well collimation, making it stable and so easier to achieve!

I always used M57 part of the sky as reference (this also if anyone will read this topic coming from the other about collimation), so tonight as well as final confirmation I went to M57 for 300s subs.

First of all I was able to improve guiding numbers making it again more aggressive as I did before: when seeing is decent and no clouds is probably good, if not I make it more smooth, but now it looks great:



Then, this is M57 from full frame (not cropped just resized to fit here in the topic): is great considering is full frame sensor on a small 6"



If I crop that image to APC (non full frame) frame, I obtain an almost all useable field of fiew with no vignetting and almost flat field (for my camera this is a pic measuring more than 4k pixels wide):



The same image can be analysed in CCD Inspector. If analysing the full frame one, I can see I got the best collimation I ever got, even if borders are obviously off being a full frame and not using (yet!) any field flattener:



That might look bad but is instead excellent...cropping the same image to APC non full frame DSLR, I obtain an analysis that confirms what I can see: I got an almost completely FLAT FIELD on a normal sized DSLR sensor :urock:



And now...next topics will be not about problems, but about the pics I took, and possibly the tests of the Field Flattener and the Focal Reducer used on a GSO Ritchey Chretien with a full frame attached!

Again my big thank goes to Chris...you linked that post about opening the mirror, and I started from there, thank you, you helped greatly solving my problems with this great scope :)
AA 8" RC + AT Flattener, SW Esprit 100 + SW Flattener, Daystar Quark Chromosphere
Canon 6D modded, Nikon D750 unmodded, ASI174MM-COOL, SX Lodestar X2, ASI120MM
Canon & Nikon various prime lens
SW HEQ5 Rowan Belt Mod, AA 60mm Guidescope, Astrotrac, SW Star Adventurer
Mac 15" Retina Parallels: EQMOD, PHD2, SGP, PlateSolve2, BYN, CDC, Pixinsight, Photoshop
William Optics binos, Baader Hyperion eyepieces, Meade & Celestron binoculars
http://theski.es

Online chris.bailey

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Great stuff. Glad to have helped!

I think RA Aggressivenes at 100% is a bit high. If you look at the graph you are getting a lot of corrections that are bigger than the error they are trying to correct leading to a reversal correction. At least you can now tweak guide settings knowing everything else is working well.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline rofus

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Indeed for the rest of the night (yes I went on till early morning) I tweaked settings, in the end I lowered stuff a bit again, more smooth, thanks!

Brilliant stuff, wherever I pointed this little gem of a scope I got pinpoint stars, basically perfect collimation, perfect tracking even using the small finderguider. As Nick from Altair said is not a telescope for everyone, but once mastered and now with addition of native field flattener and laso the focal reducer to have it down to f6/900mm when needed, it's unbeatable quality and versatility.

The whole setup is so light on my HEQ5 that I'm planning to either upgrade in the future to 8" OR add piggyback a small(ish) ED Triplet widefield, so I can easily image on the narrow or wide field without changing a thing (if not the camera from one scope to the other!), while the finderguider can guide both scopes.

Most beautiful view of the night was Albireo...single frame 120s unedited straight from camera and with bright moon nearby. Cannot think to a better way to celebrate, never got before such a lovely (and correctly coloured) view of this beauty


AA 8" RC + AT Flattener, SW Esprit 100 + SW Flattener, Daystar Quark Chromosphere
Canon 6D modded, Nikon D750 unmodded, ASI174MM-COOL, SX Lodestar X2, ASI120MM
Canon & Nikon various prime lens
SW HEQ5 Rowan Belt Mod, AA 60mm Guidescope, Astrotrac, SW Star Adventurer
Mac 15" Retina Parallels: EQMOD, PHD2, SGP, PlateSolve2, BYN, CDC, Pixinsight, Photoshop
William Optics binos, Baader Hyperion eyepieces, Meade & Celestron binoculars
http://theski.es

Offline mechanoid

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Well, I had a similar problem with my modded DSLR. Eventually I tracked it down to the image sensor itself moving relative to the camera body as the temperature changed. I took me nearly a year to realise this. The only solution was to ditch the DSLR and go to a QHY10. It was difficult to identify because of the ever changing relationship between ambient cooling and camera warming.

So it may not be flexibility in the guide train at all.  Worth considering ...



Skywatcher Quattro 200mm C/F, Vixen GPDX, QHY10
Skywatcher ST80, QHY5II, PHD2
Images Plus

Offline rofus

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Interesting indeed!

The sensor itself was fine, indeed for me at least was mirror moving, I can now track forever without problems and with either aggressive or smooth guide, stars very nicely round even on my small small pixels. I love the hires of my full frame and its low noise and very high sensitivity in the shadows.

Got confirmation about the RC scopes being shipped this way to avoid damage during transportation, and a small percentage being too loose (like in my case).

Now is so perfect I'm considering upgrading to bigger RC :)

Interesting to hknow that camera sensor as well can give such problems!
AA 8" RC + AT Flattener, SW Esprit 100 + SW Flattener, Daystar Quark Chromosphere
Canon 6D modded, Nikon D750 unmodded, ASI174MM-COOL, SX Lodestar X2, ASI120MM
Canon & Nikon various prime lens
SW HEQ5 Rowan Belt Mod, AA 60mm Guidescope, Astrotrac, SW Star Adventurer
Mac 15" Retina Parallels: EQMOD, PHD2, SGP, PlateSolve2, BYN, CDC, Pixinsight, Photoshop
William Optics binos, Baader Hyperion eyepieces, Meade & Celestron binoculars
http://theski.es

 

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