So I finally got PHD2 working okay. I think. Sadly, I'm not super thrilled with the results, but I'm unsure where the problem is. This is a fairly new OTA, and I'm using an ED80 as a guidescope with just the default PHD2 settings.
Good old Windows 10 started its automatic updates 20 subs into a 50 sub attempt - Windows 10 is SO AWESOME, I totally don't hate it and it absolutely hasn't caused me to tear my hair out repeatedly - so only using 20 light frames here. Here's the rig:
NEQ6
GSO 8" f/5 with GSO coma corrector
ED80 with QHY5-LII as guide camera (plugged directly into mount's ST4)
Nikon D3300 at ISO 800
20 x 150 seconds
Flats, darks, bias applied
Stacked & processed in DSS, lightly edited in Lightroom
Firstly, the focus doesn't seem great to me, though I went to great pains to make it spot in the very centre on before starting.
The stars aren't perfectly round, which I'm a little disappointed by - thought guiding would take care of that. The 20 frames I got were all perfectly aligned anyway - no visible difference between the first and last.
The framing isn't great. Took me about 10 mins to get guiding working properly in which time it had drifted a little.
Possible explanations:
- collimation. I've struggled with it. This OTA has been a little disappointing; it was WAY off when I picked it up and I possibly haven't yet gotten it as good as it could be.
- using an ED80 as a guidescope probably requires some better knowledge of PHD2 to set it up properly; I expect the default setting is better for a much smaller guidescope (but maybe it's fine, I don't know).
- it's a little bit windy tonight. The scope is fairly well protected, I honestly don't think this was a factor. No one sub was any less sharp than any other. However, it may have made the seeing less than great...?
- GSO's coma corrector. It came with no instructions; I'm apparently using the right spacing for my DSLR, but there's definite coma on the stars, and not just in the corners.
- cheap DSLR. My wife needed the better cameras for a shoot tonight. I'm quite sure they'd be less noisy; didn't realise NGC 55 was so big, so will definitely try a full frame on it next time. I'd hoped the D3300 would do better at ISO 800 but it's pretty noisy so possibly a lot of detail lost.
- light pollution. It was closer to the horizon than the zenith when I started, and right in the direction of Sydney where the most light comes from.
- not nearly enough exposure time at 50 mins. It's magnitude 7.9; no idea if you can expect reasonable results with a low-end DSLR with under an hour. Would doubling it help much?
Any suggestions would be hugely appreciated. I'm about 5-6 months into this hobby now and am starting to plateau significantly - haven't produced anything I'm happy with for a month or two! Need help but unsure where to look for it. I think I need a book or two, or possibly a good YouTube channel...?
Well it's a start, don't be too critical, its not something you learn I overnight, over even over six months. Most of use learn by making mistakes, at least i did and still do. . Re the GSO Coma corrector, i never liked the one i had bought, and sold it for a Baader MPCC which was a great move. The Baader is smaller, lighter, and just works, but it expects 55mm of working distance. There is a thread on Cloudy Nights all about setting up the GSO Coma Corrector, its a sticky thread at the very top of the Reflector forum on CN.
Well it's a start, don't be too critical, its not something you learn I overnight, over even over six months. Most of use learn by making mistakes, at least i did and still do. . Re the GSO Coma corrector, i never liked the one i had bought, and sold it for a Baader MPCC which was a great move. The Baader is smaller, lighter, and just works, but it expects 55mm of working distance. There is a thread on Cloudy Nights all about setting up the GSO Coma Corrector, its a sticky thread at the very top of the Reflector forum on CN.
Yeah I think that's the thread where I learnt I needed a 30mm spacer. The guy at Bintel thrust it into my hand about three seconds into me saying "I've got a GSO coma corrector, going to use it with a Nikon DSLR, do you know what else I... ah. Thanks".
Thought I was being so clever saving the $200 extra that the Baader costs. Sigh. All good, I think I know someone who might be selling one.
Great start Chris. You should not be so critical, nobody got the guiding working straight away.
Few hints:
Regarding the focusing, if you can use live view on the PC software or on the LCD on the camera pick a star and zoom in all the way on it and then adjust focus. Note that very bright stars don't work too well, at least on my DSLR. You can even get the focus right on a bright star/moon and then recompose to your target. A mark on the focuser will help find the focus quicker the following night.
Which PC software are you using for the image acquisition? Dithering helps a LOT when imaging with DSLR. Usually it only requires a tick of the right box and it will be done automatically for you.
You should spend some time just playing with the guiding and trying to understand it. There are several great guides for PHD2 on the net, study them during daytime.
Use the guiding assistant (in menu Tools of PHD2), it will recommend settings to use.
Take screenshot of the guiding graph and post it here for people to comment and give advice.
Did I already say you should study the PHD2 guides from the net
Keep going, you are almost there. Seriously. From personal experience guiding can be a pain to get right but once you got it, it will be a great step forward... until you decide that you need bigger mount/scope/camera/etc
Great start Chris. You should not be so critical, nobody got the guiding working straight away.
Few hints:
Regarding the focusing, if you can use live view on the PC software or on the LCD on the camera pick a star and zoom in all the way on it and then adjust focus. Note that very bright stars don't work too well, at least on my DSLR. You can even get the focus right on a bright star/moon and then recompose to your target. A mark on the focuser will help find the focus quicker the following night.
Which PC software are you using for the image acquisition? Dithering helps a LOT when imaging with DSLR. Usually it only requires a tick of the right box and it will be done automatically for you.
You should spend some time just playing with the guiding and trying to understand it. There are several great guides for PHD2 on the net, study them during daytime.
Use the guiding assistant (in menu Tools of PHD2), it will recommend settings to use.
Take screenshot of the guiding graph and post it here for people to comment and give advice.
Did I already say you should study the PHD2 guides from the net
Keep going, you are almost there. Seriously. From personal experience guiding can be a pain to get right but once you got it, it will be a great step forward... until you decide that you need bigger mount/scope/camera/etc
Thanks heaps. I knew getting into this hobby that it would be two steps forward, one step back; for a while it felt like I was avoiding the back steps but yeah they found me with the OTA upgrade and guiding....!!
Yeah that is how I currently focus - using live view on a dim star centred and zoomed right in. I think the coma corrector is probably more to blame than anything there; if the centre is perfect then everywhere else is out of focus.
Not using capture software. Because I usually use the little D3300, which doesn't work with BYNikon, I just use a cheap intervalometer and upload the RAW images from the SD card. So no dithering possible. BYNikon does work with my other Nikon bodies so I might try those; although it would be a shame to lose the extra magnification the crop sensor offers, maybe some wider field subjects would be better to learn the ins & outs of guiding. The lower noise & better dynamic range of the superior sensors wouldn't be a bad thing either.
Orright, a plan is forming. I'll work on collimation, look into those PHD2 guides, use the guiding assistant, get BYNikon working with my D600 or D750 & try dithering, and (when I can afford it) swap out the GSO coma corrector for the Baader. Cool. Thanks!
Hi Chris, I am at the same stage as you, got tracking pretty good for up to 60sec subs. Then I got myself an auto guide camera a couple of weeks ago and that's where things started going backwards. My guide star was jumping all over the place, a bit of tweaking with the settings tamed it a bit but not enough for what I was expecting out of auto guiding. What I have found after 3 nights of no results. It is really important to have the guide star well focused and of the right magnitude (not saturated ie. too bright) I then spent a while adjusting the worm drives on the mount and after a few goes found the sweet spot, not too tight or loose and the phd graph is looking a lot more steady. Now I have to play with the settings again to tighten the software side of the guiding. In my case soft focus stars were caused by the guide star moving around too much.
My setup is a Heq5 pro with a side by side RC6 (1350mm fl) and 120mm f5 (600mm fl) SW guide scope.
Chris
Really good result for the first guided attempt. Had a zoomed in look at the stars in the corners. The is some elongation there but it is all in the same direction and there is in orange halo below each star.
I am happy to be contradicted but if is was coma, the elongation would radiate away from a central point. How are you doing your collimation BTW?
If it was me I would try taking a fw frames with and without the coma corrector. That would isolate what issues it may or may not be introducing. If you take it away and you see coma but it is radiating around a central point in the image you will know that collimation is OK (remembering that collimation does not eliminate coma only, places the coma free area in the centre of the image pane) If the orange halo disappears then you will know it is being introduced by the coma corrector.
You mention the ED80 being an issue with PHD. I assume you have set the focal length and pixel size in setup? If so, it should handle guiding OK with the default settings. Best way to assess the guiding is to have a look at the graph even it is moving around a bit as long as it correcting back to the centre line it should be fine. One thing to be aware of is not to have you guide camera taking images too quickly. If it is taking 1s exposures, PHD can end up chasing the seeing rather than guiding out mount issues. I now use 2.5 or 3 second issues, which is probably still a little short.
Turning off updates in Windows is a good start. I have setup a dedicated imaging lappy. Nicely isolated from updates and stuff so it just runs imaging software.
It is fractionally out of focus, can tell by the hard edges on the stars. No star has a hard edge. I've been there a number of times, it's hard to tell from the rear screen of a DSLR. That's the only reason I bought a Canon or two, for the BYEOS focusing tool and software control capability.
And yes, big bright stars are NOT your friend for guiding. A smaller slightly isolated star will give a nice parabola shape that the software can interpret the brightest point and centre the guiding much better. You can change the period or the gain to improve the process as well. I'm running about 2 secs with about 50% gain and hardly have to move the guide scope to find something suitable, except round Octans of course !!
I am glad you got guiding to work, i haven't read through all the comments so this might have been brought up before. you mentions that by the time you got the guiding working the framing was out, this suggests to me that polar alignment wasn't that great. if that is the case, the guider has to work harder to get perfect stars and it may cause eggs, also, guiding wont stop any field rotation brought in by bad polar alignment. The other thing is differential flexure, with your ED 80, just make sure the connection is absolutely secure. Wherever there is a connection, the possibility of movement is introduced. also you want to make sure that you are guiding with the movement of the OTA, so that means if you are attached to the rings, they need to be solid to the OTA itself. sometimes you can be guiding perfectly to the rings but the rings might not perfectly follow the movement in the OTA itself.
a good way to determine what the problem is is to look at the PHD graph. if it pushes in a single direction predominately then it is likely a PA issue. if you get big spikes from time to time then there is some movement in the system.
Chris, I'm with Malcolm, doesn't look like coma as the drift is all the same way, suggesting tracking/guiding errors.
The thing with guiding is that you need your polar alignment to be spot on, guiding is not the solution to fix rough polar alignment.
How did you stack the images? To me, it looks like the stars are figure of eights, as if the stacking didn't register the stars correctly.
For focus, I use a Bahtinov mask...inexpensive and not ambiguous. Collimation being out will result it seemingly out of focus or off-round shaped stars over the length of a sub too.
It _is_ possible to get decent results with low-end DSLRs, many have been using 1100D, 450D, etc for years, but getting the results doesn't happen overnight, you've got to get a feel for your kit...I tinkered with guider settings for new Moon after new Moon and slowly got to grips with judging the seeing and setting the guiding accordingly.
But seeing that you have a full frame DSLR, go with that instead. Several reasons for me saying that...firstly, the sensor performance will be superior. Then you can control it with BYN. But also you get a much larger FOV to see what your scope is doing. It doesn't matter if you crop the corners out aesthetically, but the corners might give you some interesting information about how your scope and mount are performing. For example, I would expect to see coma and/or spacing artifacts in the corners of a full frame sensor, but you'd also be able to judge your tracking by seeing if they all go the same way (tracking or spacing issues) or are radiating from the centre (coma). Oh and the crop sensor doesn't give you more magnifcation, the focal length is really the same, the crop sensor just gives you less FOV to work with
Enabling dithering will help get rid of random and DSLR pattern noise, but it won't help if the basics aren't nailed...you need to balance your scope well for the region of the sky you will be imaging. Your polar alignment needs to be spot on. Focus precisely. Try taking shots unguided and see how long you can go until you get star trails. Whatever it is, aim for longer I'd aim for 30-60s before enabling guiding. Guiding is only really good at correcting RA/Dec for deficiencies in the manufacturing (periodic error in the mechanisms).
Hope all this helps...you're doing well for 6 months in, just hang on in there and take one step at a time...
I'd aim for 30-60s before enabling guiding. Guiding is only really good at correcting RA/Dec for deficiencies in the manufacturing (periodic error in the mechanisms).
