Ngc6188

[Jeffkop]

Hi again all.

Well the G11 finally arrived and I have taken 2 nights to digest how to use it properly. Am able to autoguide fantastically now, and so I thought I would share first light pics with the TSA102S and I guess the G-11.
Have found out that I have a limitation with clearance of the G-11 tripod with any objects passing near the zenith. Shame because there are a lot of very picture worthy objects in that area at the moment, so I went looking for something interesting a little further out and came up with this object. The G-11 faithfully slewed to it and whilst I have to admit I didnt really know where abouts I was orientated in the nebula, I decided that wherever it was, that will do me. I ended up with this picture and after processing, I have been able to place its where abouts in the bigger picture.

Whilst it represents a beginners photo, at the same time it is a quantum leap forward compared to any of my previous efforts, and testimony to the hotly debated fact in these forums that, "you get what you pay for". I employed the exact same principals and techniques that I was doing with my other "inferior equipment", its just that this stuff WORKS.

I have looked at other pictures of this nebula and realise that my 5 minute exposures need to be longer or stacked with others to extract all the beautiful detail this object has to offer, so tonight is another night.

Have been playing with flats and the like too, which I will add to the pics and if there is any significant change to the quality I will repost this pic.

I am enthusiastic to say the least now, and ... its NOT raining !!!

Any comments, as usual, are helpful.

Jeff

[renormalised]

If that's your first attempt with a good setup, then you're going to go a long way with astrophotography!!!:eyepop::)

That is a really nice piccie....good colour, even if it might be a little pinkish in parts, but that's due to the brightness of the stars in those areas. The background is gorgeous....jet black....as it should be, and the stars are nice and round.

Great shot:D:D

[jase]

You're on the right path Jeff. You are acknowledging where you feel you need improvement i.e. longer subs and more of them. Always a good start. I would suggest keeping an eye on the histograms during processing. The data is black clipped in all channels, thus you've lost some of the fainter nebulosity. Keep at it and look forward to seeing more of your output.

[leon]

A great start Jeff, and if that is your first attempt with the new set-up I'm sure we can expect some awesome imaging in the near future, keep at it.

Leon

[beren]

Great start Jeff, it must be exciting and energising to start like that with the gear/setup you have :thumbsup:

[Hagar]

Hi Jeff, Looks like you have a ver nice setup now. The picture is a very good early shot. As you say stacking more images will definitely improve the quality and SNR somewhat. Your guiding seems great with lovely round stars and even with active guiding looks like you alignment is good.

Well done
Keep at it

[Ric]

A fine start Jeff, you have some fine equipment there as well. I'm sure it wont be too long until we see some spectacular images.

Cheers

[Kirkus]

Let me just say that I'm jealous. That's just beautiful. I'm so looking forward to more from you, Jeff.

[Robert_T]

Jeff, now why did you have to go and post this...I'd convinced myself it's me is the reason I can't get decent guiding on the LXD75 and that there's no point upgrading to a decent mount.. you're destroying all my excuses to avoid shelling out for another big shiny thing:P

[skeltz]

You are on the right path jeff, a very good start,longer subs and as you get to know your equipment more, things will only get better.
Welcome to the jungle!!!:thumbsup:

[Jeffkop]

Hello and thanks all for your comments, I really enjoy this stuff and like many of my previous posts suggest, I have waited a LONG time to do this.
Robert_T .. Im afraid that no amount of fiddling and the like would make my previous mount (and I had 2 of them) track good enough for this sort of photography. Same camera same techniques as this photo. :lol::lol: and I thought I was past the biggest hurdle learning to drift align. Its one hurdle after another in this game, just when I had everything going good, I rotated the camera last night to frame M104 better and then NO and I repeat NO amount of changing calibration times would successfully work in CCDSoft5. It kept on saying movement too small in X axis ... and I could see the star move position NO problems, didnt matter that I could select a calibration time that would make the bloody thing slew the star out of the pic !!!
So a good night of imaging lost to I dont know what.

But I will be out there again tonight;)

[gregbradley]

Hi Jeff,

Ah the callibration curse - I know it well!

I personally think callibration is a weak spot of CCDsoft but haven't used other software to know for sure but I'm suspicious!

Here's how to handle callibration:

1. First of all callibratioon here means to set the scale of amount of time a command to move is given to the mount and the resulting motion of the stars in the image to keep something still.

2. Make sure everything is well balanced.

3. Make sure you are well drift aligned.

4. Make sure your scope is well focused - a poor focus makes autoguiding weaker.

5. Make sure your guide rate on your mount is set correctly (some mounts have a fast slew rate and a guiding rate).

6. If you are using CCDsoft in the autogduiing tab there is an auto button. If have an autoguiding image up and click it then a box will flash around the software selected star. This is the brightest star in your image. I generally use this star.

7. I also generally callibrate using the imaging chip rather than the tiny 237 guide chip but you can use either.

8. Now here is where you are having trouble. The software picks the brightest star in the image. So if you have a hot pixel or you have another bright star just outside the FOV that moves into the FOV when callibrating the software will pick that star up and think it is the original star. The movement won't compute and you'll get an error usually "invalid motion in one of the axes". But you can also get increase callibration time if the software is selecting a hot pixel as of course it does not move in the image and it reads the same spot twice in a row and computes that the star did not move so increase callibration time to make it move more.

There is a plug in you can put in CCDsoft - a hot pixel remover. Only difficulty with it I have found is it seems to disable the auto button in the Autoguiding tab which is handy. It is hand as when you start to autoguide it makes the star centred in the autoguiding box so there is less wait time for the errors to fall if you selected it not quite centred.

Make sure you callibrate with autodark selected as well.

Another trick is to use the sub-frame function of CCDsoft.

I take an image using the imaging chip. I click on subframe. Then you drag a box around a lone brightish single star (not a double star) and take another iamge. Now the resulting image is just the box you dragged. Now
recallibrate. If you click on auto and it flashes a box with no star there it means it selected a hot pixel so drag a box around some other star and start again. This way you can control what part of the chip the callibrating is being based on and there is no hot pixel in that part of your chip.

Another solution is to simply slew to a spot where there is a lone brightish star and callibrate off of that. If it is a crowded star image it is going to be harder to callibrate than an image with few stars and one brightish star.

So in summary it sounds like you have a few hot pixels and the software is selecting one of those rather than the star you chose to callibrate off (I always chose a star and don't let it automatically select one).

If you get really stuck one trick is to write down the callibration results (click on the tab that shows the resulting callibration figures) from a time when autogudiing was working well for the same camera/scope. Then just simply type them into that same section. I haven't done this successfully but have been told it works.

A few other things I have learned about autoguiding:

1. Refocus occasionally if there is a temperature shift. Perhaps every 2 or 3C. Roalnd Christian refocuses every 1C shift.
2. If you are getting worse autoguiding errors than a bit earlier - select another star. Apparently not all stars in the same image give the same tracking errors. Sounds strange but very true. I usually pick one that is fairly bright but also appears quite sharp - no double stars.
3. Make sure there are no cables dragging.
4. If the errors go up rebalance. Perhaps your mount is out of balance at the angle you are imaging at yet balanced when horizontal.
5. I fiddle with the guid rate for both axes to get the errors as low as possible. I let it settle down for a while and watch the errors reported. I then will adjust one or the other if one axis is giving more errors than the other until I get them as low as possible.
6. You can also change the minimum or maxium move time so if the seeing is poor increase the minimum move so it doesn't try to correct for a seeing shift rather than drift.
7. I have found lower errors using an external guide scope rather than internal guide chip. I put that down to better focus as the internal guide chip on a large chipped camera is now outside most scopes coma free area and can be distorted rather than round. Also the guide scope gives a brighter image and you can get shorter guide exposure times.
8. For me I go for a low aggressiveness setting - 5 or less, and the minimum almost of guide rate for the different axes. You can overcorrect. Watch the numbers - you see them go from -.4 to +.2 then its probably overcorrecting. Back it off.
9. Some recallibrate when imaging in a new part of the sky or if they do a meridian flip. I have done this too but haven't noticed a difference particularly. If I start getting worse errors after a big slew I will recalibrate or check balance.
10. Do all this with the lowest temperature setting you can get. Sbig manual says set cooling to 60% or so. I found this way too conservative an go for broke andf try to get max with a small buffer. I am happy with 90-95% cooling as once it hits a temp it doesn't go outside it much. Also using adaptive darks minimises the need for exact matching of temperatures and darks. Although I prefer an exact match.
11. I autoguide trying to get 1 second guide exposures. I have been told that is chasing seeing. Well perhaps my dark site has excellent seeing as that works the best by far. If I can see the seeing is unusually bad and that shows up in the guiding errors and you can see the image of the guide star shifting shape from one exposure to the other then I go 2 to 4 seconds and watch the guide errrors until I hit an optimum for that night.

I have also autoguided with a Starfish guide camera and used .26 second guide exposures and that worked well too.

My policy on autoguiding is to have several setups to autoguide with. If one is not ideal I can switch to another.
I have a Losmandy dovetail adapter and a remote guide head and an efinder that simply slips and locks onto the dovetail underneath the scope. Very handy. I also have an eternal guidescope - an Astrotech 66ED , cheap light, well made and an excellent guide scope. Also gets rid of the blue filter needing longer guide exposure problems.


I hope this helps.

Greg.

[Jeffkop]

Thanks Greg for your time here, no doubt some valuable tips ... and for certain .. you dont get this sort of information in the help section !!!!!

I was selecting a guide star .. well I was clicking on one and the small coordinate boxes were being filled with information ... but for some reason ... yep ... you hit it on the head .. "invalid motion in X axis", and I couldnt get it to do anything about it ... at the time from memory there were 6 or so very distinct and what I call bright stars ... anyway, armed with this extra piece of knowledge .........

Am going to try it all out tonight :thumbsup:

Thanks again for your input, hope it solves someones else's problem as well

Jeff

[gregbradley]

Hi Jeff,

You're welcome.

What's happened is one of those bright stars has moved into the image once the mount moved and the software thinks the new star is the one you selected and so the movement doesn't compute.

So you either need to select a lone star in another part of the sky or use the subframing trick to select only part of the image to be used for callibration and select the imaging chip rather than the guide chip.

I asked the question once on the Sbig yahoo group if selecting the imaging chip instead of the guide chip makes any difference and the answer was no.
I have never noticed a difference and it makes the process a lot easier.

Greg.