The joy of guiding

[hjw]

Hi everyone,

I got myself some guiding gear (SW ST80, ZWO ASI120MC and my first ever laptop) and after what seemed like endless weeks of clouds I saw some clear sky this evening. It was my first chance to see whether all the bits are talking to each other. I did a very rudimentary polar alignment to actually have the guiding scope work for it's money. After all I did want to see whether the communication train worked. Pointed the scope to the lagoon nebula and took 5 minute frames (ISO800). The intention was 10 subs but after 8 the clouds had moved in.

The result, which, for the effort, I am more than happy with:

Only hiccup, a possum which we sometimes feed jumped on the table with the laptop looking for food and bit me in the hand. I'm happy there is no rabies in Australia!

Perils of spending the night outside .

Clear skies!

HJ

[michael.h.f.wilkinson]

I would be well pleased with that! Very nice indeed

[Michael-H]

Oo, very nice. And lucky, to be bitten by the only non-lethal animal in Australia.

[Cpaulo]

That looks great, please keep them coming.

[Scott]

nice image and the guiding seems to be doing it's job, but sorry mate...I'm still laughing at the possum. They can be savage little beasts. I remember as a kid, my dad trying to coax one out of the b&d roller door with a broom. instead of leaving via the other end, it "charged" him and scratched his arm to pieces, making him fall off the ladder.keystone cops springs to mind

[laudropb]

Very nice image. Glad we don't have possums here. The most I have to contend with is an inquisitive hedgehog.

[ollypenrice]

I heartily applaud any pro-autoguidng thead because (at sub 10 Micron budgets) anything else is messing about. You just do need to autoguide. That isn't my fault!!!

Olly

[Stub Mandrel]

nice image and the guiding seems to be doing it's job, but sorry mate...I'm still laughing at the possum. They can be savage little beasts. I remember as a kid, my dad trying to coax one out of the b&d roller door with a broom. instead of leaving via the other end, it "charged" him and scratched his arm to pieces, making him fall off the ladder.keystone cops springs to mind

I know a guy who used to work for the RSPCA - he said the most dangerous animal in the UK was a muntjac deer, having had to deal with them several times, the worst being a very angry one in a garden shed that ripped his welly to pieces with its tusks!

[ollypenrice]

I know a guy who used to work for the RSPCA - he said the most dangerous animal in the UK was a muntjac deer, having had to deal with them several times, the worst being a very angry one in a garden shed that ripped his welly to pieces with its tusks!

Heheh, they are lovely things, those deer. If a boar rips your welly to pieces it might be with your foot still in it! The Muntjacs look dainty but, round here, the mountains often rise very steeply from the roadside and the little deer power up them with a raw strength which is awe inspiring. The pure strength in their back legs is mighty.

Olly

[hjw]

nice image and the guiding seems to be doing it's job, but sorry mate...I'm still laughing at the possum. They can be savage little beasts. I remember as a kid, my dad trying to coax one out of the b&d roller door with a broom. instead of leaving via the other end, it "charged" him and scratched his arm to pieces, making him fall off the ladder.keystone cops springs to mind

Thanks to everyone for your kind comments. I had my trepidations about guiding but in the end it turned out easier than expected. Can't wait to get a good night!

Regarding the possum I should have known better. They don't sniff, they TASTE new stuff. It jumped up and I was going to show it that I didn't have food and it drew blood...

I shall be smarter next time. I still think they are cute I just will keep my fingers to myself next time.

Clear skies!

HJ

[Thommy]

Congrats, mate! I'm sure you'll find that from time to time guiding will fail. It's inevitable  . My guiding has been working flawlessly, but last night it just couldn't keep up with the movements of the mount. Perhaps the wind was a little too strong or the setup was a bit too balanced or ...

Very nice image, by the way!

[Ceames]

That's a great image HJ! 

I'm on the verge of moving onto guiding (kit has arrived and everything seems to be talking to each other - just need a clear night to try it out...) hopefully it will go as easily for me as it has for you! There are no possums here to cause trouble at least

C.

[Astrosurf]

Superb image! I'm so tempted to go back to DSLR imaging. I'm just not getting on with my Atik!

Alexxx

[hjw]

Superb image! I'm so tempted to go back to DSLR imaging. I'm just not getting on with my Atik!

 

Alexxx

Thanks Alexxx,

I don't think I am anywhere close to the limitations of my current setup so the temptation to go to a CCD is a long way off. The DSLR gives me more or less the image of what it would look like if I had more sensitive eyes, while narrowband CCD images are coloured in B/W pictures.

Just my primitive, simplified take on it.

Cheers

HJ

[Pete Presland]

Great image you right to be happy with it!

[hjw]

This is a post scriptum of my original post. It was my first guided image hence I was happy with the result. A night later I tried the eagle nebula (M16) with 6 minutes exposure and I noticed little, light streaks in the image and once you know they are there, they ruin the whole picture. To a lesser extend the streaks are there in the original post as well. So far, I have not seen the need for darks, but looking at the two pictures with much longer exposure times I asked myself "Could it be?!"

To cut things short, I put my camera in the fridge (the night when I took the frames was cold) and took 10 dark frames. Voila, the streaks are gone. I also re-balanced the colors a bit to reduce the green and the result is far more pleasing. 

I'm still a happy convert of guiding but will take dark frames from now on .

Clear skies!

HJ

[Knight of Clear Skies]

Interesting to hear. Darks become more important with longer exposure times and when imaging at higher temperatures. I've been a bit dubious about the value of DSLR dark frames as it can be difficult to get the sensor temperature to match that of the imaging run, but it sounds like your experiment was successful.

[StuartJPP]

Darks do help for sure, it is difficult to get exact since the beginning to the end of an imaging session can have temperature differentials of 10 or more degrees C...I am not too precise about darks because of this fact but try to keep it as close as possible. You can always run a stack with/without darks to see if you are eating away at any signal.

Don't do like I did once in the early days and run off darks in the camera bag...it heats up quite a bit more than ambient.

Regarding guiding, I recently did a run of 45 subs of 5 minutes each without dropping a single sub, so yes guiding is good.

[Diripio]

That is very very good,

Feelings of inadequacy are running rampant

[hjw]

Interesting to hear. Darks become more important with longer exposure times and when imaging at higher temperatures. I've been a bit dubious about the value of DSLR dark frames as it can be difficult to get the sensor temperature to match that of the imaging run, but it sounds like your experiment was successful.

It certainly did make a difference and yes I would do it under the same conditions next time. Below are a couple of detail crops, enlarged 400%. The processing was different therefore it is not a true comparison. But you can see, that the artifacts are reduced even though the noise increased. In a more perfect world I would get both optimized 

That's a detail without the darks substracted

And that's after the darks were added to the processing.

Not ideal, but I am convinced that the darks made a big difference. My eagle nebula was a bit out of focus but on demand I can show the before and after shots for M16 too.

Cheers

HJ

[MarsG76]

Nice image... Guide kit is definitely working... worth he battle with the possum...

[Knight of Clear Skies]

Nice illustration thanks. Clearly there are times when darks are very beneficial but some DSLR users report that they can degrade the image quality rather than improve it, so it's quite difficult to work out when they are required. My understanding is that dark current increases with both sub time and temperature, so become more worthwhile when taking long subs in warmer conditions. With short subs it might be better to take more lights instead and use kappa-sigma mode when stacking. It's very effective at removing noise and artifacts, especially when used with dithering. If you're interested it might be worth re-stacking with just dark bias frames, to get a handle on how much of the noise above is read noise and how much is dark current.

I've managed to ignore darks up to now (although I always take dark bias), but it sounds like if I start guiding I'm going to have to take them more seriously.

[Gerhard]

Fantastic image!!

And lots of food for thought in this discussion...

Sooner or later I will switch to guiding as well, and I'm guessing it would improve my images loads... Your images give us hope... :-)

I'm surprised to learn some people don't bother with darks.... I thought they were "standard" for any stacking...

I will have a go at stacking my latest images without the darks, see what the effect is... 83 second subs...

ps: the only "wildlife" I had to contend with lately were two pensioners walking by where I was set up at 23h, asking me what I was doing... :-D

[Knight of Clear Skies]

I'm surprised to learn some people don't bother with darks.... I thought they were "standard" for any stacking...

The importance of darks is definitely oversold to beginners. Here's an album of images taken without any darks or flats, although I believe they've all had dark bias frames applied. I've found dithering, kappa-sigma clipping and occasional use of noise reduction in post-processing to be sufficient so far. I'm not against darks but when conditions are good I'd rather image the night sky than my lens cap.

However, my experiences may not be relevant for everyone. As a lens imager I'm taking quite short unguided subs and working with slightly faster optics than most 'scope users, so my subs may have a higher signal-to-noise ratio to begin with. I suspect that 20 light frames will beat 10 lights and 10 darks, but it's difficult to prove or generalize this.

[Gerhard]

Ah, I agree on the "more light, less dark subs" thing...

Somebody (maybe you) already explained to me what dithering was, but my memory is ... well, faulty... Was it the repositioning of the tube/camera on the subject after a few subs?

Anyway, yesterday I had a go at stacking with just the bias, and no darks, but it didn't do much... Looked quite the same with or without the darks...

AWESOME widefield photos on flickr!!