Help. Bad image Saturn with NexImage

[Bigwings]

On the good side with my first attempt to use the NexImage kit I managed to find Saturn. Track it and get the camera in as well as the Barlow. The problem is the image on the Laptop was jumping around like a mad thing and I couldnt seem to get a sharp image. Is this just air currents at higher magnification or am I not using the kit correctly.

Here is the very bad pic but at least it shows its the right target.

Thanks for the help I know will come.

Mike

[Sam]

Mike,

If the image is bouncing around a lot then that is probably the seeing causing trouble. For imaging planets (and anything really) it takes ages to get the focus just right. You also have to adjust the gain and frame rate to get a good image that's not too bright.

Sam

[dweller25]

Hello Mike,

The image is overexposed - try reducing Gain and then Brightness - do it in that order as more gain = more grain !!

Jiggles when imaging could have been down to the wind ?? or the platform you had the scope on is not stable ?? or the magnification you used - a x2 Barlow will be enough for this scope.

You did well to get the image on chip - quite hard at first.

Keep going - it's a fair start.

[dark knight]

That looks just like my attempts too. It is so difficult to get good focus, I've still not got the hang of it.

[gataki]

Hi,

Thank you for starting this thread ~ I was thinking of posting a picture of my first attempts at imaging Saturn (I was using my Nexstar 102) in the hope of getting some advice - but wasn't brave enough!

I followed the instructions in the 'webcam tutorial' that I found in this forum but when it came to the last stage of switching from the webcam to the barlow and webcam, although Saturn was briefly in view it moved too quickly. The goto's tracking is excellent but I guess at that magnification it was just too windy here (Surrey) last night.

I'll just have to keep trying!

Well done though - at least your picture looks like Saturn - which is more than can be said for my effort!!

Back to the drawing board!

Liz

[BlueAstra]

I have a NexImage too, and in my (little!) experience the image bouncing around is nearly always the wind on the scope or footfall vibration near the scope. The other cause is touching the scope to focus or move the goto. I invested in a motorised focus attachment which means I never have to touch the scope to focus it.

Focus on a star first with the Neximage before moving to Saturn. You may have to search for it since you are now relying on the finder for location. It does look a little overexposed. Try to adjust the gain, exposure time, fps (down) and the brightnes up until you can just see it on the laptop.

[dark knight]

Are they sensitive enough to even pick a star up??

[BlueAstra]

Go for the brightest star you can see near the target. Saturn's magnitude is about +0.7, and you can see that with the Neximage, so any star with similar magnitude should do. eg Regulus +1.4, Arcturus -0.1.

[mgregory]

I thought you did pretty good Bigwings!

I was trying my new Neximage and my ETX-70 last night and couldn't get much out of it. I couldn't get the neximage to center with my barlow. I'll try again tonight on Saturn. But hey, you got the rings. I could only get a ball of light.

[Psychobilly]

I agree that a pretty good foundation to build on...

Saturn is really past its best now as its dropping low down in the west soon after dusk so you hav a lot of relatively unstable atmosphere to image through as the air hasn't had much time to cool down...

Like others have said focus on a bright star if possible using a Mask and then slew to Saturn seeing as your using an SCT the closer the star is to Saturn the better as you will have some mirror flop to "worry" about...

I also use a motor focuser which makes life a lot easier...

Peter...

[Milamber]

That's not bad - but it *is* over-exposed. When you are recording, the image needs to be very dim, many make the mistake of upping the gain 'til they can see a good pic of the target then hit record. Remember you are going to be adding lots of these frames together so a set of bright images is going to cause an over-exposed final image. I am sure if you think about it you will see why this will also make the image appear out of focus... point your camera/scope again at saturn and turn the gain up... despite a good focus, the image will get larger - this is what you see in your pic - the washover into surrounding pixels on the sensor from over-exposure (and also from seeing...).

Also remember that at this magnification and bearing in mind Saturn's current position, it will be jumping around because of seeing. (Seeing is like laying at the bottom of a swimming pool looking at a light above the pool, on a good day the water is only a few inches deep, on a bad day it's 10 feet!). You may have the most perfectly-rigid mount ever but you cannot stop this. The only way to fight is is a faster frame rate - which is why such cameras as the Lumenera and DMK have become popular for planetary, they increase your chances of hitting the good bit of seeing that happens now and then. If seeing is bad, your image will not only dance around, it will distort as well. If you try to stack a pile of frames of a distorted Saturn (a set where in many of the frames, Saturn is egg shaped due to the seeing - though not always egg shaped in the same orientation) you will also get a seemingly out of focus and over exposed image image since there will be more images with Saturn centre (over exposed) overlaid by a lesser amount of Saturn distorted (apparently out of focus).

As a starter it is an excellent pic, I am sure once you understand the mechanics of what you are trying to do then your images will improve rapidly. One way to improve this image would be to look through the stack and find a fram where Saturn is the right shape and use that as your reference frame. Set the rejection % quite high (maybe so you only get left with 10%) and run the stacking - you could be surprised at what you get since you look to have a good capture there if you can only ditch the rough frames. Be brutal, more frames is not always best.

Arthur

[MeerkatinBKK]

Since you're using the same setup as me I'll add my tuppence to the good info already given here.

For me the biggest single boost in getting Saturn to stay on the chip using the 8SE was to suspend the powertank (approx 9kg/20lbs) from the tripod tray using a belt. I've since bought a luggage strap to do the same thing allowing me to keep my trousers on! Even when focussing, the mount/tripod is almost rock-steady - not something the 8SE is famous for. In fact until I did this, using the NexImage with even just a 2x barlow was basically impossible. Having said that, I'll still invest in a motor focuser at some point.

It's set up on grass too which helps - if you're on a hard surface it's recommended getting antivibration pads (NB I haven't used these so can't comment on how good they are).

As to the image itself, as others have said you need to adjust gain/brightness right down so you can almost barely see the planet. It looks wrong when you're imaging, but will right itself after stacking and rebrightening later on. Make sure to note down what settings you use for each take and see how they compare.

You might also want to check out the simple and reversible RAW modification for the NexImage; I posted details and an example of what you might expect here (albeit when Saturn was much higher in the sky than it will be for you now), and as you can see it's a long way from my earliest images with the cam, shown here!

Finally, if you're still using the AMCap software that comes with the cam, I'd really recommend trying wxAstroCapture instead, available for free here. I found it much less clunky (although that could just be something to do with my laptop).

Hope this helps,

Nick

[MeerkatinBKK]

To give you an idea of just how dim the image might look while capturing, have a look at the three images in my album, here. These were uploaded after a request by PM as to how I did the workflow for my image linked to above. The third image in the album is simply the first raw frame of the capture avi, with nothing done to it at all (except blown to twice the size by accident). Very dark!

Nick

[brianb]

What other people have said ... turn the gain up and the gamma down for focusing, then turn the gain down & increase exposure (if necessary) to make the actual exposure. It takes me ~5 mins to get something like a satisfactory focus even with a really solid mount. Jupiter is easier, focus on one of the moons, but Titan is a bit too faint to be useful even with an 11" scope.

Your image is way over exposed, you need to have some space between the brightest pixels and saturation as sharpening uses up the leeway. Try various exposures until you get it right. Make notes of what you're doing .... with experience much less trial & error will be necessary.