Newbie question

[davidowenrogers]

Hi there,

I've just joined and I'd like to say, "Hello" to all.

I've had a refractor and a 6" Newtonian on an EQ mount for many years but these were relatively modest instruments and in a moment of staggering generosity my neighbour offered my his Nexstar 5 (original version) which he purchased in the States many years ago.

A number of very kind people in a number of Astronomy suppliers have offered boundless advice and I've added Celestron X-Cel eye peices (25mm, 12mm and 9mm) a Celestron x2 barlow and a Televue x3 barlow along with a ZWO 120MC camera along with a new HP i5 laptop with lots of RAM running SharpCap 2.6, Registax 6, Castrator and VirtualDub.

The goal has been to get a "good" image of Jupiter but I'm struggling to do better than the attached image.

The scope is collumated at the start of each session. I've tried a Bhatinov mask to aid focusing and I think I can get better results without using it. What I find suprising is that the image through the eyepeice is fantastic but I can never get close to that level of image sharpness on the laptop screen. I'm putting down to poor seeing conditions and problems focusing but am very willing to accept that I may not have the patience to achieve the very best focus possible as every time I touch the focus knob the image takes an age to stabilise and the very finest of focusing moves are lost in the general abberation of atmospheric variation. There doesn't seem to be a better focuser available for this original model Nexstar nor an available motor focuser (an American company lists one but no-one has been able to supply it)

So, hello from Deddington and any suggestions other than move to Barbados and buy a 14" are very welcome!

PS - Merry Christmas.

David

[ronin]

Just I suspect a load of questions:

What frame rate is the camera running at?

What is the length of the .avi file that you are taking to stack?

How many of the captured frames are you stacking?

Frame rate should be a high as you can get without the process failing. The idea being that you get as many short duration frames and then you should extract out the good ones that occur when the atmosphere is stable for a short period.

Jupiter revolves fast and I think that the general idea is that your movie is less then 90 seconds. Otherwise the features move and cannot be aligned and stacked accurately by the software.

Try selecting the best frame and then stacking a lower matched percentage or number, the idea being you have less but those fewer are better.

It does look a little out of focus, or at least not sharp,

Is Barbados good for astronomy and are the scopes less cost there ?

[davidowenrogers]

Hello Ronin,

Many thanks for responding.

I'm taking 30 second series of images and allowing 60 seconds to refocus and recentre the planet before the next set.

There are about 160 images per series and I'm guessing at the best 80% of images in Registax.

[ZWO ASI120MC]
Pan=0
Tilt=0
Output Format=AVI files (*.avi)
Binning=1
Capture Area=1280x960
ColourSpace=RGB24
Sensor Temp=5
Discard Split Frames=Off
High Speed Mode=On
Turbo USB=80(Auto)
Flip Image=None
Frame Rate Limit=Maximum
Gain=50(Auto)
Exposure (ms)=0.05
Timestamp Frames=Off
White Bal (=95
White Bal ®=52
Brightness=0
Gamma=50
AutoExpMaxGain=50
AutoExpMaxExp=30

[jsmoraes]

Planetary image depends very much from good quality of atmosphere. Focus is very important and actually you can lost many time do get the best one.

Did you use barlow ? With it you get bigger planet size although you can loose quality of image because you catch more the refraction.

I use ASI120MC and about your information:

1) I never set brightness to zero. I use 1 to 10. I think  that  zero damage the image with noises.

2) I never set Gain more than 50 % . I use around 10 to 30 % because of noise. I use the exposition time to get good signal from the planet. If I need more gain, I use dark subtraction  option.

3) I prefer don't use capture Area with 1280 x 960. The frame rate is very slow. And there are an issue about this:

The AVI movie can not stop or wait for download of frames. If the computer can't receive the frame, the AVI will have a duplication of the previus frame. So, you think you have, for example, 100 frames, but you have actually only 50 or less different frames. You can see this at status bar of the program that capture image by two informations: captured frames and dropped frames.

4) if I capture around 1000 frames, I use only 10 to 30 % of them. To center the planet you can use the Castrator free program. To stack you can use AS!2 free program. AS!2 shows a quality graphic of the frames. Think the horizontal middle line as the limit. With it you can do a good choise of percent to use to stack.

It is better stack few very good frames than many good and bad frames. Only one bad frame can destroy your image.

About your image:

If I want to show the planet and moons I do two different set of capture. Two AVIs. One for the planet, and other for moons. I mix the result in graphic processor, masking to present only the moon over the image of planet.

Your jupiter is saturated because you tried to catch him together with moons.

For good process of details of jupiter you can use the wavelets filter from Registax 6.0. They are powerfull. 

[jsmoraes]

I forgot:

Adjust  Gama up to don't blow up the brightest area of the planet. Brightness set acts on the background, Gama will act on the planet.

[laudropb]

The fact that you have so much vibration each time you focus would suggest that the mount and tripod you are using are not steady enough for photography.

[D4N]

If there is no stock motor focuser available you could make your own if you are ok with a bit of DIY.

They are pretty cheap to make with an arduino and a stepper motor.

It seems that you are running at around 5fps, your camera can do a lot more than that even at full frame.

Test out of you get better frame rates from different USB ports or different cables. Your camera is quite heavy on the USB traffic so will be slowed down a lot by other USB devices on the same USB bus or by cables that are too long. USB hubs can also cause it to slow down.

It can also be slowed down by data transfer speeds to your storage if you are using removable media or if Windows decides it is a good time to do some indexing.

/Dan

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[davidowenrogers]

Thank you all.

I have been using a longer USB cable than supplied with the camera mostly coz I walked into the shorter cable and nearly put the lot on the floor.

I'll try 60 second series and go for a higher frame rate with a shorter USB cable and will look at making a USB focuser.

The tripod is the bog standard £150 Celestron one which probably isn't up to the job but was a keen price.

Many thanks for the tips on SharpCap and Registax - will try these recommendations.

I've tried no barlow, x2 and x3 barlows and it's certainly easier without.

Very many thanks to all, just need some good seeing.

[davidowenrogers]

Taken last night
 
Celestron Nexstar 5, x2 Barlow, ZWO ASI120MC, standard USB cable.

60 second sequence at about 10 frames per second. (578 frame AVI file 800 x 600) SharpCap 2.6

Dan suggested making a focuser and I saw one on ebay for a different scope (£35) based around a Futaba S3003 servo and some DIY wheels. Changed the bracketry to suit the Nexstar and it's certainly easier to change focus.

Dew was a new issue, I've got a sheild tube  but wondered what you all thought on heaters?04_20_15Z.bmp

[D4N]

Nice capture

I leave my heater on all the time in the winter.

A simple arrangement of resistors wired up in parallel and a PWM dimmer to control it.

/Dan

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