Fuzzy Moon - Neximage 5

[Ryohei56]

Hi.

 

I was imaging the Moon last night, but the results were a bit less than satisfying.

My equipment consists of a Celestron Nexstar 6SE and a Celestron Neximage 5 camera. A 2x Barlow was also fitted. Processing is done with Registax and Photoshop.  Now, as far as I can tell, the focussing was spot on, but due to a bit of a breeze it was near-impossible to keep the scope totally stationary at all ties. I had the scope using the lunar tracking rate, which helped keep things in the field of view long enough for me to get video clips, but none were particularly sharp.

I suspect that either the scope's wobble caused by wind will not have helped, but I also wondered whether the magnification involved was higher than my scope can reasonably cope with. I've seen online calculators, but they all seem to assume an eyepiece is used and not a webcam. Is it possible to check the total magnification, assuming a 6SE, 2x Barlow and Neximage 5?

I'd really appreciate any thoughts or suggestions

 

Alan Stewart

[spillage]

Hi Alan,

I would say that the scope and mount should be fine for this. I used my neximage 5 on my old 127slt mount with half decent results. Might be worth posting the image so other can see the issues.

cheers

Mark.

[Cornelius Varley]

26 minutes ago, Ryohei56 said:

Hi.

 

I was imaging the Moon last night, but the results were a bit less than satisfying.

My equipment consists of a Celestron Nexstar 6SE and a Celestron Neximage 5 camera. A 2x Barlow was also fitted. Processing is done with Registax and Photoshop.  Now, as far as I can tell, the focussing was spot on, but due to a bit of a breeze it was near-impossible to keep the scope totally stationary at all ties. I had the scope using the lunar tracking rate, which helped keep things in the field of view long enough for me to get video clips, but none were particularly sharp.

I suspect that either the scope's wobble caused by wind will not have helped, but I also wondered whether the magnification involved was higher than my scope can reasonably cope with. I've seen online calculators, but they all seem to assume an eyepiece is used and not a webcam. Is it possible to check the total magnification, assuming a 6SE, 2x Barlow and Neximage 5?

I'd really appreciate any thoughts or suggestions

 

Alan Stewart

Do you have a photo you can post ? It might be easier to identify the problem. Also, magnification is an irrelevant term in imaging so shouldn't be considered. The Neximage 5 has quite small pixels so you shouldn't need to use a barlow to achieve the optimum pixel scale.

[Oddsocks]

On 06/04/2017 at 12:20, Ryohei56 said:

Is it possible to check the total magnification, assuming a 6SE, 2x Barlow and Neximage 5?

For imaging the term "magnification" is rather meaningless, the important factor is "arc second per pixel" (image scale) which determines how many pixels a particular object occupies for a given telescope and camera.

The formula to calculate this is 205 x ((pixel size in microns) / (focal length of telescope in mm)) =  arc second / pixel.

For your telescope and camera without Barlow this works out as 205 x ((2.2um)/(1500mm)) = 0.300 arc sec per pixel.

For your telescope and camera with the Barlow fitted (this doubles the focal length from 1500mm to 3000mm) works out to 205 x ((2.2um)/(3000mm)) = 0.150 arc sec per pixel.

So you see that using a x 2 Barlow effectively halves the arc sec per pixel. When you know the angular size of the object you are imaging then it is fairly easy to calculate how much of the object will be captured by the camera.

But it is always easier to visualise this than sit down with a pencil, paper and calculator so you might be interested in a free planetarium program for your PC such as Stellarium or Cartes Du Ciel which once configured with your telescope focal length and aperture plus CCD sensor dimensions will display for any object in it's database the actual view that your camera will see (Field-Of-View indicators).

Link for Stellarium: http://www.stellarium.org/en_GB/

Link for Cartes Du Ciel: http://www.ap-i.net/skychart/en/start

At the bottom of this reply are examples of the field of view you should have seen last night for your telescope and camera both with and without the Barlow fitted (using a paid-for planetarium program called Starry Night).

Without seeing a sample of your image it is not possible to say why the image seems out of focus but I was imaging last night down here in Dorset and the seeing was terrible due to thin high level cloud and turbulence and in fact gave up a little after 2am with no useful images captured.

When imaging the moon and planets a really good quality Barlow is needed, the stock Barlows supplied with the basic telescope kit are often of rather poor quality and may well introduce a level of "unsharpness" so unless you are prepared to pay a little more for a good quality Barlow you will be better off imaging the moon without the Barlow, imaging at 0.3 arc sec per pixel is still going to give you a pretty good image scale. Also check what rejection settings you were using in Registax, the software will drop poor quality frames from the final stacked image but only if you tell it to and set the rejection threshold you want, if you include too many poor quality frames in the stack then the result will be rather poor, if you set a high rejection threshold then the stack will use fewer but sharper frames and the resulting image will be of higher quality so you need to play around with the settings and run Registax several times with different rejection settings to find a good compromise. In poor observing conditions I often find that using a video of over a thousand frames only fifty or so were good enough for the stacked result where in better conditions several hundred may be used.

As you reduce the arc sec per pixel by adding Barlows then the seeing becomes more important to the end result so you have to match the image scale you use on any particular session to the quality of seeing and not be tempted to push for too high an image scale.

You may also be interested in the free Autostakkert software in preference to Registax for basic frame quality sorting and image assembly then move Autostakkert's resulting image back to Registax for wavelet sharpening. Autostackert's frame quality routines and general ability have surpassed Registax for some time and only lack the wavelet sharpening routine of Registax to make it a dominant application. Link provided following: http://www.autostakkert.com

Simulated image without Barlow using Starry Night 6 PRO:

 

 

Simulated image with Barlow using Starry Night 6 PRO:

 

 

[Ryohei56]

Thank you to all who replied. Some highly technical info there, which I shall need time to digest. I'm  sure it will  benefit me, and I do appreciate the help you''ve kindly offered. 

[Pro2001]

Ryohei if you could post photos it would help you better . As we could tell the problem easily