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Equipment Discussions >> Electronically Assisted Astronomy

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Atl
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5740757 - 03/18/13 01:47 PM Attachment (36 downloads)

M13 at f12. 200 frames stacked.

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GlennLeDrew
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5741713 - 03/18/13 08:50 PM

Not to be a nitpicker, but I was under the impression that post-processed images are not permitted here; only single frames as would be seen 'live' are allowed. Unless software solutions which automatically do these tasks 'on the fly' are acceptable? (But then, how long would it take for 200 multi-second exposures to stack? Would this lie within the realm of semi-live viewing?)

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Atl
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Re: the ultra low end of video astronomy new [Re: GlennLeDrew]
      #5741979 - 03/18/13 10:41 PM

That is why I noted it. In this case it was NOT live or semi live. It is purely processed. The video was 15 seconds and after separating the frames I selected 200 of the best. I wasn't aware there was a rule. If so I will respect it. Thanks for the input.

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Dragon Man
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5742410 - 03/19/13 08:17 AM

Yes Atl, it has been brought up many times in the past, but new people to This section wouldn't be aware of it.

Stacking constitutes 'imaging' which is another section in Cloudy nights.
The images people want to see in here are ones that show what the camera sees 'Live' (or what is actually Semi-Live).
That way they can see how a Camera performs in a 'Live' viewing situation.
Imagine having an electronic eye to look in your telescope with. That's what we show in here.

The rule is probably buried a couple of hundred threads back

EDIT: This will give you an idea: http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4232772/page...

Edited by Dragon Man (03/19/13 08:23 AM)


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Atl
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Re: the ultra low end of video astronomy new [Re: Dragon Man]
      #5742500 - 03/19/13 09:38 AM Attachment (19 downloads)

One interesting thing I have noted is that the videos actually look better than individual frames...even if the frames in question were extracted from the video. Maybe posting video is the truest representation. So to set things straight here is the "live" version of the same image like the other images taken with the C90. I am finding that the issue with the diminuative C90 is finding the object in the eyepiece. Compared to my dob it is like looking through an opaque piece of glass. Getting the image on video once I have it centered in the eyepiece is easy. The camera enhances things substantially.

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mclewis1
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5742606 - 03/19/13 10:40 AM

Many folks will adjust an image slightly to make it more representative of what is seen on a high quality monitor (it's usually better than what shows up on a single image capture on a PC).

Viewing the video stream often does look better to me too but many video hosting sites seem to impart additional compression which doesn't help the images.

It's very clear that any more than slight tweaks can really make a substantial improvement in an image and this would now be something that isn't representative of the "live" image thus the comments about not posting images that have been extensively processed. ATL's great images show this progression very clearly as do many of Nytcam's images.

I think the best course of action is to post as many details about an image as possible. That way folks can better understand, interpret, and compare the images.


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Atl
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Re: the ultra low end of video astronomy new [Re: mclewis1]
      #5742621 - 03/19/13 10:46 AM

The processed M13 is "slightly" more detailed. It only has about a billion more stars visible...lol. The other images are completely representative of what can be seen on the screen with a camera and a c90. It would be pretty awesome to get my 12.5" dob up on a driven mount...oh well...

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Pharquart
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Reged: 11/11/09

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Re: the ultra low end of video astronomy new [Re: Atl]
      #5754523 - 03/24/13 05:25 PM

Atl,

Are you creating these images using prime focus, or are you using an afocal setup?

Brian


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Atl
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Reged: 04/13/12

Re: the ultra low end of video astronomy new [Re: Pharquart]
      #5754604 - 03/24/13 05:54 PM

I used a focal reducer for the nebula and prime focus for the cluster. Roughly 45 and 90x respectively.

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Pharquart
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5754717 - 03/24/13 06:47 PM

How are you calculating the magnification? What is the equivalent focal length of the camera?

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Atl
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Re: the ultra low end of video astronomy new [Re: Pharquart]
      #5755019 - 03/24/13 09:33 PM

The ccd is .5" and the FL is 1200mm. So actually it is 96x and 43x. I have been wanting to add some more images but the moon has been early and bright lately.

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GlennLeDrew
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5755048 - 03/24/13 09:47 PM

A magnification value ascribed to an image is arbitrary, for the result depends also on the angular size of the image on the viewer's retina. If you stick your face near your monitor, an image has a higher 'magnification' than when viewed from across the room.

To first order, one can say a detector is equivalent to an eyepiece whose focal length equals the detector's width. And so a 6mm wide CCD is about equal to a 6mm eyepiece. But this is open to debate, for one can choose a longer f.l. eyepiece having a small apparent field or one of a shorter f.l. but larger apparent field and have the same field of view.

Far better to simply state the field width, in degrees or arcminutes. This is unambiguous.


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Atl
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Re: the ultra low end of video astronomy new [Re: GlennLeDrew]
      #5755091 - 03/24/13 10:13 PM

That is definitely precise. Now for my newbie question: How does one determine and state the field width given the information I have provided?

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GlennLeDrew
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5755196 - 03/24/13 11:21 PM

Find the CCD's actual imaging area's dimensions, then divide this by the scope's focal length and take the inverse tangent.

Example, a 6mm wide chip with a 1,200mm focal length has a field width of:

ARCTAN ( 6 / 1200 ) = 0.286 degrees = 17.19 arcminutes.

Note that for such small angles it's valid to simplify like this. For larger angles, exceeding approximately 10 degrees, the correct formula is:

(ARCTAN ((CCD width / 2) / focal length)) * 2

In other words, you first calculate the semi-angle due to the tangent function, the multiply this by 2 to get the full angle.


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ccs_hello
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Re: the ultra low end of video astronomy new [Re: GlennLeDrew]
      #5755304 - 03/25/13 12:31 AM

Also can try CCD Calculator:
http://www.newastro.com/book_new/camera_app.php

Clear Skies!

ccs_hello


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Atl
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Re: the ultra low end of video astronomy new [Re: GlennLeDrew]
      #5755520 - 03/25/13 05:18 AM

Nice! Thanks for the info!

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Atl
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5768033 - 03/31/13 02:34 AM Attachment (21 downloads)

I got the C90 back in action. I am focal reduced to about F6. I thought I might try a dimmer target so here is m51 at 128x sens up.

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mclewis1
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5768698 - 03/31/13 12:23 PM

That's an absolutely great shot for 2.1s with a 90mm scope. That EXview HAD sensor is really impressive.

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Atl
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Re: the ultra low end of video astronomy new [Re: mclewis1]
      #5768739 - 03/31/13 12:49 PM

I'm dumbfounded myself. When you look through a C90 the views are very dim. The camera is doing most of the work. Even in my big dob I just see a big blob and a little blob. The whole point of my thread is that this tech is accessible at nearly any price point...and it gives me a reason to play with my little telescope.

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Atl
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Re: the ultra low end of video astronomy new [Re: Atl]
      #5769494 - 03/31/13 06:55 PM

I implemented an upgrade. I ditched the C90. It seems to have a lot of internal reflections from bright stars. I replaced it with the 114mm Orion Imaging Newtonian today. It is F3.9...so I will probably be maligned for not using an f12.5 ...lol. It did cost me much less than the C90 so economically speaking I am even lower end than before. I am still using an eq1 with a 25$ drive.

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