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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036138 - 08/20/13 10:03 AM

Some day, hopefully soon, I hope to have an 8300M or the QHY9 mono. They have the same chip I think but the QHY9 has 2 stage cooling and is cheaper. I'm leaning towards the QHY9M. Right now I'm using a modded Canon T3 1100D. Would the field curvature be better or worse with the T3 vs. the 8300? I think I have a slightly larger fov with my T3 than what I'd have with the 8300 so I think the curvature with my T3 would be worse. Is this correct? Thanks

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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036184 - 08/20/13 10:30 AM

The field curvature would be somewhat worse.

The T3 is 22.2mm x 14.8mm in size.
The KAF 8300 is 17.96mm x 13.52mm.

Still it probably isn't hugely worse, and you would have to crop very much to get down to 8300 size.

Edited by Madratter (08/20/13 10:30 AM)


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036333 - 08/20/13 11:59 AM

Worse with the T3?

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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036359 - 08/20/13 12:06 PM

Yes, worse with the T3 because the sensor is larger and thus extends out further where the field curvature becomes more of an issue. But as shown above, it isn't a huge difference and worse comes to worse, you just crop the edges down to 8300 size.

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036364 - 08/20/13 12:09 PM

Thats what I thought. Just planning ahead and dont want to buy something to make it worse than it is now. I'm a total camera noob and I'm trying to research what would be a good one to match with the RC. Do you think any of the KAF-8300 sensor cameras would work well?

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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036403 - 08/20/13 12:30 PM

I think a KAF 8300 based sensor will be somewhat over sampled at the Native f/8 focal length. Specifically you have a focal length of 1600mm. The 8300 pixel pitch is 5.4 microns. That gives an image scale of .7 arc-second per pixel.

If you have seeing good enough for 2 arc-seconds that is almost 3 pixel sampling instead of 2 pixels.

All that said, I would rather be somewhat over sampled than under sampled. And the Sony cameras tend to have even smaller pixels. For example the Sony 460 EX monochrome camera has pixels of 4.54 microns.

I have been imaging recently with my C8 at the native f/10 2032 mm focal length, so I am even more over sampled than you would be.

(Also in comparison, assuming you have the T3 and not the T3i, the pixel size of that is 5.1 microns).

Edited by Madratter (08/20/13 12:39 PM)


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036452 - 08/20/13 12:54 PM

Yes, I have the T3 (1100D). I believe it is 5.2 microns which would put me at 0.67 arcsec/pixel. What would you go with for this RC then? Also keep in mind though that I'd like something to work with my other scopes as well. I have an AT65EDQ and the AT8IN that I also enjoy imaging with. Thanks

Edited by rflinn68 (08/20/13 01:08 PM)


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036491 - 08/20/13 01:13 PM

The Atik-314L is 6.45 and would produce an image scale of 0.83 arcsec/pixel. Would this camera be a better choice for my RC? It would certainly "zoom" in on the smaller targets which was really why I wanted a long focal length scope. I can always continue using my T3 on the other scopes and just use the CCD on the RC.

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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036496 - 08/20/13 01:17 PM

No one camera is going to be ideal for all of those. The AT65EDQ has a focal length of only 420mm. The AT8IN is in the middle at 800mm. The AT8RC is at 1600mm.

Any camera that is sampled at 2x for the AT65EDQ is going to be way over sampled for the AT8RC.

That said, KAF-8300 is well matched to the AT8IN if your seeing is around 2.8 arc-seconds. And for wide field with scopes like the AT65 EDQ, a lot of people are under sampled and live with it.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036510 - 08/20/13 01:23 PM

The Atik-314L has not got much FOV. Personally, I would rather live with the oversampling of the 8300 (which can be mitigated by binning if you wish). Binned 2x2 the 8300 has even bigger effective pixels at 10.8 microns, and still has a larger FOV. Binned 2x2 it would be well matched for seeing of 2.8".

Of course there are other factors to consider too such as the noise of the chip, cost, etc.

Edited by Madratter (08/20/13 01:25 PM)


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036539 - 08/20/13 01:35 PM

Now I'm really confused. I got that the 8300 would be good with my AT8IN. I dont know anything about under-sampled or over-sampled or binning.

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jrcrillyAdministrator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036599 - 08/20/13 02:10 PM

Quote:

Any camera that is sampled at 2x for the AT65EDQ is going to be way over sampled for the AT8RC.




That's one reason I switched to an 8300-based camera. When I want small pixels I have them, and when I want larger ones I can bin and still have a 2MB pixel count (larger than the 314L). It is quire versatile.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036609 - 08/20/13 02:16 PM

The basic idea is this. Stars are not just points when they are imaged. Instead, they are spread out somewhat in (ideally) an image circle. According to sampling theory, you need at least 2 samples in each dimension to get the usable information that is there.

If you have less than two samples, you lose information and are under-sampled. The practical result is that your photographs will tend to have square looking stars. You can see this in many Wide Field photographs.

If you have more than two samples in each direction, you are over-sampled. The practical affect of this is that you are losing signal to noise ratio. The reason is that each of those separate pixels has noise in it and that noise tends to be higher than if a chip was made that had the larger pixels that was sampling at 2x.

Binning is a way of combining multiple pixels into one pixel. When this is done in hardware, one of the sources of noise (read noise) is minimized.

Binning has its own problems however. For example, with the 8300 chip you can get so called horizontal aliasing if a binned pixel gets saturated.

At any rate, the bottom line is that you will not find a camera that is ideal for all 3 of those telescopes. It doesn't exist.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: jrcrilly]
      #6036621 - 08/20/13 02:20 PM

Quote:

Quote:

Any camera that is sampled at 2x for the AT65EDQ is going to be way over sampled for the AT8RC.




That's one reason I switched to an 8300-based camera. When I want small pixels I have them, and when I want larger ones I can bin and still have a 2MB pixel count (larger than the 314L). It is quire versatile.




I also have an 8300 based camera (a SBIG STF-8300m). And in practice, I like it and find the binning quite useful.

However, even at 1x1, it is under-sampled on the AT65EDQ but then so is his T3.

Edited by Madratter (08/20/13 02:22 PM)


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jrcrillyAdministrator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036636 - 08/20/13 02:28 PM

Quote:

However, even at 1x1, it is under-sampled on the AT65EDQ but then so is his T3.




Yup. Anything will be - but it's not as bad as the 9 micron pixels lots of folks use at those focal lengths. That's why my STL-11000 left. Not sufficiently versatile.


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: jrcrilly]
      #6036655 - 08/20/13 02:35 PM

So what would you say is the ideal camera for each of my 3 imaging scopes. In a medium resolution class ~$2000

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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036688 - 08/20/13 02:52 PM

I can't say I have enough knowledge to make that kind of recommendation.

What I will say is that 8300 based cameras are very popular because you get a pretty reasonable FOV at a pretty reasonable pixel size at a reasonable price.

What the Sony camp will point out is the nice low noise of their sensors.

In practice what that really means is fewer hot-pixels. I find the 8300 quite liveable in that department since the software does a good job of dealing with them as long as you have good darks, flats, and some movement between frames (either from dithering, or small amounts of flexure).


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HunterofPhotons
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036844 - 08/20/13 04:09 PM

Quote:

....What the Sony camp will point out is the nice low noise of their sensors.

In practice what that really means is fewer hot-pixels.....




Are you saying that low noise sensors have fewer hot pixels?
As compared to what?
I was not aware of this correlation between 'low noise' and hot pixels and would like to learn more about it.
Can you provide a link to studies or research that establish this correlation?

dan k.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: HunterofPhotons]
      #6036888 - 08/20/13 04:37 PM

I recall that from a thread over in the CCD forum. Someone with a huge library of calibration images and such from different cameras was making this point on the Sony chips. I don't know if that is true in general or not.

I doubt I can find the article at this point.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! [Re: Madratter]
      #6036911 - 08/20/13 04:48 PM

I found the thread. See the statement by Kevin Nelson from QSI.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/ccd/Number/57...


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