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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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rflinn68Moderator
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Levenhuk carbon fiber 8" RC on the way!
      #6029302 - 08/16/13 02:34 PM

Mary @ Levenhuk gave me a deal I just couldnt refuse so now I'm in deeper debt. But I cant wait to see it! Should be here monday! Info and specs here

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raf1
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6029310 - 08/16/13 02:38 PM

New scopes are always exciting. Looking forward to your "first light" report.

CS, Ron


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CounterWeight
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: raf1]
      #6029482 - 08/16/13 04:11 PM

Looks like a great scope are you getting the reducer for it as well?

I'll look forward to reading your experiences. Got to have something special to inaugurate the new observatory ! Don't forget the pictures...


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6029528 - 08/16/13 04:43 PM Attachment (11 downloads)

Hey Jim.....in addition to the scope I was also "forced" to buy the ADM dual saddle for my CGEM DX to accept the Vixen dovetail of the new scope. With all this plus the new observatory under construction I'm in enough trouble with the wife. I think the reducer will have to wait a while. I need to get the scope paid for first!

Honestly, she's very supportive but I'm not gonna push it.

I'm hoping to test the observatory out sunday night. I just need to set a couple more poles in concrete tonight and tomorrow mount my gables and beams and screw on the sheet metal. Should be ready to roll the roof off by sunday evening!

Oh....you can count on some pictures of the new scope being posted by monday evening or sometime tuesday.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6029663 - 08/16/13 06:07 PM

Grats. I'll be VERY interested how that works out for you. I know that I want to replace my C8. I just haven't decided what exactly I'll be replacing it with. The Comet Hunter is one strong possibility, but this or some other other brand of it is another.

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6029674 - 08/16/13 06:11 PM

Quote:

Grats. I'll be VERY interested how that works out for you. I know that I want to replace my C8. I just haven't decided what exactly I'll be replacing it with. The Comet Hunter is one strong possibility, but this or some other other brand of it is another.




I'll let you know asap. I believe these to be the same scopes as the Astro Tech. I just got an unbelievable deal on this one and got tired of waiting for the AT carbon fiber to become available.


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frozen.kryo
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6030309 - 08/17/13 03:15 AM

Congrats on the new scope to go with your obs!

I'm also considering an RC to replace my C8, but I don't have an obs.

+1 on your first light report.


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TimN
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: frozen.kryo]
      #6030460 - 08/17/13 08:34 AM

Congratulations on the new scope. I think you are correct, it sure looks like the Astor Tech model. I have been looking at this one as well and am looking forward to seeing your images.

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: TimN]
      #6030493 - 08/17/13 08:59 AM

Quote:

Congratulations on the new scope. I think you are correct, it sure looks like the Astor Tech model. I have been looking at this one as well and am looking forward to seeing your images.




The AT's have a D-style dovetail on the bottom and Vixen on top. I needed the Losmandy style to fit my CGEM DX mount but this turned out to be a bargaining point. I ended up getting the scope and an ADM dual saddle for the CGEM for still quite a bit less than the regular price of the scope(s) alone.


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6035225 - 08/19/13 07:18 PM

Just got the scope! No dents or scratches so thats a good thing. Moon will be bright but I plan to give it a quick test run tonight. I'll let you know how I like it and post some pictures this evening or tomorrow.

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CounterWeight
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6035383 - 08/19/13 09:03 PM

Glad to hear it - I'll be staying tuned Hope you have good skies tonight.

Edited by CounterWeight (08/19/13 09:04 PM)


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SergeC
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6035427 - 08/19/13 09:38 PM

Way cool, 'grats. Look forward to your report (and images).

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: SergeC]
      #6035707 - 08/20/13 01:06 AM Attachment (9 downloads)

No report but here are a couple quick shots I took after I closed the roof tonight. I will have to learn how to collimate an RC before I can do anything else. Just a quick spin around the block tonight with the near full Moon out. It was out of collimation but it also seemed like it has some field curvature or coma. Not sure which it is with these scopes?? I hope getting it collimated will give me a flat field corner to corner because the main reason I bought this scope was for the long focal length and I dont want to have to put their 0.75X reducer/(corrector?) on it. I thought they were supposed to have a flat field without using a flattener? If anyone has any advice to pass along as far as flatteners and collimation goes on these scopes please share it with me. Anyway, here's a couple shots of it and I have 45 days to test it out and decide if I want to keep it. I hope its a good one because it sure is pretty!

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6035710 - 08/20/13 01:09 AM Attachment (8 downloads)

How the heck do you put 2 pictures in one post? Here's the other one....and yes, this is where the scope sat in the saddle and where my counterweight was with my camera attached!

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Jeff2011
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6035727 - 08/20/13 01:30 AM

That's a beauty Richard. Fits nicely in your new observatory. Perfect timing. Can't wait to see your images with it.

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CounterWeight
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Jeff2011]
      #6035837 - 08/20/13 04:07 AM

Nice , love that look of CF tubes!

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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6036040 - 08/20/13 09:07 AM

Thanks guys! Any tips on collimating it? Its not like a Schmidt-Cassegrain. It also has primary mirror adjustment screws. I wonder if I can use my laser like I do on my newts?

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SergeC
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036111 - 08/20/13 09:48 AM

I'm afraid I have to report this to the mods, since you're posting telescope porn.

That's a seriously sweet setup, certainly in looks and I'm sure in performance once you get eveything dialed in. Looking forward to your images.

Congratulations again!


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6036116 - 08/20/13 09:52 AM

I have no experience collimating them, but from what I hear, they are a bear if you have to do both the primary and the secondary. Sometimes you can do just the secondary and I would certainly start with that and see what it gets you.

As for coma, they have none. Field curvature they do have. My understanding is that for a 8300 size chip, they are pretty good even without a flattener. Stars will be very slightly oblong in the corners but not bad.

At any rate, until you get the thing collimated, any impressions of curvature in the corner are going to be worse than things really are.


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Madratter
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6036129 - 08/20/13 09:59 AM

Here is a thread that would be a good read on the amount of field curvature.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6022916/page...


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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! new [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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CounterWeight
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6037187 - 08/20/13 07:31 PM

These days,

I'd only worry if I was undersampling by a margin large enough (as John mentions) to rob you of image quality - and you won't be doing that with the 8300M. There's plenty of reason not to worry about oversampling within reason - and if the supporting chipset allows binning pixels, there goes that worry. The 8300 chip's wild popularity among the manufacturers speaks for itself - as do the images made from them so I think you can buy with confidence.

I do think it's important to understand what the expression is taking about, detail or lack of it, and where in the grand scheme it matters. For us in general, small pixels and lots of real estate = good.

More important to me is the issue of using a 'OSC' version with it's Bayer matrix for color (and it's debayered resolution in each color plane), or the mono version where every pixel can provide resolution and detail. Also look at the aperture and filter discussions as relates to focal ratio. Also if the CCD is anti blooming or not, is microlensed, and then it's temp regulation specs.

There are reasons FLI, QSI, Apogee, SBIG, others adopted the 8300 chip, and there are differences in the exact models that were brought to market. So don't assume all the same and only different $. When I was going through it all when SBIG and possibly others initially announced I found it very helpful to spreadsheet all the offering and all the specs/options between them.

Re-reading your post (trying to be certain I'm not wandering OT) I think going 'mono' 8300 at your price point may not be possible outside a fantastic deal on the used market (and I wouldn't rule it out entirely). Adding in the cost of a filter wheel and filters puts you up and out of that bracket.

With the color or 'OSC' version I'd take a look at how they get the color and what that has to do with final resolution (arcsec/pixel and over/under sample) even after all the software bells and whistles.

When I jumped into imaging I bought an OSC and then sold it after saving some more $$ for a mono variant. I was in a hurry to get started and see what it was all about.


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rflinn68Moderator
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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6038132 - 08/21/13 11:10 AM

Thanks for chiming in about CCD's Jim! I understand I wont get filters and a wheel for that price. I was talking about the camera by itself. The SBIG 8300M is on sale at Astronomics for $1995 and QHY has their QHY9 mono (8300 sensor) with a filter wheel for $2099. The QHY9 looks pretty nice to me with a 2 stage TEC cooling and the SBIG is a single stage. I'm kinda leaning toward the QHY but they havent answered my email from several days ago regarding the filter wheel. It says its a 2" filter wheel and I was wondering if it will hold the 36mm filters. I also dont know how many filters it will hold. I suspect just 5 and I'd like to have an 8 position wheel. Then I could get the LRGB filters, Ha, OIII, SII and have 1 open for exposing my flats. Is this how you do it or do you expose flats with the Luminance filter?

I was able to get the RC collimated last night........sort of It looks near perfect on the intra-focus side but it doesnt look concentric outside of focus. What causes this? Also, stars in the bottom corners look pretty good but the top corners still look pretty bad.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038173 - 08/21/13 11:31 AM

Personally, I expose my flats using the luminance filter.

EDIT: Ideally you would take a set of flats for each filter actually used.

As for the collimation problems and it changing between intra and extra focal positions, I don't know how that can happen without slop in the focuser. If the star is staying centered in the exact same place (i.e. no slop), I'm at a loss.

I'm also wondering if you have some camera tilt.

Edited by Madratter (08/21/13 11:35 AM)


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038180 - 08/21/13 11:35 AM

Quote:

have 1 open for exposing my flats. Is this how you do it or do you expose flats with the Luminance filter?





The really serious folks do flats for each filter. That does have the advantage of handling dust on the filters. I think most of us do flats through the L filter. When I use flats (which isn't always) I use the L filter. I keep my filters clean, though.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6038292 - 08/21/13 12:43 PM

Quote:

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...




Thanks for the link.
I read it and the subsequent links, but I didn't see where there was a connection between 'low noise' and the number of hot pixels.
Temperature can affect the number of hot pixels, but that was the only direct connection that was cited in a subsequent link.
It's easy to fall into the trap of assuming a correlation is evidence of a cause-and-effect. I guess I'll remain skeptical. <g>

dan k.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: jrcrilly]
      #6038293 - 08/21/13 12:43 PM Attachment (2 downloads)

Ok, After looking at these on my desktop I can see I still have work to do but you can still clearly see the difference in how it looks inside of focus vs. outside of focus. This first one is outside of focus. I was on Arcturus and at ISO 1600 even 3.2sec over-exposed it for a test like this but when I cropped it I included the star to the left.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038298 - 08/21/13 12:45 PM Attachment (3 downloads)

And here it is on the inside of focus....

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038342 - 08/21/13 01:18 PM

Argh! just lost a post?! Must have forgotten to push the button after checking it over.

What I wrote was that I agree, flatting it all depends where the offending item is. If not on the filter directly using the Lum channel seems to work just fine on both the Baader and Astrodon filters I have used.

On another tack, the SBIG and flats requires special mention because of the mechanical shutter. I have the original 'ST' version and wheel and learned quickly that I had to increase my expose times for flats very dramatically to get rid of the shutter effect - more than 2.5 seconds or ~3 seconds seems adequate. This was what drove me to getting an illuminated panel for flats.

In all my astro purchases support figures in very heavily, and SBIG is fantastic. I think it's important to mention this. Clear nights to image are a premium in cloudyopolis, and may be when the problem shows is after a long wait to image again (it can and has been months between at times) and waiting days on end for support and 'all that' just does not float my boat. Neither does getting someone who has no actual expertise or concern and urgency when I finally do get through.

SBIG has exceeded my expectations which are high. I've sent mine in twice with the filter wheel and turn around was as fast as I could hope with clear communication always from them. If I remember correctly the first visit I was out only the shipping, and they went beyond the minimum in servicing the units.

Good luck with the final tuning of the optics. Takes some patience to learn each scope's 'personality' when it comes to tweaking in the optics. When these came out there were some pretty huge threads on dialing them in, i think in the 'Cat and Cass' forum?


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6038424 - 08/21/13 02:05 PM

I can't tell much from Arcturus other than the collimation is not perfect.

The fainter star makes that completely clear. What is also clear is that there is some astigmatism. That is why the orientation of the overall oval shape changes.

I would not jump to conclusions on that. First off, the star isn't centered (I realize this is a crop so it is probably pretty close but still).

Second that astigmatism could be caused by things like camera tilt rather than the optics. Are you seeing the same behavior visually. Also, is there a diagonal involved in any way? It is very common for diagonals to be miscollimated.

Third, I am no expert on this stuff. I am a duffer at best. I would head over to the Cat/Cas forum and post there.

It is possible that it is normal for RCs to show this kind of intra/extra focal image when off axis.

At any rate, I would be very leary of making any pronouncements of optical quality until it is collimated properly.

And again, I could be all wet. The people in Cat/Cas will be much more helpful than I could ever be, simply because some of them actually know what they are talking about.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6038604 - 08/21/13 03:44 PM Attachment (2 downloads)

Thanks guys....Madratter, yes it is cropped and no I do not use a diagonal when imaging. I would be VERY interested in this astigmatism issue!! They have a 45 day return policy and I might want to take them up on that. Its not the most expensive scope in the world but it was a lot of money for me and I want a nice scope for that kind of money. Here is the image uncropped to give you an idea of where the other star was in the frame. I know Arcturus was overexposed and thats why I cropped it and included the other star.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038635 - 08/21/13 03:58 PM

That other star is so far off axis, I wouldn't make any conclusions based on it.

AND it turns out that RC telescopes have this particular abberation (astigmatism) off-axis.

http://starizona.com/acb/basics/equip_optics101_astigmatism.aspx

Edited by Madratter (08/21/13 03:59 PM)


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6038655 - 08/21/13 04:10 PM

Thanks!! This is good to know. You scared me for a minute there! I'll try to tweak on it a little more over the next night or two and hopefully get it lined out by the start of our dark window. Its way too pretty of a scope to send back.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038693 - 08/21/13 04:28 PM

But the article says they employ a "correcting lens" to eliminate any residual astigmatism. So they are calling the secondary mirror a corrector lens? Please forgive my ignorance.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6038776 - 08/21/13 05:22 PM

No. Apparently the expensive RC scopes, have lens elements (just like a normal scope might have a field flattener or coma corrector) to get rid of it.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6039030 - 08/21/13 07:39 PM

Quote:

No. Apparently the expensive RC scopes, have lens elements (just like a normal scope might have a field flattener or coma corrector) to get rid of it.




I can't think of a single example of an RC with an internal astigmatism corrector, let alone "most". I think it's just the unfamiliarity of the writer with his topic. For the most accurate information on a telescope design it's probably best to go almost anywhere other than to a vendor who sells only competing designs.

Folks who buy RC scopes tend to do so because they prefer pure reflectors. Folks who don't mind a requirement for add-on internal optics can usually save a bunch of money by selecting CDK or EdgeHD models (or Starizona's Hyperion). A couple of the top end RC vendors do offer optional flatteners, though.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: jrcrilly]
      #6039306 - 08/21/13 10:40 PM

I feel much better now after a little more tweaking with the collimation tonight. I'll post some new pics tomorrow but it looks a lot better on both sides of focus now. Now I'm ready for some dark skies!

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6039441 - 08/22/13 01:00 AM

John C,

Take a look at RCOS and DSI - the top names as far as I know in the scope design true R/C that is - both offer the corrector.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6039481 - 08/22/13 01:45 AM

Quote:

John C,

Take a look at RCOS and DSI - the top names as far as I know in the scope design true R/C that is - both offer the corrector.




Hi, Jim.

Those are both flatteners, which I did mention.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: jrcrilly]
      #6039520 - 08/22/13 02:29 AM

John - Ah... Ok, I was just going for the 'additional lensed element' in true R/C design, sorry - not wanting to muddy the waters.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: CounterWeight]
      #6039693 - 08/22/13 08:03 AM

I'm definitely happy things are looking up for you.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6039777 - 08/22/13 09:29 AM Attachment (6 downloads)

Quote:

I'm definitely happy things are looking up for you.




Thanks! I think things will be ok with it.

Does this look better to you guys? This one is extrafocal


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6039781 - 08/22/13 09:30 AM Attachment (5 downloads)

And here's an Intrafocal shot

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6039808 - 08/22/13 09:51 AM Attachment (7 downloads)

Couldnt do much more last night other than some star test and the Moon. Cant even fit all of the Moon vertically at prime focus. I might have a tiny bit more tweaking to do but I think I'm gonna love this RC. Now that I have an observatory it might not even come off the mount for a while!

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6040352 - 08/22/13 03:29 PM Attachment (8 downloads)

Sharpened it up a bit. Man I'm ready to get out and do some imaging! I missed the entire last dark window building the observatory. I'm jonesin' for some real imaging and processing now!

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6040497 - 08/22/13 05:25 PM

I've been following this thread with interest. T think this could be my next scope.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6045434 - 08/25/13 03:50 PM

Quote:

Quote:

I'm definitely happy things are looking up for you.




Thanks! I think things will be ok with it.

Does this look better to you guys? This one is extrafocal




Sorry I didn't get back to you earlier. I was out of town without access.

This is definitely looking better. These look pretty good to me.

That said, the real test is at high magnification with a 2x Barlow and something like a 7mm eyepiece.

But the images look pretty similar and things look pretty well centered.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6045508 - 08/25/13 04:49 PM Attachment (2 downloads)

A very very short test before the Moon made me pack it in Friday night. This is with the Canon T3 and cropped very slightly to 98% of the original size. Its just 4 subs of 300 seconds at ISO 800. I cant wait to really test it out. I'm hoping to get some time in on the Helix nebula next week.

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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: rflinn68]
      #6045658 - 08/25/13 06:12 PM

Looking good at least at this resolution. I'll look forward to seeing it with more subs.

In my experience, the critical test of optics for DSO astrophotography is on small galaxies and how much detail they reveal. There differences in FWHM will really show up.


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Re: Levenhuk carbon fiber 8" RC on the way! new [Re: Madratter]
      #6045893 - 08/25/13 08:26 PM

Quote:

A very very short test before the Moon made me pack it in Friday night.




Richard, you know you can't say that 'pack it in' anymore with that ROR!

Nice test image! Like the Luna shots too!


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