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Camera recommendations for an Edge 11

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#1 Lead_Weight

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Posted 14 February 2019 - 08:16 PM

I've picked up a used one, and am having it cleaned. Only 3 years old. I'm going to image with it reduced .7x using Celestron's reducer. I'm on a CGX mount, and doubt I can image at the native focal length without issues.

 

My intent is to image small galaxies, planetary nebula, and some planets. 

 

Current cameras, ZWO ASI1600MM-C, ASI224MC, ASI290MM Mini. with 31mm Astrodon filters.

 

Should I stick with the existing camera, or get something with larger pixels? I think the 224 will be fine for planets. But possibly need something for DSOs.

 

OAG, guiding needs possibly. Looking to get a focuser as well.

 

I have no existing accessories for this thing either. Any considerations for cooling, etc?

 

No real budget at this point. Just looking to see what I should consider.

 

Thanks.



#2 GregsCNAccount

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Posted 15 February 2019 - 12:33 AM

All of your cameras have pixels 3.75 um or smaller.  That's really way too small for the HD1100 at f/7 for DSO imaging.  I have the same scope at f/7 and use a QHY10 with 6.05 um pixels which yields 0.62 arcseconds per pixel.  The central spot size is around 12 um with this set up, so the QHY10 has about optimal pixel scale for a fully sampled image if seeing conditions were ideal, which they never are, of course.  So an even larger pixel scale would be reasonable.  An alternative would be to bin 2x2 with your current cameras which would give a 2 times larger image scale and 4 time the full well capacity

 

One of the advantages of larger pixels is the larger full well capacity.  This increases the potential dynamic range that can be captured in a single subframe and minimizes the saturation of bright stars which helps preserve star color in processing.

 

I highly recommend off-axis guiding at all focal lengths but especially at the longer focal lengths like 2000 mm. 

 

I have not found the need for an additional focuser.  I find that with a Bahtinov mask I can get very accurate focusing with the stock knob.  Remember to always finish focusing by turning the knob counterclockwise so you are pushing the primary mirror up hill.  I think more important is to combat the focus change with temperature that is magnified by the SCT design.  This could be done with an external focuser, but I think attacking the fundamental cause makes more sense.  I have replaced the aluminum optical tube with a carbon fiber replacement from Public Missiles.  I have very little focus change now over a 20 degree F temperature change so I can go several hours without worrying about focus.

 

You mention cooling and that is more important with a carbon fiber tube, which has less thermal conductivity than the aluminum tube and will thus cool slower.  I use the Starizona Cool Edge SCT Cooler to get the optics to ambient temperature at the start of the night.  This draws large amounts of air through the secondary opening and cools both the primary and secondary pretty quickly.  You may want to take a look at this review of both the Cool Edge and the Tempest fans that replace the rear vents:   

 

http://compubuild.co...0HD/thermal.htm  

 

I don't have the Tempest fans and have yet to do any planetary work, but I do not see any evidence of tube currents with the carbon fiber tube after initial cooling.  This may be due to the lower thermal conductivity of the carbon fiber over aluminum which keeps the side wall cooling rate closer to that of the primary mirror.  That's purely my speculation, though.


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#3 Dimperev

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Posted 15 February 2019 - 01:49 AM

    I have the same hardware, but my configuration is different.
    I use the Celestron 0.7x gearbox and the CCD47 (https://www.teleskop...pe-bis-F-8.html) 0.67x cgearbox in series with it. It is necessary to choose a little arrangement of elements for a flat field.
As a result, I have a focal ratio F5.2. The display scale with the ZWO ASI1600MM-C camera is 0.52 arc-seconds per pixel. This is a little less than my expectations, but it works well. This scale is convenient for subsequent alignment and integration of images.
     The second change that is important is the thermal insulation of the Edge 11 case and its rear panel (reflex). There have been many discussions. It works very well.

 

I wish you good luck and a clear sky!


Edited by Dimperev, 15 February 2019 - 01:56 AM.


#4 einarin

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Posted 15 February 2019 - 01:59 AM

So you have 2 reducers ?

I thought that it would work only for small chip size cameras.

How are you stars at the edge of ASI1600 ?



#5 freestar8n

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Posted 15 February 2019 - 02:54 AM

Many of my recent images are with ASI1600 at f/7 - and some are even at f/10:

 

https://www.astrobin...ers/Freestar8n/

 

If you guide well with OAG and you have good seeing, you may get stars with fwhm below 2" and for that I would want pixels the size of the ASI1600.  And even if your stars are 3-4" fwhm, the low read noise means you can bin or low pass filter to smooth the result - and have minimal negative impact from the small pixels.

 

I have also done some guidescope guided imaging with that configuration - but I haven't posted examples.  With short enough exposures (1-2 minutes) you may do ok with guidescope.  But I strongly recommend OAG for best results.

 

But I think you can get good use out of your ASI1600 and I would spend money on a good OAG and guide camera - preferably a 1.25" sensitive cmos camera.

 

Oh - and I focus with a stepper motor on the primary focusing knob directly.  As long as you remove backlash it works very well with autofocus - and greatly simplifies the imaging train.  I autofocus about every 40 minutes, and it handles temperature drift very well.

 

Frank


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#6 Dimperev

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Posted 15 February 2019 - 03:29 AM

If I am focused on the center of the frame, then the size of the star in the corner of the frame is about + 15-25%.
If I focus on 1/4 of a frame from the center, then the size of the star in the center of the frame and on the long side of the frame is + 5-7%, and in the corner of the frame is about + 10-15%. It depends a little on the filter used. For some reason, "Ha" is a little worse.
But I have not yet picked up the correct location of reducers.
This is the third option. Soon I will go to my observatory, which is located 5,000 km from my house. I hope to get good results after small changes. I hope for the weather!


Edited by Dimperev, 15 February 2019 - 03:33 AM.


#7 einarin

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Posted 15 February 2019 - 03:36 AM

Is the F5.2 calculated or platesolved(measured) value ?



#8 Dimperev

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Posted 15 February 2019 - 05:03 AM

5.2 is the measured value.
I had to reduce the distance to the camera to align the image plane.



#9 Lead_Weight

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Posted 15 February 2019 - 01:19 PM

I'm definitely going to look into the cooler. And possibly the camera with the larger sensor. OSC sounds like it might be nice to use. Since I have the 1600, might as well try it. But longer term, think I will be happier with a better sensor for this scope. 

 

Don't think I want to try dual reducers, I do want a longer focal length. Just not sure what I can manage with the mount I have. I also like the preciseness when focusing with my Moonlite's so not quite sure what direction I'll go with focusing on this thing. Wondering if that inexpensive focuser from Celestron is any good. Can't imagine its great with the inherent design issues in these things with the mirror flop. Assuming you could account for backlash and flop it might work.



#10 pyrasanth

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Posted 15 February 2019 - 01:30 PM

This is a case for the Edge 11 where a 16803 would be pretty much an ideal camera with a pixel size of 9 um. However that is quite a sizeable investment & the next best option would be to choose a sensor of around 6 um which makes the 16200 sensor ideal especially when binned 2x2 giving you a pixel size of 12 um- seems big- not at all for that image scale.

 

I used to fear binning thinking that detail would be lost but unless your on the moon, on most days, the detail is never there and your just increasing resolution and capturing nothing. Some of my best images have been at 9 um with the edge 11 ( Atik 460 at 2x2 bin). I can't wait to roll out the new 16200 camera. I've just finished shooting the dark frame set but I'm waiting for Bisque to ship me a new telescope control board as the one I have has failed. The camera is ready to go for first light and on the C14 I will have no fear of 2x2 bin giving me an image scale of 0.90 arc secs per pixel with the reducer. This pretty much mostly is the limits of my suburban seeing so I fear no data loss.

 

Have fun & clear skies to you all.


Edited by pyrasanth, 15 February 2019 - 01:30 PM.

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#11 Lead_Weight

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Posted 15 February 2019 - 04:01 PM

Yeah, I'm kinda curious how seeing is going to have an effect on a large scope. I'm outside of Houston, and it's fairly humid, so seeing is often limited due to humidity in the air or rapid changes in temp.



#12 astroian

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Posted 17 February 2019 - 05:23 AM

A good match for the C11 is the ATIK 414 camera. You can see some examples on my AstroBin page, e.g. https://astrob.in/319323/0/

The QSI6120 binned at 2x2 also appears to be a good match with the .7 reduced C11. See https://astrob.in/383345/0/

Cheers,
Ian


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