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The Gibbous Moon with a Stellarvue SV50ED and ZWO ASI183MM

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#1 james7ca

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Posted 27 December 2018 - 10:34 AM

Taken on the morning of December 27, 2018 using a Stellarvue SV50ED (50mm aperture, f/6.6), an Astro-Physics Advanced Convertible Barlow (at 2.3X), a ZWO ASI183MM Pro camera, and a Baader CCD-filter R (red). Best 50% of 451 frames using Autostakkert!, sharpened with Registax, and finished with Photoshop CC2017.

 

This was about a 50% reduction from the final master image that was resized to conform to the CN posting guidelines. With the barlow the SV50ED was working at about f/15.2 and an effective focal length of 760mm.

 

This was a test to see how much detail I could obtain by matching the moon's full disk to the frame bounds of the ASI183 camera. To do so you need to use a focal length of about 800mm, so at 760mm I was a little under the maximum. I'd rate the seeing conditions when this image was taken as only fair (with some passing high clouds), so I expect better results in the future.

 

In addition to the image of the moon, I've included a picture of the SV50ED with the extensions used to mount the A-P barlow and the ASI183MM camera (with filter wheel). In the future I plan on using an uncooled, Color IMX183 so there will be no need for the filter wheel and the total package will be significantly smaller with less weight on the focuser.

Attached Thumbnails

  • Gibbous Moon with SV50ED (Small).jpg
  • Frankenstein SV50ED (Small).jpg

Edited by james7ca, 28 December 2018 - 05:02 AM.

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#2 james7ca

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Posted 27 December 2018 - 10:47 AM

Here is a crop out of the center of the frame with what I consider the "normal" image scale for presentation.

 

This picked up some of the craterlets near Copernicus and in the original scale image you can just barely make out some of Hadley Rille near to the landing location of Apollo 15. Neither of these features is particularly difficult until you remember that this was taken with a 50mm telescope. The crater Hadley C which has a diameter of approximately 5.4km is clearly resolved (located along Hadley Rille). This crater when viewed from earth will appear to be about 3 arc seconds wide whereas Dawes' Limit for a 50mm scope is 2.3 arc seconds.

 

In the original capture the moon was 3025 pixels high (from north to south) whereas the frame height on the IMX183 sensor is 3672 pixels (so the image used about 82% of the available height of the sensor).

 

[UPDATE]

The smallest crater that I've found that seems to be resolved is 4.9Km in diameter (measured on a LRO image), that's about 2.7 arc seconds (although there are smaller features that appear just as bright spots). I think it should be possible to get closer to Dawes' Limit on a crater, but it would require better seeing and better technique and maybe a shift to a green filter. Note that when adjusting for red light Dawes' Limit would probably be closer to 2.9 arc seconds, so I'm already pretty much there given that I used a red filter for this shot.

 

Maybe I'll try to image the Double Double in Lyra which would be a good test of the optics (and seeing conditions). However, that target is getting pretty low in the sky so that may make it somewhat difficult (impossible?). Those double stars have separations of 2.3 and 2.4 arc seconds so I think it would be very difficult to image a clean "split" with a 50mm scope. I've resolved them using an AT72ED, but I suspect that maybe a 60mm scope should be a more reasonable limit for this task. That said, I have resolved a 0.9 arc second double in blue light using a 5" refractor and scaling that down to 50mm would indicate something around 2.3 arc seconds as a limit. But, it would require really, really good seeing with Lyra being so low in the sky.

[/UPDATE]

Attached Thumbnails

  • Gibbous Moon with SV50ED (Detail).jpg

Edited by james7ca, 28 December 2018 - 05:03 AM.

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#3 Achernar

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Posted 28 December 2018 - 09:03 AM

Impressive image, and I am amazed at the resolution you got with a 50mm refractor.

 

Taras



#4 james7ca

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Posted 28 December 2018 - 09:36 AM

Taras, thanks.

 

I'm trying to assemble a system that will image the entire disk of the moon using a color Sony IMX183 sensor while also coming as close as possible to the critical sampling for the sensor/scope combination. That means a system with an 800mm focal length and an f-ratio near to f/15. So, maybe something between 50mm and 60mm in aperture with a fully corrected field that would be about 10mm in diameter. Unfortunately, it seems to be a little difficult to find something like that.

 

A good 60mm refractor at around f/13 would probably be ideal, but they don't make many scopes like that today. Either that or a small reflector at between f/8 and f/10. There is a 76mm f/9.2 Newtonian that is sold under quite a few brand names but I don't think they can reach focus with a camera. Another option is a small ED or APO refractor with a barlow, but those are kind of expensive (at least given the limited use that this system will see -- just full-disk images of the moon).



#5 Achernar

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Posted 28 December 2018 - 09:44 AM

Taras, thanks.

 

I'm trying to assemble a system that will image the entire disk of the moon using a color Sony IMX183 sensor while also coming as close as possible to the critical sampling for the sensor/scope combination. That means a system with an 800mm focal length and an f-ratio near to f/15. So, maybe something between 50mm and 60mm in aperture with a fully corrected field that would be about 10mm in diameter. Unfortunately, it seems to be a little difficult to find something like that.

 

A good 60mm refractor at around f/13 would probably be ideal, but they don't make many scopes like that today. Either that or a small reflector at between f/8 and f/10. There is a 76mm f/9.2 Newtonian that is sold under quite a few brand names but I don't think they can reach focus with a camera. Another option is a small ED or APO refractor with a barlow, but those are kind of expensive (at least given the limited use that this system will see -- just full-disk images of the moon).

 

What you're describing sounds like an ideal system for imaging the Sun too with an over the aperture solar filter, and not just during an eclipse.

 

Taras



#6 james7ca

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Posted 28 December 2018 - 10:09 AM

The SV50ED is a candidate, but it's also my primary guide scope so I'd prefer not to have to switch constantly between each function.

 

Stellarvue marketed a 60mm, f/5.5 refractor with FPL-53 glass which would be a step up from the SV50ED but they dropped it from their lineup about one year ago and I don't think anyone else is currently selling it.

 

Astro-Tech makes f/6 doublets with FPL-53 glass in 60mm and 72mm apertures, but no one seems to have those in stock. Beyond that there is the WO ZENITHSTAR 73, F/5.9 but that's getting kind of expensive ($600 to $700 in the configuration that I'd like). They also make a less expensive 61mm f/5.9 at about $500.

 

One additional preference, I'd like a fully threaded camera connection and that's one reason why I like the ZENITHSTAR 73 as they sell an M48 adapter that threads directly into their 2.5" R&P focuser.


Edited by james7ca, 28 December 2018 - 10:14 AM.


#7 Tom Glenn

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Posted 29 December 2018 - 12:37 AM

Very nice looking image James, and yet another example of how small scopes can do quite well on the Moon.  The other nice thing about images such as these, is that they can be acquired in seeing conditions that would be quite disappointing with a larger scope, yet can still reach nearly the diffraction limit in a small scope.  



#8 james7ca

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Posted 29 December 2018 - 01:34 AM

Tom, thanks for the notice.

 

I may have changed my plans for a dedicated system for full-disk lunar imaging. I have an old AT72ED which probably wouldn't work that well with a color camera but I'm going to try to use that system with a barlow and then image with either a 10nm Baader Solar Continuum filter (green) under good seeing or a Baader 610nm Long Pass filter during times of lesser seeing.

 

I think I can also go a little longer in focal length and still cover the full disk of the moon, so maybe 820mm and that means a 1.9X barlow for the AT72ED (f/ratio about 11.4, which should be fine for critical sampling with a mono IMX183 camera). I know that my AT72ED produces pretty good images on axis, although it does have chromatic aberration so that's why I've decided to go mono.

 

In fact, I may just try green and red CCD filters for those two seeing conditions since a red CCD filter blocks some of the longer IR.

 

That said I have done full-color imaging of the moon using an APS-C camera with the AT72ED and a Baader semi-APO filter and it wasn't too bad.

 

It might have a little difficulty covering the full 0.5 degrees of the moon, but it shouldn't be any worse there than a more expensive f/6 APO and the smaller SV50ED f/6.6 looks like it did fine on field coverage.


Edited by james7ca, 29 December 2018 - 02:18 AM.


#9 tholan

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Posted 01 January 2019 - 11:38 AM

Very nice.



#10 james7ca

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Posted 01 January 2019 - 07:45 PM

Tholan, thanks.

 

You might want to compare this image to one I took a few days later with an Astro-Tech AT72ED. LINK

 

They are somewhat similar although I haven't had any nights yet with seeing conditions that can really take advantage of either of these scopes.




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