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04-21-2016, 11:59 AM - 1 Like   #16
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Q10 and 1000mm Focal Length

It so happened that a front passed the other night, which in my climate usually means some winds, but also a very transparent and - most importantly of all - a steadier seeing than usual. So, although I had some sleep to attend to, I dragged out my vintage 4" f/10 Newtonian (anno 1980) and made a quick and dirty north-south alignment.


Pentax Q10 on Vixen Polaris R100-L Newtonian and Mead LX75 Equatorial Mount

First a look at Jupiter at 1000mm F.L.:


Composite of 'long' exposure of Jupiter with Galilean Moons and 'short' exposure of Jovian disk.
10 images of 1s and 38 images of 1/200s, all at ISO400, stacked in Registax4.
54% crop of original - click on image to see a larger, 87% crop.


The 'dancing' of the moons shows that seeing is far from perfect but I cranked up the Effective Focal Length by means of a 2.5X Apochromatic Barlow Lens, in this specific set-up providing me with an EFL of about 2100mm, and kept exposure time as short as possible, providing me with this:


Single exposure: EFL= 2100mm, 1/60s at ISO800. 100% crop

And let's see, if stacking will help improve a bit:


Stack of 26 images at EFL=2100mm, 1/60s, ISO800 and 46 images at 1/30s, ISO400. 100%

Sure, with a better seeing, this could probably be a good deal better, but I am actually not at all unhappy with this first result.

Next over to the Moon. Again, stacking is mandatory for such large focal lengths, otherwise, all fine detail will be lost and one would be better off with shorter focal length ordinary lenses. Further, we are closer to Full Moon and thus, shadows are shorter and the Moon's appearance more 'flat':


The north-eastern part of Moon with Pentax Q10 and 1000mm F.L: 1/80s, ISO 100. Downsized to 20% of original Q10 frame.
48 images stacked in Registax4.
Click on image to see larger, 32% size of original image.


Still, the rugged highlands near the Moon's south pole provide some interesting views worth a closer look:


The region around Mare Humorum on the Moon with Pentax Q10 and 1000mm F.L: 1/80s, ISO 100.
48 images stacked in Registax4.
42% crop. Click on image to see larger, 67% crop.


All images were shot as raw (DNG) and pre-processed in Digital Camera Utility 5 and a slight post-processing (curves and levels) was applied in PhotoImpact X3. Was it worth the effort and some hours of lost sleep? For me it was. I am truly happy with my 'new' Pentax Q10!

04-21-2016, 05:13 PM   #17
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Terrific astrophotography Stone G! Planets are hard to capture. Very well done.

When stacking 48 shots to make one image, how do you make sure they are all sharp? If the camera/scope doesn't track perfectly for the whole length of time, will the stacking program line up all the images?
Thanks for sharing.
barondla
04-21-2016, 11:42 PM   #18
kwb
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Hey Stone G, thanks again for sharing. I feel your sense of awesomeness permeating through your pictures and your writing, which makes me happy.
And your Newtonian delivers! I have a 3" Newtonian (OK technically it's my daughter's) and two refractors, they all have pros and cons, but as far as the sharpness/price ratio is concerned, Newtonian is the king.

Best,
kwb

Last edited by kwb; 04-21-2016 at 11:43 PM. Reason: typo, of my own name!!
04-22-2016, 08:40 AM   #19
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Thank you BigMackCam, kwb and barondla. I'm glad that I didn't disapoint you (and didn't disgrace the Q10)!


QuoteOriginally posted by barondla Quote
When stacking 48 shots to make one image, how do you make sure they are all sharp? If the camera/scope doesn't track perfectly for the whole length of time, will the stacking program line up all the images?
The technique in brief is as follows: You select manually the best frame in your series and place one or more reference points on that frame. Registax will then align the other frames according to these points - and some drift from frame to frame is acceptable, as was the case with my crude alignment. If in doubt, Registax will ask you if you want to place your alignment point(s) manually on frames, where Registax cannot do so automatically. Furthermore, in this alignment process, Registax will assign a quality rating to each frame and at the end of the alignment process it will suggest a limit, based upon the quality ranking, to the number of frames being used for the stacking. You can then accept that suggestion or manually override it and include more frames. In my case, I let Registax decide, and I seem to remember that some 50-60% of the 48 frames were actually used.

QuoteOriginally posted by kwb Quote
And your Newtonian delivers! I have a 3" Newtonian (OK technically it's my daughter's) and two refractors, they all have pros and cons, but as far as the sharpness/price ratio is concerned, Newtonian is the king.
Yes, small, f/10 Newtonians (with good, parabolic mirrors) may produce almost refractor-like results. They may not be fast enough for most deep-sky work, but they are wonderfully forgiving in respect of errors in collimation and they are indeed very cost-effective tools for lunar and planetary photograhy.

04-22-2016, 01:47 PM   #20
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Thanks for the info Stone G. Might have to try this some day. Wish it were easier to get scopes tracking accurately.
You are doing a great job with the astro Q!
Thanks
barondla
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