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Delta Cyg, Pi Aql

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#1 Bonco

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Posted 04 November 2013 - 04:11 PM

Had a stunning, clear split of Delta Cyg with my 75mm f/16 @250X. I remember over the years many wrote this was a good test object for a 6 inch. I've found that smaller scopes all the way down to 60mm can view the secondary. Pi Aql was much tougher but was a dim figure 8. My polluted skies didn't help the brightness factor. None the less it was a nice view for a 3 inch telescope. Bill

#2 Asbytec

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Posted 05 November 2013 - 08:53 PM

You know, at a sep of 2.7" arc and delta mag 3.4, it might seem difficult in a smaller aperture. The companion is relatively dim and not too far from the primary. But with the ease I observed it in a 6" at (40x and 50x per inch), surely it can be had in a smaller aperture. Especially in an unobstructed aperture with more light in the discs and less in the rings. I would not consider this a real test for a 6", though. It was just too easy. It may be a test for a 75mm scope, especially in light polluted skies. Your first dark space is at 1.84" already, and the first ring is approaching that separation at ~2.5" arc. So, well done.

It's curious you were at 250x, the same as my observation at 40x per inch. At that magnification, there is nothing more to see, but surely image scale helped discern the companion from the brighter primary. I found it a bit easier at 320x than 240x.

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#3 Cotts

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Posted 05 November 2013 - 11:13 PM

Delta Cyg. 8-inch f/15.5 TEC MakCass, Canon 60Da in 640x480 movie crop mode, best 20 frames selected and stacked in Lynkeos software. No other processing. Seeing was about Pickering 4-6, that is to say, pretty crummy.

Dave

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#4 Asbytec

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Posted 06 November 2013 - 05:48 AM

Dave, nice image...that certainly looks like Delta Cyg. We even have the same orientation. Weird. :)

Maybe some smarter folks can chime in, but is it possible to match your subject to the focal length and cover an optimum number of pixels for higher res images? I started learning imaging back when imaging was in it's infancy (when less capable equipment was twice as expensive.) But, it has advanced well beyond my knowledge at this point. I'm sure there is a lot to learn about getting the chip and focal length to work at some optimum.

#5 Cotts

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Posted 06 November 2013 - 07:15 AM

I'm shooting at 3100mm focal length. I can't remember my pixel size at the moment. I'll figure out my "arcsec per pixel" ratio later today.

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#6 Cotts

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Posted 06 November 2013 - 08:41 AM

So, here are my numbers.

Pixel size on canon 60Da. 4.31 microns

Focal length. 3100 mm

Full field of view. 24' 43" x 16' 30". (5184 x 3456 pixels)

Crop field of view: 3' 3" x 2' 17". or 183" x 137". (640 x 480 pixels)

And the most important number: Sampling is 0.286 arcsec per pixel. Since the resolution limit for my scope is about 0.5 arcsec I am probably oversampling somewhat causing me to lose a bit of magnitude reach. In terms of high resolution, though, I don't see how I can improve the resolution of my pictures... The seeing is the limiting factor....

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#7 Asbytec

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Posted 06 November 2013 - 10:25 AM

Yea, seeing doesn't help. I was just wondering if you are at optimum focal ratio relative to the pixel size. I cannot remember how to calculate that, maybe your numbers are just fine.

#8 Bonco

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Posted 06 November 2013 - 03:53 PM

You know, at a sep of 2.7" arc and delta mag 3.4, it might seem difficult in a smaller aperture. The companion is relatively dim and not too far from the primary. But with the ease I observed it in a 6" at (40x and 50x per inch), surely it can be had in a smaller aperture. Especially in an unobstructed aperture with more light in the discs and less in the rings. I would not consider this a real test for a 6", though. It was just too easy. It may be a test for a 75mm scope, especially in light polluted skies. Your first dark space is at 1.84" already, and the first ring is approaching that separation at ~2.5" arc. So, well done.

It's curious you were at 250x, the same as my observation at 40x per inch. At that magnification, there is nothing more to see, but surely image scale helped discern the companion from the brighter primary. I found it a bit easier at 320x than 240x.


I agree Delta is not a challenge for a 6 inch but back in the late 50's some thought so. Likely because they never had a quality 6 inch to view it. Even Burnham wrote, "It may be reguarded as a fairly severe test for a 3 inch or 4 inch telescope." Personaly, I think it rather easy in my 75mm but truely a "fairly severe test" for a 60mm.

Bill

#9 Rutilus

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Posted 06 November 2013 - 04:53 PM

With my 60mm scope I have always found it easier than with my 80mm. In the 80mm scope the secondry of Delta sits in the diffraction ring,
with the 60mm it sits in the inter space between spurious disk and diffraction ring.
I will have to check my records but I'm sure that I have even managed it with a 50mm

#10 Cotts

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Posted 06 November 2013 - 04:54 PM

Norme, from what I hazily recall about the Nyquist sampling theory The ideal situation is to be at a focal length that puts the spurious, central disc of the diffraction pattern onto at most 2 adjacent pixels. So, for my scope's approximate resolving power of about 0.6" I would want about 0.3" on each pixel. My calculation gives very close to that....

If I were to, say, double my focal length to 6200mm I would have a plate scale of around 0.14" per pixel. - my diffraction pattern would be spread around a number of pixels (8?) and I would be losing a lot of gain, not being able to image faint stars etc. And, more importantly, I would not gain any resolution. The situation is analogous to using too great a magnification when observing visually - the so-called 'empty magnification'.

Perhaps someone more versed in the Nyquist Theory could chime in.....

Dave

#11 Asbytec

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Posted 06 November 2013 - 08:24 PM

David, you're probably correct in your technique. It's been so long since doing any form of imaging, the thought just crossed my mind. I guess it's curious why your first ring doesn't show. That may be very normal (given seeing or image scale or something) but it triggered the question.

Bill, "Burnham wrote, 'It may be regarded as a fairly severe test for a 3 inch or 4 inch telescope.'" Yes, that sounds right.

#12 Bonco

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Posted 10 November 2013 - 03:35 PM

Had excellent view and split of Delta with my 6omm using original .965 eyepieces. Detected with a 9mm (100X), better view with 7mm (128X). Pickering about a 7.
Bill






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