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Refractors vs SCTs and Maks for uneven doubles

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#26 7331Peg

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Posted 06 January 2013 - 01:13 AM

Hi John,

Sorry, I didn't mean to put words in you mouth or imply you said something specific. I guess what I was getting at was the message I was taking away from your post, i.e. you found refractor images to be better.

There's no doubt I can see the effect of the CO. But in some cases it comes to light grasp too and that's where the SCT's have the advantage.

Actually one question about your previous use experience with the SCT's. Where did you store them? Were you having to deal with any kind of cool down other than relative drops through the night?

Clear skies,


I've always made sure the SCT's get plenty of time to cool down because they're kept in the house, along with the refractors.

Temperatures here rarely fall below 40 degrees, so acclimation isn't a huge issue, and rapidly falling temperatures are rare. I'm a stickler for collimating the SCT's, too, so no issue there.

I would agree that the larger aperture of an SCT can be an advantage on the dimmer pairs that are tough to get with a six inch refractor. But even then, I can't recall ever splitting a faint pair with an eight inch SCT that I couldn't also split with a six inch refractor.


John :refractor:

#27 WRAK

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Posted 06 January 2013 - 04:34 AM

Over perform...

I don't know what that entails, ...


It means a compliment for significantly "beating" the Dawes limit even if the term "limit" is not correctly used here as it is an average value from empirical data and therefore prone to be "beaten" under favorable conditions with some 50% probability. But still you have to do it as it is not this easy.
Wilfried

#28 Asbytec

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Posted 06 January 2013 - 06:01 AM

Wilfred, here's a list for tonight. I picked some stars with fairly bright primaries and seps ranging from as close to Dawes (thank you, by the way) as possible out to about 2" arc.

WDS04348+2242 STF562 4,5793 22,692 1,9 6,82 9,94 135
WDS03544+1601 BOV28 3,9066 16,017 0,9 7,2 8,60 154
WDS04160+3002 STT78 4,2673 30,036 2 7,82 10,49 137
WDS05055+1948 STT95 5,0922 19,807 0,9 7,02 7,56 140
WDS05436+1300 A117 5,7267 12,996 0,8 8,81 9,24 163
STF554 04h30m06s +15°38' 1.7 5.7 7.8 13
STF749 AB 05h37m06s +26°55' 0.7 6.5 6.6 24

I'll work more of the list above as time permits. Results later tonight or tomorrow.

#29 Asbytec

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Posted 06 January 2013 - 09:49 AM

Observing report from some of Wilfred's Tau list and two of my own. Some unequal pairs, some equal pairs. All of them under 2" arc sep.

http://www.cloudynig...ber=5607971&...

#30 fred1871

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Posted 06 January 2013 - 07:36 PM

Wilfried, thanks for the Taurus doubles list - it's quite a collection. Your "aperture needed" numbers on the far right - the sorting order of the list - are a bonus because we can evaluate the usefulness of the current formula from that.

I will say that I think we have, broadly, two types of doubles listed here, as well as some intermediate pairs and near equal pairs - and these classes will give different results with telescopes around 15cm aperture.

Class 1 is uneven pairs that have a reasonably bright companion, so typically a bright primary as well. Class 2 are dimmer, and are likely impacted by both light pollution, and by the reduced capacity of the eye to see at very low light levels. I think they're Lewis's two categories of "bright uneven pairs" and "faint uneven pairs".

So, for example, among the "bright uneven pairs" we would have STF 562, LEI4, BU 1238.

More challenging due to dim magnitudes are pairs such as BU 536 or A 2419 (possible with 18cm refractor - with smaller? haven't tried yet); CHR 213; and pairs such as A 117 where you have 9th magnitude stars closer than 1 arcsecond - I've seen some of these with an 18cm refractor, but those I've looked at with a 14cm refractor show the effect of too little light combined with being near the Dawes Limit figure for bright pairs - generally too difficult.

There are also intermediate pairs (good) such as BU 91. So there's a good gradation of difficulty.

I'm inclined to the view that the difficulty index, implied by the aperture numbers given, does not fit real world observing as well as might be hoped. For example, I'd expect STT 78 to be slightly easier than STF 562 because of the smaller delta-m (2.67 versus 3.12) at the same separation despite the secondary star being a 1/2 magnitude fainter - unless you're observing in heavy light pollution or bright moonlight. Mag 10.5 is not too bad with around 15cm aperture - my experience in middling light pollution is that close secondary stars become noticeably more difficult at mag 11.0, quite a lot harder still at 11.5, and are very difficult at mag 12.0 with telescopes of 14 and 15cm. The drop from 10.0 to 10.5 is less significant than from 10.5 to 11.0 (etc). For smaller telescopes, 10.5 will be noticeably harder - I have a short 80mm refractor and notice the difference compared to the 140mm (3x the light-gathering is striking on fainter stars).

So I'd also expect BU 91 (despite Dm of 2.5) to be possible with 15cm; but unlikely for A 117 (9th mag components, DL separation). Based on past experience, the 18cm apo I once had the use of would show both.

One small advantage I'd mention here is slightly greater light throughput for refractors compared to some SCT/Mak systems and basic Newtonians. My 14cm refractor has about the same light throughput as the 6-inch (15cm) f/8 Newtonian I had for many years. That can help with threshhold stars. Some Maks appear to be slightly low on throughput - some recent SCTs are surprisingly bright (such as Celestron's XLT versions).

The list has a good collection of doubles. There are several on it I had overlooked and will now observe. :)

Re BOV 28 - that's one of quite a few doubles, particularly in Taurus, that have IR magnitudes instead of V (visual) magnitudes - the warning is the 'K' in the notes column indicating an IR-band magnitude. They're not bright in terms of V magnitudes.

#31 fred1871

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Posted 06 January 2013 - 07:47 PM

Gord, thanks for the information on your 10-inch Newtonian. It sounds very nice. Having the primary mirror re-worked by a master mirror maker is a good step - I've come across a similar upgrade here, where the original mirror (Meade in this case) was marginal, the reworked version is superb.

I can only agree that refractors, if good, give "cleaner" images of stars than mirrored scopes. But the aperture advantage of the mirrors, if they're good, will outperform the smaller refractor. Aesthetics vs performance? Like many observers I incline to have both types of scope.

#32 fred1871

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Posted 06 January 2013 - 11:39 PM

Norme, in one of your notes above, you asked:

Does Sissy Haas research include variations in ring brightness with CO and the intensity of the central disc of the companion

to which the answer is "no". That I think is a limitation with her project, unless there's an intention to analyse results later with the CO being taken into account, at least nominally.

But there are a lot of variable factors that need to be known - observer experience, thermal issues, optical quality, as well as CO. I don't know if she'll get enough data on these other factors to make a meaningful analysis of their possible effects.

I'm inclined to think that the pessimism about the project expressed by Neil English and some others has a degree of justification. But I'm also of the view that we can get some reasonable parameters set up from the Haas project and similar studies, such as Wilfried (WRAK) is attempting.

Past attempts? - It's pretty clear that Lewis's work a century ago did not adequately analyse the data sets he collected. More can be learnt by re-analysing Lewis's data. Treanor offered useful ideas, based on Rayleigh. Peterson has only minor relevance. Chris Lord made a big attempt on the issue, but as Wilfried notes, and I agree, Lord's analysis breaks down in some areas. Overall, I don't think it's the answer we're looking for, and Lord also doesn't seem to account for CO issues.

The Haas table published in her Double Star book is simply an analysis based on published results in the French Observer's guide, Revue des Constellations. It's not a result of observers deliberately pushing the boundaries - it's more in the style of "with this size scope I could see X, with a smaller one I couldn't". A not too bad starting point but not really more than that.

Hence the various threads in Double Stars forums on these matters, including this one that I thought was needed as well. And it needn't exclude Newtonians, but SCTs particularly, and Maks often, have bigger central obstructions than Newts so the effects might be more obvious on uneven close pairs.

#33 Asbytec

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Posted 07 January 2013 - 05:03 AM

Yes, I am interested in the response of close unequal doubles with respect to the CO and light redistribution. I hope some of my work might be helpful.

Maybe there is some gradient factor that can be applied, for example creating a curve from the peaks of each ring and finding a magnitude equivalent at varying radii. Then figuring out what magnitude star is needed to peak above that curve enough to be seen. I tend to see the gradient as "lumpy" because of ring brightness, if that's the main factor. There may be some general OPD difference that causes some destructive interference in the primaries minimum making close unequal pairs difficult by dimming them. Dunno, but maybe a rule of thumb can be derived and tested. It's an interesting topic pertinent for us amateurs. (And, I must confess, its enjoyable beating that rule of thumb. :) )

Anyway, I am clouded out tonight and could probably use a break. Unfortunately, I will be traveling for the remainder of our observing season, so I have about 3 weeks to toss up some observations. It's a fun thing to do, something to offer a challenge in retirement.

Edit: I am not familiar with Sissy's nor Wilfred's work. Interested to get spun up on the Wilfred's ideas on the rule of thumb. It seems so many variables affect resolution visually, you mentioned many of them. Mainly, those variables might be considered either perfect or negligible, including observer experience.

It seems the way to go is to present the unequal pair to the focal plane with enough contrast for a good chance of detection on a good night and let the observer decide. In that sense, what matters is the changing differences between the ring brightness and the peak intensity of the companion. They are inversely related with CO. The larger the obstruction, the brighter the rings and dimmer the companion's peak PSF. A brighter primary or a larger CO will offer a larger brightness radius requiring even more separation for a given dim star to poke through.

Just thinking about the topic.

#34 Asbytec

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Posted 08 January 2013 - 10:40 AM

BU 1238 report. Sorry, did not make progress on any others.

http://www.cloudynig...5611674/page...

#35 fred1871

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Posted 09 January 2013 - 07:19 PM

I'd hoped to try some of the most difficult pairs on Wilfried's list, but the weather isn't cooperating thus far - somewhat tremulous and slightly bloated star images on recent nights, not suitable for the most difficult pairs.

And my C9.25 has gone into out-of-collimation funk, and I'll have to play around with a rotated secondary and other issues before I can experiment with that as my obstructed scope. So perhaps I should devise a 30% central stop for my refractor.... to see what the difference might be.

I don't expect the look of the diffraction pattern to change radically; but uneven pairs would be impacted. That suggests a difference between real change and our ability to discern it under various conditions - straight star image, slight effect; dim secondary star close to bright star, noticeable effect. Same CO in both cases.

Christopher Taylor in the Argyle book comments on this - comparing a refractor with a New that had 37% CO, "the greater relative intensity of the rings in the reflector was so small as to be barely detectable..."
However, he elsewhere remarks, "Unequal close pairs are much more difficult than equal pairs at the same separation, especially in reflectors generating accentuated diffraction rings, in which an inequality of even 1 magnitude may cause considerable difficulty in the clear sighting of a companion anywhere near the first ring, and a magnitude disparity of 2 or only a little more makes it practically invisible".

I think that's a fair description. Taylor's reflector has a small CO, only 16% - I've found the effect (unsurprisingly) even more obvious with the Newtonians and SCTs I've used, with CO sizes in the 25% to 36% range.

#36 Asbytec

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Posted 09 January 2013 - 10:12 PM

What is the fall off in contrast for an obstructed scope out to about 3 or 4 rings compared to an unobstructed aperture. For moderate obstructions, I think it's about 10%. That might be hard to see. But, 10% more light outside the rings might reduce the SN ratio by some amount, maybe sufficiently if the companion's signal is weak to begin with.

I reduced my CO by about 10% of the aperture diameter, from 52/140 (37%) effective aperture to 42/150 (28%) full aperture. The third ring on brighter stars disappeared and the second ring dimmed and is only seen when the image is steady...on the brighter stars.

If the background noise is below the visual threshold and the companion exceeds the visual threshold, there /should/ be enough signal to noise ratio for detection to occur. No? But, somehow this may not be the case. For example, it seems a star with an easy separation at 1.6" and an otherwise easy 11th magnitude is difficult close to a moderately bright primary. Regardless, the noise is still present, so maybe we need to consider it even if it's not visible.

I hope to observe these in the coming days, they are in order of increasing required aperture. I will look for a distinct companion disc. I understand the required aperture is a figure for clear aperture, so this might be interesting especially in light of STF562 (134mm ap req) being a beautiful split. I suspect I will find a limit somewhere in (maybe before) this list, if seeing remains good.

WDS04294+2433 LEI4 4,4901 24,551 1,3 7,55 9,77 145
WDS03463+2411 BU536 3,7711 24,19 1 8,13 9,39 146
WDS03362+2959 BU1040 3,6032 29,983 3,5 7,8 11,50 154
WDS03576+1130 HU24 3,9599 11,497 1,4 8,65 10,66 159
WDS04594+2012 A2427 4,9905 20,194 4,3 8,49 11,98 159
WDS05476+2056 BU91 5,794 20,941 1,5 8,1 10,60 161
WDS05436+1300 A117 5,7267 12,996 0,8 8,81 9,24 163
WDS04458+2840 COU706 4,7639 28,661 5,9 7,1 12,00 164
WDS05013+2632 BU1238 5,0219 26,534 1,6 7,56 10,52 164

#37 fred1871

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Posted 10 January 2013 - 02:18 AM

What is the fall off in contrast for an obstructed scope out to about 3 or 4 rings compared to an unobstructed aperture. For moderate obstructions, I think it's about 10%.



Norme, the transfer of light from disc to rings runs as follows (numbers are from Sidgwick):

obstruction ratio / intensity of disc (%)

0.00 83.8%
0.15 79.5%
0.25 73.2%
0.30 68.2%
0.40 58.4%

From that, you can see that having a 30% CO (diameter, of course) puts about 32% of the light into the rings, whereas zero CO puts about 16% of the light in the rings.

Most of the light in rings is in the first and second ring; this remains true with increasing CO.

So in going from zero to 0.30 CO you've DOUBLED the amount of light in the rings. Whereas at 0.15 CO, the increase is only from 16% to 20.5%.

Incidentally, the ratio of light in rings relative to disc gets worse faster than the above comparison suggests. At 0.30 CO, disc to rings ratio is 68:32, where at zero CO it's 84:16. So in the 0.30 CO case, just over twice the light is in the disc compared to rings; in zero CO case, over 5 times the light is in the disc compared to rings.

Fortunately real world images don't look as bad as the numbers suggest. Or no one would use scopes with appreciable CO ratios.

#38 WRAK

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Posted 10 January 2013 - 03:34 AM

Lord's paper "Resolution of Unequal Binaries" (the Brayebrook observatory website is meanwhile out of service but you can find it with "http://web.archive.o...RESOLUTION.pdf") shows in page 6 a table on this topic. Most interesting are the rows indicating the magnitude differences between spurious disk and first/second/third ring. This would mean that with CO zero you can see companions in the first ring up to 4.39mag fainter than the spurious disk and with a CO of 33% this value goes down to 3.17mag. Interestingly the second ring is fainter with CO than without so the shift of energy from spurious disk to the rings seems to go primarily into the first ring.
Wilfried

#39 Asbytec

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Posted 10 January 2013 - 06:27 AM

Frank, yes, those figures agree with my approximations. Normalized to 1 (refractor), my scope puts 0.85 of the light in the central disc. Taking aberration into account, that figure drops to 0.80 (effective Strehl-like performance.) A refractor works at a peak intensity equal to it's Strehl. Advantage: refractor out to two ring radius.

On moderately bright primary stars, though, nothing past the first ring can be seen. In fact, on BU 1238, the first ring was barely seen. Yet, the companion has a magnitude that should be easy...but isn't. Does the light below the visual threshold affect a companion's peak intensity that should exceed that background diffraction by a large amount?

In other words, how does the SN ratio apply here if I cannot see the noise and should see the companion? There should be enough SN ratio for detection. That's the mystery to me.


Wilfried, thank you for the publication. Will dive into it tomorrow. Yes, it is interesting the second ring is dimmer. And I was looking for the magnitude difference to get a feel for the relative brightness of the rings. And there it is, saved me the math! :)


Anyway, never knew doubles were so interesting and challenging. It's getting dark and the skies look promising. Gotta do my observing plan. More later.

#40 Asbytec

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Posted 10 January 2013 - 10:46 AM

Clear all afternoon right up until sunset. By the time the scope cooled, completely overcast and will remain so through the weekend.

The following are on my short list, they are reasonably easy for star hopping and exist on my mag 8.5 charts.

WDS05416+1913 STF770 5,693 19,22 1,1 8,76 9,77 142
WDS03463+2411 BU536 3,7711 24,19 1 8,13 9,39 146
WDS03362+2959 BU1040 3,6032 29,983 3,5 7,8 11,50 154
WDS03576+1130 HU24 3,9599 11,497 1,4 8,65 10,66 159
WDS05476+2056 BU91 5,794 20,941 1,5 8,1 10,60 161

Will try again when the tropical disturbance passes Sunday or Monday.

Read the link above. I did not understand all of it, but it was a good read. I may have been screwing up on identifying my 2nd and 3rd ring, they are much dimmer than I thought. Mistook the 4th ring for the second. Weird, but the fourth ring seemed at the right distance, but my scale was off. No wonder a 1.6" companion was closer than I thought it should have been. That might account for its difficulty.

#41 fred1871

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Posted 10 January 2013 - 07:16 PM

Wilfried, you're correct in noting the uneven change in light distribution in the various rings as CO increases. I was careless in the wording. Essentially, the first ring continues to brighten with light transferred from the disc, with increasing CO, but the other rings vary in how much energy is transferred to them individually as CO increases. Nevertheless, total energy transfer increases in proportion to CO.

To look at an aspect of the details of that energy transfer - Rutten and van Venrooij give some overall figures for CO figures of zero, 0.25, and 0.50. The first ring gets 7% of the light with 0 CO, 18% with 0.25 CO, and 35% with 0.50 CO.

The total for the other rings is interesting - 9% for 0 CO, 9% for 0.25 CO, and 17% for 0.50 CO. The changing pattern can be seen in pictorial form in Suiter and other references. I'm also thinking that it's reflected in the contrast transfer graphs that show the effect of different obstruction ratios, as these show some differences in pattern with different obstruction ratios - though that's currently just a speculation on my part.

Lord's table is useful for estimating delta-m limits for different obstruction ratios. In this regard it provides another version of what Treanor did. That Lord thinks Treanor's modification of Rayleigh "was much too optimistic for very unequal pairs resolved using large telescopes" is essentially what Treanor himself said - hence Treanor's dividing line around 15-inches aperture, and recognition that seeing reduces large telescope effectiveness more than small telescope effectiveness.

#42 Asbytec

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Posted 11 January 2013 - 03:53 AM

This thread and pursuing difficult doubles has taken me deeper into the diffraction pattern. It's a very interesting subject, a learning experience. Some folks might be embarrassed, but I actually found some answers about what I am seeing at the smallest scales: confusion over where the second and third rings really are and what they look like.

For the longest time, I had wondered what those very thin, fairly bright dancing arcs of light were just outside the first ring. They had not the form of the first ring, nor the visible fourth ring. They are very thin and often just dancing thin arcs of light. I had always thought they might have been some sort of noise in the optic, some blur or artifact of spherical aberration, maybe contributing to some sort of Hairy Disc. So, not recognizing them as part of the pattern (just garbage), I assigned the second ring to the fourth position and assumed the second minimum was further out than it really is.

The second and third ring are extremely hard to see well, any amount of seeing disrupts them easily. The fourth ring, too, because it's broader and somewhat dim. I had only seen them once as distinct rings, the inner second ring slightly brighter than the third (prior to my CO modification.) Anyway, below is somewhat to scale of what an .3D obstructed scope pattern looks like (I am sure you've seen them.)

But, for me, the striking thing was the change in scale I have to adjust to. The rings are so very close together, and not as widely separated as I had thought. When observing a star with less than 2" arc sep, it appeared way too close to the first ring. Now, I know why. This is a learning curve provided by studying difficult double stars, and that's an interesting aspect of this type of observation. So, I discovered I had been mistaken at times. Cool.

Anyway, I think the image below (Aldebaran) is almost to scale. The radii are taken from the following link.
http://www.telescope...obstruction.htm

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#43 WRAK

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Posted 11 January 2013 - 05:28 AM

Norme, the numbers on your image are arcseconds I assume?
A simulation with the AtmosFringe program shows the effect of a smaller Airy disk and a "fatter" first ring due to CO very clearly - but this is still theory. I will try to get an empirical measurement for a 30% obstruction (compared to zero) by an optical labor.
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#44 Asbytec

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Posted 11 January 2013 - 05:45 AM

My apologies, yes, in arc seconds. I am trying to get a feel for double separation.

#45 fred1871

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Posted 12 January 2013 - 12:09 AM

Wilfried and others - I've posted brief observing notes on two more of the doubles from Wilfried's list of Taurus doubles - the note is in the thread on Taurus doubles.

In both cases the suggested aperture was greater than what I used. So these might help in providing further data points.

I'm still working on making a central obstruction for my refractor, with thin support arms. That will allow comparing unobstructed versus obstructed views with the same optics, eyepiece, observer, seeing....

#46 WRAK

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Posted 20 January 2013 - 04:45 AM

After adding some observation reports from Norme and the reflector observations from Lords paper on "Resolving unequal binaries ..." with assumed CO of 28% for 150mm and 33% for 254mm scopes to my data set I modified my RoT model to include the influence of CO. While the statistical quality of the data set is still by far not good enough there is an interesting intermediate result as the uploaded image shows for the example of a fictive double with 1" sep and increasing delta-m starting with m1=5 and m2=6: The reflector with CO33% has an advantage up to a delta-m of 2 and then the reflector takes over. So if your topic are close doubles with small differences in brightness then the reflector is your choice - if you are ready to handle topics like collimation, coma, thermal issues, dew ...
Wilfried

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#47 Asbytec

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Posted 20 January 2013 - 08:07 AM

Wilfried, so that's fascinating. For close nearly equal pairs the obstructed aperture has an advantage with 1" sec separation. It's interesting that the change occurs up to about 150mm aperture, that's approximately the aperture where 1" separation roughly equals the Raleigh limit.

For example, with 5/6 mag pair at 1" arc separation, the required obstructed aperture looks to be about 102mm while unobstructed aperture seems to require closer to 115mm. An 0.33D obstructed 102mm scope has an Airy disc approximately 138/102 = 1.3" arc in radius and a Dawes limit at 116/102 = 1.1" arc. Reduced for the CO by about (1-o^2) ~ 89%, Raleigh limit is 1.2" arc and Dawes is 1.0" arc with a perfect aperture. The first ring is near 1.8" arc.

So, these appear to be Dawes splits a 102mm clear aperture is incapable of.

What's interesting is how this changes with the magnitude of the companion. For example, a 350mm scope has a Raleigh limit of 126/350 = 0.4" arc and a Dawes limit ~ 0.3" arc. It is certainly capable of a tighter split, but it's first ring lies at about 1.16 * 550 * 0.206/D = 183/350 = 0.5" arc. A second ring is at 2.73 * 550 * 0.206/D = 309/350 ~ 0.9" arc. So, it appears for 1" arc split, the (brighter) rings begin to interfere with the faint companion in an obstructed aperture.

Surely, at an intermediate aperture (about 180mm), the brighter first ring would interfere at 1" arc with a somewhat brighter companion. That seems to occur near delta Mag of about 3 or so. In this zone, it appears the dimmer ring structure of a clear aperture allows easier detection in smaller scopes.

As delta Mag falls, we need a larger obstructed scope for the same 1" arc split. Presumably, this is because the outer diffraction ring brightness is less, due to the reduced angular diameter of the Diffraction pattern, and possibly equaling the apparent "brightness" of a smaller clear aperture with fainter (if larger) ring structure. In other words, for a 1" split, the scope needs it's first or second ring to be within that 1" angular radius at larger delta mag, a clear aperture can manage it with less energy in those same rings.

Interesting. Excuse the math and thinking out loud. I'm still absorbing what this graph might be telling us.

#48 fred1871

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Posted 20 January 2013 - 08:20 PM

A very interesting graph, Wilfried. I'm a little surprised that the turnover point is at delta-m of 2 magnitudes - I'd have expected somewhere closer to 1 magnitude, at least for telescopes with larger (33% diameter) central obstructions.

A question - why have you set the CO for 254mm at 33% ? This would be unusual for a Newtonian unless of short focal ratio. Lord's 10 1/4-inch reflector mentioned in his paper is of long focal ratio, therefore is likely to have a smaller CO.

More thoughts when I've studied the graph further. Though I suspect there are issues it'll show with regard to the 1" separation, related to varying apertures; rings differentially affect different apertures for the same separation (does the secondary star fall on a ring or a space for a given aperture). I read Norme's comments as partly relating to this.

And I now have some more observations of difficult doubles; data on those soon.

#49 Asbytec

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Posted 20 January 2013 - 09:06 PM

Fred, it is an interesting question. I failed to split an unequal pair (BU1040) where the companion was 3.5" arc as sat on my 4th ring. Curiously, the 4th ring was certainly not visible, so it appears there is more at work than the visual threshold. Also, at each minimum there is a bit of destructive interference occurring from the primary. I wonder if it affects the companion's brightness. Something causes the MTF beyond the first ring to have a constant slope, it's not lumpy at each ring's spacial frequency.

#50 azure1961p

azure1961p

    Voyager 1

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Posted 21 January 2013 - 12:12 AM

Very nice work Wilfreid. The shift in scope design advantage is curious and compelling particularly as I've been reading along as this has developed. Great work by all parties involved.

Pete






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