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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5607081 - 01/05/13 06:11 PM

Quote:

...the actual Airy disc itself ... is smaller ...



The slightly smaller size of the diffraction pattern due to CO alone seems to have no real impact - the additional reduction of the size of the spurious disk due to the loss of energy seems to have more effect I think.

Here the list I promised (all from Taurus with a required refractor aperture of 150mm +/-10% error range and for an assumed NEML of 4.5):
WDS ID Name RA Dec Sep M1 M2 Req. Ap
WDS04348+2242 STF562 4,5793 22,692 1,9 6,82 9,94 135
WDS03598+2848 A465 3,996 28,806 1,9 9,53 10,89 136
WDS04160+3002 STT78 4,2673 30,036 2 7,82 10,49 137
WDS05175+2250 HO334 5,2923 22,829 2,2 9,16 11,07 138
WDS04391+1024 A2036 4,6511 10,399 2,8 9,76 11,42 138
WDS03355+0625 A1933 3,5918 6,4106 1,2 8,91 9,99 140
WDS05055+1948 STT95 5,0922 19,807 0,9 7,02 7,56 140
WDS05305+2223 J590 5,5097 22,361 4,8 9,4 11,80 141
WDS04197+2750 LEI12 4,3281 27,83 1 8,84 9,47 141
WDS05416+1913 STF770 5,693 19,22 1,1 8,76 9,77 142
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
WDS05340+2225 A2106 5,5668 22,424 1,5 9,7 10,80 146
WDS03578+2255 COU364 3,9631 22,924 2,6 8,99 11,39 146
WDS03520+0632 KUI15 3,8667 6,5349 0,8 6,26 6,56 152
WDS03374+2632 COU690 3,6233 26,539 4,2 9,7 12,00 152
WDS03362+2959 BU1040 3,6032 29,983 3,5 7,8 11,50 154
WDS03544+1601 BOV28 3,9066 16,017 0,9 7,2 8,60 154
WDS05293+2816 MLB519 5,4892 28,267 3,7 9,82 12,00 155
WDS05428+1806 CHR213 5,7131 18,097 1,7 9,5 11,20 156
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
WDS03552+0417 A2349 3,9208 4,2887 1,8 9,33 11,30 159
WDS03372+0121 A2419 3,6206 1,3494 0,8 8,73 8,93 160
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
WDS03588+0230 HEI637 3,9796 2,5079 2 9,17 11,49 164
WDS04285+1059 HEI457 4,4757 10,988 1,4 9,13 10,95 165
With a 150mm refractor the split probability for the 135mm req. Ap. should be 85% and for the 165mm req. Ap about 15%.
Norme, may be you can check this list with your 150mm MCT as you are anyway interested in difficult pairs for your scope and may be somebody else with an 6" refractor.
Wilfried
PS: You have already covered from this list KUI15 (31 Tau) with a req. Ap of 152mm and outside of this list STF412 (7 Tau) with a req. Ap of 173 - it seems you have a tendency to overperform


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Gord]
      #5607130 - 01/05/13 06:36 PM

Fred,

No this Ronchi wasn't misread, it was actually a good mirror. It just wasn't my cup o joe though. I must confess though I never really had it collimated much better than you can get out of the collimating aperture or peep that came with the scope . Perhaps that was the reason? I never liked the beast and sold it after a couple months. Funny I don't mind that same size CO in a sct though. Maybe lack of coma, I don't know. The eight was a revelation though.

Pete


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: WRAK]
      #5607156 - 01/05/13 06:59 PM

Quote:

Quote:

...the actual Airy disc itself ... is smaller ...



The slightly smaller size of the diffraction pattern due to CO alone seems to have no real impact - the additional reduction of the size of the spurious disk due to the loss of energy seems to have more effect I think.

...outside of this list STF412 (7 Tau) with a req. Ap of 173 - it seems you have a tendency to overperform




I am starting to agree with you on the CO affects. The most improvement tends to be on a very small scale of the central disc, while the degradation occurs on the scale of the first ring. Maybe further out. So, the whole right side of the MTF is trapped in that small confine and creates so much discourse. To me, that's interesting - putting a face on the argument.

On over performing, I took that as a compliment. Thank you. I do struggle to report and interpret what I see. hopefully such interpretations are not violations of the laws of physics. For example, is the apparent limb shading of 7 Tau Airy discs considered a drop off in contrast? And does that constitute resolution? In my interpretation, it does.

Taurus is well placed, thank you for the list. I will observe a few tonight.


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5607309 - 01/05/13 09:14 PM Attachment (15 downloads)

Forgive me posting profusely, again this is just fascinating for me. Also, a eureka moment occurred when one realizes the scale we're talking about. If you already know this, excuse the redundancy. But, it seems to explain why unequal doubles behave like planetary contrast - because they are on the same scale (1x to 4x Raleigh.)

The illustration below is only approximate. But it seems to show something close to 2x the Raleigh limit might be very hard. Further out to about 4x the Raleigh limit might be hard, depending on the CO and the light scattered in that distance (CO, aberration, or otherwise.)

It illustrates how a CO can improve very fine resolution very near the Airy disc itself. It suggests a brighter primary will flood that scale (2x to 4x Raleigh) with additional rings. If the magnitude difference is not sufficient, the companion can struggle to be seen. So, the smaller or cleaner you can make that range the "better."

Edit: Zeta Ori fits within that scale at 2.4" arc and at 2 delta M was an easy split.

Credit for the MTF goes to the link below, I added the diffraction pattern to give some sense of scale.
http://www.handprint.com/ASTRO/ae3.html#centobs

Edited by Asbytec (01/05/13 11:45 PM)


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azure1961p
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Reged: 01/17/09

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5607561 - 01/05/13 11:46 PM

Over perform...

I don't know what that entails, what's performing when its on the mark? He's for a well trained eye and seeing conditions that have t seen Connecticut since ... August?

Pete


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7331Peg
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Reged: 09/01/08

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Gord]
      #5607661 - 01/06/13 01:13 AM

Quote:

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


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: azure1961p]
      #5607764 - 01/06/13 04:34 AM

Quote:

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


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: WRAK]
      #5607806 - 01/06/13 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 +1538' 1.7 5.7 7.8 13
STF749 AB 05h37m06s +2655' 0.7 6.5 6.6 24

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


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Asbytec
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Reged: 08/08/07

Loc: La Union, PI
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5607976 - 01/06/13 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.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=5607971&...


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: WRAK]
      #5609107 - 01/06/13 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.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Gord]
      #5609125 - 01/06/13 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.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5609473 - 01/06/13 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.


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Asbytec
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Reged: 08/08/07

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: fred1871]
      #5609640 - 01/07/13 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.

Edited by Asbytec (01/07/13 10:14 AM)


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Asbytec
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Reged: 08/08/07

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5611692 - 01/08/13 10:40 AM

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

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5611674/page...


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5614326 - 01/09/13 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.


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Asbytec
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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: fred1871]
      #5614596 - 01/09/13 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

Edited by Asbytec (01/09/13 10:30 PM)


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fred1871
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Reged: 03/22/09

Loc: Australia
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5614836 - 01/10/13 02:18 AM

Quote:

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.


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WRAK
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Reged: 02/18/12

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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: fred1871]
      #5614885 - 01/10/13 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.org/web/20111203102746/http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/TELESCOPIC%20RESOLUTION.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


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Asbytec
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Re: Refractors vs SCTs and Maks for uneven doubles new [Re: WRAK]
      #5614934 - 01/10/13 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.

Edited by Asbytec (01/10/13 06:41 AM)


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Asbytec
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Reged: 08/08/07

Loc: La Union, PI
Re: Refractors vs SCTs and Maks for uneven doubles new [Re: Asbytec]
      #5615227 - 01/10/13 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.

Edited by Asbytec (01/10/13 02:22 PM)


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