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STF 384 and 385 in Cam

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#1 John Fitzgerald

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Posted 24 December 2019 - 12:02 AM

STF 384 mags 8.1,8.9, sep= 2.0"  PA 273

STF 385 mags 4.2(var),7.8, sep= 2.3"  PA 162

These two pairs were observed well within the same field with my 7mm Delite at 173x in my 6" triplet.

 

Imaging list, anyone?cool.gif


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#2 fred1871

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Posted 24 December 2019 - 01:20 AM

Interesting - Sissy Haas lists these two together, in her book, and quotes colour descriptions from TW Webb the assiduous 19th century observer of double stars with "common telescopes". From that book, she gives the Webb observed colours as "gold, blue" for STF 384; and, for STF 385, "Yellow, no colour given", but I find in my copy of Webb the abbreviations 'y.,o' which I take to mean "yellow, orange".

 

These doubles are in the (naked-eye) wilderness of Camelopardalis, which has very few naked eye stars visible in suburban areas. In my time in the Northrn Hemisphere I could see why it was described as 'the absence of a constellation' by a past writer. 

 

Both pairs, incidentally, showed in my C8 back in the day; STF 384 was seen double at 200x, and STF 385 with more difficulty, no doubt due to the brightness difference of the stars, which made it more seeing-dependent.


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#3 R Botero

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Posted 24 December 2019 - 03:25 AM

John

 

I observed these two most recently in November/December last year. No particular notes for STF384 but for 385 I have: “Very difficult in wind. Large delta. Brilliant white and pale blue. PA175.”  This with my 10” f/20 Mak at 315X. 

 

Roberto


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#4 ssmith

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Posted 30 December 2019 - 07:03 PM

I went out with the intention to check out CS Cam (STF385) but didn't have much luck getting a good image due to its brighter magnitudes and larger delta mag.  STF 384 was another story as it was quite a surprise to me as to how vivid the colors were - Perhaps it had something to do with the frigid temps (7 deg F).
 
Here is a photo - single frame.
 
STF384 Cam C9 f10 12-29-19 105e Bahtinov.jpg

Edited by ssmith, 30 December 2019 - 09:03 PM.

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#5 c2m2t

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Posted 31 December 2019 - 03:00 PM

Hi Steve! 

How many times were you able to get a clear double star image through a Bahntinov focusing mask and better yet, what inspired you to try that? smile.gif  I have taken so many of those kinds of images getting focus before an imaging run, but never had I attempted it on a double...and never have I achieved a clean star image. Going to have to investigate that a bit further. 

Cheers, Chris!



#6 dmdouglass

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Posted 31 December 2019 - 04:47 PM

Howdy Steve...

 

A quick question. Was the presence of the mask intentional, or an "oops"" moment !

Just curious.  I think all of has done it....   more than once !



#7 ssmith

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Posted 31 December 2019 - 05:45 PM

Hi David & Chris - Happy New Year!

The use of the mask was intentional. I took photos with and without the mask. The mask tends to tame the seeing a bit and I can get cleaner separations without having to bump up the magnification.

I got several reasonable photos without the mask but the ones with the mask were just a bit sharper.

If you look at some of my earlier posts you will find a few which also had the mask in place.  It is a recognized technique to use some sort mask when imaging high delta mag double stars.  I think that my use of a Bahtinov focusing mask for this purpose is an original application.

 

Here is a link to a photo of Antares that I took with the mask.


Edited by ssmith, 31 December 2019 - 08:08 PM.

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#8 The Ardent

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Posted 31 December 2019 - 09:07 PM

Steve, whats your average separation resolution in arc-seconds with the C9.25 at f/10? Asking for a friend ;)



#9 ssmith

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Posted 01 January 2020 - 12:25 AM

Happy New Year Ray -

 

First off is your friend asking about visual resolution or photographic resolution? - They are very different things.

 

If Visual then it’s best to consult the various resolution criteria such as Rayleigh etc.

 

If photographic then I’m tempted to say that your camera choice has a much bigger effect on the possible resolution than the scope.  Here we are getting back to image scale (arc-sec/pixel). 

 

I really can’t say what the average resolution for my C9.25 @ f10 would be since every double-star is different - sep, magnitudes, delta magnitude etc.  All I can say is that under certain circumstances I can get close to 1 arc-sec resolution using my C9 and my particular camera, a powermate, along with excellent seeing and the imaging Gods looking over my shoulder.

 

Looking at my photo above, if you were to increase the brightness  of the two stars by 1.0 mag each, the stars would probably be just touching  - thus for mag 7 stars you could probably resolve down to  2.5”. This limit would increase for brighter stars and decrease for fainter stars.


Edited by ssmith, 01 January 2020 - 03:34 AM.

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#10 Adam Long

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Posted 13 February 2020 - 05:51 AM

I'm finding Σ385 a tough nut to crack in my 10" dob. Third visit last night, and I'd just located it and switched to high power when high cloud began to roll in. Despite the cloud holding back the primary to varying amounts to give some views of a steady airy disk, I got only the vaguest glimpses of a companion that I couldn't place more confidently than in the SW quarter (PA is 162).

 

I wonder if an aperture mask might be worth a try? I know occultation bars are often mentioned but I've not come across any examples of anyone actually sourcing or using them. Guessing 2.3" might be a bit tight anyhow...



#11 c2m2t

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Posted 13 February 2020 - 09:18 AM

Hi Steve!

I just noticed your link to your Antares images using the mask. What ISO and exposure settings were you using? I was recently experimenting with Sirius in similar fashion, with no success. It way also be a question of rotating the mask so that the main spikes are perpendicular to the PA...didn't think of that while out in the pod...possibly brain freeze! lol.gif

 

Cheers, Chris.



#12 c2m2t

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Posted 13 February 2020 - 09:22 AM

Hi Steve!

Another thought! I am guessing that larger optics are an advantage using this process. I suspect it is wishful thinking to have this kind of success with a SW100 Pro ED.

 

Cheers, Chris.



#13 ssmith

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Posted 13 February 2020 - 10:50 AM

Hi Chris -

 

The Antares photos were taken with the C9  exp 1/20th sec ISO 1000.

 

I actually tried the bahtinov mask on Sirius a couple of nights ago with no success.

 

The Bahtinov mask actually puts out some secondary spikes 90 perpendicular to the main spikes.  These aren't always visible on faint stars but on bright stars like Sirius they are quite prominent and reduce the clear viewing area.

 

If I were to use a mask for Sirius I would use a triangular shaped mask which would project 6 equally spaced spikes.

 

When it comes to the Pup I'm a big fan of using refractors with their high contrast views.  My best views have been with my 120mm.  Also viewing at twilight or with the moon shining helps cut down the glare of the primary

 

Here is a photo of Vega with the bahtinov mask and you can see the secondary spikes.  They are even more prominent on Sirius and the central region gets very fuzzy.

 

Vega Bahtinov C9 9-7-18 245.jpg


Edited by ssmith, 13 February 2020 - 10:56 AM.


#14 rugby

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Posted 13 February 2020 - 01:26 PM

Fred,

If you look under Abbreviations (additional) and Symbols in COCT just prior to Andromeda, or is orange and o is no colour given. Like you I always mistook the letter o as meaning orange.



#15 c2m2t

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Posted 13 February 2020 - 01:40 PM

Hi Steve!

Thanks for that! I am aware of the secondary spikes, but looking at your Antares images, they didn't come into play. I suspect that much of this has to do with the magnitudes and delta M's of the components as well as the separation. I have tried the triangular mask with Sirius but the primary is simply too bright and still generates too large a 6 pointed star, consuming the pup. A closer look at the Rigel image I made a couple of months ago with the triangular mask has me thinking that the faint star that I thought was the secondary, may have been another star a bit further separated from Rigel. What led me to that conclusion was the PA of the secondary...it wasn't matching up with the visible star between the spikes. I guess one has to try many combinations of ISO and exposure duration to find that magical combination. Just a bit tough swapping out telescopes on a single evening given the cold temps. It may take a year or two to try all the possible combination for this exercise!!

 

Cheers, Chris.



#16 fred1871

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Posted 13 February 2020 - 08:49 PM

Fred,

If you look under Abbreviations (additional) and Symbols in COCT just prior to Andromeda, or is orange and o is no colour given. Like you I always mistook the letter o as meaning orange.

Useful find. The colour notes in Webb are, incidentally, a hotch-potch - sometimes partly spelled out, as with Alpha Herc : "Orange, blsh. grn., '55", and at other times the briefest abbreviations, or various mixes of full terms and abbreviations. I shall hope there are no other (than 'o') potentially ambiguous terms lurking in the text.
 


Edited by fred1871, 13 February 2020 - 09:30 PM.



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