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Taming of the Slew – Transforming Your Dobsonian into a Dutiful Companion

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21 replies to this topic

#1 morgan a.

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Posted 01 December 2024 - 10:13 AM

Six years ago I got around to pursuing a long-held desire to educate myself on astronomy and cosmology. I started to learn the fundamentals with an inexpensive four inch reflector, learned the lay of the night sky, and read numerous books and resources. As a newcomer to the hobby I advocate the manual approach - the learning is in the doing, rather than having it done for you by a magical box with a motor. Give me a 1:24,000 topo map and quality compass any day over a GPS. Five years ago I moved on to a 12 inch reflector. I fully expected a beautiful mail order bride to arrive. Instead I received a monstrous, difficult to handle mistress in a casket-sized box. I was nevertheless certain she was the one for me…..with a little grooming. Perhaps some of my features and modifications may inspire you to make those changes to your outfit that will improve handling quality and make viewing more manageable and enjoyable.

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#2 Sincos

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Posted 01 December 2024 - 10:30 AM

Taming of the slew(shrew) , no way . Learning to live with each other’s idiosyncrasies. Love what you two have done to live together. No weights on the backend but a chinstrap on the front .   ; =  )



#3 DXVictor

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Posted 01 December 2024 - 01:53 PM

Impressive project. I have always thought of getting a DOB. But, the ones I've seen weren't very good quality and having never learned star hoping, it would be quite a challenge. Your solution is very imaginative. Your wood-working is superb. Almost makes me want to run out and buy a DOB so I could build the mount like you have done. Congratulations on such a well documented project. Inspiring.  


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#4 morgan a.

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Posted 02 December 2024 - 11:00 AM

I merely combined my passion for wood woring with that of astronomy and modified the chassis.  I  marvel at folks who grind optics and build scopes from scratch - beyond my knowledge, skills, and abilities.  As has been rightly said, 'a large Dob is the best bang for the buck,' providing you mitigate its two limiting factors:  mobility and balance.  If  you are willing to apply home-made ingenuity to address these, then a large Dob is a good venture.

 

As with any modification, the formula = function over form, i.e. performance over beauty.  If you can achieve both, then great. My setup is constrained to home use.  Were I wanting to trasnport a large Dob to the field, I would absolutley go with a truss design.

 

Since this article I have replaced the outriggers with four each veneer presses with 7/8" dia screws with the large Acme threads and have largely completed the azimuth ring to be sammiched between the base plates and rotate around the lazy susan bearing.  Whether wood working or any task, I thrive on self-discovery:  what works, what doesn't.

 

m


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#5 flyboyu777

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Posted 11 December 2024 - 10:56 AM

Wow that is a nice setup-thanks for sharing this!



#6 Jon Isaacs

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Posted 12 December 2024 - 08:57 AM

That is a non-traditional approach to "taming" your 12 inch Dob. Some interesting stuff. 

 

I took the more traditional approach with my 12.5 inch Discovery Dob.  In the 25 years I have owned it, it had gone through several transformations.  It began as Sonotube Dob which was upgraded to a plywood base with Ebony Star-Teflon bearings.  In 2007, I got lucky and I was able to acquire a truss conversion for a local builder.  

 

It's a classic truss Dob with large diameter altitude bearings. It's compact, the footprint is 19" x 20" and it nests so the rocker box, mirror box and and upper cage are 28" high when disassembled. It takes up the seat space of one person.  

 

Jon



#7 RedRover

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Posted 13 December 2024 - 08:03 AM

Nice write up, thank you for sharing! I noticed your variety of lens, would you be willing to share which ones you use the most and under what circumstances?

 

Thanks again for the time and effort you put into the article.

 

Mike 



#8 morgan a.

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Posted 13 December 2024 - 05:46 PM

Jon,

 

I admire your set up and parameters for a Dob that size. There are far worse passengers who could ride shotgun, rather than a beloved Dob. I have enteratained an 18" truss model for mobile deployment, but have so many irons in the fire I needn't add another now, as I also use a 6" SCT and 3 astro binos.  I like your incremental improvements.  Stars change in their evolution and proper motion in 25 years, so should your equipment.  In the spirit of the New Mexico motto, "It Grows as it Goes."  I am unorthodox in most all my approaches, which by no means indicates "smart," just different and labor intensive. 

 

m


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#9 morgan a.

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Posted 13 December 2024 - 07:26 PM

Mike,

 

After initial collimation I seem to always start with  the 26mm (Q 70) 2" as a calibration EP to test tranparency/seeing, as a middle-of-the-road magnification.  I use the 38mm (Q 70) 2" the least. 

 

Caveat #1:  while there is no disputing the merits of some of the top brand name EPs, I must say the Asian mfg 2" Q series and the (chinese) Celestron 1.25" X-cels are surprisingly good for price/performance ratio and are part of my regular ocualr retinue in all viewing sessions with the Dob and a 6" SCT.  I bought all my EPs/X-cels pre-pandemic, and all the X-cels ran $60ish at the time - now circa $100 ea. I admittedly have more glass than necessary and would not claim it is necessary to invenst in that many EPs, especially at today's prices, to cover your needs with a Dob and have meaningful viewing sessions.

 

Caveat #2:  I have 59 year old retinas and I wear glasses, but never when using telescopes or binos.  I'll try to note the EPs that are particularly problematic with glasses.

 

Caveat #3:  When I made my foray into amateur astronomy I made some mistakes not understanding the various applications of EPs and their compatability with particular scopes.  Hence, I purcahsed some EPs that were superfluous, e.g. a Celestron X-Cel 2.3mm sitting new/unused in my closet.  I recommend an ecclectic appraoch:  pick and choose select EPs from a variety of brands upon researching and do not get into the collector mindset thinking you have to buy into every EP in a given series - not so.  Strength is in variety, not continuity of a set.

 

I usually juggle both 2" and 1.25" EPs in most sessions.  If my intended targets are open clusters, broad/general meandering, or macro navigating to known targets, I use the following in 2":  32mm, 26mm Q 70s (some times the 38mm) and the 20mm coke can Meade (I believe now discontinued and very problematic/nigh impossible for glasses, but offers a satisfyingly immersive view).  I frequently use the TeleVue 2X Powermate with these EPs for DSOs and globular clusters for starters before increasing magnification. I like the graduated approach and go throiugh 3-4 EPs on a target requiring high(er) magnification. I prefer finding nuances with increased magnification rather than just jumping to high power. The Powermate takes both size EPs and I bought it after I purchased the X-cel Barlow, which I seldom use (even with the 6" SCT), much preferring the superior Powermate with the Dob.  I highly recommend investing in a top quality Barlow/Powermate/Parracor, etc. over doubling up on EPs.  My favorite general purpose EP to balance magnification and field of view is the TeleVue 17mm Nagler Type IV (now discontinued).  Some nights after testing with the 26mm this is the only EP I use if I'm not going deep or planet hunting.  In the 1.25" for this general use I am very fond of the 32mm TeleVue Plossl with a Baader Coma Corrector (another accouterment I would highly recommend for Dob use).

 

I am fond of hunting galaxies and multiple star systems (throw in all the sundry DSOs in this bin).  I now gravitate toward the Baader 14mm, 8mm, sometimes the TeleVue Plossls (nigh impossible to use with glasses), and the 1.25" EPs in the 18mm - 9mm range.  Bear in mind light intake diminshes with increased magnification.  Often you can achieve a more satisfying view of some DSOs with a mid/upper-range magnification EP gathering more light, rather than a high-range one that is more occlusive, especially with filters (broad/narrow band, OIII, etc).

 

When I am looking at planets I rely on the Baader 8mm, 1.25" EPs in the 12mm - 5mm range and particularly the TeleVue 7mm DeLite (nigh impossible to use with glasses), providing transparency/seeing permits desired magnification.  Summers in the South are problematic and often prelude max capabilities. The greatest challenge with a manual Dob at these very high powers is the rapid drift of the target across the EP's field of view and learning to manually track/adjust. (probably the greatest detriment of a Dob, whereas they excel at panoramic views).  Guess I have to lump the moon in this category.  I tend to use the 2" 26mm and/or Powermate with a 2" variable polarizer when the moon is half to full, and the 1.25" TeleVue Plossls and Celestron X-Cels in the 18mm-9mm range when half or less, with/without a 13% filter.

 

In summary, were I to distill my inventory to the bear necessities based on my preferences and historical use I'd keep the 32mm TeleVue Plossl, 26mm Q70, 17mm TeleVue Nagler, 14mm Baader Morpheus, 8mm Baader Hyperion and 1.25" X-Cels in the 12mm - 5mm range, and the TeleVue 2X Powermate and Baader Coma Corrector.

 

Hopefully I answered your question without digressing too much.  If not, hit me again.

 

Thx,

m



#10 morgan a.

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Posted 14 December 2024 - 01:30 PM

Addendum to OTA

 

Several modifications not previously mentioned:

 

1.  In 2022 I replaced the 1/4 wave OEM secondary mirror with a 1/15 wave Astrosytems version.  I have read various positions about the efficacy of such upgrades due to limitations/capacity of the human eye (I'll leave the opining and pontificating to the opticians and astronomy mavens).  The Astrosystems iteration is dimensionally a little different than the OEM at 2.6" long axis.  I separated the OEM mirror from the stalk and sent in the stalk, which had to be somewhat shortened and the replacement mirror attached ($180 for mirror and $40 for modification/attachment at that time).  I subjectively believe it resulted in some perceptible improvement.  I heavily darkened the mirror edge with a Sharpie prior to installment.  Two years in, the Sharpie pigment has held up well.

 

2.  I wanted to flock the tube.  However, when I removed the secondary mirror for upgrade and the primary mirror to clean it, I just heavily coated the OTA with ultra flat black camo spray paint.  The OEM paint was markedly lighter, more of black/olive drab and not super flat.  I subjectively believe it resulted in some perceptible improvement in contrast and reduced reflectivity.

 

3.  I initially used the OEM cooling fan attached to the rear of the cell and secured the battery carriage to the OTA with industrial Velcro.  Oddly, the mounting screws for the fan are only accessible from inside of the cell, requiring cell removal to remove the fan.  The fan motor ceased working after I had removed the cell/cleaned the primary.  It is now dead weight and I will remove it upon next primary cleaning.  Because my rig is for home use only, I use a floor/box fan to expedite cooling, which is far more efficient.  I raise the OTA to about 45 degrees and use a 20" fan on low.

 

m



#11 Jon Isaacs

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Posted 15 December 2024 - 10:33 AM

 

3.  I initially used the OEM cooling fan attached to the rear of the cell and secured the battery carriage to the OTA with industrial Velcro.  Oddly, the mounting screws for the fan are only accessible from inside of the cell, requiring cell removal to remove the fan.  The fan motor ceased working after I had removed the cell/cleaned the primary.  It is now dead weight and I will remove it upon next primary cleaning.  Because my rig is for home use only, I use a floor/box fan to expedite cooling, which is far more efficient.  I raise the OTA to about 45 degrees and use a 20" fan on low.

 

I do this same thing with my 13.1 inch F/5.5 Starsplitter. It has a full thickness mirror so it's slow to cool and since it's also a backyard scope, I use a 2000 cfm drum fan to cool the mirror. I keep it running during the night so I have move it around.

 

If you decide to replace you old fan, I recommend the Floyd Blue design. It's a full baffle made from 1/16" ABS that's fitted to the mirror cell and mounted using Velcro. The Velcro provides vibration isolation.

 

10 inch GSO Fan assembly 1.jpg
 
(Just in case you want to do something the old fashioned way. :)  )
 
Jon
 
Jon


#12 morgan a.

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Posted 15 December 2024 - 02:57 PM

Jon,

 

info much appreciated.  I am not familiar with this fan assembly, will have to research. I see potential for DIY, as well based on your pic.  I'm just an old school guy shuffling down the halls of the new school smiling at all the 'youngsters' who don't know there is nothing new under the sun.  Always a good practice to begin the day shaving with Occam's Razor.

 

m


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#13 Leeseafish

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Posted 16 December 2024 - 03:37 PM

Here's a link for  floating azimuth scale. 

 

https://eastridingas...k/help-DIY.html

 

The benefits of this arrangement are that the setting circle can be adjusted, find a know star in the FOV and turn the setting circle until it matches the Az in your app.

 

I use a digital inclinometer for the Alt angle.  



#14 morgan a.

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Posted 17 December 2024 - 10:10 AM

Addendum to upgraded outriggers:

 

The enclosed pics show the replacement of the 3/8" threaded rod/improvised lifters to the veneer presses (Fox Shop brand).  The press screws are more robust and have a coarse pitch Acme thread facilitating quicker motion.  The press is a male screw and female threaded cylinder receiver.  It is intended for wood working clamping applications, but can function as a press/clamp, spreader or jack (merely a spreader separating and lifiting something from the earth against gravity).

 

The last pic shows one in original condition that I used to make a tail vise on a workbench I built.  The handles and grip knobs were too long and obtrusive for the chassis of the scope.  I drove out the roll pins and separated the handles from the screws, cut the handles down on a metal bandsaw (not hardened, hacksaw or elec handsaw with metal blade sufficient), softened the cut edges on a bench grinder and painted the handles and swivel feet with black enamel paint and reattached the handles to the screws.  I removed  the threaded T nuts I originally installed, enlargened the mortises in the base frame and installed the veneer cylinders.  I dressed up the tops with cedar cover plates and notched the inner corners with a mildly curved radius to roughly match the radius of the OEM baseplate.

 

m

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Edited by morgan a., 17 December 2024 - 10:21 AM.


#15 morgan a.

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Posted 17 December 2024 - 10:41 AM

Leeseafish, thanks for the info/link from across the Pond.  I'll check it out. 

 

I am still experimenting with the azimuth circle build/design, though mostly complete.  I went with making a plywood ring with tempered Masonite on the bottom with a circumfrential rabbet that rides upon four sassafrass bearings similarly rabbetted that I have already made and installed just outside the lazy susan bearing between the OEM baseplates.  The height of the upgraded bearing permits such an install.

 

I had a local printer make the scale.  I attached it to the ring with double-sided tape.  However, I tried to attach it to the ring monolithically and put a wrinkle in it.  I should have incised a cut through it perpendicularly to prevent this.  Once I redo the scale sans wrinkles it will be ready for install.

 

In anticipation of the azimuth circle I previously built the holder for a Wixey brand elec angle finder complete with a spare AAA battery well actuated by a simple lift/plunger.

 

m

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Edited by morgan a., 17 December 2024 - 10:41 AM.


#16 kas20amc02

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Posted 21 December 2024 - 12:14 AM

Can you please tell me which Lazy Suan bearing you used?  I found this one on the website you recommended.  1000 pound capacity and 10 inches in diameter.  Is this the one?

https://www.leevalle...gs?item=12K0104
 

 

I also found this one:

https://www.amazon.c...7ON2&gQT=1&th=1



#17 morgan a.

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Posted 21 December 2024 - 09:30 AM

Mariner 2

 

Lee Valley offers multiple diameters from 9" - 29.5".  My base plates are circa 24" dia.  I utilized the nearly 18" version which permitted circumfrential space for the azimuth ring.  If you do not need this space I'd say going with the biggest possible bearing the best option:

 

https://www.leevalle...sicD0-OFQ&gQT=1

 

m



#18 morgan a.

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Posted 21 December 2024 - 12:00 PM

Also, the iteration of the Lee Valley bearing has good friction/tension, such an improvement in use over the OEM plastic needle sheet and metal plates.  However, preventing swivel during transit is an issue with any bearing on a Dob of this design and size.  I simply drilled a hole through both base plates into the frame and affixed with a walnut dowel and wooden head.  I installed a short register pin to prevent the head from rotating.....little of which flourishment is necessary for an effective fix.  Any bolt or metal pin with a head will suffice. 

 

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#19 kas20amc02

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Posted 22 December 2024 - 02:56 PM

Thanks.

 

 

Mariner 2

 

Lee Valley offers multiple diameters from 9" - 29.5".  My base plates are circa 24" dia.  I utilized the nearly 18" version which permitted circumfrential space for the azimuth ring.  If you do not need this space I'd say going with the biggest possible bearing the best option:

 

https://www.leevalle...sicD0-OFQ&gQT=1

 

m



#20 morgan a.

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Posted 28 December 2024 - 11:52 AM

Collimation:

 

Veteran and seasoned users have established methods and preferred tools for collimation.  However, if you are new to amateur astronomy or new to a reflector, collimation may be initially challenging, if not a consternation.  I have come to favor the AstroSystems Light Pipe coupled with a laser collimator (separate device by another mfg). 

 

 https://www.astrosystems.biz/

 

 

 

Between the two I rely on the pipe far more than the laser.  I made the mistake when I first began astronomy of over-working the secondary mirror and making too many adjustments too frequently, consequenty losing time and gaining frustration.  Once the secondary is centered under the focuser and initially collimated it requires very little further adjustment, and just minute ones when necessary.  I barely have to tweak it on a rare occasion. The primary mirror gets the most attention.  Again, required adjustments should be small and not have you going all over the place, teetering on going gimble.  Even with significant tranist of my Dob from the house to the driveway over a threshold and with a small drop/step, careful transport never causes significant misalignment.

 

I usually set up the Dob a couple hours prior to intended use.  In the summer this is still during daylight or twilight hours1.  In winter it is late twilight (Astronomical) or darkness.  I let the box fan cool the OTA and purge the tube while I do other things.  Obviously winter witnesses the greatest temperature variation from a warm house to a cold environment.  Consequently, I learned collimating prior to fully cooling and allowing the primary mirror to acclimate is an exercise in futility.  I do not collimate until I am ready to begin a viewing session.

 

Herein lies the beauty of the Light Pipe.  It has a translucent head that pulls in sunlight and permits veiwing to make adjustments.  Additionally, it works about as well under artificial light, even with a red light to preserve your night vision (see pics).  This facilitates subsequent collimation throughout a viewing session, especially when temperatures vary significantly.  It is helpful to rotate your Dob and raise/lower it in altiitude a couple times as well, prior to initially collimating.  I never collimate in sunlight or white light.

 

1.  Twilight:  Civil = center of the sun 6 deg below the horizon, Nautical = center of the sun 12 deg below the horizon, Astronomical = center of the sun 18 deg below the horizon, neglible solar component of sky glow (Observer's Handbook 2025, Royal Astronomical Society of Canada, Marquis Book Printing, page 204).

 

m

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Edited by morgan a., 28 December 2024 - 11:55 AM.


#21 morgan a.

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Posted 28 December 2024 - 12:31 PM

Accessorizing:

 

Familiarity and comfort with your Dob over time will permit you to modify it, even drilling into the OTA, etc.  If you are not keen on this or have an SCT or refractor with a sealed OTA, one alternate option to attach optical accessories is to use a Telrad mounting base with 3M foam adhesive tape (supplied with base) and modifying the Telrad risers to receive the desired accessory.

 

I attched one to my Dob as well as one on a 6" SCT (see pics).  The tape is very strong/efficient and long-lasting, resulting in a 'permanent' feature, so make sure you are happy with the exact placement prior to attaching.  You may want to modify the riser and connect optical accessory to base and hold or temporarily attach it to the OTA while you view through it and determine desired placement prior to fully attaching with the adhesive tape.

 

I attacehd a Synta style shoe to a riser/base on my Dob to accept a red dot finder (I favor both a 'macro' red dot and 'micro' StellarVue 9x50 scope for navigation).  Additionally, I can swap the red dot for a Telrad in under 60 seconds.  On the SCT I bolted the scope mounting rings to the riser which mates with the base.  Again, a swap of the scope with a Telrad is fast and efficient.  The tape has held up with no issues on the SCT to support the StellarVue scope at all angles on a manual German Equatorial Mount.

 

On the Dob I modified a 2" riser by cutting down the front/back portions to reduce the size of the mounting surface to accept the shoe. The 2" elevation was necessary for visual clearance.  On the SCT I cut off the vertical legs and top plate and bolted the rings to the base portion of a 2" riser which mates with the Telrad mounting base.

 

A current perusal of Agena seems to show the riser design has changed, which may change the approach.  The older design appears to offer more latitude in modification than the new(er) design, if you can find them:

 

https://agenaastro.c...esult/?q=telrad

 

 

 

 

m

 

 

 

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#22 morgan a.

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Posted 30 December 2024 - 02:09 PM

Addendum to collimation and accessorizing:

 

I was remiss not to mention the following brief recommendations in the two previous posts

 

1.  Collimation - one legitimate issue/complaint with many mass market laser collimators is the beam diameter and resultant dispersion of laser light on the primary mirror when attempting to center it on the mirror's donut for alignment.  It usually obliterates a clear view of the donut's outer and inner ring and reduces accuracy of alignment.  You can minimize this with an improvised insert in the end of the collimator's barrell with an exactly centered pin hole.  More expedient yet, and counterintuitive is to shine a red lensed flashlight down the OTA on the primary mirror during collimation.  It surpriisingly cleans up much of the light scatter and makes the laser beam more discernible within the donut for a more accurate alignment.

 

2.  Accessorizing - should you pursue using a Telrad mounting base on your OTA (for optical devices other than a Telrad, or with a Telrad), you can accurately mark placement with blue painter's/masking tape to delineate position.  Affix the desired optical device to the modified riser and mounting base, hold or temporarily affix it to the OTA and test placement and performance.  Once satisfied, (place tape tightly around, but not under the edge of the base), place tape around the perimeter of the mounting base or just at the corners/ends as an index.  Ensure the base is parallell to the long axis of your OTA and not cattywampus.  Peel off tape backing and affix within marking tape.  Once applied there is no readjustment.  It will be stuck like........well, use your own analogy.  The painter's tape is then easiy removed and will leave no adhesive residue or tackiness on your OTA.

 

m


Edited by morgan a., 30 December 2024 - 02:09 PM.



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