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stratocaster
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Reged: 10/27/11

My tale of Trapezium F - finally
      #5444712 - 09/28/12 06:15 AM

I've been back into the hobby solidly for the last year. I have an SV102ED and a Zhumell 10" dob. The standard mirror on the dob wasn't much good for planetary and splitting doubles. I couldn't even make out the E star with the dob. The E was not obvious with the SV102, but I could make it out. But I could not detect the F star with either scope to save my life - even on nights that appeared to have fairly good seeing.

I've since replaced the stock mirror with a Zambuto. I'm still getting my legs with it a bit and am going thru many old favorites to see if there's anything new I can make out with my new mirror.

Seeing was supposed to be very good tonight, so I was looking forward to see how the Zambuto would do on planetary. I waited for Jupiter to come up. It was glorious at 400x when the seeing steadied. Spent a couple hours looking at it. I started to pack up around 2 am and realized Orion was coming up. So I thought I'd check out the nebula.

The nebula was still very low - maybe 20 degrees above the horizon, but I swung the scope over at low power and checked it out. Even without a filter there appeared to be much more nebulosity than I remember - love that Zambuto. Beautiful. Ah yes, the trapezium! Could I see the F star?!

I put in a 7mm Pentax XW and took a look. When I think of all the times I tried to see the F star and failed, and here it was as easy as pie - at 20 degrees above the horizon. Wonderful. Seeing stars A-F is really a beautiful thing.

Now, maybe the skies were just particularly steady, or the Zambuto is just a way better mirror than the stock mirror, or both. But it was almost funny how easy I could see A-F.

I've seen many posts here how the F star has been seen with 80mm - 100mm scopes. Wow. Maybe one of these days I'll be able to pick it up with my refractor.


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tomharri
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Re: My tale of Trapezium F - finally new [Re: stratocaster]
      #5444822 - 09/28/12 08:42 AM

Quality optics make all the difference, welcome to the Zambuto club!!!

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Rich (RLTYS)Moderator
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Re: My tale of Trapezium F - finally new [Re: stratocaster]
      #5444871 - 09/28/12 09:31 AM

Resolveing the E and F components depends a lot on the seeing conditions. With my 10" Dob sometimes the two stars are easy other times they are difficult.

Rich (RLTYS)


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RAKing
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Re: My tale of Trapezium F - finally new [Re: stratocaster]
      #5445093 - 09/28/12 11:52 AM

Quality optics + good seeing = priceless!

Don't get too wrapped up in why it happened, just enjoy the fact that it did happen.

I love quality optics and have a lot of money invested in Zambuto and Russian mirrors, plus the finest American refracting lenses. But it's those nights when the jet stream leaves me alone that spending all that money is worthwhile.

Congrats!

Ron


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Rutilus
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Reged: 12/17/10

Re: My tale of Trapezium F - finally new [Re: RAKing]
      #5445388 - 09/28/12 03:15 PM

Seeing the F star with an 80mm is really very, very good indeed. I've lost count of the hours I've spent observing
this object with my Tak 102mm APO. Only on nights when the seeing plays ball, do I manage to spot it.
With my cheap as chips 150mm f/8 Chinese Achro (which cost me less than the 7x50 Tak finder) I always see both E and F.
It has to be really bad seeing for me not to pick-up F in my large Achro.


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Bonco
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Re: My tale of Trapezium F - finally new [Re: Rutilus]
      #5445437 - 09/28/12 03:45 PM

E and F are frequently viewable in my Original Zhumell 10". I've viewed them several times with my 4 inch f/5 Genesis.
However, sometimes they are just not doable, reguardless of quality of the optics. Bill


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azure1961p
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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5445722 - 09/28/12 07:32 PM

I agree that seeing conditions can really make the E and F difficult. Really bad seeing can net me the A thru D while a little better but not great can get me a fifth and flat out good seeing lets me see both. I had a ten inch F/5 that Parks SWORE had a great mirror and not even one time did either e or f show. First try with my 8" and they were there and with the trap showing beautiful diffraction patterns at 200x . That 10" is still an enigma to me as NOTHING. Looked great thru it. The scope that followed was a revelation by comparison.

Pete


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Tamiji Homma
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Re: My tale of Trapezium F - finally new [Re: stratocaster]
      #5446367 - 09/29/12 08:03 AM

Congrats on Trapezium A-F.

Seeing is really a key. I've been trying to observe them with 60mm refractor for some time. A-E was not so difficult but F isn't easy with small aperture.

I was able to see them this morning for the first time. Seeing was excellent this morning 4am PDT. Unfortunately we have high thin clouds. Waiting for half an hour, view got steady momentarily and I was able to see 6 stars

I hope coming few day, warm weather clears early morning fogs (marine layers) to reconfirm the observation with larger scope side-by-side.

Setup was Takahashi FS-60Q + 1.6x extender (f/16, 960mm), prism diagonal and Leica Zoom eyepiece at 8.8mm, yielding about 110x.

Tammy


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stratocaster
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Re: My tale of Trapezium F - finally new [Re: Tamiji Homma]
      #5446753 - 09/29/12 12:55 PM

60mm. Impressive. And congratulations!

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Tamiji Homma
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Re: My tale of Trapezium F - finally new [Re: stratocaster]
      #5447748 - 09/29/12 11:55 PM

Quote:

60mm. Impressive. And congratulations!




Ha ha, not yet congrats I saw them for less than 10 seconds. But the way E is seen, I am hopeful to catch F under better condition with 60mm scope.

It is different kind of fun to challenge well known same target again and again with more challenging setup. I enjoy that very much.

Even Polaris is fun when you look at the double at low power, 15x, 16x. It is quite a challenge and good indicator of eye condition, at least to me

Tammy


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Erik Bakker
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Re: My tale of Trapezium F - finally new [Re: Tamiji Homma]
      #5448089 - 09/30/12 08:59 AM

Hi Tammy,

60mm might do it, but with a little more magnification. I consistently saw both E and F in my 70mm f/8 fluorite at 140x.


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mikey cee
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Re: My tale of Trapezium F - finally new [Re: Erik Bakker]
      #5457899 - 10/06/12 12:39 PM

My 10" R30 Istar I feel has to small of a spot size. The stars' discs are so darn pin point I've been having trouble unless the seeing is pardon the pun..."spot" on! Mike

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azure1961p
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Re: My tale of Trapezium F - finally new [Re: mikey cee]
      #5457990 - 10/06/12 02:01 PM

Spot in airy disc or central obstruction? At anyrate on both counts though the diffraction rings with a smaller central obstruction serve to make stars more discernible and as fad as a smaller airy disc due to larger aperture here to one of the reasons e snd f ought to show better. I'm not clear on your statements.

Pete


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Starman81
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Re: My tale of Trapezium F - finally new [Re: azure1961p]
      #5545939 - 11/29/12 06:12 PM

I was observing last night with my 8" dob during the full moon and put the scope on Trap and as I stared E was clearly visible and F showed itself briefly as well. I was using medium power (109x) and I did not know beforehand where they were situated in respect to A, B, C, D. Instead, I saw these 'unexpected' points of light and quickly took out my phone and verified on SkySafariPro what I saw. I was thrilled! A little while later I decided to put in an ortho to see if they would be easier to see, but they were not; instead they were gone! That's when I knew they were heavily dependent on seeing.

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Jacques
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Reged: 08/11/02

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Re: My tale of Trapezium F - finally new [Re: Starman81]
      #5549100 - 12/01/12 05:08 PM

Even in very good seeing applying the right magnification(s) is key, especially with smaller instruments. Too low power won't show 'em, too high power and they're gone. Some years ago I saw both E and F with a 4"F10 achromat in very, very good seeing but only at 80 and 100x (12.5mm and 10mm eyepieces). F actually "felt" a good deal closer to C than its actual distance would indicate.

Edited by Jacques (12/01/12 05:17 PM)


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C_Moon
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Re: My tale of Trapezium F - finally new [Re: Jacques]
      #5553128 - 12/03/12 11:50 PM

Quote:

Even in very good seeing applying the right magnification(s) is key, especially with smaller instruments. Too low power won't show 'em, too high power and they're gone. Some years ago I saw both E and F with a 4"F10 achromat in very, very good seeing but only at 80 and 100x (12.5mm and 10mm eyepieces). F actually "felt" a good deal closer to C than its actual distance would indicate.




This has been my recent experience. I find that 135x seems to be perfect. I'm thinking that times in the past where I had trouble seeing E & F I was at too high of a magnification.


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blb
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Re: My tale of Trapezium F - finally new [Re: C_Moon]
      #5553711 - 12/04/12 10:33 AM

Viewing the E and F stars is harder than you would think, simply because they are located in a nebula. The nebula reduces the contrast and makes seeing faint stars near brighter stars harder to see. Do not forget that the glare from those brighter stars tends to over power the view of E and F too. E and F are about 3 to 5 magnitudes fainter than the closest brighter star and located only about 3.5 to 4.0 arc seconds away from them. Still they can both be seen with a small scope on a good night from a dark sky site. So scope size is not a factor but seeing (atmospheric steadiness) is a factor and will determin whether or not you will see these stars. So don't give up, keep trying and one night you will see them too.

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nirvanix
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Loc: Saskatoon, SK
Re: My tale of Trapezium F - finally new [Re: blb]
      #5563205 - 12/09/12 09:46 PM

To never see e and f in a 10 inch dob is very surprising. Either that mirror was really bad or it was something else like improper mounting of primary/secondary, thermal problems, collimation problems...

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Tom S.
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Reged: 02/16/07

Loc: Benicia, Calif.
Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5606014 - 01/05/13 04:34 AM

After reading the preceding comments, I don't feel so bad about never yet spotting F with certainty with my SV102ED 4" 'frac.

Tonight I was outside and thought I MAYBE saw F, but it could have been my imagination.

But I saw several beautiful doubles tonight, especially Theta Aurigae and the perpetually cool CASTOR.

What FUN!


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Messyone
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Re: My tale of Trapezium F - finally new [Re: Tom S.]
      #5707682 - 03/01/13 07:31 PM

I found the f star last night for the first time with my 6" f8 achro and a Pentax XW 7mm. Jumping for joy as I also got the 'pup' for the first time with a 5mm XW
Matt
Had to use a green filter on the pup

Edited by Messyone (03/01/13 07:33 PM)


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nirvanix
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Reged: 06/07/07

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Re: My tale of Trapezium F - finally new [Re: Messyone]
      #5707782 - 03/01/13 08:55 PM

Quote:

I found the f star last night for the first time with my 6" f8 achro and a Pentax XW 7mm. Jumping for joy as I also got the 'pup' for the first time with a 5mm XW
Matt
Had to use a green filter on the pup






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CelestronDaddy
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Re: My tale of Trapezium F - finally new [Re: Messyone]
      #5708531 - 03/02/13 10:48 AM

Hot dang, WTG

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Messyone
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Reged: 05/02/12

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Re: My tale of Trapezium F - finally new [Re: CelestronDaddy]
      #5709177 - 03/02/13 05:25 PM

Just to prove to myself it wasn't a fluke I did it again tonight! This time the pup was easy to see, no surprises there but now I'm wondering why it took so long in the first place Spent the best part of 4 months looking for this one. On to the trap and now hoping to see some of the others in there....not likely but worth a try. I love my scope.
Matt


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WRAK
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Reged: 02/18/12

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Re: My tale of Trapezium F - finally new [Re: Tamiji Homma]
      #5711913 - 03/04/13 04:04 AM

Quote:

... A-E was not so difficult but F isn't easy with small aperture...Tammy




If the current WDS data is correct, then the C-F pair has as separation of 4.5" with magnitudes +5.06/11.5mag - this is certainly a double very hard to split with an aperture below 150mm even under perfect conditions means ignoring the fact that there is also a nebula to consider.
Is +11.5mag not already at the telescope magnitude limit of a 60mm scope?
Wilfried


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Bonco
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Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5712807 - 03/04/13 04:06 PM

I've found the F member is doable in a 100mm. Actually I think I've viewed it in my 75mm but to be sure I'd have to search my unorganized notes.
Bill


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WRAK
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Reged: 02/18/12

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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5713829 - 03/05/13 03:49 AM

Wow, sounds good. If you ever do a session in UMa could you please try WDS11593+3310 BU919 RA 11h 59m 18s Dec +33:10:01 +5,96/12mag 4,7" - should be a very similar challenge.
Wilfried


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nirvanix
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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5714232 - 03/05/13 11:19 AM

Quote:

I've found the F member is doable in a 100mm. Actually I think I've viewed it in my 75mm but to be sure I'd have to search my unorganized notes.
Bill




I've tried for F in a 100mm in my light-polluted backyard, but never found it. I suspect that it could be found with that scope in darker skies.


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Bonco
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Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5714729 - 03/05/13 03:47 PM

Nirvanix,
I too have very light polluted skies. Your main disadvantage compared to my home site is Latitude.
Bill


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nirvanix
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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5714998 - 03/05/13 06:02 PM

Quote:

Nirvanix,
I too have very light polluted skies. Your main disadvantage compared to my home site is Latitude.
Bill




Well that's a good point Bonco. I forget how good M42 must look for you folks way down there. It's always a bit in the soup for me.


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WRAK
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Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5715812 - 03/06/13 03:50 AM

Light pollution is not such a topic concerning resolution of double stars - it may add a few mm to the required aperture for a split but usually less than 10 even for heavy light pollution. Given stable air without any turbulences (Pickering 7 or better - this certainly excludes altitudes below 35) and high transparency (no haze or air pollution for example by air traffic) you can more or less ignore light pollution. The exception are very faint companions near the telescope magnitude limit as LP takes some tribute here. This is why I am a bit sceptic about small telescopes below 150mm for resolving F especially given the surface brightness of the M42 nebula adding some haze even in the best of conditions.
Wilfried


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Kon Dealer
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Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5715839 - 03/06/13 05:01 AM

Did "E" abd "F" with my 8SE for the first time last night.
I can see "E" quite easily with my 4" 'frac and 6SE.
Never seen "F" in either and they are out alot more than the "8".


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HCR32
sage


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Re: My tale of Trapezium F - finally new [Re: Kon Dealer]
      #5715850 - 03/06/13 05:31 AM

I see them no problems with a 6" APO at 125x.

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Bonco
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Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5716661 - 03/06/13 03:30 PM

Quote:

Light pollution is not such a topic concerning resolution of double stars - it may add a few mm to the required aperture for a split but usually less than 10 even for heavy light pollution. Given stable air without any turbulences (Pickering 7 or better - this certainly excludes altitudes below 35) and high transparency (no haze or air pollution for example by air traffic) you can more or less ignore light pollution. The exception are very faint companions near the telescope magnitude limit as LP takes some tribute here. This is why I am a bit sceptic about small telescopes below 150mm for resolving F especially given the surface brightness of the M42 nebula adding some haze even in the best of conditions.
Wilfried



I have documented observations of F with my 4 inch f/5. It is very doable in the right conditions. I've observered it many times in a 10 inch but I've also not been able to see it or E in the bigger scope. It's fickle. I checked my notes concerning my 75mm. Notes reflect positive observations of E but questionable views of F. So I won't say the 75mm viewed F, but I can guarantee you the 4 inch has revealed it.
Bill

Edited by Bonco (03/06/13 04:01 PM)


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cpsTN
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Re: My tale of Trapezium F - finally new [Re: Messyone]
      #5717863 - 03/07/13 07:58 AM Attachment (22 downloads)

That's great. With the seeing we have here in Middle Tennessee, I have to work a little to see star E and have never seen star F. ...and that is with the 12" dob. I included a diagram to help people.

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bhuloka
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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5717952 - 03/07/13 09:11 AM

Last November, under better-than-average seeing, red zone, I set up my 8" edge HD and my 16" Hubble optics dob, as a test of the 16" mirror, since I knew the 8" was very good. The 8" showed F star faintly and only intermittently. The 16" showed it clearly and steadily, very easy. So aperture does play a big role here. BTW, I used a variety of magnifications.

On other days, when seeing was not as good, neither scope revealed F. E was usually there in the 16" even under mediocre seeing. Light pollution didn't seem to be a major factor.


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nirvanix
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Re: My tale of Trapezium F - finally new [Re: bhuloka]
      #5718032 - 03/07/13 10:06 AM

I find in my backyard the theoretical limiting magnitude of my scopes cannot be reached - I'm assuming it's light pollution. E and F are magnitude 11 which is a stretch for my 4" refractor in the city. In fact I find the 10" dob can only reach about magnitude 12 from the yard. Under good seeing, it's not the separation of the doubles that presents the problem with the trapezium. I've split tougher doubles that are brighter using the 4" in town, Porrima for example.

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WRAK
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Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5718752 - 03/07/13 04:21 PM

Surprise - after a cloudy day a clear sky in the evening. NEML about +3mag and Pickering 6-7. M42 about 33 altitude so I gave STF748 AE and CF a try with a 140mm refractor. With x140 magnification I could barely make out the faint spot of E with a magnitude of +11.1mag but I could not resolve F with +11.5mag. This is my telescope magnitude limit with this degree of light pollution (without it would be about +13.4mag). Now and then there was a flicker in the diffraction pattern in the right position but then - there were also flickers in wrong positions, so no resolution.
Wilfried


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azure1961p
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Re: My tale of Trapezium F - finally new [Re: cpsTN]
      #5719951 - 03/08/13 07:45 AM

Quote:

That's great. With the seeing we have here in Middle Tennessee, I have to work a little to see star E and have never seen star F. ...and that is with the 12" dob. I included a diagram to help people.




Charles,

F can be a frustrating object for me in common seeing in winter from Connecticut. I will say though , if you haven't done it, running a small 5" DC fan rated 12v off a boxy 6v flashlight battery purrs along with no vibration for me and significantly less flaring in star patterns. My 5" is the typical computer type DC fan of the variety like the more common 3 or 4" had at RadioShack. I wouldn't rule out running two 4" DC fans behind that large a glass.

If you already are doing something similar than its probably seeing/collimation related.

In 7/10 its nicely shown for me, but in 3-4 its basically invisible and 5/10 barely there.

Pete


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nirvanix
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Loc: Saskatoon, SK
Re: My tale of Trapezium F - finally new [Re: azure1961p]
      #5720295 - 03/08/13 11:06 AM

Good idea Pete. Right now I have a little 50mm fan at the back of my 10" dob and I don't run it during observing because of vibration. The 120mm fan will move much more air and do it with less vibration.

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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5721178 - 03/08/13 08:49 PM

My experience with E and F is similar to many others' experience - E is much easier to see than F, and is less likely to disappear when seeing gets unsteady.

Nights I've seen both with 140mm refractor there's a big difference in the look of E and F - E pretty easy, F a tiny pinpoint of light.

These days, with both AE and CF being a little wider than the earliest measures, the AE and CF separations are near enough identical - 4.6" for AE, 4.5" for CF. Not enough to account for the difference.

The big factor is the magnitudes of A and C - A is listed at 6.55, C at 5.06. So you're looking at an 11th magnitude star not far from a much brighter one in each case - but C is ~4 times as bright as A. That by itself makes a big difference. Comparisons with brighter, closer, near-even pairs (such as Porrima) are meaningless - there's a totally different factor set involved.

The other thing that might make a small difference is the brightness level of the nebulous background - is it the same, to the eye, in both cases? I don't know, but in marginal cases a difference could affect visibility.

For smaller telescopes a further factor is that m11.5 is closer to the magnitude limit than m11.1 - especially when the other factors (above) are also in play.

So I'm surprised when F is seen with less than about 100mm aperture - even at 100mm it's doing very well. I'd expect it to take very good conditions and very good eyesight with 70-80mm telescopes. Exceptional in fact. It doesn't mean it can't happen, but it won't be the standard experience, as the many and varied comments in this thread show.


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jrbarnett
Eyepiece Hooligan
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Re: My tale of Trapezium F - finally new [Re: mikey cee]
      #5721335 - 03/08/13 10:34 PM

That's odd. I'd figure the spot size would be just as small in a 10" or 12" Dob, and I've never had any trouble with E or F in such scopes. In fact, I find it pretty easy in any scope down to 4" so long as it has decent optics and seeing cooperates.

Regards,

Jim


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jrbarnett
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Re: My tale of Trapezium F - finally new [Re: bhuloka]
      #5721365 - 03/08/13 11:09 PM

"So aperture does play a big role here."

Not really. None of these are particularly tight splits, so resolution is irrelevant. The issue with targets like Sirius B and Trapezium E and F is suppression of glare and stray light control. Quality and effectiveness of baffling, not aperture, are key with these targets. A high quality small scope (3" to 4") will have little problem with any of these targets. Heck, a good 80mm handles Sirius B at a mere 70x. Trapezium E and F are easy in a quality 4-incher at just over 100x. Often a larger scopes, and also an obstructed scope, have considerably more difficulty with these targets due to reduced contrast, increased scatter and excessive brightness and glare. Seeing is important too, and larger scopes suffer worse under poorer seeing - another indication that aperture may be the OPPOSITE of what is required on these targets on some nights.

Perhaps the Hubble just has considerably better contrast than the 8" SCT? 8" SCT have monster COs and even with (impossibly) perfect optics, can't achieve diffraction limited system performance. I'll bet that 16-incher has a much smaller CO than the C8, and accordingly a higher potential system Strehl and less scatter.

Regards,

Jim


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azure1961p
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Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5721418 - 03/09/13 12:03 AM

Quote:

Good idea Pete. Right now I have a little 50mm fan at the back of my 10" dob and I don't run it during observing because of vibration. The 120mm fan will move much more air and do it with less vibration.




Lol well if the 50mm is shaking your system the 125mm will too. I don't know why I've been so lucky with the lack of vibration . The tube is 6' long so that's a dampening effect I guess. Try lower voltage to bring the shakes down. I will say I don't run any fan at its rated voltage - its too much power to say nothing of the noise. Try different rubber bands .

Good luck Nirv.

Pete


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buddyjesus
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Re: My tale of Trapezium F - finally new [Re: azure1961p]
      #5721550 - 03/09/13 03:04 AM

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.


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Bonco
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Re: My tale of Trapezium F - finally new [Re: fred1871]
      #5722541 - 03/09/13 04:03 PM

Fred from Australia is spot on. Good explanation.
Thanks, Bill


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Bonco
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Re: My tale of Trapezium F - finally new [Re: buddyjesus]
      #5722549 - 03/09/13 04:09 PM

Quote:

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.




I'm not sure CF would ever look elongated. Because of the magnitude difference you must have sufficient magnification to create black space between the stars. Best wishes, Bill


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buddyjesus
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Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5722612 - 03/09/13 04:38 PM

i can definitely say I didn't see black space. I wasn't fully convinced about elongation either since I couldn't even pick a most likely position angle.

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WRAK
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Re: My tale of Trapezium F - finally new [Re: buddyjesus]
      #5723393 - 03/10/13 05:35 AM

If +11.6mag STF748F would be a single star without nebula you would be able under else perfect conditions so resolve it with a 60mm scope as the TML for 60mm is theoretical +11.6mag.
Given that F is near glaring C and within a nebula then under not so perfect conditions (Pickering 7, NEML 4.5, M42 below 45 altitude, some haze ...) I think it also impossible to resolve it with a 100mm scope with a theoretical TML of +12.7mag as the TML-loss due to these conditions is certainly larger than 1.2mag.
With some more light pollution as it usual near or on the fringe of big cities means NEML about +3mag even a 140mm scope will no longer resolve a +11.6mag star regardless if double or not and certainly not in competition with a glaring primary.
Wilfried


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fred1871
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Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5723467 - 03/10/13 07:36 AM

Wilfried, I think you're right about 60mm telescopes. But NEML isn't as bad as 3.0 on the fringe of every city, even large ones. It varies a lot.

From a suburban area with 2 million city population, where I was observing some years ago, I could see mag 4.5 normally on moonless nights. Another example - outer suburb, local population 400,000, NELM 5.0-5.5 on moonless nights.

Worst case from my recent experience - in outer parts of Sydney I can see mag 4-4.5 stars from some locations (moonless). Sydney area, 4+ million. Now there are areas of (suburban) Sydney that are overlit, so NELM of 3.0 would apply there.

But there's no universal level of light pollution in cities. I'm sure other people will make the same point. Obviously, you're in a difficult location for light pollution. What's your local population total? High, I'd expect, given your NELM figure often being around 3. That makes Trapezium F very difficult even with 140mm.


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WRAK
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Re: My tale of Trapezium F - finally new [Re: fred1871]
      #5723481 - 03/10/13 08:12 AM

Fred, I am located in the southern part of Vienna/Austria and my average NEML is about +3mag (on very transparent nights 3.5 and on hazy ones about 2.5).
Wilfried


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hazilim
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Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5737808 - 03/17/13 12:39 AM

Just saw F. I've tried many times before, without success. I didn't do anything different than previously:
Celestron 8SE (C8) reasonably well collimated.
Nagler 13mm T6.
Moon was not far away (1st quarter).
Maybe the seeing was better than usual - I don't know!
E was a cinch, while F was harder, but definitely there.
For E & F, perseverance seems to be the key.
Bob


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