23 replies to this topic

[Pauly63]

I'm not sure if this will work... I'm trying to get a full view of the M45 Pleiades Cluster. I have a Celestron Nexstar 8SE SCT. I use Baader Maxbright II Binoviewers. Both are for 1.25 barrel opening. I have low power eyepieces (32mm and 40mm) Plossyls but their FOV (Field of view is only 43 to 50) and i can't get the full view of pleiades. Usually only 2 of the 7 main star clusters in can achieve without moving the telescope finder left. right, up, down, etc. I see various brands sell extra wide or super wide eyepieces (32mm to 40mm) with FOV (field of views) ranging from 72 to 100... But they are all 2 inch diameter eyepieces. I was thinking of getting (2) Blue Fireball 1.25 to 2 inch eyepiece adapters and inserting them into the binoviewer eyepiece holders and then (buy) 2 of these 2 inch eyepieces. BUT I'm just not sure if this will achieve getting the full view of Pleiades. I do notice that using the binoviewers does seem to reduce the FOV a bit. But I'm also concerned that i might encounter that i will not have enough back focus to even focus on the object. Any information / and opinion from you all whether i should attempt this or not or if there is another viable way is very much appreciated. 

 

[havasman]

When we select our observing tools, telescope in this case, we select our targets. You have a very long focal length medium-small aperture telescope that will never be a preferred widefield instrument and M45 subtends 2^o by most definitions. You will be happier when you select observing targets that match well the capabilities of your very nice telescope. Don't worry, this failure to recognize instrument capability is very common among inexperienced observers. It is also the best illustration why few of us that've been doing this a while have but one scope.

 

true field of view  =  (eyepiece field stop diameter / scope focal length) x 57.3

 

Eyepiece field stop diameters can be found in the spreadsheet here:  https://www.cloudyni...e-buyers-guide/

Edited by havasman, 23 March 2025 - 04:24 PM.

[SeattleScott]

The full Pleiades cluster is 1.9 degrees wide. The Seven Sisters are 1.3-1.4 degrees wide. Without binoviewer, using a focal reducer and max FOV 1.25” eyepiece, or a max FOV 2” eyepiece without focal reducer, you can get 1.2 degrees out of a C8. With a reducer and 2” eyepiece, you could fit all seven sisters. There are a number of issues, such as operating at less than 8” aperture, vignetting, SAEP from the extreme focus with a reducer and 2” diagonal, generally some reflections and loss on contrast on planets from the reducer, potential clearance issues clearing the fork if you have a fork mounted SCT (especially Nexstar), etc. Is it worth it to view something the SCT wasn’t designed to view? Or just put a 50mm finder on there and check out Pleiades in the finder?

As for viewing all seven sisters with the binoviewer, it ain’t happening with that scope. You are limited to 1.25” format, probably have constraints around clear aperture in the binoviewer, etc. You might as well try pulling an RV with a moped. That would probably work out better for you.

If you really want to view the Pleiades in a binoviewer, look for a small refractor.

[SeattleScott]

Are you using the BV with a GPC or natively?

Install an f/6.7 reducer/flattener and no GPC. The 32mm eyepieces should work and the 40mm will as well.

That would help, assuming he can reach focus, which is very questionable. But even so it wouldn’t show all seven sisters, maybe five.

[ewave]

Yikes, you are trying to squeeze a 2⁰ field of view inside a 1⁰ field of view instrument.

 

As others pointed out already, this looks like a job for a refractor.

 

Here is a calculator that might help you:

 

https://astronomy.to.../field_of_view/

[Procyon]

Unfortunately you won't be able to see the entire Pleiades with that scope as it's almost a full 2 degrees wide. Your telescope can achieve up to a 1.04º True Field of View. Best to use binoculars or another type of telescope.

 

 

Baffle Opening Diameters:

C14 / 54mm
C11 / 54mm
9.25 Edge / 54mm
C9.25 / 46.5mm
8 Edge / 42mm
C8 / 37mm
C6 / 27mm
C5 / 27mm
C90 Mak / 15mm

[Matthew Trail]

Personally, I prefer to frame the Pleiades in binoculars. Even the 3.7 degree field in a Pan 35 in my refractor feels just a tad tight…

Edited by Matthew Trail, 23 March 2025 - 04:38 PM.

[havasman]

My favorite views of M45 have come via 10x50 binoculars. If you have a pair of binoculars around, give them a try.

[Bob4BVM]

When we select our observing tools, telescope in this case, we select our targets. You have a very long focal length medium-small aperture telescope that will never be a preferred widefield instrument and M45 subtends 2^o by most definitions. You will be happier when you select observing targets that match well the capabilities of your very nice telescope. Don't worry, this failure to recognize instrument capability is very common among inexperienced observers. It is also the best illustration why few of us that've been doing this a while have but one scope.

 

true field of view  =  (eyepiece field stop diameter / scope focal length) x 57.3

 

Eyepiece field stop diameters can be found in the spreadsheet here:  https://www.cloudyni...e-buyers-guide/

"why few of us that've been doing this a while have but one scope"

So true !

 

First, Be patient with your fine C8 !

While you may not get all 7 main stars in one FoV, you will be able to:

Study M45's smaller groups of stars and individual stars in great detail... 

Have you looked for the beautiful nebulosity around Merope and other bright members ?

Have you looked for the intricate groupings of fainter stars in the cluster ? 

How many close visual doubles and triples can you count in there ?

How many precise little triangles can you count in M45 as you scan across the cluster with your scope ?

Your C8 is a great tool for all that and more.

 

Different scopes are tools for different tasks, each has its place, just like you would not expect a screwdriver to function as pair of pliers

 

As much as I love binocular viewing, I still have a couple cyclops scopes, just because they are such great specialists.

In addition to my big workhorse BT, I still keep a 6"F5 frac and a 6"F15 frac.  VERY different tools, each with their own unique "personality"...

 

The Big BT is an amazing DSO tool for those distant galaxy groups and other DSO's up to about 1.4* TFoV.

 

6"F5 frac delivers a stunning 5.2+* TFoV at the wide end, perfect when i want to just relax and enjoy those sparkling wide field views.

 

And the 6"F15 frac delivers superbly crisp, very high magnification views, albeit at much narrower TFoV, but it's unbeatable when i really want to get close to Saturn's rings, lunar craters, or put M51 in a picture-frame view.

 

Sure these 3 examples can do cross-over duty to some degree, but the inescapable fact is that they are very different instruments, and each has its well earned place in my toolbox as I roam the heavens. 

 

Clear Skies,

Bob

Edited by Bob4BVM, 23 March 2025 - 05:24 PM.

[vtornado]

You could put a 50mm finder on top of your C8 and view the plieades through that.

[25585]

A 40mm 2" 68 AFOV single eyepiece will show most of the Pleiades.

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[SeattleScott]

The 40mm SWA will come close to showing all seven sisters, but probably come just short. I have heard the max is 1.22 degrees, and the seven sisters are 1.3 degrees.

So why does the illustration show them fitting? Because it can only work with the information fed into it. Bad data in, bad illustration out. An SCT with a 2” diagonal operates at around F11 instead of F10. So that kills the outer 10% or so. And distortion means the actual field stop of the eyepiece is a few percent less than the estimate provided using AFOV. So the actual view would be perhaps 15% smaller than the illustration, because it doesn’t account for the actual effective focal length (which is unknown) and it uses AFOV instead of field stop, which is often unknown. So it is an estimate and it is generally useful for comparing different eyepieces to each other. But the actual size of the FOV might not quite match what you would actually see through the scope.

In my opinion, it isn’t worth trying to fit Pleiades, or even the seven sisters, in an 8” SCT (other than in the finderscope). Just the wrong tool for the job.

[Polyphemos]

There’s no substitute for a short focal length refractor for this kind of job.

[Procyon]

Heh, try it. But I think it will vignette the outer field as the ES 40mm 68's field stop is 46mm and the C8's baffle opening is only 37mm.

 

If it doesn't work out, pan a bit to the east and check out the Beehive Cluster. M44

 

Target: The Pleiades, M45

Telescope: C8

focal length EP 40 mm

magnification 51 x
apparent FOV 68°
true FOV 1.3°
exit pupil 4.0 mm
 

 

Edited by Procyon, 24 March 2025 - 09:19 AM.

[SeattleScott]

It’s not a bad idea to get a 40mm SWA for a C8. If nothing else, it just barely squeezes in the Double Clusters (1.1 degrees wide). Beehive is still too big, and 7 sisters will likely be a touch to big also, but at least you can do some justice to Double Cluster (although it definitely looks better with more than 0.1 degrees for framing). And I can help with M35 or other large but not huge clusters, Hyades should fit, and it can make finding targets a little easier. I have one for my 6” Mak. Just don’t expect it to come close to doing justice to Pleiades.

[T1R2]

Use your 50mm finder scope to view M45....its way more satisfying  

[SeattleScott]

Use your 50mm finder scope to view M45....its way more satisfying

This is what I do with my Mak, which can even go a touch wider than a C8.

[izar187]

As others pointed out already, this looks like a job for a refractor.

________________________

 

Also 4", 5", and 6" short tube newts.

[RichA]

I'm not sure if this will work... I'm trying to get a full view of the M45 Pleiades Cluster. I have a Celestron Nexstar 8SE SCT. I use Baader Maxbright II Binoviewers. Both are for 1.25 barrel opening. I have low power eyepieces (32mm and 40mm) Plossyls but their FOV (Field of view is only 43 to 50) and i can't get the full view of pleiades. Usually only 2 of the 7 main star clusters in can achieve without moving the telescope finder left. right, up, down, etc. I see various brands sell extra wide or super wide eyepieces (32mm to 40mm) with FOV (field of views) ranging from 72 to 100... But they are all 2 inch diameter eyepieces. I was thinking of getting (2) Blue Fireball 1.25 to 2 inch eyepiece adapters and inserting them into the binoviewer eyepiece holders and then (buy) 2 of these 2 inch eyepieces. BUT I'm just not sure if this will achieve getting the full view of Pleiades. I do notice that using the binoviewers does seem to reduce the FOV a bit. But I'm also concerned that i might encounter that i will not have enough back focus to even focus on the object. Any information / and opinion from you all whether i should attempt this or not or if there is another viable way is very much appreciated. 

Not a fan of eyepieces that can show a lot of the Pleiades in an 8 inch SCT.  Most of them suffer from distortion and I dislike a misshapen star clusters.

[25585]

There is the 41 Panoptic and 31 Nagler which are said to be distortion-free.

[eblanken]

Hi Pauly63 & All,

 

I'm not sure if this will work... I'm trying to get a full view of the M45 Pleiades Cluster. I have a Celestron Nexstar 8SE SCT. I use Baader Maxbright II Binoviewers. Both are for 1.25 barrel opening. I have low power eyepieces (32mm and 40mm) Plossyls but their FOV (Field of view is only 43 to 50) and i can't get the full view of pleiades. Usually only 2 of the 7 main star clusters in can achieve without moving the telescope finder left. right, up, down, etc. I see various brands sell extra wide or super wide eyepieces (32mm to 40mm) with FOV (field of views) ranging from 72 to 100... But they are all 2 inch diameter eyepieces. I was thinking of getting (2) Blue Fireball 1.25 to 2 inch eyepiece adapters and inserting them into the binoviewer eyepiece holders and then (buy) 2 of these 2 inch eyepieces. BUT I'm just not sure if this will achieve getting the full view of Pleiades {IT WILL NOT, says Ed}. I do notice that using the binoviewers does seem to reduce the FOV a bit. But I'm also concerned that i might encounter that i will not have enough back focus to even focus on the object. Any information / and opinion from you all whether i should attempt this or not or if there is another viable way is very much appreciated. 

 

 

Personally, I prefer to frame the Pleiades in binoculars. Even the 3.7 degree field in a Pan 35 in my refractor feels just a tad tight…

 

 

My favorite views of M45 have come via 10x50 binoculars. If you have a pair of binoculars around, give them a try.

 

 

You could put a 50mm finder on top of your C8 and view the plieades through that.

 

 

A 40mm 2" 68 AFOV single eyepiece will show most of the Pleiades {BUT OP doesn't have 2 inch, Richard}.

 

 

The 40mm SWA {BUT OP doesn't have 2 inch, Scott} will come close to showing all seven sisters, but probably come just short. I have heard the max is 1.22 degrees, and the seven sisters are 1.3 degrees.

So why does the illustration show them fitting? Because it can only work with the information fed into it. Bad data in, bad illustration out. An SCT with a 2” diagonal operates at around F11 instead of F10. So that kills the outer 10% or so. And distortion means the actual field stop of the eyepiece is a few percent less than the estimate provided using AFOV. So the actual view would be perhaps 15% smaller than the illustration, because it doesn’t account for the actual effective focal length (which is unknown) and it uses AFOV instead of field stop, which is often unknown. So it is an estimate and it is generally useful for comparing different eyepieces to each other. But the actual size of the FOV might not quite match what you would actually see through the scope.

In my opinion, it isn’t worth trying to fit Pleiades, or even the seven sisters, in an 8” SCT (other than in the finderscope). Just the wrong tool for the job {I agree 100%, Ed}.

 

 

It’s not a bad idea to get a 40mm SWA for a C8. If nothing else, it just barely squeezes in the Double Clusters (1.1 degrees wide). Beehive is still too big, and 7 sisters will likely be a touch to big also, but at least you can do some justice to Double Cluster (although it definitely looks better with more than 0.1 degrees for framing). And I can help with M35 or other large but not huge clusters, Hyades should fit, and it can make finding targets a little easier. I have one for my 6” Mak. Just don’t expect it to come close to doing justice to Pleiades.

 

Hi All,

 

The bottom line is that the variety of reasons why this can't work:

 

{A} SCT is too slow at native f/10

{B} SCT is native at 1.25 inch format by design

{C} SCT can do 2 inch, but there are limitations (for one Baffle tube restrictions)

{D} SCT with 2 inch Diagonal (like I own several of) "pushes" the design toward f/11 (as Scott has said)

{E} Original Poster (OP) is using 1.25 in format BINO-Viewers, which further restrict TFoV and compounds the issues

{F} Ase several have suggested, the desired object is TOO WIDE for SCT and better suited by a faster scope (a Refractor, etc.)

{G} Good suggestions are (1) 50mm finder, (2) Binoculars, (3) Piggy-back 60-72mm Refractor, (4) Separate 80-100mm Refractor . . . 

{H} Also, consider "changing the quest" and SCT config . to 2 inch diagonal and open the door to get "Much" of what the TFoV that can be gotten, but that gives up on the BINO-Viewer . . .  

 

My $0.02,

 

Best,

 

Ed

 

P.S. Note that suggesting 2 inch eyepieces for a post that said 1.25 inch format BINO-USER is just "un-cool", says me . . . 

Edited by eblanken, 24 March 2025 - 01:29 AM.

[25585]

A C6 or 127 MCT OTA, being shorter in FL, is an alternative.

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Edited by 25585, 24 March 2025 - 06:02 AM.

[Jon Isaacs]

A C6 or 127 MCT OTA, being shorter in FL, is an alternative.

A C-6 has a 1 inch diameter rear port. A 40mm 68 degree has a 46mm = 1.81 inch field stop.  

 

Something's got to give.

 

Jon

Edited by Jon Isaacs, 24 March 2025 - 07:36 AM.

[Procyon]

Kind of like trying to fit and bake a 46cm diameter sized frozen pizza on a 27cm diameter sized baking pan. 19cm of the outer dough's circumference will fall out.

 

 

Same as trying to view a 40mm ES 68 with a 46mm Field Stop through a C6 with a 27mm baffle opening.

 

Won't the outer 19mm of the eyepiece's field stop vignette?

 

Probably better off using a a 32mm Plossl with 50º Afov or a 40mm Plossl with 43º Afov, both have a 27mm field stop.

Edited by Procyon, 24 March 2025 - 08:34 AM.