78 replies to this topic

[JohnnyMac]

It was nuts in Coma and Virgo.

Might have to go buy one

[Procyon]

This looks interesting, Skywatcher 6" F/4 with an included coma corrector that brings it down to F/3.45.  4 deg field with a 21mm Ethos @ 6mm exit pupil. ST80 fields with 6" of aperture...

 

https://www.firstlig...-corrector.html

 

Anyone tried this visually?

These newtonians are bargains at these prices!

 

https://www.bhphotov...tonian_ota.html

[Houdini]

They are a bargain.

I bought a similar 200 mm F/4 Newtonian to test the Houdini eyepieces, and the views are very nice (40X and 2.15° field with the 20 mm), but the focuser is rather poor. Perhaps not surprisingly, some good focusers cost more than this entire telescope.

Also, in daylight, when your pupil is not that large, the shadow of the secondary can be visible.

[Bob4BVM]

For me it's gotta be my 6"'F5 Jaegers.

At 5.3*, it's pretty awesome at my B1 high desert sites in E. Oregon.

I have a couple of EP's that can get to over 5* with it.

 

If i'm staying for more than 2 nights, i pack up the binoscpe too, has its own rich field feeling even though it's only 1.4*.   The bino feed plays some tricks in the visual cortex that makes it seem alot wider.

 

CS

Bob

Edited by Bob4BVM, 27 April 2025 - 07:50 PM.

[stomias]

SV 102   32mm Koenig

[Roger Belveal]

Going to go old school with my Celestron Comet Catcher and my Meade 18mm HD-60 eyepiece. Sure hope it's summertime viewing...

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[msc8]

For me it's gotta be my 6"'F5 Jaegers.

At 5.3*, it's pretty awesome at my B1 high desert sites in E. Oregon.

I have a couple of EP's that can get to over 5* with it.

 

If i'm staying for more than 2 nights, i pack up the binoscpe too, has its own rich field feeling even though it's only 1.4*.   The bino feed plays some tricks in the visual cortex that makes it seem alot wider.

 

CS

Bob

Umm how do you get to a 5.3 degree field with this set up?  what eyepiece focal length combo gets you that much field

[ABQJeff]

What I most use for rich field….
For 4 degrees: ST120 and ES 30mm 82 degree
For ~3 degrees (2.9 really): 140mm F/6.5 with Pentax 40XW

4 degrees is nice to get North America and Pelican, or both East and West Veil.

~3 degrees will just fit M31, North America, East or West Veil, Sagittarius Star Cloud.

As Tom Dey points out, don’t forget two eye viewing. My 23x110 (2.9 degree) binoculars gives better M31 and Milky Way Star Cloud views than my 140 f/6.5 in mono.

 

Also as Jon and Tom both point out, it is about maximizing exit pupil in dark skies.  This can be done with big telescopes.

 

My C11 Edge with 0.7x reducer and Masuyama 50 degree eyepiece gives fantastic 1.35 degree, 40x, 7mm exit pupil views (many don’t consider SCTs as RFTs,  )

 

ST120, 23x110s, 140 F/6.5 with C11 Edge, 80mm F/6 with 150mm Mak.

Edited by ABQJeff, 29 April 2025 - 09:11 PM.

[Procyon]

What I most use for rich field….
For 4 degrees: ST120 and ES 30mm 82 degree
For ~3 degrees (2.9 really): 140mm F/6.5 with Pentax 40XW

4 degrees is nice to get North America and Pelican, or both East and West Veil.

~3 degrees will just fit M31, North America, East or West Veil, Sagittarius Star Cloud.

As Tom Dey points out, don’t forget two eye viewing. My 23x110 (2.9 degree) binoculars gives better M31 and Milky Way Star Cloud views than my 140 f/6.5 in mono.

Also as Jon and Tom both point out, it is about maximizing exit pupil in dark skies. This can be done with big telescopes.

My C11 Edge with 0.7x reducer and Masuyama 50 degree eyepiece gives fantastic 1.35 degree, 40x, 7mm exit pupil views (many don’t consider SCTs as RFTs, )

ST120, 23x110s, 140 F/6.5 with C11 Edge, 80mm F/6 with 150mm Mak.
IMG_9674.jpeg

Whoa, wait a minute, what's going on here? Created your own star party? And how is the Edge's dew shield white, unless it's reflectix? : )

PS> Just this morning I was thinking what would the view look like through my CPC 1100, an f/6.3 focal reducer and my 25mm ES 100...and 48mm Brandon.

Great stuff. The whole lot lol.

Love the hanging accessory sacks for each mount also, have a big black one from B&H, so useful.

Edited by Procyon, 29 April 2025 - 09:28 PM.

[ABQJeff]

Whoa, wait a minute, what's going on here? Created your own star party? And how is the Edge's dew shield white, unless it's reflectix? : )

PS> Just this morning I was thinking what would the view look like through my CPC 1100, an f/6.3 focal reducer and my 25mm ES 100...and 48mm Brandon.

Great stuff. The whole lot lol.

Love the hanging accessory sacks for each mount also, have a big black one from B&H, so useful.

C11 Edge wrapped in Reflectix as you surmised. 

 

Regarding "equipment explosion"... Yeah if Milky Way is up I get out all the toys (for mentioned wide field targets, NA, Veil, Miky Way core clouds plus the high mag equipment for globulars, plantary nebula, etc.).)  

 

The 80mm triplet apo and 150mm Mak I only had out this one time to my dark site to check them out before bringing on an airline trip (that is my biggest air travel set-up.)

 

For galaxy season and winter I will just bring out the C11 Edge and 140mm because mainly small targets.

 

(note: I always bring some handheld binoculars as well in any season, namely the Canon 15x50IS and Maven b1.2 8x42s). 

 

And yes "tripod hammocks" are useful for storage and functional for lowering center of gravity.

Edited by ABQJeff, 29 April 2025 - 09:56 PM.

[Bob4BVM]

Umm how do you get to a 5.3 degree field with this set up?  what eyepiece focal length combo gets you that much field

The 6"F5 OTA has a focal length of 762mm.

The EPs are:

32mmPlossl 5* TFoV
40mmPlossl 5.3* TFoV

35mmErfle 5.2*  TFoV

 

The field stops in those three are 68, 72, 70 mm respectively

Magnifications are 24, 19, 22X

Low mags, and large exit pupils, but wonderful in a truly dark sky !

Edited by Bob4BVM, 30 April 2025 - 01:46 AM.

[davidgmd]

The 6"F5 OTA has a focal length of 762mm.

The EPs are:

32mmPlossl 5* TFoV
40mmPlossl 5.3* TFoV

35mmErfle 5.2*  TFoV

 

The field stops in those three are 68, 72, 70 mm respectively

Magnifications are 24, 19, 22X

Low mags, and large exit pupils, but wonderful in a truly dark sky !

    
Are those 2” eyepieces? How does a 2” Plössl or Erfle with a 2” (50.8 mm) barrel have a field stop > 50 mm?

[havasman]

+1 for an NP101/31T5 combo

 

 

That is unless you can go for this one  -  https://www.bbastrod... Telescope.html

Edited by havasman, 30 April 2025 - 03:49 PM.

[davidgmd]

Dick, that 25” f/2.6 is pretty nifty, as is the mount! Lotsa light, but still not close to 4 degrees.

  
What is a “slumped” mirror?

[havasman]

What is a “slumped” mirror?

I only know what I remember from the bits I have read about them and that may not be correct. But I think they are really thin mirrors that have been heated to a point of elasticity and shaped into close approximations of the desired parabolic curve and then ground into their final shape. That makes them lighter than a mirror shaped from a standard blank, possibly easier to grind but probably in need of very good support from their mirror cell.

 

Maybe somebody else can come along and correct my impressions.

[havasman]

https://www.cloudyni...lumped-mirrors/

 

Post #4 in that forum string is Pierre Lemay defining slumped mirrors with pics of some of his work with them and he refers us to Mel Bartels, here  - https://bbastrodesig...l comments.html

 

I expect there's more on Bartels' site about the mirror.

[Bob4BVM]

https://www.cloudyni...lumped-mirrors/

 

Post #4 in that forum string is Pierre Lemay defining slumped mirrors with pics of some of his work with them and he refers us to Mel Bartels, here  - https://bbastrodesig...l comments.html

 

I expect there's more on Bartels' site about the mirror.

Mel is the master at this.  IIRC he said the thin glass is laid onto a negative "mold" shaped like the finished mirror, and then heated in the kiln until it slumps to the shape of the mold, thus eliminating a lot of grinding.

He has made a few like that, but his masterpieces are a pair of 30"F2.7's

Amazing mirror, amazing scope to look thru and at

 

Mel has a pair of slumped 42" blanks in his shop. I keep pestering him about a serious binoscope !

[kasprowy]

My TV76 and Orion Megaview 28mm.

4.8 deg fov

[Bob4BVM]

    
Are those 2” eyepieces? How does a 2” Plössl or Erfle with a 2” (50.8 mm) barrel have a field stop > 50 mm?

It doesn't.  For those kind of TFoV's, 2-inch EP's need not apply

 

(click on image for better view)

Edited by Bob4BVM, 30 April 2025 - 08:05 PM.

[Jon Isaacs]

It doesn't.  For those kind of TFoV's, 2-inch EP's need not apply

 

(click on image for better view)

1.25 VS 3 inch EPs.jpg

 

What's the field stop on the 35 mm Erfle?

 

I calculate for a 5.3 degree field, it would require a 70.5 mm field stop 

 

To do that with a 35 mm eyepiece would require a ~115° AFoV and the exit pupil would be 7 mm.

 

To do it with a 50 mm eyepiece would require a ~81° AFoV and provide a 10 mm exit pupil.  For someone with a 7 mm dark adapted pupil, the effective aperture would be about 106 mm 

 

 Somehow, for me, the numbers don't add up. 

 

Jon

Edited by Jon Isaacs, 30 April 2025 - 08:37 PM.

[Procyon]

I calculated a 32mm Eyepiece with 120º, a 35mm with 115º and a 40mm with 101º

 

Interesting  

 

Siebert 3"ers?

Edited by Procyon, 30 April 2025 - 09:43 PM.

[Bob4BVM]

What's the field stop on the 35 mm Erfle?

 

I calculate for a 5.3 degree field, it would require a 70.5 mm field stop 

 

To do that with a 35 mm eyepiece would require a ~115° AFoV and the exit pupil would be 7 mm.

 

To do it with a 50 mm eyepiece would require a ~81° AFoV and provide a 10 mm exit pupil.  For someone with a 7 mm dark adapted pupil, the effective aperture would be about 106 mm 

 

 Somehow, for me, the numbers don't add up. 

 

Jon

See post 61

[Jon Isaacs]

See post 61

The 6"F5 OTA has a focal length of 762mm.

The EPs are:

32mmPlossl 5* TFoV
40mmPlossl 5.3* TFoV

35mmErfle 5.2*  TFoV

The field stops in those three are 68, 72, 70 mm respectively

Magnifications are 24, 19, 22X

 

 

As I said, things don't compute.

 

AFoV = 57.3 deg/rad x FS/FL

 

For the 32mm Plossl:  AFoV = 57.3 deg/rad x 68mm /32 mm = 122 deg AFoV

 

40mm Plossl:  AFoV = 57.3 deg/rad x 72mm/40mm = 103 deg AFoV

 

The 35mm Erfle:  AFoV = 57.3 deg/rad x 70mm/35mm =  115 deg AFoV. 

 

Jon

[Procyon]

Siebert Optics lists their 3" eyepieces as such:

 

3" 40 -70mm $999  (Brass) add $299*

All have 25mm E.R.

The 3" 40mm 75 deg FOV

The 3" 42mm 75 deg FOV

The 3" 50mm 70 deg FOV

The 3" 55mm 70 deg FOV

The 3" 60mm 65 deg FOV

The 3" 65mm 63 deg FOV

The 3" 70mm 58 deg FOV

The 3" 75mm 55 deg FOV

The 3" 80mm 50 deg FOV

4.0 pounds

 

PS> On Don's eyepiece spreadsheet there are 3" with such wide field stops. 

 

Brand Model MFR Category FL Diam. AFOV Wt. Eye Relief Mfr's Field Stop  Calc.FieldStop

 

Harry Siebert Optics Observatory Elite Series HSO Medium Field 80.0 3.00 60  25.0 ? 83.8
Harry Siebert Optics Observatory Elite Series HSO Medium Field 75.0 3.00 60  25.0 ? 78.5
Harry Siebert Optics Observatory Elite Series HSO WideField 65.0 3.00 65  25.0 67.0 73.7
Harry Siebert Optics Observatory Elite Series HSO Medium Field 70.0 3.00 60  25.0 67.0 73.3
Harry Siebert Optics Observatory Elite Series HSO WideField 60.0 3.00 65  25.0 67.0 68.1
Harry Siebert Optics Observatory Elite Series HSO WideField 55.0 3.00 70  25.0 67.0 67.2
Harry Siebert Optics Observatory Elite Series HSO WideField 50.0 3.00 70  25.0 67.0 61.1
Harry Siebert Optics Observatory Elite Series HSO UltraWideField 42.0 3.00 75  25.0 67.0 55.0
Harry Siebert Optics Observatory Elite Series HSO UltraWideField 40.0 3.00 75  25.0 67.0 52.4
Explore Scientific 3" Series JOC Hyper Wide Field (XWA) 30.0 3.00 100 2353 17.0 52.2 52.4

Edited by Procyon, 01 May 2025 - 10:23 AM.

[Procyon]

Can one use an AT72EDII with say a 31mm Nagler or a 35mm Panoptic? Or will vignetting occur? 

 

I asked TS Optics if a TSFLAT2 field corrector could be used with a 72 APO and they replied this:

 

"thank you for your interest. The TSFLAT2 will work with the 72mm f6 refractor. Working distance is 130mm but we suggest the corrector only for sensors up to 25mm diameter and smaller. Than you will have good stars also in the edges."

 

I replied to them asking:

 

Oh thank you very much, I will use it for visual widefield only. You think it will be good with eyepieces 40mm field stop?

 

and they replied:

 

"yes it will work. The Flattener should be adapted into the 2" Filterthread of the diagonal."

Edited by Procyon, 01 May 2025 - 10:34 AM.