Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Borg 101ED vs 107FL

Refractor Visual
  • Please log in to reply
22 replies to this topic

#1 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 21 January 2022 - 10:51 AM

Right now I'm using a Borg 101ED with a Zeiss binoviewer and 2 Pentax XW 20mm EPs. That gives a magnification of 32X and an exit pupil of 3,15mm. I use it for birding, and it works OK, I just miss some more light and contrast unless it's really bright sunshine. So I'm considering to get a 107FL objective, that will fit my 80mm tube, and being 600mm vs 640 it will give me an enlargement of just 30X and an exit pupil of 3.56mm. The smaller enlargement is no problem, rather an advantage, but it's a very expensive objective and hard to find second hand, so I wonder if it's worth doing that upgrade?

 

I'm not sure how visible the increase in exit pupil from 3.15 to 3.56mm will be, and how much better the contrast will be in the 107FL? In terms of sharpness there'll probably be very little difference at so low power.

 

Unfortunately I have no possibility to try it out for myself, I live in Denmark, where there is no Borg dealer, and I don't know anyone having this objective. So I'm interested to hear, if anyone from this forum has compared the 101ED directly to the 107FL and can give me an idea, if there is a clearly visible difference between these 2 objectives.

 

Thanks for your time,

Henrik.



#2 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 21 January 2022 - 11:54 AM

It's often said that in bright daylight your eye pupils open to only 2-3 mm, in which case only a transmission difference, if any, would affect the brightness difference seen between the two objectives. Personally I think that is an underestimation and that you will have some effect from the increased exit pupil size.

 

Have you thought about using slightly longer eyepieces? 24mm would give 27x magnification and 3.8 mm exit pupil, for example.

 

I'd be interested to see what combination of parts and accessories you use to attach your binoviewer.


  • 25585 likes this

#3 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 22 January 2022 - 05:50 AM

Hello Mark,

 

Thanks for your reply. Yes, I am also using longer EPs. When it's really hazy in the summer time, I use a pair of APM UFF 24mm, but they are only 65 degree AFOV, and for catching birds in flight or finding them at the sky, I really prefer 100 degree. It's really hard to find +20mm 1.25" EPs with a wide field of view. I'm trying to find a pair of 20mm Wide Scan Type III 84 degree, but haven't managed to find them, they're not produced any more. So I'm considering to try making a modification of my binoviewer, so I can use 2" Masuyama 26mm with 85 degree AFOV, that would be nice. But don't know if it will work, I think it should though. Tried to hold one EP in front of the opening, it looked fine, so I just need another one and some way to attach them.

 

To attach my Zeiss binoviewer I just use this Baader #2456313 adapter in combination with a 2" T2 threaded nose piece: https://www.baader-p...2-part-06).html

 

Of course the binoviewer splitting technique reduces the amount of light a lot, so that's maybe the main bottleneck and not the exit pupil? I really hope, I can get a brighter image some way though, that's more important for terrestrial viewing than for astronomy. But in cloudy weather my pupils should also be open more than 4mm, I suppose, even if I'm soon 67 y.o. Now I just tried to attach my APM UFF 24mm in one side, I could see it actually had a slightly brighter image and better contrast than the Pentax XW 20mm.

 

Cheers Henrik.


  • Mark9473 likes this

#4 25585

25585

    James Webb Space Telescope

  • *****
  • Posts: 16,311
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the SW UK. 51°N

Posted 22 January 2022 - 11:24 AM

You might do better for birding using binoculars in 80mm or 100mm sizes. Does anyone know what magnifications 24 UFFs give with those?



#5 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 22 January 2022 - 11:30 AM

The advantage of a scope + binoviewer is that you can get terrific close-focus views by just adding extension tubes.

#6 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 22 January 2022 - 06:11 PM

Binoculars of course give much more light than a binoviewer, but these large 80 or 100 mm binoculars like for instance APM or Oberwerk are useless for birding, since you have to focus each eyepiece individually. You need a fast and very smooth central focusing wheel.


Edited by Birder, 22 January 2022 - 06:11 PM.


#7 Spikey131

Spikey131

    Gemini

  • *****
  • Posts: 3,028
  • Joined: 07 Feb 2017

Posted 22 January 2022 - 07:18 PM

It is hard to imagine that you will be able to see the slightest difference in brightness between a 101 mm and 107 mm object.

 

I am also doubtful that you will find anyone on CN who has directly compared the 101ED with the 107FL objectives.  But I have been surprised by things like this on CN before, so it is possible.


  • Birder likes this

#8 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 22 January 2022 - 07:48 PM

Henrik, as an afterthought, have you made a diagram of your 101ED with the binoviewer installed? It's a fast objective and the binoviewer takes up a significant amount of back focus. You should check if the more forward position of the focuser isn't restricting the light cone.
  • Birder likes this

#9 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 23 January 2022 - 04:35 AM

Mark, I don't know how to make a diagram or what kind of diagram you're thinking of? It's true the focuser has a forward position, I only use a 150mm tube between the Borg Rack'n'Pinion focuser and the objective.

 

Of course I use a 45 degree erect image prism for birding, that maybe reduces the amount of light as well. But I didn't know there could be a problem having the tube too short.


Edited by Birder, 23 January 2022 - 04:59 AM.


#10 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 23 January 2022 - 04:45 AM

Spikey, it's not only due to brightness I'm considering the upgrade. I'll get 30X in stead of 32X enlargement, that will give me a slightly wider actual field of view, and then I want some more contrast as well. So even if the increase in brightness is minimal, I would consider the upgrade, if I got some more contrast in the image. But that's maybe minimal as well, 101ED is definitely not a bad objective.


Edited by Birder, 23 January 2022 - 04:47 AM.


#11 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 23 January 2022 - 04:59 AM

Mark, I know you can get some correctors to use with binoviewers, that don't reduce the actual focus length, so you can use binoviewers with telescopes, where it's not possible to shorten the tube, as it is with Borg. But they are quite expensive, and I'm thinking the fewer optical elements, the better image. But of course, if I'm loosing light by using so short a tube, that might be the solution, I just don't know how to calculate that?

 

Maybe I could try with a 200mm tube, then I can only focus at close range, but that might give me an idea, if the image gets a lot brighter that way.


Edited by Birder, 23 January 2022 - 05:02 AM.


#12 markb

markb

    Vanguard

  • *****
  • Posts: 2,286
  • Joined: 16 Jun 2006
  • Loc: Arizona at last, goodbye NY. Light pollution still awful though

Posted 23 January 2022 - 12:39 PM

Birder, the 20mm Widescans should readily pop up for you if you post want ads but don't specify the Type III. You might end up buying from the US though.

 

UO University Optics sold large numbers in the US, and I never had problems locating them with want ads. Orion (US) sold a version with slightly different fl markings but I believe they match the UOs. I recall there was a third retailer in North America, and KK labeled ones appeared in Europe.

 

To my knowledge your best, and possibly only, barrel limited 'widest' alternatives in 1.25 barrels are the KK/UO Widescan 20s, APM UFF 24s and I think the 24mm Pans, beloved by many. Check Don Pensack's spreadsheet pinned to the top of the eyepiece forum, too.

 

All three have about the same effective field stop, and about the same True FOV. All three are very good eyepieces, the Widescans being an older design with limitations caused by the widest AFOV design, but still great in use.

 

I would contact Markus Ludes at APM and ask him if he has any ideas, he retailed the KKs at one time.

 

The 20 was the sweet spot of the design and I have bino pairs and singles with scopes. They get used all the time at night. I don't feel the Type IIIs are worth searching for. To some extent the line's reputation was damaged by the widely cloned, eventually inexpensive 30mm, not a happy match to a fast newt with resulting obvious coma, or big f5 refractors with heavy field curvature. I seem to recall Tom Trusock did a fair and impartial write up of the line, it might be here in the CN Reports, I am not sure.

 

That said, my recollection is that the APM UFF 24s share essentially the same field stop, so the True FOVs are essentially the same (I guess one day I should try both in a binoviewer and compare them).

 

The UFFs give a slightly larger ep and may be brighter, the WS will give the smaller exit pupil and may appear to have dimmer fields; I'll leave effective use of the ep in comparision to the eyes pupil in daylight to others, I'm sure you can easily compare the two by using any 20mm regardless of FOV. 

 

I have only noticed field curvature issues on the 30mm, the 20mm WS never bothered me. I'm sure the UFF is a better choice if field curvature is an issue for you.


Edited by markb, 23 January 2022 - 12:44 PM.

  • Birder likes this

#13 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 23 January 2022 - 04:40 PM

Thanks for your comments Mark, I've had ads searching for the Widescans for around a year now, have been only offered a single one, which was too expensive. But you write I shouldn't search for type III, that's the only one I know, are type 1 and 2 better in some ways and are they 84 degree as well? I can't get the image wide enough for birding, it's so much easier to find flying birds with a wide field, my standard EPs when I'm not binoviewing are Nikon NAV-HW 12.5 and 17mm, both 102 degree.

 

But maybe it would be easier to find the KK 20mm here in Europe, I'll ask Markus, I deal with him regularly. I know there are also 24mm Hyperion, ES and Panoptic at 68 degree AFOV, but from what I've read, and you seem to agree, the UFFs are quite as wide, and optically I'm very satisfied, they are just far too narrow for me. I'm not at all sensitive to field curvature, that is not really noticeable for birding, the birds are often just surrounded by water or sky.



#14 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 23 January 2022 - 05:45 PM

Mark, I don't know how to make a diagram or what kind of diagram you're thinking of? It's true the focuser has a forward position, I only use a 150mm tube between the Borg Rack'n'Pinion focuser and the objective.

 

Of course I use a 45 degree erect image prism for birding, that maybe reduces the amount of light as well. But I didn't know there could be a problem having the tube too short.

What I mean is that you draw a large triangle 101 mm high and 640 mm long (to scale, on paper or your computer) and measure the diameter of all internal openings and their distance to the objective lens, in the tube, focuser, adapter, diagonal, ... whatever comes between the objective and the eyepiece. If you position these correctly and to scale on the drawing you can see if anything clips the light cone and reduces the effective aperture, which would cause a dimmer view.

 

raytrace.PNG


  • Birder likes this

#15 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 23 January 2022 - 05:50 PM

Mark, I know you can get some correctors to use with binoviewers, that don't reduce the actual focus length, so you can use binoviewers with telescopes, where it's not possible to shorten the tube, as it is with Borg. But they are quite expensive, and I'm thinking the fewer optical elements, the better image. 

 

The usual correctors used with binoviewers, actually improve the image quality by correcting for the chromatic aberration caused by the prisms in the binoviewer.


  • Birder likes this

#16 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 05 February 2022 - 09:19 AM

Mark, thanks a lot for the drawing, but I have no idea how to make those measurements, as there are lots of parts in the chain. But wouldn't I see some vignetting, if some parts were clipping that cone? There is no vignetting to see at all.



#17 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 05 February 2022 - 09:25 AM

Just use a ruler.
But if that's too difficult, just forget it, I won't hold it against you.
  • Birder likes this

#18 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 15 February 2022 - 08:56 AM

Borg 101ED diagram.jpg

What I mean is that you draw a large triangle 101 mm high and 640 mm long (to scale, on paper or your computer) and measure the diameter of all internal openings and their distance to the objective lens, in the tube, focuser, adapter, diagonal, ... whatever comes between the objective and the eyepiece. If you position these correctly and to scale on the drawing you can see if anything clips the light cone and reduces the effective aperture, which would cause a dimmer view.

 

attachicon.gifraytrace.PNG

 


Mark, now I tried to take my telescope apart and measure all the inner diameters down to the correct image prism. It seems there is no cutting of the light cone till there. The drawing is not 100% accurate in dimensions, bet it seems it is at least minimal the light cone will be clipt, if I understand the theory right. I'm not quite sure about the length, you write I should draw a cone of 640mm, which is the focal length of the objective, but my tube is only 370mm long till where the prism begins. What's going on from there physically until my pupil, I have no idea about.

 

Regards Henrik


Edited by Birder, 15 February 2022 - 08:57 AM.


#19 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 22 February 2022 - 01:54 PM

Good work! If there's no clipping up to the prism entry then you're fine I think.
  • Birder likes this

#20 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 22 February 2022 - 03:20 PM

Well, that's good if that's the fact Mark, but the diameter of the prism entry is 31mm, so the light cone width of 20mm is MUCH smaller than the actual prism. But since the first reduction from 112 to 80mm is built into the telescope and can't be changed, I suppose it's impossibble to get a light cone that is 31mm wide at the entry of the prism. The other clips of the light cone follow the same line as the first clip, which so to say dictates the line direction. So with this telescope I suppose you're right, that's the max light, I can get.

 

But if I used another telescope allowing a wider light cone, so the 31mm width of the prism was fully illuminated, would I then have a much brighter image?


Edited by Birder, 22 February 2022 - 03:21 PM.


#21 Mark9473

Mark9473

    Voyager 1

  • *****
  • Posts: 12,341
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 22 February 2022 - 05:08 PM

Well if you would find another refractor with 101mm aperture, the only way to get a wider light cone at the location of the prism entry is if the objective lens has a longer focal length - on condition that the light cone isn't clipped (the 80mm tube would have to move backwards, for example).

A wider lightcone at the prism doesn't do anything for the brightness of the view, however. That brightness is determined by the exit pupil size, minus transmission losses.
  • Birder likes this

#22 Birder

Birder

    Explorer 1

  • *****
  • topic starter
  • Posts: 93
  • Joined: 07 Feb 2019
  • Loc: Denmark

Posted 22 February 2022 - 05:30 PM

OK, thanks for all your help Mark, when a wider light cone doesn't result in a larger exit pupil, then I understand it will not give a brighter image. A longer focal length will not be good for my use, as I already have problems at 640mm finding 1.25" EPs long and wide enough to get as low power as max 32X with 70 degree AFOV or more.



#23 markb

markb

    Vanguard

  • *****
  • Posts: 2,286
  • Joined: 16 Jun 2006
  • Loc: Arizona at last, goodbye NY. Light pollution still awful though

Posted 22 February 2022 - 05:59 PM

I'll apologize for not reading through the thread for the details on your EP issue, but in 1.25 the two most likely candidates are the long discontinued but wonderful University Optics/KK Widescan 20, 80 degrees, and the current  Baader Hyperion 24mm 68 degree eyepieces. 

 

Both have maximum fields limited by the barrel inside diameter. 32x and 27x, respectively. 

 

The 20 mm Widescan was, my opinion, sharp and the best in the WS range, but that can only be obtained used, usually in the $100-140 range, and a want to buy it is probably the best way to go. I believe they are all multi-coated.

 

EDIT I just realized I had previously giving you all the information on the wide scans, I assume you've been unable to find one in Europe.

 

But, since I was looking for an alternative myself I did come up with the following:

 

The 24mm,  68 degree Hyperion is current, a much newer design with Baaders great Phantom coatings, and reviews should be easily located. I have not had one, but I have several Baader optical items, all are excellent.

 

It should be very easy to locate in Europe, and should come as close as possible to meeting your specs. According to calculating the values, it should get you about another tenth of a degree TFOV over the UFF.

 

The 1.25 barrel is your enemy, and caps your true field at approximately 2.55° calculated without respect to your specific glass and tube. There are different mm and AFOV combinations to reach that number, but you will be held within a narrow range by your field and power goals.


Edited by markb, 22 February 2022 - 06:08 PM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Refractor, Visual



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics