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Eyepiece 16-20mm for 100/740 refactor

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#1 jarolym

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Posted 26 February 2021 - 04:02 PM

In short, I'm *very* happy about the high power views I get in the 4" f/7.4 Tak with my pair of Pentax XL 5.2mm (65dev AFoV), and I'd like to have similar experience in lower power as well. What EPs would provide it?

 

Long version:

I'm agonizing over low(er) power WA eyepieces for my setup:

- Tak FC-100DF: ED fluorite doublet 100/740 => convex field curvature with ~250mm radius, if I get it right (?)

- Baader Zeiss T2 prism

- Baader Maxbright II binoviewer

- dioptrix/custom-made alternative/my glasses (astigmatism, required)

 

I'm trying to match the following:

- something around 2.5mm exit pupil.

- good fit for the FC of my scope

- AFoV of 65deg or above would be nice, I'd settle for 60 if it were the only compromise.

- 1.25" diameter and 20mm eye relief

 

A nice bonus would be if they worked very well with my binoviewer & 1.7xGPC in my 250/1180 Dob too. The coma-correcting GPC gives ~f/8 - close to f/7.4 of my refractor, but the field curvature is different, I guess. So excellent performance in my Tak is the priority.

 

(Note about prices: Televue EPs are often recommended here, but cost about 150% of US prices in Europe, where I could get them - this makes them perhaps less obvious choice for me, compared to japanese EPs)

 

The candidates so far, and my concerns:

- Baader Morpheus 17.5mm (76°) - BillP reports "a small amount of FC" in a setup very similar to mine

- Televue Delite 18.2mm (62°) - inflated price in my case and a narrower FoV

- Nikon NAV SW 17.5mm (68°) - none, lack of relevant reports?

- Pentax XW 20mm (70°) - presumably the FC of the EP mismatches that of my scope?

- other options...?

 

Of course I don't want to spend more than necessary, but I'm also willing to bite the bullet once, cash out and be done with it for life, if the performance is *optimal*. My intention is to *use* that pair, rather than to get into an endless cycle of experimenting, doubting if there is a better option, reselling, hunting for next...

 

I do have pairs of 52° EPs that provide *either* the TFoV *or* the exit pupil I'm after, and also another pair of EPs that ticks all the boxes above *except* the sharp outer field. If there is no solution to my problem, I'll just accept it and will continue to use those I have.

 

I'm especially interested in real, hands-on experience of people using a scope of comparable dimensions/optical properties to mine.



#2 SeattleScott

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Posted 26 February 2021 - 06:00 PM

My 10mm Nikon is excellent and well regarded, but the only review I remember seeing of the 17.5 was by Ernest, and it wasn’t flattering. Hence people don’t buy them, and hence you don’t see reviews.

Of course used 17 LVWS come to mind, but availability is an issue.

Otherwise you are looking at the right ones.

Scott
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#3 sevenofnine

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Posted 26 February 2021 - 08:18 PM

Just a suggestion from the peanut gallery. If you update your signature so forum members can see exactly the equipment you have you will get better suggestions from those who have experience with high end equipment. Good luck! waytogo.gif



#4 Hesiod

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Posted 27 February 2021 - 05:19 AM

I do not use the binoviewer but as low power EP for my DF switch between a 32mm Plossl and the XW20.

To my eye with the XW20 the FC is not intrusive enough to make a lasting impression


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#5 25585

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Posted 27 February 2021 - 07:17 AM

My 10mm Nikon is excellent and well regarded, but the only review I remember seeing of the 17.5 was by Ernest, and it wasn’t flattering. Hence people don’t buy them, and hence you don’t see reviews.

Of course used 17 LVWS come to mind, but availability is an issue.

Otherwise you are looking at the right ones.

Scott

I use a pair of Nikon NAV SW 17.5mm for bino viewing. They are 70° AFOV, so the same as Pentax XWs. Much lighter than my pair of 17mm Vixen LVWs (65°). 17.5mm Morpheus come in between for weight but have the 76° AFOV. With my pair of those I have not noticed any field curvature.

 

WRT i.p.d., the Nikons are smallest & I find being lighter and their 70°, they are ideal ergonomically.

 

Pentax XL 5.2mm is a great eyepiece, my favourite 5mm, I only have one though. 


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#6 jarolym

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Posted 27 February 2021 - 08:08 AM

17.5mm Morpheus come in between for weight but have the 76° AFOV. With my pair of those I have not noticed any field curvature.

 

With which scope(s)?




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