Takahashi 28mm Erfle

[JTEC]

Does anyone have any experience of this eyepiece please?  Thinking of mono and possibly binoviewing.  I’ve read some comments online but can’t find much recent or detailed. Thanks.

[Louis D]

Contact user 25585 here and on CN (same ID).  He's the only one I know of with one.  He seems to think highly of it.

[JTEC]

Many thanks,  Louis 👍🏻

[Scott42]

I had this eyepiece for a while.  It has the high-quality Takahashi glass and coatings I like, but the Erfle design had very bad edge correction in the f/7-f/8 refractors I use.  It seemed like the eyepiece was designed to be used at f/10 and above.  I've had other "Erfle"-marked eyepieces that did better at f/8.   It might work well in a bino-viewer if the f-ratio is mulitplied up into the f/10-f/15 range.

I would recommend something like 30mm Tak LE's instead.  The FOV is a little smaller but they perform well at all f-ratios.

Edited August 6, 2019 by Scott42

[JTEC]

Many thanks, Scott42.  Pretty much as I thought.  I want to like the Erfle because I’m interested in those more traditional designs, but it sounds as though there are better options.  I’ve used 10mm and 18mm Tak LEs in the binoviewer which is a Baader Mk V.  I also have pairs of the 9 and 12.5mm Tak orthos.  I sold one of the 10s - good imv but not exceptional and outperformed to my eye and that of an experienced observer friend on planets in the bino by 8 and 11mm TV Plossls - but kept the 18mm LEs which perform very well indeed. I use the bino with either the 1.7 gpc or, lately, with the 2x 2in Powermate up front. With this latter config, which I now favour, I definitely preferred the view with 18 LEs over that given by a pair of 17.5mm Morpheus’s - good those these were individually. Noted your advice around fov. I’m happy with a moderate fov, so no prob there. Thanks again for your suggestion - I’ll probably end up going with it or perhaps with another pair of the Tak orthos. Appreciate your help. 😊👍🏻

[plyscope]

I have one of these since they came out a couple of years ago. It is very well made with great coatings.

The field stop is a little fuzzy and it is does not have very good edge correction compared to a 24mm Panoptic.

Its big advantage is in its lightweight and better eye relief than a 24mm Panoptic. It has no undercut which I like. It is ideal in a lightweight turret setup especially with an f8 or f9 refractor.

It is not ideal in fast scopes. If I could choose only one then the 24mm Panoptic is better.

 

[JTEC]

Hi plyscope. Many thanks for the useful detail and your advice. (Happy to debate eyepieces but, right now, less keen to talk about cricket ... 😐)

[Scott42]

Maybe it's premature to give up on these Erfles, if you're using a 2x barlow for binoviewing the eyepiece will get an f/15 light cone (assuming an f/7-8 telescope).  It might work OK there, I only used it at f//7-f/8.   It's not possible to make a slim, lightweight wide-field eypiece that works well at f/7.  I'm thinking the Tak Erfle must perform better at f/15 or they wouldn't have started making it again.

 

[JTEC]

Thanks for pointing this out ...  Yes, the bino is always going to be used with either the 2x Powermate or the Baader (nominally x 1.7 but really more like x 1.5) GPC.  So maybe this config would clean the edges up a little bit.  I’d have no reason to want to Barlow it in mono because I already have a a 13mm Ethos, except perhaps, as plyscope mentions, weight - but that’s not an issue at the moment.  

I have a few eps in the 20s range but nothing longer - a pair of 20mm Smart Astronomy plossls, a pair of 28mm Edmund RKEs and a single ES 24mm. I bought two of the ESs but didn’t like the way they performed in the bino. I kept one and like it on its own; it gets used quite a bit.

if I had to pick out my ‘best’ binoviewing pair in moderate fl, it would be the 18mm Tak LEs - sharp, clean, decent contrast, comfortable but not excessive eye relief, no distracting curvature or eye placement issues and very well built. So, I’d like to give the Erfle a go but, thinking head not heart, I’ll probably end up with a pair of the longer LEs or orthos.

BW

John