Carl Zeiss Jena 25mm Huygens

[badhex]

Hello all, 

My vintage 0.965" collection grows! Picked up a Carl Zeiss Jena 25mm Huygens from a German (non-astro) buy and sell site for what I think is a decent price (€50), and it arrived today. 

Looks to be in largely good condition for the age, well used and perhaps could do with a bit of a clean but otherwise sound. As far as I can tell, this version of the eyepiece is 1970s era according to a Japanese site which has pictures and details of the different CZJ EPs. Obviously would prefer it to be a ortho but not sure I'd get one that easily and certainly not for that price. 

I'll give it a clean up and see how it performs in a modern scope, and report back! 

[Don Pensack]

6 hours ago, badhex said:

Hello all, 

My vintage 0.965" collection grows! Picked up a Carl Zeiss Jena 25mm Huygens from a German (non-astro) buy and sell site for what I think is a decent price (€50), and it arrived today. 

Looks to be in largely good condition for the age, well used and perhaps could do with a bit of a clean but otherwise sound. As far as I can tell, this version of the eyepiece is 1970s era according to a Japanese site which has pictures and details of the different CZJ EPs. Obviously would prefer it to be a ortho but not sure I'd get one that easily and certainly not for that price. 

I'll give it a clean up and see how it performs in a modern scope, and report back! 

Should be decent at >f/12, but also will have a quite narrow field of view.

Just be aware Huygens eyepieces are not designed for chromatic correction.

https://www.telescope-optics.net/eyepiece_raytrace.htm

[badhex]

19 hours ago, Don Pensack said:

Should be decent at >f/12, but also will have a quite narrow field of view.

Just be aware Huygens eyepieces are not designed for chromatic correction.

https://www.telescope-optics.net/eyepiece_raytrace.htm

Thanks Don. Yes, had understood that it would need to be a slow scope to perform at its best, along with the narrow field of view. Not exactly sure what you meant by "not designed for chromatic correction" though. Meaning they display CA? 

[Highburymark]

Very nice - eye lens looks nice and clean. Look forward to hearing how they perform.

[Louis D]

59 minutes ago, badhex said:

Not exactly sure what you meant by "not designed for chromatic correction" though. Meaning they display CA? 

Yes.  Notice how the red and blue patterns in the diagram don't overlap very well for the Huygens design.  You would see CA even on axis.

[badhex]

39 minutes ago, Louis D said:

Yes.  Notice how the red and blue patterns in the diagram don't overlap very well for the Huygens design.  You would see CA even on axis.

Thanks Louis. I was struggling to understand the diagrams a bit tbh. 

[badhex]

1 hour ago, Highburymark said:

Very nice - eye lens looks nice and clean. Look forward to hearing how they perform.

Thanks! Will probably have to "make do" with my F10 C5 but will be interesting nonetheless!

[Roy Challen]

I had one of these, I found it to be a very good low-mag double star splitter...in an f/16 achro. Probably the best Huygens around.

[markse68]

I have one too Badhex- came with my Telementor. It performed quite fine in that scope (f13). I do wonder though if they included it as a standard ep as it's suitable for ep projection of the sun  (no cemented elements) and it was designed as an educational scope? The other "standard" eps seem to all be orthos. I have a CZJ 25mm Ortho that I also got for a reasonable price from a German non-astro auction site but haven't compared the 2 yet

Mark

[badhex]

Thanks all. The slowest scope I have at the moment is an F10 C5, but my end game is to use my 0.965 EP collection with an old 0.965" Charles Frank newt I have in storage which is around F7.7. I knew when I purchased this particular EP that it would not perform well in that scope but as it was a CZJ I wanted to get it anyway as I think it was a good price. All of which bring me to my next question. 

If for example I have a decent quality Barlow - for the sake of argument, something that is nearly invisible to the optical train like a Televue - will the resulting slower FR of the scope improve the performance of a decent Huygens like this Zeiss? So let's say I use a 2.5x Barlow in my F7 TS102 bringing it up to an effective F17.5 - would the Huygens then perform accordingly, as if it were in a native F17.5 scope? 

If so, it would possibly be worth me adding the best 0.965" Barlow I can find (no Televues, of course!) to the collection as well. A 2x barlow would make my F7.7 newt F15.4, or a 2.5x would be F19.25. 

 

Edited July 14, 2022 by badhex

[michael.h.f.wilkinson]

Should you be interested, there is a Pentax SMC Ortho 9mm 0.965" EP on sale here (I don't know the seller):

http://www.te-les-koop.nl/BekijkAdvertentie.php?key=43151

It is a Dutch site, and there are no photos, but it might be of interest

[badhex]

4 hours ago, michael.h.f.wilkinson said:

Should you be interested, there is a Pentax SMC Ortho 9mm 0.965" EP on sale here (I don't know the seller):

http://www.te-les-koop.nl/BekijkAdvertentie.php?key=43151

It is a Dutch site, and there are no photos, but it might be of interest

Good spot, thanks!

[Louis D]

7 hours ago, badhex said:

If for example I have a decent quality Barlow - for the sake of argument, something that is nearly invisible to the optical train like a Televue - will the resulting slower FR of the scope improve the performance of a decent Huygens like this Zeiss? So let's say I use a 2.5x Barlow in my F7 TS102 bringing it up to an effective F17.5 - would the Huygens then perform accordingly, as if it were in a native F17.5 scope? 

If so, it would possibly be worth me adding the best 0.965" Barlow I can find (no Televues, of course!) to the collection as well. A 2x barlow would make my F7.7 newt F15.4, or a 2.5x would be F19.25. 

That should work.  I get much improved performance from my microscope and Svbony eyepieces in my binoviewer when Barlowed by about 3x to f/18 or so in my scopes.  The rays will be strongly diverging, so there could be exit pupil issues because eyepieces are generally designed for converging light cones.

[badhex]

17 minutes ago, Louis D said:

That should work.  I get much improved performance from my microscope and Svbony eyepieces in my binoviewer when Barlowed by about 3x to f/18 or so in my scopes.  The rays will be strongly diverging, so there could be exit pupil issues because eyepieces are generally designed for converging light cones.

Thanks Louis. I can give the EP a try with my 1.25" Barlow and an adaptor for now and see if it cleans up the view a bit. I have already seen one Celestron 0.965" long barlow which looks to be quite a lot better quality than the usual cheap plastic ones, but I'm never really sure what constitutes a reasonable price for a lot of the 0.965 stuff, as there's so little info on it.

[Don Pensack]

One manufacturer still making 0.965" eyepieces and Barlows--good glass and all aluminum construction barrels--is Harry Siebert of Siebert Optics.

He's in the US, but I think he will ship to the UK.

His website is a bit primitive, but I'm sure you can handle it.

[badhex]

8 hours ago, Don Pensack said:

One manufacturer still making 0.965" eyepieces and Barlows--good glass and all aluminum construction barrels--is Harry Siebert of Siebert Optics.

He's in the US, but I think he will ship to the UK.

His website is a bit primitive, but I'm sure you can handle it.

Thanks Don, I've been recommended his business before on SGL actually but had forgotten about it. Looks like some good quality kit. 

[badhex]

So I managed to give the Huygens a quick test in the daytime to see how it performs in my F7 TS102, and I have both good news and bad! 

The good news: So, obviously not a completely fair test as it was daytime only, but I was surprised at how well it performed even at F7, especially given that I was expecting it to be a total mess. Quite a 'natural' sort of tone to everything with very little CA (except for the field stop which is essentially a purple halo). Pretty sharp across the centre 50-60% of the FOV, and eye relief was copable. Field stop reasonably defined, when you can position your eye correctly. I tried it with a 2.5x barlow making the scope F17.5, and the view was even better, as expected, but with a small amount of rectilinear distortion. 

 

The bad news: First viewing was fine, but after having taken the EP out to rearrange the thumbscrews for the various adaptors needed to get from 2" to 0.965", suddenly there was a large black artifact in the FOV! I checked again and realised that there were around four pieces of detritus freely floating around inside the large gap (per Huygens design) between the eye lens and field lens. I'm not sure exactly what they are, but they look slightly curved, and if I knew exactly the construction of the EP I might guess at a perished washer or spacer from the field lens or maybe where the metal barrel meets the upper Bakelite part of the EP. Photos included at the bottom of this post. 

I did test to see if the metal barrel would unscrew like is commonly the case but it didn't want to budge with moderate hand force, and I as I don't know if it does actually unscrew I don't want to force it and destroy the EP. 

My other options appear to be using a small lens spanner to unscrew the eye lens holder which is bakelite and possibly fragile (already seems a bit chipped), or unscrew the field lens which is about 2cm inside the barrel and not easy to get out or put back. I also don't know if the spacing between the two lenses is set by stops within the body of the EP, or whether it is determined by how far you screw in each of the parts. Nightmare! 

It's a bit of a shame as otherwise this EP is in good condition for its age and its entirely possible that the seller was not aware of the problem. I took a bunch of pictures and thoroughly inspect the EP on arrival and did not see anything so I'm not going to go down that route.

Any thoughts or advice on how I might proceed to fix this would be welcome! 

 

Chimney in focus with detritus in FOV

With 2.5x Barlow

[DaveL59]

I'd hazard that if the lens ring looks chipped that its maybe been apart before and the lens edges and rings blackened? So could just be paint flaking away that is now floating about in the air gap. Only way to know would be to dismantle but that of course implies a risk of the lens ring is indeed bakelite or any thread lock has been used. Probably safest to remove the field lens as you'd have more space to work?

[markse68]

Pretty sure i had mine apart for cleaning and the barrels do unscrew, though there were several different versions of these eps with different looking construction. But all my barrels unscrew.

The eyelens retaining rings are painted brass i think - it’s paint chips you are seeing. Only the outer ring thing is bakelite.

Mark

[badhex]

1 hour ago, DaveL59 said:

I'd hazard that if the lens ring looks chipped that its maybe been apart before and the lens edges and rings blackened? So could just be paint flaking away that is now floating about in the air gap. Only way to know would be to dismantle but that of course implies a risk of the lens ring is indeed bakelite or any thread lock has been used. Probably safest to remove the field lens as you'd have more space to work?

Thanks Dave, you could right about the paint, it's very lightweight and clearly fragile as it is in at least four bits. Re the field lens, I'd need a lens spanner with long, thin and straight shanks which should be possible, but it's quite awkward to get to so might end up being quite specific. I'll see what I can pick up online, hoping not to spend too much more money though 😅

Edited July 16, 2022 by badhex

[Don Pensack]

Easy fix.  90% chance it works:

--slam the eyepiece sideways into your other hand and then hold the eyepiece up to look through it.

--repeat until the pieces of debris move over to the side, out of the field of view.

Is this a permanent fix?  No, only dismantling this eyepiece and blowing out the pieces of debris will be, but it could work, and usually does on such large pieces.

[badhex]

1 hour ago, markse68 said:

Pretty sure i had mine apart for cleaning and the barrels do unscrew, though there were several different versions of these eps with different looking construction. But all my barrels unscrew.

The eyelens retaining rings are painted brass i think - it’s paint chips you are seeing. Only the outer ring thing is bakelite.

Mark

Thanks Mark. The link I posted to the Japanese page has photos of many of the variants, so I'd be interested to know if any of yours are the same era as mine. You can see that the font appears to be lighter weight in the early '70s examples of this design which matches mine. I think you might be right about the retaining ring, I've had a look close up with a camera and it does look like chipped paint:

[badhex]

Just now, Don Pensack said:

Easy fix.  90% chance it works:

--slam the eyepiece sideways into your other hand and then hold the eyepiece up to look through it.

--repeat until the pieces of debris move over to the side, out of the field of view.

Is this a permanent fix?  No, only dismantling this eyepiece and blowing out the pieces of debris will be, but it could work, and usually does on such large pieces.

Actually, they will move out of the way if turn the EP on its side and gently tap it, and just as gently turn it back upright and into the focuser. It actually took me a few goes to get all the bits into the FOV for the photos 😂

[markse68]

Hi Badhex, I have a really bad memory- was sure the barrels unscrewed but I just tried and none of the 3 orthos I have do and I can't find the Huygens to try- it's around somewhere just not sure where... I think that's why there are the 2 retaining rings at the top- both lenses must drop in from the top

Mark

[badhex]

2 minutes ago, markse68 said:

Hi Badhex, I have a really bad memory- was sure the barrels unscrewed but I just tried and none of the 3 orthos I have do and I can't find the Huygens to try- it's around somewhere just not sure where... I think that's why there are the 2 retaining rings at the top- both lenses must drop in from the top

Mark

Thanks Mark for looking, appreciate it. I did actually try the larger of the two retaining rings when I first discovered the issue, and it's actually just a flat disc threaded on the edge, possibly so they could use the same EP body for different FLs. It does appear to be functional in the construction as such. 

The fields lens does have its own retaining ring underneath.