242 replies to this topic

[lylver]

Thanks to those data : KF3 Schott is the nearer glass for the design diagrams for the 100-800 and the 100-1000

Approximative strehl of the FC 100-1000

Edited by lylver, 11 January 2024 - 04:30 PM.

[davidc135]

My 1989 Schott catalogue makes KF3 as chemically resistant as pretty well any glass. It gives acid resistance (FR) as 0 although above, that is given as 2. Even if that is right, it's hard to see KF3 suffering such a degree of attack due to moisture, as it's climate resistance (CR) is in the top category.

 

I also found the glass to be very hard, noticeably more resistant to polishing than Pyrex type glasses.

 

I wonder why R2 next to the fluorite lens suffered so much more than R1. One possibility is that, IIRC, fluorite is slightly hygroscopic perhaps trapping liquid water between the surfaces whilst any condensed moisture on the outer surface would be freer to evaporate.

 

And whilst fluorite is very resistant to moisture could minute amounts of fluoride ions act as catalysts speeding up attack on the glass? But I haven't come across any mention of this.

 

David

Edited by davidc135, 11 January 2024 - 05:10 PM.

[Moonlit Knight]

I read this thread with a mixture of intrigue, horror and admiration. I am so happy that you got your lovely scope sorted, your determination and dedication to the project in this crazy throw away world is a credit to you sir.

[m2k]

I read this thread with a mixture of intrigue, horror and admiration. I am so happy that you got your lovely scope sorted, your determination and dedication to the project in this crazy throw away world is a credit to you sir.

That goes for me also, don't think I could have put the sentiment any better. Hats off Steve and David! BTW- I too have an FC-100 from 1990...

Regards,

-Mike

[davidc135]

Thankyou m2k and Moonlit knight for your comments. Unfortunately, I must own up to the FC100 having some astigmatism. Not huge but it's disappointing and I think enough to affect performance.

The interesting thing is that both lenses suffer from centre of field aberration, the astig rising and falling as one lens is rotated against the other. Which means that Takahashi could have been managing the astig of one surface instead of avoiding it completely in all four.

 

My work is probably to blame but, as R2 is so fast, it's hard to check without the right interferometric equipment.

 

David

Edited by davidc135, 24 January 2025 - 05:10 AM.

[ETXcetera]

This thread was an excellent read! A real-life drama!

 

 

You know how sometimes you hear in the news or other announcement that your favorite show is going for another season, or they are finally making a sequel to your favorite movie? I think maybe I can be that news for this thread!

 

I recently turned to the darkweb (Zenmarket) trying to find the dedicated focal reducer for a Vixen FL-102S. What was such an innocent search "Vixen Telescope" became a rabbit hole I wished I never entered. It is just not possible to ignore all these amazing instruments and mounts that have suffered neglect for too long. Items that just need a new home and a LITTLE TLC.  Suffice to say, I did not last long. I bought something. Nope, not the focal reducer I needed, I got a different focal reducer I didn't need.  But I did not stop there and not even the translated title "★Junk item★ Telescope..." could stop me. So stay tuned for Part 2 of Zen-Ugh, as in a few weeks time I will be the proud owner of a very dirty FC-50 and Spaceboy mount.

 

I suppose buying a broken version of a fancy scope is not much different than buying a brand new one, but not using it because it is too precious (except a broken one is much cheaper!). I will have a fun time making it look nice, and as too the lens, well it doesn't look like the typical fog, but it doesn't look great either. So who knows!?!?

 

My main question before the saga continues is if a fogged lens completely unusable? Can it still be a guide scope or finder? Or is it destined to just sit on display?

 

Thanks again to all that shared their knowledge and experience in Zen-Ugh Part 1. See you soon :-)

[deSitter]

This thread was an excellent read! A real-life drama!

 

 

You know how sometimes you hear in the news or other announcement that your favorite show is going for another season, or they are finally making a sequel to your favorite movie? I think maybe I can be that news for this thread!

 

I recently turned to the darkweb (Zenmarket) trying to find the dedicated focal reducer for a Vixen FL-102S. What was such an innocent search "Vixen Telescope" became a rabbit hole I wished I never entered. It is just not possible to ignore all these amazing instruments and mounts that have suffered neglect for too long. Items that just need a new home and a LITTLE TLC.  Suffice to say, I did not last long. I bought something. Nope, not the focal reducer I needed, I got a different focal reducer I didn't need.  But I did not stop there and not even the translated title "★Junk item★ Telescope..." could stop me. So stay tuned for Part 2 of Zen-Ugh, as in a few weeks time I will be the proud owner of a very dirty FC-50 and Spaceboy mount.

 

I suppose buying a broken version of a fancy scope is not much different than buying a brand new one, but not using it because it is too precious (except a broken one is much cheaper!). I will have a fun time making it look nice, and as too the lens, well it doesn't look like the typical fog, but it doesn't look great either. So who knows!?!?

 

My main question before the saga continues is if a fogged lens completely unusable? Can it still be a guide scope or finder? Or is it destined to just sit on display?

 

Thanks again to all that shared their knowledge and experience in Zen-Ugh Part 1. See you soon :-)

"Junk" of course is a poor Japanese->English translation for "used". Always sort of startling however to see a Tak fluorite scope referred to as junk

 

-drl

[tturtle]

I bought many things from zenmarket last year and they were all excellent purchases but it does take some time to sift through all the offerings and find the jewels.  Here’s a quick list of the bigger stuff. These items were all bought well below what they would typically sell for. Zen is really the only place I buy used stuff from now. 
 

1. takahashi 965 18 and 7mm eyepieces 

2. vintage vixen 102mm f13 doublet, sealed but without lens cell 

3. Takahashi 60mm fluorite doublet with lens cell and tube

4. Takahashi focal extender for fc60

5. Carton 60mm refractor mint condition fully accesorized

6. Takahashi .965 diagonal

 

This thread was an excellent read! A real-life drama!

 

 

You know how sometimes you hear in the news or other announcement that your favorite show is going for another season, or they are finally making a sequel to your favorite movie? I think maybe I can be that news for this thread!

 

I recently turned to the darkweb (Zenmarket) trying to find the dedicated focal reducer for a Vixen FL-102S. What was such an innocent search "Vixen Telescope" became a rabbit hole I wished I never entered. It is just not possible to ignore all these amazing instruments and mounts that have suffered neglect for too long. Items that just need a new home and a LITTLE TLC.  Suffice to say, I did not last long. I bought something. Nope, not the focal reducer I needed, I got a different focal reducer I didn't need.  But I did not stop there and not even the translated title "★Junk item★ Telescope..." could stop me. So stay tuned for Part 2 of Zen-Ugh, as in a few weeks time I will be the proud owner of a very dirty FC-50 and Spaceboy mount.

 

I suppose buying a broken version of a fancy scope is not much different than buying a brand new one, but not using it because it is too precious (except a broken one is much cheaper!). I will have a fun time making it look nice, and as too the lens, well it doesn't look like the typical fog, but it doesn't look great either. So who knows!?!?

 

My main question before the saga continues is if a fogged lens completely unusable? Can it still be a guide scope or finder? Or is it destined to just sit on display?

 

Thanks again to all that shared their knowledge and experience in Zen-Ugh Part 1. See you soon :-)

[davidc135]

This thread was an excellent read! A real-life drama!

 

 

You know how sometimes you hear in the news or other announcement that your favorite show is going for another season, or they are finally making a sequel to your favorite movie? I think maybe I can be that news for this thread!

 

I recently turned to the darkweb (Zenmarket) trying to find the dedicated focal reducer for a Vixen FL-102S. What was such an innocent search "Vixen Telescope" became a rabbit hole I wished I never entered. It is just not possible to ignore all these amazing instruments and mounts that have suffered neglect for too long. Items that just need a new home and a LITTLE TLC.  Suffice to say, I did not last long. I bought something. Nope, not the focal reducer I needed, I got a different focal reducer I didn't need.  But I did not stop there and not even the translated title "★Junk item★ Telescope..." could stop me. So stay tuned for Part 2 of Zen-Ugh, as in a few weeks time I will be the proud owner of a very dirty FC-50 and Spaceboy mount.

 

I suppose buying a broken version of a fancy scope is not much different than buying a brand new one, but not using it because it is too precious (except a broken one is much cheaper!). I will have a fun time making it look nice, and as too the lens, well it doesn't look like the typical fog, but it doesn't look great either. So who knows!?!?

 

My main question before the saga continues is if a fogged lens completely unusable? Can it still be a guide scope or finder? Or is it destined to just sit on display?

 

Thanks again to all that shared their knowledge and experience in Zen-Ugh Part 1. See you soon :-)

Good luck with the FC-50.  David

[ETXcetera]

Update: It looks like there will be no sequel. The lens is toast in fact it appears it was already taken apart previously :-(.

My gamble was that the circular patterns shown in the images were just built-up gunk that was poorly cleaned. It does not have the same haze or fog covering the lens like I've seen in many other ads/photos for the non-MC FC series scopes. Maybe this is the doing of some unqualified persons.

 

The circular patterns are in-fact between the lenses and are not easily removed with isopropyl alcohol or windex.

 

The Fluorite lens is spotless. The Space Boy mount is pretty neat and should clean up nicely although now there is nothing to put on it. The MC 7mm, MC 18mm orthos and prism diagonals are nice. Finder is nice.

The Zenmarket experience was otherwise really nice and the packaging was first class and UPS got it to me in two days!

 

[Bomber Bob]

Looks like a previous owner "cleaned" the Flint with a Floor Buffer!!

 

Since it's already ruined, I'd remove it, and soak it pure bleach -- Couldn't hurt.

[davidc135]

That's disappointing. It's very odd that they appear mostly as concentric rings, as if from cleaning. The etching of R2 of the FC-100 could be seen with a back to front 25mm Plossl or similar, held up to a light.

 

David

[davidc135]

It doesn't look good but have you tried out the scope?

 

David

[ETXcetera]

The concentric rings are weird! I think I will check the surface with the plossls and then go for the bleach! Not too worried about making it worse! I do like the idea of learning how to polish a lens, but there is so much to learn and practice on before going at it on this little guy.

[semlin]

looks like someone put an electric buffer to it centred over the objective.  probably a desperate attempt to remove haze.  that may be some kind of polish residue as opposed to scoring of the glass/coating but who knows..

 

i agree with bleach.  i have a boat hull cleaner fluid that i bought off the internet on the recommendation of a boat forum.  it is a very nasty alkali fluid and removes substances deeply adhered to fibreglass instantly that nothing else i know can budge (deep rust stains and black tire marks for example).  i mention it because it instantly removed some leftover haze from a boat polishing compound on my boat windshield that i had given up on trying to get off.

[ETXcetera]

It doesn't look good but have you tried out the scope?

 

David

When I first got it I immediately put it on the mount and did some daytime tests on a cloudy murky day. The testing did not go well I felt like it was very foggy/cloudy and did not put up a good image. I was very bummed/discouraged and thought the lens was unusable. In the week prior to delivery after I won the auction, I read just about everything I could find about these scopes and this issue. In haste, I took apart the lens and got to work seeing if the rings would easily clean up. I wanted to try less aggressive cleaner prior to trying bleach, so I did a 36-hour white vinegar soak and this was not successful in removing any marks. Thinking I would need to put this project on hold for a while I decided to attempt a re-assembly, mainly so I would not lose any parts, and the order of assembly was still fresh in my head. After re-assembly I took it outside not expecting much and the daytime views were excellent. Much better than when I got it. I forgot to mention the other thing I did was clean the orthos and diagonal that came with the scope. For all I know all the cloudy/foggyness was due to those being really dirty? I found a powerline insulator that was reflecting the sunlight and I used that as an artificial star. The diffraction pattern looked pretty good! I tried to keep my expectations low for night testing. It was really windy and clouds were sweeping through but there were many good openings to test on. Plus we had a nice crescent moon, Jupiter, Mars, and Orion. The night test went great!  I had a blast with this little thing on the Space Boy mount. Everything was VERY solid.

 

As for performance, for any real testing I needed to use my 1.25" gear because the included 18mm (22x) and 7mm (57x) orthos could not provide enough magnification.  I was lucky to have a 43mm male to 1.25" visual back that came with my Vixen FL102 which has the same diameter threads as the FC-50 (but different pitch), and this was able to get enough turns to make a solid connection. for viewing of Jupiter, I would say the 7mm ortho was a very nice view, but magnification was not enough. I think the 2x barlow with my 8mm plossl (100x) gave a great views of Jupiter and Mars. Probably the 4mm hi-or would be an excellent companion to this scope. The maximum magnification I can do is 200x with my 3x 4-element barlow and 6mm plossl.  I tried this on the moon to see if I could detect any false color on and there was zero/zilch/nada. I forget which magnification I was using, but I saw a very interesting crater on the moon with what looked like a channel running through it. While looking it up I'm pretty sure it was the Petavius crater. 

 

But what about all that crap on the lens. Surely that ruins the image right? Well what I noticed at 200x on the star test is that it does not have a perfect diffraction pattern. This could be a collimation issue or an artifact of the lens markings. I am going to order a cheshire eyepiece to check collimation and adjust it if required. The main artifact that can be noticed at the normal 57-100x magnification is a dim haze around Jupiter. It is similar to the view you see when there is a light dew on the lens, or your eyepiece fogged up. However dew usually creates a circular haze, this has more of an elongated haze. It is VERY mild though and you don't notice it when you are trying to pick out planetary detail, but when assessing the image overall you can tell something is there. I didn't notice is on the moon or stars. I wonder what the views through Steve's FC-100 looked like prior to his repair? So as to the markings on the lens, they are still a mystery of how they got there, but it does not appear to have damaged the lens figure since the image is still quite excellent for 50mm.

 

I am very happy that the scope is in a useable state. Unfortunately, It will be hard for me to leave well enough alone, and I will probably try to polish this lens (or get it polished).

[davidc135]

That's very good news. You know what the little lens is capable of even in its present state and that it could be even better with the fog removed.

 

If the damage is similar to that of the FC-100, the affected layer of glass may need removing by fine grinding. I had tried hand polishing for perhaps 2 hours and saw absolutely no change, but your lens may be different.

 

David

[davidc135]

Jak (ETXcetera) took me up on my offer to have a look at the FC50 and sent me the OTA. Here's the flint lens:

 

 

David

[davidc135]

And a close up under the microscope lit at a shallow, glancing angle.

 

 

The finer thread in the ep is the equivalent of 7 microns on the lens which suggests that the damage is shallow and might polish out.

 

David

Edited by davidc135, 25 May 2025 - 05:21 PM.

[davidc135]

A DPAC Ronchi test:

 

 

David

 

 

Edited by davidc135, 25 May 2025 - 05:27 PM.

[ETXcetera]

I was excited at the opportunity to fix this lens and after much research and communications with David, it became clear pretty quickly that I lacked the needed equipment and experience to fix this. I am grateful for David’s help in restoring this cool little scope! Thank you for sharing your progress!

[kgb]

And a close up under the microscope lit at a shallow, glancing angle.

P5160152.JPG

The finer thread in the ep is the equivalent of 7 microns on the lens which suggests that the damage is shallow and might polish out.

David

Hey David,

Are those scratches or is it etched?

Karl

[davidc135]

R2 is etched superficially. I've made a start polishing with good results. As well as a small amount of fogging on R1 which I'm sure will polish out there are also fine scratches. Some of these will probably stay but I don't think they do much harm.

 

David

[davidc135]

I compared the FC50 to my FC100 stopped down to 50mm, both at x44. Although the FC50 may have shown the same detail, the view of a distant flock of sheep in the evening sunshine seemed subdued and lacking the vividness of the FC100. What hampered the side by side was the need to change over the 1.25'' fitting from one scope to the other, so the immediate comparison was lost.

 

I also viewed an artificial star at 27yds.

 

In a random orientation of the lenses there was no astigmatism. What did cause astig, but no coma, was altering the collimation via the three sets of push/pull screws. The best position was where the two flanges were touching with the collimation screws doing nothing.

 

It was very sensitive to wedge in the air-space, any slight difference in the spacers causing fan shaped coma (but no astig), and so it was hard to centre the Airy disc within the diffraction rings.

 

Hoping that polishing would be up to the task, I protected the flint with kitchen film and made a plaster base for the pitch polisher. After sealing the plaster, I poured a 1/4'' lap of 55 Gugolz pitch contained by a wrap of decorator's masking tape.

 

 

A pressed piece of net curtain gives the stippled effect.

Edited by davidc135, 26 May 2025 - 02:11 PM.

[davidc135]

After an hour of short strokes using cerium oxide polish and with the lens on top there was a big improvement.

 

 

Maybe another hour will do it.

 

David

Edited by davidc135, 26 May 2025 - 01:41 PM.