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Looking for suppliers of achromats - large and small

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#1 Klaus_160

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Posted 22 May 2024 - 09:28 AM

For a telescope build of mine I am looking for various achromats and I am wondering if anyone here knows any good suppliers for these.

 

 

Specifically, I am looking for two groups of lenses:

 

Large: Cemented achromats in the range of 70-110mm aperture with a focal length between 700-1000mm

 

Small: Achromats with a diameter of either 1/2" or 1" and various focal lengths between 75 to 200mm.

 

 

 

For the large group I can only find them on Aliexpress. There are many offerings there, with some of which you can clearly see from the description that the seller knows little about optics. That seems risky, maybe they are selling factory seconds or of the like.

 

Has anyone here purchased such a lens and what was your experience?

Is there a direct supplier (incl. from China) that would sell small quantities directly?

 

 

 

For the small lenses, they can also be found on Aliexpress with the same concerns and questions - does anyone have experience there? There is also Thorlabs and Edmunds, of course, but those get quite expensive quickly, esp. for the 1" size. In addition, they do not always have the focal length I need. 

Are there any other options I am missing.

 

 

 

Thanks for reading this - any input would be much appreciated!

 

 

Klaus

 


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#2 Steve Dodds

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Posted 22 May 2024 - 09:32 AM

I always use these guys. Surplus Shed

 

https://www.surplusshed.com/


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#3 schiefspiegler

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Posted 22 May 2024 - 09:42 AM

All of these lenses as well as lens cells are available from the eBay sellers "Lens-Store" and "Fresnel Lens Shop"  I have found the quality of these Chinese lenses to be very good and the prices reasonable.


Edited by schiefspiegler, 22 May 2024 - 09:42 AM.


#4 rob1986

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Posted 22 May 2024 - 10:14 AM

Cool!!!

#5 Bob4BVM

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Posted 22 May 2024 - 12:48 PM

I always use these guys. Surplus Shed

 

https://www.surplusshed.com/

Is SS still open ?

I thought Fred retired a while back...

-B



#6 walt r

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Posted 22 May 2024 - 02:23 PM

Is SS still open ?

I thought Fred retired a while back...

-B

Yes, still open but only on-line purchase.

Did you check the link posted?

 

SS has lower cost lenses.

Edmond & Thor have Industrial priced optics but well specified.



#7 Klaus_160

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Posted 22 May 2024 - 02:28 PM

Thank you for all the responses!

 

I did check SS but forgot to mention it - the problem there is that they have a lot of odd sized lenses (in diameter) which greatly complicates the mechanical design.

 

The ebay stores seem indeed the same as on aliexpress, including the delivery times. It is encouraging to hear the quality is good - maybe the strangle description is because of the language barrier ...

 

I will think some more and see what I order.

 

 

 

 

Thanks again and clear skier,

Klaus



#8 sunrag

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Posted 22 May 2024 - 02:54 PM

I have had good luck with both SS and AliExpress. The optical elements are quite good, but they tend to use rings (made of plastic or tin) instead of 3 spacers placed 120 degrees apart. Replacing the rings with your own spacers (5mm x 2mm rectangles cut from postage stamp borders or similar thickness tape) would make the spacing uniform.

I have made several achromats ranging from 130mm to 80mm aperture with these. If they come with plastic cells, they are adequate as long as you replace the single ring spacer with the three small spacers.

#9 alg460

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Posted 22 May 2024 - 07:23 PM

Surplus Shed never seems to list anything good in the 60 to 100mm range. When they do they are usually out of stock. I have bought many Chinese achromats from the likes of Aliexpress. I can only speak of lenses in the 50mm to 100mm range. If you want perfection, its the luck of the draw.  For cemented lenses stay with smaller diameters or faster lenses where you are not expecting too much. In air spaced they seem to be all over the place. None really bad and some really good.  For comparison I have both a cemented 70mm f10 and an air spaced 70mm f10. The 70mm air spaced is near flawless. The cemented is not awful but side by side with the air spaced the difference is noticeable.  I have an 80mm f9 air spaced that I cant quite seem to sort out. Its good but just leaves something to be desired. There are a couple of sellers offering a 60mm f5 fk61 cemented doublet at around $130. I have one and its quite nice.


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#10 robertasumendi

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Posted 23 May 2024 - 05:53 PM

Arcturus Store and Yingju are overall reliable vendors on Aliexpress. Some lenses get mislabeled from time to time though. Generally vendors are quick to send the correct lens if you do get the wrong one. "Standard" sizes/focal lengths are the most reliable in terms of quality and receiving the correct one.



#11 alg460

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Posted 23 May 2024 - 08:08 PM

As others have mentioned here some of the sellers have no clue what they are selling. IMHO just about all of them have no knowledge of optics or telescopes. I once bought on Ali a 75D 600F lens. When it arrived I found it was only 330mm focal length. When I told the seller of the problem their answer to me was "How could you possibly  know what the focal length is?". DUH. Had a similar problem with a 70mm 320F. When it arrived it was only 275mm fl. Both sellers subsequently changed their listings to the correct FL after having their supplier confirm my findings. My advice is buy the Chinese achromats for the fun of it. Don't pay more than you are willing to lose. Don't expect perfection. You may get a perfect one but more likely it will be just mediocre. Also a small chance that you will get one that performs quite badly and is useless.



#12 alg460

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Posted 24 May 2024 - 05:41 PM

For the sake of science and for the fun of it, today I ordered from Aliexpress, the doublet in the link below. Why? Because I'm a sucker and a glutton for punishment. The lens is as odd as can be. 88mm overall diameter, 85mm working caliber (as they call it) and 830mm focal length which works out to F9.75 . Contrary to what the listing states this lens was probably never intended for use in refractor telescope. We shall see. Should be interesting.  I'll post back in a couple weeks when it gets here. Probably a real dog, but maybe I'll have the sole distinction of being the only kid on the block with an 85mm achromat telescope.

https://www.aliexpre...rch|query_from:



#13 sunrag

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Posted 24 May 2024 - 06:31 PM

Since this comes without a cell, optical performance is going to greatly depend on how well you make the cell, and adjust the spacing, tilt, centering etc. It will not show its true potential, if you just stick it into a tube (I am speaking from experience, because this is how I made my first Achromat a D106/F900) 

 

Every one of my Ali-Express achromats have performed well, and I regularly use them to split tight double stars. One of them even went head to head with my Tele Vue NP101. 


Edited by sunrag, 24 May 2024 - 06:32 PM.


#14 Steve Dodds

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Posted 24 May 2024 - 06:34 PM

Hope there is some instructions on how to assemble these lenses



#15 sunrag

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Posted 24 May 2024 - 06:35 PM

I created a thread on collimating refractors. It is mostly based on my experience with my ATM refractors. Hope you find it helpful

 

https://www.cloudyni...eps-to-success/



#16 alg460

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Posted 24 May 2024 - 07:29 PM

Hope there is some instructions on how to assemble these lenses

No lenses I have ever bought from Aliexpress or the likes ever came with any instructions. Sometimes the lens may have some barely legible sharpie marks on the edge. If anyone building a refractor needs instructions on orienting/assembling the lenses then they are in for a boatload of trouble throughout the whole build. "Mans got to know his limitations."



#17 alg460

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Posted 24 May 2024 - 08:03 PM

Since this comes without a cell, optical performance is going to greatly depend on how well you make the cell, and adjust the spacing, tilt, centering etc. It will not show its true potential, if you just stick it into a tube (I am speaking from experience, because this is how I made my first Achromat a D106/F900) 

 

Every one of my Ali-Express achromats have performed well, and I regularly use them to split tight double stars. One of them even went head to head with my Tele Vue NP101. 

Just for fun I have built countless small refractors over many years. My sky sucks so its the only thing that keeps my interest alive. Many years ago I had free, at will access to a complete machine shop. I could make a lens cell as good as any manufacturer. I no longer have that privilege so I have since learned to improvise when making lens cells. If I have time tomorrow I will post pics of one of my precision lens cell made out of PVC pipe.

 

Post a link to the lens you bought that went head to head with the Tele Vue NP101. I'd like to try one. Post a pic of the scope.



#18 alg460

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Posted 24 May 2024 - 08:18 PM

I created a thread on collimating refractors. It is mostly based on my experience with my ATM refractors. Hope you find it helpful

 

https://www.cloudyni...eps-to-success/

Nice. The newton ring thing kinda blows my mind. I have seen them occasionally on some scopes but none ever stood out like the pics you show. Whats the trick to get them to stand out?



#19 RLK1

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Posted 26 May 2024 - 07:45 PM

Noticed this one on Aliexpress:

 

https://www.aliexpre...You|query_from:

 

I suppose you could also try shoving an eyepiece, somehow, on the backend of this thing and see how it does!

 

https://www.aliexpre...You|query_from:



#20 RichA

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Posted 26 May 2024 - 09:16 PM

Just for fun I have built countless small refractors over many years. My sky sucks so its the only thing that keeps my interest alive. Many years ago I had free, at will access to a complete machine shop. I could make a lens cell as good as any manufacturer. I no longer have that privilege so I have since learned to improvise when making lens cells. If I have time tomorrow I will post pics of one of my precision lens cell made out of PVC pipe.

 

Post a link to the lens you bought that went head to head with the Tele Vue NP101. I'd like to try one. Post a pic of the scope.

I got one of the 5 inch Wollensak branded lenses SS sold.  It was bested by a blue Sky Watcher 120mm achromat.  There are variations in quality of these inexpensive lenses, they probably range from 1/2 to 1/5 wave or so.  Considerable.


Edited by RichA, 26 May 2024 - 09:25 PM.


#21 alg460

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Posted 27 May 2024 - 06:57 PM

I got one of the 5 inch Wollensak branded lenses SS sold.  It was bested by a blue Sky Watcher 120mm achromat.  There are variations in quality of these inexpensive lenses, they probably range from 1/2 to 1/5 wave or so.  Considerable.

To me the whole ATM thing is a lost cause. All reasonably priced sources of good achromats, Newtonian mirrors or mirror making kits have all dried up. The only reason to do it any more is for s**t's and giggles and something to do. I had mentioned in another comment on another post, one way to buy a halfway decent achromat lens is to simply wait for the likes of Explore Scientific to offer a Black Friday or Christmas special on a scope for 1/3 or less of the regular price. Take the lens out and scrap the rest. Nobody agreed with me.

 

As far as these cheap Chinese achromats, as I said its the luck of the draw. As you said "variations in quality of these inexpensive lenses, they probably range from 1/2 to 1/5 wave" I think some may be a bit better than that but you could probably buy 5 of the same lens and all will be different.

 

The other day I stumbled on to these. The only review on them is one star. I think I'll buy one in F8 just for laughs.

 

https://www.aliexpre...rch|query_from:



#22 RLK1

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Posted 27 May 2024 - 07:36 PM

Don't forget the cells:

 

https://www.aliexpre...o2usa4itemAdapt



#23 alg460

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Posted 28 May 2024 - 07:26 PM

Don't forget the cells:

 

https://www.aliexpre...o2usa4itemAdapt

Just about all cells being sold on Aliexpress have no dimensions given. Makes it a total crap shoot. Just goes to prove that the sellers have no clue what they are selling or how they will be used.



#24 Astrokg

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Posted 29 May 2024 - 11:50 PM

I have built scopes using Aliexpress lenses. An 80mm open tube refractor, it worked out great and lens was good quality cemented achromat and very cheap. After that good experience I bought another D63F216 lens, this I used to make a very wide angle finder. I stuck to cemented lens and made lens cell from wood. Not sure about non cemented lenses.

#25 alg460

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Posted 30 May 2024 - 04:18 PM

For the optics experts out there these are star test images with an Aliexpress 80mm D 700mm fl achromat. The test was done indoors with artificial stars. The test duplicates what I see outside on a real star. My photography skills are poor but visually, indoors or out, inside of focus, the rings are very well defined, less well defined outside of focus. The point is though the very bright center outside of focus which is much more obvious visually. This telescope IMHO performs barely OK. Best focus is noticeably soft above 80x or so. The moon shot was done with this scope. Visually there is some color on the moon. My exposure times on all pics was probably way off.

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