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New 6" f/8 Achromat Lenses in Cell

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#1 BillP

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Posted 29 December 2016 - 01:57 PM

Just received this email.  Seems Surplus Shed has sourced newly made 6" f/8 Achromat lenses in cell.  $325 for pre-order!

 

http://us6.campaign-...45&e=c571d34552

 


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#2 csrlice12

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Posted 29 December 2016 - 02:23 PM

Very interesting...same length as a 4" f9.8, but 2 extra inches of aperture.   And f8, so the CA shouldn't be bad.  Wonder what the weight would be with an aluminum tube and 2-speed focuser?



#3 Richard O'Neill

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Posted 29 December 2016 - 03:10 PM

"... f8, so the CA shouldn't be bad."

 

 To a variable extent CA is in the eye of the beholder. To my eye CA in a 6" f/8 doublet made with typical crown and flint glass is easily noticed.


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#4 bobhen

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Posted 29 December 2016 - 03:13 PM

Very interesting...same length as a 4" f9.8, but 2 extra inches of aperture.   And f8, so the CA shouldn't be bad.  Wonder what the weight would be with an aluminum tube and 2-speed focuser?

A 6" F8 achromat has about the same CA as a 4" F6 achromat. A 4" F6 achromatic refractor is not really optimum for planetary observation. Not that you can't point a 6" F8 refractor at the planets or the moon, its just that you can push better corrected refractors to higher powers and they will remain sharp and have better color fidelity.

 

Bob


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#5 plyscope

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Posted 29 December 2016 - 03:58 PM

It is a bit more expensive but the Skywatcher 6" f8 lens in cell is available from TS.

 

http://www.teleskop-...150-1200mm.html


Edited by plyscope, 29 December 2016 - 03:59 PM.


#6 precaud

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Posted 29 December 2016 - 05:08 PM

I saw that too. Problem is, one can pick up a complete used 6" F/8 achro for that much or less. So unless these lenses (and cell) are known to be superior...


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#7 stevew

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Posted 29 December 2016 - 09:47 PM

Just received this email.  Seems Surplus Shed has sourced newly made 6" f/8 Achromat lenses in cell.  $325 for pre-order!

 

http://us6.campaign-...45&e=c571d34552

Hmm.....

I would think that if they are "superb" as the add hype mentions why are they not in tube assemblies and being sold for more money.....


Edited by stevew, 29 December 2016 - 10:07 PM.


#8 De Lorme

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Posted 29 December 2016 - 10:37 PM

I wish they would think bigger like an 7"- 8" F/8 or 10.  I can forgive a little color on the stars and then stop it down on planets. Then it would be worth the hassel to put one together.

 

No I'm wrong about what I just said.   Big is tempting but color correction first than size. 

Nothing beats clarity. 

 

Clear Skies,  De Lorme


Edited by De Lorme, 29 December 2016 - 11:07 PM.


#9 starcanoe

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Posted 29 December 2016 - 10:55 PM

Weight and cost for a lens probably go something like the cube of the size, give or take.

 

Cube 6, then 7, then 8. Those numbers are gonna be quite different.


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#10 astrosky123

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Posted 30 December 2016 - 09:40 AM

theres a 6" cr6 on canada buy and sell for 250 cdn and the  complete ota

j



#11 junomike

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Posted 30 December 2016 - 09:55 AM

theres a 6" cr6 on canada buy and sell for 250 cdn and the  complete ota

j

Seen one on there for $400 CDN?  Is there another?

 

Mike



#12 astrosky123

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Posted 30 December 2016 - 10:05 AM

yes theres a 400 one and a 250 one


Edited by astrosky123, 30 December 2016 - 10:05 AM.


#13 astrosky123

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Posted 30 December 2016 - 10:10 AM

just checked both 6" refractors are both on pg 1 still, the 250 is from calgary halfway down the page.

Cant go wrong at that price

j



#14 junomike

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Posted 30 December 2016 - 12:02 PM

Ah Yes I did see that (shipping prohibitive for me).

 

Mike



#15 Max Power

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Posted 31 December 2016 - 09:47 AM

Built a 5" f/5.5 with Surplus Shed lens, total cost $615. Yes coulda bought a completed scope cheaper, but building is half the fun, right?

#16 precaud

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Posted 02 January 2017 - 03:26 PM

This was sent out by SS in response to requests for additional specs:

 

The crown optical glass has an Nd index of 1.516 and an Abbe V number of 64.1
The Flint optical glass has an Nd index of 1.613 and an Abbe V number of 37.0

The sample we purchased shows nice straight lines in our Ronchi test.



#17 jgraham

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Posted 02 January 2017 - 03:41 PM

These don't show up very often, so I am curious. However, there is no mention of AR coatings, and they cost about the same as a used 6" f/8 refractor, though you can never tell when one of these will pop up.

 

Fun to ponder...



#18 Rutilus

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Posted 02 January 2017 - 03:43 PM

Any idea who is manufacturer of these lenses, as they have clear aperture of 153mm, according

to the add.  So far, only found makers that do this spec of lens in 150mm clear aperture.

Usually this spec of lens gets more than its fare share of a slating. i.e. poor colour correction,

inability to take high powers. Below is a drawing made with two scopes, one was a Takahashi

TSA-102, with stunning optics. While the other was made with a Synta made 150mm f/8,

optics 1/4 wave standard. But which drawing is which, is it the one on the right or the left. :undecided: 

or is it the other way around. Anyone want to have a guess?

Apologies for the poor reproduction, we get a couple of hours of

daylight at this time of year and then it tends to be rubbish quality.  

Attached Thumbnails

  • Mars-cn2.jpg

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#19 orlyandico

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Posted 02 January 2017 - 09:18 PM

the SS ad states that the lenses are multicoated.

 

The crown optical glass has an Nd index of 1.516 and an Abbe V number of 64.1

The Flint optical glass has an Nd index of 1.613 and an Abbe V number of 37.0

 

The crown is almost certainly BK7 (Nd=1.52, Abbe=64) and the flint is F2 (Nd=1.62, Abbe=37) so it's a bog standard achromat.



#20 Jeff B

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Posted 03 January 2017 - 12:17 AM

Tak on the right



#21 stevew

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Posted 03 January 2017 - 02:15 AM

Below is a drawing made with two scopes, one was a Takahashi

TSA-102, with stunning optics. While the other was made with a Synta made 150mm f/8,

optics 1/4 wave standard. But which drawing is which, is it the one on the right or the left. :undecided:

 

That's not fair, as you left out all of the unfocused violet in one of the images....


Edited by stevew, 03 January 2017 - 02:24 AM.

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#22 Astrojensen

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Posted 03 January 2017 - 03:52 AM

Tak on the right

No, it's the other way round. The Tak image is on the left, the 150mm achromat is on the right. I have a Sky-Watcher 150mm f/8 achromat, which I have to stop down to 125mm when observing the planets, due to turned down edge, but even then, it shows quite a lot of details on Mars and the false color is far less than on Jupiter. I know from writing with Rutilus that his 6" is way better than mine, so I have no doubt that it can outperform a 4" apochromat on Mars.

 

 

Clear skies!
Thomas, Denmark


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#23 jgraham

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Posted 03 January 2017 - 12:30 PM

Ahah! I missed the comment on the coating in the first sentence. That makes it a better deal.



#24 precaud

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Posted 03 January 2017 - 03:30 PM

If they were so confident it is better than your typical C6R objective, they should have made it drop-in compatible. Hundreds of instant potential customers.



#25 Wildetelescope

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Posted 03 January 2017 - 06:25 PM

For those unfamiliar with surplus shed, it is sort of a clearing house for optical odds and ends, as well as gears and some electronics. Much of what the sell is reclaimed from military hardware. They occasionally put together things like ep's, but are not really set up to build telescopes, lens cells etc....... it would be interesting to know where they got these lenses from. An f8 achromat is was it is, but if it is military grade, it likely has an excellent figure!

JMD


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