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Equipment Discussions >> Refractors

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BarrySimon615
Pa Bear
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Reged: 03/01/04

Loc: New Orleans, LA
6.1" f/1.2 APO Triplet Refractor
      #5966429 - 07/11/13 10:00 PM

Saw this in CloudyNights Classifieds

http://www.cloudynights.com/classifieds/showproduct.php?product=83262&sor...

Anyone care to critique?

Barry Simon


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gezak22
professor emeritus
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Reged: 08/15/04

Loc: On far side of moon. Send help...
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: BarrySimon615]
      #5966443 - 07/11/13 10:12 PM

Without some technical details showing why this is called an APO I would not be willing to hand $800 to a stranger with no credible history on this forum.

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daniel_h
Carpal Tunnel
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Reged: 03/08/08

Loc: VIC, Australia
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: gezak22]
      #5966464 - 07/11/13 10:26 PM

initially SS sold it for that price -but it has since been reduced to under 200, a few in the atm forum tried to construct but afaik no-one got one to roduce good images-there is a bolt on element to improve the unit

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gezak22
professor emeritus
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Reged: 08/15/04

Loc: On far side of moon. Send help...
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: daniel_h]
      #5966627 - 07/12/13 12:11 AM

Quote:

initially SS sold it for that price -but it has since been reduced to under 200, a few in the atm forum tried to construct but afaik no-one got one to roduce good images-there is a bolt on element to improve the unit




... and they advertize it as an achromat ( Reference ). So if that particular lens is used, then the classifieds ad is false advertizing.


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GlennLeDrew
Postmaster
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: gezak22]
      #5966693 - 07/12/13 12:52 AM

There's an image of the Sgr/Sct Milky Way which is fully 20 degrees wide. If the focal length is about 180mm, the detector would have to be about 63mm wide. I suppose 6X7 medium format film could have been used. If (and in my mind that's a significant IF) this lens was used to obtain that image, the lens must have been stopped down considerably. The stars are astonishingly sharp across the field.

Moreover, it's my impression that at f/1.25, this lens is not complete, requiring a rear assembly to perform as designed. And the final focal length would probably be longer, and the f/ratio slower. Based on results posted by owners of this lens in the Video Forum, even on small detectors it performs poorly.

Finally, the seller mentions visual useage. At such an extreme speed, even a 10mm eyepiece would yield an 8mm exit pupil. Longer focal length eyepieces would result in aperture reduction, with the effective exit pupil always equaling the observer's iris diameter.

My main concern is that astonishingly sharp image, which I cannot see as being possible to obtain, based on my limited understanding of this lens, and results by other users. No three-element lens--certainly this FAST--is going to cover 20 degrees like that image purports. My spidey sense is tingling...


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: BarrySimon615]
      #5967351 - 07/12/13 12:43 PM

Quote:

Saw this in CloudyNights Classifieds

http://www.cloudynights.com/classifieds/showproduct.php?product=83262&sor...

Anyone care to critique?

Barry Simon




Barry:

There are long threads in the ATM forum concerning this objective. As has been noted, this is available from the Surplus Shed for $250.

It's a 6.1 inch F/1.25 achromat... Do you believe in magic?

Jon


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Simoes Pedro
sage
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Reged: 02/03/09

Re: 6.1" f/1.2 APO Triplet Refractor new [Re: Jon Isaacs]
      #5967567 - 07/12/13 02:46 PM

There is an objective at surplus shed in exactly the same barrel. Not the one you have been posting.

http://www.surplusshed.com/pages/item/l13007.html


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terraclarke
Post Laureate
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Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: Simoes Pedro]
      #5967632 - 07/12/13 03:17 PM

The seller states that he doesn't own a mount that can handle it. This make me wonder how he took that amazing picture of the Milky Way.

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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: Simoes Pedro]
      #5967700 - 07/12/13 03:49 PM

Quote:

There is an objective at surplus shed in exactly the same barrel. Not the one you have been posting.

http://www.surplusshed.com/pages/item/l13007.html




It is the same objective.

"These are the same as our L13001 but mounted in our M3471 Barrel"

Jon


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GlennLeDrew
Postmaster
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: Jon Isaacs]
      #5967821 - 07/12/13 05:12 PM

The more I consider that fine, 20 degree wide image appearing in the ad, the more convinced I am that it cannot have been produced by this lens at anywhere near full aperture. No amount of magic, be it exotic glass or aspherics, can be put into a 3-element lens of this aperture and produce such a sharp image over such a rather wide field. *Perhaps* if stopped down to f/5.6 (still not likely, methinks) or f/8 or f/11 (and with filtration to boot?). But not at f/1.25! (Nor f/2, nor f/2.8, nor f/4.)

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andysea
Pooh-Bah
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Reged: 09/03/10

Loc: Seattle, WA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: BarrySimon615]
      #5967924 - 07/12/13 06:24 PM

Barry, if you want to do wide field imaging I would recommend the Canon 200 f2.8L, or the f2L. I have also seen good results with the old Nikon 180mm ED f2.8.
The Canon f2 is pricey but the other two are very reasonable. The Canon f2.8 can be had used for ~$600 and it's a proven performer, tack sharp. The nikon is probably even less money.
With this f1.2 lens, like Glenn said, you will end up having to stop it down anyway to get decent results.

Andy


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BarrySimon615
Pa Bear
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Reged: 03/01/04

Loc: New Orleans, LA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: andysea]
      #5968418 - 07/13/13 01:26 AM

Quote:

Barry, if you want to do wide field imaging I would recommend the Canon 200 f2.8L, or the f2L. I have also seen good results with the old Nikon 180mm ED f2.8.
The Canon f2 is pricey but the other two are very reasonable. The Canon f2.8 can be had used for ~$600 and it's a proven performer, tack sharp. The nikon is probably even less money.
With this f1.2 lens, like Glenn said, you will end up having to stop it down anyway to get decent results.

Andy




I was just curious about the ad plus the results posted.

At one time (back in my film days) one of the best camera lens that I ever had was an Olympus 100 mm f/2. It had 7 elements in 6 groups and it had special low dispersion glass plus extraordinary partial dispersion glass in the front groups. This kept chromatic aberration to a minimum. In addition it had an extremely flat field. Field coverage was approximately 14 x 21 degrees. Great lens!

The Olympus 200 mm f/4 was also a favorite and this one also had a flat field and little in the way of chromatic aberration. It had 5 elements in 4 groups. Much more affordable than the 100 mm f/2. It did a great job.

Barry Simon


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andysea
Pooh-Bah
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Reged: 09/03/10

Loc: Seattle, WA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: BarrySimon615]
      #5969270 - 07/13/13 04:27 PM

I think some camera lenses can give excellent results. Afaik all canon L lenses have at least low dispersion glass. Some of the ones I own have fluorite.
On the other hand I am toying with the idea of getting a Tak fc60 with reducer for wide field. It would probably perform better than the 200mm or 300mm canon L and it's very affordable.

Edited by andysea (07/13/13 04:28 PM)


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: andysea]
      #5969280 - 07/13/13 04:38 PM

I "read" that the Canon 135/2L is a notable exception.. not a good AP lens unless stopped down..

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andysea
Pooh-Bah
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Reged: 09/03/10

Loc: Seattle, WA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: orlyandico]
      #5969354 - 07/13/13 05:34 PM

Yes, I think the 100 f2.8 is a better option. They also have a tilt/shift that is extremely sharp even tho it is not L.
I also heard that the Zeiss 100mm Makro-Planar is exceptional. It will set you back 2.6k tho.


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stevew
Now I've done it


Reged: 03/03/06

Loc: British Columbia Canada
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: BarrySimon615]
      #5969368 - 07/13/13 05:49 PM

Quote:



At one time (back in my film days) one of the best camera lens that I ever had was an Olympus 100 mm f/2. It had 7 elements in 6 groups and it had special low dispersion glass plus extraordinary partial dispersion glass in the front groups. This kept chromatic aberration to a minimum. In addition it had an extremely flat field. Field coverage was approximately 14 x 21 degrees. Great lens!





Oooo, I still have this lens. Gathering dust with the rest of my Olympus film gear. Great lens.
I used it mainly for portraits, but i'm sure it would take great astro photos.
Gotta dig out my film gear one of these days.

Steve


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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: stevew]
      #5969384 - 07/13/13 06:00 PM

Old lenses should work great. The only caveat is that old optics where designed to work with film. Modern digital sensors have far superior resolution and in general they demand much more precise optics. So a digital sensor might reveal defects and aberrations that were not visible when the same lens was used with film.

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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: andysea]
      #5971178 - 07/14/13 08:56 PM

There was a previous thread about these by Sedat. The info brought up there is this objective is about 40% of the telescope. The rest is a large flattening and zoom control unit with a diaphram which makes this objective do something.

The best I think you could do is find an old zoom telephoto lens to tear down and use the back end with this objective. But it'd be a low probability of success, if there's any realistic hope at all without the custom lens group.

-Rich

Edited by Starhawk (07/14/13 08:57 PM)


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: Starhawk]
      #5971620 - 07/15/13 02:57 AM

Andy, I have the Canon 180/3.5 Macro, and it's a disappointing AP lens. Seems my sample has some tilt in the internal elements, stars are not round across the field. That's what one gets with a bazillion elements (14 elements in 12 groups!) one wonders how the newer IS macro would work out...

And no, it's not tracking or mount issues.. it was quite overmounted, sitting by itself on Uncle Rollo's creation.


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BillP
Postmaster
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Reged: 11/26/06

Loc: Vienna, VA
Re: 6.1" f/1.2 APO Triplet Refractor new [Re: andysea]
      #5972685 - 07/15/13 04:53 PM

Quote:

Old lenses should work great. The only caveat is that old optics where designed to work with film. Modern digital sensors have far superior resolution and in general they demand much more precise optics. So a digital sensor might reveal defects and aberrations that were not visible when the same lens was used with film.




There are a few sensors available out there that can "rival" film from a resolution perspective, but still very difficult for them to achieve the same latitude (dynamic range) that film can. So actually, film is still a superior product. However, there are some newer digital back for medium format cameras that are finally getting close, but they will set you back at least $16,000...and upwards of $50,000.


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