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6.1" f/1.2 APO Triplet Refractor

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#1 BarrySimon615

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Posted 11 July 2013 - 09:00 PM

Saw this in CloudyNights Classifieds

http://www.cloudynig...ct=83262&sor...

Anyone care to critique?

Barry Simon

#2 gezak22

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Posted 11 July 2013 - 09:12 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.

#3 daniel_h

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Posted 11 July 2013 - 09:26 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

#4 gezak22

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Posted 11 July 2013 - 11:11 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


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

#5 GlennLeDrew

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Posted 11 July 2013 - 11:52 PM

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...

#6 Jon Isaacs

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Posted 12 July 2013 - 11:43 AM

Saw this in CloudyNights Classifieds

http://www.cloudynig...ct=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

#7 Simoes Pedro

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Posted 12 July 2013 - 01:46 PM

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

http://www.surplussh...tem/l13007.html

#8 terraclarke

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Posted 12 July 2013 - 02:17 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. :question:

#9 Jon Isaacs

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Posted 12 July 2013 - 02:49 PM

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

http://www.surplussh...tem/l13007.html


It is the same objective.

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

Jon

#10 GlennLeDrew

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Posted 12 July 2013 - 04:12 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.)

#11 andysea

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Posted 12 July 2013 - 05:24 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

#12 BarrySimon615

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Posted 13 July 2013 - 12:26 AM

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

#13 andysea

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Posted 13 July 2013 - 03:27 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.

#14 orlyandico

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Posted 13 July 2013 - 03:38 PM

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

#15 andysea

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Posted 13 July 2013 - 04:34 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.

#16 stevew

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Posted 13 July 2013 - 04:49 PM


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

#17 andysea

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Posted 13 July 2013 - 05:00 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.

#18 Starhawk

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Posted 14 July 2013 - 07:56 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

#19 orlyandico

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Posted 15 July 2013 - 01:57 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.

#20 BillP

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Posted 15 July 2013 - 03:53 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.


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.

#21 GlennLeDrew

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Posted 15 July 2013 - 04:03 PM

Bill,
As I recall, film offered a dynamic range of about 7 f/stops within the more-or-less linear regime between the toe and shoulder of the response curve. This is a factor of 128 in brightness, which is equivalent to a mere 7 bits. How can this begin compete with a 16 bit digital format?

The headroom within which stretching can be performed on digital images leaves film in the dust.

#22 BillP

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Posted 15 July 2013 - 04:34 PM

There is a lot more to consider than this. Digital camera have an big problem getting latitude on bright subjects. Film does not. Many rely on taking multiple digital shots exposed differently, then on the computer adding the various photos to get a final picture with some good latitude. Sony NEX actually can do this in-camera. But still, they can't compete...especially when you consider that most all digitals use Bayer interpolation and most professionals shoot 2 1/4" film. So with sensors, there is a separate pixel for each color. So a 3MP camera means you have 1MP of Red, 1MP of Blue, etc. Film does not behave this way and any "pixel" in the film can record any color...no interpolation needed. Considering a 2 1/4" film format, one would really need a 1 gigapixel censor to do the same capability of a 2 1/4" film.

Film Resolution

and

Why we love film.

Basically, yes, film has about 7 stops of latitude. However, that is negative film, reversal film (slides) has more, about 9 stops, why so many 35mm pros shot slide film. And film has 9 stops regardless of the intensity of the light. Digital does not have constant latitude, but it varies by brightness, so overall not a good contender against film in this catagory so most details are gone from bright portions of the image that film shows very clearly.

Digital is great...and hands down super convenient and a time saver. But better than film? Not yet. Film has a gestalt of features so not just about resolution. Digital does not have that gestalt yet. Some day I'm sure, just not now. For most though, the convenience gives it the winning edge, and I fall into that lot as well. But I've done lots of film over the years, and would not go back, but I for sure realize that much has been lost that digital just can't do yet (not at my budget)!

Last thing digital does is leave film in the dust (in terms of recorded image). Like I mentioned, with a proper 50MP digital back one gets near, but still not there. And there are "scanning backs" which do wonders, but not good for speed needs.

#23 GlennLeDrew

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Posted 15 July 2013 - 04:54 PM

Bill,
Sensor size has nothing to do with dynamic range. Whether it's 8mm or 2-1/4 film, or 300k or 16M pixels, it makes no difference.

Nine f/stops is still only 9 bits dynamic range. Still nothing compared to 16.

A Bayer matrix is only a filter array. If the sensor has 16 bits of dynamic range, each color channel intrinsically has this range.

Digital images have permitted to penetrate to depths in low surface brightness and (more importantly) low contrast unheard of for film. Peruse digital images of galactic cirrus, or vast tracts of reflection nebulosity illuminated by general Galactic light to see what I mean.

#24 andysea

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Posted 15 July 2013 - 06:26 PM

Hi Orly, I remember you complaining about the 180mm f3.5. I have never tried that lens. My 200mm f2.8 is very sharp with good stars to the edge. Another lens that I really like is the 400 f5.6. My 300mm f/4IS is also good. Those are the ones that I prefer for AP. I tried the 100-400 once and it seemed OK. I will have to give it another go. The 70-200 f/4 non IS seems to be good too but I only used it once. The 70-200 f2.8 II is super sharp.
A small high end apo is probably going to outperform most L lenses tho.
You can send the lens to Canon and they will service and collimate it for you.

Andy.

#25 orlyandico

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Posted 16 July 2013 - 10:25 AM

Andy, it works just fine for close-up portraits of bugs :D which is its main function... I have a small WO 70mm and flattener if ever I need a short FL...






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