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Full moon with Canon nFD 2.8/400 plus multiple converters
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PostPosted: Tue Dec 01, 2020 9:21 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
Blazer0ne wrote:
Reproduced this with a slightly different setup.

First test shots of the moon using this lens. Not the exact same one used by Stevemark, but close. The revised formula to the 400mm f2.8 L nFD which is the L II in EF mount connected to a Kenko 3x Teleplus PRO 300 TC on a sony a6300. This lens only works wide open and it is manual focus only.

To me, it doesn't look bad at all. I would guess that the EF 2.8/400mm L (II) has a better color correction than the nFD which I had used. I can see lots of detail. The relatively low contrast of these details may be caused by the high pixel density of the A6300, and / or the 3x converter you have used. Good converters (even if its only a 2x converter) need the most expensive glass available - preferrably LD or ULD glass for the positive lenses and high refractory / low dispersive glass (e. g. three lenses out of "Noctilux glass" with nD 1.9 in the Leica non-APO 2x converter) for the negative lenses.

Blazer0ne wrote:

Prior to removing color information there was a thin green line on the right side of the moon and also some very faint color blooming at the point highlights. Edited to match the tones other samples on this thread. ISO 100 1/250 APS-C


Does the EF 2.8/400 L II have fluorite glass? Or just ULD glass, as the nFD 2.8/400mm L?

S


PostPosted: Wed Dec 02, 2020 1:18 am    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
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Last edited by Blazer0ne on Tue Feb 22, 2022 6:15 pm; edited 1 time in total


PostPosted: Wed Dec 02, 2020 12:06 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
Blazer0ne wrote:

I think the following conditions were met. This photo was taken within 24 hours of the beaver moon, which seems to be a glowing phase. Also, the lens was pointed near the edge of a roofline of a house on a cold night, which may have caused thermal distortion.

Yeah, certainly a potential source of distorting air movements.

Blazer0ne wrote:

I was using a ball head and I was standing next to an open door of a heated house.
Someone mentioned the distortion may appear as waves where one side of the moon is in focus on one frame and the next frame another section is better focused and that may introduce a motion blur effect.

You can see also in my images that one side of the moon is sharper than the other side.
Looking at the live-view - especially uoomed in for focusing - it was completely obvious that air movements were limiting the resolution of the 1600m and 2400mm lens/converter combinations - and not the limited optical performance of the stacked converters!


Blazer0ne wrote:


As for optical performance, residual chromatic aberrations have been minimized with one fluorite element and two UD-glass elements to obtain high image quality. (The EF 400mm f/2.8 USM had only two UD-glass elements and no fluorite element.)

...
The optical system of the EF 400mm f/2.8L USM lens is identical to that of the FD 400mm f/2.8L lens. The two UD-glass elements correct axial and lateral chromatic aberrations. The EF 400mm f/2.8L II USM lens further minimizes chromatic aberrations with a new optical system incorporating a fluorite element in group 2 and a UD-glass element in group 3 and 5. Residual chromatic aberrations have thereby been minimized as much with the EF 300mm f/2.8L USM lens. Image outlines have no color fringing, resulting in high resolution and high-contrast images.

...

If UD glass is subjected to a sudden temperature change (thermal shock), the glass can break. Therefore in the case of the EF 400mm f/2.8L USM lens, two protective glass elements were provided to prevent thermal shock.

In the case of the EF 400mm f/2.8L II USM lens, the fluorite element, which is more resistant to thermal shock than UD-glass elements, is positioned right behind the protective glass. This made it possible to have only one protective glass element.


Ok, that's really interesting information. It was always a mystery to me why the FD had two protective glasses!

Thanks a lot.

Stephan


PostPosted: Sun Dec 06, 2020 9:03 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
Blazer0ne wrote:



High Image Quality

The optical system of the EF 400mm f/2.8L USM lens is identical to that of the FD 400mm f/2.8L lens. The two UD-glass elements correct axial and lateral chromatic aberrations.

..............

Copyright 1996 by Canon Inc.
Masaru Kobayashi



I dare say that the above statement by Mr. Masaru Kobayashi is technically incorrect. The two UD-glass elements DON'T "correct" axial and lateral chromatic aberrations, the two UD-glass elements ARE the VERY source of axial and chromatic aberrations!

What I am going to say may seem strange at first, but it is the dispersive lenses (negative lenses) made with "bad" high chromatic dispersion glasses that correct the axial and lateral chromatic aberrations of the UD and fluorite collective lenses (positive lenses)!


PostPosted: Sun Dec 06, 2020 11:50 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
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Last edited by Blazer0ne on Tue Feb 22, 2022 6:14 pm; edited 1 time in total


PostPosted: Mon Dec 07, 2020 10:54 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
Blazer0ne wrote:


For the sake of the argument, this quote was from a technical service manual used to repair the camera lens and electronics. There was no algebra or lens theory, only what I quoted.


I understood perfectly well that it was a quote from an official Canon document. Be assured that my intention was not to criticize anyone, but to draw attention to the fact that there are many half-truths in the marketing of photographic equipment and lenses, in particular.

A very common misconception is that a lens made of ED, UD, ULD or XLD glass exhibits itself an extremely low level of chromatic aberration. This is far from true!

The Abbe numbers (also known as v-numbers) of exotic low-dispersion glasses are not so high as to themselves guarantee a low chromatic aberration. For example, BK7, an extremely common crown glass, has Abbe number equal to 64, while FK51A, one of the best XLD glasses from Schott XLD, has Abbe equal to 84.

Consider now this statement taken from a Schott document, with which I fully agree:

The size of the chromatic aberration of a single lens is the quotient of the focal length and the Abbe number.

(from: https://www.schott.com/d/advanced_optics/c0e4b75e-14a9-4080-b19c-cec864f1a7ac/1.3/schott-fluoro-phosphate-glasses-may-2014-neu.pdf)

That means that a single FK51A lens will exhibit LoCA 24% smaller than a BK7 lens. That is, the chromatic aberration of a single FK51A lens will be only slightly less than that of a BK7 lens. Therefore, the names used by optical glass manufacturers such as ED (Extra Low Dispersion), ULD (Ultra Low Dispersion), XLD (Extremely Low Dispersion), etc. are misleading and serve more to the advertising purposes of lens and optical glass manufacturers to impress people than as a technically appropriate description of the properties of these glasses.

That said, what matters in the end is not to minimize the chromatic aberration of each individual lens, but the residual chromatic aberration of the composite lens. Suffice it to say here that in order to obtain a low residual chromatic aberration, what matters most is not so much that the optical glasses have a high Abbe number, but that these glasses exhibit a marked anomalous partial dispersion. Fortunately, glasses with Abbe number above 70 tend to exhibit significant anomalous partial dispersion. But that's another story.

Later, I will show a picture of the moon that I took with a 400mm apochromatic lens plus two teleconverters. The most interesting is that the manufacturer claims the lens does not have exotic glasses in its construction!


PostPosted: Sat Dec 12, 2020 7:40 pm    Post subject: Reply with quote
Sadly, I am not fortunate enough to own a Canon 400mm F2.8 lens, which really is a beautiful lens, but I would like to show a photo of the moon I took with an APO Sigma 400mm F5.6. This lens was Sigma's first attempt to produce a telephoto lens with a chromatic correction that standed above the average of the time.



Unfortunately, many of these Sigma lenses have had problems with progressive degradation of cement between the first and second elements:





Sigma claimed that he had achieved apochromatic correction by using an innovative optical formula that did not need to rely on special optical glasses. Well, let's see how the lens performs in practice:




(Click twice on the image to see it in its full glory! Smile )


The picture was taken with a 24 MP Sony A99 plus two 7-element Komura Telemore MC7-II teleconverters. The diaphragm was closed one stop to F8, the exposure was 1/2 sec with ISO 50. Note that the effective diaphragm was F32! Even with two 2X teleconverters, it was not possible to frame the moon tightly. It was necessary to crop a little, so the final image ended up with approximately 10 MP. Stephan was more fortunate than me because he could use an additional 1.4X teleconverter, which alleviated the need to crop the image. Looking back, it seems the ideal solution is to use two 2X teleconverters with a sensor of at least 20 MP.

I live in a city with a population of one million and an altitude of about 700 m, certainly not the ideal location to take astronomy pictures. Anyway, I think my picture of the moon is not unlike Stephan's, even though he used better teleconverters and a much more expensive lens. At the pixel level, it seems to me that the resolution of the two pictures are not markedly different. If you look closely, you will notice that the details of the lunar surface that can be seen in one photo are also visible in the other.

One of the advantages of using an F2.8 lens over an F5.6 together with multiple teleconverters is that with the faster lens the diffraction effect is less significant. I should also note that Stephan's photo is a little clearer (better signal-to-noise ratio) because he could use a less radical cropping.


PostPosted: Sat Dec 12, 2020 8:09 pm    Post subject: Reply with quote
Should try to do one with the Minolta RF 800 mm f8 plus 300-L ...once curfew is over...

Great pictures indeed


PostPosted: Sat Dec 12, 2020 8:29 pm    Post subject: Re: Full moon with Canon nFD 2.8/400 plus multiple converter Reply with quote
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Last edited by Blazer0ne on Tue Feb 22, 2022 6:14 pm; edited 1 time in total


PostPosted: Tue Dec 29, 2020 10:50 pm    Post subject: Reply with quote
Gerald wrote:
Sadly, I am not fortunate enough to own a Canon 400mm F2.8 lens, which really is a beautiful lens


To be honest - I bought one just for a book project where I had to document some frescoes high up in a church in Rome (Italy). Since it was for one project only, I did refrain from buying a modern 2.8/400mm.

Gerald wrote:
but I would like to show a photo of the moon I took with an APO Sigma 400mm F5.6. This lens was Sigma's first attempt to produce a telephoto lens with a chromatic correction that standed above the average of the time.

That's interesting information, and I wasn't aware of this Sigma lens! I've never seen it here in Sitzerland; only the later versions (APO and non-APO). They appear from time to time on local websites or in local shops, but often they have haze as well. I have such a sample which still needs to be cleaned ... (same problem also with a Sigma APO zoom 50-200mm which seems to be surprisingly sharp and CA-free).

S


PostPosted: Wed Dec 30, 2020 5:00 am    Post subject: Reply with quote
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