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This great answer by @gerrit discussing planetary phases seen in visible light contains the image I've included below. According to the Wikimedia Commons link these are ESO images from the Venus transit 2004 VT-2004 observing campaign.

The ESO, or European Southern Observatory:

Organisation Européenne pour des Recherches Astronomiques dans l'Hémisphere Austral) is a 16-nation intergovernmental research organization for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky. (emphasis added)

These images are very high quality, and the last one, dated 8/6/04 (08-June-2004) appears to be taken at/near inferior conjunction, when Venus is almost directly between the observer and the Sun.

Question: I'd like to understand with what instrument this image was taken, and how the technical challenges imaging Venus with such a small angular separation between it and the Sun were overcome! I did a quick check and during the UTC day of June 8th, 2004, Venus moved from about 0.6 to 1.1 degrees from the Sun as viewed by Earth. How was Venus imaged so nicely? Was this really imaged from the ground through Earth's daytime atmosphere, or from space? In either case, how was a high quality telescope pointed so close to the Sun and shielded from stray light and protected from damage?


below: Phases of Venus, from here.

enter image description here

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I think you'll have to live with an incomplete answer. It appears this was taken by an amateur astronomer using a simple 4.5 inch telescope. You can find, on the ESO website, a collection of many images taken during the 2004 transit. On this page, is the image you are asking about (along with some other images by the same person). The credit for that image is given as:

The Phases of Venus

Statis Kalyvas
4.5-inch Mizar telescope
Nikon Coolpix 750
February 27 - June 8, 2004
Thessaloniki, Greece

I'm assuming (because I can't find any reference to state otherwise) that the name "Mizar telescope" is just the personal name Statis Kalyvas gave to his telescope. Although you can see that the equipment was nothing an amateur astronomer couldn't buy. A pretty typical telescope with a standard camera. Nothing "professional" or extremely high tech.

We can probably guess at some other pieces of the puzzle though. From the image below, you can see that the 2004 transit began (from Thessaloniki's local time) at 7:13 AM and ended at 1:25 PM.

enter image description here

Given that the observation period of the transit itself happened during the day, Statis definitely would have needed a solar filter for his telescope, which would have blocked upwards of 99.999% of the light from the Sun, allowing him to view the transit safely.

For the other images leading up to the transit, my guess is that he made his observations during in the evening when the Sun was near the horizon and not very bright (due to much of the light being scattered). Venus should've been higher in the sky than the Sun and still visible at that time. An eyepiece which gives a small field of view would've been useful here.

You can possibly guess that the image was taken near the horizon because a 4.5 inch telescope should have a resolution of $1.21\ \mathrm{arcsec}$ at best whereas, near conjunction, Venus is almost an arcminute in size. Venus should be well resolved, but it looks a bit fuzzy. This is likely attributed to the high airmass near the horizon. The drastic difference between the clarity of the image on 3/4 and 13/4 (just ten days later) leads me to believe the telescope was capable of better resolution and was simply impeded by the atmosphere near the horizon.

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    $\begingroup$ OK it looks like you've solved yet another astronomical mystery! With a DLSR that can shoot 6.5 fps and a 114mm aperture, I'm sure there are "lucky imaging" or other tricks to get a fairly-good image even through a high air mass. It turns out Mizar-Tec is a Japanese optics maker that at least used to sell telescope. Here for example is an image of a150 mm reflector; i.stack.imgur.com/bit5Z.jpg which I found here in e-bay. Thanks! $\endgroup$ – uhoh Oct 25 '17 at 4:15
  • $\begingroup$ For example, here is their "1970's product line-up:" i.stack.imgur.com/bXH4i.jpg Also, in the thread cloudynights.com/topic/407804-mizar there is a link to this 1970's catalog of Hino Kinzoku, which I believe is marketed as Mizar in English. yumarin7.sakura.ne.jp/retrokan/Mizar1973.pdf $\endgroup$ – uhoh Oct 25 '17 at 4:26
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    $\begingroup$ @uhoh Good find on the Mizar telescope. My googling kept finding pictures of the star with telescopes. $\endgroup$ – zephyr Oct 25 '17 at 14:14

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