The supreme APO lens, the Mamiya APO-Sekor Z 500mm F6. This is a so-called medium-format (6×7) lens.
Some time ago, I purchased a ZWO full-frame CMOS camera, the ASI2400MC PRO, at an unbeatable 30% discount off the list price during a ZWO campaign. However, even when paired with a Canon EF 300mm F2.8 IS USM full-frame lens, the vignetting was severe. I realized that to eliminate vignetting completely, I would need to use a medium-format lens. After searching through various options, I found this relatively affordable, top-of-the-line lens.
This lens is a high-performance optic that K-ASTEC highly praises. However, it does not have a built-in focusing mechanism, nor does it provide a straightforward way to mount it on an equatorial mount. Therefore, a bit of ingenuity is required to use it effectively.
Chromatic aberration characteristic curves and MTF Chart by ianbfoto.com
For focusing, I obtained a mount adapter from Fotodiox that converts Mamiya RB67/RZ67 mount lenses to the Canon EF mount. The adapter includes a built-in helicoid, allowing precise focus adjustment.
To mount the lens on an equatorial mount, I purchased a special optical tube band (TB-89AS) from K-ASTEC. Unfortunately, it is already sold out and not available for overseas customers. It was released in limited quantities. Incidentally, a standard 90mm optical tube band also fits, so equivalent products from other manufacturers can be used.
The used lens did not include the original rubber hood, so I purchased a 105mm metal hood from Amazon. I customized the hood with vinyl cut stickers. Doesn’t it look cool?
This is an example of astrophotography taken with the SVBONY SV220 dual narrowband filter (OIII and Ha, FWHM 6nm) using the ASI2400MC PRO. The image consists of three 180-second exposures live-stacked.
The result is an extremely clean image with no vignetting.
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