Opteka 6.5mm f/3.0 HD

Physical Characteristics

Available Mounts: Canon EF, Nikon F
Lens type: Fisheye (Diagonal on crop sensor, Circular on full frame)
Focus type: Manual only
Aperture range: f/3 – f/22
Filter size: n/a
Dimensions (with caps on): 105mm high, 90mm wide
Height (from camera front to lens front; caps off): 85mm
Weight (with caps on): 580g / 1 lb. 5 oz.
Weight (with caps off): 524g / 1 lb. 3 oz.
Other: removable plastic lens shade

Star Tests

2 min. single exposure at f/3.0, ISO 1600, Canon EOS Ra, Bortle 3 sky.
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f3 crops — Same image at f/3 with 200% zoomed-in crop boxes showing star performance. Note: the Opteka lens I purchased did not properly focus to infinity (see commentary), so it was impossible to do a proper test as the star shape and chromatic abberations are mostly hidden when the lens can’t focus. Open full-size image in new tab.

2 min. single exposure at f/4.0, ISO 1600, Canon EOS Ra, Bortle 3 sky.
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Same image at f/4 with 200% zoomed-in crop boxes showing star performance. Note: the Opteka lens I purchased did not properly focus to infinity (see commentary), so it was impossible to do a proper test as the star shape and chromatic abberations are mostly hidden when the lens can’t focus. Open full-size image in new tab.

4 min. single exposure at f/4.5, ISO 1600, Canon EOS Ra, Bortle 3 sky.
Open full-size image in new tab.

Same image at f/4.5 with 200% zoomed-in crop boxes showing star performance. Note: the Opteka lens I purchased did not properly focus to infinity (see commentary), so it was impossible to do a proper test as the star shape and chromatic abberations are mostly hidden when the lens can’t focus. Open full-size image in new tab.

4 min. single exposure at f/5.6, ISO 1600, Canon EOS Ra, Bortle 3 sky.
Open full-size image in new tab.

Same image at f/5.6 with 200% zoomed-in crop boxes showing star performance. Note: the Opteka lens I purchased did not properly focus to infinity (see commentary), so it was impossible to do a proper test as the star shape and chromatic abberations are mostly hidden when the lens can’t focus. Open full-size image in new tab.

Commentary

The big disappointment with this lens was moving the manual focus ring did very little in terms of changing focus. The fixed focal plane was not set to infinity, but just short of it, so the stars never really would come in to focus. For a very wide-field shot like this, it doesn’t matter too much in a single exposure until you zoom in, and can see all the stars and details are a bit blurry. I hope to modify this lens to see if I can get it to focus. If successful, I will update this review.