First Light test with Pentax SMC Takumar 200mm f/4 M42 lens at f/5.6. Chromatic aberration less noticeable than f/4 and vignetting gone with sharper stars in the corners, however bridge edge stars show internal reflection flare. See f/4 variant. DeepSkyStacker 3.3.4 Stacked 100% (6) of 6 Images at 200mm f/5.6, ISO 1600 @ 30 Sec, 0 DARK, 0 BIAS, 0 FLATS, Post-processed with Adobe Photoshop CC 2018 Pentax SMC Takumar 200mm f/4 M42/EOS adapter, No filter, Baader BCF modified Canon 70D DSLR field 381' x 254' , Ambient ~15C. SkyWatcher Star Adventurer EQ mount unguided sidereal drive.
First Light test with Pentax SMC Takumar 200mm f/4 M42 lens at f/5.6. Chromatic aberration less noticeable than f/4 and vignetting gone with sharper stars in the corners, however bridge edge stars show internal reflection flare. See f/4 and f/6.9 variants. DeepSkyStacker 3.3.4 Stacked 100% (7) of 7 Images at 200mm f/5.6, ISO 1600 @ 30 Sec, 0 DARK, 0 BIAS, 0 FLATS, Post-processed with Adobe Photoshop CC 2018 Pentax SMC Takumar 200mm f/4 M42/EOS adapter, No filter, Baader BCF modified Canon 70D DSLR field 381' x 254' , Ambient ~15C. SkyWatcher Star Adventurer EQ mount unguided sidereal drive.
Comparison of internal iris f/stop vs external stop down for diffraction reduction. Refer to 30/11/2018 images of these and the lens. Even the first internal stop at f/5.6 creates noticeable diffraction points to bright stars (see Orion's belt) and these get more pronounced at f/6.9 and again at f/8. By comparison, the external stop down rings on the front of the lens leave round star images. Pentax SMC Takumar 200mm f/4, M42/EOS adapter, No filter, Baader BCF modified Canon 70D DSLR field 381' x 254' , Ambient ~20C. SkyWatcher Star Adventurer EQ mount unguided sidereal drive.
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