The cheap 400mm f/6.3 lenses and company
PW M43 wrote:
You could also look at the cheap T2 preset lenses from a variety of manufacturers, including ‘reputable’ ones like Soligor. Being designed for manual aperture use I often find them easier to work with than adapted auto aperture lenses.They also typically have many-bladed apertures, if you like the bokeh that this can produce.
If you mean the multitude of 400mm f/6.3 (what Spiratone used to market as the “Girlwatcher” lenses… yeah, that is a little creepy), they’re of very mixed optical quality.
For B&W, most are actually ok. The problem is huge amounts of transverse CA. Usually, one thinks of transverse CA as the “easy to correct” CA, but it’s only easy to correct if the magnification varies with color in a way that leaves each of R, G, and B fairly sharp — which many don’t. For example, my Tele-Astranar is a “C” optically with 6-9 pixels of blurry color fringe, but my Soligor is a solid “B” because the CA it has is much more correctable. Given the very low cost of these optics, I wouldn’t be surprised if the quality varies more with sample than with brand.
BTW, my one 500mm refractive lens is a Kimunor 500mm f/8, which is actually better than both the above 400mm (but still a “B”). So it isn’t clear that things always get worse as the focal length gets longer…. However, the longer ones often are bundled with a 2X teleconverter, and let me say unequivocally that is a bad idea — especially for APS-C. The best of these lenses isn’t able to challenge a 10MP APS-C sensor’s resolution, so a 2X teleconverter just costs you 2 stops of light loss with no IQ gain over cropping… and wait till you see how big 2X magnified CA is!
Incidentally, all these super-cheap long lenses are really physically long lenses, making them a real pain to pack. However, they are so lightweight that they are easy to hand hold and to brace to be steady. They’re basically aluminum tubes with about 4 thin pieces of glass in them — and most even have a tripod mount so you can balance them well on a tripod.