Sunday, January 29, 2012

Gear mania: Close focus Lens comparison test with Orchids: Minolta AF 50/1.7 Canon FD 100/2.8 Minolta 70-210/3.5-4.5


Click HERE for full resolution picture:
Full resolution picture (Zoom possible)

What do you do when your up at night
with no sleep in sight?
Right,
you do a lens test oh so bright :-)

I wanted to compare the image quality of these lenses when used at close focus instead of the usual infinity landscape tests.  Comparing a 50mm prime, with a more expensive legacy tele prime and with an average tele zoom lens should be interesting.


The lenses:
-- Minolta AF 50/1.7 manually focussed with cheap adapter on Nex 5n. My current low-light lens.
-- Canon FDn 100/2.8. Fresh at home.
-- Minolta 70-210/3.5-4.5 @100mm. This lens is best at longer focal lengths, at 70mm it is supposed to be not quite a performer.

All shots at ISO 100 except otherwise noted, tripod, 2 sec time delay. Normal wolfram indoor light with WB set to indoor. Pictures are OOC JPG, the raw files from ACR show further improvement in resolution.

Of course the longer lenses were setup at double the distance of the 50 mm prime. Focus was set to cropped orchid.

The outcome is shown in the composite picture. As expected, the 50mm wide open exhibits lower contrast, but the level of detail is still good. At 3.5 the IQ is very good, to be excelled only marginally at 7.1.

The Canon FDn 100mm starts at 2.8 and its IQ wide open is already very usable. Maximum IQ is achieved at 5.6 in terms of contrast. Manual focus is a dream with the smooth mechanics over 180° turn compared to the cramped Minolta AF lenses 100°.

The Minolta zoom starts at 4.5 at 100 mm when EVs are compared to the Canon prime. So its offical rating of 3.5 to 4.5 was more of a marketing. IQ is not bad, but I would guess that it lags about 1 EV behind the Canon prime in terms of contrast. So you would have to stop this lens down to the next aperture to reach similar IQ. At aperture 14, IQ has already dropped off, though this also might be due to ISO 200 used for this shot.
Still, for a zoom lens with the advantage that you can carry a range of 70 to 210 mm focal reach with you, it is quite acceptable.

So as summary, all lenses are very usable with the 50mm offering the best IQ, lowest weight and even closer minimum focussing distance (25 cm compared to 1.0 or 1.1 m). The Canon tele lens has similar IQ and better usability compared to the Minolta zoom because of wider aperture (1.3 EV), better IQ, and still handholdable focal length. The Minolta zoom's field of application is for airplane photography or other bright-light, long-distance setups.

Some further remarks on these lenses:
http://forums.dpreview.com/forums/readflat.asp?forum=1042&message=40462797

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