Wikipedia:Reference desk/Archives/Entertainment/2012 January 24

= January 24 =

SLR, DSLR, and crop factor
I'm currently kinda confused. I've inherited an old Minolta Dynax 2xi 35mm still photo camera (the Dynax models were sold as Maxxum in the US). I've been looking for some ultra wide angle lenses for it and eventually got me a Sony 18-55mm with a fitting Sony Alpha mount (which is how Sony has re-named Minolta's old AF mount when they bought the company) for only 80 Euros.

I've received the lens now, and other than the ad (which had my Dynax 2xi in a long list that this lens can be used for), the lens manual states "not usable for full-frame 35mm cameras". The lens fits perfectly on the mount, and when looking through the viewfinder, I see a thrilling ultra-wide angle view without any noticeable vignetting (the only problem is a kinda low DOF, but that might be due to my dark conditions in here with my aperture at maximum).

So I went online to check whether there's any information out there as for what's the story with this lens and full-frame cameras. What's most frustrating is that 99% of Google hits are nothing but vendor ads (many of which name my Dynax 2xi as compatible again). The remaining hits are either where the lens has seen APS-C usage, or some vague forum mentions of "not usable for analogue SLR because you'll see a solid black tunnel with a circular image in the middle" due to crop factor or something. However, I've also come across one or two threads on a German forum dedicated to the old analogue full-frame Dynax cameras where people post their photos taken with this modern Sony 18-35mm (unfortunately it requires forum registration to see those photos).

So what's the story here? The camera's an SLR, so I should be seeing the real deal through the viewfinder, right? And from what I can see with the naked eye, it all looks mighty fine. What's even more confusing is the fact that I can't use the included plastic lens hood because it always shows at 18mm, however when removing it, the image is just fine at the edges, judging by what I see through the viewfinder. --79.193.32.40 (talk) 03:09, 24 January 2012 (UTC)


 * I don't know much about the particular systems you're talking about, but it sounds like situation akin to the Canon EF-S lens mount system, which only works on cameras with APS-C sensors, not the full frame sensors. It's certainly worth reading that fairly short article as it sounds an almost identical issue. An issue with those is that the lens can contact the mirror or sensor (can't remember for sure) if used on the full frame cameras, causing damage to the inner workings. Now with film, perhaps it's a slightly different issue, I can't really say. It also talks of the vignetting, etc in that article, explaining why it's a problem. On the next question, yes, you're right, you should be essentially seeing the 'real deal' in the viewfinder (with some variations from camera to camera; on some you don't see the whole frame) but realistically it's hard to tell exactly how a photo will come out through the viewfinder in terms of vignetting and the like, particularly if it's only a minor issue. Now I'm also guessing you bought this secondhand given your mention of the bargain price, so perhaps they've simply included an incorrect lens hood with it thus explaining why it's visible at the wide end. A good lens and hood should not have this issue. Maybe you just need to whack some film in and take some photos, if you're satisfied you're not going to damage the camera? --jjron (talk) 08:11, 24 January 2012 (UTC)


 * Normally I'd expect vignetting to be the issue. Maybe there's a lot of chromatic aberration at the corners, but that's usually fixable.  But digital SLRs are less tolerant of some things than film SLRs: in a film SLR it doesn't matter what direction the light rays come from as long as they hit the film, but in a digital SLR they must be at a certain angle to the sensor.  Hence if the lens sends light rays at a sharp enough angle to the corners there may be vignetting on a DSLR but not on a film SLR.  (I can't find a reference about this happening with real lenses but this Olympus page discusses the problem.)  I'd agree that as long as the lens doesn't seem to be making contact with anything it shouldn't, your best option is to take photos and check the results. --Colapeninsula (talk) 09:44, 24 January 2012 (UTC)


 * Traditional (film) SLRs usually show over 95% of the full frame in the viewfinder. If you can't see any vignetting in the viewfinder, it is likely to be small.  However, with a focal length of just 18 mm I would expect some distortion of the final image (perhaps a bit like this).  Just to check, shoot off a few frames with your lens and see if you like the results.  Astronaut (talk) 14:27, 25 January 2012 (UTC)


 * Went on a shooting spree this afternoon throughout the city, and in bright daylight I did indeed see a.) black corners (not from vignetting, but actually because I saw the edges of the image circle, or rather the inside of the lens body), and b.) some light barrel distortion on the edges. Though not as strong as yours on both counts. After all, while it's 18mm, it's not a fish-eye lens.


 * I'll probably have the processed negatives plus prints plus photo CD by next week. From what I could tell through the viewfinder in bright daylight, the barrel distortion is small enough to be fixable in Paint Shop Pro. Actually the barrel distortion seemed to be pretty much the opposite curves of the black edges (even with the same degree of curvature as the edges, so that each of the four corners looks like )( or with solid black outside), so that distortion correction will probably even end up with straight black edges that will easily be removable by a rectangle selection&crop without losing any image information. --79.193.36.122 (talk) 19:17, 25 January 2012 (UTC)


 * I'm a little curious why you want to correct the distortion. The distortion is usually the reason for buying such a wide angle lens in the first place - it allows for some dramatic composition.  If you just want a wider view you might be better with a standard lens (50 mm) and take several pictures which you can stitch together.  You would also get better low light performance.  Astronaut (talk) 12:39, 26 January 2012 (UTC)


 * It's the converging lines that I'm after, not *CURVED* lines. Perspective distortion of ultra-wide angle lenses is sophisticated 3-dimensional distortion, while fish-eye distortion is primitive 2-dimensional distortion. Think especially Terry Gilliam, and partly also Stanley Kubrick. See perspective distortion (photography) (especially the section perspective distortion (photography)), rectilinear lens, and this image: . --79.193.25.191 (talk) 19:35, 26 January 2012 (UTC)

discovery HD world ad music
friends, please let me know the track/music name of the following (discovery HD world) advertisement. http://www.youtube.com/watch?v=wuif3XiVBQI — Preceding unsigned comment added by 199.224.149.10 (talk) 08:17, 24 January 2012 (UTC)
 * Sounds like something that was composed for the advert. --Viennese Waltz 08:40, 24 January 2012 (UTC)