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	Username   Password FM Forum Rules Canon SLRs, primes, and zooms lenses reviews FM Forums | Canon-mount SLRs | Join Upload & Sell    Search Used end    Archive 2010 · The Point of Infinity Focus?

Sinsear Offline Upload & Sell: Off p.1 #1 · The Point of Infinity Focus? So I was trying to shoot some astrophotography last night with a 16-35mk2, and, since the autofocus won't work on a black sky, I set it to MF and put it all the way to the right on the focus guide (@ infinity). However, my shots came out misfocused and the stars were giant blobs or blob trails. I found a light post in the distance and set it to autofocus and focused on that, then switched to MF and did another long exposure. This time, the stars were absolutely sharp and crisp and the star trails were slim lines (instead of thick blobs like before). However, I noticed that on the focus guide pointed to slightly left of infinity. Why is this? I mean, shouldn't stars be pretty much at infinity distance away? And how come it is not in focus when you set it to infinity? Aug 07, 2010 at 07:01 PM

gasrocks Offline Upload & Sell: Off p.1 #2 · The Point of Infinity Focus? But, many lenses, especially good ones have some focus past infinity. If you crank it all the way it will be focused past infinity. Use LiveView and 10X to check your focus for stars. Aug 07, 2010 at 07:16 PM

Ariel Bravy Online Dedicated FM Upload & Sell: On p.1 #3 · The Point of Infinity Focus? Yeah, I've heard that one of the reasons that lenses can focus to infinity and beyond is that due to temperature fluctuations, the point at which infinity rests physically in the lens may change as the lens expands and contracts a bit. Not sure how true this is though. I suppose you could test it by focusing in one temperature and going out to shoot in a vastly different temperature. I know some of the Zeiss lenses actually focus exactly at infinity when you crank the focus ring all the way over. Aug 07, 2010 at 07:38 PM

nathanlake Offline Dedicated FM Upload & Sell: On p.1 #4 · The Point of Infinity Focus? Ariel Bravy wrote: Yeah, I've heard that one of the reasons that lenses can focus to infinity and beyond is that due to temperature fluctuations, the point at which infinity rests physically in the lens may change as the lens expands and contracts a bit. Not sure how true this is though. I suppose you could test it by focusing in one temperature and going out to shoot in a vastly different temperature. I know some of the Zeiss lenses actually focus exactly at infinity when you crank the focus ring all the way over. Hmmmm..."exactly at infinity". Not sure I an wrap my head around that concept. Aug 07, 2010 at 08:32 PM

Matt Leitholt Offline Dedicated FM Upload & Sell: On p.1 #5 · The Point of Infinity Focus? Metals (ie. the lens barrel) expand in the heat, causing the need for room in the focusing ring. Aug 07, 2010 at 08:43 PM

David Baldwin Offline Upload & Sell: On p.1 #6 · The Point of Infinity Focus? Yes, the infinity mark is completely useless in practice, Live View at 10x is your friend. In fact I am beginning to think that any kind of focusing/distance scale is completely redundant these days. Aug 07, 2010 at 09:08 PM

kakomu Offline Dedicated FM Upload & Sell: On p.1 #7 · The Point of Infinity Focus? Slight correction: The infinity mark of AF lenses are useless. The AF lenses are built with looser tolerances. The expansion and contraction of materials seem to move the point of infinity. MF lenses will frequently have a hard infinity stop (the end of focusing is infinity), presumably due to the greater tolerances that are used with many MF lenses of yore. When I want to focus to infinity with my UWA lens, I point it at anything > 6 feet away and I'm almost guaranteed to be at infinity. Aug 07, 2010 at 09:26 PM

stanj Online Dedicated FM Upload & Sell: On p.1 #8 · The Point of Infinity Focus? Using LV in complete darkness (just stars) is not very feasible, especially if I want something in the foreground in focus (say a tree 50m in the distance). Can't illuminate that with a flashlight (none that I own, anyway). Matt Leitholt wrote: Metals (ie. the lens barrel) expand in the heat, causing the need for room in the focusing ring. Somehow, strangely, my FD lenses do lock at infinity, as does the 24TSE (mk1), and somehow they managed to deliver sharp images in the summer and in the winter in the 70s and 80s... Aug 07, 2010 at 10:22 PM

geniousc Offline Upload & Sell: On p.1 #9 · The Point of Infinity Focus? Requiring that AF lenses focus exactly to infinity would pose all sorts of additional design requirements to the makers. Such as keeping the camera bodies from trying to drive the lens past infinity depleting batteries sooner, burning out focusing motors, noise and lens damage generated by lenses repeatedly slamming into the stops etc. It's just easier overall to *float* the infinity setting. I don't think it has anything to do with temperature tolerances. gene Aug 08, 2010 at 03:45 PM

David Baldwin Offline Upload & Sell: On p.1 #10 · The Point of Infinity Focus? "Somehow, strangely, my FD lenses do lock at infinity, as does the 24TSE (mk1), and somehow they managed to deliver sharp images in the summer and in the winter in the 70s and 80s... " Yes, I had the same experience with film, but digital is much much sharper than film IMHO, and needs dramatically greater focusing accuracy/lens quality. Seems to me that's one reason Canon are now working their way through the Ls upgrading from Mk1 lenses to Mk2s. Digital just shows up every tiny imperfection in lens and technique, especially with stars, and this includes infinity focus which varies with temperature etc. Film was so forgiving! Aug 08, 2010 at 05:09 PM

geniousc Offline Upload & Sell: On p.1 #11 · The Point of Infinity Focus? David Baldwin wrote: "Somehow, strangely, my FD lenses do lock at infinity, as does the 24TSE (mk1), and somehow they managed to deliver sharp images in the summer and in the winter in the 70s and 80s... " Yes, I had the same experience with film, but digital is much much sharper than film IMHO, and needs dramatically greater focusing accuracy/lens quality. Seems to me that's one reason Canon are now working their way through the Ls upgrading from Mk1 lenses to Mk2s. Digital just shows up every tiny imperfection in lens and technique, especially with stars, and this includes infinity focus which varies with temperature etc. Film was so forgiving! Essentially sharpness and film really don't have much to do with floating the infinity setting and varying temperatures at least on short lenses. You can take a quality alternative lens, mount it on a properly spaced adapter, set the lens at infinity and snap your picture. The shot will be properly focused at any temperature, it's done everyday of the week. The real issue is, how do you make a $150 plastic zoom with plastic mount with 13 elements, some plastic and make it precise enough to focus at infinity on every camera. Answer is you can't, so you float the infinity setting and let the AF do it's thing. gene Aug 08, 2010 at 06:21 PM

aborr Offline Upload & Sell: Off p.1 #12 · The Point of Infinity Focus? ED glass is a lot less stable with temperature than conventional lens elements, so there has never been a hard stop at infinity on super telephotos. This was as true with 30 year old manual focus lenses as it it now. As for run-of-the-mill lenses, I expect that it is just too hard (expensive) to make the short focus scales accurate with modern AF lenses and the manufacturers just don't bother. I expect that this is particularly true with zoom lenses, because it's hard to make a perfectly parfocal zoom. (That is, it's difficult to make a lens that doesn't shift focus a bit as you change the focal length by zooming.) Since few photographers have any need for scale focussing now that they have AF, the manufacturers just no longer try to callibrate the lenses at infinity anymore. Modern first-quality manual focus prime lenses generally (except for super teles) still have a hard infinity stop. Zooms usually don't have one. Aug 08, 2010 at 06:47 PM

David Baldwin Offline Upload & Sell: On p.1 #13 · The Point of Infinity Focus? hello Gene, Seems to apply to my £1500 24L as much as anything cheaper! I suspect that at least for star photography in the film era alot of us were using pushed film that was so grainy that small focus errors were invisible. With the exception of the Tokina 12-24 I have never seen a digital lens have an infinity mark that gave perfect infinity focus on stars. Lots of even shorter focal length lenses have exotic glasses these days, and I suspect also that these are more susceptible to temperature. If you take a digital era AF lens, set it to focus on the infinity mark on the scale, I can practically guarantee that the star images will not be perfectly sharp, and in my experience this applies to expensive wides as much as anything else so for perfect infinity focus disregard the scale, and get to 10x Live View. As it happens this focus issue prevented me going digital for years,until Live View arrived to solve the problem. Mind you its only the astronomical people who are going to notice exact infinity, for landscape work stopped down such accuracy is academic. Aug 08, 2010 at 07:42 PM

parsons Offline Dedicated FM Upload & Sell: Off p.1 #14 · The Point of Infinity Focus? just use Af, find the brightest star, simple as! Aug 08, 2010 at 08:06 PM

geniousc Offline Upload & Sell: On p.1 #15 · The Point of Infinity Focus? David Baldwin wrote: hello Gene, Seems to apply to my £1500 24L as much as anything cheaper! I suspect that at least for star photography in the film era alot of us were using pushed film that was so grainy that small focus errors were invisible. With the exception of the Tokina 12-24 I have never seen a digital lens have an infinity mark that gave perfect infinity focus on stars. Lots of even shorter focal length lenses have exotic glasses these days, and I suspect also that these are more susceptible to temperature. If you take a digital era AF lens, set it to focus on the infinity mark on the scale, I can practically guarantee that the star images will not be perfectly sharp, and in my experience this applies to expensive wides as much as anything else so for perfect infinity focus disregard the scale, and get to 10x Live View. As it happens this focus issue prevented me going digital for years,until Live View arrived to solve the problem. Mind you its only the astronomical people who are going to notice exact infinity, for landscape work stopped down such accuracy is academic. Hi David. I'll go along with your comments and observations. It's notable that Zeiss and Leica are still making the quality lenses that we veteran users miss so much. It can be done but then again these are not AF lenses and cost more than most users are willing to pay. gene Aug 08, 2010 at 08:18 PM

wickerprints Offline Dedicated FM Upload & Sell: Off p.1 #16 · The Point of Infinity Focus? Just to make sure that people aren't misreading the focusing barrel, but you will notice that the infinity mark is not actually where the infinity symbol is located. There should be an "L"-shaped indicator next to the infinity symbol, and the location of the vertical line is the nominal infinity focus. If you turn the focusing ring all the way to the right until it doesn't turn any further, you are focusing past infinity. There is a lot more "slop" that is built into EF lenses around the infinity focus than what would be required for temperature variations alone. Aug 08, 2010 at 09:05 PM

James Taylor Offline Upload & Sell: Off p.1 #17 · The Point of Infinity Focus? wickerprints wrote: Just to make sure that people aren't misreading the focusing barrel, but you will notice that the infinity mark is not actually where the infinity symbol is located. There should be an "L"-shaped indicator next to the infinity symbol, and the location of the vertical line is the nominal infinity focus. If you turn the focusing ring all the way to the right until it doesn't turn any further, you are focusing past infinity. Yes, my understanding is that for IR focus it needs to go past the infinity mark. The infinity mark on my 24L works great with my 5D MKII. I use it all the time for landscape work. Just make sure you are on the L shaped indicator. Aug 09, 2010 at 01:26 AM

garycoleman Offline Upload & Sell: Off p.1 #18 · The Point of Infinity Focus? yes it seems like infinity is useless. when i turn the focus ring to infinity, things far away are not focused Aug 09, 2010 at 06:29 PM

David Baldwin Offline Upload & Sell: On p.1 #19 · The Point of Infinity Focus? Gary, Yes the infinity mark on modern AF lenses is useless. Frankly. A bit like an appendix really, a nod to how things used to be. Aug 10, 2010 at 10:22 AM

John_T Offline Upload & Sell: On p.1 #20 · The Point of Infinity Focus? ...by definition, infinity means not finite, and therefore not definable, so trying to define where infinity should be is simply pursuing futility. Give up. Aug 10, 2010 at 11:20 AM

scott f Offline Upload & Sell: On p.1 #21 · The Point of Infinity Focus? "To infinity.........and beyond!", Buzz Lightyear Aug 10, 2010 at 01:00 PM

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