rsg@cbscc.UUCP (Bob Garmise) (03/11/85)
I, too, am a stickler for sharp pictures. I've owned an Olympus OM-1 and now an OM-2N. Both are ok, but I guess I'm a perfectionist. But are the almost perfect, but not quite perfect, pictures due to camera shake or owner shake? Only my developer knows for sure. It seems to me that one answer to resolving this problem is (ta-da) mirror lock-up. Now, I know this doesn't work most of the time, but it will work for tripod pictures, and for scenes that tend not to move too much (e.g. mountains, lakes, sky). I admit that I don't use the feature (does Olympus have it? I can't rightly say right off hand.) because of my inability to see through the viewfinder at the time I'm taking the picture. BTW, it suddenly occurs to me that perhaps the problem is tiny movement as the picture is being taken. Have you tried using a cable release? Try it first with your tripod pictures, and then with your hand-held ones. Maybe, just maybe, your finger is depressing more than just the shutter release button. This would show up more in slower (less than 1/30th second) pictures, and in streaked lights (rather than pinpoints) in night photos. ...bob garmise...at&t bell labs, columbus...
phl@drusd.UUCP (LavettePH) (03/12/85)
I'm afraid I confused resolution with brilliance in a previous article. What I meant to say was that, all other factors being equal, when you double the aperature there is a two-fold improvement in resolving power, light gathering is boosted by a factor of four and the area of the Airy-disc is cut to one quarter. This all results in a sixteen-fold gain in image brightness. This phenomenon is very pronounced in small telescopes and binoculars and can be easily seen by comparing the images seen through 7X35 and 7X50 binoculars. Check how well each one defines the small twigs on a dead tree at a hundred yards and the contrast between the twigs and their background. Similarly, there is a two-fold increase in brilliance achieved when a 60mm main lens is substituted for one 50mm in diameter. A lot of the advantages of a larger aperature are lost when a compound lens refracting telephoto is used due to internal reflections between the glass surfaces. Cassegrian and catidiop- tric lenses perform better in this respect due to their simplicity. Before you spend too much money why not perform two simple tests? First, get a resolution test sheet (Librarys usually have them.) and test your lens to see just what its capabilities are. It could be out of spec for any number of reasons. Second, cover a large reflector with a sheet of foil with small pinholes poked in it. Photograph the pinholes from a good distance using your tripod and cable release or whatever other release method you wish. B&W negatives are all you need and the exposure isn't critical. When you get your negatives, mount them in slide mounts and project them as large as you can. Circles will indi- cate everything is A-OK. Commas or bars indicate camera movement. This is a cheap and dirty way to compare methods or cameras. It's also a good way to find out how slow a shutter speed you can hand-hold any lens. BTW it is the shape of the image you should be interested in. Some halo-ing is normal. I suggest you isolate your problem as much as much as you can before changing equipment. The subtle differences caused by small variations in position during exposure, focus, resolution and contrast are very hard to isolate by looking at a regular slide or print of a landscape or any other normal photograph. Now explain to me why a slide that looks razor sharp on a fifty inch screen comes out a fuzzy mess on an 8X10 glossy :=) - Phil
hkr4627@acf4.UUCP (Hedley K. J. Rainnie) (03/13/85)
I believe that the OM-2 does not have a lockup, though the OM-1 does. Lots of cameras lack mirror lockup. A trick that works with Nikons (and probably others) without mirror lockup us to use the self-timer. The mirror locks up at the beginning of the timer interval and when the timer expires, the shutter fires and the mirror flips down. If the timer interval is not sufficiently long to wipe out vibrations from the mirror flip-up and the timer is mechanical, one may arrest the motion of the timer for an arbitrary length of time then release it.
jordan@ucbvax.ARPA (Jordan Hayes) (03/14/85)
I've been shooting various Nikons for years (not exactly the quietest of shutters...), and don't have too much of a problem except when I use my motor drives (although the F36 for my '67 F is wonderful), but it wasn't always that way. One of the most important things to remember when shooting slow (good rule of thumb --> 1/focal length of your lens... ~1/30 or 1/60 for a 50mm...) is to take a deap breath just before SQUEEZING the shutter release. My FM-2 (fully manual, thank god, but let's not start *that* discussion again !!) is about the most predictable shutter release I've ever used (this includes assorted Olympusi, Canon, Minolta AND (gasp) leicas (believe it or not...). With proper breathing control and squeezing (does this belong in net.singles ?? :~> ), I can hand-hold my 180mm f/2.8 ED at 1/2 second (without wind...), so this could be part of the problem... /jordan
daveb@rtech.ARPA (Dave Brower) (03/14/85)
> It seems to me that one answer to resolving this problem is (ta-da) > mirror lock-up... I admit that I don't use the feature (does Olympus have > it? I can't rightly say right off hand.)... The OM-1 and (I think) The OM-2 have a handy mirror lock up lever on the right hand side of the lens mount, opposite the PC connector for the flash. The OM-3's & 4's seem to have lost it in the race to modernization. -- {ucbvax, decvax}!mtxinu \ ihnp4!amdahl / !rtech!daveb "If it worked, we wouldn't call it High Tech"
ark@alice.UUCP (Andrew Koenig) (03/15/85)
Phil Lavette says: > Similarly, there is a two-fold increase in brilliance achieved when a 60mm > main lens is substituted for one 50mm in diameter. A lot of the advantages of > a larger aperature are lost when a compound lens refracting telephoto is used > due to internal reflections between the glass surfaces. Cassegrian and catidiop- > tric lenses perform better in this respect due to their simplicity. I do not see how I can parse this as a true statement. The obvious meaning -- that a 60mm lens puts twice as much light on the film as a 50mm lens -- is false. How much light reaches the film depends on only two things: the amount of light on the subject and the f-number of the lens. Focal length has nothing to do with it. Phil, what did you mean?
phl@drusd.UUCP (LavettePH) (03/15/85)
>I do not see how I can parse this as a true statement. >The obvious meaning -- that a 60mm lens puts twice as much >light on the film as a 50mm lens -- is false. How much light >reaches the film depends on only two things: the amount of light >on the subject and the f-number of the lens. Focal length >has nothing to do with it. > >Phil, what did you mean? > > Andrew Koenig Let me give you an example instead of a lot of formulas. If you know a back- yard astronomer, he or she can give you a demonstration. On a good clear night assume three telescopes are set up. The first is a small spotting scope with a 50mm diameter objective; the second, a spotting scope with a 90mm objective; the third is a *small* astronomical telescope with a 200mm objective. The objective is the front lens. The three scopes are set up for the same power and trained on a cluster of stars. M13 is a good choice. Through the 50mm you will see a faint green round smear. Through the 90mm you will see a smaller, but brighter, green round smear surrounded by a pattern of stars extending out to the diameter of the smear you saw through the 50mm. Through the 200mm you will see a pattern of bright stars the same size as the smear you saw through the 50mm and with more stars than you saw in that cir- cumferential band of stars you saw through the 90mm. The overall increase in *brightness* resulted from the change in effective ap- erature (f-stop) caused by the change in objective sizes while holding the same effective power of magnification. The disappearence of the smear resulted from both the increase in resolution and the reduction in the size of the Airy-disc caused by the increase in objective diameter. The image you see through the 200mm is brighter, it is better resolved and the brilliance (the definition between the light and dark areas - photographers call it contrast) is much im- improved. Lack of sharpness in prints or slides can be caused by any number of other problems and all of them should be considered before anybody lays out big bucks for that magic camera or lens that will solve all his or her troubles. Assuming the problem is not in the slide projector or darkroom: Poor focus - inexact focus by the photographer or poor correlation between the image projected on the film vs on the viewfinder screen Poor stability - flimsy tripod - defective lens mount - shakey photographer - mirror slap - low shutter speed Poor definition - dirty or chipped lens or filters - low quality lens or filters Poor contrast - too many elements in lens design causing reflections - not enough or poorly designed light baffles in lens and camera - forgetting to use a lens hood - high speed, low contrast film The longer the lens, the more the problem is magnified :-) There is no difference between telescope and photographic lenses except for the outward appearance. You can (and I regularly do) hang a camera on the back of a scope or mount an eyepiece on a camera lens. Some camera lenses make fine tele- scope eyepieces. My 1000mm, f11, Celestron C90 will resolve the whiskers on a muskrat at 50-75 yards. When I want to resolve the feather detail on a Canadian goose at 100-150 yards I use my 2000mm, f-10, C8. - Phil
rgb@hou5g.UUCP (Rich Bantel) (03/15/85)
If you want the sharpest pictures you should use a tripod. Modern/Popular Photography did a study which showed image resolution as a function of whether the camera was mounted on a tripod or hand held. The test results showed highest resolution for tripod mount with hand held resolution varying depending on the photographer's holding technique. My opinion is that camera vibration due to not using a tripod is the predominate cause for resolution loss with mirror slap being a second order problem. Besides loss of resolution due to poor optics, film flatness and alignment are also factors in determining sharpness. It doesn't take much of a shift from the "behind the lens focal point" to cause a loss in sharpness (apparently depth of field is very shallow there). That's why you can have two different cameras, both with the same optics, and one will give better resolution test results. (I didn't say better pictures. I don't know how much quantitative change in resolution it takes to be noticable. It's kind of like high-end audio where people are concerned with barely measurable amounts of distortion - which are probably below the audably discernable level anyway.) A camera repairman once told me that its best to take the picture within 3 seconds of winding the film. After that, the film begins to curl slightly which results in decreased sharpness (probably only at some points on the negative).
jans@mako.UUCP (Jan Steinman) (03/17/85)
In article <3468@alice.UUCP> ark@alice.UUCP (Andrew Koenig) writes: >Phil Lavette says: > >> Similarly, there is a two-fold increase in brilliance achieved when a 60mm >> main lens is substituted for one 50mm in diameter... > >I do not see how I can parse this as a true statement. The obvious meaning > -- that a 60mm lens puts twice as much light on the film as a 50mm lens -- >is false. How much light reaches the film depends on only two things: the >amount of light on the subject and the f-number of the lens. Focal length >has nothing to do with it. 1) Phil specifically mentions "diameter", or focal width. It should be obvious that a wider lens gathers more light. 2) Less obvious is that focal length has as much to do with light gathering ability as focal width. The "f-number of the lens" (ignoring losses from difraction and internal reflection) is actually the ratio of focal width to focal length. If "focal length has nothing to do with it", why does a 200mm f4 lens have a larger front element than a 50mm f4 lens? Without defending Phil too much (I don't have the original posting), you are wrong, Andrew. -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::
darryl@ISM780.UUCP (03/19/85)
[] Just for the sake of completeness, the OM-1 does have a mirror lockup, but the OM-2n does not. Although I have both, I have never had a need for the mirror lockup. But then, I haven't got a darkroom yet; when I do, I may become pickier about it. Olympus ads always used to claim that their mechanisms were the quietest and most vibration free of the 35 slrs. Do any of the photo rags back this up? --Darryl Richman, INTERACTIVE Systems Inc. ...!cca!ima!ism780!darryl The views expressed above are my opinions only.
rob@ptsfa.UUCP (Rob Bernardo) (03/23/85)
In article <647@mako.UUCP> jans@mako.UUCP (Jan Steinman) writes: > >2) Less obvious is that focal length has as much to do with light gathering >ability as focal width. The "f-number of the lens" (ignoring losses from >difraction and internal reflection) is actually the ratio of focal width to >focal length. If "focal length has nothing to do with it", why does a 200mm >f4 lens have a larger front element than a 50mm f4 lens? Am I missing something? The focal length has nothing per se to do with light gathering ability, but if we know the focal length and the ratio of focal width to focal length, then we can determine the focal width, which does have something to do with gathering ability. In other words: If the two lenses have the same f-number, i.e. ratio of focal width to focal length, but they have different focal lengths (200mm vs 50 mm), they must have different focal widths as well. -- Rob Bernardo, Pacific Bell, San Francisco, California {ihnp4,ucbvax,cbosgd,decwrl,amd70,fortune,zehntel}!dual!ptsfa!rob _^__ ~/ \_.\ _ ~/ \_\ ~/ \_________~/ ~/ /\ /\ _/ \ / \ _/ \ _/ \ \ /
dmmartindale@watcgl.UUCP (Dave Martindale) (03/25/85)
In article <1257@drusd.UUCP> phl@drusd.UUCP (LavettePH) writes: >>I do not see how I can parse this as a true statement. >>The obvious meaning -- that a 60mm lens puts twice as much >>light on the film as a 50mm lens -- is false. How much light >>reaches the film depends on only two things: the amount of light >>on the subject and the f-number of the lens. Focal length >>has nothing to do with it. >> >>Phil, what did you mean? >> >> Andrew Koenig > The problem is that you are discussing things using atronomical terminology when the audience is photographers. Your 50mm and 60mm figures are lens diameters, but photographers are used to seeing millimeters being used to measure only focal lengths. If you'd used the more normal photographic terminology of f/stop, it would have been clear. For example, assuming that the lens focal length was 100mm, the 50mm lens is then f/2 and the 60mm lens is f/1.7. > >On a good clear night assume three telescopes are set up. The first is a small >spotting scope with a 50mm diameter objective; the second, a spotting scope with >a 90mm objective; the third is a *small* astronomical telescope with a 200mm >objective. The objective is the front lens. The three scopes are set up for >the same power and trained on a cluster of stars. M13 is a good choice. > >Through the 50mm you will see a faint green round smear. Through the 90mm you >will see a smaller, but brighter, green round smear surrounded by a pattern of >stars extending out to the diameter of the smear you saw through the 50mm. >Through the 200mm you will see a pattern of bright stars the same size as the >smear you saw through the 50mm and with more stars than you saw in that cir- >cumferential band of stars you saw through the 90mm. > >The overall increase in *brightness* resulted from the change in effective ap- >erature (f-stop) caused by the change in objective sizes while holding the same >effective power of magnification. The disappearence of the smear resulted from >both the increase in resolution and the reduction in the size of the Airy-disc >caused by the increase in objective diameter. The image you see through the >200mm is brighter, it is better resolved and the brilliance (the definition >between the light and dark areas - photographers call it contrast) is much im- >improved. Well, yes, but the performance of these telescopes is limited by diffraction (if I understand correctly). The analogous situation in photography is that a lens that is stopped down all the way will produce a somewhat unsharp image, and that opening it up several stops will produce much better "brilliance". But continuing to open it up will produce less sharp images again, due to aberrations in the lens that get worse at larger apertures. Often, a f/1.4 lens will produce a poorer image than a f/1.7 or f/2 lens when both are used wide open, in direct contradiction to what you are trying to tell us. >There is no difference between telescope and photographic lenses except for the >outward appearance. Not really true. How close does your telescope focus? How light is it? These are important in photographic lenses. So is cost. Telescopes and photographic lenses obey the same optical laws, but different tradeoffs are taken in their design, producing final results whicy may differ.
phl@drusd.UUCP (LavettePH) (03/26/85)
>Well, yes, but the performance of these telescopes is limited by diffraction >(if I understand correctly). The analogous situation in photography is that >a lens that is stopped down all the way will produce a somewhat unsharp >image, and that opening it up several stops will produce much better >"brilliance". But continuing to open it up will produce less sharp images >again, due to aberrations in the lens that get worse at larger apertures. >Often, a f/1.4 lens will produce a poorer image than a f/1.7 or f/2 lens >when both are used wide open, in direct contradiction to what you are >trying to tell us. Sure it gets worse. But why? Take a look at the design of the refracting tele- photo lens. Particularly the popular zooms. Count the number of internal lenses. Each element adds reflecting surfaces, abberations, etc., that detract from image sharpness no matter how well the lenses are coated or how well the lens is internally baffeled. Add the problems of positioning internal moving elements and throw in a tele-converter and its a miracle anything in the way of an image makes it to the film. Don't get me wrong here. The modern zoom lens is a marvel of compromise and computer aided design. There is nothing like it when you don't want to lug a lot of lenses around with you. They work great if you don't try to push the zoom ratio too far and realize (as you do) that their best capabil- ities are achieved at around three to four stops back from their maximum open- ing. For long lens telephoto work you need as large a front lens as you can carry and one that is designed to work wide open without a lot of intervening glass to screw up the image. The sharpness of variable aperature lens also falls off at the extremes because of the diaphram,itself. The aperature of the diaphram affects the image quality. Back in antiquity a "good" normal lens worked between f6.3 and f128. Later on the range became between f3.5 and f22. Lately, the range is between f1.2 and f16. The manufacturers of variable aperature lenses realize this limitation and design the lens to work best at some median point with equal degradation of the image at the extremes. For optimum sharpness you need a lens that is *designed* to work best at its maximum aperature. (Or use the variable lens only at its best aperature if you have no alternative.) This all started over sharpness problems in telephoto shots. Who but a masochist or astronomer would attempt long lens work at f2? Think about it: APPROXIMATE DEPTH OF FOCUS AT f2 WITH LENS FOCUSED AT 100 YARDS FOCAL LENGTH NEAR POINT FAR POINT DEPTH OF FOCUS 150mm 167 ft 1500 ft - 300mm 250 ft 375 ft 125 ft 500mm 280 ft 323 ft 43 ft 1000mm 295 ft 306 ft 11 ft 2000mm 299 ft 301 ft 2 ft APPROXIMATE DEPTH OF FOCUS AT f11 WITH LENS FOCUSED AT 100 YARDS FOCAL LENGTH NEAR POINT FAR POINT DEPTH OF FOCUS 150mm 55 ft inf - 300mm 143 ft 1nf - 500mm 215 ft 496 ft 281 ft 1000mm 273 ft 333 ft 60 ft 2000mm 293 ft 308 ft 15 ft I've used a rough approximation here by assuming a 0.004" circle of confusion in determining the hyperfocal distance. If you halve that circle diameter you drastically reduce the depth of focus. (e.g. For the 150mm lens the NP becomes 254 ft, the FP becomes 367 ft and the depth of focus becomes 113 ft at f11.) Cut your point of focus down to fifty or a hundred feet and your depth of focus becomes so shallow at f2 that you have to ask that pretty snake to hold still while you measure the distance to his fangs and rattles with a steel tape. :-) A 1000mm, f2, cat might be nice for low light work but it would be a little hard to carry around. I think a lot of problems thought to be shortcomings in camera or lens design could simply be the photographer's inability to focus precisely. Could it be that a hunter's optical rangefinder might be a better investment than a more perfect lens? >>There is no difference between telescope and photographic lenses except for >>the outward appearance. >Not really true. How close does your telescope focus? How light is it? >These are important in photographic lenses. So is cost. The only difference between the Celestron C-90 spotting scope and telephoto lens is the barrel of the scope is painted orange and the telephoto is black. They both focus to ten feet, they have identical Maksutov-Cassegrain optics. Mine weighs in at about 3 pounds. The lens costs somewhere around $300-$450 depending what goodies you buy along with it. It has a 1000mm focal length, a 90mm objective diameter and a focal ratio of f11. My Celestron C-8 focuses down to 25 feet, weighs 21 pounds and cost about $1200. It has a 2000mm focal length, a 208mm objective diameter and a focal ratio of f10. The Schmidt-Cassegrain optical design is quite similar to the flat fronted mirror lenses used in general photography. Many serious amateur astronomers spend more time photographing than star-gazing. They have to with exposure times measured in fractions of an hour. :-) >Telescopes and photographic lenses obey the same optical laws, but different >tradeoffs are taken in their design, producing final results whicy may >differ. No argument here. The problem is that the photographer must trade off resolution and contrast for portability. Unfortunately, those are essential elements of any truly sharp photograph. If you want the details of a spider spinning its web at 30 feet, the whiskers on a muskrat at 50 yards or the limb and branch detail of a tree at a half-mile you have to be willing to give up some of the portability. There is a good example of photographic sharpness and contrast for various tele- photo lens diameters in the current Celestron catalog. Meade and Questar probab- ly have them, too. Look for the moon photographs taken with the various diameter lenses at the same effective focal lengths. Look particularly at the small cra- ter detail and the overall contrast (the brilliance). The only difference be- tween photographing the moon and a terrestrial subject is the amount of atmos- pheric distortion between the photographer and the subject being photographed. The same rules of visible light optics that yield the small craters around Tycho also get you the wing detail on a dragon fly on the other side of the pond or the rigging on the sailboat far out on that lake. (A photograph of a quarter, half or three-quarter moon makes a good test of any telephoto lens 300mm or above, by the way. Some of the craters should begin to appear on your negative.) I sometimes go picture taking in the outback with a friend. We both use Pentax bodies. He uses the 1000 ASA print film, a rather expensive zoom lens and an equally expensive 2X extender that brings his effective focal length up to about 280mm. He uses no filters or lens hood. When I don't feel like lugging the 1000mm big gun around I usually use one of Joe Spira's 300mm mirrors with a pol- arizing filter (also a great substitute for a ND filter) and a hood. I usually load 400 ASA film. He is endlessly bewildered by my getting prints that are us- ually both sharper and have more "snap" than his with a lens that cost less than his extender. The only difference he can see is that I usually brace my camera- hand against a rock or tree while he just holds his up to his eye and shoots. There are many factors at work here. Aperature is only one of them. My advice remains the same. That is, if you want really sharp telephoto shots: 1. Support the camera on a solid base. 2. Get the mirror vibrations settled down before you release the shutter or damp them out as much as you can. 3. Get as much useable glass up front as you and your wallet can carry. 4. Avoid high speed/low contrast film. 5. Avoid as many unnecessary lenses and filters between your main lens and film as you can. Find something creative to do with those little filters that are intended to screw into the back of the cats. They are nothing but trouble on a dusty day. 6. Shade your lens. 7. The longer the effective focal length, the tougher it becomes to focus accurately. Your split image range-finder becomes useless. Make sure the focus on the ground glass corresponds to the focus on the film plane. 8. Make sure you know what your problem is before you try to solve it with a Nikon or Questar lens. Sometimes expectations just aren't realistic. - Phil
jordan@ucbvax.ARPA (Jordan Hayes) (03/27/85)
In article <1539@watcgl.UUCP> dmmartindale@watcgl.UUCP (Dave Martindale) writes: >Often, a f/1.4 lens will produce a poorer image than a f/1.7 or f/2 lens >when both are used wide open, in direct contradiction to what you are >trying to tell us. Yes, but thet same f/1.4 lens will (most likely) outperform the other two at f/8. >>There is no difference between telescope and photographic lenses except for the >>outward appearance. > >Not really true. How close does your telescope focus? How light is it? >These are important in photographic lenses. So is cost. Also, what happens in the corners ? Every telescope I've ever used with a camera mount has had terrible response in the corners of the image... /jordan ------- ARPA: jordan@berkeley.ARPA UUCP: ..!ucbvax!jordan