50mm f/1.8 AIS pancake hot spot/flare

[ntd]

<p>Hello everybody,</p>

<p>I have two copies of the 50mm f/1.8 ais, the pancake version that was available only in japan and which focuses down to 0.45m.</p>

<p>I noticed that the combination of <em><strong>uniform bright light</strong></em> (clouds, bright skies etc) and a <em><strong>small aperture</strong></em> (f/16, f/22) produces a weird <em><strong>bright area/hot spot</strong></em> that is visible in the viewfinder when enabling dof preview. It is more easily visible on cameras with matte focusing screens like the F3 or FE2.<br /> <br />Both copies of the lens show this behavior, and none of my other lenses show such hot spots in similar situations. I have also seen other people mentioning here in photo.net that this particular pancake version is the only 50mm ais exhibiting such behavior. However, the comments seem a bit confusing and it is not always clear which 50 mills have this issue.</p>

<p>I would really appreciate if anyone could confirm this, and also comment if the long barrel versions of the 50mm f/1.8 ais exhibit such flare/hot spots.</p>

<p> </p>

[Brad Cloven]

<p>I have tested all of the following on my back porch on the same camera (FA), roll (Fuji Provia 100)and a tripod at f/4:</p>

<p>2.0 AI<br /> 1.8 AIs long nose (2 copies)<br /> 1.8 AIs short nose (2 copies)<br /> 1.8 Series E <br /> 1.4 AIs<br /> 1.4 AF (not-D)</p>

<p>Some were tested with a lens hood, some without. The uniform conclusion I had was:</p>

<p>The further the glass was recessed from the front, the better the contrast, clarity and sharpness. Limiting incidental light striking the front of the glass was the unifying factor in quality. The worst was the Series E followed by the 1.4s, all of which have glass right out front.</p>

<p>2.0 AI was best, with it's normally well-recessed front element, though the color rendition was noticeably cooler than all the other lenses. 1.8 Long nose with lens hood was second-best. Third best was long nose without lens hood. Fourth and fifth were the 1.8 short nose. The 1.4s were poor, and the un-shrouded Series E is essentially un-shootable under controlled conditions or in the field to my eyes (I sold it immediately).</p>

<p>Take a close look at Ken Rockwell's review of 50mm Nikon glass. Think about how recessed the glass is from the front of the nose on each lens. His results are exactly like mine: The best lens is the one with the most recessed front glass (55mm Micro), and proceed to the worst with the glass way out front collecting stray light (1.2s, IIRC). He doesn't attribute that quality to the recession of the front glass. But I believe his results conform to that theory anyway.</p>

<p>I'd be happy to be proved wrong. But all my observations, reading and experience tell me: GET A LENS HOOD and never take it off. And if you have a choice among lenses that are roughly the same, opt for the one with more recessed front glass.</p>

<p>Separately, you may wish to study up on "Diffraction", a bad optical thing that occurs with small apertures. I try hard to avoid f/16 or more. I crank up my shutter speed as necessary to keep my F-stop around f/8.</p>

[ntd]

<p>Hi Brad,</p>

<p>thank you for your comment. In general i avoid small apertures, i just found this behavior strange.</p>

<p>I would like to clarify what i mean by hot spot. I do not mean overall loss of contrast.</p>

<p>For <em><strong>both copies</strong></em> of the specific pancake lens and small apertures, there is a <em><strong>hot spot</strong></em> that is about <em><strong>1.5x-2x</strong></em> the brightness of the rest of the frame. Its size is similar to the central <em><strong>12mm circle</strong></em> on my F3. It shows up even with a lens hood on.</p>

<p>I also tested the following: 50mm f/1.2, 50mm f/1.8g, 75-150mm series e and for small apertures and bright uniform subjects, the image in<em><strong> the viewfinder dims uniformly</strong></em> as i push the dof preview lever down to f/16 or f/22. With the aforementioned pancake, u can clearly see the fat hot spot.</p>

<p>What i see closely resembles the following description from an old thread (http://www.photo.net/nikon-camera-forum/00Fyur)</p>

<p>"There was a change in the optical formula at some point, and I remember that you can tell by comparing the radius of the rear element by looking at reflections. One particular version will produce a small circular bright spot in the middle of the frame when shooting bright scenes at small apertures. The other ones don't do this. Unfortunately, I don't remember which one suffers from this, though I know I own one! Avoid that one if you shoot bright outdoor scenes at small apertures."</p>

<p>Can you comment if you see something similar for the short/long nose versions? You don't need to burn film, it should be clearly visible in the viewfinder (at least with old matte focusing screens).</p>

<p> </p>

[jose_angel]

<p>Out of curiosity, I have checked the images I have taken with my "medium nose" cheap 50/1.8E chrome.<br>

I don`t use to shoot @ f22 quite often, and rarely with bright backgrounds, but neither of my images (quite a few family pics) show a noticeable hot spot. I know what you mean, this topic has been adressed here many times.<br>

Maybe the spot is there but the subject or background minimizes it; the only issue I found in my lens is a somewhat softer, less crispy rendition if compared with other lenses.</p><div></div>

[jose_angel]

<p>I also have shots @ f22; if there is a spot, it`s very difficult to see (coloured or busy background). At least on this ones it can be guessed.<br>

I`ll check tomorrow the lenses on the F3 as you mention. Right now it`s night time here.</p><div></div>

[ntd]

<p>Jose, it should be easier to see if the sky is <em><strong>full</strong> </em>of bright clouds (or anything filling the frame uniformly and brightly). Stopping down at f/16 or f/22 the image will dim in the viewfinder but not uniformly. There would be a pronounced, fat, hot spot around the center area and you should be able to see it easily if it is there.</p>

<p>I remember seeing some long/short nosed 50s f/1.8 on ebay and remember noticing that the rear element looked bigger than usual. Maybe these ones do not have this issue. It would be interesting to verify which one do and which ones don't.</p>

[kari_oinonen]

<p>What you see in the viewfinder may not be what you get in to the film or sensor. If the brighter area is actually captured, then I'd be a bit worried. But only a bit as those F numbers like 16 or 22 are rarely used - by me.</p>

[jose_angel]

<p>Just for fun I took my "E" lens today to check for that spot... it was a bright day, and shot dozens of images from all angles to all kind of bright things. I think this lens doesn`t show the "spot" flaw.<br /> I always thought it is the very same optical formula but on a different barrel design of the previous pankake Japan version, don`t know about the rear element diameter thing; right now I have two f1.8s, more than two decades between their designs, and both have the very same rear element diameter.<br /> The only pics I had with ghosting&flare were taken almost in front of the sun; the one below show not a spot but a softened ghosting line after being the lens closed to f22. Obviously, a sun shade or a more recessed front element would have helped to avoid this issue (I don`t use to force my lenses this way). And I don`t think the "best" 50s are simply the more recessed, this is only one part of the lens design.<br /> The doubt I have now is about the performance of the "E" compared to the AFD; I consider the later one of the sharpest Nikkors I have used, and the "E" a quite usable lens but always a bit softer (I like that softness, BTW). Are they really the same optical formula? Never tested them side by side.</p><div></div>

[ntd]

<p>btw, i would have already contributed samples but i do not have a dslr around :)</p>

[ntd]

<p>A few months back when i checked it on a d40 i think i saw it but i didn't pay much attention. I got more startled when i saw it in the viewfinder even in the second copy of the lens that i acquires recently :)</p>

<p>Regarding the AF-D version, back when i had one and tested it against the series e they looked identical. However, i just pixel peeped photos and didn't do very formal tests. Sharpness, softness and colors wide open looked the same.</p>

<p>Regarding the pancakes, there are 3 versions. The series e version and the usual ais one seem to have the same optical formula, coatings (purplish...) and both focus down to 0.6m. I have a series e back in my hometown, i will try to test it again and contribute my observations, but it might take a while until i do it.</p>

<p>The japanese pancake version focuses down to 0.45m. I think the optical formula is the same, but it has different coatings (greenish...). It also has a rubber focus ring and is the sharpest and most contrasty of all when shot wide open. I could observe the differences <em><strong>clearly</strong> </em>just by looking at images, no formal tests needed. There was also an informal test on a japanese website that demonstrated this. On a d40 the colors were also a lot warmer, but i did the test years ago and i am not sure if the camera was doing any weird white balance compensations.</p>

<p>In the end it is my understanding that the sharpest and most contrasty 50mm f/1.8 are the early short/long nosed ais and the japanese pancake (minus the small apertures with the weird hot spot). I think these also share the same greenish multicoating.</p>

[SCL]

<p>Dimitris - I was initially puzzled by your description of the phenomenon you observed, but then remembered something similar in my past. It happened with a particular focusing screen designed to be extra bright for telephoto lenses...looked normal at wide apertures, but the central area was bright and the rest of it went dark as very small apertures. I replaced the screen with one which was cut differently and the problem disappeared. BTW, the observed effect had no bearing on the actual exposure, it was merely the viewing screen. Hope this is helpful to you.</p>