optics – Aperture iris in front of lenses (in object space)

I am looking for such lenses as well.
In general putting the aperture at the front or outside is avoided because not good; best is to put the aperture more or less in the center of the objective. With the aperture in front you’ll have more aberrations and/or need bigger and more expensive design.
Only in two cases the front aperture design is used:

  1. if the lens is very small and simple, like, really just one group (see the Kodak vest camera and the Triplet), here you cannot put the aperture in the middle! Choose, in the front or in the back.
  2. Otherwise, you put the aperture in front only if you are absolutely forced to do that, typically for coupling with other optical systems.

Small & simple:
Mobile phone lenses; to make them so compact, the aperture is usually placed at the brim of the front lens. Not really outside, but on the brim.

Pinholes and many probe objectives, that need to peep from an hole; the hole is the natural aperture and the lens must be built to use all the light that goes through such hole; putting another aperture will cause vignetting. Nice example the SO spy lenses by Zeiss Jena:
Marco Cavina or see the catalog of Marshall Electronics.

Non-photographic lenses:

  • Laser scanning lenses, called F-theta Rogonar; the laser light is coming form the aperture position.
  • All eyepieces: the aperture is well outside, at the “exit pupil”, so I can place my eye with my iris in this place.

If you are curious about aberrations etc, the best short introduction I’ve found are those slides from Jena:
Gross Jena 2017; lecture 11/3, stop position.

lens – Does it actually matter considering DxOMark’s Perceived MPix Score for lenses?

Does this make the lens better than an L Lens?

It all depends on what way you mean when you use the word “better”:

  • Sharper at common apertures and focal lengths? At the center of the frame or over the entire field of view?
  • Less chromatic aberration at a particular focal length and aperture?
  • Less light falloff at a particular focal length and aperture?
  • Wider maximum aperture? (hint: that’s the biggest difference in the two lenses’ DxO Mark overall score)
  • Value for price?
  • Ruggedness and ability to withstand harsh environmental conditions?
  • Light and compact for hiking or long shooting session?
  • Guaranteed compatibility with future Canon camera bodies?
  • Autofocus accuracy? Autofocus speed? Autofocus frame-to-frame consistency?

As is often the case with comparisons between two zoom lenses, one might perform better at certain focal lengths and apertures and the other will perform better at other focal lengths and apertures. One might perform better in terms of chromatic aberration, the other may do better with regard to light falloff in the corners. One might give better image quality when carefully focused manually (as all tests at DxO Mark are conducted), the other may give better AF performance when tracking moving subjects.

There’s no simple way to define which lens is “better” than another. On order to decide which lens is “better” for a particular use case, the requirements of that use case must be considered and applied to the performance of each lens.

In the case of the two lenses in question used for sports/action in daylight conditions the superior AF performance of the Canon 70-200mm f/4 IS is probably a larger consideration than the slightly better optical performance (as measured by DxO Mark) of the Tamron SP 70-200mm f/2.8 Di VC. The comparison of the same two lenses at The-Digital-Picture is a much more mixed bag, with the Canon sharper in the corners across the focal length range and even in the center at 200mm and f/4 than the Tamron. The Tamron has a reputation for less than stellar AF performance when use on moving subjects.

On the other hand, for portraits and concerts the larger f/2.8 aperture of the Tamron is probably the largest differentiator between the two. Especially when used with an APS-C camera that limits the low light performance of the smaller sensor.

P.S. – Someone please explain to me how that is a 13 P-MPix vs. 9 P-MPix score at DxO Mark based on their own measurements?
enter image description here

The same comparison (200mm @ f/4) at The-Digital-Picture.

Please keep in mind that most online testing sites test a single copy of a particular lens model. Copy-to-copy variation between one example of a specific lens model and another example of the same model can, and often does, vary as much or more than differences between comparing a single copy of lens X and a single copy of lens Y when both lenses have similar focal lengths, maximum apertures, and build quality.

Roger Cicala, founder and chief lens guru at lensrentals.com, rarely publishes test results of lenses unless he has tested and averaged the results from a minimum of ten samples of a particular lens. But Roger tends to only measure MTF, or “sharpness”, at various points in the lens’ field of view. He doesn’t measure other things such as geometric distortion, peripheral light falloff, out-of-focus rendering (bokeh), etc. He’s published more than a few blog entries regarding copy-to-copy variation between “identical” lenses.

Measuring Lens Variance
Fun with Field of Focus II: Copy-to-Copy Variation and Lens Testing
Things You Didn’t Want to Know About Zoom Lenses

depth of field – DOF comparison between two lenses

Someone told me:

To compare the amount of DOF of two lenses I just would need to
calculate the size of the entrance pupil. The lens with the bigger
entrance pupil has less DOF thus creates nicer backgrounds.

(read my thoughts about the focus distance – which is totally neglected – below). I try to understand that. I think it’s false. Lets look at two lenses:

Lens A: 100mm F/2.0

Lens B: 200mm F/4.0

Both lenses have an entrance pupil of 50mm. So the statement above claims them to have the same amount of DOF. The question is: At what focus distances? When we compare both lenses at the same focus distance then lens B has a smaller DOF than lens A because focal length has an higher impact on DOF than the F-stop. But it also creates a complete different image of our subject.

To get the same subject magnification we need to adjust the focus distance of lens B by a factor of 2 (since lens B has twice as much focal length as lens A). At that point lens A has a smaller DOF than lens B. Actually the DOF of lens A at a given focus distance is half of the DOF of lens B from double of that focus distance.

So what (correct) statement can be made to compare the DOF of two lenses (with adjusted focus distances) based on the size of the entrance pupil?

equipment recommendation – What should I be careful about while buying used mirrorless camera and lenses?

I am interested in purchasing a new mirrorless camera. I am new to photography but am quite interested in pursuing it. I have used a super-zoom for a while on priority modes and occasionally on manual mode, so I have some basic understanding of the workings of a camera.

I am confused whether I should purchase a new camera and lens or a used one. While I think that I should get a used one for first few years while I learn and invest in (or save money for) good lenses in the meantime, I am worried that I don’t know what to look for while purchasing used cameras to avoid being cheated. Especially, when I am purchasing them online as opposed to in store. I have the same concern with the lenses. Since I didn’t find a nice guide for new buyers I hope that this question also motivates people to answer in a fashion that might be helpful for others in future.

Coming to some personal choices: my budget is about $1000 with body and lens but I am a little flexible. Right now, I have options for purchasing Fuji X-T2 (fairly used $500), X-T3 (claimed to be like new $980) and X-H1 (claimed to be new $870) all used on a website in Switzerland (I believe I can negotiate the prices). Since I plan to shoot landscapes I am giving importance to weather sealing and not considering X-T#0 series. I also have the option to purchase Fujinon 16-55mm 2.8 R LM WR (claimed to be like new for $880) or XF 18-55mm (fairly used for $400, sold along with X-T2 with a myriad of other lenses that I am not interested in).

I could just get a new X-T3 with XF 18-55mm for slightly more cost too but I am tempted by X-T2 as a beginner since it is considerably cheaper especially if I am able to negotiate the price further. Any help on what I should look for when going to have a look at the camera will be greatly appreciated.

Will Nikon "G" lenses work on D3x00 series cameras?

Will an AF-S Nikkor 50mm 1:1.8G work well with my with Nikon D3100?

lens – Will Nikon AF-S “G” lenses autofocus on D3xxx bodies?

When I checked the site of Nikon for D3300 camera, I found following description

Autofocus is available with AF-S and AF-I lenses; Autofocus is not
available with other type G and D lenses, AF lenses (IX NIKKOR and
lenses for the F3AF are not supported) and AI-P lenses; Non-CPU lenses
can be used in mode M but the camera exposure meter will not function
The electronic rangefinder can be used with lenses that have a maximum
aperture of f/5.6 or faster


I am confused with what it means. Does it mean that auto-focus is not supported for following version (for example)

  • Nikon 18-200mm F/3.5-5.6G IF-ED AF-S VR II DX

because it has “G” mentioned in aperture? I am confused because it says that it is auto focus.

I usually choose focal point to focus on subject while taking pictures but I use auto while shooting videos. As now I am planning to shoot more videos so do I have to worry about these properties?

Compatibility of lenses – Photography Stack Exchange

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nikon – How do I decide amongst several prime lenses for fast-moving sports?

It really depends on the sport that you’re shooting. Some sports let you get fairly close (e.g. hockey, curling, basketball); other sports require you to use long lenses at a distance (baseball, cricket, football/soccer, gridiron football).

Fast lenses are best because of the lighting conditions in some sports, especially indoor sports or games/matches played at night under stadium lighting. Modern DSLRs give you more room for error on the ISO side of things than was the case in the film days, but a fast aperture will still help you shoot isolate the subject against the background, and let you use faster shutter speeds with higher quality.

Knowing the sport well, and knowing where to anticipate action, will help you considerably.

It’s been awhile since I’ve shot curling or hockey, but when I did (as an amateur) I used a 35-135/3.5-4.5 (on 35mm film/full frame) and it was a pretty successful endeavour. On the other hand, with gridiron football I used much longer lenses. My 80-200/2.8 was my most useful lens (I lacked anything longer that was as fast) but I also got a lot of good use out of a modest 75-300/4.5-5.6. In fact, my best football shot was shot with this lens, at the nearer end of the range, as a running back ran toward me on the sideline. (Luckily he turned the corner. 🙂 )

Using what you have, and learning its limitations, will teach you more about what lens to add to your stable than any advice we have. Go experiment and try, see how things turn out, and figure out what limitations you’re running into – that will tell you what lens to get next.

lens design – Why there are so few lenses with small minimum focus distance?

The focal length of a lens is a calculation made when the lens is imaging an object at infinity. This is a distance as far “as the eye can see” symbol ∞. As we focus on objects nearer than infinity, we must lengthen the distance, lens to sensor (film). The now elongated distance is called “back focus”. The lens to sensor/film extension becomes large. As we focus to achieve “life-size”, often called “unity” or 1:1 magnification, the lens will be racked forward 1 complete focal length, and the distance object to sensor/film will be 4 times the focal length. What I am trying to tell you is, the amount of mechanical extension to reach magnification 1 (life-size), is one compete focal length.

So, to make a lens close focus and reach unity requires lots of room to rack the lens forward. This is actually not too difficult, but now for the rest of the story. The f/numbers we know and love, that are engraved on the lens, are calculated from the infinity focus position. As we close focus, the engraved position marks for the f/number settings become invalid. At magnification 1 (unity), the error is 2 f/stops. This is a problem because we tend to underexpose when we close focus.

This f/number error is called “bellows factor”. If the camera reads the exposure measuring thru-the-lens, bellows factor is not an issue. If the exposure is determined by an external light meter, it is a big problem. As rule of thumb — most camera makers (lens makers) stop the forward travel of the lens when the bellows factor error approaches 1/3 of an f/stop. The macro lens design is clever in that the lens array portion ahead of the iris diaphragm is a strong magnifier. As we focus close-up the magnification makes the diameter of the aperture opening appear larger. This magnification of the aperture allows more light to transverse the lens. This is how the macro design nullifies the bellows factor error.

Naturally it costs more to incorporate this design; so many lens makers stop the forward movement as the bellows factor approaches 1/3 f/stop.

optics – Why is there an air gap between lenses and digital sensors, as opposed to continuous glass-like higher refractive index?

Thinking about ultra-fast lenses (ƒ<1), it would seem useful to have a solid+liquid medium between lens and sensor. This wouldn’t have been very practical (presumably) at the time of film, but with a digital sensor I don’t think there’s much issue with coating it with transparent glass. Removable lenses would be somewhat cumbersome, but not hopelessly so with the right index-matching fluid (as common in high-NA microscopy). Of course lens designs would have to be altered but I’m curious as to why this is not a thing (that I know of, beside a few esoteric mentions here and there)?