#lens+

[chancctv]

How do Aberrations Manifest Differently At Different Focal Lengths?

Aberration refers to the deviation between the actual image formed by an optical system and the ideal image; it is an unavoidable phenomenon in optical system design.

Lenses with different focal lengths exhibit significant differences in the types and manifestations of aberrations due to variations in their angle of view, lens curvature requirements, and physical structure.

The following are the specific manifestations of several common types of aberrations as they vary with focal length:

1.Distortion

The relationship between distortion and changes in focal length is direct and obvious. At short focal lengths, lenses are prone to barrel distortion, with the degree of distortion increasing as the focal length decreases; at long focal lengths, lenses may exhibit pincushion distortion, though the magnitude is generally minor; and at focal lengths of 85mm or greater, distortion becomes virtually negligible.

2.Spherical aberration

Spherical aberration is inversely proportional to the cube of the focal length; in other words, the shorter the focal length, the more pronounced the aberration. Therefore, short focal length lenses with small focal lengths are more affected by spherical aberration, which mainly manifests as a significant difference between the focal points of the center and the edges, forming obvious blurred circular spots.

This effect is even more severe under large aperture conditions. While spherical aberration decreases relatively as the focal length increases, issues may still persist when using large apertures.

Aberrations vary with focal length

3.Coma aberration

Coma is a function of the field of view, which is inversely proportional to the focal length: the shorter the focal length, the wider the field of view.

Therefore, the large field of view of short focal length lenses results in a large incident angle of off-axis rays, leading to significant coma, which manifests as a comet-like tail in the image of a point light source; while long focal length lenses have a small field of view and relatively small coma.

4.Astigmatism

Astigmatism is a function of the field of view and typically occurs during wide-angle shooting. In wide angle lenses with short focal lengths, light rays passing far from the optical axis traverse asymmetric surfaces; this can result in differing focal lengths for the meridional and sagittal planes, causing the image to appear blurred in one direction while remaining relatively sharp in the other.

In contrast, telephoto lenses are less affected by astigmatism because the light rays within the field of view travel closer to the optical axis.

5.Field curvature

Field curvature refers to the tendency of the image plane to curve naturally, a phenomenon particularly pronounced in short focal length lenses. Wide angle lenses have a large angle of incidence of light at the edge of the field of view, and the optimal focal plane is obviously curved, which can cause the center and the edge of the image to not be in sharp focus at the same time.

Manifestations of various types of aberrations

6.Chromatic aberration

Chromatic aberration primarily manifests as light of different wavelengths focusing at different points, a phenomenon with a complex relationship to focal length. Differences in the refractive index for various wavelengths cause the focal points of different colors to separate (longitudinal chromatic aberration) or result in varying magnification levels (lateral chromatic aberration).

Short focal length lenses have a shorter optical path and exhibit less chromatic aberration, but due to their wide angle of view, they are prone to displaying purple or green fringes at the edges.

Telephoto lenses have a long optical path, resulting in more noticeable chromatic aberration. This manifests as purple or green outlines around the edges of objects in focus, and this chromatic aberration is evenly distributed across the entire image. The purple fringing is particularly severe when shooting high-contrast objects.

Furthermore, the effect of aperture changes on aberration control varies at different focal lengths.

For example, stopping down the aperture of a wide-angle lens can improve astigmatism and chromatic aberration at the edges, but the improvement in distortion is negligible; stopping down the aperture of a telephoto lens can improve axial chromatic aberration and spherical aberration, but usually requires stopping down 1-2 stops to achieve optimal resolution and eliminate spherical aberration.

[dinnickhowellslikes]

[photographer-jefkoel]

Lens.

[eksovichea-tito-hak]

Sigma 50mm f1.4 EX HSM EF lens

https://ebay.io/m/ikJXdK

I'm sort of in two minds about selling this lens, as it seems I was fortunate enough to have an issue/reproduction of it that doesn't have any of the issues that plagued many of these lenses that were originally sold. It was loathed by early adaptors of it, as it was renowned for having serious issues with slightly off, miss-focus ruining people's pictures, as people's canon DSLR devices would give focus confirmation, for things to look fine in the view finder, but for it to be slightly off when reviewing the images afterwards.

I was unfortunately one of those people who had managed to acquire a refurbished issue of this lens with the unfixable focus issue/problem back then, at under half price, but I just put up with it, to still be able to get usable results, where I used the slightly janky move of leaning in, and leaning out slightly across multiple frames, which I continued to use for many years, until it unexpectedly got stolen. Many years later, I had re-acquired the lens for even less, knowing full well of it's serious shortfalls, and its technical inadequacies, in part having developed my own way of using the lens over the many years I had it prior, and in part for it producing slightly more interesting images than I would take using the solidly reliable Canon 50mm f1.4 USM EF on canon DSLR bodies, purely because I'd gotten so used to using the slightly awkward Sigma 50mm f1.4 EX HSM EF, whilst knowing how to get round its focusing issues to some extent. It was just unexpected, and very fortunate that the second refurbed copy of it that I'd managed to get my hands on last year, didn't have the focusing issues at all!

It seems I now have one of the rare examples of this lens here that didn't have any such issues when used with a Canon DSLR. Even then, it's still not perfect when used on a Canon DSLR, for being a third party lens that isn't granted the same levels of mechanical AF reliability as Canon's own 50mm F1.4 USM on Canon's DSLR devices, and the fact that it has more obvious chromatic aberration under certain circumstances (which can easily be fixed in an an instant with DX0 optics/photo labs, ACR, Affinity Photo 2, or the now completely free Canva Affinity anyway).

Geometric optical distortion on this lens is extremely low, less than 1% at 0.4 of a percent on a full frame sensor, and apparently 0.69% on an x1.6 APS-C sensor.

However, it was not until I had the chance to use it with a Sony mirrorless A7R II via the Sigma MC-11 EF to FE adaptor did it suddenly feel like I was using a completely different lens, as AF was even faster, and more accurate than it ever had been on a Canon DSLR, for it to produce tac sharp images every time when used in AF-C with expanded Flexi spot lock on AF mode. Devices such as the Sony A9 (and most likely any device from the A7 iii and onwards) set to AF-C expanded Flexi spot lock on AF mode literally turns this lens into a fast focusing tac sharp lens that's completely unrecognisable when compared to how it is on a Canon DSLR (whether the be 5D, 6D, or a crop sensor device of any iteration). However, it does make me curious as to how it would handle as an adapted lens on something like a Canon R5, or R6. I didn't include devices such as the A7R II, because despite being as capable as it is, the use of the same MC-11 adaptor limits it to a central cluster of AF points, with no option made available to use lock on tracking modes at all, unfortunately, although it is able to immediately acquire tac sharp focus with the central focus point cluster, at which point your only option is to use old-skool focus re-compose. On the other hand, the Metabones IV adaptor does allow for it, and does assist towards producing tac sharp images too even when shooting wide open at f1.4, its just that it does it far more assertively, with far less focus pulsing on the AF algorithms, and the processors of the A7 iii generations of mirroless devices, and onwards.

The lens itself is very capable of producing stunning images even today, where a quick Google search of 'image sample taken with the Sigma 50mm F1 4 EX HSM EF lens' will turn out a whole slew of stunning examples/aesthetic image samples.

However, I recently finally managed to acquire a used example of a Sigma 50mm f1.4 ART HSM EF to replace it, which on the surface gave me less reason to keep the EX version. The problem is, that the EX HSM version of the lens still has its advantages in other situations where a more compact, and lighter 50mm f1.4 lens might be more suitable for a given photographic task, especially since I now had one of the rare examples of it that didn't suffer from the same issues that were widely reported, and complained about by many 11 to 12 years ago.

Again, I bought these lenses myself, and I haven't been given these lenses by Sigma, nor have they paid me, unfortunately. Back then, they were vastly more affordable than the Canon L versions, and still are today even as used refurbed examples. These opinions of these sigma lenses are purely my own. If you're interested, you can find more details at the eBay link for it.

https://ebay.io/m/ikJXdK

[eksovichea-tito-hak]

Tamron SP 70-200mm f2.8 Di VC USD (A009) EF lens

https://ebay.io/m/EEwmH2

Still a great lens even today from an optical standpoint in a made for high resolution digital sensors kind of way, whether it's being used on a Canon DSLR device or some description, or as an adapted lens on a Sony full frame mirrorless device, which it surprisingly functions very well as, for which I'd even go as far as saying that it can function even better as an adapted lens on a Sony mirroless device (from the A7 iii onwards) than it did on a Canon DSLR. Again, you can find out more at the eBay listing link if you're interested.

[chancctv]

Applications of Industrial Endoscope Lenses in The Electric Power Industry

In the electric power industry, industrial endoscopes are key tools for non-destructive testing. They enable visual inspection of confined, high-temperature, high-pressure, or radiation-exposed areas inside equipment without disassembling, shutting down, or only briefly stopping the machine, allowing for the intuitive discovery of potential faults.

Ⅰ.Key characteristics of industrial endoscope lenses

To withstand the harsh operating environments of the electric power industry, industrial endoscope lenses typically feature the following characteristics:

1.High-definition imaging

Industrial endoscope lenses are typically equipped with CMOS sensors that offer high resolution (such as 1080p or even 4K) and adapt to bright or low-light environments, enabling the clear capture of minute cracks or weld quality issues.

2.Flexible probe, easy to operate

Industrial endoscope lenses are typically designed as flexible tubular or foldable types to fit small-diameter pipes and narrow gaps. The front end of the lens can be bent in multiple directions (up, down, left, and right) and has 360° all-round guidance, enabling observation without blind spots and allowing observation of blind areas without repeatedly inserting and removing the probe.

3.Intelligent assistance

Most modern endoscopic systems now integrate AI algorithms, which can automatically identify corrosion spots or cracks in images, improving detection efficiency.

4.Strong environmental adaptability

Industrial endoscope lenses typically possess characteristics such as waterproofing, dustproofing, corrosion resistance, vibration resistance, and high temperature resistance, enabling them to adapt to high-temperature environments such as thermal power plants and avoid damage or image distortion caused by heat.

Industrial endoscope lenses exhibit strong environmental adaptability

Ⅱ.Application scenarios of industrial endoscope lenses in the electric power industry

The following are some typical application scenarios for industrial endoscope lenses in the electric power industry:

1.Power generation equipment testing

Industrial endoscope lenses are frequently used in power generation equipment inspections, particularly for large rotating machinery and high-temperature, high-pressure vessels.

For example, inspecting the blades, impellers, combustion chambers, and nozzles of steam turbines and gas turbines typically requires high-definition, wide-angle, or side-view lenses, and even 360° panoramic scanning capabilities, to detect problems such as blade cracks, corrosion, carbon buildup, foreign object damage, and coating peeling.

Inspecting the stator windings, rotor retaining rings, ventilation holes, and end structures of generators can reveal problems such as insulation aging, wear, loosening, foreign object residue, and overheating discoloration.

2.Testing of power transmission and transformation equipment

Industrial endoscope lenses are also frequently used to inspect power transmission and transformation equipment, particularly targeting enclosed or high-risk components within the power grid.

For example, inspecting the coil windings, core, tank interior, and bushing interior of a transformer can reveal problems such as damaged insulation paper, winding deformation, foreign objects, sludge deposits, and discharge traces; inspecting cable ducts and joints can reveal problems such as damaged cable sheaths, overheated and melted joints, collapsed ducts, water accumulation, and blockages by foreign objects.

Industrial endoscope lenses are commonly used for the inspection of power transmission and transformation equipment

3.Piping system maintenance

Industrial endoscopes can inspect steam pipes, cooling water pipes, fuel oil pipes, etc. for internal corrosion, scaling, and blockage, and can be used with professional analysis software to assess the health of the pipes.

In addition, during the installation phase of electrical equipment, it can help check the cleanliness and assembly quality of pipes and manifolds, avoiding malfunctions caused by impurities or misaligned parts.

4.Safety inspection of power equipment

Industrial endoscope lenses can also be used for safety inspections of power equipment and facilities. During on-site operations in the power sector, these lenses allow for the inspection of the internal condition of equipment and facilities, enabling the detection of potential hazards—such as electrical leakage or fire risks—so that timely measures can be taken to prevent accidents.

In summary, industrial endoscope lenses play a significant role in the electric power industry; they help enhance the safety and reliability of equipment operation, reduce the likelihood of malfunctions, and ensure the normal functioning of power systems.

[countlunagaron]