Friday 5 July 2019

focal length - 70-200mm lens or 18-200mm lens for small studio like 25 feet?



I am new to fashion photography. I have Canon 700d (cropped body) with 50mm 1.8 lens. I have few soft boxes and other studio equipment. I want to buy a new lens. From a canon training workshop guy recommended 85mm prime lens or 70 x 200mm lens (considering full frame body). I don’t have a large studio so larger than 65mm can’t work in the studio. Can I buy 18-200mm lens instead of 70-200mm?


Normally i shoot in the studio but i can also shoot outside the studio (open location).


Can you also suggest me focal length range which is suitable for me?



Answer



Any zoom lens with a 7.5X or 10X or greater ratio between the minimum and maximum focal length is going to compromise optical quality in several areas to get to that focal length flexibility. These include overall sharpness, geometric distortion, vignetting, sharpness at certain focal lengths, narrower maximum apertures, etc. While it is true that many of these can be "corrected" in post, doing so comes at a price. This is especially impactful when such correction is applied to an image taken with a lens that has less than stellar overall sharpness to begin with and fairly narrow maximum apertures.


There are affordable prime lenses or zoom lenses with a much smaller ratio between the widest and longest focal lengths that will give much better optical image quality than an "all-in-one" zoom lens. Even a set of 18-55mm and 55-200mm or 55-250mm kit lenses will give better quality at most focal lengths than an 18-200mm or 18-300mm all-in-one.



Lenses for APS-C only cameras such as the Canon EF 17-55mm f/2.8 IS or The Tamron SP 17-50mm f/2.8 XR Di II are very affordable for the image quality they give. So are prime lenses such as the Nikon 35mm f/1.8G AF-S DX (if you're a Nikon shooter), the Canon EF 40mm f/2.8 STM. The EF 50mm f/1.8 STM is also a significant improvement over the EF 50mm f/1.8 II and shouldn't be overlooked. The EF 85mm f/1.8 is indeed a very good lens for its price as well, but you do need room to use it properly.


In general, lenses within the normal focal length range are the most affordable while also having the potential to produce very good image quality. For the 35mm sized full frame cameras this is around 45mm. The diagonal of a 36x24mm film frame or sensor is roughly 43mm. The registration distance (the distance from the image plane to the lens flange) of the Canon EOS system is 44mm. In the EOS system anything from about 24-28mm up to about 65-70mm is considered normal. Below that is considered wide-angle while past that is considered telephoto territory. Although the sensor diagonal of Canon EOS APS-C cameras is only about 27mm, the registration distance is still 44mm and many of the lower priced lenses designed for FF cameras are also very good on the APS-C cameras.


You have to weigh all of these factors and decide which is more important to you. It basically comes down to the flexibility and convenience of an all-in-one zoom lens versus the better image quality that can be had fairly affordably with a prime lens or limited ratio zoom lens. If you want near-prime optical quality in a zoom lens you need to look at zoom lenses that only have about a 3:1 ratio between the longest and widest focal lengths (e.g. 24-70mm or 70-200mm). You also need to be willing to pay a lot more for them.


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