Distance from the subject

[hirohhhh]

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Can someone explain the science behind this situation:

I was shooting some bugs with my Fuji x100f 23mm lens, and the closest I can get to the subject in focus is around 20cm roughly. Then I picked up my SL2 with 24-90mm lens, and when it's on 24mm focal length, I have to be much further away to get the subject in the focus - I'd say at least double then Fuji. But then the subject is smaller. I know I can get further and zoom, but I wanted this wide look, and I'm wondering why is this, since the focal lengths on both lenses are pretty much equal?

Edited October 30, 2020 by hirohhhh

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[agencal]

Most of the lenses at the same focal lenght have different minimum focusing distances.Nothing strange.You can buy a helicoid macro adapter for M lenses to use on SL and focus wide angles closer to subject.

[Jeff S]

At 24mm, the SL zoom focuses to 30 cm.  
 

Jeff

[hirohhhh]

7 hours ago, Jeff S said:

At 24mm, the SL zoom focuses to 30 cm.  
 

Jeff

Is there a chart somewhere, for different focal lengths and different lenses?

[pop]

vor 6 Stunden schrieb hirohhhh:

Is there a chart somewhere, for different focal lengths and different lenses?

You have to consult the technical data sheet for every single lens you want to use. It's different for each lens.

The 'theory' behind this all is simple. When you focus at infinity (i.e. the moon or so), the distance between the lens and the sensor is the smallest. It's exactly the focal length of the lens. That's how the focal lens is defined and measured. In order to focus on anything closer than the moon, you have to move your lens forward, away from the sensor. The closer you want to come to your subject, the longer the distance between lens and sensor. There comes the moment when the length of the lens barrel is reached. It can not move forward any further . This defines the closest distance you can reach with that lens.

With old-style prime lenses, you can see quite easily how the lens moves forward and backward. With zoom lenses and some modern designs for prime lenses, it's not visible very well because the movement of the lenses takes place in the interior of the lens.

[Stuart Richardson]

Typically, lenses that are designed to focus very close are called macro lenses. It is understandable to want a wide angle perspective, but the reason why few wider lenses are true macro lenses is twofold.

1. Perspective distortion can become an issue, such that the object is not represented naturally, but with distortion (closer parts of the object appear proportionally larger).

2. Wide angle macro lenses often require the front of the lens to be extremely close to the subject matter in order to achieve focus. This is problematic for several reasons. With living objects like insects or animals, it is often close enough to disturb the animal or frighten it away. With any subject, the lens may be so close to the object that the lens and camera cast a shadow on the object or make it difficult to use flash.

Those are some of the main reasons why you do not see too many wider macro lenses.

As to why all lenses do not focus to the same distance, it is just a function of the lens design. As you focus closer, the lens elements have to get further away from the sensor. Any lens can focus to 1 to 1 or greater, but you need progressively long and longer lens barrels. Lets say you have a 23mm lens. The 23mm means that in a symmetrical lens design, you need to have the lens 23mm away from the sensor to focus to infinity. To focus to 1 to 1 (life size...so the object is the same size on the sensor as it is in real life), you need to extend the lens to 46mm, twice that distance. So you can see that lens size grows pretty quickly as the focus extends.

Another issue is that most lenses are not equally good at all distances. Generally a lens designer has to make a choice as to where the lens is best. For most standard lenses they might choose infinity or 4 or 5 meters depending in their needs. With a macro lens, they will try to design the lens so that the close up performance is better.

In your own X100F, the 23mm is rather soft in close focus because they did not anticipate that most photographers would use that kind of camera for that kind of photography. Nevertheless, one of the biggest improvements they made in the X100V is to improve the close up performance of the standard lens. 

[jaapv]

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12 minutes ago, Stuart Richardson said:

1. Perspective distortion can become an issue, such that the object is not represented naturally, but with distortion (closer parts of the object appear proportionally larger).

That depends on the subject. For instance photographing scale models (like model railways ) requires a wide-angle macro lens  to maintain a natural perspective.

[Mute-on]

The focal lengths of both lenses are not at all equal. The 23mm Fuji is on an APS-C sensor, which gives it an equivalent full frame focal length of approximately 35mm. 

Since the SL2 is a full frame sensor, you are comparing the SL2 at 24mm with 35mm equivalent on the Fuji. It is no surprise that the image in the SL2 appears smaller, particularly if both lenses have the same minimum focus distance. 

If you zoom the SL2 to 35mm you will be comparing like with like. Then you can measure the actual minimum focus distances of each combination. As @Jeff S said, on the Leica this should be 30cm  

Enjoy experimenting! 

[Jeff S]

2 hours ago, Mute-on said:

If you zoom the SL2 to 35mm you will be comparing like with like. Then you can measure the actual minimum focus distances of each combination. As @Jeff S said, on the Leica this should be 30cm  

 

The MFD of the SL 24-90 at 35mm will be higher; it’s 30cm at 24mm, but increases to 45cm at the 90mm position.

Jeff