How to simply calculate CL vocal lengths on SL cameras?

[Robert E]

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Well, I'm not the OP but I've read this whole thread and I'm entirely confused. There must be a lot of incorrect thinking out there in the photography world as far as crop factor goes.

So, in the final analysis, if I put a TL 55-135mm lens on my SL2, it automatically senses it and goes to APS-c mode. But the FOV is still 55-135mm? Not 80-200mm? Correct?

[lct]

29 minutes ago, Robert E said:

[...] So, in the final analysis, if I put a TL 55-135mm lens on my SL2, it automatically senses it and goes to APS-c mode. But the FOV is still 55-135mm? Not 80-200mm? Correct?

In APS-C mode you must multiply by 1.5x so it gives 82-202mm equivalent FoV in your example. Think of your SL2 as a bulky CL when you use a TL lens on it. It is just another APS-C camera then. 

Edited April 1, 2021 by lct

[hillavoider]

this always gets made deliberately complicated 

 

just times it by 1.5 

 

[pop]

vor 3 Stunden schrieb hillavoider:

this always gets made deliberately complicated 

 

just times it by 1.5 

 

... or download the technical data sheet for the lens from Leica's web site, which carefully enumerates all the relevant figures.

[Robert E]

OK, here's the confusing part as I see it. The TL lens is marked as a 55-135mm FOV lens, correct? So that Leica lens is designated a 55-135mm. The lens is made for the TL-CL cameras which are of course APS-C sensor cameras. So an owner of a CL camera says I have a 55-135mm on my camera today,  With me so far?

So then what you are saying is you take that 55-135mm lens and now place it on a SL2 full frame sensor camera; which electronically senses it is an APS-C TL lens 55-135mm. Then the SL2 automatically goes into APS-C mode for that lens, but, BUT, suddenly the FOV changes to a 82-202 mm FOV lens?????

Sorry, but does that make sense to you guys?

[BernardC]

3 minutes ago, Robert E said:

Sorry, but does that make sense to you guys?

The problem is that people try to establish equivalences. It's probably an earnest attempt to simplify things, but in reality it confuses everybody.

The lens is a 55-135. That doesn't ever change, no matter what camera you attach it to.

APS-C is a smaller format than "full frame" (23.6mm wide vs. 35.8mm). With some rounding, APS-C is 2/3 as wide as full frame. That's where "crop factor" comes-in. People try to be helpful by telling you what lens would give approximately the same field of view on a bigger sensor, but they explain it in such a way that almost everybody thinks that the lens has physically morphed into a different lens. It hasn't, it's still a 55-135.

It's bad enough with just two formats, it's even worse when you throw "medium format(s)" and "large format(s)" into the mix. And then people confuse you further by helping with nuggets like this: "it's not 2/3, it's 1/1.5 !"

 

That's why I suggested that you think of each format as its own thing. APS-C is the cinema format that has been in use for over 100 years: 18 is very wide, 28-32 is normal, 50 and above is long. Same thing with 4x5 inch large format: 90 is very wide, 135-150 is normal, 210 and above is long. Don't waste your time converting between the formats. Use the time you save to look at your subject and consider what type of lens would suit it best.

[lct]

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27 minutes ago, Robert E said:

OK, here's the confusing part as I see it. The TL lens is marked as a 55-135mm FOV lens, correct? So that Leica lens is designated a 55-135mm. The lens is made for the TL-CL cameras which are of course APS-C sensor cameras. So an owner of a CL camera says I have a 55-135mm on my camera today,  With me so far?

So then what you are saying is you take that 55-135mm lens and now place it on a SL2 full frame sensor camera; which electronically senses it is an APS-C TL lens 55-135mm. Then the SL2 automatically goes into APS-C mode for that lens, but, BUT, suddenly the FOV changes to a 82-202 mm FOV lens?????

Sorry, but does that make sense to you guys?

55-135 is not the FoV per se but the focal length of the lens. On a FF camera it would have a 55-135 FoV if it could cover the whole frame. On an APS-C camera (or an FF one in APS-C mode) it has a 55-135 x 1.5 = 82-202mm FoV.

[RoySmith]

The TL 55-135mm lens on a APS-C size sensor produces the same field of view as an 82-202mm lens on a Full Frame sensor.

It does not matter if the sensor is the entire APS-C sensor in a CL, or the cropped sensor in a SL.

Refer to the Leica Spec Sheet:  “At 55 mm: approx. 28°, 24°, 16°, at 200 mm: approx. 12 °, 10°, 7°, corresponding to around approx. 80 - 200 mm focal length in 35 mm format.“

If you are using an APS-C size of sensor just multiply by 1.5 to get Full Frame equivalent field of view.

[Robert E]

I thought the 1.5x crop factor only applied when you put a full frame lens on an APS-C camera?

[Robert E]

The Leica Spec sheet says:

Quote

At 55 mm: approx. 28°, 24°, 16°, at 200 mm: approx. 12 °, 10°, 7°, corresponding to around approx. 80 - 200 mm focal length in 35 mm format

Which seems to indicate the T 55-135mm on a Leica CL is equivalent to a 80-200mm lens (not the 55-135) on a FF sensor camera. That is clear.

But, here comes the but, the original question if I understand it, is what happens when you put the T lens, whether its a 18-56 or 55-135mm, on a full frame sensor camera, (let's say one that does NOT go automatically into APS-C mode)  then what is the equivalent focal length?

[lct]

1 hour ago, Robert E said:

I thought the 1.5x crop factor only applied when you put a full frame lens on an APS-C camera?

The 1.5x crop factor applies when you put any lens on an APS-C camera. Reason why a so-called "full frame lens" like the M 18/3.8 has the same FoV as a so-called "crop lens" like the TL 18/2.8 when using both on APS-C cameras. 

[lct]

11 minutes ago, Robert E said:

what happens when you put the T lens, whether its a 18-56 or 55-135mm, on a full frame sensor camera, (let's say one that does NOT go automatically into APS-C mode)  then what is the equivalent focal length?

One cannot crop anything to a larger format so it will remain a 18-56 or a 55-135 lens with more or less strong vignetting on the FF camera.

[BernardC]

21 minutes ago, Robert E said:

what happens when you put the T lens, whether its a 18-56 or 55-135mm, on a full frame sensor camera, (let's say one that does NOT go automatically into APS-C mode) 

The lens does not cover full-frame, so you get a circular image, or a squared-off circular image. The sharp parts of that image (in the middle) will correspond to the APS-C image format.

[jaapv]

 

3 hours ago, Robert E said:

OK, here's the confusing part as I see it. The TL lens is marked as a 55-135mm FOV lens, correct? So that Leica lens is designated a 55-135mm. The lens is made for the TL-CL cameras which are of course APS-C sensor cameras. So an owner of a CL camera says I have a 55-135mm on my camera today,  With me so far?

So then what you are saying is you take that 55-135mm lens and now place it on a SL2 full frame sensor camera; which electronically senses it is an APS-C TL lens 55-135mm. Then the SL2 automatically goes into APS-C mode for that lens, but, BUT, suddenly the FOV changes to a 82-202 mm FOV lens?????

Sorry, but does that make sense to you guys?

No it doesn''t. At all.

A focal length is not a Field of View (which is valid at one particular distance anyway, you mean Angle of View)

[oldwino]

If I remember correctly, Leica printed the equivalent focal lengths on the barrel of the X-Vario lens. 
For us old guys, who grew up using 35mm film cameras, seeing “28-70” on the lens made a whole lot more sense than “18-47”. I know what the FOV of 28mm lens looks like, or a 50mm. When I put my 50mm Summar on my (digital) CL, it’s not a “50” anymore..

Edited April 1, 2021 by oldwino

[beewee]

14 minutes ago, oldwino said:

If I remember correctly, Leica printed the equivalent focal lengths on the barrel of the X-Vario lens. 

This is not applicable to any TL lenses.

[beewee]

1 hour ago, Robert E said:

the original question if I understand it, is what happens when you put the T lens, whether its a 18-56 or 55-135mm, on a full frame sensor camera, (let's say one that does NOT go automatically into APS-C mode)  then what is the equivalent focal length?

It’s still the same original focal length. The APS-C lens’ image circle is smaller so it’ll look like you have a ton of vignetting on the outer section of the image of a full frame sensor because the image circle of the lens does not cover the entire sensor area.

[vielhilftviel]

Funny how I said in the post that google just confused me more and now we have several different answers in here so wtf lmao

[beewee]

2 minutes ago, vielhilftviel said:

Funny how I said in the post that google just confused me more and now we have several different answers in here so wtf lmao

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Hallo,

Look here: Leica L-Mount

[Robert E]

 

2 hours ago, beewee said:

It’s still the same original focal length.

Bingo! That's the correct answer.