# Mirrorless focal length question



## Dhalevi

Can anyone explain me how to choose a mirrorless lens?
How does the mm (like 18-55) works?
If regular dslr uses 18-200 mm what does it mean Ib mirrorless cameras?


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## jaomul

Focal length is done the same on dslr and mirrorless. It's based on full frame or 35mm lens. You then apply crop factor. 

18-55 mm lens on apsc dslr gives field of view of approximately 27-82mm on Nikon, or 28-85 approx on Canon.

If you use a mirror less apsc 18-55 is same, if you use m43, crop factors differ so it's approx 14-42 lens , Fuji or Sony is 18-55 mm


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## Dhalevi

Can you explain it again please? 
Lets say I'm buying 18-55 lens. 
What do I need to look at in the camera ( sensor Size/...) and what calculation do I need to do?  
Thanks!


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## astroNikon

You have to first understand what size of sensor you are buying in the camera.

Mirrorless comes in all sizes from a FullFrame 35mm sensor to small sensors.

The size of the sensor determines the "crop"
35mm FullFrame sensor = 1 to 1
APS-C sensor = 1.5x (or 1.6x) to 1 
other smaller sizes increase that amount ==> https://lensvid.com/wp-content/uploads/2014/01/Sensors-size-01-01.jpg
as below - crop factor is the 4th row.






You then take that crop factor, such as 1.5x for APS-C and multiple it to the lens focal length. 
So a 18-55 on a APS-C sensor would
18 x 1.5  - 55 x 1.5  = 27 - 82.5 in perceived field of view


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## astroNikon

So just looking at SONY mirrorless cameras ONLY
==> DSLR-like Cameras | Full Frame Mirrorless Cameras | Sony US

the first & second row is all FF sensors. Thus a 1x crop factor.  18-55 would be 18-55

the 3rd, 4th rows are APS-C and thus are 1.5 crop factor.  18-55 would be 27-82.5

A Canon EOS M10 is supposedly  a APS-C sensor

PowerShot G9x is a 1.0 inch sensor which is a 2.7x crop factor,  thus a 18-55 would be 49 - 149

Thus you have to first determine the sensor size before you figure out the crop factor.


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## Dhalevi

Thank you very very very much!


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## Bebulamar

The crop factor made the assumption that people are familiar to 35mm camera. They made the assumption that people would know what it looks like in the viewfinder for a certain focal length lens when mounted on a 35mm camera. For example it makes the assumption that you know what the view is when you have a 50mm lens on the 35mm camera. 
For people who are not familiar with the 35mm camera and in fact nowaday many people never used a 35mm camera then it may be easier to describe by angle of view / focal length.


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## petrochemist

astroNikon has pretty much covered it. It's exactly the same for mirrorless than for DSLRs except for the sizes of the sensors. 
I don't think there are currently any mirrorless cameras with sensors bigger than full frame, or any DSLRs with sensors smaller than 4/3. The most common sizes are covered by both alternatives.


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## beagle100

petrochemist said:


> It's exactly the same for mirrorless than for DSLRs except for the sizes of the sensors.
> I don't think there are currently any mirrorless cameras with sensors bigger than full frame, or any DSLRs with sensors smaller than 4/3. The most common sizes are covered by both alternatives.



true,  I don't think there are any medium format mirrorless models (yet)
www.flickr.com/photos/mmirrorless


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## Ysarex

beagle100 said:


> petrochemist said:
> 
> 
> 
> It's exactly the same for mirrorless than for DSLRs except for the sizes of the sensors.
> I don't think there are currently any mirrorless cameras with sensors bigger than full frame, or any DSLRs with sensors smaller than 4/3. The most common sizes are covered by both alternatives.
> 
> 
> 
> 
> true,  I don't think there are any medium format mirrorless models (yet)
> www.flickr.com/photos/mmirrorless
Click to expand...


Sure there are -- you just got to pay to play with the big boys:






That's a Phase One A series mirrorless medium format digital (film too) that uses an Alpa body.

Joe


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## astroNikon

It's kinda funny. My P7800 is a full DSLR featured pocket camera with no mirror box.  It even has CLS (which the D3x00's don't) and a bright Digital ViewFinder, but isn't considered mirrorless as it does not have an interchangeable lens.

And isn't the Nikon V1/J1 things have a sensor smaller than 4/3rds  at 1" (13.2 x 8.8mm) and an interchangeable lens ?


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## beagle100

Ysarex said:


> beagle100 said:
> 
> 
> 
> 
> 
> petrochemist said:
> 
> 
> 
> It's exactly the same for mirrorless than for DSLRs except for the sizes of the sensors.
> I don't think there are currently any mirrorless cameras with sensors bigger than full frame, or any DSLRs with sensors smaller than 4/3. The most common sizes are covered by both alternatives.
> 
> 
> 
> 
> true,  I don't think there are any medium format mirrorless models (yet)
> www.flickr.com/photos/mmirrorless
> 
> Click to expand...
> 
> 
> Sure there are -- you just got to pay to play with the big boys:
> 
> 
> 
> That's a Phase One A series mirrorless medium format digital (film too) that uses an Alpa body.
> 
> Joe
Click to expand...


I stand corrected !

www.flickr.com/photos/mmirrorless/


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## Gary A.

My Fuji X100S has a fixed, non-interchangeable lens and it's considered mirrorless.


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