21mm lens cropped to 90mm versus 90mm lens

[MEC]

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Hello - I own an M10R. What is the difference between cropping a 21mm image to 90mm versus just using a 90mm lens? Thanks. 

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[John McMaster]

Quality?

john

[pegelli]

Two main differences:

1. The cropped 21 mm image will have a larger DOF
2. The cropped 21 mm image will have less resolution

[MEC]

30 minutes ago, John McMaster said:

Quality?

john

21mm 1.4

90mm 2.0 

[MEC]

25 minutes ago, pegelli said:

Two main differences:

1. The cropped 21 mm image will have a larger DOF
2. The cropped 21 mm image will have less resolution

Thank you. 

[pegelli]

Sorry, forgot to mention, my DOF statement assumes you use the same f-stop on both lenses for the comparison.

 

[MEC]

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I figured. 

[John McMaster]

21 minutes ago, MEC said:

21mm 1.4

90mm 2.0 

I meant the crop factor for anything useful.  If it is only for web JPEGs then fine.....

john

[FrozenInTime]

1 hour ago, MEC said:

Hello - I own an M10R. What is the difference between cropping a 21mm image to 90mm versus just using a 90mm lens? Thanks. 

Seriously, no one who deserves to own a Leica M should have to ask that question !

On the other hand Leica's Q3 marketing team would say your are good to go ... crop away 🙂 

[MEC]

55 minutes ago, pegelli said:

Two main differences:

1. The cropped 21 mm image will have a larger DOF
2. The cropped 21 mm image will have less resolution

 

25 minutes ago, pegelli said:

Sorry, forgot to mention, my DOF statement assumes you use the same f-stop on both lenses for the comparison.

 

 

6 minutes ago, John McMaster said:

I meant the crop factor for anything useful.  If it is only for web JPEGs then fine.....

john

Likely JPEGS, maybe RAW, but I don’t do much in post. 

[UliWer]

I tried this - just for fun - with the 1:3.8/24mm Elmar and longer focal lengthes. Here you see the result from a 90mm Apo-Summicron and the cropped version from the Elmar:

If you think that the crop is acceptable besides the full frame from the 90mm lens you will have to take into account that the difference between 21 and 90mm is much larger (and the 21mm Summilux does not resolve as well as the 24mm Elmar, or the 21mm Super-Elmar). 

[Hans-Dieter Gülicher]

If the crop meets your requirements everything should be o.k. But how often do you need such crops really?

I myself have the 28 mm, 35 mm, 90 mm Summicron and the 135 mm APO-Telyt. But in most cases I use the 35 mm lens. Sometimes to takea crop  up to  about 90 mm and it`s no problem from my point of view. That means I think about selling the APO-Telyt and may be the 75 mm Summicron, too.

[MEC]

Thanks for the photo link and discussion! I’m trying to find a reason for using my 90mm but I just don’t love it. (But will use for the eclipse) The resolution drop off I expected, but I forgot to consider the reduced DOF, which kills me. My second favorite lens is an old 28mm 2.0 - much more compact, but not as special as the 21mm 1.4 which is worth the extra ounces.  Thanks again.