35mm focal lenghts to digital

Tim Sainsbury

Tim Sainsbury

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How does an M42-fit 24mm lens translate to digital focal lengths, say on a Canon 350D? Is it divided by 1.6?

(I understand digital to 35mm, you just times by the crop factor)
 
I never really understand the point of doing this?

A lens is what it is.
 
puddleduck said:
I never really understand the point of doing this?

A lens is what it is.
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I don't understand why people want to convert Digital Focal Lengths into 35mm lengths. But I want to do the opposite, which to me is slightly more important...........................................................................
 
A 24mm film lens on a 1.6x body would be a 38.4mm equivalent field of view, but it's still a 24mm lens...
 
Flash In The Pan said:
A 24mm film lens on a 1.6x body would be a 38.4mm equivalent field of view, but it's still a 24mm lens...
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I totally agree that a 24mm lens is still 24mm whether it is on a full-frame camera on a 1.6x crop camera. The image on the crop camera is simply equal to a portion of the full frame 36mm x 24mm image cropped to 22.5 x 15mm. See: http://www.the-digital-picture.com/Canon-Lenses/Field-of-view-crop-factor.aspx

HOWEVER: The perspective of an image is not dependent upon the focal length used to shoot that image; rather it is dependent upon the lens to subject distance.

As an example:

For head and shoulders portraits:

If I were using a 50mm lens to fill the 22.5 x 15mm frame of a 1.6x camera, I would stand approximately 8 feet (2.44 meters give or take) from my subject to fill the frame with the head and shoulders portrait.

However, if I were to fill the 36mm x 24mm frame of a full frame camera with the head and shoulders portrait, I would shoot from approximately 5 feet (1.52 meters give or take) from the subject to fill that frame with the head and shoulders portrait.

This difference in distance would change the perspective of the portrait. The portrait from 5 feet would be more exagerated (longer nose, etc.) than the portrait shot from 8 feet.

Sure, if I shot them both from 8 feet (2.4 meters) and cropped the 22.5 x 15mm image from the full frame - the perspective would be the same.

HOWEVER, I WOULD NOT DO THAT... I normally fill the frame with the image that I am shooting.

So in reality, on the 1.6x crop camera, a 50mm, in normal usage, provides the perspective of an 80mm lens on a full frame camera.

A photographer will most often shoot an image using a 1.6x camera from a farther distance than the photographer would if shooting with the same focal length lens on a full-frame camera. Thustly, the perspective changes....
 
Does this mean that to get the same perspective in a portrait (i.e. keep the nose length the same:D), I need a 31mm lens for my 400D?

Neil
 
ndwilson said:
Does this mean that to get the same perspective in a portrait (i.e. keep the nose length the same:D), I need a 31mm lens for my 400D?

Neil
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Same perspective as what?

If you shot a portrait using a 5D and a 50mm lens from a particular distance and you liked both the perspective and the composition, then using a 400D you would need a 31mm lens to shoot from the same position and achieve the same perspective and composition.

Does that answer your question? If not, you'll need to re-state it more precisely.
 
Thank you StewartR, that does answer my question. My next question is are 31mm (or thereabouts) lenses available for 1.6x cameras or are 'good' 50mm's all that are available?:)

Neil
 
ndwilson said:
Thank you StewartR, that does answer my question. My next question is are 31mm (or thereabouts) lenses available for 1.6x cameras or are 'good' 50mm's all that are available?:)

Neil
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Why not just stand 8ft away? :lol:
 
ndwilson said:
Thank you StewartR, that does answer my question. My next question is are 31mm (or thereabouts) lenses available for 1.6x cameras or are 'good' 50mm's all that are available?:)

Neil
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Prime lenses tend to come in 20mm, 24mm and 28mm at f/2.8 (Canon, Nikon and Sigma anyway) - the 50mm and 85mm primes are generally found at f/1.8 and f/1.4
 
Alasdair,
thanks, I know of the f2.8 sub-50mm lenses, but I'm looking for a large aperture lens for portrait work and was thinking of a 50mm f1.2 (expensive), f1.4 (most likely) or maybe even f1.8; f2.8 seems a bit small:thinking:.
I guess I could stand further away, but I'm typically limited for space, so I'd prefer to stand closer;) while still getting a true representation of their features:gag:
All comments appreciated,

Neil
 
The further away you are from the subject the less 'distortion' you will get, hence 90 & 105mm being popular focal lengths for portrait. 50mm is a resonable compromise but at f/1.4 you'll struggle to get everything in focus, unless it's pug dog.
 
sprog said:
The further away you are from the subject the less 'distortion' you will get, hence 90 & 105mm being popular focal lengths for portrait. 50mm is a resonable compromise but at f/1.4 you'll struggle to get everything in focus, unless it's pug dog.
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Well said that Tog
:thumbs:
 
Very useful reading all of this, I'm looking on eBay for an M42 - 4/3 adaptor so I can use the lenses from my ST605 on my E420. It's also all very confusing!
 
Tim Sainsbury said:
Indeed it is and no single explanation seems to be making it any clearer.. :thinking:
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What part of it is confusing? No matter whether it's a "digital" 50mm lens or a "film" 50mm one, it's a 50mm lens.

If however, you put either lens on a digital camera with, say a 1.6x crop factor it will give a field of view equivalent to what you would get from an 80mm lens (50mm x 1.6) on the film camera.

Simple really ;)
 
Indeed, and for the most part...
Canon = x1.6
Nikon = x1.5
and i thiiiiiiiiink Olympus is x2
 
Correct.

Oh, and Sony and Pentax are 1.5.

Then you have 35mm size sensors in 1Ds and 5D Canons, D3 and D700 Nikons, and the Sony A900.

Not forgetting the 1.3 crop sensor in the Canon 1D (NOT the s model)...

So yes, the same lens, on different bodies, will give you different FOV, perspective, DOF, etc, dependent on the sensor format.

Olympus seem to have the widest range of lens adaptors available. Check out Cirrus Gao on fleabuy, for reasonable prices, and decent quality.
 
Tim it is worth researching to make sure you will be able to use the lens you have in mind on your camera. Some of the M42 lenses have a rear element that extends back into the camera and can interfear with the mirror (bad thing). I came across a list on the web a while ago when I was picking up manual lenses but I don't have the list or the link anymore.

There are some bargains on Ebay if you are ok with manual focussing. The 55mm 1.8 I picked up for less than £20. No use for mocing subjects but for any stationary objects it takes great pictures.
 
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