Velocity Reviews > Another question - How to convert medium format lens to equivalencyof a 50mm normal lens (35mm camera) in APS-C digital cameras

# Another question - How to convert medium format lens to equivalencyof a 50mm normal lens (35mm camera) in APS-C digital cameras

Woody
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Posts: n/a

 05-31-2009
"Woody" <(E-Mail Removed)> wrote in message
newsAzUl.192988\$(E-Mail Removed)2...
> "Rob Morley" <(E-Mail Removed)> wrote in message
> news:20090531180949.58a0297b@bluemoon...
>> On Sun, 31 May 2009 10:13:23 +0100
>> "Woody" <(E-Mail Removed)> wrote:
>>
>>> What needs explaining here is what at 'standard lens is - and
>>> that is simple.
>>>
>>> It is the lens which has a focal length equivalent to the
>>> longest
>>> measurement of the format in use, i.e. the diagonal. It this
>>> follows that a 'standard' lens for 35mm will, by Pythagorus,
>>> be
>>> about 42mm, and for 645 will be 75mm.

>> 44.4mm 70.6mm
>>
>> Just in case anyone thought Pythagoras was playing up.
>>
>>

>

Let's split the difference shall we? (36^2+24^2)^0.5 = 43.2.
(60^2+45^2)^0.5=75 as I said. (This using Windows Calculator.)

--
Woody

harrogate three at ntlworld dot com

Rob Morley
Guest
Posts: n/a

 05-31-2009
On Sun, 31 May 2009 19:04:40 +0100
"Woody" <(E-Mail Removed)> wrote:
>
> Let's split the difference shall we? (36^2+24^2)^0.5 = 43.2.

It seems I succumbed to one of the fundamental laws of Usenet.

> (60^2+45^2)^0.5=75 as I said. (This using Windows Calculator.)

The neg size of 645 is more like 56×41.5mm, because 120 film is based
on 2 1/4", not 60mm.
>
> Try your Pythagoras again maybe?
>

Next time I'll double check before posting. Or just try to abstain
from nitpicking.

Matt Ion
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Posts: n/a

 05-31-2009
Doug Jewell wrote:
> So 33mm (APS-C), 50mm (35mm)
> and 90mm (645) can be said to be "equivalent" because on their
> respective formats they all give basically the same image.

This is an excellent and succinct explanation of "crop factor".

Doug Jewell
Guest
Posts: n/a

 05-31-2009
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:
> Thanks Doug, but I am still a little bit fuzzy as shown below
>
> On May 31, 3:57 am, Doug Jewell <(E-Mail Removed)> wrote:
>> (E-Mail Removed) wrote:
>>> On May 30, 9:32 pm, (E-Mail Removed) wrote:
>>>> I need help on this one (also), as I seem to have a block in my brain
>>>> to do the math and follow the logic. Perhaps someone can explain this
>>>> in a more practical and easy to understand way?.
>>>> I just recently used my old Mamiya M645 lenses on my digital camera
>>>> (APS-C) using a lens adapter. I recall the following:
>>>> 1. 50mm normal lens in a full frame (35mm camera) will be equivalent
>>>> to approx. 31-33mm APS-C lens (crop factor of 1.5 or 1.6).
>>>> 2. I heard a long time ago that for a 6x4.5cm medium format camera,
>>>> the normal lens will be around 90mm. Normal means as a standard 50mm
>>>> lens in the 35mm camera.
>>>> So, if I have 35mm, 90mm and 210mm M645 lenses, what are the focal
>>>> lengths represented by these lens in the digital APS-C cameras
>>>> (equivalency of the stardard 35mm camera)? When I tried them with my
>>>> digital camera, the 35mm was a little too short for being called a
>>>> wide angle, the 90mm lens was great, useful and powerful, but the
>>>> 210mm did not appear to have the effect of a long telephoto lens. It
>>>> could just be in my mind, as I perhaps expected the 35mm and 210mm to
>>>> be a wide angle and a telephoto lens, respectively.
>>> I am trying to answer my own question here. Could someone confirm if
>>> this is correct?
>>> 90mm M645 = 50mm normal 35mm = 33mm APS-C Crop factor 90/33= 2.7
>>> Therefore 35mm M645 will be equivalent to 13mm, and 210mm M645 will be
>>> equivalent to 78mm

>> Not quite. A 90mm lens is a 90mm lens regardless of what
>> camera you put it on. The only thing that changes is how
>> much of the image that the lens casts that you are looking at.
>>
>> So if you stick the 90mm lens on a 645 camera, because the
>> film is quite large, you are looking at a large area of the
>> image. When you put the 90mm lens on a 35mm film camera you
>> see a smaller amount of the image, and on an APS-C camera
>> you are looking at a smaller portion again. Because a
>> smaller amount of the image fills the sensor/film frame, you
>> have a smaller field of view.
>>
>> The concept of "35mm equivalent" etc comes because to get
>> the same field of view you need a lens with a different
>> focal length. So when you put your 90mm lens on your 645
>> camera you get a certain field of view. If you put the 90mm
>> on a 35mm film camera you will have a smaller field of view.
>> If you want the same field of view that you had with the
>> 645, you will need to mount a 50mm lens. If you want the
>> same field of view on an APS-C camera, you would mount a
>> 33mm lens. So 33mm (APS-C), 50mm (35mm) and 90mm (645) can
>> be said to be "equivalent" because on their respective
>> formats they all give basically the same image.> The 35mm lens did not look like it has a wide angle view than, say, my
>>> Nikkor 18-55mm lens at the 18mm zoom, though?

>> That's right - when you put the 35mm lens on the Nikon it is
>> still a 35mm lens.

> I agree
>
> If you dial your 18-55 lens to the 35mm
>> position, it will give exactly the same image that your
>> 35mm(645) lens gives when mounted to the Nikon.
>>

> You dial 18-55 lens to the 35mm position meaning 18-55 APS-C lens?
> Then this would be around 50mm normal 35mm camera, and it is not the
> same as 35mm(M645)
> I am getting fuzzy here again.

Ok, One camera, your Nikon APS-C. Mount the 35mm 645 lens
with adaptor to it. It will give a certain field of view.
Now take it off and put your 18-55 zoom lens on the Nikon.
Dial it up to the 35mm position. The field of view will be
exactly the same. Both lenses are 35mm, so both will give
the same view, when fitted to the same camera.
If you put the 35mm lens on the 645 camera, it will give a
much wider angle view than it does on the APS-C camera,
because the 645 camera is looking at more of the image that
the lens produces.
>
>> Your 13mm figure is correct though, you are just applying it
>> the wrong way. When you put the 35mm lens on the 645 camera,
>> it will give a very wide angle view - the same as you would
>> get if you put a 13mm lens on your Nikon.

> I agree
>
> You will only get
>> that wide angle of view with in on the 645 though - on the
>> Nikon it will be the same as any other 35mm lens on the Nikon.

> I thought the 35mm(M645) would be equivalent to 13mm(APS-C)?

Yes - the 35mm lens WHEN FITTED TO THE M645 CAMERA will be
roughly equivalent to a 13mm lens FITTED TO THE APS-C CAMERA.
When the 35mm lens is fitted to the APS-C camera it is
exactly the same as any other 35mm lens fitted to the APS-C
camera. The 35mm stays fixed, so on the SAME CAMERA the view
is fixed. It doesn't matter whether the lens was designed
for 645, 135, APS-C, 8x10, it is still a 35mm lens. You
could have 4 35mm lenses designed for each of the above
formats, but when fitted to the APS-C camera every one of
them will give the same image.

>
>> --
>> Don't blame me - I didn't vote for Kevin Rudd or Anna Bligh!

>

--
Don't blame me - I didn't vote for Kevin Rudd or Anna Bligh!