Help with calculating focal length on Helios 44M

Started 7 months ago | Questions
SirBisgaard
SirBisgaard New Member • Posts: 9
Help with calculating focal length on Helios 44M

Hi There!

I have acquired an Helios 44M 58mm F2.
I also have an K&F M42 to Fuji X mount adapter. (KF06.058)
My question is:
What is the actual focal length with the 2 combined on my X-S10?

Thank you in advanced!

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Novice photographer from Denmark.
My work is @ MartinBisgaard.dk

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ANSWER:
petrochemist Veteran Member • Posts: 3,371
Re: Help with calculating focal length on Helios 44M
6

SirBisgaard wrote:

Hi There!

I have acquired an Helios 44M 58mm F2.
I also have an K&F M42 to Fuji X mount adapter. (KF06.058)
My question is:
What is the actual focal length with the 2 combined on my ?

Thank you in advanced!

Unless the adapter has optical elements the focal length will be 58mm!

Your camera is APSC so the field of view you get will be similar to that produced by a 87mm lens on a full frame camera, but that's not much use to you, it will have the same FOV as any 58mm lens designed for your camera.

The links I get for that part no are adapters without any glass so there's nothing to change the focal length. I think I have heard of focal reducer (speed booster/lens turbo...) type adapters for M42 lenses to fuji - these will contain optical elements designed to compress the image so as to be closer to the lenses designed FOV and will have a crop multiplier (0.71X for my reducer) If you got one of those & adapted the helios via it you would get a brighter image with a wider FOV as the focal length will have been changed by the elements in the reducer (to roughly a 42mm)

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Michael Fryd
Michael Fryd Forum Pro • Posts: 15,270
Re: Help with calculating focal length on Helios 44M
5

Remember, "Focal Length" is not a measurement of Angle of View. It describes a physical aspect of the lens.

The combination of focal length and sensor size determine angle of view.

Do not confuse "focal length", with "equivalent/effective focal length". "Effective focal length is not really focal length, it's simply a cumbersome method of describing angle of view. When we say a lens has an "effective focal length of 50mm" we are saying that the angle of view is the same as a lens with a 50mm focal length that is mounted on a traditional 35mm film SLR.

Thus a 58mm f/2 lens is always a 58mm f/2 lens, no matter what camera it is mounted on, and no matter what camera it was designed for.

If you mount a 58mm lens on a 1.5X crop body, then it will have the same angle of view as an 87mm lens mounted on a 35mm film SLR. Therefore some would say that the combination of a 58mm lens on a 1.5X crop has an angle of view of "87mm effective focal length".

Just to keep things confusing, some manufacturers advertise focal length, and some advertise effective focal length. You need to know which they are talking about. It seems to me, that with interchangeable lenses, the focal length is what they tell you. When the lens is permanently attached to the camera, they tend to tell you effective focal length.

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selected answer This post was selected as the answer by the original poster.
Dem Bell Contributing Member • Posts: 814
58 mm
3

Your Helios is a 58 mm f/2 lens. The adapter doesn't change this because it doesn't have any glass in it. The adapter's job is to hold the lens at the right distance from the sensor. The adapter does not affected lens' optical properties. If you take the lens off the camera and put it in the camera bag, it will remain a 58/2 lens whether the adapter is attached to it or not.

There are two Fuji lenses that are close to the Helios in terms of the focal length and the angle of view it produces: the XF 56 f/1.2 and the XF 60 f/2.4. Your lens is 58 mm and it sits right between these two Fuji lenses.

SirBisgaard
OP SirBisgaard New Member • Posts: 9
Thanks for the answers!
2

Thank you all for the educational answers. 
What confuses me is that my camera is a crop sensor, and my Fuji lens is 23mm equivalent to a 35mm in full frame format.
So I was worried about the adapter "width" to my Helios would change anything.

It is nice to know that I can use the general rule to multiply with 1.5.
The result of that would be my full frame equivalent.

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Novice photographer from Denmark.
My work is @ MartinBisgaard.dk

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