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Jupiter 36B Medium Format - Do I have the conversion right?
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PostPosted: Thu Jan 04, 2018 4:26 pm    Post subject: Jupiter 36B Medium Format - Do I have the conversion right? Reply with quote

Picked up some Russian Medium format lenses and the one I am most interested in is the Jupiter 36B 250mm F3.5. I will mount this to an A7R2 with a fotodiox adapter. From my research, and there seems to be much mis-information on the net about MF lenses on FF, but I believe this lens will shoot "Like a native" 380mm F3.5 on FF (yes I understand its still a 250mm lens), but only will be taking part of the image circle in the frame.

If I also understand correctly the depth of field will be much shallower than a 380mm f3.5 on FF would be if there were such an animal.

Correct or am I still confused?


PostPosted: Thu Jan 04, 2018 4:48 pm    Post subject: Re: Jupiter 36B Medium Format - Do I have the conversion rig Reply with quote

Gatorengineer64 wrote:
Picked up some Russian Medium format lenses and the one I am most interested in is the Jupiter 36B 250mm F3.5. I will mount this to an A7R2 with a fotodiox adapter. From my research, and there seems to be much mis-information on the net about MF lenses on FF, but I believe this lens will shoot "Like a native" 380mm F3.5 on FF (yes I understand its still a 250mm lens), but only will be taking part of the image circle in the frame.

If I also understand correctly the depth of field will be much shallower than a 380mm f3.5 on FF would be if there were such an animal.

Correct or am I still confused?

Confused from the sound of things!

IIRC the A7 is FF.
On a FF body it will shoot EXACTLY like a FF 250mm f/3.5, the only difference being the lens has a larger image circle which is not seen on FF (and is corespondingly heavier etc)
As you say you're only using the central portion of the image circle but that's the same portion a FF camera sees. The lens will give a wider FOV on it's native camera.
It would be possible to use a focal reducer (if a suitable type is available) to compress the image circle & give a faster shorter focal length combination., more similar to what it would produce on it's native medium format camera.


PostPosted: Thu Jan 04, 2018 4:54 pm    Post subject: Reply with quote

So from what you are saying a 50ff would shoot "like" a 50ff on M4/3rds? I know this to not be the case. It shoots like a native 80mm of m4/3rds.....


PostPosted: Thu Jan 04, 2018 5:06 pm    Post subject: Reply with quote

Focal length is a property of the lens, not the sensor size. The field of view does change with respect to sensor size.


PostPosted: Thu Jan 04, 2018 5:23 pm    Post subject: Reply with quote

ok, let me rephrase the question, the field of view of a 250 F3.5 will be like that of a 380mm native lens on FF, correct? but the DOF will be shallower


PostPosted: Thu Jan 04, 2018 5:49 pm    Post subject: Reply with quote

No. A 50mm Medium format lens will work EXACTLY to a 50mm Native FE mount lens on your A7R2.


PostPosted: Thu Jan 04, 2018 10:08 pm    Post subject: Reply with quote

If I may add my attempt to explain :

You take a Jupiter-36 250mm.

On the Kiev-6 (6x6 medium format), field of view will be like a 150mm on a FullFrame.
On a FullFrame camera, it will be a 250mm
On an APS-C, field of view will be like a 375mm on FullFrame.

In other words, even if it's not really correct to say that, you can keep in mind that whatever the format it is made for, the focal is always like for a FF camera. That's why for very large format (like an Orion-1 aero photography camera), a 100mm lens is an ultra-wide angle camera.


PostPosted: Fri Jan 05, 2018 9:34 am    Post subject: Reply with quote

Gatorengineer64 wrote:
So from what you are saying a 50ff would shoot "like" a 50ff on M4/3rds? I know this to not be the case. It shoots like a native 80mm of m4/3rds.....

No it doesn't! I don't have a native 50mm prime for my MFT kit, but my native kit zoom includes 50mm, and surprise surprise the FOV from an adapted 50mm prime (I have loads of these) on MFT is the same.

A 50mm FF lens shoots EXACTLY like a 50mm MFT lens on MFT. The result will be similar to a 100mm FF lens on a FF body. (MFT has a 2x crop, but the normal aspect ratio is different so the image is less similar than with FF-APSC crops)

In all such cases the significant difference is the outer part of the image is not captured on the smaller format camera.

This is the same situation as mounting a medium format lens on FF. The outer part of the image is cropped (by the sensor not being big enough to see it) and the result is the FF image is the same as you'd get from a FF lens of the same focal length.

The increased coverage can be useful if the adapter being used allows movements (tilt or shift) but most don't.


PostPosted: Fri Jan 05, 2018 6:15 pm    Post subject: Reply with quote

The format of the lens has no influence on the field of view other than a smaller format lens won't cover the sensor/frame of a larger format camera, it's the focal length of the lens plus the sensor size that determines field of view.
So a large format 250mm lens, a medium format 250mm, and a FF 250mm lens will all have the same FOV on a FF camera, now lets take a m4/3 250mm lens which has a FOV of a 500mm lens on FF, now lets mount it on a FF camera, it's image circle won't cover the larger sensor, and on medium and large format, this same m4/3 lens will project the same size image circle.

I think you are getting confused with the use of FF as a reference point for adapting to smaller formats and getting a crop factor, will, the crop factor still happens with medium format to FF, it's just that you are shifting the reference to medium format without realizing it, so a 250mm lens on MF will behave like a longer focal length lens on MF when mounted on FF.

A simple way to help keep this all straight in your mind, the focal length doesn't change, only it's FOV will depending on the sensor size, smaller sensor = a shift towards tele, larger sensor = a shift towards wide angle.


Last edited by Lightshow on Fri Jan 05, 2018 9:42 pm; edited 1 time in total


PostPosted: Fri Jan 05, 2018 7:51 pm    Post subject: Reply with quote

Lightshow wrote:
...getting confused with the use of FF as a reference point for adapting to smaller formats and getting a crop factor, will, the crop factor still happens with medium format to FF, it's just that you are shifting the reference to medium format without realizing it, so a 250mm lens on MF will behave like a longer focal length lens on MF when mounted on FF.


This was very very difficult for me to understand. I still struggle somewhat. Tip: forget about crop factor.

There are only two factors at play: Focal Length, and, FOV of that focal length on FF (this FOV is the reference point referred to above).

Any format lens of any focal length will have the same FOV on FF Camera as the lens had on it's camera!


PostPosted: Fri Jan 05, 2018 8:59 pm    Post subject: Reply with quote

visualopsins wrote:
Lightshow wrote:
...getting confused with the use of FF as a reference point for adapting to smaller formats and getting a crop factor, will, the crop factor still happens with medium format to FF, it's just that you are shifting the reference to medium format without realizing it, so a 250mm lens on MF will behave like a longer focal length lens on MF when mounted on FF.


This was very very difficult for me to understand. I still struggle somewhat. Tip: forget about crop factor.

There are only two factors at play: Focal Length, and, FOV of that focal length on FF (this FOV is the reference point referred to above).

Correction: Focal Length and Sensor Size determines FOV, using FF as a reference point is arbitrary.
Quote:

Any format lens of any focal length will have the same FOV on FF Camera as the lens had on it's camera!


Not quite, you're in error with the last part... Any format lens with the same focal length will have the same FOV on a FF camera(assuming it covers the sensor, smaller format lenses will vignette), period.
Said another way, a lens with a given focal length(it doesn't matter which format) will have different FOV depending on the sensor size, small sensor = narrower FOV, larger sensor = wider FOV.

Now an illustration using my favourite analogy, a flashlight shinning on a wall, the size of the light pattern will be like the lenses format(large image circle = large format, small image circle = small format), now, draw 3 rectangles of different sizes(these will be your different sensor sizes), notice that the different sensor sizes don't change the image circle size, and that the image that is projected would not change, but you either see more or less of that image depending on the sensor size. A camera lens and sensor behave the same way.
25mm on m4/3, 35mm on APS-C, 50mm on FF.... all have a similar FOV

I found this interesting, take any 2 sensor sizes, measure the sensor diagonal and mount a lens with a focal length that matches this dimension and they will both have the same FOV. 43mm on FF for example. Note, Pentax made a 43mm lens exactly because of this dimension.


PostPosted: Fri Jan 05, 2018 9:40 pm    Post subject: Reply with quote

Konica, Minolta, Nikon, Zeiss and Pentacon all made 43mm lenses too. The Minolta MD 2/45 and Hexanon 1.8/40 for example, are both actually 43.2mm, as are most '45mm' lenses for 35mm film.


PostPosted: Fri Jan 05, 2018 9:47 pm    Post subject: Reply with quote

Lightshow wrote:
Lightshow wrote:
visualopsins wrote:
..getting confused with the use of FF as a reference point for adapting to smaller formats and getting a crop factor, will, the crop factor still happens with medium format to FF, it's just that you are shifting the reference to medium format without realizing it, so a 250mm lens on MF will behave like a longer focal length lens on MF when mounted on FF.


This was very very difficult for me to understand. I still struggle somewhat. Tip: forget about crop factor.

There are only two factors at play: Focal Length, and, FOV of that focal length on FF (this FOV is the reference point referred to above).

Correction: Focal Length and Sensor Size determines FOV., using FF as a reference point is arbitrary.

...

Now an illustration using my favourite analogy, a flashlight shinning on a wall, the size of the light pattern will be like the lenses format(large image circle = large format, small image circle = small format), now, draw 3 rectangles of different sizes(these will be your different sensor sizes), notice that the different sensor sizes don't change the image circle size, and that the image that is projected would not change, but you either see more or less of that image depending on the sensor size. A camera lens and sensor behave the same way.


Beautiful example of the mistake! The example has used the len's format as reference -- you are referencing the large format to derive the narrower fovs of the lens on the other smaller formats. This is the case for using FF fov as reference to calulate APS-C fov.

OP has medium format lens. The fov of that focal length on FF is whatever it is. The lens on APS-C has different fov given using crop factor referencing FF fov. Also referencing FF fov, to get the same fov on medium format as FF requires a lens about 2x fov.


Last edited by visualopsins on Fri Jan 05, 2018 10:34 pm; edited 1 time in total


PostPosted: Fri Jan 05, 2018 10:27 pm    Post subject: Reply with quote

Lightshow wrote:
visualopsins wrote:
...
Any format lens of any focal length will have the same FOV on FF Camera as the lens had on it's camera!


Not quite, you're in error...


Oops! Thanks. Completely erroneous!


PostPosted: Fri Jan 05, 2018 10:59 pm    Post subject: Reply with quote

If you're a medium format photographer your lenses will have a narrower fov when used on ff camera.

However, if you are a FF photographer, that adapted medium format lens will have the same fov as a ff lens of same focal length on your FF camera.

Different frames of reference...

thus 100mm medium format lens has same fov as 100mm FF lens when lenses are used on ff camera,

but a 200mm lens is required on medium format camera to get the same fov as medium format 100mm lens gives on FF.


PostPosted: Fri Jan 05, 2018 11:11 pm    Post subject: Reply with quote

Thanks for the responses, I am not sure if I got an answer, I know some of the above is factually inaccurate from having owned cropped sensors cameras, and knowing that a 50FF shoots longer as a longer FF equivalent on M4.3rds or APS C. Thats why we have speed boosters and the like for manual lenses. I think what my bad assumption was is that this is going to shoot as a longer MF equivalent on a FF camera. Doing more research I believe that based on the hasselblad diagonal FF equivalent is 135MM, applying the crop ratio of frame sizes is 84.85 for 6x6 diagonal to 43.26 35mm diagonal, this should shoot like a 265mm FF lens....

As far as Depth of field, I understand from further research that the Depth of field will be the equivalent of a 3 stops faster full frame lens. so from a Depth of field and isolation standpoint this should shoot as an F2 FL something from a Depth of field perspective so it should have very nice isolation. if it shoots like a 265mm f2 lens from a DOF standpoint I will be a happy puppy.

What I actually get I guess I will find out when my fotodiox adapter gets here whenever that will be.

I also have the russian 30mm fisheye which is supposedly 180 degree FOV, which makes my head hurt thinking about what this will do on my FF.


PostPosted: Fri Jan 05, 2018 11:44 pm    Post subject: Reply with quote

The 30mm lens will have the same fov as a 30mm ff lens has on your camera regardless of what format the len comes from. But if you want that same ff field of view on the original camera, a crop factor is applied to determine the focal length lens needed.


PostPosted: Sat Jan 06, 2018 12:40 am    Post subject: Reply with quote

Gatorengineer64 wrote:
... I think what my bad assumption was is that this is going to shoot as a longer MF equivalent on a FF camera. Doing more research I believe that based on the hasselblad diagonal FF equivalent is 135MM, applying the crop ratio of frame sizes is 84.85 for 6x6 diagonal to 43.26 35mm diagonal, this should shoot like a 265mm FF lens....


yes, just like a 265mm lens on 6x6 camera, and it'll shoot just like a 135mm FF lens on FF camera.. Same fov!