GH2 + legacy lens in video mode - S35 crop factor?

Riker

First and foremost I would like to apologize to everyone at Personal View for making a crop factor thread. But if I may pose this one stupid crop question, I promise you I will send you an Airbus full of happy and smiles, promise!

Question: I recently got my hands on few nice old lenses, Helios 50mm, Vivitar 28mm etc. and just out of geeky curiosity, when recording videos on GH2 with those lenses, what would be the equivalent FOV in Super 35 film terms?

Far as my research goes, the crop factor for GH2 compared to S35 is somewhere around 1.3 or 1.4 ...

But Vivitar 28 acts like 50 mm (35mm speaking) on GH2 so am I correct to say that when filming, Vivitar 28 on GH2 has the same FOV as 70mm on a S35 film camera?

Or to put it bluntly, someone fill in the blank - shooting video with Vivitar 28 mm on GH2 has the same FOV like _______ mm on S35 film camera.

goanna

@Riker

40mm

I used:

http://www.abelcine.com/fov/

Choose AF100 to show similar results to GH2

Riker

@goanna : hm, if I take my 14-140 lens and lock it around 50mm mark, that FOV is nowhere to compare with the 50mm of a legacy lens like Helios 50mm that I have.

This is why I asked this question.

Say I have a 50mm lens made exclusively for m43 camera, and this old Helios 50mm. Clearly they have absolutely different FOV's, so how can I know their FOV in "S35 terms", they can't be both regarded as 50mm in the abelcine calculator? Doesn't make sense to me.

goanna

Crop factor of a given focal length lens changes according to sensor (or film frame) size.

http://www.personal-view.com/faqs/camera-usage/general-camera-usage-faq

Riker

I know that. Old legacy 50 mm lens is 100mm in "photographic terms" on GH2, but how to calculate those 50mm on GH2 in video mode to S35 cinema numbers is where my brain stops lol.

matt_gh2

@Riker I once read somewhere that old vintage glass sometimes had inaccurate focal lengths put on them. That may be why the Helios 50 FOV doesn't equal the 14-140 when set at 50. Perhaps test your legacy lenses for FOV and see what they equal on the 14-140 and use that focal length in the abelcine conversion chart supplied by @goanna. That's just an idea - hopefully someone who knows for sure can chime in to confirm that idea will work correctly.

Riker

I hate to open this can of cropped worms. I took a test. Hope it helps.

Same position, same subject. Used Lumix 14-140 and went 52 (eyeballed), 70, 100 and then took the Helios 52 mm.

Left side 24p video mode screenshots, right side is 16x9 aperture priority images. Can someone explain where does the x2 factor come in? Why is this old school 52mm lens not acting like 104mm?

And - how to translate these focal lengths into S35 field of view terms, my original question :D

inqb8tr

@Riker

Everything looks OK to me, your Helios has roughly the same FOV as Pany at 52mm.

(EDIT: Ok, it is closer to pany at 70mm, but this might be the lens variation as Matt said)

That's what it's supposed to look like. 52mm is 52mm on any lens, m43, m42, or whatever.

Super35 FOV is around 1.4-1.5 x FF, so when you put any 50mm lens it will have FOV like 75mm on Full frame sensor. If you could put some 50mm m43 lens on Super35 sensor, this would also be the same, it would have FOV same as 75mm on FF, but it would probably vignette.

inqb8tr

@Riker

Why is this old school 52mm lens not acting like 104mm?

It is! They both are, Helios is like 104 and Pany 14-140 is as 28-280!

:)

Riker

Like Gob from Arrested Development would put it - I've made a huge mistake.

The Helios is 58mm, not 52.

So 58mm legacy lens has the exact same FOV like m43 lens @ 67mm.

I've read somewhere (not necessarily here) that crop factor babble doesn't apply on GH2 when in video mode.

So not only that I don't get the crop factor, I don't get the difference. From what I can see from my test today, there is absolutely no difference between FOV on film stills and photos on GH2. They're completely identical.

inqb8tr

In 16:9 it uses a bit more on the sides of sensor so crop factor is slightly smaller than native m43 4:3 mode. That is multi aspect sensor in GH2. But that is like 5% difference.

goanna

@Riker

Just what camera are you attaching your 58mm Helios to?

miked

I remember the consensus being that GH2 M4/3 sensor has a crop factor of 1.18 when compared against APC-S/S35.

Riker

@goanna GH2

Helios at 58mm is not the same FOV as Lumix zoom at 58 mm (I eyeballed the 58)...but it looks identical in every way to Lumix's 67mm.

Both in video mode and in photo mode.

goanna

@Riker

But isn't the Helios for a 35mm film camera (Pentax) SLR? Have I missed something? At a rule-of-thumb doubling factor, a 58mm lens on a [edit] GH2 35mm still camera should look like a 116mm native M 4/3 on the GH2.

goanna

To estimate what lens on a micro 4/3 camera will match the lens used in a Super 35 movie:

In the converter at http://www.abelcine.com/fov/,

choose Super 35 Film - 16x9 from drop down list at A;
Choose - or type the S35's lens focal length into the LENS field in the centre column;
Choose Panasonic AF100 from the drop own list at B.

then...

Note the angle of view figure (in blue text) of the S35 lens at A;
to keep the previous values, optionally open http://www.abelcine.com/fov/ in another browser tab;
Tweak the lens focal length into the LENS field in the centre column, typing values until the M43 lens's Angle of View is the same as the angle you noted for the S35.

The figure in the centre column is an approximate value for what you want.

Note: these values are all ballpark values. What matters in a movie is how big the actor's face looks on the screen. The vertical size of the sensor used is a better benchmark than this site's diagonal size.

eg (from Wikipedia), Two aspect ratios compared with images using the same diagonal and then vertical sizes:

4:3 and 16:9 (1.77:1) Diagonal sizes are equal

4:3 and 16:9 (1.77:1) Vertical sizes are equal

Super 35 ratios have included 1.85:1 ("flat" print), 2.20:1 (70 mm), 2.39:1 (anamorphic print), 16:9 (widescreen video), and 4:3 (fullscreen video). Wikipedia

Riker

@goanna

I've tested myself and seen for myself, Helios 58mm on my GH2, in movie mode and in photo mode, 16x9, shows the same exact image, so I guess same FOV, as Lumix 14-140 zoomed out to 67mm (as the exif says).

Now, the doubling comes from comparing Lumix m43 sensor with photo 35mm frame, which I'm not particularly interested in.

When comparing GH2 to Super35, they're very close, 1.3... I think

goanna

Is it me or does this topic come up every 6 months? ( @vicharris )

http://www.personal-view.com/talks/discussion/comment/145423#Comment_145423

Riker

I'm just being curious about the unnecessary :) as you can see in another example, Lumix zoom at 25 is identical to Fuji CCTV 25mm

You're confusing the audience now, in your original post yesterday you said that 58mm lens on GH2 should look like a 116mm native M 4/3

Which can't be right, I just tested it for the second time :)

goanna

@Riker

Please check my post again. I corrected it minutes after posting - and couldn't help noticing you understood that I'd been thinking of 35mm equiv :-)

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