Focal length math for this image...

[janeenadamsmartin]

My husband spotted something in the sky with his naked eye. I couldn't see it, so he took my EM1.3 with the 40-150mm lens and snapped a photo. And then I enlarged it to see what it was.


The photo properties say it was shot at 150mm...

1) Was it shot at 150mm, or using the crop factor, it was really 300mm?

2) If 50mm is normal eyesight, does it mean my husband could see 3x better than my naked eye, or 6x better?


3) is this a weather balloon or an incredibly high mylar balloon from a party?

 

[Skeeterbytes]

Nicely spotted!

To my eye it's a mylar party balloon with a "regular" balloon attached, headed for some far away destination. 150mm sounds reasonable, it's about 6.6X magnification in four-thirds (similar to a small pair of binoculars).

Cheers,

Rick

p.s. Always surprised how often I find mylar balloons in the Sierra Nevada backcountry. IDK if they're from the valley or the coast, but they sure seem to end up there.

--
Equivalence and diffraction-free since 2009.
You can be too; ask about our 12-step program.

 

[flektogon]

Really a nice spotting! Now, when we claim that the human eyesight "focal length" (it would be better to refer the angle of view) is around 50mm (more precise 43mm), it is meant as a comparison the the 35mm film (i.e. FF) lenses' focal length. So, moving to the M43 format it would correspond to 22mm lens. And a 150mm lens (in the M43 format) would yield 150/22 times higher magnification.

--
Regards,
Peter

 

[janeenadamsmartin]

Thank you! yeah, we are kinda betting on mylar balloon vs a weather balloon.

My husband has incredible distance sight!

 

[janeenadamsmartin]

Whew! I think they both came out about 6x better than my eyesight.


Thank you for the explanation!

jan

 

[JosephScha]

Without using the loupe, you can just barely see the white and red dots:


Of course a large screen high res monitor helps!

--
js

 

[bclaff]

This is a fun question but unfortunately you don't have sufficient information.

To know the actual size of the object you would need to know the subject distance.

The math works out to

O = S * I / f

Where O is object size, S is subject distance, I is the size of the image, and f is the focal length.

For the white object I get 19 pixels or about 0.63mm for I

Assuming f is 150mm then we have

O = S * 0.00042mm

Of course the 0.00042 factor does tell us about the angle which works out to about 1.4 minutes of arc. This iasabout the limit of normal visual acuity, so well spotted.

 

[Regor250]

To answer the 1st question, a 150mm lens is still a 150mm lens no matter what sensor you put in front of it. When I adapt my old OM Zuiko 50mm FF (35mm film) macro lens to my M43 camera, the label still reads 50mm macro on it, that does not change magically. Don't confuse focal length with field of view.

Because 35mm film (aka FF) has been around for one and a half century, people like to relate to its equivalent field of view for any given focal length, hence the constant talk of equivalency between formats, though that debate can go on for ever.

 

[olavsm]

...When I adapt my old OM Zuiko 50mm FF (35mm film) macro lens to my M43 camera...

Hi Roger,

I am considering acquiring an old OM Zuiko 50mm f3.5 macro lens, but have also experienced that old OM Zuiko lens may not necessarily perform miracles on mft cameras. I believe that this particular lens, a late multicoated version, probably was a good lens for its time.

Could you say something about how the lens performs on your mft camera(s)? Is it worth it, compared to sourcing a second hand m.zuiko 35mm or 60mm macro lens? The price would be approx 50% of a reasonably decent 35mm macro lens, and way less than the 60mm macro lens.

Olav