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What is the equivalent focal lenth? (120 pano to 35 pano)

  
 
Pindy
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p.1 #1 · p.1 #1 · What is the equivalent focal lenth? (120 pano to 35 pano)


If you're using the 90mm lens on a Fujifilm GX617, what is the closest FL on a Fujifilm TX-1 or Hasselblad XPAN for the same FOV? Anyone know how to reckon this?


Apr 20, 2024 at 11:12 PM
jcolwell
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p.1 #2 · p.1 #2 · What is the equivalent focal lenth? (120 pano to 35 pano)


The GX617 with a 90mm lens in landscape mode, has a horizontal angle of view (AOV.h) of 87 degrees, and vertical AOV.v of 35 degrees, see diagram. (I have an AOV spreadsheet, an early version is on my old site www.jcolwell.ca).

The TX-1 pano mode has the 24mm x 65mm image size you mentioned. Based on matching the horizontal angle of view (or field of view), a 35mm lens on the TX-1 gives the same horizontal field of view as the 90mm on GX617. Since the aspect ratios are not very different, the same 35mm lens on TX-1 comes as close as you would need to matching the GX617’s vertical field of view, too.









Edited on Apr 21, 2024 at 12:26 PM · View previous versions



Apr 21, 2024 at 07:59 AM
Pindy
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p.1 #3 · p.1 #3 · What is the equivalent focal lenth? (120 pano to 35 pano)


Looks like I just stepped into the crazy world of jcolwell! Ask and you shall receive. MUCH appreciated, this is impressive. I'm gonna now try to get my head around all this.


Apr 21, 2024 at 11:23 AM
Pindy
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p.1 #4 · p.1 #4 · What is the equivalent focal lenth? (120 pano to 35 pano)


Oh wait a minute—are we talking about the same Fuji TX-1? My understanding is the TX-1/XPAN has a frame size of 24x65mm roughly, which would make me think these aspect ratios are not wildly different (6x17 vs 24x65).

This guy:







Apr 21, 2024 at 11:30 AM
jcolwell
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p.1 #5 · p.1 #5 · What is the equivalent focal lenth? (120 pano to 35 pano)


No. I dyslexed to the XT-1. At least, I wrote it down correctly. No wait, I actually used both XT-1 and TX-1. It was early.

Anyway, the TX-1 pano puts a 24 x 65mm rectangle on the bottom. Much larger. Much better. I'll re-do and post the results, in a bit.



Apr 21, 2024 at 11:50 AM
 


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Pindy
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p.1 #6 · p.1 #6 · What is the equivalent focal lenth? (120 pano to 35 pano)


We should have a tip jar at FM.


Apr 21, 2024 at 12:11 PM
jcolwell
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p.1 #7 · p.1 #7 · What is the equivalent focal lenth? (120 pano to 35 pano)


P.S. The 40mm TX-1 lens has AOV.h = 78 deg (vs. 87 deg for 90mm on GX617), and the TX-1 30mm has AOV.h = 95 deg.


Apr 21, 2024 at 12:31 PM
Pindy
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p.1 #8 · p.1 #8 · What is the equivalent focal lenth? (120 pano to 35 pano)


jcolwell wrote:
P.S. The 40mm TX-1 lens has AOV.h = 78 deg (vs. 87 deg for 90mm on GX617), and the TX-1 30mm has AOV.h = 95 deg.


OK so sounds like the 617 is right in the middle of the two, with the 30mm being every so slightly closer. My inner-Koudelka thanks you!



Apr 21, 2024 at 12:52 PM
mcbroomf
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p.1 #9 · p.1 #9 · What is the equivalent focal lenth? (120 pano to 35 pano)


Great info from Jim!

The (relatively) easy way to figure this out is to use the ratio of the frame widths to multiply the lens FL to get the 2nd.

So for the 90mm on the 617 film you simply multiply it by the ratio of 65/170 to get the FL on the narrower film

90 * 65 / 170 = 34.4



Apr 21, 2024 at 01:31 PM







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