Telephoto Weight Efficiency

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vvgogh Junior Member • Posts: 28
Telephoto Weight Efficiency

What do you think is a fair way to compare the weight efficiency of different systems and telephoto lenses?

Here is one figure of merit for focal length limited subjects: (System Weight in grams) / [(Focal Length in mm) x (# Pixels)]

System............................................. FOM (Weight)

Fuji X-T30, 70-300mm F 4.5-5.6... 0.124 (963g)
+ 1.4 Extender............................... 0.100 (1,093g)

Sony A7RIV + 70-350mm F4.5-6.3.. 0.0923 (1,296g)
using 40 MP Square Crop

Sony A7RIV + 100-400mm.............. 0.0858 (2,066g)
+1.4 Extender................................... 0.0662 (2,233g)

Sony A7RIV + 200-600mm............... 0.0828 (2,990g)
+1.4 Extender.................................... 0.0624 (3,157g)

The above comparison has the same pixel density.  I suppose another factor would be needed if the pixel densities differ.

Do you know of a lower weight efficiency according to that FOM for a telephoto setup than the above?

TAGooty
TAGooty Forum Member • Posts: 94
Re: Telephoto Weight Efficiency
2

vvgogh wrote:

What do you think is a fair way to compare the weight efficiency of different systems and telephoto lenses?

Here is one figure of merit for focal length limited subjects: (System Weight in grams) / [(Focal Length in mm) x (# Pixels)]

...

Do you know of a lower weight efficiency according to that FOM for a telephoto setup than the above?

You may like to call this "weight penalty", with efficiency higher is better.  Or, use efficiency = focal len/wt.  Max. aperture is another important variable.

I think this is actually a constrained optimisation problem.  There are limits that depend on the use: max. price, min. focal len, max wt, min. pixels.  A single FOM may be too simplistic to be useful!

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TAG

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SilvanBromide Veteran Member • Posts: 5,055
Re: Telephoto Weight Efficiency

vvgogh wrote:

What do you think is a fair way to compare the weight efficiency of different systems and telephoto lenses?

Here is one figure of merit for focal length limited subjects: (System Weight in grams) / [(Focal Length in mm) x (# Pixels)]

System............................................. FOM (Weight)

Fuji X-T30, 70-300mm F 4.5-5.6... 0.124 (963g)
+ 1.4 Extender............................... 0.100 (1,093g)

Sony A7RIV + 70-350mm F4.5-6.3.. 0.0923 (1,296g)
using 40 MP Square Crop

Sony A7RIV + 100-400mm.............. 0.0858 (2,066g)
+1.4 Extender................................... 0.0662 (2,233g)

Sony A7RIV + 200-600mm............... 0.0828 (2,990g)
+1.4 Extender.................................... 0.0624 (3,157g)

The above comparison has the same pixel density. I suppose another factor would be needed if the pixel densities differ.

Do you know of a lower weight efficiency according to that FOM for a telephoto setup than the above?

Interesting approach - at least as an academic exercise.

In practical terms, I'm not sure how useful it is to compare between systems and formats where the features and results will be quite different. Whereas using a FOM index for comparison only really makes sense if all else is equal (and therefore weight is the only or primary consideration).

So I can see it being a way to consider and compare options within the same system and format (such as your last two examples. Otherwise it seems a bit like allotting a score to apples so that you can compare it with the score you've allotted to oranges. Whereas if, like me, you're not particularly partial to oranges, the comparison is rendered largely moot... ; )

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turke
turke Regular Member • Posts: 167
Re: Telephoto Weight Efficiency

i just use a monopod

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OP vvgogh Junior Member • Posts: 28
Re: Telephoto Weight Efficiency

I was curious how the Fuji compared to the Sony.  They have the same pixel spacing/density.  About 300mm APS-C seems to be a bit of a break point in weight.  There are still a lot of things outside the metric, but I was surprised that the Sony 70-350mm came out a little better on the metric due to the better match between the square crop circumscribed inside the circular lens profile.

For the longer focal lengths, the weight is mostly in the lens.  For efficiencies' sake, I don't know why they stick this heavy lens on a smaller rectangular sensor.  Circumscribing a square sensor inside the circular lens profile is more efficient.... I guess we have that choice by using an ASP-C telephoto on full-frame to bump up that efficiency like the 70-350mm.  The unused edge pixels are a very small fraction of the system weight.

I'll run 20+ miles with the 200-600mm for wildlife photo opportunites, but sometimes I'm confident there won't be any good wildlife on a run, so a lighter camera lets me go a little faster.... but I still bring something just incase I'm wrong.

And yeah, that should probably be inversed as higher efficiency is better.

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