Sigma 18-35mm f/1.8 FX equivalent

Started 9 months ago | Discussions thread
SushiEater Forum Pro • Posts: 11,347
Re: A perfect proof......

Serjojeee wrote:

SushiEater wrote:

Serjojeee wrote:

SushiEater wrote:

bjn70 wrote:

Sounds like you need a z50 to go with that sigma.

That sigma was almost enough to make me buy a d7500 or another d7200. I had a d7200 for a short while with a tamron 17-50 that worked well enough. The sigma didn't promise enough more to warrant the cost, but I always wanted to try it. Indoors wide open was where my tamron disappointed, the sigma would probably have been better but f1.8 would make AF more critical and that could have been the limiting factor.

on d750 I get good enough results with tamron 24-70, considering full equivalence it is mostly equal to the sigma. I also sometimes use 35mm f1.8G but again at f1.8 the AF and limited depth of field can be problematic. I know in my mind that f2.8 on FX is equal to f1.8 on DX but my mind is still irrationally attracted to f1.8.

It only equivalent in DoF but not in the light transmission. F1.8 will allow you to shoot at over a stop faster.

Do you understand that that double amount of light is projected on twice smaller sensor?

Yes, I do. But more

Double the amount of photons.

light from F1.8 lens falls on every

Twice smaller area.

sq. mm.

Imagine for a second that you are standing on a beach in bright sun. No matter where you stand the light is the same.

This is irrelevant to the topic.

Extremely relevant!!!! That is why you are the one who don't understand.

And you'll have the same amount of photons cause of that with the same time of exposure. It actually amazes me why equivalency is still not a fact for many photographers. After all those holy wars. I guess that's why flatearthers still exist.

Just look at my photos few posts above. One is taken with Sigma 70-200mm F2.8 on FF camera at 150mm 1/60 and the other is with 50-100mm F1.8 on DX camera at 100mm 1/160. Both have equal framing and exposure

But not the same amount of SNR cause DX camera received roughly half the amount of photons.

No one cares. The final output is the most important. It is either acceptable or not. With F2.8 lens on FF body and not just FF but the best body in the world which is Nikon D5 the result is not acceptable but with F1.8 on lesser body, D500, the result is acceptable.

(meter was in the middle on both cameras) because F1.8 lens allows more light to get in so I was able to to shoot at higher speed. Now, I know what you see more noise from D500 but my dog was in a very dark place. I could have shot in another place at 100 ISO and you would not see any noise but the F1.8 lens will always allow more light and higher shutter speed than F2.8 lens no matter what camera.

It doesn't cause while the lens allows to collect roughly double the amount of photons per exposure time the sensor of DX camera is twice smaller and can collect half the amount of photons.

Th DX camera collects the light from brighter lens to allow faster shutter speed compared to slower speed lens. And that is more important than your theory or math you actually don't understand how to apply.

I may someday end up with another DX body but I have to resist buying an arsenal of lenses for it to compete with my FX gear.

All of your FX lenses can be used on crop factor body with narrower field of view. I have 3 FX body and one DX body and lso one DX lens because it allows me to do my job. I have no plans to buy another DX lens unless it is something special like 50-100mm F1.8.

And while I think that I can't say anything more on that topic I bet you don't get it.

No you are the one who doesn't get it.

That's why flatearthers exist. Some people are just not that good at mathematics. Not a big deal. But it helps to squeeze all the available light into quality of the photo. I'm not that good at really tough math but this is 3rd grade math. If you'll open the article about equivalence, take a calculator and a peace of paper you'll get over it in an hour. I can't help you with that.

Math has nothing to do with it. Mathematicians don't make progress as much as practicalist do. You can have as much math as you want but until you put it in practice you would not know if it actually works. The problem is that you don't understand math in this concept. You might want to go to the first grade arithmetic. The proof is in the pudding. I have a perfect sweet pudding and you don't.


It just came to me why you are even more wrong.

If I used D850 in DX mode with 50-100mm F1.8 lens instead of D500 which has identical pixel size and density to D500 thus noise characteristic is the same I would obtain the same result but your math of "equivalence" just went in to a toilet . HaHaHa.

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