Sigma 18-35mm f/1.8 FX equivalent

Started 9 months ago | Discussions thread
SushiEater
SushiEater Forum Pro • Posts: 11,347
Re: A perfect proof......
1

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 light from F1.8 lens falls on every 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.

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 (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.

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.

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