Is fast lens necessary?

[Artosoft]

can i easily conclude any prime lens below or f2.8 is considered as fast prime lens...the lower f, more faster lens...

The aperture number for fast lens also depend on prime lens' focal length.
50mm f/1.4 is fast lens. But there is 50mm f/1.2 too (faster than f/1.4). And there is (consider slow) f/1.8 50mm.

But, f/2.8 for 300mm is consider fast prime lens already. Because there is also f/5.6 for 300mm.

Regards,
Arto

 

[totoro17]

The aperture number for fast lens also depend on prime lens' focal length.
50mm f/1.4 is fast lens. But there is 50mm f/1.2 too (faster than f/1.4). And there is (consider slow) f/1.8 50mm.

But, f/2.8 for 300mm is consider fast prime lens already. Because there is also f/5.6 for 300mm.

Regards,
Arto

what about tamron 90mm f2.8 macro lens is it considered as fast lens?

 

[diediealsomustdive]

what about tamron 90mm f2.8 macro lens is it considered as fast lens?

Slow if you consider it as a portrait lens, as the fast ones are 85/1.4, not so fast 85/1.8. But if you consider it as a macro lens, it is pretty standard now-a-days. In days gone-by macro lenses used to be f3.5.

When you move away from the 50mm range, to the longer or shorter focal lengths, you tend not to be able to make really fast lens. This I guess has to do a lot with the bending of lights (more for wideangle) and long focal length (for teles). You can have a 300/1.4 if you are willing to carry a say 20 kg (I am speculating the size here) lens with a front diameter of humongous proportion (but you will have to commission the lens, as no maker will have that in the catalogue). Sensible lenses are smaller, check out catalogues and you will see.

So fast ones, hope I am not too outdated:

20/2.8
24/2.8
28/1.8
35/1.4
50/1.4
85/1.4
105/1.8
135/2
180/2.8
200/2
300/2.8
400/2.8
500/4

Lens shorter than 20 and longer than 500 are rather scarce.

 

[diediealsomustdive]

IIRC, fast lenses are typically made for the super professional, super rich, or super devoted guys and gals, who spare no expense to get the sharpest possible lens. I was eyeing, and eventually bought, the AF85/1.8, which was, to me, ideal as it is fast, reasonably priced, and boy, sharp, beautiful bokeh, etc. My pal Paul, on the other hand, can do no less than the AIS85/1.4, as that lens is, sad to admit, that slightly better than my AF85/1.8. Paul bought the 85/1.8.

Mostly the manufacturers put in more effort to create the super lens, that frequently will become a legend in their line-up, nevermind most people enticed into buying that brand will never buy these legends, but end up with pitiful kit lenses better serving as paper weight. Spare no expense also applies to the lens maker, so mostly, not all the time, these super fast lenses are sharper, mechanically better, more beautifully crafted, have better bokeh, less vignetting, etc etc, as no expense is spared.

As many bros and sis have mentioned, if you stop down 1 to 2 stops (I hazard to guess better 2 stops), you will be hard pressed to find the difference. That's why I settled on the 85/1.8, although the size of my wallet and the number of kids I have to put (eventually) through Uni also figured. But occassionally I will "splurge" on the bigger one, like I have the AF50/1.4, after owning a series of 50mm lenses with f1.4, f1.8, f2 (even one with f1.7 for my odd minolta x-700). Honestly I love the AI50/2 the best, but now-a-days convenience is more important and I use AF50/1.4.

So, if you must have the ultimate legendary lens that will usually provide that bit more in performance, go for it. If you pretty much want a good lens, you save more than half for sacrifising that half to 1 stop.

I am not venturing into the ego part of the equation as I fear repercussion. But honestly when I turn up in non-pro circle with the 85/1.8 you can see the people going ooo-aaa over such a big beautiful front element... There you go, even the not-so-fast prime can have an effect. The trick is to get the one lens with the biggest most impressive looking front (and side, gold letters do wonders!).

I am still eyeing the 180/2.8 after all these years....

 

[lsisaxon]

So fast ones, hope I am not too outdated:

20/2.8
24/2.8
28/1.8
35/1.4
50/1.4
85/1.4
105/1.8
135/2
180/2.8
200/2
300/2.8
400/2.8
500/4

Lens shorter than 20 and longer than 500 are rather scarce.

Fast ones I know which are not in your list or faster than what you have already listed...
14/2.8
18/2.8
20/1.8
24/1.8, 24/2.0
28/1.4
50/1.2, 50/1.0L
135/2.0
300/2.0
600/4.0
1200/5.6

 

[diediealsomustdive]

Hey you can calculate the front element size of the 300/1.4 and estimate the weight of the lens too, as I recall from our recent exchanges in the forum. This is one witty guy with all the knowledge. I just play play only. He he he...

 

[lsisaxon]

Hey you can calculate the front element size of the 300/1.4 and estimate the weight of the lens too, as I recall from our recent exchanges in the forum. This is one witty guy with all the knowledge. I just play play only. He he he...

300/1.4? The front element diameter would have to be at least 21.5cm.

 

[creampuff]

300/1.4? The front element diameter would have to be at least 21.5cm.

At that size, you won't even be able to afford to buy a filter if attached to the front element!

 

[diediealsomustdive]

It would cost heck of a lot to mold the glass, and polish the behemoth to spec, and then another heck of a lot to mount onto lens, and keep it there. Maybe somewhere in the starting range of prices of what NASA buys....

 

[Artosoft]

what about tamron 90mm f2.8 macro lens is it considered as fast lens?

Can consider it as a fast lens for Macro dedicated lens. Of course, like others mentioned, there are comparable focal length lenses which is faster than Tamron 90mm f/2.8, but that's not dedicated macro lens (which don't have macro lens magnification ratio, close distance, and smaller distortion for planar subject).

Best regards,
Arto.

 

[Artosoft]

At that size, you won't even be able to afford to buy a filter if attached to the front element!

As you know, fast lenses tend to be heavy. But, some company like olympus with their 4/3 system, similarity to nikon DX range lens, can have smaller lens than for their 35mm slr camera. I am not familiar with 4/3 system, but IIRC they make fast lenses in the smaller form than their 35mm slr camera counterpart. But, IIRC the first lens' element can't be made smaller as the rules for aperture.

Regards,
Arto.

 

[lsisaxon]

As you know, fast lenses tend to be heavy. But, some company like olympus with their 4/3 system, similarity to nikon DX range lens, can have smaller lens than for their 35mm slr camera. I am not familiar with 4/3 system, but IIRC they make fast lenses in the smaller form than their 35mm slr camera counterpart. But, IIRC the first lens' element can't be made smaller as the rules for aperture.

Regards,
Arto.

For a 70-200mm on 135 format equivalent field of view, Olympus has the 35-100/2.0 (2x crop factor). To get f/2.0 for 200mm, the diameter would be at least 100mm. This would result in a huge lens. For the Olympus, only 50mm diameter is required to give f/2.0 for 100mm. This would result in a much smaller lens to achieve the same FOV on 4/3rd system.

 

[raincool2005]

F1 coming to SG...

u will need fast lens for tat racing car.

 

[Artosoft]

For a 70-200mm on 135 format equivalent field of view, Olympus has the 35-100/2.0 (2x crop factor). To get f/2.0 for 200mm, the diameter would be at least 100mm. This would result in a huge lens. For the Olympus, only 50mm diameter is required to give f/2.0 for 100mm. This would result in a much smaller lens to achieve the same FOV on 4/3rd system.

Ah yes..., understand. Because of the crop factor, equivalent FoV for focal length to 135mm lens, 4/3 system or DX lens can achieve smaller front lens element size. Result on smaller lens than its 135mm lens counterpart .

Regards,
Arto.