Having an f/1.4 lens and not using it wide open ...

bobbyz wrote in post #12121544
Not as simple, my 300mm f2.8 IS will focus lot faster than 85mm f1.2. Even 400mm f5.6 focus lot faster than most f1.4 lenses. But I get your point.

You're absolutely right, aperture is not the ultimate determinant of focusing speed, and it would only be relevant in lower lighting.

cancan7 wrote in post #12121219
Well, if you use it at f2.8 or smaller apertures, why not use a fast zoom, yeah it's bigger, but you have much more flexibility.

Generally speaking, using a fast prime at f/2.8 is different than using a f/2.8 zoom at f/2.8 if we're talking in terms of sharpness.

smythie wrote in post #12121469
A bunch of reasons already mentioned:
- much brighter viewfinder (the lens will sit wide open until you squeeze the shutter)
- arguably better optics from the prime over the zoom
- some like the shooting experience of a prime more than a zoom

If you want a fair bit of depth of acceptable focus (i.e. smaller than f/2.8) at a 50mm focal length and you had the time and inclination to do the image the best justice would you pick the 17-55 over the 50L?

Don't get me wrong, I love fast primes so much I've got 2
Just that I find shooting events is so much more practical with a fast zoom. I think the 17-55 doesn't give up much in terms of sharpness, it has IS and I need to shoot wide since Canon doesn't have a 35mm or wider equivalent prime for crop cameras(not the ultra expensive 24L please).

So I have the 17-55 on my 7D, and the 50L on the 400D, to have the best of both worlds.

dmnelson wrote in post #12121550
Hmm, good to know. The difference is certainly visible on my 1Ds Mark II, though it's barely perceptible if only stopping down from 1.4 to 1.8, for example.

I recently found out my 7D wont show much difference beyond f/4 when it comes to DoF, Makes manually focusing lenses a bit of a pain

Most other focusing screens are calibrated for f/2.8 and slower, there are special ones for faster lenses that arent as bright but more accurate

Basically grinding a screen brighter means it wont show DoF as well with faster lenses....but it will make slower lenses look brighter in the viewfinder

smythie wrote in post #12121490
the difference will be two stops. Try setting your lens at an aperture two stops smaller than its widest setting (eg your 1.4 at 2.8) and pressing the DOF preview button. The viewfinder will become darker.

I did read on this site somewhere that some camera bodies limit what you see through the viewfinder to f/3.5. I have just tried it on my 5Dc with an f/2 lens but it does seem to get fractionally darker from f/2 to f/2.2 so maybe it doesnt happen on that camera. I did try it a long time ago when I had my 50D so maybe its crop cameras that limit it?

Related to this, can you tell me:

A lens has a sweet spot in the aperture which is not at it's widest, and not at it's smallest.

If you have a faster lens, say a 1.4 as opposed to a 2.8, then would the sweet spot be at a slightly wider aperture? This would mean you would get the benefit of sharper images whilst using a wider aperture (but still not have to use the widest).


Cheers

@rusty, I don't have my 50 f/1.8 with me at the moment but playing with my 28-75 and Sigma 150 (both 2.8 so apply necessary salt) on my 40D shows a difference stopping down from 2.8. This is noticeable at each 1/3 stop, though the difference between 2.8 and 3.2 in the viefinder is less so the longer the focal length used.

There are quite a few folks that shoot wide open with fast lenses on bright sunny days outdoors and use ND filters to still get the desired DOF effects in the photo. So having an f1.4 lens providing it is sharp in the center wide open can be used for more then low light captures.

http://www.bhphotovide​o.com …75657&is=REG&A=​details&Q=

Regards,

Silverfox1 wrote in post #12123031
There are quite a few folks that shoot wide open with fast lenses on bright sunny days outdoors and use ND filters to still get the desired DOF effects in the photo. So having an f1.4 lens providing it is sharp in the center wide open can be used for more then low light captures.

It's really annoying hitting 1/8000s or whatever the fastest shutter speed is and having it over exposing. I've never considered getting an ND filter until recently getting some shots in bright sun just recently @ F/2 and wishing the camera had ISO50 (or even lower).

gonzogolf wrote in post #12120714
If I had a lens that fast it would be because of the quality of the glass, not for my need to shoot at 1.4. I dont know that 1.4 would give me enough depth of field anyway so I doubt I would use it much.

Exactly my line of thinking. Glass quality, build quality and performance leads to the results we look for. Not so much being able to narrow DOF to a quarter inch!

dave

Invertalon wrote in post #12121050
Me love some 85L wide open... Stopped down, it just gets eye-bleeding sharp. So it works well on both ends

Now THAT'S what I'm talking about!!!

dave

I admit that I have the wide open phobia. I'm trying to combat it though, but I'll still aperture bracket if it's critical.

phreeky wrote in post #12123089
It's really annoying hitting 1/8000s or whatever the fastest shutter speed is and having it over exposing. I've never considered getting an ND filter until recently getting some shots in bright sun just recently @ F/2 and wishing the camera had ISO50 (or even lower).

I agree and if i were really into landscape or horizon captures i would consider the Lee or Cokin rectangular holders, but for what i do the screw on ND`s work just fine.

http://maxsaver.net/Ho​ya-Neutral-Density.aspx

http://www.cokin.fr/ic​o1-p1.html

http://maxsaver.net/se​arch.aspx?find=cokin+h​older

http://www.cs.mtu.edu …ide/filter/filt​er-ND.html

Regards,

krb wrote in post #12121106
Regardless of what aperture you are using for your images the lens will be f/1.4 during all the other times while you are looking through the viewfinder, focussing, etc. Besides, even if you only ever really need it once a year, at least you will have it that one time each year.


You obviously don't do macro. Depth of field gets smaller as the distance gets shorter and at macro distance the depth of field is razor thin even at very small apertures. f/1.4 at macro distance would give a depth of field that is literally razor thin.

Yeah, and just the edge of the razor, not the rest of the blade. I've already done shots where the DOF was less than "paper thin": the surface of the top sheet was in focus while the surface of the next sheet in the stack was not.

It looks like the restriction to an apparent f/3.5 through the view finder only applies to the 7D (see post number 25 onwards):
https://photography-on-the.net/forum/showthre​ad.php?t=844294

However I know I read it somewhere else as well that in some cases the viewfinder will not show the DoF of fast lenses. I will see if I can dig further....