f2.8 nowhere near the same as f2.8??

D

Deon

New member
Hi guys.
I have a question.
I am currently in pre production for a short film which we will be shooting on super16 with an Aaton LTR camera and either a zeiss zoom or nikon primes.
During our pilot shoot my director and I relied heavily on my d90 as a point of reference; setting the camera up as per recomended light meter readings eg. set at 200 iso/asa, 1/50th at f2.8. This worked very well as a confidence boost (it was our first film shoot) and the rushes we got back were almost identical exposure and colour wise to the shots I took on the nikon.

This is where my question comes in though. I just purchased a second hand nikkor 50mm f1.4 a little while ago. After taking a reference shot with this lens at f2.8 and comparing it to a shot at 2.8 with my other fully manual lens (being a nikkor 60mm f2.8 macro) the results are so far different it's rediculous (the 50mm at f16 started to look similar to the 60mm at 2.8). Can any one shed any light on why this would be the case. I mean, I know the 50 is a "fast" lens but surely that only refers to the fact that it can open up to 1.4 and not how much light it lets through at 2.8?!? If so why would the ever trusted light meter reading be based around a recomended fstop/t stop.

Obviously I plan to use what I know works accuratly to the light meter's reading as a point of reference (being the 60mm) but Im just a little curious (and maybee slightly frustrated) as to why they are so different. Also, If possible we may actually use these nikon lenses on the aaton if we can track down a mount. With this conundrum on my mind though how will I ever be able to trust my little 50mm against a light meter?
It's a beautiful lens but is it freakish as well... a rouge? haha.
Any help will be much appreciated!
Cheers,
Deon.
 
This doesn't make any sense at all. Are you sure the iso and shutterspeed is the same?

If not, there is no good explanation that I know of. I have the same lenses, and no sign of your problem.
 
Not sure if this might be your problem-- but is your 50mm an AF or MF lens? If it's a AF 1.4D it does have an aperture ring, but to get fully manual control, you'll have to either tape over the contacts between the lens and body, or just not twist the lens fully into place when you mount it so the contacts don't align. That will effectively turn it into a fully manual lens. If it is the newer 50mm G lens (AF-S), it has no aperture ring and it won't be a very good lens to use. Hope this helps...
 
thanks guys.
yeah it has me really stumped!
I have taken cidentical shots with the same iso and shutter speed and they are way different.
The 50mm lens I have is completely manual and has no electronic contact points.. The 60 macro does have an electronically controlled aperture with a manual aperture ring also.
hmmm no good..
 
Not to insult your intelligence, but you're taking stills photos for reference right? Does the 60mm look similar to the 50mm at a given aperture in Aperture Mode when you hold down the Depth of Field button too? This has me stumped too.
 
You are discovering the difference between f-stops and t-stops. T-stop is a measurement of light coming through the lens, whereas f-stop is a ratio of the aperture opening, and as you've seen can vary depending on the lens. Most pro cinema lenses use t-stops for this very reason. I only have a limited understanding of this myself, so perhaps someone with more knowledge can shed more light (pun intended) on the subject.
 
Tim Joy said:
You are discovering the difference between f-stops and t-stops. T-stop is a measurement of light coming through the lens, whereas f-stop is a ratio of the aperture opening, and as you've seen can vary depending on the lens. Most pro cinema lenses use t-stops for this very reason. I only have a limited understanding of this myself, so perhaps someone with more knowledge can shed more light (pun intended) on the subject.
Click to expand...


Would it be that different being at f/11 = f/2.8 on another lens though? I thought Nikkors were supposed to be abit good. My 50mm f/1.4 (probably the same as the OPs), is only a little bit brighter and more colourful than my other Nikkor lenses but no more than 1 stop difference...
 
f-stops and t-stops are for all practical purposes the same on modern lenses. on some older ones the difference can be a stop, but mostly it's less than half a stop. there's absolutely no way of explaining this except that something is broken, either your lens or your test procedure. if the 50mm blades are a bit stuck they won't have time to close until the image is taken, a pretty common reason for overexposure. the lever that closes the aperture can also be broken, or the camera for that matter.
 
...hmmm interesting... I think, U dont able to control shutter and iso on D90...just the exposure. If U set 2.8 D90 set automaticli the shutter and ISO even U lock AL. D90 has no manual control, except exposure with D lenses...what U see on the lcd about shutter and ISO they are not the true data.
 
Yes, something is broken here. Allthoug, you should know that when u use the 60mm in macro mode it is no longer 2.8, probably around 3.2 and 4.5 actually even if the iris ring is set to 2.8.

However, you can't do comparison in macro since the 50mm is not a macro, and also the difference wouldn't be that great.
 
That's a really interesting point about the macro lens not being able to reach f2.8 when it's in "macro". I didn't know that the lens had a macro mode so to speak. I know it has a limit on the focus yet I never understood what that was for. Does this limit act as reference point as to when the lens is being put into macro mode? Eg. any closer focus past the limit point is the "macro mode".
Sorry for being so ignorant about this I really should be doing my own research on the lens!
Any way, regardless, the shots that I have taken were only with ambient light and I didn't use a controlled or unified light source. Although the light to my eye remained the same between shots I need to set up a proper test. I'll set up a proper test in a studio when I get a chance (probably next week) and get back to you all with what I find.
Thanks so much for the help.
Deon.
 
I'm an idiot! I just had a look into the fstop change on the macro lens and that's my problem. I'm guessing that as the barrel extends so much during changes in focus so does the ratio between the aperture and the overall length of the lens. I can't believe I have never picked up on this. I've been using it for months too. That's really bad! haha.
Hmm this could mean steering away from using it on the aaton if I can't get an accurate fstop setting as I set focus. We must have fluked it on our pilot..:thumbsup:
Thanks again for all your help, I really appreciate it.
Deon.
 
why do you use macro? is this a model shoot? and i still don't think this explains the difference between 2.8 and 16. the macro probably only loses a stop or so. so you haven't tested it, just guessing huh? that could definitely be the most plausible explanation yet.

/matt
 
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Sounds like you should have shot your project on the reference D90, he he. But seriously, you have a problem that can only be worked out by trials of the lenses. I reckon the problem is probably simple, I don't think it is to do with the extension of the barrel as you have claimed. but you will find it with trials.
 
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