Urgent help needed on Teleconverters!


Status
Not open for further replies.

Tweek

Senior Member
Jan 17, 2002
2,027
0
0
38
East
www.weekai.com
#1
I just got a Kenko MC-7 2X TC, intend to use it on my 80-200 f2.8. The loss of 2 stops of light to f5.6 isn't reflected by the camera, I could still dial to f2.8 with the TC attached.

My question is, do I need to dial to f5.6 myself (say in Av mode), to make sure that the exposure will be correct? I remember Edmund mentioning this in one of the threads. But then, Daniel from TCW told me that there is no need to, just shoot as normal. A nature photography website says the same thing. I tested the exposure of a same scene with and without the TC, at f2.8. Without the TC it was 1/15s, with the TC it was 1/4s (both at f2.8). This seems to show that the metering system has taken into account the loss of 2 stops of light already, is that right?

Need the answer by tonight as I will be using the TC tomorrow. Don 't wanna screw up the exposure. :(

oh yah one last question, when I use a 2X TC on a f2.8 lens, do I get the DOF of a f2.8 or f5.6? Cuz only less light comes in, physical diameter of aperture remains the same, means DOF still stays at that of f2.8?
 

Adam Goi

ClubSNAP Idol
Staff member
#2
Originally posted by Tweek
I just got a Kenko MC-7 2X TC, intend to use it on my 80-200 f2.8. The loss of 2 stops of light to f5.6 isn't reflected by the camera, I could still dial to f2.8 with the TC attached.

My question is, do I need to dial to f5.6 myself (say in Av mode), to make sure that the exposure will be correct? I remember Edmund mentioning this in one of the threads. But then, Daniel from TCW told me that there is no need to, just shoot as normal. A nature photography website says the same thing. I tested the exposure of a same scene with and without the TC, at f2.8. Without the TC it was 1/15s, with the TC it was 1/4s (both at f2.8). This seems to show that the metering system has taken into account the loss of 2 stops of light already, is that right?

Need the answer by tonight as I will be using the TC tomorrow. Don 't wanna screw up the exposure. :(

oh yah one last question, when I use a 2X TC on a f2.8 lens, do I get the DOF of a f2.8 or f5.6? Cuz only less light comes in, physical diameter of aperture remains the same, means DOF still stays at that of f2.8?
The reason why you can't get the 'real' reading is that the TC can't 'communicate comprehensive enough' with your camera. (Sheeze...dunno which technical word/phrase to use but I guess you get my point). With the TC, your lens is actually @ f/5.6 max, i.e. you lost 2 f-stops. Don't worry about the accuracy of the corresponding aperture and shutter reading...they are metered as per normal (just that they are not 'displayed properly'), no need to compensate 2-stops or whatsoever. However, as per normal, do your bracketing when it comes to extra white/bright or ultra dark/black subjects and backgrounds.

In short shoot as per normal, just add 2 f-stops mentally whenever your look at the LCD, i.e. if it shows f/5.6, it's actually f/11.

To the experts, am I right? :dunno:
 

skf

Senior Member
Jan 18, 2002
607
0
16
Visit site
#3
as Adam pointed out, the system isn't smart enough to know that you added a TC in between the lens and the body. However, since the metering is thru' the lens, then the light loss effect has already been taken into consideration and hence you are not likely to screw up your metering, ..
 

Tweek

Senior Member
Jan 17, 2002
2,027
0
0
38
East
www.weekai.com
#4
thanks adam and skf, now I feel more assured. :) Was damn blur after reading all the variety of stuffs on the net. Thanks a lot!

Anyone can answer the DOF part? ;)
 

YSLee

Senior Member
Jan 17, 2002
2,326
1
38
Visit site
#5
Since effective aperture is f/5.6, what'd you think? For starters, measure check your meter readings through the same scene with and without the TC. And as for DOF, see my question..
 

NitroTech

New Member
Apr 4, 2002
546
0
0
43
In Paradise
Visit site
#6
Originally posted by Tweek
I just got a Kenko MC-7 2X TC, intend to use it on my 80-200 f2.8. The loss of 2 stops of light to f5.6 isn't reflected by the camera, I could still dial to f2.8 with the TC attached.

My question is, do I need to dial to f5.6 myself (say in Av mode), to make sure that the exposure will be correct? I remember Edmund mentioning this in one of the threads. But then, Daniel from TCW told me that there is no need to, just shoot as normal. A nature photography website says the same thing. I tested the exposure of a same scene with and without the TC, at f2.8. Without the TC it was 1/15s, with the TC it was 1/4s (both at f2.8). This seems to show that the metering system has taken into account the loss of 2 stops of light already, is that right?

Need the answer by tonight as I will be using the TC tomorrow. Don 't wanna screw up the exposure. :(

oh yah one last question, when I use a 2X TC on a f2.8 lens, do I get the DOF of a f2.8 or f5.6? Cuz only less light comes in, physical diameter of aperture remains the same, means DOF still stays at that of f2.8?
maybe you can read this and see if it helps?? most probably not... :)

http://www.kenrockwell.com/nikon/kenko.htm
 

jon33

New Member
Aug 18, 2002
495
0
0
37
go north!
www.imagestation.com
#7
was thinking of getting the kenko mc-7 2x teleconverter as well. how much did you pay for yours tweek?

any compatibility issues for this teleconvertor with the canon ef 75-300 III (non usm) or the 100-300 usm?
 

Tweek

Senior Member
Jan 17, 2002
2,027
0
0
38
East
www.weekai.com
#8
thanks nitro. :)

jon, I got it at TCW for $95, it's 2nd hand. It's the last piece there, even the Kenko Pro 300 is out of stock too. You may want to try fotoguide.

you can't autofocus with the 70-300, cuz effective aperture is f11 with the TC. The AF will hunt and give up. Also at f11, it's hard to get a good shutter speed esp when u are at the 300mm (eq. 600mm) end. It is recommended that you stop down the aperture by 1 to 2 stops for better sharpness when using TC, so that's f16 or even f22. You will get terribly slow shutter speed. Actually TCs are more suited for lenses of f4 and below, preferably 2.8 and below.
 

skf

Senior Member
Jan 18, 2002
607
0
16
Visit site
#9
Originally posted by Tweek
thanks nitro. :)

...

you can't autofocus with the 70-300, cuz effective aperture is f11 with the TC. The AF will hunt and give up. Also at f11, it's hard to get a good shutter speed esp when u are at the 300mm (eq. 600mm) end. It is recommended that you stop down the aperture by 1 to 2 stops for better sharpness when using TC, so that's f16 or even f22. You will get terribly slow shutter speed. Actually TCs are more suited for lenses of f4 and below, preferably 2.8 and below.
Generally, if the effective aperture is 5.6 or faster, you can maintain the AF function. Note that the key word here is effective. Here are a couple of examples
1) for a f2.8 lens;
with a 1.4 TC, effective max aperture is 4.0 (1 stop loss for 1.4) - so still can AF

2) same 2.8 lens with 2X TC => effective aperture is 5.6 (2 stops); still can AF.

3) for a f4.0 lens (eg 500/f4.0), with 1.4TC, effective it is a 5.6 lens, still can AF.

3) with the 4.0 lens, you get a effective aperture of 8.0. The TC manufacturer 's specs will probably say you cannot maintain AF function, but you may or may not be able to get AF and if you do, probably it may hunt a bit during the AF.

Well, off course, the above examples assume that the lens are AF lenses. ;)
 

Jed

Senior Member
Jan 19, 2002
3,911
0
0
UK
Visit site
#10
You get, for all intents and purposes, a 160-400/5.6 lens.
 

Status
Not open for further replies.
Top Bottom