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03/02/2006 11:04:55 AM · #1 |
I have a Canon EF-S 18-55mm F-3.5 -5.6 lens. I want to buy a 2X converter. If I do I am pretty sure I will get a 36-110mm lens pretty much. But what will my F stops be will they double as well?
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03/02/2006 11:12:38 AM · #2 |
Not sure about the converter, but remember you have a 1.6 crop factor with your camera. So your 18 to 55 is really like a 28.8 to 88 mm lense.
Message edited by author 2006-03-02 11:13:54. |
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03/02/2006 11:12:51 AM · #3 |
Yes, you will loose 2 stops. Your lens would be something like F8-11. Now, it is possible your camera won't be able to autofocus the lens. I don't know about Canon gear, but on Nikon, it can't autofocus at F8 and up.
That's why teleconvert are used on f2.8 or f4 lens only. |
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03/02/2006 11:16:13 AM · #4 |
| Now that someone is on this subject (I've been meaning to ask). How do you figure the difference between a 1/3 or 1/2 stop compared to a whole one? IE how do you know if the jump from f2.8 to f5.6 is a whole stop or whatever? Thanks! |
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03/02/2006 11:16:35 AM · #5 |
Originally posted by fplouffe:
Yes, you will loose 2 stops. Your lens would be something like F8-11. Now, it is possible your camera won't be able to autofocus the lens. I don't know about Canon gear, but on Nikon, it can't autofocus at F8 and up.
That's why teleconvert are used on f2.8 or f4 lens only. |
ouch!! Thats good to know in advance. Does anyone know if this applies to the 350D?
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03/02/2006 11:19:10 AM · #6 |
Originally posted by tristalisk:
ouch!! Thats good to know in advance. Does anyone know if this applies to the 350D? |
I think for Canon, you lens should be able to support F5.6 for autofocus to work. So you can't really add an extender to an already F5.6 lens. |
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03/02/2006 11:23:00 AM · #7 |
Originally posted by goinskiing:
Now that someone is on this subject (I've been meaning to ask). How do you figure the difference between a 1/3 or 1/2 stop compared to a whole one? IE how do you know if the jump from f2.8 to f5.6 is a whole stop or whatever? Thanks! |
I know there is a scientific explaination behind the F stops numbers; but I never remember it. Basically, all you have to remember is that 1 and 1.4 are the first two full stops. Then, you create two series where you double the F stop number:
1 -> 2 -> 4 -> 8 -> 16 ...
1.4 -> 2.8 -> 5.6 -> 11.2(rounded to 11) -> 22 ...
when you mix both series in sorted order, you get full stops increments
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22
Message edited by author 2006-03-02 11:23:33. |
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03/02/2006 11:27:39 AM · #8 |
Originally posted by goinskiing:
Now that someone is on this subject (I've been meaning to ask). How do you figure the difference between a 1/3 or 1/2 stop compared to a whole one? IE how do you know if the jump from f2.8 to f5.6 is a whole stop or whatever? Thanks! |
I keep mine at 1/3 stop increments. so my fstop would look like
2.8, 3.2, 3.5, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1, 8.0
1-stop increments would have been 2.8, 4.0, 5.6, 8.0
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03/02/2006 11:30:52 AM · #9 |
Originally posted by tristalisk:
I have a Canon EF-S 18-55mm F-3.5 -5.6 lens. I want to buy a 2X converter. If I do I am pretty sure I will get a 36-110mm lens pretty much. But what will my F stops be will they double as well? |
Forget the idea! The 2x will not work with the EF-S series of lenses - nor will the 1.4x. They do not mount to it. |
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03/02/2006 11:55:44 AM · #10 |
Even if you could mount an EF-S on a 2x TC, you'd still find it doesn't make much of a difference for your needs though. You move from a moderately useful, but slow 18-55 to an optically poor lens that has a maximum aperture of something like 6.x and won't autofocus.
Pointless.
I thought of this idea too when I was first getting into things.
Really, you are going to be far better off with a separate lens.
The Sigma 70-300mm is a wonderful complement to the 18-55 and costs pretty close to what the 1.4x TC does.
I guarantee that it will kick the poopin's out of any jury-rigged 18-55+ 1.4xTC with taped contacts.
If you want some really nice quality in the 120mm range, you could consider an 85mm 1.8 by Canon. They sell for around 300-350 dollars and can be found even cheaper in the 2nd hand market.
Fantastic lens.
The internal workings of the autofocus system need to be able to see light that comes in from the edges of a certain area. It is this refracted light that allows the comparison in the split-prism focusing design used by Canon Cameras. The light from the center of the lens doesn't have a dramatic enough angle to allow really clear focusing decisions. This means that the wider the overall lens aperture is (remembering that when you look through the lens, you are going to see wide open, the aperture only shuts down when you take the picture or use the DOF preview), the easier it is for the camera to make the decision. Hence some upper end cams (20D, 30D, 1D series) have extra AF sensors that take advantage of really wide lenses which have really wide light paths. Once you pass a maximum of 5.6, you will lose AF because it is like you are putting a blindfold over the sensors that need to see.
It is possible that there are still some sensors that are able to 'see' in the center AF zone and it seems that some people have taken advantage of that. You can read up on it. I forget who, but someone here has reportedly used stacked TC's with a max aperterure of around F11, and still had some use of Center AF with the taping trick.
Incidentally, the 1.4x TC loses 1 stop and the 2x TC loses 2 stops. The 1.4x is usually reported as not detracting noticeably from optical quality, whereas the 2x is generally considered to add softness.
They are generally recommended only for constant aperture lenses. They aren't even supposed to work with the 70-300mm.
Some older Canon lenses don't work with the Canon TC's either. Kenko is sometimes a better choice apparently. |
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03/02/2006 03:45:37 PM · #11 |
Wow thanks for the help. I glad I asked before I waisted my money. Guess I will have to wait a little while and buy the cannon or sigma 70-300mm.
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03/02/2006 04:09:49 PM · #12 |
Had a follow up question on this info:
If I use a 1.4 Teleconverter on my Canon 100 2.8 macro and I will lose 1 Stop. Does that mean If I shoot at 2.8 my effective F Stop is really 4? Or do I need to set the Camera on 4. Or is setting it on 4 just going to make it an effective F Stop of 5.6?
Thanks. |
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03/02/2006 05:34:57 PM · #13 |
Originally posted by seenosun:
Had a follow up question on this info:
If I use a 1.4 Teleconverter on my Canon 100 2.8 macro and I will lose 1 Stop. Does that mean If I shoot at 2.8 my effective F Stop is really 4? Or do I need to set the Camera on 4. Or is setting it on 4 just going to make it an effective F Stop of 5.6?
Thanks. |
It is just like putting on a filter that saps off some of the light, the camera will adjust automatically. With the camera set to Apperature priority, Shutter priority or Program you will see only F4 as the widest apperature available. At least that is how Nikon works.
Message edited by author 2006-03-02 17:35:19. |
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03/02/2006 06:42:46 PM · #14 |
| I use on a regular basis a Kenko 2X 300 PRO on a Canon 70-200 f/4 L lens and it gives great results. It does not auto focus so you have to be ready or quick is the subject is moving. If most of your shots are sunny day shots it will work fine with manual focus. If you have a problem up the ISO to 200 or 400 and give it a try. If I focus correctly and accurately the results are very sharp. I'm glad I went with the 2X over the 1.5X. |
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03/02/2006 07:03:19 PM · #15 |
Originally posted by fplouffe:
I know there is a scientific explaination behind the F stops numbers; but I never remember it. Basically, all you have to remember is that 1 and 1.4 are the first two full stops. Then, you create two series where you double the F stop number:
1 -> 2 -> 4 -> 8 -> 16 ...
1.4 -> 2.8 -> 5.6 -> 11.2(rounded to 11) -> 22 ...
when you mix both series in sorted order, you get full stops increments
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 |
the scientific explanation is rather easy.. it's the focal length of the lens divided by the with of the aperture..
like 50mm lens you divide 50mm with the with of the aperture (EF 50mm f1.4 is 35.7mm) wich will give you the max aperture of f1.4.
each fstop is the sqrt of 2 x the number of the last fstop..
so the biggest possible fstop is 1 (don't know if there is a lens with f0.7 ;)
so it goes f1*2sqrt=f1.4*2sqrt=f2*2sqrt=f2.8*2sqrt=f4*2sqrt=f5.6*2sqrt=f8*2sqrt=f11*2sqrt=f16*2sqrt=f22*2sqrt=f32*2sqrt=f45*2sqrt=f64
or f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64
that's the scientific explanation...
Message edited by author 2006-03-02 19:05:06.
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03/02/2006 07:04:34 PM · #16 |
Originally posted by jbsmithana:
It is just like putting on a filter that saps off some of the light, the camera will adjust automatically. With the camera set to Apperature priority, Shutter priority or Program you will see only F4 as the widest apperature available. At least that is how Nikon works.
I don't think this is happening on my camera. I'm using the Canon 5D. I almost always shoot manual. When I put the 1.4 converter on my 100mm 2.8 Macro USM the 2.8 Fstop is still available so I'm still confused. Let me ask the question one more time. Maybe i'm just a little slow on the uptake. LOL : -P
Originally posted by seenosun:
------------------------------------------------------------------------
If I use a 1.4 Teleconverter on my Canon 100 2.8 macro and I will lose 1 Stop. Does that mean If I shoot at 2.8 my effective F Stop is really 4? Or do I need to set the Camera on 4. Or is setting it on 4 just going to make it an effective F Stop of 5.6?
Thanks. |
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03/02/2006 07:12:07 PM · #17 |
seenosun.. you do not have the Canon EF 1.4x II converter, I have the 100mm f2.8 macro and the 1.4x from Canon and they do not fit together..
many of the cheap converters do not tell the lens that they are attached so you can fool the camera in thinking you have the max aperture of the lens, even if you actually are loosing 1-2 stops.
I've not tested it, but I think you might be underexposing your shots by 1 stop by shooting this way.
I have a 2x converter from Kenko and if I put it on my 5D and then the 1.4X with the 70-200L f2.8 IS then the camera thinks I only have the 1.4X on and gives me max aperture of f4 instead of f8, so autofocus works perfectly.. but image quality is rather poor since the Kenko converter is a cheap $90 crap ;)
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03/02/2006 07:39:20 PM · #18 |
DanSig - Thanks for the reply. i'm using the Tamro SPAF 1.4 Teleconverter. My Autofucus works. I will test to see if the exposure is one stop less.
Edited to Add:
DanSig - Based on my test ... It looks like i'm losing 1 stop of light.
Message edited by author 2006-03-02 19:48:55. |
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03/02/2006 08:36:53 PM · #19 |
Originally posted by DanSig:
seenosun.. you do not have the Canon EF 1.4x II converter, I have the 100mm f2.8 macro and the 1.4x from Canon and they do not fit together..
many of the cheap converters do not tell the lens that they are attached so you can fool the camera in thinking you have the max aperture of the lens, even if you actually are loosing 1-2 stops.
I've not tested it, but I think you might be underexposing your shots by 1 stop by shooting this way.
I have a 2x converter from Kenko and if I put it on my 5D and then the 1.4X with the 70-200L f2.8 IS then the camera thinks I only have the 1.4X on and gives me max aperture of f4 instead of f8, so autofocus works perfectly.. but image quality is rather poor since the Kenko converter is a cheap $90 crap ;) |
Kenko makes a couple different TC. The 2X 300 Pro is a fine piece of glass and I've seen very litte problem with it. The cheaper $90 may not be as good. As with all companies, there are several different levels of quality. The Kenko 300 Pro's are very good. |
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03/02/2006 09:08:30 PM · #20 |
| You may want to look at the Canon 70-300 IS lens. (or if you've an unlimited budget, the 70-200 f/2.8 IS lens). Note there was a 75-300 IS lens, but it was not as good. |
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03/02/2006 09:11:20 PM · #21 |
Not reading all of the replies, forgive me if there are redundant answers, but:
A Canon 2x tele (nor the 1.4x) will work with that 18-55.
Also, third party lenses may work, but I have a feeling the back element of the 18-55 will touch the teleconverters glass, not a good idea.
Finally, for the price of a Canon 2x (cheaper actually), you could just buy yourself a 28-105 3.5-4.5. It's a good lens for 200 dollars new, and while it's not tack sharp, it's USM, well built, and compact.
If you got the cash, the 24-105 would be suitable, and if you needed faster glass, the 24-70 would be great (though you could opt for a tamron 28-75 and save uber bucks).
Max
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03/02/2006 09:17:47 PM · #22 |
Originally posted by seenosun:
DanSig - Thanks for the reply. i'm using the Tamro SPAF 1.4 Teleconverter. My Autofucus works. I will test to see if the exposure is one stop less.
Edited to Add:
DanSig - Based on my test ... It looks like i'm losing 1 stop of light. |
FYI - Tamron also makes two versions of their televonverters. I use the pro version and it does "talk" to the camera. Like DanSig says not all teleconvertes communicate properly so that is likely the issue. |
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03/02/2006 10:16:00 PM · #23 |
| Jbsmithana - If i'm not mistaken the SP AF 1.4 teleconverter is the pro model. Maybe it's just a Canon thing. |
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03/02/2006 10:47:05 PM · #24 |
Originally posted by DanSig:
Originally posted by fplouffe:
I know there is a scientific explaination behind the F stops numbers; but I never remember it. Basically, all you have to remember is that 1 and 1.4 are the first two full stops. Then, you create two series where you double the F stop number:
1 -> 2 -> 4 -> 8 -> 16 ...
1.4 -> 2.8 -> 5.6 -> 11.2(rounded to 11) -> 22 ...
when you mix both series in sorted order, you get full stops increments
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 |
the scientific explanation is rather easy.. it's the focal length of the lens divided by the with of the aperture..
like 50mm lens you divide 50mm with the with of the aperture (EF 50mm f1.4 is 35.7mm) wich will give you the max aperture of f1.4.
each fstop is the sqrt of 2 x the number of the last fstop..
so the biggest possible fstop is 1 (don't know if there is a lens with f0.7 ;)
so it goes f1*2sqrt=f1.4*2sqrt=f2*2sqrt=f2.8*2sqrt=f4*2sqrt=f5.6*2sqrt=f8*2sqrt=f11*2sqrt=f16*2sqrt=f22*2sqrt=f32*2sqrt=f45*2sqrt=f64
or f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64
that's the scientific explanation... |
It goes like that (multiplied by sqrt2) because every time the diameter of the aperture is multiplied by sqrt2, the area of the aperture doubles so you get twice the light. So, in every stop you get twice as much light as in the stop that follows it.
Since whatever you do to the f/number, you do the opposite to the diameter of the aperture, then every time you increase (multiply) the f/number times sqrt2, you are decreasing (dividing) the diameter of the aperture by sqrt2.
The change in the area of the aperture (the amount of light) is whatever happens to the diameter of the aperture, squared, and since you divided the diameter of the aperture by (sqrt2), then you divide the area of the aperture by (sqrt2)^2 = 2... thus halving the amount of light.
I think the key part is: change in area = (change in diameter)^2
Let's say you want to compare the amount of light you get with f/4 and f/5... well you increased (multiplied) f/4 times (5/4)=1.25 to get f/5, which means you divided the diameter by (1.25), which means that you reduced (divided) the area by (1.25)^2 = 1.5625. another example, if you increase (multiply) your f/number by 9, then that decreases (divides) the diameter by 9, and your area is now divided by 9^2 = 81. etc.
Message edited by author 2006-03-02 22:52:58. |
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03/02/2006 11:13:19 PM · #25 |
okay one more FStop / Exposure question:
If I shoot:
100 iso / F4 / 25mm Lens / on 16mm Film
will the exposure match if I shoot:
100 iso / F4 / 50mm lens / on Full Frame Digital SLR (like Canon 5d)
I have a 16mm Motion Picture film camera and was wondering if I could use my DSLR to check the lighting and exposure before I start burning film at the rate of 24 frames per second.
edit to add:
Both are shot at the same shutter speed (1/50th of a second)
Message edited by author 2006-03-03 01:41:13. |
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