EF-S Crop Factor

[KevC]

Hey guys,

Ever since I got my drebel (I haven't played with it too much), I've been using my dad's old EF35-105mm f/3.5-4.5. The 35mm @ 1.6x crop factor is a little too big for me, so I'm gonna start using the kit lens a bit more. Now I'm wondering, since the EF-S is designed *specifically* for the 20D and 300D (right?) Does it still exhibit the 1.6x crop factor? Or is 17mm truly 17mm... instead of 28mm...?

Sorry for the newbish question.

[pcasciola]

Yes, you still need to multiply by 1.6x to get the effective focal length

[RJSorensen]

Crop factor is the same with the EF-S lens . . . @ 1.6

[Redbird_xo]

The drebel kit lens is not fast enough for almost all indoor situations. Be prepared to use flash a lot while taking indoor pictures.

My 2 cents.

[KevC]

Hm. That's disappointing. I was hoping for a fishy wide angle haha. Thanks for all the replies though!

[Alexia]

The drebel kit lens is not fast enough for almost all indoor situations. Be prepared to use flash a lot while taking indoor pictures.

My 2 cents.

I have noticed as long as there is good contrast on the AF point, the kit lens focuses immediately. Almost always have to use a flash, but I have gotten away with 1/100 handheld with no flash. I don't have another kit lens to compare mine to, but it is rather solid in construction. (Except for the barrel wobble.)

Yeah, silly 1.6 crop factor. Makes me want full frame! :lol:

[Sicily1918]

Yes, you still need to multiply by 1.6x to get the effective focal lengthSo the purpose of labeling them as EF-S is what? Because it's cool? :confused:

I mean, they're certainly not cheap (well, some are) lenses -- what's the point of the new format? And will any of my sentences not be questions?

:mrgreen:

[gcogger]

EF-S is a different mount for a start.
The main reason for them, however, is that an EF-S lens will NOT work on a full-frame camera. The image circle they project is smaller than a 35mm frame, so the corners would be black.
Theoretically, they should be smaller , lighter and cheaper than a lens designed to work on full-frame. Doesn't seem to be the case on the EF-S 17-85, however ;-)

[tim]

AFAIK the only point of EF-S lenses is for a lighter, cheaper lenses, like gcogger said.

[Jesper]

As far as I know, the S in EF-S is for Short back focus.

That means that the glass element of the lens at the back protrudes further into the camera than with other EF lenses. If it would be possible to mount an EF-S lens on a full-frame EOS camera, the mirror could hit the back end of the lens and get damaged - that's the reason that EF-S lenses do not physically fit on other cameras than the 300D and 20D.

Because of the 1.6x crop factor, the 300D and 20D have smaller mirrors, which don't hit the back end of the EF-S lenses.

The lens mount of the 10D is not compatible with EF-S simply because EF-S wasn't invented yet when the 10D was introduced.

[RDKirk]

Hey guys,

Ever since I got my drebel (I haven't played with it too much), I've been using my dad's old EF35-105mm f/3.5-4.5. The 35mm @ 1.6x crop factor is a little too big for me, so I'm gonna start using the kit lens a bit more. Now I'm wondering, since the EF-S is designed *specifically* for the 20D and 300D (right?) Does it still exhibit the 1.6x crop factor? Or is 17mm truly 17mm... instead of 28mm...?

Sorry for the newbish question.

The lenses are what they are marked. A 17mm is a 17mm, period. If you don't use a 35mm camera, there isn't any particular need to know what it would be on a 35mm camera--you only need to know what it is on your camera.

The APS-C format is its own format, just like medium format is its own, just like 4x5 is its own format. It's just smaller than 35mm instead of larger. APS-C cameras happen to be able to mount lenses that also fit 35mm cameras, but don't worry about them.

The problem, though, with using lenses designed for 35mm cameras is that few of them are short enough to provide ultra wide angles on an APS-C camera. That's because for one thing, it's really, really hard to design a good ultra wide lens that covers the entire 24x36mm format of SLRs because they have a big mirror box that keeps designers from getting any closer to the film (there are quite a few ultra-ultra-wides for 35mm rangefinder cameras because they don't have that mirror box).

However, APS-C cameras can have a smaller mirror (didn't happen with earlier models because Canon was in a hurry to get them to market) and they have a smaller format. So it's a tad easier to design very short lenses for them--a good thing because they need it.

This does NOT mean that EF-S lenses will be either lighter, smaller, or cheaper, only that they can be shorter (or, if zooms, start out shorter). Canon could make longer EF-S lenses that were lighter, smaller, or cheaper, than the current EF lenses, but that wouldn't fill any market voids--Canon already has cheap EF lenses.

[Akreager]

The multipliers are for us old farts who learned the old system an think that way. It is sort of like asking someone is it cold outside....They say it's 20 degrees....thats cold....no 20 deg C.....Oh that's warm isn't it....let's see what is 20 C.....

Get my point. No it is not that hard... At least an effort to set/keep with a standard.

That being said. Whithout going into it deeply the idea that you can make a digital crop lens equal the quality of of a full frame lens and do it smaller and cheaper does have merit. When manufacturing a lens element it is for sure easier to make the same quality element if you make it smaller. The problem is it does not really scale down equal. Making the lens perfom edge to edge is less dificult as it get smaller but if you are using an L type lens on a digital system you are only using the "sweet spot" of the lens. Sounds good right. Then you have to pay the full price of an L and lug the weight around. You also have to deal with the crop factor. There is a good reason why the standard lenses came in their focal lenths. 28-70 for example. Now that is 45-112. Much less useful.

There are other things to consider. All things being equal. The physics say the smaller lenses will focus faster. The thing is they don't. Canon just has to spend less to get them to focus the same. The other thing is depth of field. The physics dictate (and Canon can do nothing about it)that the smaller lenses will have larger depths of field at equal Fstops. This is an advantage or not depending on what you want/need.

Bottom line is each lens is diferent. Evaluate it for what it is and how it works for you/your needs. A specific example (Nikon - sorry I started with the D70) for me is as follows:

Got the kit lens with the D70. 18-70(28-105). Performed equal to Nikons consumer 28-105. Did not focus faster. Was not cheaper. Was just a little lighter and smaller - who cares the original was small and light enough. It was not cheaper than the 28-105....In fact they charged more. What I got was a consumer grade kit lens with a convienent focal length that allowed me to dangle my toes in the digital ocean.

Wow...I like this digital stuff. I want to go deeper. What to buy next? Nikons standard 28-70F2.8 at $1600. It will convert to 42-105 - not a great length. How about the 17-55F2.8DX for $1300. Now we are talking. It is just ever so much smaller than the 28-70. It had an edge to edge sharpness = to if not better at all focal lengths, It had good contrast..... it focused like a rocket and it converted to 27-82....PERFECT. The only thing is - I just spent $1300 on a lens that will only work on the 1.5 crop factor cameras. If Nikon comes out with full frame, I am screwed. Problem solved - see below.

Now this won't work for everyone, but this is what I did. I always wanted a lens that would give pro quality and go from 20mm to 500mm - WE ALL DO! We all went thru some type of learning curve to determine it would not happen. Well I got a 1DMarkII and a 70-200F2.8L IS along with a 1.4 converter. I now walk around with my D70 and the 17-55 and the MII with the converted 70-200. It gives me pro quality range from (27-82)&(127-364). I retained my 3 SB800 flashes for use with the D70. I also got a Canon 15mm Fish, 35(45)F1.4L for low light, 50F1.4, and 300F4L IS. I will probably replace my D70 with the D100 replacement that will be out this summer and an 85mm F1.4ED (Nikons L type) to match. It is my dream system. There is not one combo of situations that I will not be able to handle quickly and efficiently. I plan to stick with it for the next five years at least even if they come out with a new system that will pick you up at your house, fly you to all the most exotic locations, provide you with professional models, and then help you with all your dificult post processing issues - and it is free. I am not biting. I am going to quit researching pixels and spend the next five years taking pictures....what a crazy idea!

Please no comments about sticking with one system etc. My point is this worked for me. You need to find what works for you. Do not always just go with the flow and what everyone else does.

[Jon]

The multipliers are for us old farts who learned the old system an think that way. It is sort of like asking someone is it cold outside....They say it's 20 degrees....thats cold....no 20 deg C.....Oh that's warm isn't it....let's see what is 20 C.....



I LIKE that! Says it all, and it should cut down on follow-up posts arguing about (never mind!).

[pierrot]

:mrgreen:

[T'Kethry]

An EF-S lens on a Digital Rebel/20D modifies the multiplication factor from 1.6 to 1.3; that's what the the "short" in the short back focus is for.

[Jesper]

An EF-S lens on a Digital Rebel/20D modifies the multiplication factor from 1.6 to 1.3; that's what the the "short" in the short back focus is for.Huh ??? You're wrong. The 300D and 20D both have "1.6x crop factor" sensors. EF-S lenses do not modify the multiplication factor at all.

An EF-S lens set at a focal length of 18mm will give the same field of view as an 1.6 x 18 = 28.8mm lens on a full-frame 35mm camera.

There's nothing with the 1.3x factor involved. The 1D and 1D Mark II have a sensor with an 1.3x crop factor, but EF-S lenses don't fit on those cameras. The 1.3x factor doesn't have anything to do with EF-S lenses.

[Jon]

All right class, repeat after me:
"A focal length is a focal length is a focal length"

Cra^hop factor has absolutely nothing, as Jesper says, to do with it.

[gcogger]

Um... who said a focal length was anything other than a focal length?

[Jon]

Not you, me or Jesper, but several others are ringing in the focal length/cra^hop factor relationship.