Stupid question - F-stops / Lens Speed - Help

[slr_newbie]

I have asked this question of my photog friends and I am embarassed to say that I am still not sure I totally understand the answer, so I thought I would try my luck posting here.

I just purchased a 30D and I am a total newbie to using the creative side of the dial.

I have been reading several photography books to get an understanding of aperture, shutter speed, ISO, f-stops, etc. From what I have read, by looking at my lens I can see what my maximum aperture is for that lens.

For example, one of my lenses is a Canon 18 - 55 with 3.5 - 5.6 listed on the lens. I understand that this is a consumer grade lens and that there are faster lenses on the market that are used by the pros. With that said, I am trying to understand, what if any, limitations I have in using a given f-stop with the above lens.

Is this thinking correct?:

The smallest f-stop I can use with the above lens is 3.5, but I should be able to use any f-stop up to 22 when at focal length 18? When at focal length 55, the smallest f-stop I can use is 5.6 and any other f-stop (up to 22?) when zoomed in at focal length 55?

Anyone out there understand this concept enough to help clarify it for me? I have googled, etc., but I have not found an explanation that ties the aperture as inscribed on the lens to the f-stop. All I know is that in the books I have read the suggest using f-stops like f2, f8 or f11 (and they say ... "set the aperture") and it was unclear to me whether I could use these f-stops with this lens since the maximum aperture is 3.5 - 5.6 depending on the focal length.

Thanks for the help!

Anne

[HFMarshburnJR]

Anne -

Your self explanation is correct. I think you have a good handle on the concept. If you are shooting primarily landscapes and want to shoot at f-stops in the f11-f22 range, this lens is perfectly usable across it's entire zoom range. The issue wth this lens comes when you get into low light scenarios where you are trying to capture moving subjects. This lens should do everything that you need to do in an everyday good light environment.

Some of the books/articles you are reading may be making suggestions about blurring the background by shooting at large apertures (small f-stops). If this is what you are trying to accomplish, this lens will not be your best friend. Keep after it - it sounds like you have a good start on this SLR thing.

HFM

[DEMDeepEllumMusic]

OK on your lens the fastest that it can be opened up to is 3.5 and that is only at 18mm as you zoom in to 55mm that number will increase to 5.6 in stages (if you zoom very slowly and check you will see that it shifts from 3.5 to 5.6 in steps and not as a real curve so you may still be at 3.5 at 25mm and then it may jump to say 4.0 at 30mm-testing your own lense will get you when it steps and by how much).

Now there are lenses that are in your 18-55mm range that have a fixed maximum F in most cases the manufacturers pick 2.8 but here is a case of one that is a 4.0 over the range http://www.bhphotovideo.com/c/produc..._USM_Lens.html
(price is a bit high because of special high quality glass in the optics).

Now most lenses do not perform their best when wide open but usualy when they are stepped down 1/3 or more of a stop from wide open (nature of the beast) and in many cases their best performance is in the f 8-11 range.

As stated above you can close down your apererature on your lens down to f22 no matter where you are on your zoom range but it is best not try to to shoot with it closed down all the way (see note above) unless you are trying to get maximium depth of field in focust. As the opening gets smaller from f3.5 to f 22 your depth of field will deepen in the photo and if you have a model that allows you to step down your lens and your viewfinder is bright enough you can see the results in it before shooting. As a learning experience try shooting the same scene going from a depth of field from the max to the min on the lense and then look at your results-try to shoot something like a fence running off into the distance where you can really see the changes.

Otherwise your on the right track.

[mgadell]

Anne,

You are correct.

Lenses are usually described by their largest aperture (the smallest f-number). In the case of a zoom like yours, the maximum aperture ranges between f/3.5 and f/5.6 as the lens zooms between 18mm and 55mm. So at 18mm the largest aperture you can use is f/3.5, and at 55mm the maximum aperture you can use is f/5.6. The smallest aperture (the largest f-number) you can use is usually constant on a lens like that. It's probably f/22, but you can find out for sure by setting the camera to either aperture priority mode or manual mode and then, on the camera controls, adjusting the aperture number as high as it will go. It won't let you go any higher than the lens is capable of.

Assume you discover that the minimum aperture (highest number) for this lens is f/22. Then, with the lens zoomed to 18mm you'll be able to use any aperture between f/3.5 and f/22, inclusive. And with the lens zoomed to 55mm you'll be able to use any aperture between f/5.6 and f/22, inclusive.

The other thing to remember is that the 30D is smart enough to know the limitations of whatever lens is mounted to it, so it won't let you do something that the lens is incapable of.

Hope this helps.

Mike

[slr_newbie]

Thanks so much for the replies! This concept has been giving me some trouble so I am glad that I have figured it out analytically -- now I need to actually apply it!

Originally Posted by HFMarshburnJR

The issue wth this lens comes when you get into low light scenarios where you are trying to capture moving subjects. This lens should do everything that you need to do in an everyday good light environment.

Some of the books/articles you are reading may be making suggestions about blurring the background by shooting at large apertures (small f-stops). If this is what you are trying to accomplish, this lens will not be your best friend. Keep after it - it sounds like you have a good start on this SLR thing.

HFM

I have a couple more lenses and I am wondering if any of these would be better for low light / moving subject. I primarily will be photographing my children so I am trying to figure out what my go to lens should be when I want to blur the background using a larger aperture. Of course, I enjoy photographing flowers, landscapes, etc when the opportunity presents itself.

Other lenses:

100-300 Sigma f/4.5 - f/6.7
28-105 Sigma f/3.8 - f/5.6
28 - 135 Canon Ultrasonic f/3.5 - f/5.6

I am not opposed to selling some of the above lenses to invest in a good "go to" lens.

[iCe]

I would learn to use what you have before you sell any of them. You've got a nice focal range with what you have. The 30D is a nice camera so that's covered.

Low light typically means expensive. It's just how it is. My all time favorite lens is the 70-200mm f/2.8L from Canon (not counting the two big primes that I have) and at f/2.8 it's at the edge of what I call "low light". My favorite lower light lens is my 85mm f/1.2L. If John Stovall sees this thread he'll bust in here with some kind of f/-2million mondo glass o-matic lens that they only made one copy of because more than one would suck all of the photons from the center of the galaxy and all matter as we know it will revert back to whence it came but I digress Actually... John owns some seriously fine low light glass... so I hope that he does chime in...

Canon makes an 85mm f1.8 that I hear is a good piece of glass.

[HFMarshburnJR]

Anne -

Many of us on here justify our vice in the name of photographing our children. In my case it is my almost 6 year old daughter. I ended up buying my first piece of "fast" glass after a particular disastrous shooting evening at her very first dance recital. All of that background leads up to this question ...

Photographing your children ...doing what?

As far as reasonably inexpensive low light / "fast glass" goes, you can get the Canon 50 / 1.8 (approx. $100), the 85/1.8 that Michael mentioned above (approx. $350) and the Sigma 24-60 or 24-70 /2.8 (approx. $425). All of these are reasonably inexpensive first additions for low light. If you are shooting indoor events with the kids, any of these lenses would be useful. If you are shooting evening sports activities, then you are probably going to come to the bridge where you are looking at a longer telephoto (the most popular of which seems to be the 70-200mm /2.8 lens) - and that is when you are going to have to start robbing the kids piggy banks.

Isn't this a great hobby? Hope this helps. Have fun.

HFM

[DEMDeepEllumMusic]

If your not doing sports but just portrait/posed type shots look at one of the primes 50, 55, 85, 100, 125 etc in at least a 2.8 an preferabley 1.8 or faster glass and don't forget considering a used lens that has been kept up. Going to a prime (fixed focal length vs zoom) helps the designer/engineer of the lens cut down on the number of elements inside of the lens and to specifically match the glass for a very specific focal length which can allow some inexpensive but fast glass over that of a zoom. The faster you go -closer to 1.0 (Yes there are some 1.0 f stop glass out there and even some rarer sub 1.0 glass)- the more you can create that wonderful background that is blurrred while the subject is crystal sharp that many people like in a portrait shot that can not be achieved with slower glass.

[slr_newbie]

I think that I am going need both, LOL! I love doing the standard portrait stuff, so a faster fixed lens might just do the trick for that and give me the effect that I am looking for. Ultimately, as my boys get older (they are 3 months and 2.5 years right now) I know that I am going to need a faster telephoto lens, but I might be able to hold off on that right now ... unless it just makes more sense to bite the bullet and get the Canon 70-200mm /2.8. What do you think? Will that lens give me the effect I want for portraits as well or is it better to get both? I would prefer to only invest once ...

Decisions, decisions, decisions ...

[HFMarshburnJR]

Anne -

You are going to ultimately want both. At that age, you are never going to be that far away from them, so I would start with the 50/1.8. It will give you the good bokeh (background blur) effect for your portrait type shots when you are shooting at aperatures of 1.8-4.0. It is an inexpensive and versatile lens and it is very sharp. As they get older and you start shooting them at t-ball and soccer games, you will probably want to invest in the bigger lens. No need to do that just yet...unless you just want to!!!

Have fun!

HFM

P.S. As far as investing goes - these lenses, with proper care, will last you a long time. They are not throw away investments. I use my 50mm 1.4 lens as a general indoor lens when everyone is generally pretty close. This is for family events and dance recitals (when I am up close!). So don't look at the choice as an either / or...different horses for different courses is the norm in this hobby.

[iCe]

If you have the resources, the 70-200 f/2.8L IS lens is probably one of the most versatile lenses that Canon makes. For the longest time it was seemingly glued to my camera. It's a little short for football, it works great for basketball. I always use my 300 f/2.8L for soccer (and football) so I can't speak to that. I would think that the 70-200 will work fine for t-ball and soccer though. It doesn't like a 2x TC so be aware of that (images are soft).

When you spend the money on "good glass" it's not wasted. Nobody that owns the 70-200 f/2.8L IS or non-IS complains about it

BTW- I don't disagree with Howard. Dollar for dollar the "nifty fifty" is a good lens.

[johnastovall]

Originally Posted by iCe

I would learn to use what you have before you sell any of them. You've got a nice focal range with what you have. The 30D is a nice camera so that's covered.

Low light typically means expensive. It's just how it is. My all time favorite lens is the 70-200mm f/2.8L from Canon (not counting the two big primes that I have) and at f/2.8 it's at the edge of what I call "low light". My favorite lower light lens is my 85mm f/1.2L. If John Stovall sees this thread he'll bust in here with some kind of f/-2million mondo glass o-matic lens that they only made one copy of because more than one would suck all of the photons from the center of the galaxy and all matter as we know it will revert back to whence it came but I digress Actually... John owns some seriously fine low light glass... so I hope that he does chime in...

Canon makes an 85mm f1.8 that I hear is a good piece of glass.

Just ordered my 85/1.2MkII yesterday. Will have it in hand Wednesday and I'll have completed the Canon sharpness trinity, 35L, 85L, 135L.

Right now except for the f/1.0 (which takes a lot of work and understanding to ring out it's best at f/1.0) my two favorite low light SLR lenses are the 35L and the 24L.

This was with the 35L hand held wide open at ISO3200.

On the range finder side of the house the CV Nokton 35/1.2 is very fine. This was at 1.2 ISO1600.


I think once you get above 1.4 you are needing a tripod or very steady hands and a brace at lest at the light levels I'm working with at 5am.

Here are some serious low light folios I've labeled the ones with tripod all the Zeiss 21/2.8 is off a tripod and the 24L of the moonset on clouds is off a tripod.

http://www.texasphotoforum.com/galle...ry.php?cat=885

http://www.texasphotoforum.com/galle...ry.php?cat=705

[zepp]

Originally Posted by johnastovall

Just ordered my 85/1.2MkII yesterday. Will have it in hand Wednesday and I'll have completed the Canon sharpness trinity, 35L, 85L, 135L.

Canon's sharpest lens by far is the 200mm f/1.8L. No other canon lens impresses me as much as this lens every time I use it.

[johnastovall]

Originally Posted by zepp

Canon's sharpest lens by far is the 200mm f/1.8L. No other canon lens impresses me as much as this lens every time I use it.

But it's not in production... I should have prefaced my remark about in production...

It's a shame they have not tried to make a Green version of it....

[zepp]

Canon's 400m f/2.8L is also an exceptional performer and highly regarded lens. Perhaps not as razor sharp as the 200mm f/1.8L but very near.