Board index Photography Technical Questions Help with lenses please.

Technical Questions

Help with lenses please.

Discuss technical aspects of photography
becky_stead
 
Posts: 365

Help with lenses please.

Post Thu Mar 22, 2007 12:38 am


Hi everyone i need your help again im afraid. I recently took part in a discussion in the artistic question page on a topic about wedding photography. Someone suggested getting a 5omm prime for the wedding im shooting and i think it would be useful for my portrait work too. My problem is i recently spoke to a firend who said that because i use digital the lense would be equivilant to around 80mm. Firstly id like to know, just out of curiousity and the need to learn, how you work that out and secondly id like to know if 80mm will be ok for the job or if i should get a different lense that would be equivilent to 50mm. Its all complicated stuff and im sure on day i will finally put all the pieces together and actually know what im doing lol. Thanks in advance.

Becky

dang
 
Posts: 3780


Post Thu Mar 22, 2007 12:53 am


Hi Becky,
Yes.. they're correct. Most lenses are still rated for use on a 35mm camera which has a film size of 36x24mm. Most digital sensors are smaller, meaning that it sees more than the sensor. Thus, the crop factor. On most Canon DSLR's, the crop factor is 1.6, with some Pro Models being 1.3, and full frame such as used in the 5d.

The conversion for a 50mm works well for portraits, and the 50mm having a faster f/stop allows shooting with less light. So, most everyone adds one to their bag since it's priced so reasonable. Years ago, most portraiture photographers used a lens in the 75 to 100mm range since it's compression factor is flattering. Also, a faster f/stop allows you to easily set the subject apart from the background. All in all, it's a great choice and one I'd highly recommend for your intended purpose.

You'll still have your standard zoom for group shots if you need wider. So, it's a choice I think you'll enjoy.

rickl52
 
Posts: 239


Post Thu Mar 22, 2007 1:53 am


As dang pointed out, most cameras, unless they claim to be full sensor (same as 35mm film), have a crop factor. The sensor only sees a smaller piece of the image than traditional film at a given distance from the subject, therefore you have to back up to create the same composition with a smaller sensor. That is where the 1.6 crop factor comes in.

Let's say you have a 35mm film camera with an 80mm lens on it and you're composing for head and shoulders. Let's say this puts you about 8 feet from your subject.

With a copped sensor camera and a 50mm lens in order to get the same composition you would have to back up to about the same distance. This means the 50mm lens how sees what the 80mm lens sees on the full frame camera. Hence, the 50mm on the cropped is the equivalent of the 80mm on the full frame in terms of perspective and composition. And this is a flattering perspective for most people so the 50mm makes a good portrait lens.

Rick

becky_stead
 
Posts: 365


Post Thu Mar 22, 2007 2:03 am


Thanks for your help guys i really appreciate it. I kind of get what you say. I will get there in the end. Its a complicated business this photography lark lol, but seriously thanks i think its great i can come here and ask questions and people are so willing to help.
Becky

Actually ive just had a thought the lense doesnt come with a hood you have to buy it seperately ... do i need one??

dang
 
Posts: 3780


Post Thu Mar 22, 2007 8:13 am


Becky,
Lens hoods are good since they help with flair, but it's not going to stop you from shooting, especially inside where you're not in direct sunlight. UV filters are always a nice option too, since they protect the front element from getting scratched. Both are nice to have, but not mandatory.

supersignet
 
Posts: 101


Post Thu Mar 29, 2007 12:07 pm


You should have a look a the Sigma 30mm 1.4 HSM. It works out to be about 48mm on a 1.6 crop sensor and takes amazing pictures. Focus is fast and quiet and it is very good for low light shooting.

ericvision
 


Post Thu Mar 29, 2007 1:43 pm


becky_stead wrote:Actually ive just had a thought the lense doesnt come with a hood you have to buy it seperately ... do i need one??


I wouldn't worry about a hood for the 50mm. The front element is so far back in the casing that it really doesn't need one. For that reason you have to buy an adaptor ring to fit a hood as it doesn't have its own bayonet.

I'll PM you with an excellent contact for obtaining one at a very good price - if you get it and don't like it, you'll lose nothing by ebaying it if you promise special delivery :)

becky_stead
 
Posts: 365


Post Thu Mar 29, 2007 7:34 pm


Hi thanks for your post, but i ordered the lense before i saw it lol. It was £65 so not too bad a price although its out of stock at the moment. so ill give them a week and then give them a call and see where we are. If its still not in stock then i may cancel the order and try the link you sent me. Thanks again!
Becky

normlynch
 
Posts: 71


Post Thu Apr 05, 2007 12:56 pm


A 50mm prime on a 1.6 crop factor EOS body...


Image

madlights
 
Posts: 914


Post Thu Apr 05, 2007 1:36 pm


Just multiply the 35 mm by 1.6 for Canon xxD's
1.5 for Nikon
Who knows what for Oly 4/3rds??? LOL
Primes are nice. I wished I'd have bought some instead of my zooms...but I'm broke now :-) I find the 50mm to be pretty good for portraits, the thing is although cropped..a 50mm still has the properties of a 50mm. The same foreshortening. If you notice a tele lens shortens, or brings closer distance. Say a railroad track photo. It brings it ALL closer so the farthest point looks close, and the nearest looks close. A wide angle will give more depth. So even though you are in effect changing a 50mm into an 80mm with your camera's sensor size...The lens properties are still the same. The crop does change but the properties of the lens do not. They will shorten things up the same, or make them seem farther away the same as they would on a 35mm. So it's just something extra to complicate things when chosing a lens and comparing it to it's 35mm equiv, Some people prefer the look of a longer lens for portraits, they say it makes long noses look flatter (I've never noticed it much)..and in how it treats a subjects face etc. But then with a cropped camera you've got to stand a bit farther back.. I don't know if this makes much sense, but if I'd had the money I'd have gotten a 1ds (full 35mm frame) when I got my camera so I wouldn't have had to think about all this. ;-) Yes a 30mm or so is closer to the crop that the eye sees on a 1.6 camera I'd think. My next lens may be a wide Sigma, and most are pretty fast. For a cheap fast and sharp lens that's put together awful...the Canon 50mm 1.8 can't be beat...and 50mm sure works well on portraits to my eye..as norms beautiful portrait attests to. (not sure which 50mm he used) Oh and the hood....you can get a rubber hood very reasonably at any photo shop. I got one for my 50mm for a few $US. and the rubber hoods give a nice "retro" look.

dick_haynes
 
Posts: 8

Subject Distance

Post Mon Apr 16, 2007 7:55 am


I have to disagree about the focal length properties staying the same between full frame and 1.6x crop factor for the same focal length. e.g. 50mm.

The ONLY thing that changes your perspective is camera position, the ONLY thing that changes scale is your camera distance to subject.

Set up a tripod, shot any scene at 24mm then at 200mm. If you crop the 24mm image to show the same area as the 200mm, the perspective and scale will be identical.

I highly recommend reading "The Camera" by Ansel Adams. I find it fairy inexpensive for the wealth of knowledge it contains.

We have a tendency to get up close(literally) with a wide angle lens, this is what cause "distortion" not the lens itself. Look at a mirror from just a few inches and you nose will look huge, back up and it looks normal.

tuckeruk
 
Posts: 224


Post Mon Apr 16, 2007 1:35 pm


As Dick quite rightly points out, perspective is a function of camera to subject distance alone.

The fact that focal length directly affects perspective is one of the two most oft repeated fallacies in photography, the other being than a 50mm lens on 35mm bodies in some way replicates the human eye.

madlights
 
Posts: 914


Post Tue Apr 17, 2007 1:24 am


Yes I kind of see what you mean...dick. A 90mm or so portrait lens allows a person to stand off a ways so as the nose wouldn't appear large? I've read and had photographers tell me it was the lens itself that did it...even read some fairly well known "photo experts" who said it. But when I think of it logically...if it were the case, a bird taken with a 500mm lens would appear totally flat then...and of course it doesn't. I think in some cases perceptually there can be an effect, say a railroad track taken with a wide angle spreads out the track because it includes more of it...rather than just the track at a distance...which I can see if you cropped it would look the same. so really only the field of view changes. I stand corrected...and now I can challenge people who told me this stuff I was telling :D of course the 50mm doesn't replicate the field of view of the human eye...but it is considered a "normal" lens in 35mm by many...or closer to the field of view 'of concern' of the human eye, the human eye has in most cases much wider peripheral vision. I suppose one could argue what the field of view of concern is, depending on what a person was concerned with :) We might only see the teeth of a Tiger at 100 meters if it wanted to eat us. But I think the 50mm at 35 was promoted as "normal" so people would have a place to start...or some sort of reference point...otherwise there'd be no reference points for wide angle or telephoto and maybe all that we think we know would be meaningless.

dang
 
Posts: 3780


Post Tue Apr 17, 2007 5:16 am


Yeah.. my mistake for using the phrase. I forget and should add more about such things instead of being lazy and making general comments. Here's an article with comparison shots which is good to pass out instead. I think it should clear things up pretty well.
http://www.photonomics.com/chooselensa.htm

pgkps
 
Posts: 5


Post Tue Apr 17, 2007 10:15 am


Historically a "portrait" shooter would use an 85mm to 135mm equivalent lens, see the numbers would be different for Medium Format and of course the various large format systems. Shooting with a 35mm and with a prime in the 85mm to 135mm range would get the photographer the right distance from the subject to reduce abberations that all lenses have. Now the real problem that we run into is the "crop factor" that almost all 35mm digital cameras have so that shooting with a 55mm lense (85 or so equivalent on many bodies) will show some distortions when the same subject is shot if you compare a film vs digital print because of that distance from the subject, so I say to reduce this problem (features slightly distorted) would be to shoot at the higher mm range mentioned above and stand a bit farther from the subject. (all the above is talking about portraits of individuals not couples and groups).

Now the reason that a wedding shooter should have the Following FAST PRIMES in their possession is the problem of shooting in lower light conditions since the FAST PRIMES will help. I believe any shooter who works in low light conditions should have a lens in the 24mm range with a speed of at least f 2.0, another in the 35mm range (50mm cropped factor adjusted) in the f 1.8 or faster, the before mentioned 50mm at f 1.8 and if the wallet allows a 1.4 (don't see a reason to go to the rare 1.0's since their prices go up so much and most digital bodies today shoot past 1000 asa), another in the 80mm range in the f 2.0 range and one final one in the 100mm range in the f 2.0 range also but starting off with the 50mm and building up from there because it will be your workhorse. You can go with other lenses in the higher mm range if you are forced many times to stand a distance from your subjects but going much faster than f 2.8 on them will make them costly and also large, while the other lenses mentioned before are rather small and many can easily fit into a mens trousers pocket if the shooter needs to carry a couple with them and they don't want to carry a bag with them in it.

I shoot a nikon based KODAK SLRN which allows me to use even the older NIKON lenses even though I don't shoot weddings and the camera is full frame.

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