Some technique advice sought from the resident experts... (1 Viewer)

[Jack Gilvey]

I've had a Canon EOS Digital Rebel XT for years now and have recently been trying to actually learn how to use it outside of "Auto" mode with the kit lens. So, my first step was to purchase an EF 50mm f/1.8 II due to what I'd read about its low-light/fast performance. While I learn what's what I've been sticking to Aperture Priority (Av) mode, 1.8-2.8. I'm having trouble with focus, though. I don't get anywhere near the "tack sharp" results I see from sample low-light/hand-held shots posted on the net (I use auto-focus, center point). No problem in flash mode, but I hate a flash and that was the main reason I got this lens.

Here's a shot with a bit of sun:





And on a cloudy day:





Any pointers,critiques would be greatly welcomed. Should I expect sharp results hand-held with room light in Av mode?


Thanks!

 

[Citizen87645]

What kind of shutter speeds are you shooting at? That can make a big difference.


Rule of thumb has always been to use the inverse of the focal length as the guide. So with the 50mm it's equivalent to an 80mm lens, so you should be shooting at 1/100 of a second and above for handheld shots.


It would be worth doing a check of the lens under controlled conditions. The simplest is to put the camera on a tripod, shoot at something like 1/125 and photograph something that has well-defined focus points, like a sheet of notebook paper shot at an angle. There are also focusing grids out there to perform these kinds of tests. This will help check for focusing problems in the lens itself. I've learned the hard way that with any new lens you should do this kind of focusing test.

 

[Scott Merryfield]

In addition to maintaining a high enough shutter speed for a hand held shot (as Cameron mentions), be aware that the Canon 50mm f/1.8 is not very sharp when shot wide open, and its auto focus motor is very slow if you are trying to shoot a moving target. There is a reason this is Canon's least expensive EF lens. I own this lens, but rarely use it.


Try stopping down the aperture to at least f/2.8. Also either try a tripod or get your shutter speed faster than 1/125sec, as Cameron suggested.

 

[Patrick Sun]

Boosting the shutter speed may require you to bump up your ISO at the expense of some graininess to the photo for proper exposure (or use some editing tools to brightening up the photo file in post). I have that 50/F1.8 lens too, and don't use it much anymore, never did like the colors I got from it.


I'm sort of saving up for the 50/F1.4 (not quite an L lens), as the 50/F1.2L costs an arm and a leg.

 

[Citizen87645]

I still use my 50mm from time-to-time, but I LOVE the 85mm 1.8.

 

[Scott Merryfield]

Originally Posted by Cameron Yee

I still use my 50mm from time-to-time, but I LOVE the 85mm 1.8.

I have an 85mm f/1.8 lens, too. It's a terrific lens for the price.


My only other prime (other than the 50mm f/1.8) is a 28mm f/1.8. It's very comparable in image quality and AF performance to the 85mm f/1.8.

 

[Sam Posten]

Indoors even at 1.8 you are going to find a lot of occasions at base ISO where you simply do not have enough light to make a compelling shot. There's a reason why wedding shooters pay the big money for full frame and boost their ISO as needed. Make sure you focus on the eyes. This can be especially a bitch with Canon's crazy diamond shaped autofocus layout....


Edit: My canon 85 1.8 is one of the only 3 lenses I kept in case I ever went back. It's a stunner.

 

[Jack Gilvey]

Wow guys, great stuff...thanks much. Will apply the suggestions and report back, and I'll check the lens as you suggest Cameron.

 

[Ed Moxley]

The lower the light, the higher the ISO, when no flash is used.

On a cloudy day, you may want an ISO of 400-500. Depending on how cloudy and dark it is, you may even need to go to 800 ISO. Same rules apply inside too basically. You can take the first shot in Auto, and see what settings the camera used. If you like those results, you can stay around those settings, with maybe trying a step or two each way on Aperture mode and Shutter mode. Experiment with settings. You can always delete the bad shots.


Here are some tips to check out: http://www.photographytips.com/page.cfm/122

Here's an interactive site to play with aperture and shutter speed settings, to show how they affect exposure: http://www.photonhead.com/exposure/simcam.php

I hope this helps.

 

[ManW_TheUncool]

The other thing to consider is that presumably the tack sharp images you see elsewhere have been postprocessed whereas I'm guessing you may not have done much, if any, of that since you're only just now trying something other than "Auto" mode. In fact, I'd venture a guess that taking your XT out of Auto mode might yield a less processed look by default and make you think your shots are less sharp as a result. Auto mode on many of these DSLRs will probably behave a bit like "torch" mode on displays in the HT world, and perhaps, you've gotten used to that kind of straight-from-the-camera default results.


I remember a long time ago that a former coworker thought the shots from my then new D70 didn't look sharp to him most likely because he just wasn't used to seeing images from a DSLR, especially w/ the rather shallow DoF (compared to typical compacts) -- and yes, they were sharp alright where they ought to be.


But yeah, there can be a number of different factors involved that makes you think it's not sharp -- some of them may just be perception and some may be real.


_Man_

 

[Cees Alons]

(I don't feel a right to the tag "expert", but here's my $0.005):


At f/1.4 depth of focus is almost non-existing and at f/1.8 it's still not very much. One tiny move (of the photographer or the subject) can move the latter out of focus. With apertures that large, you need to use a tripod (and it may still fail if the baby moves out of focus), or at these short distances go for a smaller aperture, e.g. f/2.8 or smaller.


As others have said that may influence other settings.


Portraits are historically believed best with an 85mm or 135mm lens. If you're using a 50mm lens on a DX body, you will have roughly 75mm equivalent framing alright, but the DOF is that of a 50mm!



Cees