so last night I picked up a friends 75-300mm lens to play with and I was VERY disappointed in how slow it focuses.

are there any numbers on the lens that I should look for that gives away info on how fast it focuses?


any recomendations on a zoom lens that focuses fairly quick... maybe something in the 50-250mm range?


TIA
Beezwax

should be faster than what your using now. What lighting conditions were you in? Its common for a lens to search on auto focal points. If you know what subject you want, you can manually select the focal points in the camera.

there are no real markers on the lens aside from the USM notations. I believe that lens is a USM III unless it was an older model. If you notice the kit lens is not equipped with a USM motor, thus its noisier and slower than the 75-300. Most lenses with the USM equipped will have a small gold ring around them and say ultrasonic somewhere.

Im not awake yet so someone may correct me.

Originally Posted by subimatt

should be faster than what your using now. What lighting conditions were you in? Its common for a lens to search on auto focal points. If you know what subject you want, you can manually select the focal points in the camera.

there are no real markers on the lens aside from the USM notations. I believe that lens is a USM III unless it was an older model. If you notice the kit lens is not equipped with a USM motor, thus its noisier and slower than the 75-300. Most lenses with the USM equipped will have a small gold ring around them and say ultrasonic somewhere.

Im not awake yet so someone may correct me.

it's this exact lens
http://www.amazon.com/Canon-75-300mm...9405618&sr=1-1

and much slower than my 18-55 kit lens

^ yea that should be faster and quieter than your kit lens.

Keep in mind that expanded focal ranges need faster shutter speeds to compensate for hand holding movements. You could also use the AF lock function.

Originally Posted by subimatt

^ yea that should be faster and quieter than your kit lens.

Keep in mind that expanded focal ranges need faster shutter speeds to compensate for hand holding movements. You could also use the AF lock function.

but even when I was focusing on a static object in my house it was slow... I tried adusting the DOF to make the light coming in equal to the light in the house and it ws just.....blah... not the pic quality but just the slow focus.

Are you sure it was the speed of the AF motor, and not the lack of light that was causing problems? Most consumer telephotos don't do well in poor light as far as AF. Were you able to lock focus easily once the lens got there?

Obviously, not being a Canon guy, I can't speak for USM, but I imagine it's comparable to Sigma's HSM, and Nikon's AF-S lenses which are both lightning fast compared to using the motor in the body. Any chance you were mistaken about it having USM?

I just recommended this lens to a co-worker for his daughter who is getting started in photography with film and wanted a cheap telephoto for her Rebel. She was delighted with it.

^ adjusting the DOF will help expose the photo, but the af sensors will still have a hard time searching if the subject is not properly lit. Keep in mind its just a tool, it searches the area for what it thinks is the subject, so at times you may need to force it on the proper subject.

Originally Posted by LateApex

Are you sure it was the speed of the AF motor, and not the lack of light that was causing problems? Most consumer telephotos don't do well in poor light as far as AF. Were you able to lock focus easily once the lens got there?

Obviously, not being a Canon guy, I can't speak for USM, but I imagine it's comparable to Sigma's HSM, and Nikon's AF-S lenses which are both lightning fast compared to using the motor in the body. Any chance you were mistaken about it having USM?

I just recommended this lens to a co-worker for his daughter who is getting started in photography with film and wanted a cheap telephoto for her Rebel. She was delighted with it.

in all honesty... I adjusted apeture from bottom to top numerous times and it still was slow on the focusing. I'll have to check if it's USM. The lens was bought for an EOS 35mm and not a digital... it's about 3 years old now... I hope it's NOT USM because I wasn't pleased at all with it IMHO...but that was speed only, the pics looked just fine

Originally Posted by beezwax

it's this exact lens
http://www.amazon.com/Canon-75-300mm...9405618&sr=1-1

Thats a USM III telephoto. Most likely it was your subject being improperly lit.

Adjusting the aperture won't really do that much, since it's wide open until you activate the shutter. Set the aperture value to a high number, and snap a photo while looking into the front of the lens, you can see how this works.

I vote for too dark also, pretty normal. Try it outside and see how it goes.

The other way to see the aperature go is to hit teh DOF preview button on your camera.

Originally Posted by thechickencow

I vote for too dark also, pretty normal. Try it outside and see how it goes.

The other way to see the aperature go is to hit teh DOF preview button on your camera.

thats what I did... I literally snapped a pic, turn by turn of the wheel... no joke...

I guess I'll just have to try it outside and hopefully it'll be different

Originally Posted by LateApex

Adjusting the aperture won't really do that much, since it's wide open until you activate the shutter. Set the aperture value to a high number, and snap a photo while looking into the front of the lens, you can see how this works.

can I hit the DOF button also to see how open the shutter WILL be when I pull the trigger?

As mentioned there are three major things that affect how fast a lens can autofocus.

The first being the autofocus system in the camera. Some are more sophisticated and faster than others at determining what signals to tell your lens in order to focus.

Secondly, the motor in the lens. That lens has an Ultrasonic Motor (USM) which is the fastest and quietest type of motor Canon offers. Other manufacturers have similar technologies.

Thirdly is the optical speed of the lens. You can determine this from the f#. That 75-300 is an f4 to f5.6. That means at 300mm when it is an f/5.6 it allows half as much light though than it does at 75mm when it's f/4. As a result, focusing will be slower at 300mm than 75mm. Neither aperture is particularly fast but f4 in a well lit room or outside should have no trouble focusing fairly quickly.

Originally Posted by beezwax

can I hit the DOF button also to see how open the shutter WILL be when I pull the trigger?

Hitting the DOF preview button doesn't open the shutter, it only stops the lens down to the aperture you have selected. The image gets darker but your DOF increases as you select smaller and smaller apertures (larger f numbers). DOF preview is designed to allow you to know what your image is going to look like, but it's hard to use when there isn't much available light or you stop the lens down a lot.

Originally Posted by beezwax

can I hit the DOF button also to see how open the shutter WILL be when I pull the trigger?

yes, what f stop did you start with?

Much confusion in this thread I see.

-yoda

(i'm confused now on what you're even asking, beezwax)

Originally Posted by subimatt

yes, what f stop did you start with?

I wouldn't respond to that with a yes, the wording of it suggests that the shutter might open when he presses the DOF preview button!

Originally Posted by emorphien

I wouldn't respond to that with a yes, the wording of it suggests that the shutter might open when he presses the DOF preview button!

Good point carl,

The DOF preview button will close the aperture to your current setting. Since the aperture does not move to its setting until the photo is taken. This is a good way to gauge lighting without firing a shot.

So this will display how "open" meaning how much light your current setting will allow.

It's pretty much covered. But, I would bet a great deal that you were indoors in normal dim light. Only super fast primes (f/1.8 and lower) focus well indoors, the lens you were using is not one of them. Try it outside in normal light, it will be just as fast as your kit lens.

As for focus speed, usually the lower (wider) the maximum aperture the fast the AF of a lens in all situations (especially lower light). A 70-200 f/2.8 or 100-300 f/4 would be a quicker focusing lens in that range, but with faster focusing and wider maximum apertures (lower numbers) comes a good deal more money involved.

at 300mm I was at f5.6 and at 75mm I was at f30 I think... honestly I don't remember.

so, should I NOT judge the light coming in by holding the DOF?


I was going to bring my gear with me to work today but forgot it... I may run home a grab it so that I can take some pics and post them up here today for y'all to help more effeciently..

I know the information that I'm providing is not the best... I'll try get the cam and lens in a little while... take a few pics and post them.



to be continued...

Originally Posted by beezwax

so, should I NOT judge the light coming in by holding the DOF?

Not entirely. It allows you to judge the DOF, but when stopping down the aperture each consecutive stop corresponds to halving the amount of light allowed through the lens.

When you actually take the photo, the shutter speed compensates. For example f4 to f5.6 is one stop difference, half as much light reaches the sensor when you change from 4 to 5.6. As a result, if the shutter speed at f4 was 1/60, the shutter speed at f/5.6 would be 1/30 (1/60 * 2 = 1/30) to result in the same amount of light reaching the sensor. When you use DOF preview there's no way to change the "shutter speed" to your eye so it just gets darker.

Originally Posted by emorphien

Not entirely. It allows you to judge the DOF, but when stopping down the aperture each consecutive stop corresponds to halving the amount of light allowed through the lens.

When you actually take the photo, the shutter speed compensates. For example f4 to f5.6 is one stop difference, half as much light reaches the sensor when you change from 4 to 5.6. As a result, if the shutter speed at f4 was 1/60, the shutter speed at f/5.6 would be 1/30 (1/60 * 2 = 1/30) to result in the same amount of light reaching the sensor. When you use DOF preview there's no way to change the "shutter speed" to your eye so it just gets darker.

IC....

I just went home to get my cam and gear...it seems that my light inside the house was making it hard for the lens to focus quickly... the lens IS the USM III 75-300mm. here are a few samples of what I just took... I don't have PS at work so these are just resized..

Posting shots tells us nothing about the AF other than the fact it appears to be working correctly.

Originally Posted by Stime187

Posting shots tells us nothing about the AF other than the fact it appears to be working correctly.

oh... the lens seems to work well outside... focuses much faster than inside...

FALSE ALARM!!!!

Originally Posted by beezwax

oh... the lens seems to work well outside... focuses much faster than inside...

FALSE ALARM!!!!

Yeah, just as I/we expected. Never judge anything about a lens off shooting inside unless you know what you're doing. Indoor light is generally very dim.

Originally Posted by Stime187

Yeah, just as I/we expected. Never judge anything about a lens off shooting inside unless you know what you're doing. Indoor light is generally very dim.

well geez man.. that is why I posted... to learn

Originally Posted by beezwax

well geez man.. that is why I posted... to learn

Well, I didn't mean it like that. What I mean is, unless you're a sports/wedding/otherwise photographer that spends a lot of time shooting indoors and understand the ins/outs of it, don't base anything off the performance of a lens indoors.

Just FYI, I don't judge lenses by how they work/focus indoors. It's just not the typical setting I normally shoot in.

Originally Posted by Stime187

Well, I didn't mean it like that. What I mean is, unless you're a sports/wedding/otherwise photographer that spends a lot of time shooting indoors and understand the ins/outs of it, don't base anything off the performance of a lens indoors.

Just FYI, I don't judge lenses by how they work/focus indoors. It's just not the typical setting I normally shoot in.

gotcha.. thanks again