Oo Lens Theory oO

A

Andii

Active member
Hello all. I have a couple of questions on lens theory I wondered if some of you could could clear up for me. I currently have a Canon XL H1. But I am sure these questions will be relevant to all hd/hdv cameras and lens.

Lens softness:
Now I have been told two completely different answers to this question.

Fully zoom out is the best way to keep ultimate sharpness and that using a closed
iris is the the best way to keep the best sharpness possible.

BUT

I have also been to told that I should the iris as wide open as it will go and just use
nd filter to reduce the light.

Which is best for landscape shots? I am totally confused now as the best way to keep the resolution as sharp as possible. Can anybody shed a little light for me?

Cheers.

A.
 
zoom lenses tend to perform best about 1/4 - 1/2 way through the zoom, and stopped down to about F5.6.
 
Andii said:
Hello all. I have a couple of questions on lens theory I wondered if some of you could could clear up for me. I currently have a Canon XL H1. But I am sure these questions will be relevant to all hd/hdv cameras and lens.

Lens softness:
Now I have been told two completely different answers to this question.

Fully zoom out is the best way to keep ultimate sharpness and that using a closed
iris is the the best way to keep the best sharpness possible.

BUT

I have also been to told that I should the iris as wide open as it will go and just use
nd filter to reduce the light.

Which is best for landscape shots? I am totally confused now as the best way to keep the resolution as sharp as possible. Can anybody shed a little light for me?

Cheers.

A.
Click to expand...

Try not to use lenses all the way stopped down. Usually when lenses are closed down (all the way) light starts diffracting and the image actually looses quality. Lenses are generally BEST stopped down a couple of stops from wide open.

The reason you would want a ND filter is in case it were so bright outside, the ND would help you NOT close down all the way, escaping the hazard mentioned above. Another reason is if you were trying to milk as little depth of field as you could.

Since your shot is a landscape, I assume you will be set at infinity focus therefore I would see little reason to use ND, unless it is very bright outside.
 
Thanks for the advise guys, so from your advise:

The lens is at its best quality zoomed in by roughly a 1/4

And better (sharper) results when not fully open

Correct?

My other question is, do you have to be zoomed out all the way in order to use infinity focusing? I have tried infinity focusing but it does not seem very sharp at all on my xlh1

Could it be something to do with 'Back flange"? I dont know what this is, as i have not looked it up yet, could this have something to do with infinty sharpness?

Thanks guys, appreciated your time and knowledge. :Drogar-Happy(DBG):

Any advice?
 
You should be able to get infinity focus at any focal length. The lens mount should be perfectly distanced from the chip.

If your back focus is off, that could prevent you from getting to infinity focus, but like I said, the camera should have been made correctly. Did you change anything?

If your backfocus is messed up, you will either not be able to reach infinity focus, or you will be able to pass it. Sometimes when zoomed out (since details become smaller), it may just LOOK less sharp. I would run some tests and blow the image up.
 
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Are you judging sharpness from the camera's viewfinder or LCD? It is always best o make image judgements from a properly calibrated full resolution external monitor. The images the camera shows you onboard are generally down ressed from what you're actually recording.

Check your shots on a good monitor to see if your backfocus is truly out of whack.
 
Thanks for the help guys.

I re set the back flange as it was laid out in the manual, but it still looks a little blurry to me, maybe I am expecting super super HD resolution I am not sure. I think the best thing to do is to post a screen shot. it will be:

XLH1 stock lens
25f
Back of the lens
Infinity setting

What;s the best way to output the best quality for you guys to view here?
I captured as prores on a progressive timeline.

Cheers

Andy.
 
if you're in an HD timeline, export a screengrab as a jpg with maximum resolution or a .tiff file. As long as you make sure you set the image file to maximum quality it should be enough for us to see your issue
 
BUT

I have also been to told that I should the iris as wide open as it will go and just use
nd filter to reduce the light.
Click to expand...

The iris wide open will give you the most shallow depth of field - which is usually not what you want in landscape shots, but more in portrait/talking heads type of situations.
Rule of thumb is that the lens will perform best at medium F-stops (around 5.6 for most lenses) and you will achieve the highest depth of field at near to maximum F-stops. If you close down the iris too much the image quality gets worse, so if your lens goes up to 16, then use 11 or 8.
The image quality also gets worse at iris wide open, but with 1/3" chip camcorders you don't have a choice if you want some kind of shallow depth of field.
 
Here is the image from my timeline,

25f
1080i
xlh1
infinty setting

Quicktime conversion > still image > jpeg best quality

I thought the chimneys in the distance would be in focus, am I asking too much from the lens?

Also the image does not appear to be 16.9 not sure why.

infinity.jpg
 
It seems like you have been shooting this through a window. Does it look the same if you open the window? I mean window-glass is not exactly what I would call high-quality glass... :)
 
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