Auto Focus or manual?

abowie · 23rd December 2006, 01:59

Quote: (Originally Posted by jhaaja)

In my case I think the problem with the focusing was due to the lack of light. We were inside a cave so no natural light was available.

I think I need to attach my 21W HID with the video reflector to the other flash arm that I do not own yet

to get enough light to get the focus locked.

Another good place to look for advice is Wetpixel.com :: Underwater Photography and Videography

Johnny Christensen · 23rd December 2006, 09:12

Quote: (Originally Posted by jhaaja)

I think I need to attach my 21W HID with the video reflector to the other flash arm that I do not own yet

to get enough light to get the focus locked.

I just hold the light with my left hand, lock the focus on the camera and before shooting the picture, take the divelight out of the picture again.
That way you avoid the divelight making any unwanted hotspots. With a videolight there is less tendency for hotspots.
But a videolight needs to be really bright to assist the camera in finding focus. That's why I don't use that. I have both narrow focus and videolight head for my 50w HID (metalsub 200) but prefer the narrow focus. Now if I had a 200w HMI, that would be another matter...

Another reason that I take the divelight out of the picture before shooting, is so it's easier to find out if one of your strobe is positioned the wrong way. It's often only minor ajustment in the strobeangle that makes the difference in how much backscatter you will get in the picture.
Too many variables makes it more difficult to get it right the first time.

PeteS · 23rd December 2006, 09:36

Quote: (Originally Posted by Sutty)

Johnny is right in thinking that I have a "compact" camera (Canon G2).
The optics of a dome port mean that once immersed in water it produces a virtual image at a very short distance from the lens (I think its usually a only a few inches, but don't rely on this). It is this virtual image that the camera has to focus on. With my camera in order to focus so close you have to change to "macro" mode. If your camera cannot focus close enough you will have problems focusing.
One way around the problem (I haven't tried this) is supposed to be to add a close-up lens (dioptre) on the front of your lens (or on top of a wide-angle lens if this is what is fitted to match the port - this then enables your camera to focus close enough.

Ahhh, it's a compact..... The reason for my confusion was that my Nikon 10.5mm focuses at the correct distance from (140mm to inf) under a 10" dome - for wide angle. I assumed that most other cameras did the same. Ho hum.

jhaaja · 23rd December 2006, 12:39

Quote: (Originally Posted by Johnny Christensen)

I just hold the light with my left hand, lock the focus on the camera and before shooting the picture, take the divelight out of the picture again.
That way you avoid the divelight making any unwanted hotspots. With a videolight there is less tendency for hotspots.
But a videolight needs to be really bright to assist the camera in finding focus. That's why I don't use that. I have both narrow focus and videolight head for my 50w HID (metalsub 200) but prefer the narrow focus. Now if I had a 200w HMI, that would be another matter...

Another reason that I take the divelight out of the picture before shooting, is so it's easier to find out if one of your strobe is positioned the wrong way. It's often only minor ajustment in the strobeangle that makes the difference in how much backscatter you will get in the picture.
Too many variables makes it more difficult to get it right the first time.

I will try your techinique next time Johnny. Thanks for the tips. I will let you know how succeed

Unfortunately my main dive site has poor viz at the moment. Hopefully it will clear out when the ice cover comes.

Nemo1957 · 23rd December 2006, 22:54

If you do not have adequate light for the auto focus to get a good lock you will likely have soft images. A trick I use when shooting WA in low light is to manually focus on something I know the distance to, like my fin. Then if you know the depth of field range of a given lens at various f stops (usually in the literature that comes with the lens) you will be assured of sharp images thorughout the dive without having to adjust the focus during the dive. Just be sure to select an f stop that will give you the depth of field you need for the image you are setting up. This is generally easy with a WA lens like a 15mm since the depth of field is large at most f stops compared to the distance you can shoot in water.

jhaaja · 24th December 2006, 10:28

Quote: (Originally Posted by Nemo1957)

If you do not have adequate light for the auto focus to get a good lock you will likely have soft images. A trick I use when shooting WA in low light is to manually focus on something I know the distance to, like my fin. Then if you know the depth of field range of a given lens at various f stops (usually in the literature that comes with the lens) you will be assured of sharp images thorughout the dive without having to adjust the focus during the dive. Just be sure to select an f stop that will give you the depth of field you need for the image you are setting up. This is generally easy with a WA lens like a 15mm since the depth of field is large at most f stops compared to the distance you can shoot in water.

That I also thought. The lens seems to draw sharp images on quite big area. I will test that also. I have used that technique with video and got quite good results.

Hey, learning is fun

Thanks!

23rd December 2006, 01:59	#11 (permalink)
abowie Fighting Girl Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: May 2005 Location: Land of Oz Posts: 573	Re: Auto Focus or manual? Quote: (Originally Posted by jhaaja) In my case I think the problem with the focusing was due to the lack of light. We were inside a cave so no natural light was available. I think I need to attach my 21W HID with the video reflector to the other flash arm that I do not own yet to get enough light to get the focus locked. Another good place to look for advice is Wetpixel.com :: Underwater Photography and Videography __________________ Andrew Bowie Rebreather-friendly Buddy
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23rd December 2006, 09:12	#12 (permalink)
Johnny Christensen Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Apr 2006 Location: Denmark Posts: 298	Re: Auto Focus or manual? Quote: (Originally Posted by jhaaja) I think I need to attach my 21W HID with the video reflector to the other flash arm that I do not own yet to get enough light to get the focus locked. I just hold the light with my left hand, lock the focus on the camera and before shooting the picture, take the divelight out of the picture again. That way you avoid the divelight making any unwanted hotspots. With a videolight there is less tendency for hotspots. But a videolight needs to be really bright to assist the camera in finding focus. That's why I don't use that. I have both narrow focus and videolight head for my 50w HID (metalsub 200) but prefer the narrow focus. Now if I had a 200w HMI, that would be another matter... Another reason that I take the divelight out of the picture before shooting, is so it's easier to find out if one of your strobe is positioned the wrong way. It's often only minor ajustment in the strobeangle that makes the difference in how much backscatter you will get in the picture. Too many variables makes it more difficult to get it right the first time. __________________ www.johnnychristensen.com Wreckphotography from the cold north
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23rd December 2006, 09:36	#13 (permalink)
PeteS Consent Issued! Current Rebreather/s: Inspiration Classic Inspiration Vision Other Rebreather/s: Join Date: Jun 2005 Location: New Zealand Posts: 515	Re: Auto Focus or manual? Quote: (Originally Posted by Sutty) Johnny is right in thinking that I have a "compact" camera (Canon G2). The optics of a dome port mean that once immersed in water it produces a virtual image at a very short distance from the lens (I think its usually a only a few inches, but don't rely on this). It is this virtual image that the camera has to focus on. With my camera in order to focus so close you have to change to "macro" mode. If your camera cannot focus close enough you will have problems focusing. One way around the problem (I haven't tried this) is supposed to be to add a close-up lens (dioptre) on the front of your lens (or on top of a wide-angle lens if this is what is fitted to match the port - this then enables your camera to focus close enough. Ahhh, it's a compact..... The reason for my confusion was that my Nikon 10.5mm focuses at the correct distance from (140mm to inf) under a 10" dome - for wide angle. I assumed that most other cameras did the same. Ho hum. __________________ Pete S. http://www.steggle.co.nz Every silver lining has a cloud
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23rd December 2006, 12:39	#14 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Auto Focus or manual? Quote: (Originally Posted by Johnny Christensen) I just hold the light with my left hand, lock the focus on the camera and before shooting the picture, take the divelight out of the picture again. That way you avoid the divelight making any unwanted hotspots. With a videolight there is less tendency for hotspots. But a videolight needs to be really bright to assist the camera in finding focus. That's why I don't use that. I have both narrow focus and videolight head for my 50w HID (metalsub 200) but prefer the narrow focus. Now if I had a 200w HMI, that would be another matter... Another reason that I take the divelight out of the picture before shooting, is so it's easier to find out if one of your strobe is positioned the wrong way. It's often only minor ajustment in the strobeangle that makes the difference in how much backscatter you will get in the picture. Too many variables makes it more difficult to get it right the first time. I will try your techinique next time Johnny. Thanks for the tips. I will let you know how succeed Unfortunately my main dive site has poor viz at the moment. Hopefully it will clear out when the ice cover comes.
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23rd December 2006, 22:54	#15 (permalink)
Nemo1957 New Member Current Rebreather/s: Optima Other Rebreather/s: Join Date: Apr 2006 Location: New York Posts: 78	Re: Auto Focus or manual? If you do not have adequate light for the auto focus to get a good lock you will likely have soft images. A trick I use when shooting WA in low light is to manually focus on something I know the distance to, like my fin. Then if you know the depth of field range of a given lens at various f stops (usually in the literature that comes with the lens) you will be assured of sharp images thorughout the dive without having to adjust the focus during the dive. Just be sure to select an f stop that will give you the depth of field you need for the image you are setting up. This is generally easy with a WA lens like a 15mm since the depth of field is large at most f stops compared to the distance you can shoot in water.
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24th December 2006, 10:28	#16 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Auto Focus or manual? Quote: (Originally Posted by Nemo1957) If you do not have adequate light for the auto focus to get a good lock you will likely have soft images. A trick I use when shooting WA in low light is to manually focus on something I know the distance to, like my fin. Then if you know the depth of field range of a given lens at various f stops (usually in the literature that comes with the lens) you will be assured of sharp images thorughout the dive without having to adjust the focus during the dive. Just be sure to select an f stop that will give you the depth of field you need for the image you are setting up. This is generally easy with a WA lens like a 15mm since the depth of field is large at most f stops compared to the distance you can shoot in water. That I also thought. The lens seems to draw sharp images on quite big area. I will test that also. I have used that technique with video and got quite good results. Hey, learning is fun Thanks!
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