Brevis35 + 50mm Canon FD at DVinfo.net

Dennis Stevens · May 30th, 2008, 01:59 PM

Hi-
Just got a Brevis35, and was using a Canon fd 50mm lens on my JVC GY HD 100UA.

I notice I have to zoom in a lot to get past the adapter, so much it doesn't seem I can get a wide shot. Is there something I have to adjust? Do I need a different lens?

Total newbie question - be kind!

Paul Nixon · May 31st, 2008, 02:24 PM

Zooming is all part of the fun - it's seems typical of how these things work.

If you don't mind, I have a question for you - I'm also using a Canon FD 50mm lens on my "homebrew" attached to my HC1, and I'm having an issue with focus being off away from the center.

Could you please let me know if you get sharp focus from edge to edge with your setup? For example, compare:

http://i120.photobucket.com/albums/o...35mm_no_fc.jpg

to

http://i120.photobucket.com/albums/o...m_attached.jpg

Thanks.

Dennis Stevens · May 31st, 2008, 03:13 PM

I haven't noticed that issue, but I just got it.

I believe the brevis you sometimes have to adjust the achromat so it's centered on the camera's focus center.

Dennis Wood · June 16th, 2008, 09:41 PM

Dennis, actually the achromat always stays dead center on the video camera lens, but we've designed in two XY adjustments after that point to ensure that any camera's with off-center imaging blocks can be accounted for. Paul, if you're seeing focus that is not sharp at the edges then this could be a result of many factors. For one thing, your imaging screen, lens mount and camera attachment points should be accurately placed with a tolerance of better than +0 .05mm in the Z axis which is almost impossible unless you're using CNC equipment to machine your parts. There's a number of optical issues that may be at hand too ranging from using a generic achromat, edge softness issues with the lens, etc. etc.

Troubleshooting is a matter of breaking down each error factor one by one, starting with the bare camera. Baseline the camera first, focusing on a target a similar size and distance as your imaging screen. The adapter image you posted looks to have about 25% of the right and left sides of the frame out of focus so I'd start (after testing the camera with a close 24x36mm target) with alignment checks.

Hope that helps,
Dennis.

Paul Nixon · June 18th, 2008, 10:15 PM

Thanks Dennis,

I agree regarding troubleshooting and breaking the problem down to find out the root cause, and I've been working hard toward that end. Unfortunately, I'm beginning to believe it's a combination of issues conspiring against me, and my lack of knowledge isn't helping. I know my rig is not precise in the least, but I'm assuming that because the focus issue I'm experiencing looks evenly distributed then it's not caused by the focus screen being skewed on one side or the other, or top or bottom - as far as I can tell. The issue remains: sharp focus in center, soft focus out from center.

I did as you suggested and shot a GG-sized target with nothing but my video camera. http://i120.photobucket.com/albums/o.../HD_zoomed.jpg

This would seem to suggest the issue is not caused by the adapter (since no adapter is attached at this point). The issue appears to be caused by zooming on a close target, and it seems to be a function of the camera. A Sony TRV740 D8 does not exhibit the focus issue under the same conditions. Indeed, I shot a series of pictures each with slightly more zoom than the previous, and you can clearly see the "issue" get progressively worse.

However, the focus issue can be affected by the achromat - some I've tried are better than others. None, thus far, has completely fixed the issue. My latest experiments seem to result in fair-quality close up and a "not too bad" distance shot, relative to some other results I obtained. Not sure why the distance shot has the vignetting - I guess the difference in light or background or something.

close up: http://i120.photobucket.com/albums/o...o_x1_close.jpg
distance: http://i120.photobucket.com/albums/o...ino_x1_far.jpg

Paul Nixon · June 24th, 2008, 06:38 PM

These shots were taken using a different lens - a Canon 35-70mm Zoom. The achromat involved is a 50mm single lens from a binocular, and it is in only fair-at-best condition.

http://i120.photobucket.com/albums/o...zoomed_out.jpg

http://i120.photobucket.com/albums/o.../zoomed_in.jpg

Not sure what to make of the result - it looks to me to be more evenly focused when zoomed out compared with the other lens I have. Is this to be expected?

Paul Nixon · June 25th, 2008, 01:56 PM

Here's another "result" -

http://i120.photobucket.com/albums/o...est_iso_fr.jpg

lens is a 35-70mm f/3.5-f/4.5 Canon zoom.

I am not sure exactly how this target is supposed to be used, so I used it the best way I could - minimum distance from camera to target with slight zoom with the lens to fill the view. Illumination was via CFL. This sample was white balanced prior to shooting.

IMO, there seems to be an overall softness, but this doesn't surprise me - my achromat is in not so good condition and awaiting replacement. Not sure what's causing the yellow halo. It's more evident in: http://i120.photobucket.com/albums/o..._test_iso1.jpg

The 50mm f/1.8 Canon lens yields very poor results with barrel distortion and edge softness much worse than this lens.

Greg Tay · June 26th, 2008, 01:07 PM

Paul,
Zoom lenses are no good for 35mm adapters as these are light hungry. Zooms usually starts at f3.5. A good f1:1.4 or 1.8 lens should give you good results with no or very little vignetting. As for your your edge softness, most likely it's your achromat. I get that when I use a cheap +10 macro lens on my FX1. Also the canon 50mm f1.8 lens might be the one giving you the barrel distortion. A PCX lens might be giving you the barrel distortion too.

May 30th, 2008, 01:59 PM	#1
Dennis Stevens Major Player Join Date: May 2006 Location: Boston, Massachusetts Posts: 425	Brevis35 + 50mm Canon FD Hi- Just got a Brevis35, and was using a Canon fd 50mm lens on my JVC GY HD 100UA. I notice I have to zoom in a lot to get past the adapter, so much it doesn't seem I can get a wide shot. Is there something I have to adjust? Do I need a different lens? Total newbie question - be kind!

May 31st, 2008, 02:24 PM	#2
Paul Nixon Regular Crew Join Date: Feb 2007 Location: Mesa, AZ Posts: 141	Zooming is all part of the fun - it's seems typical of how these things work. If you don't mind, I have a question for you - I'm also using a Canon FD 50mm lens on my "homebrew" attached to my HC1, and I'm having an issue with focus being off away from the center. Could you please let me know if you get sharp focus from edge to edge with your setup? For example, compare: http://i120.photobucket.com/albums/o...35mm_no_fc.jpg to http://i120.photobucket.com/albums/o...m_attached.jpg Thanks.

May 31st, 2008, 03:13 PM	#3
Dennis Stevens Major Player Join Date: May 2006 Location: Boston, Massachusetts Posts: 425	I haven't noticed that issue, but I just got it. I believe the brevis you sometimes have to adjust the achromat so it's centered on the camera's focus center.

June 16th, 2008, 09:41 PM	#4
Dennis Wood Major Player Join Date: Mar 2005 Location: Ontario, Canada Posts: 916	Dennis, actually the achromat always stays dead center on the video camera lens, but we've designed in two XY adjustments after that point to ensure that any camera's with off-center imaging blocks can be accounted for. Paul, if you're seeing focus that is not sharp at the edges then this could be a result of many factors. For one thing, your imaging screen, lens mount and camera attachment points should be accurately placed with a tolerance of better than +0 .05mm in the Z axis which is almost impossible unless you're using CNC equipment to machine your parts. There's a number of optical issues that may be at hand too ranging from using a generic achromat, edge softness issues with the lens, etc. etc. Troubleshooting is a matter of breaking down each error factor one by one, starting with the bare camera. Baseline the camera first, focusing on a target a similar size and distance as your imaging screen. The adapter image you posted looks to have about 25% of the right and left sides of the frame out of focus so I'd start (after testing the camera with a close 24x36mm target) with alignment checks. Hope that helps, Dennis.

June 18th, 2008, 10:15 PM	#5
Paul Nixon Regular Crew Join Date: Feb 2007 Location: Mesa, AZ Posts: 141	Thanks Dennis, I agree regarding troubleshooting and breaking the problem down to find out the root cause, and I've been working hard toward that end. Unfortunately, I'm beginning to believe it's a combination of issues conspiring against me, and my lack of knowledge isn't helping. I know my rig is not precise in the least, but I'm assuming that because the focus issue I'm experiencing looks evenly distributed then it's not caused by the focus screen being skewed on one side or the other, or top or bottom - as far as I can tell. The issue remains: sharp focus in center, soft focus out from center. I did as you suggested and shot a GG-sized target with nothing but my video camera. http://i120.photobucket.com/albums/o.../HD_zoomed.jpg This would seem to suggest the issue is not caused by the adapter (since no adapter is attached at this point). The issue appears to be caused by zooming on a close target, and it seems to be a function of the camera. A Sony TRV740 D8 does not exhibit the focus issue under the same conditions. Indeed, I shot a series of pictures each with slightly more zoom than the previous, and you can clearly see the "issue" get progressively worse. However, the focus issue can be affected by the achromat - some I've tried are better than others. None, thus far, has completely fixed the issue. My latest experiments seem to result in fair-quality close up and a "not too bad" distance shot, relative to some other results I obtained. Not sure why the distance shot has the vignetting - I guess the difference in light or background or something. close up: http://i120.photobucket.com/albums/o...o_x1_close.jpg distance: http://i120.photobucket.com/albums/o...ino_x1_far.jpg

June 24th, 2008, 06:38 PM	#6
Paul Nixon Regular Crew Join Date: Feb 2007 Location: Mesa, AZ Posts: 141	These shots were taken using a different lens - a Canon 35-70mm Zoom. The achromat involved is a 50mm single lens from a binocular, and it is in only fair-at-best condition. http://i120.photobucket.com/albums/o...zoomed_out.jpg http://i120.photobucket.com/albums/o.../zoomed_in.jpg Not sure what to make of the result - it looks to me to be more evenly focused when zoomed out compared with the other lens I have. Is this to be expected?

June 25th, 2008, 01:56 PM	#7
Paul Nixon Regular Crew Join Date: Feb 2007 Location: Mesa, AZ Posts: 141	Here's another "result" - http://i120.photobucket.com/albums/o...est_iso_fr.jpg lens is a 35-70mm f/3.5-f/4.5 Canon zoom. I am not sure exactly how this target is supposed to be used, so I used it the best way I could - minimum distance from camera to target with slight zoom with the lens to fill the view. Illumination was via CFL. This sample was white balanced prior to shooting. IMO, there seems to be an overall softness, but this doesn't surprise me - my achromat is in not so good condition and awaiting replacement. Not sure what's causing the yellow halo. It's more evident in: http://i120.photobucket.com/albums/o..._test_iso1.jpg The 50mm f/1.8 Canon lens yields very poor results with barrel distortion and edge softness much worse than this lens.

June 26th, 2008, 01:07 PM	#8
Greg Tay Regular Crew Join Date: May 2007 Location: Singapore Posts: 30	Paul, Zoom lenses are no good for 35mm adapters as these are light hungry. Zooms usually starts at f3.5. A good f1:1.4 or 1.8 lens should give you good results with no or very little vignetting. As for your your edge softness, most likely it's your achromat. I get that when I use a cheap +10 macro lens on my FX1. Also the canon 50mm f1.8 lens might be the one giving you the barrel distortion. A PCX lens might be giving you the barrel distortion too.