So I shoot some test footage. And I believe everything is perfectly in focus and looking good. However someone i trust who is good in the filmaking field informs me it looks a tad soft. So now it made me question everything because i believed i did everything rigfht. I use a IKAN HD monitor and the focus seems good. So now my question is this. Could the monitor be misleading? And when focusing using the focus ring on the lens to me it seems if something is in focus in 1.5 to say 1.8. Is focusing supposed to be exremely exact without any room for error. ? Like only one number will make it in focus.
Focusing And The Brevis
- Thread starter PIMP
- Start date
Dennis Wood
DVXuser Sponsor
Backfocus is incredibly sensitive due to the fact that you're using an achromat and an image at very close range. If you're using the HVX focus assist, and stopping down the 35mm lens to f16 or so (unit off) then you should have a good shot at setting it correctly. Another test is to use focus assist with a detailed subject and use both the 35mm focus ring, and the HVX focus ring to bring it into sharp focus. If the HVX focus ring is in the same position using the two techniques, then it's set correctly.
If you haven't, check your 35mm lens focus marks to ensure that they match with measured distances. If not, a minute or two with the mico-collimation adjustment will get it perfect. For best performance from your lenses, particularly wide angle, this needs to be correct.
If you haven't, check your 35mm lens focus marks to ensure that they match with measured distances. If not, a minute or two with the mico-collimation adjustment will get it perfect. For best performance from your lenses, particularly wide angle, this needs to be correct.
Lenilenapi
Carbonite Member
You would have to tell us more to have any intelligent response. What was your lens, what video camera, what f stops were you using on the 35mm lens and the video camera? What was your detail setting on your video camera? If you were focusing the 35mm at 1.5 feet or meters that's pretty close to get a flat field. Ditto Dennis' remarks about wide angles and back focus collimation.
I don't know about the IKAN monitor but, I like something big to really jusdge back focus. Also my experience with 4 different adapters is that back focus is tricky and very cranky. Dennis has actually suggested it changes with the temperature which even makes me cranky to think about.
On every adapter I've tried (the SGPro might be an exception but i haven't looked recently) there is a difference between best center and corner focus marks. (This makes perfect sense since its hard to get an achromat to focus flat on that close a target.) If you use focus assist to focus on the grain in the center, you will sacrifice your corners and vice versa. Stare carefully at the screen on a good monitor and you will see this and you may have a devil of a time finding the best compromise between center and corners. Frankly its a pain.
I did this with a Letus Extreme the other day. I thought I had the focus correct but we were testing lenses and noticed that that the corners were soft. We finally had three people staring at a monitor for almost a half hour trying to get it precise .Generally i think it is best to go just barely (farther ) past the best center focus and you will be at an optimum compromise - that's if you don't have a monitor big enough or enough time to check the corners. But definitely don't focus on the near end of the center.
I always bring a focus card with me which is a blow up from Kinko's (3' or 4' wide) of a standard focus chart you can find on the Web. After roughing it in with the standard method of focusing on the ground glass while looking at an out of focus image ( or one with no 35mm lens ), I put up a 35mm lens and look at the chart. Then I go back and forth focusing the 35mm lens and double checking the backfocus on my HVX checking always for corners and center. During the day I double check the chart whenever I get a chance.
To me that's the real test because you are looking through a lens at an image. Personally i don't trust the ground glass method, because i'm not sure exactly where the image is on the glass. Likewise I wouldn't trust the "auto focus" on the ground glass technique either unless I double checked it a bunch of times against the chart method. A chart will tell you the truth for sure.
My skeptism about how most people seem to set backfocus extends to my skeptism about claims made for which adapter is the sharpest, because I haven't heard of anyone testing that while being extremely careful about their initial backfocus set-up uysing a chart. Likewise claims that any adapter has a perfectly flat field.
Maybe if I can bear to take the time I'll try comparing my Brevis , SGPro and Letus Extreme for focus one of these days, but its kind of painful so i don't know if I'll really do it.
- Lenny Levy
I don't know about the IKAN monitor but, I like something big to really jusdge back focus. Also my experience with 4 different adapters is that back focus is tricky and very cranky. Dennis has actually suggested it changes with the temperature which even makes me cranky to think about.
On every adapter I've tried (the SGPro might be an exception but i haven't looked recently) there is a difference between best center and corner focus marks. (This makes perfect sense since its hard to get an achromat to focus flat on that close a target.) If you use focus assist to focus on the grain in the center, you will sacrifice your corners and vice versa. Stare carefully at the screen on a good monitor and you will see this and you may have a devil of a time finding the best compromise between center and corners. Frankly its a pain.
I did this with a Letus Extreme the other day. I thought I had the focus correct but we were testing lenses and noticed that that the corners were soft. We finally had three people staring at a monitor for almost a half hour trying to get it precise .Generally i think it is best to go just barely (farther ) past the best center focus and you will be at an optimum compromise - that's if you don't have a monitor big enough or enough time to check the corners. But definitely don't focus on the near end of the center.
I always bring a focus card with me which is a blow up from Kinko's (3' or 4' wide) of a standard focus chart you can find on the Web. After roughing it in with the standard method of focusing on the ground glass while looking at an out of focus image ( or one with no 35mm lens ), I put up a 35mm lens and look at the chart. Then I go back and forth focusing the 35mm lens and double checking the backfocus on my HVX checking always for corners and center. During the day I double check the chart whenever I get a chance.
To me that's the real test because you are looking through a lens at an image. Personally i don't trust the ground glass method, because i'm not sure exactly where the image is on the glass. Likewise I wouldn't trust the "auto focus" on the ground glass technique either unless I double checked it a bunch of times against the chart method. A chart will tell you the truth for sure.
My skeptism about how most people seem to set backfocus extends to my skeptism about claims made for which adapter is the sharpest, because I haven't heard of anyone testing that while being extremely careful about their initial backfocus set-up uysing a chart. Likewise claims that any adapter has a perfectly flat field.
Maybe if I can bear to take the time I'll try comparing my Brevis , SGPro and Letus Extreme for focus one of these days, but its kind of painful so i don't know if I'll really do it.
- Lenny Levy