Letus Extreme Resolution Chart
- Thread starter Luis Caffesse
- Start date
Hi all,
it was my camera that Luis used for the tests and it did surprise me to see the softness in the res chart corners. When I got my camera back, I looked at a chart and monitored it on a pana 17" monitor. I do see it, especially in the top right corner which I feel may be an issue with my HVX's ccd being offset to the left.
I did reset the backfocus and improved it a little but it would be great if the mount to the HVX would allow you to center the ground glass. Also, while they're at it make some sort of stop that comes off the back of the letus and rests on the HVX focus ring to stop it moving.
I have shot 3 jobs with the extreme and did not notice it in a real world shooting scenario and was very happy (as was my director ) with the shallow depth of field that the adapter provides. It now stays on my camera.
All the best,
Shane.
it was my camera that Luis used for the tests and it did surprise me to see the softness in the res chart corners. When I got my camera back, I looked at a chart and monitored it on a pana 17" monitor. I do see it, especially in the top right corner which I feel may be an issue with my HVX's ccd being offset to the left.
I did reset the backfocus and improved it a little but it would be great if the mount to the HVX would allow you to center the ground glass. Also, while they're at it make some sort of stop that comes off the back of the letus and rests on the HVX focus ring to stop it moving.
I have shot 3 jobs with the extreme and did not notice it in a real world shooting scenario and was very happy (as was my director ) with the shallow depth of field that the adapter provides. It now stays on my camera.
All the best,
Shane.
Luis Caffesse
Admin
That says it all to me.
And from what I saw, I couldn't agree more.
Thanks again Shane.
Ted Spencer
Veteran
These charts were very informative. I'd love to see more with/without adapter comparisons. Anyone got links?
reem12
Veteran
i think this is a mute issue,it's already been confirmed through test and footage by tim naylor,disjesta and others tht the letus ex is a very sharp adapter.it even prooved sharper than the acclaimed sgpro.i had the sgpro rev 3,red rock,and the letus flip and theres a reason why i haven't looked back with the letus ex.sharpness being one of them.also,i think people alot of times expect an adapter to compensate for an already crappy,soft cornered lens.if the lens is sharp to begin with then the adapter should project that,but if it's soft the adapter will not make it sharp.i think that would be asking a little much out of these sub $1500 adapters.but anyway,to me a bad adapter is one that mutilates the image of a good lens.i been toying around with sailing my whole a1 and letus ex rig with indi focus and rails in favor of the new sony camera but after shooting more test footage yesterday it's making it hard to do.as i look at my footage i keep asking myself how much more qulity do i need.as i said in a post before if letus wanted to charge more for there adapter could.personly when i used to see footage from the red rock i would always admire how beautiful the image was and never even noticed the soft edges until members on this site brought it to my attention.my point is when your watcing a movie your eyes are only focusing on that which is in focus.but like all on here i'm guilty of this nit picking to.
Luis Caffesse
Admin
I agree the image is what matters - and shot the res chart to satisfy my curiousity (mainly because I hadn't seen one from any previous testing - I must have missed it), not as a dealbreaker to see whether or not the adapter was worth buying. I was already convinced by the footage I shot that the adapter is plenty sharp.
Like I said before, everything we do in shooting is a compromise - and I just felt it was important for me (not for everyone maybe) to see what was being compromised to get the look that you get from the adapter. In the end, is the compromise worth it? I think yes, no question at all.
(by the way, just FYI - it's a 'moot' issue not 'mute')
Ted Ramasola
Veteran
Luis,
It very informative that you did this test. I have a question.
Is the achromat of the letus built in the adapter? Can you tell how big it is? Like if its 72mm like the brevis and redrock hd achromat. or if its around 55-58mm.
Im wondering because i am seeing the same soft corners even in my diy adapter and i found out that soft corners diminish as i move the achromat closer to the front element of the cam's lens. Unfortunately in my case it cant get any closer due to the fact that the hd100's stock lens has its front element recessed deeply.
I'm using the brevis achromat at 72mm which i must say is a good achromat only that i had to remove it from its 82-72mm step down ring. retrofiited it in a tube and inserted it into the focus barrel beyond the filter thread until it is snug. i experienced a significant improvement in my soft edges. But its still there, but outside in the TV safe area.
Ted
It very informative that you did this test. I have a question.
Is the achromat of the letus built in the adapter? Can you tell how big it is? Like if its 72mm like the brevis and redrock hd achromat. or if its around 55-58mm.
Im wondering because i am seeing the same soft corners even in my diy adapter and i found out that soft corners diminish as i move the achromat closer to the front element of the cam's lens. Unfortunately in my case it cant get any closer due to the fact that the hd100's stock lens has its front element recessed deeply.
I'm using the brevis achromat at 72mm which i must say is a good achromat only that i had to remove it from its 82-72mm step down ring. retrofiited it in a tube and inserted it into the focus barrel beyond the filter thread until it is snug. i experienced a significant improvement in my soft edges. But its still there, but outside in the TV safe area.
Ted
Lenilenapi
Carbonite Member
Luis,
I've spent alot of time staring at focus charts with these adapters and while they are never perfect I think your looks pretty bad. Not only are the corners too soft, but there seems to be exposure vignetting as well. However ,how much of this is the fault of the Letus would be impossible to judge. As has been mentioned -using a Nikon @ f.14 is getting its worst performance and the specific faults will be poor corner focusing, vignetting and you may also exaggerate any lens back focus issues.
Regarding whether you will see these corner issues on footage - of course you will if its the right shot.
I posted the following on a previous thread but it seemed worth redoing it here. I am surprised in general at how little careful attention is placed on exactly how people back-focus these adapters (and moreover how they set backfocus on the lens mounts themselves - but that's another issue.) Maybe I'm prickly about it because I spent years in a film rental department checking tehy backfocus of every lens that went out.
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 on exteriors of a fence. We finally had three people staring at a monitor for almost a half hour trying to get it precise, so we knew which footage readout was the best to guarantee focus. 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 using a chart. Likewise the numerous claims that any adapter has a perfectly flat field. Frankly all you have to do is very slightly bump the focus ring when you are taping it down and the comparison is tainted.
Maybe if I can bare 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. My gut feeling is that all three are close in sharpness, but that's an untested hypothesis.
- Lenny Levy
I've spent alot of time staring at focus charts with these adapters and while they are never perfect I think your looks pretty bad. Not only are the corners too soft, but there seems to be exposure vignetting as well. However ,how much of this is the fault of the Letus would be impossible to judge. As has been mentioned -using a Nikon @ f.14 is getting its worst performance and the specific faults will be poor corner focusing, vignetting and you may also exaggerate any lens back focus issues.
Regarding whether you will see these corner issues on footage - of course you will if its the right shot.
I posted the following on a previous thread but it seemed worth redoing it here. I am surprised in general at how little careful attention is placed on exactly how people back-focus these adapters (and moreover how they set backfocus on the lens mounts themselves - but that's another issue.) Maybe I'm prickly about it because I spent years in a film rental department checking tehy backfocus of every lens that went out.
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 on exteriors of a fence. We finally had three people staring at a monitor for almost a half hour trying to get it precise, so we knew which footage readout was the best to guarantee focus. 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 using a chart. Likewise the numerous claims that any adapter has a perfectly flat field. Frankly all you have to do is very slightly bump the focus ring when you are taping it down and the comparison is tainted.
Maybe if I can bare 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. My gut feeling is that all three are close in sharpness, but that's an untested hypothesis.
- Lenny Levy
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Luis Caffesse
Admin
My gut feeling is the same - but it would be great if you could do that test.
I know alot of people (myself included) would find it interesting.
As far as the backfocus on the Letus I used goes - the system was setup when I picked it up. It was not my adapter and I wasn't about to mess with the backfocus on it seeing as it had been set by the owner prior to my picking it up. I didn't just pick up the adapter, I took an entire HVX rig with adapter and rails. Shane mentioned in the other thread that he was surprised by the chart, and after seeing it "I did reset the backfocus and improved it a little"
Either way - thanks for your thoughts, and the details on proper backfocus setting.
If and when I get my hands on another adapter rig, I'll definitely give it a try the way you outlined it.
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Luis Caffesse
Admin
Yes it is.
I don't have the adapter with me anymore, so I'm really not the guy to answer that question, and I don't to guess. Hopefully someone else will chime in with the correct answer.
Lenilenapi
Carbonite Member
Well Luis I'm responding to you on this one. sorry i got things confused by the way.
When yous ay the rig was set-up are you including the focus of the HVX on the Letus. - If so i would never trust that from one day to the next. I even recheck during the day.
Let's face it, you've got some weird floating ring coupled to an auto focus system in there that's just not a solid mechanical connection. who knows how much slop is in there?
By the way i think its great that you shot the test and posted it - When I said it looked bad that was not personal - but I think you know that. Your already my hero for doing the 85 filter test.
- Lenny
When yous ay the rig was set-up are you including the focus of the HVX on the Letus. - If so i would never trust that from one day to the next. I even recheck during the day.
Let's face it, you've got some weird floating ring coupled to an auto focus system in there that's just not a solid mechanical connection. who knows how much slop is in there?
By the way i think its great that you shot the test and posted it - When I said it looked bad that was not personal - but I think you know that. Your already my hero for doing the 85 filter test.
- Lenny
Luis Caffesse
Admin
Sorry, didn't realize you posted this until just now
No, I double checked that - though I should say first that Shane checked it before I even took the rig. I checked the focus again myself at home (mainly because I wanted to see how difficult it was to focus). I actually wound up at the same focus point that he had set the camera. So either we were both right, or we were both wrong.
No worries - I don't take anything personally.
I'm just glad someone other than me cared about that 85b filter.
I think we might be the only ones.
No, I double checked that - though I should say first that Shane checked it before I even took the rig. I checked the focus again myself at home (mainly because I wanted to see how difficult it was to focus). I actually wound up at the same focus point that he had set the camera. So either we were both right, or we were both wrong.
No worries - I don't take anything personally.
I'm just glad someone other than me cared about that 85b filter.
I think we might be the only ones.
Ted Ramasola
Veteran
Luis,
After seeing your charts, i pulled out mine and did some tests on my own. Its obvious that most adapter users like to shoot as wide as their lens can, so duplicating your settings using a 50mm at f1.4 as a constant i achieved soft corners as you did by setting my relay lens, in my case a fujinon, to f5.6. BUT, maintaining the 50mm at f1.4 and changing the relay iris settings you can achieve much improved corners starting at F8. At f11 is slightly better than f8.
On the other end, opening to f4 upwards greatly deteriorates the corners.
In my tests, f4 has a big difference from F5.6.
With these results i would watch my relay's iris in situations where corners matter, i'd step it down.
I cant say these figures apply to the HVX considering its has different lens elements as the fujinon, but i believe the principle would.
What was your iris settings on the HVX?
Ted
After seeing your charts, i pulled out mine and did some tests on my own. Its obvious that most adapter users like to shoot as wide as their lens can, so duplicating your settings using a 50mm at f1.4 as a constant i achieved soft corners as you did by setting my relay lens, in my case a fujinon, to f5.6. BUT, maintaining the 50mm at f1.4 and changing the relay iris settings you can achieve much improved corners starting at F8. At f11 is slightly better than f8.
On the other end, opening to f4 upwards greatly deteriorates the corners.
In my tests, f4 has a big difference from F5.6.
With these results i would watch my relay's iris in situations where corners matter, i'd step it down.
I cant say these figures apply to the HVX considering its has different lens elements as the fujinon, but i believe the principle would.
What was your iris settings on the HVX?
Ted
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Ted Ramasola
Veteran
Luis
Im attaching a comparison "chart" on the test i made.
Note, i'm not trying to compare adapter performance with the HVX or the Letus since a.) im using a different camera, b.) i'm using a different adapter.
I just did this to resolve some issues of my own regarding some softness on my rig.
When i saw your charts i figured it wasn't just mine exhibiting the problem.
But then i discovered significant improvements on our image corners when we will tweak our relay lenses NOT just the 35mm lens.
I hope this helps other new users to an adapter.
Thanks again luis for this heads up.
Ted
Im attaching a comparison "chart" on the test i made.
Note, i'm not trying to compare adapter performance with the HVX or the Letus since a.) im using a different camera, b.) i'm using a different adapter.
I just did this to resolve some issues of my own regarding some softness on my rig.
When i saw your charts i figured it wasn't just mine exhibiting the problem.
But then i discovered significant improvements on our image corners when we will tweak our relay lenses NOT just the 35mm lens.
I hope this helps other new users to an adapter.
Thanks again luis for this heads up.
Ted
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Ted Spencer
Veteran
Interesting to note that it's sharper on the "16:9" text at f8 than f11.
Ted Ramasola
Veteran
Ted Spencer,
Thanks for pointing that out! I made a mistake in sequencing the stack layers in photopaint when i created that chart. I corrected the image above now.
The f11 is indeed sharper than f8. I checked the grabs again.
Sorry for the confusion.
Thank you again for pointing that out.
Ted
Luis Caffesse
Admin
Teddy - thanks for taking the time to do that, that's interesting.
No question that your tests show a marked difference in corner sharpness as the fstop goes up...
but then does that mean that diffraction not have the same effect when using the camera's lens as a relay lens?
I'm no optics expert (obviously) - but I know when shooting with the HVX stock lens I can see a drop in sharpness when going anywhere above f8 (and there is a slight drop between 5.6 and 8 which I can see on a chart) - so I always try to keep the HVX at a 5.6 or below for the sharpest image.
Would that no longer hold true when using an adapter? I assumed it would (but then again, I shouldn't assume anything).
If memory serves, the HVX in my setup was set to an f4.0.
No question that your tests show a marked difference in corner sharpness as the fstop goes up...
but then does that mean that diffraction not have the same effect when using the camera's lens as a relay lens?
I'm no optics expert (obviously) - but I know when shooting with the HVX stock lens I can see a drop in sharpness when going anywhere above f8 (and there is a slight drop between 5.6 and 8 which I can see on a chart) - so I always try to keep the HVX at a 5.6 or below for the sharpest image.
Would that no longer hold true when using an adapter? I assumed it would (but then again, I shouldn't assume anything).
If memory serves, the HVX in my setup was set to an f4.0.
Ted Spencer
Veteran
At the risk of making a "firm grasp of the obvious" point here, this would be yet another object lesson in why adequate light must be used with lens adapters. Wide open on an SLR film lens, or in this example, on the "host lens", will almost certainly result in severe edge-sharpness loss. That combined with extremely shallow DOF could make for a focusing nightmare of pretty staggering proportions.
Getting enough light to stop down the lens to its sweet(er) spot- *no matter what it takes to do it* - seems to be the clear imperative unless edge sharpness is unimportant for a particular shot.
Getting enough light to stop down the lens to its sweet(er) spot- *no matter what it takes to do it* - seems to be the clear imperative unless edge sharpness is unimportant for a particular shot.
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Luis Caffesse
Admin
Fair enough - though I don't think its truly all that obvious (to me at least) unless there is a clear idea as to what that 'sweet spot' is, which goes back to my relay lens/diffraction question above.
I guess some simple testing could determine the answer to that - seeing as the Zeiss has been tested alone and its pretty clear what the 'sweet spot' is on that lens. If I get my hands on an HVX/Letus combo again at some point soon, I'll give that a try.
I guess some simple testing could determine the answer to that - seeing as the Zeiss has been tested alone and its pretty clear what the 'sweet spot' is on that lens. If I get my hands on an HVX/Letus combo again at some point soon, I'll give that a try.