Joshua Cadmium
Well-known member
You might want to check out the articles. Lensrentals has the equipment to test the MTF of a bare lens alone without the influence of a sensor (including whatever sensor stack thickness they want.)
GH4 LensRentals.com - Sensor Stack Thickness Part III: The Summary
- Thread starter Bern Caughey
- Start date
You might want to check out the articles. Lensrentals has the equipment to test the MTF of a bare lens alone without the influence of a sensor (including whatever sensor stack thickness they want.)
What equipment? what stacks? the actual sensor stacks or some random glass blocks?
There is no mention in the articles I read about the equipment or methodology. Just conclusions presented as facts.
When you start splitting hair you better have your ducks in place-or you get burned- happened to me many times.
Lensrentals is a very good resource for new comers to understand basics. They should stick with it. This issue is a little too complicated for them....
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stoneinapond
Veteran
You have to be kidding....:angry:
ProfessorU
Veteran
I'm completely in awe of the Speedboosters I've used so far. Thank you, Brian. Learning how much engineering went into the optics makes me feel much more confident about spending 6x more than the Chinese models.
What about for lenses like the Zeiss CP.2s? Obviously the sensor stack is different on a 5D mark III and an Epic. Until now, I'd assumed I could just by some CP2s, have PL and EF mounts, adapt the EF mount with a speedbooster to MFT cameras like the GH4, and have my "one lens kit to rule them all." Is this a foolish idea? Would I get better performance from nice MFT glass than fullframe glass that was designed for a different stack thickness? I'm trying to get a sense for which compromises have been made in which lenses.
What about for lenses like the Zeiss CP.2s? Obviously the sensor stack is different on a 5D mark III and an Epic. Until now, I'd assumed I could just by some CP2s, have PL and EF mounts, adapt the EF mount with a speedbooster to MFT cameras like the GH4, and have my "one lens kit to rule them all." Is this a foolish idea? Would I get better performance from nice MFT glass than fullframe glass that was designed for a different stack thickness? I'm trying to get a sense for which compromises have been made in which lenses.
brianc1959
Active member
I haven't measured the filter stack on an Epic, but unless it has fancy internal ND filters like the Sony F55 I would be surprised if the total glass thickness is all that different from the 5D MkII. If you are shooting at f/1.4 or slower with SLR lenses, then a filter stack difference of a millimeter won't make too much difference. Micro 4/3 cameras like the GH4 have a total filter thickness of about 4mm, which is about twice the value generally found on DSLRs. The is obviously not a problem for native m4/3 lenses. Its also not a problem for SLR lenses like your Zeiss CP.2s adapted via the m43 Speed Booster because the SB optics are corrected for the m43 filter stack.
Barry_Green
Moderator
I would just like to take a moment to welcome Brian and thank him for his attitude of sharing knowledge so clearly and openly. That's exactly the spirit we started DVXUser for, and Brian, I very much appreciate your participation here!
stoneinapond
Veteran
Joshua Cadmium
Well-known member
Here's the equipment: http://vimeo.com/96108293 Here's the article about the equipment: http://www.lensrentals.com/blog/2014/05/introducing-the-optical-bench Here's the manufacturer's brochure on the equipment: http://www.trioptics.com/pdfs/ImageMaster_HR_IR_2012_web.pdf
People have noticed these isssues. As mentioned before, Panavision themselves addressed them in their new Primo V lenses:
"Patent-pending modifications on the Primo V eliminate coma, astigmatism (vertical and horizontal focus differences), and other aberrations caused by the extra layers of glass in digital cameras. The image from a Primo V has sharper corners, a flatter field, and exhibits greater balance from center to edge than lenses that are not optimized for digital capture." - http://www.panavision.com/products/primo-v®-lenses
And who helped develop those Primo V lenses? Brian Caldwell, AKA brianc1959. I would trust the guy backed by Panavision.
For a reverse example: why were the Zeiss Digiprimes created? Because of the glass in front of the sensors on the B4 format. You couldn't just put a Master Prime on a 3CCD 2/3" B4 mount camera without massive aberration - caused due to the lens expecting nothing but air between it and the sensor, but getting glass instead (plus the fact that each color was focused at a different plane). And you can't just put a B4 lens on a normal camera without massive aberrations - you need additional optics.
The effect of the sensor's filter stack is basically the same as the B4 lens/sensor conundrum, but on a smaller scale. It's still an issue, though, especially at wider apertures.
I highly disagree. Their conclusion is backed by hard data on highly expensive, recently calibrated, automated optical testing machinery designed solely to test MTF to a accurracy of +/-0.03 . I think even Duclos Lenses relies on a chart projected through the lens as their gold standard. (And Matt Duclos thinks highly of Lensrentals as well, hosting a full article on his blog: http://matthewduclos.wordpress.com/2013/09/14/there-is-no-perfect-lens/ .)
OK that is a great post- thank you for taking the time to research- I'm immersed in reading now ;-)
I would like to set something straight- I admire the speedbooster- it works great and essentially doubles the lens inventory with faster and wider lenses-every operators dream come true since the dawn of film making times -so to speak... my hat's off to him for that without any reserves...
This is an entirely different issue however:
FYI I worked for Panavision for a few years back n their 1980's "glory days" and I'm intimately familiar with Panavision approach to optical equipment sourcing and promoting- lets just say that the brand mystique had a definite edge in our industry...however you interpret it.... I don't think that changed much from what I see today.
If the new Primo Vs are soooo much better than everything else why doesn't Panavision do a shootout test against the MPs, UPs, S4s film lenses and show everyone how much better thay are? With the amount of testing and prep done for every decently budgeted job I'm sure EVERYONE in the industry would really appreciate THE comparison. And it would give Panavision an edge over competition- again. Panavision has all the above lenses in their rental inventory so that should be easy enough- and fantastic marketing with the lens w#ore DPs and geeks- every great DP I know is one.
Put them on a 24MPix Sony a6000 so we can see all aberrations. My guess is they have not done it because the Vs are not really sooooo much better BUT- I will retract this guess if proven otherwise- with images ;-)
Actually this statement is false- again- I have done many conversions in the 3 chip camera times and intimately know this issue.
The reason Digi primes and other 2/3" 3 CCD chip specific lenses exist are:
1.The format of 9mm diagonal for 2/3 inch creates potential for fast hi performance optics but the image has to be "shrunk" so to speak to 9mm circle to achieve that- that's obvious reason for a specific optical design requirement.
2. the 3 dichroic filters and split prisms in the camera that divide the image into 3 monochromatic images actually place the 3 colored images at different distances from the flange so the optics have to be designed accordingly to compensate. This is the reason for highly visible dispersion while imaging 3 chip specific optics on a single sensor -with or without the glass plates- no difference.
Again- I appreciate your research and time you took to make this post but please don't mix separate issues you are not familiar with only because they appear related- it takes away your credibility. Just a friendly advise.
I read the article and, in fact, they emphasize that specifically deigned OLFP/sensor combos will give different results and the results from a specific combo should not be used as a rule for another camera - which I absolutely agree with...
To summarize:
A shootout between film designed industry standard lense and the new Vs that clearly shows the latters superiority would shut me up- and help Panavision and allow scores of pros to understand.. don't forget- we are highly "visual" crowd ;-)
Just to add: I've already learned a lot from this thread- I hope more users benefitted like I feel I did and I appreciate the civil and level headed responses- it could have easily gone of the rocker....
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Joshua Cadmium
Well-known member
I'm familiar with 2/3" 3CCD Optics. I just put things in easier to understand terms because I wasn't sure how familiar you were.
The prisms that split the image are made out of the same thing that is contained in the filter stack: optical glass. It really is the same issue - optical glass in between the lens and the sensor will impact the image if the lens is not designed for it.
Any glass is going to refract light that hits it - in other words, the glass is going to change the direction the light was originally traveling in. On a 2/3" 3CCD camera, the light coming from the lens is refracted in a big way (http://www.usa.canon.com/CUSA/assets/app/pdf/whitepaper/bctv/2.3InTriImager08.pdf).
The optical filter stack in front of a normal digital sensor is going to refract the light that hits it as well (or, in other words, the refractive index of the optical path between lens and sensor is increasing from about 1.00 - the refractive index of air - to something a bit higher.)
While the filter stack may not have a huge impact on the final image - it is noticeable, especially at larger apertures.
For instance, the m4/3 Speedbooster is designed for a 4mm filter stack. When using that Speedbooster on the Blackmagic Cinema or Pocket Camera, which has a 2.4mm filter stack, there is reduced sharpness due to undercorrected spherical aberration. However, when using the Speedbooster designed for the filter stack of the Cinema or Pocket Camera, that aberration is not there. Here's the info: http://www.bmcuser.com/showthread.php?9441-Speedbooster-for-GH4-BMCC/page5 .
Here are the pictures from that thread using a Nikon 55mm F1.2:
Bare lens (lens designed for no filter stack / sensor has 2.4mm filter stack)
Lens with m4/3 Speedbooster (lens designed for 4mm filter stack / sensor has 2.4mm filter stack)
Lens with BMCC Speedbooster (lens designed for 2.4mm filter stack / sensor has 2.4mm filter stack)
You can see that when the lens is designed with the filter stack taken into consideration, there are reduced aberrations.
Happy to have more civil and level-headed dialogue!
I don't think you understand- the 3 chip prisms intentionally , by design place the three images at different distances from the flange. They are designed that way. So lenses have to offset it. Again- it's not a result of the glass between the lens and the sensors- it is purposely designed that way. It goes back to tube cameras that had the tubes offset. It was carried over to the 3CCD camera design. Single sensor bayer cameras and OLFPs are different animal- nothing is carried over from 3CCD cameras.
Now I hope it's clear...
Now I hope it's clear...
Joshua Cadmium
Well-known member
Of course it's designed that way. A point I'm trying to make, though, is that it is the prisms (which work due to optical refraction) that accomplish that design. Without optical glass in front of those 3 separate sensors, the system isn't going to work.
In the same way, without a filter stack in front of your bayer (or equivalent) sensor, the system isn't going to work. The sensor needs optics in front of it that provide protection, color filtration (UV & IR), and possibly resolution filtration (OLPF).
As I showed in the pictures I linked, a lens designed for one optical path (between it and the sensor) isn't going to look it's best when put on another optical path.
A film lens will not look it's best when there is 4mm of glass in it's path. A m4/3 lens will not look it's best on film. A bare B4 lens isn't going to look great on either.
Do you get what I'm saying?
Filters are put behind lenses all the time for film use. there are filter holders, screw in filters- you name it. the only effect is back focus change due to refraction. projected it, tested on MTF, you name it. BTW I don't see any performance variation in the pictures posted (much appreciated effort BTW) but they just confirm that there is no perceivable difference. If you look at his fingers in the first picture they are very sharp. So it culd also be focusing issue. Sorry I just don't see any difference other than the magnification which makes it even harder to perceive.
BTW Speedbooster , in its brilliance does the opposite of extender so it shrinks the image and speeds up the system. If properly designed it should improve the sharpness as extender spreading the image over larger area softens it... it only makes sense...
Just look at 16mm lens sharpness vs 35mm- day and night difference for high end optics- I won some bets on this haha
BTW Speedbooster , in its brilliance does the opposite of extender so it shrinks the image and speeds up the system. If properly designed it should improve the sharpness as extender spreading the image over larger area softens it... it only makes sense...
Just look at 16mm lens sharpness vs 35mm- day and night difference for high end optics- I won some bets on this haha
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Bern Caughey
Veteran
I couldn't agree more!
Joshua Cadmium
Well-known member
Yeah, it's basically the same concept as filters behind the lens, which can cause the same aberrations. I know that most lenses that do incorporate filtration try to avoid those aberrations by using gelatin filters, which are much thinner than glass, or they have a clear glass filter in place when not using another filter.
Like I said before, it's may not be a huge difference, but it can be significant. In the images I previously linked, I personally see a big difference between the m4/3 Speedbooster and the BMCC Speedbooster. The former looks almost unusably soft on the BMCC, while the latter looks acceptable. There's a big difference in the bokeh as well. Your mileage may vary, of course.