35mm optical adapter (No GG)

Re: 35mm optical adapter (No GG)

Thanks for the explanation Brett :). Very helpful!

I did realize that the adapter would allow the full field of view for the lens - I was just hoping that it would also (magically) retain the depth of field. Ah well!

One thing I don't understand is how you would increase your low light sensitivity. Is it just due to the better light gathering capabilities of 35mm lenses?

Maybe I'll set to work on my other idea - designing a 2.35:1 anamorphic adapter ;). Though that brings up problems too... darn!

Thanks for the explanation!
 
Re: 35mm optical adapter (No GG)

Geez, DIY lenses. Shaw just kicked it up a notch. ;)
 
Re: 35mm optical adapter (No GG)

It gives your better low light capability because you CCD is getting more light than before. This is happening not so much because of the 35mm lens but the fact that your taking the 35mm image area and squeezing it down to 1/3" size.

You can see the same thing happen when you take a video projector and use the lens to squeeze down the projected image. As the image gets smaller it also gets brighter. Focusing a mag light is another basic example.

To make your anamorphic adapter you'll need whats called a two element cylindrical lens and if you want it to give you a 2:35 image for a DV camera it will need to be aprox. 1.78X horizontal power. Thats it. Let us know how it goes.

Brett Erskine
www.CinematographerReels.com
 
Re: 35mm optical adapter (No GG)

Geez, DIY lenses. Shaw just kicked it up a notch.
Click to expand...

:D I'm actually not all that skilled in this area - I just know I have the resources to attempt it! We'll see how my attempts turn out ;)

Again, thanks for the info Brett - and thanks for the encouragement. I think I'm going to give both lenses a shot and see how they turn out. I'll be sure to post my progress and results!
 
Re: 35mm optical adapter (No GG)

hillarious! yeatserday i took out a few 35mm lenses, and started experimenting with a bright light trying to focus an image on a wall at the correct distance, then i took some various lenses i have around and tried to shift the focal plane back to see if this was possible. it went out of alignment, and i ended up looking into the darn thing to line it up, and blinded myself for a sec in that eye from the light.. :o what a dope! then i put the stuff away. i started laughing and asked myself "what the heck are you doing" ..then i decided i would leave the optics testing to the people who actually know something about it. it was a moment of laughable stupidity.

im glad this was resolved by people who actually knew about this issue with lense optics right away before any more people started frying their eyes. :P
 
Re: 35mm optical adapter (No GG)

Barry,
Interesting that you should mention aerial image...ever since
I read about the home-built Mini35 thing, I wondered why no one (apparently) has tried an aerial image design. The best "slide to video" transfers I ever had were done using this design...I built one years ago with parts from a surplus store.
A rail assembly would certainly be needed because of the weight, but it seems a viable solution...at least on paper.
Ken
 
Re: 35mm optical adapter (No GG)

Read above for why it doesnt work for DOF.
 
Re: 35mm optical adapter (No GG)

Brett,
If you're simply "rephotographing" a projected image, whether it's on ground glass, the wall, or existing in an aerial plane of 35mm film size, the DOF effect of the 35mm lens will be recorded.
Ken
 
Re: 35mm optical adapter (No GG)

Ken-
I'd love to be proven wrong for this project so please share your source that makes you believe that the DOF will also be maintained. From the real world tests over the years both mine and coutless others this has been unfortunately shown not to be true - unfortunately.
 
Re: 35mm optical adapter (No GG)

Brett,
DOH! Sorry about that...my old brain was transposing FOV with DOF.
The knees are definitely NOT the first to go. :)
Ken
 
I know, I know... I'm raising this thread from the dead but...

http://www.abelcine.com/articles/index.php?option=com_content&task=view&id=170&Itemid=45

http://www.abelcine.com/store/product.php?productid=1000394&cat=354&page=1

Apparently this IS possible, DOF, and FOV both retained :)

With that said, I'd like to start up a big discussion on how to actually make one of these.

From what I understand, the majority of this adapter is essentially just a lens to relay the resized aerial image to the cameras CCD's. With conventional ground glass adapters, this relay lens would be the cameras built in lens. According to these sources there are 11 optical elements total, most of which are probably used for resizing the image. So I'm willing to bet that only a few optical elements would be needed if you tried making something like this for a camera with a built in lens.

Anyone wanna experiment and report back?

I recently put a negative magnifying glass up to my eye and then held a 50 mm lens up in front of it. The lens was set to 1ft focus. I positioned my eye about 1 foot away from an object. I then put the lens in front of the magnifying glass and moved it back and fort till the object came into focus. I was then able to successfully pull focus. I don't know how accurate the DOF is yet. At any rate, it looked promising enough to keep on messing around with it.
 
I've read that review about the JVC adaptor a while ago. I thought it's too good to be true then two items struck me: it only maintains S-16mm FOV and has a minimum effective aperture of 2.8 (even when your PL lens is wide open). This is hardly the DOF characteristics of a 35mm size imager. Whenever I shoot S-16, I routinely shoot at 2.0 or lower just to get a "cinematic" DOF. 2.8 doesn't cut it. But the JVC shows that an adaptor without a GG is possible. To use the built in lens as part of the relay would be the solution.

quote from review:

"Transmittance

I was slightly disappointed when I determined that the maximum usable aperture of the HZ-CA13U seemed to be T2.8. The documentation states an exit aperture of f/1.4, and after a day of research, I realized that my findings of T2.8 on the lens side are a result of a basic optical imaging law known as the Lagrange invariant. This affects all lens systems in the same way. Using the horizontal frame size values of 16mm (9.35mm), 1/3” CCD (4.8mm), and the exit aperture of f/1.4, I determined mathematically that the max lens aperture is f/2.73.

The bottom line is that using high-speed lenses will have no benefit to exposure or depth of field once they are opened past T2.8. However, if you are used to shooting at open apertures in low-light on your video lens, you will be surprised to find that the equivalent T-stops marked on the ciné lenses all seem to be about 1-1/2 stops brighter than the same video zoom F-stop values. This means that T2.8 on a PL prime lens has an equivalent exposure to about f/1.7 on the video zoom lens. This phenomenon seems to be an added benefit of the optical invariant. The easiest way to manage this is to rate the camera 1-1/2 stops more sensitive than usual. "
 
Interesting catch there Tim, but I think I remember reading in the review that it wasn't a production model he was testing, but rather a prototype model. Also, this is older material... for what its worth.

I did catch this though..

"We found that the HZ-CA13U has an equivalent angle of view of standard 16mm. The fact that JVC chose a 16mm frame size aerial image will come as a surprise to most because the trend tends to be 35mm for all of the other ciné lens adapters. I was also disappointed when I first read the spec. However, I now realize that this was a calculated move on JVC’s part. There is an abundance of standard PL 16mm lenses available around the world. From film schools to rental houses, it won’t be hard to find a half-decent set of 16mm format primes somewhere in your part of the world. Of course, any PL prime or accessory (35mm or 16mm format) will work with the adapter. "

Apparently this prototype at that time was made for 16mm FOV DOF, but because the mounts are the same, can take 35mm (but not have 35mm FOV and DOF when using 35mm lenses) as well. At least thats how I read it.

Now my big question is this...

Can you make one of these devices designed with a 35mm aerial image instead?
 
I'm not surprised this adapter makes the camera more sensitive at all... It kinda makes sense really. Ever mess with a magnifying glass and ants on a summer day?

:P

Probably the same general idea going on here.
 
I've been making my own adapters for the longest time...actually they work pretty awesome. I've used them in a couple of commercials and lately in two 48 Hour Film Project films. A couple of my colleagues have the LetUs and the Brevis and Redrock and they are always begging me to make them one...I actually have a LetUs Extreme which I love...but I still think mine rocks.....

Regardless...all this munble just to say one day I was building a couple of prototypes when I had a little revelation that blew me away. While building one i attached the lens to the tube and I looked in the camera and i had the most beautiful clear image. I was so excited because I had been experimenting with GG's. SO I thought I had come up with the Holy Grail of static adapters....the grainless one.

So i get my pencil and notebook just to make notes on the GG I had used. i open the adapter and violá! I had forgotten to put the GG...yet I was getting an image! WHat the heck.

To make the long story short...Somehow I was getting a crystal clear image. I was BLOWN away! Upon further testing of this new adapter I started noticing that the DOF was not as radical as the ones you get with the regular DOF adapters out there...but it is a pretty subtle one.

While looking at the pics on the JVC article the DOF of eminds me of the one I was getting. i assure you that if they had also tested a Redrock or a Bravis the DOF would have been more noticeable. But...hey grainless, motorless, and light loss none existent? Can't beat that.

I do not undesrtand the why's of what is happening...but it does work. I still have it somewhere...maybe I should pull it out and see what the heck is going on...oh yeah and mine has no 11 elements
 
Nice info Super8. I think all optical 35mm adapters are the wave of the future as long as sub 35mm size chip cameras are around...

FOOTAGE:

http://web.mac.com/timdashwood/iWeb/sundance/HZ-CA13U_Test.html

Yeah, it looks like nice 16mm because thats what the adapter was made to give, and its grain free ;)

I wonder if you can't get more shallow than 16mm though? Just a though. Even if that turns out to be the case, I wouldn't mind 16mm DOF, its better than the cameras native lens and DOF combo... and that whole EXTRA light characteristic is mighty nice too :)
 
Super8: All GG adapters will pick up an aerial image if the GG is removed. The DOF will be the same as the equivalent focal length of the system. That is, you do not get the benefit of the shallow DOF without the GG.

Other notes:
JVC didn't really "pick" 16mm FOV for their adapter--that's the best that can be done with that technique. There are only two variables that you have to work with when trying to reduce DOF: focal length and f-stop. We already know that no combination of focal lengths gets us anywhere in the DOF battle. So...the way it works, as explained to me by an optical engineer, is that the JVC adapter increases the light thruput by 2.5 stops. The DOF difference between 16mm and 1/3" is 2.5 stops. But of course the hitch is as was mentioned about the JVC--maximum aperture is T2.8! So there goes a lot of shallow DOF capability.

The Angenieux CLA35 works the same way. It gains 2.5 stops. The DOF difference from 35mm to 2/3" is, not coincidentally, 2.5 stops. But of course it also has a maximum aperture limit that also limiits the shallowness of the DOF.

Using this same technique to go from 35mm Cine to 1/3", you would need to gain 4.6 stops, which is pretty much impossible, plus the maximum aperture would come into play again, so the useful DOF would still be limited.

(And the damn image would STILL be upside-down!)

GG is better.
 
Dan Vance said:
Super8: All GG adapters will pick up an aerial image if the GG is removed. The DOF will be the same as the equivalent focal length of the system. That is, you do not get the benefit of the shallow DOF without the GG.
Click to expand...

Dan:

I did get DOF...if i had to rate the different DOF's I was getting (and I did the comparisons) with 10 stars being the best and 1 star being the crappiest DOF I would say:

Adapter with GG = 10 stars for DOF
Adapter with no GG = 6 stars for DOF
Stock Lens = 1 Star for DOF
 
Dan Vance said:
The DOF difference between 16mm and 1/3" is 2.5 stops. But of course the hitch is as was mentioned about the JVC--maximum aperture is T2.8! So there goes a lot of shallow DOF capability.

The Angenieux CLA35 works the same way. It gains 2.5 stops. The DOF difference from 35mm to 2/3" is, not coincidentally, 2.5 stops. But of course it also has a maximum aperture limit that also limiits the shallowness of the DOF.

Using this same technique to go from 35mm Cine to 1/3", you would need to gain 4.6 stops, which is pretty much impossible, plus the maximum aperture would come into play again, so the useful DOF would still be limited.
Click to expand...

Just out of curiosity, why are you using the term stop in your explanation. Do you simply mean doubling of sensor size or something to that effect? Sorry, I just don't hear that term outside of the exposure world very often.

Could you elaborate more on this maximum aperture limit? What happens if you open the lens wider than 2.8?

You know, a cool feature for some of the GG adapters could be an easy and fast way to pull the GG out of the optical path inside the adapter. Now you could have two options: 16mm grain free look, or a grainy looking 35mm look. That would be really cool actually.

Thanks
 
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