2/3" lens on Sony F3 via homebrew adapter
 

OK folks. I wanted to see just how well a 2/3" broadcast lens would work on an F3, but don't have $5.5k to fork out on one of the Abel adapters. So with a bit of head scratching, a few, lowish cost lens purchases and a few hours in the workshop I cobbled together my own adapter. At first I tried a 2x magnifier but this didn't quite give me full sensor coverage and was soft out in the corners. With a little more work I took the magnification up to 2.5x and I have clean corners. I'm really pleased with the performance, although one lens element needs changing for a higher quality element to combat some softness when the iris is fully open.

My old Canon J16x8 f1.8 becomes a 24 to 320mm f4(ish) par-focal lens which is actually quite handy. Next step is to make up a power cable for the lens so I can use the zoom servo.

I'm considering trying to find a manufacturer that can make these up for me properly, the converter should cost a lot less than $5.5k

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Way to go Alister. I'll be looking for that.
How do you find time to work on shoots though?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

You really need a batch, my experience is that one off items have high machining costs.

Just checked and I don't know about the price, but Abakus now have their 260 Converter, which covers Super 35,

http://www.abakus.co.uk/Format_Converters.htm

Re: 2/3" lens on Sony F3 via homebrew adapter
 

£1,940 + VAT for the 260 B4 to super 35.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Is the softness in the corners a coma/astigmatism or a chromatic abberation?

Are you just using a doublet?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

The corner softness looked like astigmatism. The adapter contains a pair of doublets.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

This is around $3200.00. ZGC wants $4200 for the Abakus. Might be cheaper to go directly from Abakus if anyone's thinking of purchasing one.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

How are you correcting for standard colour offsets built into the video camera optical block?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

I'm not correcting for the colour path lengths and I doubt that Abekas or CineAble are either. So far my test shots show minimal CA, certainly no more than I get with the same lens on a prism camera. Don't forget the prisms introduce a ton of aberrations so the cleaner optical path of a single chip camera really helps get good performance from broadcast lenses.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Nothing like Venetian blinds to show those colours. Although, if you're designing from the optics from scratch it shouldn't be a big problem to apply some correction, but I gather it isn't as noticeable on a 35 mm sensor compared to 2/3" HD.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

With two doublets you have six curvatures, four indexes of refraction and four abbe numbers,
you ought to be able to remove the spherical abberation or sphero-chromatism (different spherical
per color) that is already baked into the 2/3" lens to compensate for the prism. Toss in an
asphere and it should be very good. It might be hard to use just off the shelf components
though without having a design plan and then making it fit to off the shelf stuff.

Is there a standards document that describes what optical properties a 2/3" lens must have
to properly work on a 3-CCD camera? I would imagine it would specify axial color and the
amount of spherical abberation per color needed to make it through the prism in focus.

IANALDBITSC...

(I am not a lens designer but I took some classes...)

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Jesus, the things you guys know!! And I thought I was a camera nerd.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Just be totally geeky: BTA S-1005-A HDTV Standard.

Canon have a good range of white papers:

http://www.usa.canon.com/CUSA/assets...WhitePaper.pdf

http://www.usa.canon.com/CUSA/assets...riImager08.pdf

Re: 2/3" lens on Sony F3 via homebrew adapter
 

I agree! One question - Is there a way to make an adapter with less than two stops of light loss? Since the F3 has power it would be quite a tool to have ENG & EFP in one camera but having your ENG end at F4 is kind of a drawback. F2.8 would be fine.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

This is basically a range extender and it's the size of the Super 35 sensor which will dictate the magnification required, therefore how brightly the light is spread across the sensor.

It's an old trick, the best known example being the modification of the 16mm 12-240mm zoom into a 35mm 24-480mm using a x 2 range extender. It was about T9, so not a lens for interiors.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Yes, it is basically an extender, only to get up to super 35 from 2/3" you need a magnification factor of around 2.5x. A few 2/3" lenses with built in extenders will just cover a s35 sensor without any modifications, just a simple B4 to PL adapter. Mike Tapa has one for the Panasonic AF101 but the micro 4/3 sensor is a little smaller than s35 so most 2/3" lenses with extenders will cover the AF101 sensor.

I'm investigating two approaches. One is to use the lenses built in extender with a simple doublet reduction lens with a 1.25x power the other is to use the lens without the built in extender and then an external 2.5x extender.

I'm getting similar results with both methods. Using the integral extender requires a simpler more compact design, but you must have a lens with an extender. The external extender is more complex and longer, but you can use the Canon cinestyle lenses which often don't have integral extenders. Either way compared to the non extended lens you get a 2.5 stop light loss. Consider that you are taking the same amount of light but now spreading it out over a larger area, so the amount of light falling on any given point is reduced.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Thanks for your reply. Makes sense. When I engage the extender on a Canon broadcast zoom there is a softening of the image to some extent. With the light loss and the loss of sharpness I would wonder if the final product would be as good as the 2/3" lens on a proper sensor/mount setup.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

All lenses have a finite resolution. The reason why the lens softens when you engage the extender is because if you take the lenses projected image which if we say for arguments sake has 1000 lines resolution falling on the 2/3" sensor and then enlarge it by 2x with the extender the resolution falling on the sensor is halved to 500 lines (the other 500 lines falling off outside the sensor area) and any aberrations are increased in size by two times.
So if you take that larger image, which with the extender engaged now almost covers the F3's sensor. That entire original 1000 lines now falls on the larger pixels and sensor and you get back to a sharp, 1000 line resolution image with the same size aberrations. Assuming the extender itself is well designed the difference in image quality will be minimal between 2/3" no extender and 35mm with extender.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

The light loss is exactly coupled to the amount of extension. You are changing the focal length
through the extender but the pupil size is set by the pupil installed in the main lens.

The formula for f stop is basically focal length divided by pupil size. If you double the focal length
the f number has to get bigger. Only way to keep it constant is to violate conservation of energy.
If use an image intensifier tube to pump energy into the system, you can increase the effective
f number but that's cheating.

It's probably astigmatism plus Petzval curvature since the two are closely related. Two
doublets in a row is a lot of positive power to be adding on to the end of a well corrected
system and you are going to have field curvature problems. Field curvature is the classic
limiting problem in lens design and you usually have to engineer the entire lens around
it from the start. On the plus side, you say you don't have coma so you don't have to fix that.

If I saw this problem on the test I would say add a negative element somewhere,
look the problem up in a book and call an expert. I have Sidney Ray's "Applied Photographic
Optics" book in front of me and chapter 53 has a few words on teleconverters.

What you want to do take a small image plane and convert it into a big image plane
like a barlow lens or a door peephole. Usually you do this with a negative overall power
so I'm not quite sure how your are doing this with two positive elements (are you
inverting the image?).

The two examples that Ray gives for teleconverters both involve a doublet and a singlet
and one of them is major negative power while the other is somewhat positive and
balances abberations. The major negative element keeps the field curvature down as
well.

Another book to see is Herbert Gross's Handbook of Optical Systems volume 4 but
only a major university might will have that sitting around.

I think the trick is that if you have a built in extender, you don't want the tubing/mechanics after
the extender to vignette (much). That's probably gonna limit you to 1.25x internally. There might be
a lens with a 2x extender internally that you could hack everyone off past the extender and
get a larger image "for free". Probably not as likely to produce a perfect image since the folks
designing the extender will not have optimized the picture out to a super-35 sized frame.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Thanks for your thoughtful responses guys. Very informative!

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Status update:

I have two working adapters. Both use optical extenders made up from 4 lens elements, One pair are reduction lenses followed by a second pair that provide correction for field curvature and coma.

Both work acceptably well but in different ways.

Option one is a short adapter that I have fitted with a Canon DSLR mount. So it will work on a Canon DSLR or F3/FS100 with a Canon mount adapter. It only works with broadcast lenses that have a 2x extender and makes use of the in built doubler (so yes, I am using an extender, followed by a further extender). The adapter provides an additional 1.25x image magnification.

Option two is a much longer adapter, specifically for the F3. It has a 2.5x magnification factor so works without the need to use a lens with an extender.

At the moment I am favouring option one. Image quality wise there is very little to choose between them. Option one with a top end HD lens is extremely sharp with excellent contrast. It appears to perform slightly better than option 2 due to the way the integrated lens extender is very carefully matched to the individual lens, so there is less variation in performance from lens to lens.

Option two's corner performance is more variable due to differences in field curvature from lens to lens which is then magnified 2.5x. But it still performs well and I would be happy to use it given that options for 20x zooms for the F3 are near zero. It does have the advantage that if you really want to go crazy, you can use the lenses extender! Performance is better when the lens is stopped down more than f2.8 due to flare at f1.8

The cost for either as a completed product would be around $1,300 USD. Anyone else want to express a preference: Higher IQ, Canon mount, but must use lens with integral doubler, or Dedicated F3 mount, no need to have extender, but lens should be stopped down to f2.8 or slower.


Either way you loose approx 2.5 stops.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

I'm a picture guy, it would be great to see these items Alister.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

I'm going with the 1.25x adapter design. I get much more consistent results across differing lenses with this design. I also have my first cable design up and running so you can use the lens to trigger recording in the F3 and the zoom servo works too. I think it might be possible to get the auto iris working as well. The nice thing is that by adding an external EVF the length of the lens and integral lens handgrip makes for a nice shoulder mount system.

No pictures yet, this is still a rough prototype. One a get the first fully machined version I'll post pictures.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

OK, here's a sneak preview.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Dear Alister,

I believe your canon lens is a SD lens, isn't it. How well do lenses like this perform on HD camera's like the F3 and EX3? Do you loose a lot of quality compared to the 'real' HD lenses. Is lens quality (picture) as good as using dslr lenses on these camera's?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Okay, just found a thread called "HD 2/3" Lens Tests" where amongst others Alister and steve Phillips discuse a lot of ins and outs of SD lenses on HD cameras. So found alot of my answers already, except for how it compares to prime dslr lenses.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

That depends on the DSLR lens. The Canon lens in the picture becomes roughly a 20 to 320mm lens with perfect focus tracking and constant aperture. Such a DSLR lens afaik does not exist. The pictures are sharp and with good contrast. An HD lens would possibly a perform a little better (higher contrast) I would expect.

A good DSLR prime lens should outperform a zoom in terms of contrast, flare and resolution, but the differences may be small. The question is will the versatility of a 20 to 320mm zoom (admittedly now only f4) outweigh the possibly very small and not necessarily noticeable difference in image quality. Only you can decide that for yourself based on your specific needs.

Certainly for many of the shoots that I do a decent zoom will be a godsend. For other projects primes will be preferable.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Thanks Alister,

The case is that I am using a Nikon 80-200/2.8 zoom, a 300/4 and very occasionally a 400/3.5 for wildlife filming. But i miss a decent zoom, not for making nice zooms, but mainly for finding my subject in wide and then focus in. That's why I look for an affordable broadcast zoom, but i don't want to (significantly) compromise on picture quality compared to the dslr lenses i mentioned. The 80-200 is my main lens. I see that you can buy an ocasion Canon J16x8 for less than 2000 euros. If it is as good as the 80-200 it could be a great benefit to have the 16x zoom. Would like to have a bit more tele however.
One day I might also look further for a real big zooms like the A36x14,5 you metion in the other thread. Realise that would be in another price league, but investing good money in a lens that will serve me for the rest of my life feels better than investing in cameras that will last for 5 years or so. espicailly now you prove that these lenses also do their job on large sensor camera's. That is very, very valuable information.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Image wise I would say that the Canon J16 is on a par with my Sigma 70-300 f4 APO. I'm much happier using the Canon J16 as the focus ring is so much smoother and has far greater travel, so getting spot on focus is much easier and of course servo zoom makes life much simpler.

There are plenty of low cost 20x SD zooms second hand. Most of these perform reasonably well for HD, but best if you try before you buy.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Very interesting :) I looked into doing similar for the EOS 550D, but couldn't find any reasonably priced solution.. It almost made me want to trade in the 550 for a GH1 since people have been using 2/3th inches on those for a while..

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Alister, I've got a real nice Fujinon HD ENG B4 lens that I use with my Viper. I'd love to try your adapter on my F3 and finally get a nice long range zoom with a servo on my F3. I think it'd be kind of neat to have the option to use my Fujinon HD Zoom on my F3. I'll be watching this thread to see if you're able to get these spun up at a reasonable cost.

There is no way I'd put $5k toward something like this but if it were a bit more reasonable, I'd certainly consider it.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Does your lens stay parfocal, no matter the adapter? I thought that the parfocal characteristics of the lens were related to the exact distance to the sensor the lens was designed for?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Yes it stays parfocal. I am going to get a few made up. I'm in Singapore for broadcast asia at the moment so can't do much right now, but as soon as I am home I hope to get some completed units.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Hi Alistair

I'm interested as well in buying one of your adapters. What do you think the extra weight would be? Do you think there is any issue regarding the F3 mount and your adapter taking the weight of a 2/3" ENG lens?

What exactly are the minimum criteria for a 2/3" lens? 2 x doubler? 16:9? All BL mounts? I've started sniffing around for them and your previous post about them being numerous is right. There's quite a price range so it's a little daunting if like me you're not very familiar with them. Any tips welcome.

Not so home-brew anymore
 

Spent the day with Mike of MTF services today testing the first production version of my adapter. It certainly looks good. We tested it on a variety of 2/3" lenses from super wides to long zooms and all worked well. Right out in the very corners there is some softness, but much of this is typical of an ENG zoom. Within the normal "broadcast safe" window the images are nice and crisp. I'm really pleased with the end result and the guys at the rental house (aim image, thanks guys) wanted to keep the adapter rather than let us take it back to the workshop. So, the CNC machines are now machining the first production run which should be for sale by the end of the month from MTF.

There are some pictures on my Facebook page: http://www.facebook.com/media/set/?s...9256241&type=1

2/3" lens on Sony F3 via homebrew adapter
 

Hi Alister,

This is great news. Many of us are anxiously awaiting an affordable 2/3" adapter for the F3. Speaking of affordable, any idea on what we can expect on the price?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

For the F3 kit it should be £1150 GBP.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Congratulations on your work and initiative. The main Canon zoom you've been testing with is SD, right? So you're confident that even with an SD rather than HD lens mounted on your adapter (because of the expense), the pictures should be sharp with good contrast? Is it the same with the other lenses you tested at MTF?

Have you uploaded any footage shot with the SD lens and the adapter?

Does the cable connect to the F3 and give zoom servo and iris control?

What is in the F3 kit apart from the mount?

Re: 2/3" lens on Sony F3 via homebrew adapter
 

I've been testing with an SD lens and it works reasonably well, however it is softer out in the corners than the HD lenses we have also been testing the adapter with. Contrast and centre sharpness with the SD lens (Canon J16) are what I would call acceptable, not as good as can be achieved with an HD lens, but useable.

At the moment we are only supplying the B4 to Canon mount adapter and the F3 kit which includes the B4 adapter plus a Canon to F3 adapter. The B4 adapter will be fitted with a lens support bracket on it's base.

The cable will be a separate item. Initially it will only provide power for the zoom. Pricing for the cable is to be confirmed.

Re: 2/3" lens on Sony F3 via homebrew adapter
 

Hi Alister

Any chance of uploading some frame grabs so we can eyeball the resolution, especially from your SD Canon J16 lens as well as the HD lenses?

Many thanks.