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AKAI 1:2 11.5~90mm (Canon Japan Serial) -Info request Help!
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PostPosted: Sun Sep 04, 2011 5:09 pm    Post subject: AKAI 1:2 11.5~90mm (Canon Japan Serial) -Info request Help! Reply with quote
Hi

Quick intro
New to the C Mount world (hello world!), but have been enjoying many other MF Lens for a while now.

I stumbed across this lens today for very small money and thought I'd give it a go. (nex to cmount adaptor eta wednesday.)

In the interim I thought I'd ask if anyone has anymore info, especilly re the sensor/film size for this C mount. (Having the APS-C nex....this may be rather tunnel like if for the smaller than 16mm image circle stuff)

PS will drop some sample pics when the adaptor arrives.





PostPosted: Sun Sep 04, 2011 6:30 pm    Post subject: Reply with quote
Have the same as Canon version, image size is very small, but does not focus correctly (might be a faulty lens though).


PostPosted: Sun Sep 04, 2011 8:04 pm    Post subject: Reply with quote
I have the canon version, as Klaus says it has a small image circle so no good on the NEX or M4/3.


PostPosted: Mon Sep 05, 2011 7:07 pm    Post subject: Reply with quote
Please correct me if I'm wrong Smile

Just been doing a *little* reading in the forum and these zooms(canon etc) don't seem to impress...or work for that matter(as above), other than in the reverse macro way.

I like the idea that these zooms were designed for TV where one could zoom in and out without losing focus. (Don't know if this is true)
http://members.tripod.com/~Camera_Dave/lens-theory-2.htm

My adaptor is yet to arrive and perhaps I'm jumping the gun but I'm already thinking of how I could modify this lens.

Considering how litte I paid I really don't mind chewing it up in a lathe.

OK Guys do any of you have any info on how to increase the image circle.

Should I look to play with teleconverers or jump streight into removing and playing with the rear element group?


PostPosted: Thu Sep 08, 2011 12:00 pm    Post subject: Reply with quote
Hello saffersteve,

Yes, that lens is designed to be 'true-zoom' or parfocal, meaning it will hold focus throughout the zoom provided that you adapt it properly, including registration and adjustment of front and back focus. Otherwise, it will perform like a varifocal zoom.

I don't know what success you'll have with swapping rear groups.

You could use a c-mount 2x converter.


PostPosted: Thu Sep 08, 2011 2:02 pm    Post subject: Reply with quote
Quote:
You could use a c-mount 2x converter


Thanks for the reply Ekoe, rather quiet this Cine lenses forum Wink or perhaps it's just my posts Sad

My only concern with using a C-mount 2x convertor is that this will still only produce the 16mm Image circle from the back of the teleconvertor (detail enlarged of cause by 2x) Really need a corrective optic of some kind.

anyway.....just learnt that the c - nex adator has arrived this morning in the post so will have a go and report whether the lens actually works or not or fits the adaptor or not....etc.

Playing with the rear group will in effect make this a very different lens....and more than likely produce horrible results and destroy it.....but like I said.....for what I paid for the lens...I really don't mind playing/experimenting with anyones Ideas.

Lets hope it performs so I'm not temped to play.


PostPosted: Thu Sep 08, 2011 3:32 pm    Post subject: Reply with quote
These aren't cine, nor Akai made - they were essentially a recorder maker, probably even the camera it was intended for was supplied by a third party (Canon doubtlessly supplied the lens). It is a video lens, the camera it was intended for will have had a 1/2" or 2/3" tube, i.e. a image diagonal of merely 8 or 12mm - if you really want to use C-mount CCTV lenses, you'll probably be better off (both financially and in results) simply buying a Pentax Q rather than fiddling around with converters.


PostPosted: Thu Sep 08, 2011 4:54 pm    Post subject: Reply with quote
True, it's a video lens but it's got a cine 'c' mount so I think it does belong here.
You could also pursue lenses intended for 1" video. You will still see some vignetting, but it will be better than anything you might get out of the Akai 11.5-90, even if you just happened to discover the perfect rear lens group to appropriate.
As mentioned, that 11.6-90 zoom is best suited to the Kenko c-mount camera, the Pentax Q, or for Super 8mm cameras like Beaulieu, so you may consider re-selling it and put that towards acquiring a better suited lens. I have a few fast c-mount zoom lenses that provide very good coverage of the 4/3 frame, but you will see more vignetting from them on your NEX. Let me know if you're interested.


PostPosted: Fri Sep 09, 2011 4:35 am    Post subject: Reply with quote
Ok

First off to answer the image circle size of this lens

At 11.5mm FL the image circle = 12mm (see first image below)
At 90mm FL the image circle = 16mm (see second)





PostPosted: Fri Sep 09, 2011 2:04 pm    Post subject: Reply with quote
This advice is for m4/3 sensor cameras. Nex will have greater losses.

This is good for Panasonic video. The digital zoom will use the central area of the zoom and you will have a 23-180mm zoom. In 135, 35mm, style the lens zooms from 46, or normal, to 360 all at F2!

The Pentax Q takes 1/2 lenses, so the crop factor is 5.6 or so. Even longer zoom than the 4 crop factor above. If you have a GH2 I believe the ETC mode is larger than 2x. Stills, I cannot comment, as I do not know about any digital zoom effect on Pany. There is no such redemption on the Oly except to shoot and resize when post processing. Video works OK apparently. Stills will mean you lose up to half resolution and then the crop factor is 4x. Disappointing, but usable?

I would not meddle with the innards! You may want to explore what is under the rubber bands? There may be limiters screws to restrain focus to a certain range. These are complex instruments.

There is also the Kenko that takes c mount lenses native. Similar crop factor to the Pentax Q.

Good buy! I still buy them when they are cheap! My latest, a 22.5 -90, has problems as the focus hardly works, but zooming will allow focus without much magnification!


PostPosted: Fri Sep 09, 2011 2:44 pm    Post subject: Reply with quote
pat donnelly wrote:

There is also the Kenko that takes c mount lenses native. Similar crop factor to the Pentax Q.


Does it really exist by now? None of the English language Japanese sites I'm aware of sells it, and some friends have already speculated that it either has been killed in favour of its Pentax Q sister model or was only camouflage for its prototypes.


PostPosted: Mon Sep 12, 2011 2:29 am    Post subject: Reply with quote
Sevo!

Good point!!!

Theoretically, in Japan nothing can be taken for granted, they are independent. Does the Pentax Q have a c mount? Then it was not identical to the Kenko.

Both these cameras are mythical especially as the Pentax have a price point designed to condemn it to single number sales!

Have you heard anything?


PostPosted: Mon Sep 12, 2011 2:35 am    Post subject: Reply with quote
SafferSteve

This is the quiet corner of the forum!

You are in pioneering territory here, despite the prices being charged on fleabay for relatively mediocre cine and c mount offerings! The enthusiasm of we few has caught the imagination of the warehousers who are selling accordingly! As you well know, actual sales are far more reasonable in price! Laughing

Nordentro is another frequent poster and has many fine photos showing off his lovely wife and fine c mount lens collection. Well worth checking out his posts?

Keep the faith and know you will get more responses now that you are posting here!


PostPosted: Mon Sep 12, 2011 8:56 am    Post subject: Reply with quote
pat donnelly wrote:

Have you heard anything?


No. The Pentax has its own mount. But the Pentax Q positively exists (has been tested by various camera rags and blogs, is listed on several Pentax sites and is pre-orderable at many established dealers in Europe) while the Kenko C-mount camera has only been seen once, at a trade show early this year, and looked very much like a rough prototype. With Kenko the niche market subsidiary of Hoya and EVIL not niche any more, they may have been pulled off it in favour of the higher profile brand. We'll see whether it resurfaces once Ricoh has finished taking over Pentax...
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