Author Topic: Let's talk LENSES!  (Read 678 times)

BiduleOhm

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Re: Let's talk LENSES!
« Reply #15 on: July 23, 2017, 04:50:49 AM »
I searched for a bit and I can't find a F to C-mount focal reducer. I guess we need to ask on photography forums if this kind of focal reducer exists.

Electra

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Re: Let's talk LENSES!
« Reply #16 on: July 23, 2017, 09:04:14 AM »
Some info on how they work: http://rubenkremer.nl/2013/11/26/focal-reducers-speedbooster-lens-turbo-and-light-cannon/
https://beomagi.blogspot.com.au/2014/01/focal-reducers-on-dslrs-and-light-gain.html
And a bit about them on more conventional cameras:  http://nofilmschool.com/2014/07/cheaper-budget-metabones-speed-booster-excell-1-fotodiox-pro

I did find: http://agenaastro.com/agena-c-cs-mount-focal-reducer.html
There looks to be a whole range for telescopes. Might be worth looking down that path.

Because we'll be doing something non-standard, I'm expecting half research and half trial-and-error to get this working, but unless I've got something very wrong, it should possible.
Depending on the lens/adapters, we may have to find native reducers for our lenses and then something like that c mount one for the final to get past the adapters narrowest point. One thing that might help is that C mount is made for 1" sensors(or close to it) and we have a 2/3" sensor, so even if we loose some light, concentrating what we can use further might still help.

I know there'll be looses in the optics and I'm expecting most bother, but it's too interesting a path to not at least experiment a bit.

BiduleOhm

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Re: Let's talk LENSES!
« Reply #17 on: July 23, 2017, 10:07:34 AM »
Yeah I found this one too but it's for a 1.25" telescope mount, I don't think it'll be very useful here unfortunately.

Yes, if you can find the proper reducer then it'll work no problem. The main problem is to find one for a C or CS mount and where we can mount a Canon/Nikon lens (EF or F mount) on the other side even if we need another adapter. For now I only found 1.25" to C mount reducer or some DSLR to another DSLR reducer.

nik282000

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Re: Let's talk LENSES!
« Reply #18 on: July 23, 2017, 06:02:37 PM »
Hmm, a speed booster is an element on the back of a lens compresses the image circle. So what do you call an element in front of the lens that compresses the image circle? A fisheye filter!

If you can find a strong enough fisheye filter it would give you both a wider FOV and more light per pixel on the sensor (provided that the aberrations from filter aren't too bad). Given that the Chronos sensor is 2/3" many of the aberrations from a filter may fall outside the sensor area anyway. Looks like there are a couple on ebay/amazon for <$100 but I have never personally tried one.

Any thoughts?

John DeLonghi

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Re: Let's talk LENSES!
« Reply #19 on: July 24, 2017, 06:08:45 AM »
My experience of fitting wide angle adapters to the front of lenses has never been particularly good. The optical performance is usually not very good and as they are often designed to be 'universal' they take no account of the construction of the lens they're being fitted to.
There are some good ones around but they are quite expensive and I don't think the end result will be as good as if we can find a focal reducer.

I also spent some time over the last few days trying to find a decent reducer to fit the Chronos with no real success. There won't be any demand for such a thing at the moment, but if there was a way to adapt something like a Metabones Speed Booster, I'd go for it.

I think it should be technically possible to adapt a Speed Booster designed to take Nikon G/F mount lenses to fit the Chronos, but the missing link is converting one of their camera-side mounts to C/CS.

BiduleOhm

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Re: Let's talk LENSES!
« Reply #20 on: July 24, 2017, 11:32:21 AM »
What's their camera side mount?

John DeLonghi

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Re: Let's talk LENSES!
« Reply #21 on: July 25, 2017, 03:54:21 AM »
They do various versions, all for mirrorless cameras such as Leica M/S Sony E, Fuji X.

I reckon the best bet might be the versions they do for MFT or Blackmagic as those are small diameter mounts to begin with. It might be possible for someone to machine a mounting ring which would replace their one and convert directly to C mount.

There are lots of adapters out there for fitting C-mount lenses to MFT cameras, but not the other way around.

nik282000

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Re: Let's talk LENSES!
« Reply #22 on: July 25, 2017, 10:24:48 AM »
It all has to do with the back focus distance, with mft and e-mount I believe the cmount adapters extend into the body of the camera. To make an mft or e-mount to c-mount I think that means there will be a couple mm of space in which to make an adapter.

Welp, looks like the flange to sensor distance for all 3 mounts are 17-19mm, not much room to work but not impossible.
« Last Edit: July 25, 2017, 10:36:07 AM by nik282000 »

John DeLonghi

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Re: Let's talk LENSES!
« Reply #23 on: July 25, 2017, 10:55:02 AM »
That's why I thought it might be possible with one designed for MFT in the first place. It's bound to be tight, but 17.5mm seemed enough to me looking at another C mount camera I have here.

It's the engineering of an adapter which is going to be tricky and it would be an expensive mistake if it didn't work.

I do feel the optics of the Metabones reducers are worth the money and could give excellent results if we could get one to fit. I've emailed them to ask if they think it's possible, so let's see if I get a response.

Looking at lens options generally, I'm also looking at Kowa C-mount lenses as there are a few Blackmagic camera owners using them and they have a good reputation for quality. There are plenty of old C-Mount lenses around on ebay but I suspect quite a few of them are not worth bothering with.