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Focal reducer, only for crop sensor, right?
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PostPosted: Tue Jul 25, 2017 12:33 am    Post subject: Focal reducer, only for crop sensor, right? Reply with quote
Hi there,

I'm using the Mitakon Zhongyi Lens Turbo ii on my Fuji X-T10.
Someone asked me if it would be possible to use it with a full frame Sony A7s.
My vague idea is that, although it's possible to mount it on the full frame camera, I'm not sure how much the benefit would be and, above all, there will be some severe vignetting.
I guess this is the case with wide angle lenses, would it also be true with 50mm and above?

Thanks for any clarification.

Best


PostPosted: Tue Jul 25, 2017 3:45 am    Post subject: Reply with quote
A friend of mine is using 0.75x speed booster on Sony A7S for medium format lenses, like Kaleinar 150/2.8 and others.


PostPosted: Tue Jul 25, 2017 4:00 am    Post subject: Reply with quote
Thank you, CuriousOne.
150mm sounds like a safe zone for a full frame. I think there's a threshold below which vignetting happens.
Not sure what's the minimum focal length in this case.


PostPosted: Tue Jul 25, 2017 7:12 am    Post subject: Reply with quote
The original Speed Booster can adapt any FF or medium/large format lens (with a proper adapter) to APS-C or MFT cameras only.
I've tested it and it covers a circle of ~3 cm only, no matter if the coverage of the lens in front of it is much larger than FF or its FL is longer than 50mm.
It can't be used on a FF sensor without severe vignetting. That's the case with the original Metabones Speed Booster. I have no experience with other Speed Boosters.

Kipon recently made a Speed Booster to adapt Hasselblad lenses to Sony FF E-mount cameras, but with mixed reviews. See here:
https://www.dpreview.com/articles/6113651777/kipon-to-launch-reducer-to-mount-medium-format-lenses-on-full-frame-cameras


PostPosted: Tue Jul 25, 2017 7:30 am    Post subject: Reply with quote
All focal reducers shrink the image circle of the lens, so they're only practical on lenses with coverage well beyond the sensor being used.
From thew optical requirements the lens must also be mounted closer to the sensor than it would be without the reducer, and the optics of the reducer still have to fit in the reduced gap.

These 2 factors together rule out many of the set-ups suggested by people who don't actually know anything about focal reducers. Many people seem to think of them as a teleconverter - which enlarges the image circle & needs the lens mounted further away so often usable with any lens that can be mounted direct.
Some TCs are designed to protrude into the rear of telephoto lenses so would foul on non compatible lenses. None of mine are of this type and they do work (perhaps not well) with lenses well outside their design parameters.


PostPosted: Tue Jul 25, 2017 7:44 am    Post subject: Reply with quote
Focal reducers are also light enhancers as they focus light meant for a large captor on a smaller captor


PostPosted: Tue Jul 25, 2017 10:09 am    Post subject: Reply with quote
I use speedboosters on 24x36mm cameras since years. Started with homemade ones on my Canon EOS 5D, then I bought a Sony Alpha 7II because of its shorter flange bck distance for my speedbooster work, and now I often use that medium format to 24x36mm Kipon speedbooster.

See here some images and discussion:
http://forum.mflenses.com/results-of-my-speedboosted-lenses-candc-t77297.html

Experiments with one speedbooster for crop cameras on a fullframe cameras gave no good results. Extreme vignetting.


PostPosted: Tue Jul 25, 2017 10:56 am    Post subject: Reply with quote
I still don't get the appeal of a speed booster/lens turbo. The one I tried turned great lenses (Minolta MD 1.7/50 and 2.8/28 ) into garbage with smeary edges and introduced severe CA.


PostPosted: Tue Jul 25, 2017 2:31 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
I still don't get the appeal of a speed booster/lens turbo. The one I tried turned great lenses (Minolta MD 1.7/50 and 2.8/28 ) into garbage with smeary edges and introduced severe CA.


Sounds like you had a duff one!
I've never noticed any image degradation with mine.


PostPosted: Tue Jul 25, 2017 4:10 pm    Post subject: Re: Focal reducer, only for crop sensor, right? Reply with quote
cgustav wrote:
Hi there,

I'm using the Mitakon Zhongyi Lens Turbo ii on my Fuji X-T10.
Someone asked me if it would be possible to use it with a full frame Sony A7s.
My vague idea is that, although it's possible to mount it on the full frame camera, I'm not sure how much the benefit would be and, above all, there will be some severe vignetting.
I guess this is the case with wide angle lenses, would it also be true with 50mm and above?

Thanks for any clarification.

Best

The lens turbo and most other "Speed booster's" will be designed to work with image circles of the intended sources and destinations, for example a FF source and a 1.5x or 2x crop as the destination format, moving to smaller formats shouldn't cause any issues so long as the source format has a significantly larger image circle than the destination.
On the other hand, moving the other way to larger image circles, ex medium format lenses to FF sensor will most likely cause vignetting, because the image circle on the output is likely not designed for the larger sensor, the input side of the booster will most likely not capture the full image circle of the lens, the boosters optics would have to be the size of the image circle.
So the booster would have to be designed for larger formats, and for smaller then intended formats, you may or may not get good results, only testing will prove it works well enough to use.


PostPosted: Tue Jul 25, 2017 7:25 pm    Post subject: Re: Focal reducer, only for crop sensor, right? Reply with quote
iangreenhalgh1 wrote:
I still don't get the appeal of a speed booster/lens turbo. The one I tried turned great lenses (Minolta MD 1.7/50 and 2.8/28 ) into garbage with smeary edges and introduced severe CA.


Definitely something wrong with the copy you tried.
After I tried the Mitakon Zhongyi I never went back. I personally find it actually increases the quality. Images are a little sharper.


Lightshow wrote:

The lens turbo and most other "Speed booster's" will be designed to work with image circles of the intended sources and destinations, for example a FF source and a 1.5x or 2x crop as the destination format, moving to smaller formats shouldn't cause any issues so long as the source format has a significantly larger image circle than the destination.
On the other hand, moving the other way to larger image circles, ex medium format lenses to FF sensor will most likely cause vignetting, because the image circle on the output is likely not designed for the larger sensor, the input side of the booster will most likely not capture the full image circle of the lens, the boosters optics would have to be the size of the image circle.
So the booster would have to be designed for larger formats, and for smaller then intended formats, you may or may not get good results, only testing will prove it works well enough to use.


I was afraid this would be the situation.
Thank you Lightshow and thank you all for the info.

Best


PostPosted: Tue Jul 25, 2017 7:44 pm    Post subject: Reply with quote
It was a Zhongyi one I had, I definitely do not believe it could make anything sharper, I also do not believe that it does not add abberations.


PostPosted: Tue Jul 25, 2017 10:07 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
It was a Zhongyi one I had, I definitely do not believe it could make anything sharper, I also do not believe that it does not add abberations.


I'm guessing that would be the lens turbo MK1 that they withdrew from sale as it was so bad.
Not something to judge the usefulness by!

Reviews suggest the MK2 is better than the cheap RJ version I got, which would make it pretty good IMO.


PostPosted: Wed Jul 26, 2017 12:57 am    Post subject: Reply with quote
DConvert wrote:
I'm guessing that would be the lens turbo MK1 that they withdrew from sale as it was so bad.

Yeah Ian has (had?) a version 1 product. I remember the thread in which focal reducer experiences were discussed. Ian was very unhappy with his.


PostPosted: Wed Jul 26, 2017 1:18 am    Post subject: Reply with quote
I did, put me off ever trying another, I did a bunch of experiments using various elements and combinations of such and concluded that the only way to make a focal reducer that didn't introduce aberrations would to use aspherics and exotic glasses, which they aren't doing as it would make them expensive. Sure, they have probably reduced greatly the level of aberrations since the v1 turd I had, but they will not have been able to remove them, so for me, nope, not what I want as I want the output of the objective with nothing added.


PostPosted: Wed Jul 26, 2017 8:20 am    Post subject: Reply with quote
iangreenhalgh1 wrote:
I did, put me off ever trying another, I did a bunch of experiments using various elements and combinations of such and concluded that the only way to make a focal reducer that didn't introduce aberrations would to use aspherics and exotic glasses, which they aren't doing as it would make them expensive.

FWIW - Metabones in their Ultra range of Speedboosters are using exotic glasses. Not likely to be using aspherics though. $1000 for a focal reducer would be kinda nuts Laughing


PostPosted: Wed Jul 26, 2017 11:19 am    Post subject: Reply with quote
Interesting, the Ultra sounds like it might be interesting to me one day, for video work at least. Cheers for that tip.


PostPosted: Wed Jul 26, 2017 2:59 pm    Post subject: Reply with quote
My Speedbooster Ultra combined with my Canon FD Aspherical 55mm 1.2 is a sublime combo. Speedboosters are the real deal for me.


PostPosted: Thu Jul 27, 2017 4:28 am    Post subject: Reply with quote
mackeral wrote:
My Speedbooster Ultra combined with my Canon FD Aspherical 55mm 1.2 is a sublime combo. Speedboosters are the real deal for me.

Mate... you can't leave us hanging like this... Mr. Green



PostPosted: Fri Jul 28, 2017 2:32 pm    Post subject: Reply with quote
If you're going to use the word sublime to describe it, you had best post pics that show this.... Smile
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