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Sony A6500 with adapted YASHMA 2,8/300mm and Zeiss 2x Mutar
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PostPosted: Wed Oct 16, 2019 8:17 am    Post subject: Sony A6500 with adapted YASHMA 2,8/300mm and Zeiss 2x Mutar Reply with quote

The C/Y Zeiss 2x MUTAR II converter was originally optically designed for the very rare and costly C/Y Zeiss Apotessar T* 2,8/300mm, but works also very well, recommended by Zeiss, on my C/Y Zeiss Sonnar T* 2,8/180mm telephoto lens! Years ago, I've looked at the Ukrainian telephoto lens YASHMA Apo IF MC 2,8/300mm with NIKON mount! Before I bought the lens, I could test the lens on a NIKON D90 camera. But I was using at that time a CONTAX RTSIII and CONTAX AX cameras with a number of fine Zeiss glasses! A good old friend of mine, who has sold me this lens, having a well running camera repair shop, changed the NIKON mount for me, into an automatic CONTAX bayonet mount, for my two CONTAX cameras, which was quiet complicated! But everything worked mechanical fine, even with 5 fps with both of my CONTAX bodies, for a number of years to come!

Then the time came to switched to an digital camera, a CANON 5DMkII! I worked fine with the lens with an C/Y - CANON adaptor for a couple years! The time came, and I sold my comparable bulky CANON, and I switched to a more compact SONY A7, A6000, and recently to a SONY A6500, with IBIS (in-body-image-stabilisation!)

So now, I have to try it out, the Sony A6500 with the YASHMA 2,8/300mm + 2x MUTAR II Konverter + adaptor = equals into an 900mm (!) telephoto lens! I set the IBIS to 800mm, and I can confirm now, it worked very well with this heavy and long telephoto lens combination!

As the first try, I've used this combo on my balcony, all hand held, with f/5,6 (f/11)! I must say, the IBIS worked very well, and I am very pleased with the very first hand held results on my SONY A6500, which I am using for better handling, generally with a MEIKE battery grip!!















PostPosted: Wed Oct 16, 2019 11:26 am    Post subject: Reply with quote

Quote:
So now, I have to try it out, the Sony A6500 with the YASHMA 2,8/300mm + 2x MUTAR II Konverter + adaptor = equals into an 900mm (!) telephoto lens! I set the IBIS to 800mm, and I can confirm now, it worked very well with this heavy and long telephoto lens combination!


I think you should have set IBIS to 600mm, the actual focal length of the lens plus teleconverter combo. The equivalent focal length (about 900mm) should only be used to calculate the angular coverage of the lens.


PostPosted: Wed Oct 16, 2019 12:03 pm    Post subject: Reply with quote

Like 1 Like 1

I'd agree with Gerald. Maybe not if a6500 had 48mp sensor.


PostPosted: Wed Oct 16, 2019 4:39 pm    Post subject: Reply with quote

[quote="Gerald"]
Quote:
So now, I have to try it out, the Sony A6500 with the YASHMA 2,8/300mm + 2x MUTAR II Konverter + adaptor = equals into an 900mm (!) telephoto lens! I set the IBIS to 800mm, and I can confirm now, it worked very well with this heavy and long telephoto lens combination!


I think you should have set IBIS to 600mm, the actual focal length of the lens plus teleconverter combo. The equivalent focal length (about 900mm) should only be used to calculate the angular coverage of the lens.[/Q]

Whatever, I have used for the first time IBIS on 800mm, and it worked fine! With full frame camera with 300mm telephoto lens, plus 2x teleconverter, I should then set IBIS also to 600mm!?


PostPosted: Wed Oct 16, 2019 5:36 pm    Post subject: Reply with quote

Smile yes I think so, because true focal length is printed on lenses (with some few exceptions) and camera engineers assume consumers are not expected to know about crop factors and to have to make a calculation to use the camera, i.e. the camera makes the calculation...

Setting to longer focal length merely makes ibis more sensitive than need be for most cases.


PostPosted: Fri Oct 18, 2019 1:18 pm    Post subject: Reply with quote

OPAL wrote:

Whatever, I have used for the first time IBIS on 800mm, and it worked fine!

When IBIS is set to 800mm, but the effective focal length is 600mm, what happens is an overcorrection of the camera shake by 33%.



OPAL wrote:

With full frame camera with 300mm telephoto lens, plus 2x teleconverter, I should then set IBIS also to 600mm!?

Yes, you should set IBIS to the effective focal length, which is obviously 300 x 2 = 600mm.


A technical explanation
A typical IBIS uses 3 sensors to measure the variations of the pitch, raw and roll angles caused by camera shake. Knowing these angle variations and the focal length of the lens, the processor moves the sensor accordingly, trying to keep the image stationary relative to the sensor. This article explains in detail how this works:

https://www.digikey.it/Web%20Export/Supplier%20Content/invensense-1428/pdf/invensense-image-stabilization-technology.pdf

For a perfect image stabilization, the sensor shift should be proportional to pitch and yaw angle variations, and the focal length of the lens. Therefore it is critical that the user enters the correct focal length of the lens.

To give an example of the importance of entering the correct focal length, suppose a 600mm lens is being used and the camera shake produces a 1mm linear shift of the image to the left.

If the IS system is well calibrated and the user entered the correct focal length of 600mm, IBIS moves the sensor 1mm to the left, to perfectly compensate for the camera shake.

If the user enters, for example, an incorrect focal length of, say, 500mm, IBIS will move the sensor 0.83mm (500/600)to the left, an undercorrection that results in a blur of 0.17mm.

On the other hand, if the user enters a focal length of 800mm, IBIS will move the sensor 1.33mm (800/600) to the left, an overcorrection that results in a 0.33mm blur.