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10-10-2017, 09:20 PM   #61

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QuoteOriginally posted by WPRESTO Quote
QuoteOriginally posted by WPRESTO Quote
speed boosters
Theres a standard and an ultra................................................difference is 1/3 of a stop.
standard is a 1.1 crop on apsc....ultra is 1.0,ie same FOV as FF.

Metabone$$$$$$ costalotta....fine quality but the comparisions with the ZHONGHI turbo ....theres nothing between them optically.

Then theres the el cheapos From Fleabay....and from what i see they work fine.

10-11-2017, 12:26 PM   #62
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Make A 645 to K-mount speed booster why don't you Metabones
10-11-2017, 02:32 PM   #63
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QuoteOriginally posted by zmohie Quote
Is that means that Q system moved from the fridge.
Did you mean fringe?
10-11-2017, 11:08 PM - 1 Like   #64

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QuoteOriginally posted by johnmflores Quote
Did you mean

10-23-2017, 12:42 PM   #65
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QuoteOriginally posted by WPRESTO Quote
To put it in slightly different words, or spell it out: You have a 50mm f2 Nikon lens and mount it on a Pentax Q with a Metabones speed adapter. The lens on the Q has the SAME FIELD OF VIEW it would have on a FF camera body, BUT THE LIGHT TRANSMISSION @ F2 IS ACTUALLY WHAT YOU WOULD GET @ f1.4 ON A FF SENSOR. The lens loses both AF and auto-aperture close. You must focus manually and turn the aperture ring before taking a picture if you want anything other than f1.4 equivalent light transmission. With the adapter, the 50mm f2 becomes a 25mm f1.4.
You are missing something. The crop factor of the Q system are 5,64 for the original Q/Q10 and 4,55 for Q7/Q-S1. With a focal length reducing factor of 0,5x you will not get the same field of view. A 50mm becomes a 25mm. 25mm multiplied by 5,64 or 4,55 will be a lot more then the 50mm on FF field of view.

I'm not finished with the math. Aperture is usually specified as focal lenght (f) divided by a factor. f/2 is one example. In the example of a 50 mm f/2 it means that 50 mm/2 = 25 mm aperture _diameter_. The aperture diameter is the light gathering diameter, usually aproximately the same as the front element diameter. This diameter stays the same even if a teleconverter or wide converter is applied. So when the focal lengt of a 50mm f/2 is reduced to 25mm, the aperture diameter are still 25mm. Or expressed as a division: f/1,0 (where f=25mm).

Lets try to test this logic in another way, to see if it holds true. A 25mm lens have wider FoV then a 50mm lens. Lets say both have the same aperture diameter and are used on a sensor small enough that both covers the entire sensor. When changing lens from the 50mm to the 25mm, the middle part of the image gets compressed by a factor 2, or 0,5x as I would say. Both the height and the width of the image are compressed by that factor. A scene that used to fill a 2x2 square now only fills a 1x1 square. The light that used to expose a 2x2 area are now compressed into a 1x1 area. Or 4 times as high light intensity per unit area then before.

Lets just try an example with a teleconverter in stead. A Tamron Adaptall SP 300mm f/2,8 + 2x TC. The aperture diameter is 300mm/2,8 = 107mm, very close to the 112mm filter diameter of that lens. When using a 2x TC the image on sensor is stretched by a factor 2 in both horizontal and vertical direction. That means the 300mm turns into a 600mm lens. But the light that used to cover a 1x1 unit area now has to fill a 2x2 unit area. Light intensity per unit area falls by a factor 4. That is two stops. 300mm f/2,8 becomes a 600mm f/5,6. The aperture diameter always stays the same. Lets check. 600mm/5,6 = 107mm.

This was the easy part. The tricky part is whether the image circle can cover the sensor or not. And what happens to the focus range and scale, and usability on different focal flange distances. And light loss (transmittance), and that some of the math fails for wide angle/fisheye. Sorry, I dont have an easily explained answer to that, I just say it exist. Keep to the simple rule of same aperture diameter in mm.
10-24-2017, 02:36 PM   #66
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I still don't understand the business plan behind an adapter like this, which would force the user into manual focus, manual aperture, and electronic shutter on a body that no longer appears to be supported via development by its parent. But if this gets people fired up about the "Q", I'm all in favor, so for right now I'm just going to watch and see what actually happens.
10-25-2017, 12:03 AM   #67
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IMO it because it is abandoned that the adapter is interesting.


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