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WA with floating element and adapter
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PostPosted: Sun Jan 03, 2016 9:54 pm    Post subject: WA with floating element and adapter Reply with quote
I have a technical question.
Many WA and UWA have a floating element to improve quality with focusing.
If I use an adapter which allows focusing beyond infinity . Do I loose some quality from such a lens in that case?

I have an adapter nex fd which is very precise and I have no problem with my fd 20mm and 24mm.
I struggle with a Rokkor MC 24 and my adapters go beyond infinity. is there a connection ?
Of course when I will have time I shall try to modify a nex md adapter but I would be interested by the opinion of competent people.


PostPosted: Sun Jan 03, 2016 10:18 pm    Post subject: Reply with quote
Interesting questions. I'd like to know as well.


PostPosted: Sun Jan 03, 2016 11:17 pm    Post subject: Reply with quote
Please, get a precise adapter & tell us! Smile (I am guessing there will be no difference!)


PostPosted: Mon Jan 04, 2016 2:55 am    Post subject: Reply with quote
I think it depends on how the lens was designed, on some lenses the rear element is in a fixed position, I think these are more sensitive to adapter thickness than lenses that have elements that move at different speeds through the use of helicoids.
I'm always looking for nuggets of information passed along from those that do know, so, if you do know, please share. Smile


PostPosted: Mon Jan 04, 2016 3:57 am    Post subject: Reply with quote
You have to take the glass in front of the sensor into account.

BTW, may I ask what FD->NEX adapter give you precise infinity? If it is a cheap one, it will be good to let the us know to save our time and money on trying different adapters.


PostPosted: Mon Jan 04, 2016 7:01 am    Post subject: Reply with quote
It is a no name adapter.

I don't think that the problems which I have with my Rokkor are connected with the thickness of the sensor glass.


PostPosted: Mon Jan 04, 2016 7:31 am    Post subject: Reply with quote
memetph wrote:
It is a no name adapter.

I don't think that the problems which I have with my Rokkor are connected with the thickness of the sensor glass.

Any photos or links of the adapter?

The thickness of the adapter(and sensor glass) have a greater impact of the corner performance than the center performance of a lens. If anyone want to make a test, here is the MD helicoid for E mountClick here to see on Ebay or a cheaper one with EOS mount Click here to see on Ebay.


PostPosted: Mon Jan 04, 2016 7:59 am    Post subject: Reply with quote
The answer to your initial question is no.


PostPosted: Mon Jan 04, 2016 2:32 pm    Post subject: Reply with quote
Why ?


PostPosted: Mon Jan 04, 2016 2:50 pm    Post subject: Reply with quote
calvin83 wrote:
memetph wrote:
It is a no name adapter.

I don't think that the problems which I have with my Rokkor are connected with the thickness of the sensor glass.

Any photos or links of the adapter?

The thickness of the adapter(and sensor glass) have a greater impact of the corner performance than the center performance of a lens. If anyone want to make a test, here is the MD helicoid for E mountClick here to see on Ebay or a cheaper one with EOS mount Click here to see on Ebay.


Yes , I have some experience with this.
When I have time I will simply increase slightly the flange to get infinity.
I always thought that I have a bad sample of the MC 24.

Nevertheless, I am interested to understand if a lens with a floating element works as good with a wrong infinity position . In that case the element is not where it should be.


PostPosted: Mon Jan 04, 2016 5:49 pm    Post subject: mismatched adapters Reply with quote
With the adapted lens at infinity and focus point behind the plane of the sensor, the adapter is too thin. Short focus lenses need a fairly small extension to cover its focus range. A wide-angle will need to be a nominally much closer distance than a long lens in order to bring the plane of focus forward, but with a solid block lens, this does not change its intended performance at that nominal distance -even if in reality the object is at infinity.

A lens with a moving element is designed to compensate for the errors introduced with the changing distance between object and sensor plane. If it has to be set at 1 meter distance when the object is at infinity, it performs as it should with the object at 1 metre, not as it is designed to do with the object at infinity.

An example from longer lenses; the Zeiss S-Planar 60mm is designed for a reproduction ratio of 1:10 and does not have moving elements. Zeiss informs users of the design criterion, adds that it can be used over its full range and provides the differing MTF curves for the different conjugates. The Leitz Macro Elmarit 100mm has a variable distance inside in addition to the main helix. This allows it to perform well all the way down from infinity. To make a discernible difference for this length, a fraction of a millimetre would not matter, but Leitz does not advise using the ordinary -much longer - extension rings on the M-E 100.

p.


PostPosted: Mon Jan 04, 2016 6:04 pm    Post subject: Reply with quote
WNG555 wrote:
The answer to your initial question is no.


My experiences suggest otherwise! The more comprehensive answer by paulhofseth gives some indications of why it might be.

I've come to the conclusion that adapting UWA lenses is unlikely to give great results. When focal lengths are in the region of 10mm minor errors in the adapter, that are not significant with standard 50mm lenses, are significant...
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