Very specific question on lens adaptors and image quality

[The Matt]

I have a rather specific question on image quality with lens adaptors, specifically with larger complex lenses.
I use an adaptor which mounts old manual lenses on to new digicams. It is the glassless type which brings the lens a little closer to the sensor than it should be, meaning with my 50mm I get infinity focus at around the 30 foot mark on the lens, I lose a little close-focus range and things are just blurry at the actual infinity mark. Common sense tells me that this adapter shouldn't have any affect on image quality (barring known issues about the lens mounting at an angle, or the thickness of the glass in front of the sensor). When I focus my 50mm it moves all the lens elements in unison closer to or further from the sensor/film, therefore if the adapter brings the lens closer to the sensor then I just need to adjust the focus slightly to counteract. What happens with more complex lenses, for example those which internally focus and the front element remains still? Will the fact that the stationary elements of the lens are closer to the sensor alter the image, or will altering the focus counteract this the same as with my simple 50mm?
Hope this makes sense!

 

[woof woof]

I don't think how complex the lens is will make a difference as internal focusing lenses will no doubt have the same registration distance as lenses that extend under focusing?

It sounds like you are using a camera + lens + adapter combination that gives you the wrong registration distance? Sort of like using Canon FD lenses on a Canon DSLR via a metal adapter with no correcting lens? Something like that?

What camera and lens are you using? and... why not use something that gives the right lens to sensor / film distance or includes a correcting lens?

 

[The Matt]

I'm currently using a sony E mount with either m42 or pentax k lenses. I wasn't aware the distance was off when I bought the adapter. If all I lose is a little close focus I don't much mind, but if my images will suffer then I'll endeavour to find a better adapter.

 

[BacktotheFuji]

Sounds like your adapter is a little too thin, hence you are reaching infinity too early. It's no big issue though, everything is relative with the elements as far as I am aware More of a concern is the fact that on a full frame DSLR, the rear element may get too close to the mirror and hit it. Again, no big issue other than you won't get a full image.

Edit - you are using mirrorless so it's no issue. Most cheapie mirrorless adapters I've seen are a little too thin.

 

[woof woof]

I'm currently using a sony E mount with either m42 or pentax k lenses. I wasn't aware the distance was off when I bought the adapter. If all I lose is a little close focus I don't much mind, but if my images will suffer then I'll endeavour to find a better adapter.

Looking at the adapters on ebay they look pretty standard, just like the adapters I have for Minolta, Olympus and Canon FD. There'll be more than these than you can count on ebay starting at something like £10 or you could splash a bit more and go for a Novoflex at £75 for the M42 or £139 for the Pentax k. The Novoflex specifically states that it retains infinity focus and I've no doubt that you will be able to find M42 and Pentax adapters that state infinity focus too.

Here...
Pentax with infinity, under £7...
http://www.ebay.co.uk/itm/Pentax-K-...ns_caps_hoods_adaptors_ET&hash=item418e1f42bd

M42 with infinity, under £7...
http://www.ebay.co.uk/itm/M42-Lens-...ns_caps_hoods_adaptors_ET&hash=item3ccf68b90a

Luxury... just select the lens type...
http://www.speedgraphic.co.uk/body_adaptors/novoflex_sony_nex_adaptor/20879_p.html

You should be able to find something to suit.

 

[Steve Smith]

I think the term 'retains infinity focus' means that it will actually focus at infinity rather than an assurance that it will be at infinity when at the infinity mark. Some adaptors cannot possibly put the lens in the right place relative to the sensor (of DSLRs rather than mirrorless) so do not give infinity focus at any setting.


Steve.

 

[woof woof]

I think the term 'retains infinity focus' means that it will actually focus at infinity rather than an assurance that it will be at infinity when at the infinity mark. Some adaptors cannot possibly put the lens in the right place relative to the sensor (of DSLRs rather than mirrorless) so do not give infinity focus at any setting.


Steve.

Well, yes... but the same could be said of lens mounts on cameras as there are always tolerances. What it really means is that you can focus on stuff which is a long way away whereas if you get things completely wrong you can only focus on stuff up to a relatively short distance as per in the op's original post. I'm not too sure how you are going to check if focus it critically sharp at infinity anyway

As to infinity marks, I'd imagine that the op's old lenses have an infinity mark at which focus stops as that the case with all my old manual lenses and it's only the newer AF SLR lenses I've owned which have been able to move past infinity. Difficult concept though that is it's needed 'cos of how they work

So, anyone buying an adapter which "retains" infinity focus should be able to focus on stuff a long way away

 

[Steve Smith]

So, anyone buying an adapter which "retains" infinity focus should be able to focus on stuff a long way away

Yes. Infinity is a long way off. I tried to walk there once but only got half way!

And further to my previous response, there are some adaptors which put the lens too far forward, which would normally mean no infinity focus, which have an extra lens element which restores it's infinity focusing ability at the expense of increasing its focal length. I believe the quality of these ranges from absolutely terrible to not very good.

Then there's the Metabones type which does the reverse. It makes a lens into one with a wider focal length allowing it to have the same angle of view on a mirrorless Micro 4/3 sensor as it would normally have on a full frame sensor or 35mm film frame. I have heard that these are good quality.


Steve.