Nikon 180mm ED AIS focusses pass infinity

[Zang]

Hi all,

Being inspired by your feedback in here, I have recently acquired a sample of the lens. I noticed that the lens focuses pass infinity a bit. It does not look like anyone tried fixing the lens before. All screws, rings look untouched. Do you observe the same with your 180mm AIS?

Cheers,
Zang

[Jacques Pochoy]

Yes, the 180mm AI-S does focus past infinity (a wee bit). I guess that it was to have a play with dilatation (heat), as that was told to me at that time :-) It never bothered me much, but you can't go to hard infinity and expect it to be in focus. It still is a wonderful lens :-)

[Birna Rørslett]

The 180 is an ED lens. So it is perfectly normal for the focusing ring to go "beyond" infinity.

[paul hofseth]

explanation needed, glass type in itself even if it has peculiar abilities to refract with less dispersion should not need extra meaasures to accomodate metallic temperature dependece if the glass itseld does not react to varying temparature. Admittedly, with such narrow depth of field, focus precision is paramount, so it is usual for long lenses to have some leeway beyond the nfinity mark.

p.

[Jack Dahlgren]

explanation needed, glass type in itself even if it has peculiar abilities to refract with less dispersion should not need extra meaasures to accomodate metallic temperature dependece if the glass itseld does not react to varying temparature. Admittedly, with such narrow depth of field, focus precision is paramount, so it is usual for long lenses to have some leeway beyond the nfinity mark.

p.

Calcium fluorite glass which was used in telephoto IS temperature sensitive. I’m not certain of the formula of Nikon’s ED glass, but it was common in the early days to have a bit of extra room in the focusing to accommodate any temperature sensitivity.

[MEPER]

It would have been nice for the people using the lens wide open for astrophotography to have a fixed infinity focus?
I think this lens was used in the past for this purpose?

[Roland Vink]

The problem is that infinity focus cannot be fixed, at best it can only be fixed at a particular temperature. ED glass, and to a lesser extent other glasses, expands and contracts when the temperature changes. I guess this changes the curvature of the lens which causes the focus point to shift. Nikon allows ED lenses to focus a little beyond infinity to allow for this shift. If the lens had a hard stop at infinity, at some temperatures it may not be able to focus to infinity at all.

[Zang]

Interesting! I did not know all these things. Thanks everyone for your inputs.

Does the lens in discussion have the front element made from ED glass?

[Jack Dahlgren]

Interesting! I did not know all these things. Thanks everyone for your inputs.

Does the lens in discussion have the front element made from ED glass?

Yes, you can find out the story of this lens here:

https://imaging.nikon.com/history/story/0010/index.htm

[MEPER]

I checked my 180 ED and also the "non-ED" version and ED focus past infinity while the "non-ED" stops exactly at infinity like most other MF-lenses.

[Øivind Tøien]

In Astrophotography one never relies on the infinity focus mark of long lenses, but focus manually with 100% view on the rear screen (or a computer if tethered) on a barely visible star or preferably using a Bahtinov mask to make the focusing eastier. The process typically has to be repeated if the lens is not temperated to the environment or if ambient temperature changes.

[Zang]

Yes, you can find out the story of this lens here:

https://imaging.nikon.com/history/story/0010/index.htm

Thanks... I heard ED glass is soft. That may explain a bunch of scratches left by the previous owner on the front element. I was disappointed when I found that out. During the transaction, the front element was so dirty that there was no way to differentiate dirty marks with scratches. It looks like someone was learning how to clean the glass on this lens. It's brutal...

[Zang]

In Astrophotography one never relies on the infinity focus mark of long lenses, but focus manually with 100% view on the rear screen (or a computer if tethered) on a barely visible star or preferably using a Bahtinov mask to make the focusing eastier. The process typically has to be repeated if the lens is not temperated to the environment or if ambient temperature changes.

That was how I found out the lens passed infinity when I tried it on the moon yesterday