true apochromatic lenses

does anyone know of any mega apochromatic lenses that are available for the k-mount.

i'm open to adapting lenses too.

other than the voigtlander 180/4, voigtlander 125/2.5 and leica 180/3.4 (with a leitax conversion) i can't think of any...

Isn't mega apochromatic just a term?
What's the difference with a normal apochromatic?

I think adapting one is out of the question, you need to work so precise and you are change elements of a lens so who can say that you don't need to adapt the other elements as well, you are probably looking at reconfigure the complete lens... good luck with that

Many lenses these days have apochromatic and/or aspherical elements, what focal length do you want?

This the DA 17-70 for example, it has both.

As with many things, labels are attached that are more or less accurate depending upon the price level and veracity of the manufacturer.

Apochromatic means corrected for the three colours of light - RGB - and then of course we have degrees of correction. How well are the three colours corrected? There are some cheaper APO lenses that may not be better than non-apo ones of other makes.

Achromatic means corrected for two colours, blue and green, and that of course matched the spectrum of orthochromatic film. Colour photography demands at least an achromatic lens.

I don't think any Pentax lenses are labelled apochromatic. They have various glass types within them and appear to be well corrected though.

Apparently this one is a true one:
http://diglloyd.com/articles/CoastalOptics60f4/index.html but not available as a Pentax mount.

Interesting link, thanks for posting it. It mentiones the Pentax lens as well, long discontinued!

Mega apochromatic is just a term I just made up. I am looking for a lens with minimal longitudinal chromatic abberration. There are very few lenses like this available, but they tend to be extraordinarily sharp and with a very smooth bokeh. This is at a cost, usually, since it involves using exotic glass, often calcium fluoride, which doesn't come cheap.

[quote:3496ace15f="Anvh"]
I think adapting one is out of the question, you need to work so precise and you are change elements of a lens so who can say that you don't need to adapt the other elements as well, you are probably looking at reconfigure the complete lens... good luck with that
[/quote}

You normally don't need to change elements of a lens to adapt it. If the lens to focal plane distance is longer than a Pentax K-mount, then it's mainly a matter of swapping the existing mount with a K-mount. I'd leave the lens alone for the most part. Sometimes an adjustment of infinity focus on the lens is needed, and sometimes you need to add shims to make sure the lens isn't focusing past infinity at the infinity mark (no big deal to me, so I don't normally shim).

Yep, I've come across that one before. It's achromatic to a ridiculous extent, probably more than I need. I just want a really-well corrected lens for the visible spectrum. Something more like the Voigtlander APO Lanthars (but not the 90mm, it doesn't match the other two imo).

That lens does look like a beaut though.

Your best bet, in a list of fairly unrealistic ones, would be to look for one of the following lenses:

Quartz-Takumar 85mm f3.5
Ultra-Achromatic Takumar 85mm f4.5
Ultra-Achromatic Takumar 300mm f5.6

These use Quartz and Fluorite elements, are highly specialised lenses and I can't think of many general purpose reasons that one would be needed.

However, if you can find one and have a couple of grand to spare....

Ahhhh i was thinking you want to adapt a normal lens to mega apochromatic

btw. Bokeh is not really influenced by longitudinal chromatic abberration but by spherical aberration.
And sadly the smooth bokeh is actually caused by not correcting it well, if you've smooth bokeh in the background you have hard bokeh in the foreground and vice versa.

There is nothing like them at a good price. Even if I don't really like the 180.

A former Voigt 125 user told me the Sigma 180 (or 150?? I am not sure) is as good as the 125.

yeah, i reckon the voigtlander 125mm is probably the best lens around at this price.
[quote="Anvh"]btw. Bokeh is not really influenced by longitudinal chromatic abberration but by spherical aberration. And sadly the smooth bokeh is actually caused by not correcting it well, if you've smooth bokeh in the background you have hard bokeh in the foreground and vice versa.[/quote]while smooth bokeh does arise from under-correcting spherical aberration, longitudinal ca also has an important effect; if you imagine that your out of focus highlights have green edges on them, they will not blend into each other so well if the highlights themselves are not green.