Pentax Lenses

[dp297]

I am not sure I am very happy with my Nikon 180ED f2.8 (a lot of fringing and aberrations at the corners).
I have been reading good things about Pentax lenses especially
165mm f2.8
200mm f4 SMC (5-element)
perhaps 200mm f2.5 SMC

I was wondering whether I could ask people for their opinions on these lenses...

[leon]

Hi There, although I don,t have the lenses you describe, I have used many Pentax lenses in the past and have found them to be excellent in manufacture and imaging.

Leon

[Retrograde]

Hi Dimitris,

I use the Pentax 165mm f2.8 (6x7) lens.
I've found it very sharp but it sufferes from a lot of fringing if not stopped down. So much that it's unusable at f2.8

These two were taken at f4 and still required a bit of work in post-processing to remove the magenta fringing:

http://www.astrobin.com/full/184790/0/
http://www.astrobin.com/full/187395/0/ (this one is a mosaic)

This one was taken at f5.6 and the fringing is almost non-existant (a significant crop of the full field)
http://www.astrobin.com/full/211010/0/

These are taken using an unmodified APS-C DSLR.
Hope that helps.

Pete

[gregbradley]

I wonder if you got a bad copy? Or alternatively I got a good one. I use mine with filtered imaging so perhaps that makes a difference but my copy is sharp wide open and no chromatic aberration or very little.

I don't see chromatic aberration in those samples you linked. Those bright stars are blue which is correct. Either way blue fringing is pretty easy to correct in Lightroom so long as its not too bad.

Nice images by the way.

Greg.



[QUOTE=Retrograde;1205728]Hi Dimitris,

I use the Pentax 165mm f2.8 (6x7) lens.
I've found it very sharp but it sufferes from a lot of fringing if not stopped down. So much that it's unusable at f2.8

[Retrograde]

Hi Greg,

it's interesting that you and I have gotten such different results.
There could possibly be different revisions of the lens (I just grabbed one off ebay for around $200 so no idea what year it was manufactured or anything) or it could be the type of imaging as I'm still at the DSLR stage.

I'm very happy with the sharpness - it's just the CA that I've been having an issue with.



It's not actually blue-fringes that I'm getting but rather purple/magenta-fringes on the medium-bright stars.
Here's a crop of a cluster near Eta Carina (single sub) that has not had any processing done to it to remove fringing. This is at f4.
Would certainly be interested in your thoughts on this.

Thanks,
Pete

[gregbradley]

Its been a while since I used it but I don't recall too much of that. Perhaps a bit but it cleaned up easily using selective colour and reducing the magenta in Photoshop. My lens cost around the same.

Greg.