Sigma 18-50 mm f/2.8 EX MACRO HSM

Hello,

I recently bought the Sigma 18-50 mm f/2.8 EX MACRO HSM lens for my D200 since i didn't have an allround lens for situations when you don't know what to expect. I think the Sigma is a suitable lens because it's fast, sharp and it can focus pretty close (minimum focus= 20 cm and reproduction ratio is 1:3, ...and it's 1/3 of the price of the Nikon 17-55 mm with a much longer minumum focus distance). But i have troubles with housing it perfectly.

I want to use it behind a dome port and i can't seem to get the corners completely sharp. I tested it in the swimming pool by taking images of tiles and there is some slight softness in the corners at 18 mm. I tried port extensions of various lengths (25 mm, 35 mm, 40 mm and 45 mm) and with the longest extension i seem to have the least softness. When i close the diaphragm 2 or 3 stops the image is completely sharp. So one would expect that an even longer extension would solve the problem, but then i expect to have vignetting from the port.

So what should i do? Should i add a +1, +2, +3 or +4 diopter (and end up with a slightly smaller angle?...) Or wouldn't that make a difference at all?

I didn't try to use this lens with my Fisheyeport, because that might solve the problem as well, but this port is quit bulky and i prefer not to use it when not necessary.

cheers, Udo

Udo,

I have the older non macro version of that lens and my experience has been somewhat similiar on a Canon cropped sensor (400D) and a 170mm dome (6.5")+40mm extension. Slight softness on the corners @18mm but improves with closing the aperture. I did try picking up a cheap diopter set and to be honest, in pool tests, I didn't see that much improvement. So I just shoot it without a diopter. Maybe a larger dome would help but I don't want to deal with the extra luggage.

I use the somewhat similar 17-70 and have the same issue. really those lenses need to be used at either not quite a full W/A zoom and or stopped down a bit; even on dry land.

Jack

Hi Udo.....this was exactly the lens I was thinking of getting for a new D300 setup (in addition to a Nikon 105VR Macro and a Tokina 10-17). It will be my first DSLR UW setup. May I ask what size dome you are using for the Sigma? Did you have to get lens gear such as this?;

http://www.fun-in.com.tw/catalog/product_i...a51ec98df34afd6

Sorry for the newbie questions.....there is a lot to spend and I would like to get my research right even before speaking to a retailer....

Thanks!

eskasi - I picked up that FIT lens gear last week. Not sure if the macro version of that lens is slightly different; it works well but is very snug putting it on. It tends to mash the lens lock button a wee bit.

Hey Pakman, thanks for the reply. I was also wondering about that too. When I checked with Reef Photo via email, in their quote, they mentioned a modified lens gear for the Sigma. I believe the FIT model for this Macro Lens is fairly new?

About the port though, what should I use with this lens? Especially if I have to consider travel? All my dives involve international flights. No diving in my backyard

I got mine from fun-in.com.tw. FIT (Taiwanese co.) has come out with a bunch of <$100 focus rings for various new lenses like the Tokina 10-17 Fisheye and the Sigma 18-50 macro. I think some of the Japanese shops are also selling the FIT focus/zoom rings.

As for the ports/ diopters, I am guessing that given how close the macro version of the 18-50 focuses, that a diopter might not help that much.

Hi Udo.....this was exactly the lens I was thinking of getting for a new D300 setup (in addition to a Nikon 105VR Macro and a Tokina 10-17). It will be my first DSLR UW setup. May I ask what size dome you are using for the Sigma? Did you have to get lens gear such as this?;

 

http://www.fun-in.com.tw/catalog/product_i...a51ec98df34afd6

 

Sorry for the newbie questions.....there is a lot to spend and I would like to get my research right even before speaking to a retailer....

 

Thanks!

Hi Eskasi,

I'm using this lens behind an old Hugyfot domeport which is suitable for normal WA lenses, it's the short version which isn't for sale anymore. I think the diameter of the port is 12 cm.

In total there are three different Sigma 18-50 mm f/2.8 versions which all have different dimensions (as far as i know):

1. the non-macro version has, as far as i know, a 67 mm filtersize

2. the regular macro version has a 72 mm filtersize, so i guess the rest of the lens might be diffeent as well.

3. the version that i have which has macro, filtersize 72 mm and the HSM motor. The HSM version is slightly fatter then the standard macro version. BTW the HSM version is only availalble for Nikon mount cameras, becuase the regular macro version doesn't work with the D40x.

i'm not completely sure about all this, so to be sure you should check things out better.

Anyway, for the focus gear i was very lucky, since the only focus gear i own fits this lens perfectly without silicon insert. I use the same zoomgear for my sigma 10-20 mm and my Tokina 10-17 mm FE but then WITH silicon inserts.

hopefully this infor is usefull to you.

cheers, udo