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Olympus-OM

[OM] Re: Sigma 600mm F8 reflex lens?

Subject: [OM] Re: Sigma 600mm F8 reflex lens?
From: Moose <olymoose@xxxxxxxxx>
Date: Fri, 31 Mar 2006 11:59:35 -0800
Darin wrote:
> Hello all,
>
> I purchased this lens on ebay and have a questions about it. If any list 
> members have one, or have had one in the past, I appreciate any help you can 
> give me. My question is about the mount, which shows sighs of tampering (worn 
> screws), or to be more specific the diaphram linkage tab. This being a fixed 
> aperture lens, I would think the tab would be set at a fixed position, but it 
> moves somewhat freely through out the slot in the mount. Is this normal, or 
> has the mount been replaced?
>
> Darin wrote:
> Hi Jeff,
>
> On your lens, is the tab in a slot like on a lens with a variable aperture, 
> or is it a fixed tab on the mount? I really think this is not the original 
> mount for the lens, it just makes no sense to me for the tab to be able to 
> move on a fixed aperture lens.
I have two of these, one in OM mount.

1. The OM mount has the diaphram linkage tab in a slot, like most 
lenses, but the tab is firmly fixed near the counterclockwise limit of 
the slot. I assume the slot is there because they use the same mount as 
on other of their lenses. In any case, the presence of the slot doesn't 
indicate a mount change. The loose tab probably means something just 
under the mount has broken or come loose. It should be obvious with the 
mount removed.

2. The rotating ring is for the tripod mount. One hole is for a large 
thumbscrew to lock it in place. The other two are for the tripod mount 
block itself. If there is just a ring with three threaded holes in it, 
you are missing the tripod mount.

3. The other thing to check is the filter holder. Looking at the lens 
from the rear, with the red focus point line at the top, there is an 
opening at the left, 270 deg., location near the rear of the lens body. 
There should be a plastic tab about 3/4 in. wide sticking out of it. 
This is a holder for 22.5 mm filters. It's a unique feature of the Sigma 
among mirror lenses, and much more convenient than the rear screw in 
filters of most others (Except the Zuiko, which uses only 72mm front 
filters.) The down side is that it is sometimes missing on used lenses. 
If so, the lens will still work properly, although it may then reach 
infinity focus a tiny bit before the stop. The other problem is that 
it's then a big opening for dust to get into the camera body, so it 
should be covered.

4. There is also an 86 mm screw-in hood, which slips over the lens body 
reversed for storage.

It is one of the better of these lenses for a few reasons. First, it 
tested reasonably well 
<http://brashear.phys.appstate.edu/lhawkins/photo/mp-cat-tests.txt>.

 From my perspective, the Sigma is considerably higher resolution than 
the Zuiko or any 500mm lens. My personal experience with such lenses is 
that I can almost never either choose the exact distance from which I 
shoot nor fill the frame with the subject. In that case, with a fixed 
distance, lens tests that vary subject distance to make the resolution 
target the same size on film/sensor regardless of lens fl, don't tell 
the whole story.

Shooting the same subject from the same distance, a longer lens with the 
same tested resolving power will resolve more detail in the subject than 
a shorter lens simply because it enlarges the subject more on the 
film/sensor. So the 50 and 40 lines resolutions of the Sigma are 
equivalent to 60 and 48 on a 
500 mm lens for most of the kind of shots I take with a long tele.

The build quality is much nicer than the Tamron 500/8 and, I believe, 
several others. It has, of course, the same halo effect OOF highlights 
as other mirror lenses.

If it has enough of the right pieces and the diaphram tab problem is 
just a loose screw or you are handy with epoxy - and if it was cheap 
enough, I have one in Nikon mount that I have already scavenged for the 
filter mount and which I could scavenge further. I don't see it around 
in plain sight, but if you are interested, I can check. I know it has 
the tripod mount and believe it has the hood.

And here's a post I made last year with a link to some sample shots on a 
300D:
> Using these lenses take some practice and knowledge. The first thing 
> we all seem to do is to take a shot of something really far away. And 
> the results are all too often disappointing. Movement of the air 
> between you and the subject literally moves different parts of the 
> subject image around separately from each other and changes the focus, 
> so sharp is impossible. This effect is of course greatest on those 
> nice warm, sunny days when one feels like taking such photos.
>
> Haze/water in the air makes contrast even lower than the lens on its 
> own and adds a bluish hazy look. Again, often worst on the nicest 
> days. And air pollution just makes it all worse. Much can be done in 
> post processing to alleviate this problem.
>
> So do I always follow my own advice? Of course not! How could I resist 
> the almost 1000mm effective fl of a Sigma 600/8 on the 300D? 
> Especially hard when the subject is out on an island 
> <http://moosemystic.net/Gallery/MPhotos/Sigma600/pages/02_1631.htm>. 
> That slight fuzziness isn't the lens, it's the atmosphere. Look at the 
> prior pic for a 65mm fov of the same subject, a little showy, but why not? 
>
>
> So, take those looong shots on cold, dry days....
>
> What else is it good for? How about smaller things that you can't get 
> close too, but aren't far enough away for atmospheric effects to be a 
> problem?
>
> 1682 first shows FF as it came from the camera, then with contrast 
> enhanced a bit, then my favorite crop, then full pixel 
> <http://moosemystic.net/Gallery/MPhotos/Sigma600/pages/05_1682e.htm>. 
> The full pixel shows that when you nail the focus, the sharpness is 
> there. The several other shots I didn't post show how careful you have 
> to be to nail the focus with such shallow DOF. All the critter shots 
> are at 1600 iso, by the way.
>
> In 1695, the dreaded donuts show up FF (without, then with, local 
> contrast enhancement) but they aren't a problem cropped.
>
> And you might get lucky and catch a couple of red squirrels "doin' 
> something interesting" enough that nobody will notice the donuts!  :-) 
>
> Another thing they are good for is compressing subjects and changing 
> the relative sizes of foreground, subject and background relative to 
> what a normal lens would show. Here, with a 350/5.6 mirror on an OM-4, 
> the gladiola stalks and rosemary behind are larger and both they the 
> grass in front are apparently closer to the pansies and lavender than 
> they would appear in a more normal focal lenth shot 
> <http://galleries.moosemystic.net/Garden04/pages/3649_16.htm>.



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