Can theWollensak 159mm Ex.W.A. f12.5 iris be open further?

I just received an e*ay purchase, a Wollensak Ex WA 159mm f12.5 lens

in an Alphax shutter, and noticed that "wide open" , at 12.5, there

is still quite a bit that the diaphragm can be opened. I'd guess at

least a stop and a half, maybe more. Of course I wouldn't want to do

this to expose the film, just to focus and compose the image on the

GG, as right now at 12.5 it's a little dark to see very well.

I have explored into why it stops where it does and found that it has

been set to stop at 12.5 where it does. I can easily override this by

undoing what has been done, but I wanted to ask you out there who are

more knowledgable about such things. What could it hurt? the f12.5

would still be f12.5 ans f45 would still be f45. I just don't know if

maybe it was a quality control issue that Wolensak wanted, so that

people wouldn't complain about fuzzy images when using it at all the

way wide open, which I guess would be about f8 or so.

Any insight into this matter will be greatly appreciated.

DG

I've done this on mine, which is in a Rapax shutter - it just needed a screw stop removing on that shutter.

No problems and it does seem to open up to f8 or 9 or around there. Gives you that extra bit of light for focussing.

The only thing someone has mentioned is the possibility of focus shift (only suggested in a general way - no specific references to this particular lens) i.e. that there may be a change in focus from f8/9 to say f45 but not from f12.5 to f 45. It was just a suggestion, and while I haven't actually tested for it, I certainly haven't noticed it in my images.

tim

Tim,

Thanks for your response. I remember in a post a month or so ago, you responded to someone, saying that you didn't have a problem seeing the image on the GG using this same lens, and after seeing mine today I wondered if yours had been "modified" for you to make that statement. (I tool your statement into account when buying this lens, because that was a concern I had about the lens.

I'll wait to see if others chime in before modifying mine. It was done with what looks like a chisel, to make a detent on the rotating diaphragm ring. It'll require removing the detent. This is a little more permanent than removing the screw as you did on yours.

Thanks again for the quick response.

DG

I was hoping someone more knowledgeable than I am on this subject would chime in here but they haven't so here goes.

The aperture control lever on all three of my F9 G Claron lenses in Copal shutters can be moved past the number 9 and when that's done you can see the aperture blades open up a little more than they were when the lever was at the number 9. However, the maximum aperture size is fixed when the lens is manufactured and as you know the stated maximum aperture (1:9 in my cse, 1:12.5 in your case) refers to the ratio of the size of the maximum aperture to the focal length of the lens. Wollensak's quality control (and Schneider's quality control in the case of my lenses) would have to be pretty bad if they couldn't get this ratio correct, so I've always assumed that when I move the lever past the number 9 I'm not actually increasing the aperture beyond the stated maximum. In other words, I don't think Schenider is selling F5.6 or so lenses as F9 lenses, and I don't think Wollensak was selling F8 lenses as F12.5 lenses. This seems particularly unlikely since their incentive from a marketing standpoint would be just the opposite, i.e. to overstate the maximum aperture, not to understate it. So I'm guessing that moving the apertue beyond 9 (or 12.5 in your case) just gets the aperture to its stated maximum and doesn't increase it beyond that maximum. But that's just a guess based on the difficulty of figuring out why a lens manufacturer (1) couldn't get the ratio of the maximum aperture to the focal length of the lens right, and (2) would err on the side of understating rather than overstating the maximum aperture if it was going to err at all.

Oh, the Wollensak 12.5 opens up siginificantly wider than 12.5 - without digging it out right now, if you remove the stop it probably opens up at least 1/3 more. If you do it while under the dark cloth you can also see a significant increase in brigthness. It certainly does open up to somewhere around f9 or f8.

A slightly different example would be the Kowas - the 210mm (and I think the others too) is an f9 in barrel, but put it in a shutter and it become a 6.8.

Why would the manufacturers do this? Many reasons - image quality for one. For actual photogrpahy (or in the Kowa's case, flat field reporduction), the image quality may be totally unacceptable beyond the f12.5 (and there are many reasons to shoot at the widest aperture). Better to limit it physically than have people complaining about images soft and fuzzy around the edges.

Sorry but that explanation makes no sense to me. It's considerably easier to focus and compose at F8 than it is at F12.5, especially with a 159mm lens that's designed to cover 8x10. So why would the manufacturer prevent people from using F8 to focus and compose just because they were concerned that some misguided souls would use it to make images and then complain when the images were bad? Even assuming this was a major concern it could have been dealt with in a far less draconian way than artificially preventing the lens from opening to its actual widest aperture (e.g. include a note with the lens saying not to use it at F8 to make images, which would still have allowed users to gain the benefit of F8 for focusing and composing while eliminating concerns about [people who nevertheless used the widest aperture to make images). And of course all other things being equal lenses with wide maximum apertures sell for more than lenses with small maximum apertures, so Wollensak was really cutting their throat by labelling and selling an F8 lens as an F12.5.

I don't doubt that you can move the aperture control lever beyond the labelled maximum aperture and that the shutter blades willl open more when that's done. As I said in my previous message, I can do the same thing with my F9 G Claron lenses. The question I raised was what the ratio of the aperture to the lens focal length is when that's done. It very well may be 1:8 as you say but surely there is a better explanation for why that's so than some supposed concern about complaints that might be received if fuzzy images were made with the aperture at F8.

I'm not saying it's the only possible reason. I also have had lenses which could abviously open to a larger aperture, but this is prevented by putting a physical "vignetter" or some such within the lens constrcution (i.e. part of the lens cunstrcution, the metal holding the elements together, is a physical reduction in the lens aperture via some kind of circular metal plate with a hole in it). I 'm guessing Wollensaks is, among other things, a cheaper way of doing this. But I'm sure there are other reasons.

As has been suggested, focus shift could well be one - though I just haven't seen it on this lens.

Thanks Tim for the answer I was looking for. I disabled the aperture stop, and with my Pentax Digital spotmeter I measured a spot on the GG with the aperture set at the "old" maximum, f12.5. Then I opened up the aperture fully and took the same reading. I had gained a full stop. It really brightened up the image on the GG. I've got a JML lens that I'm planning on doing the same modification to.

Again, I don't plan on shooting with the lens wide open, just want the extra light to help composition and focusing.

DG

Significantly brighter isn't it...

as I said, the only problem I can think of is focus shift - well described in the last post here:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005H2c

I guess I could run some tests, but as everything tends to look pretty darn sharp, it doesn't seem to be a problem (mine is a pretty snappy little lens with a reasonable amount of coverage when you get down to f32/45

tim

I don't seem to be experiencing this focus shift. The 8x10 negatives I shot look sharp. I focused at the new wide open aperture and stopped down to f45 for the exposure. I'll know for sure when I go to printing them.

Now I'm wondering what lens "design" this would fall under?

DG