Graflex.org

worldphoto · Posted: Sun Feb 22, 2004 6:03 pm Post subject:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2988301174&category=30045

[ This Message was edited by: worldphoto on 2004-02-28 09:19 ]

[ This Message was edited by: worldphoto on 2004-03-02 03:20 ]

RichS · Posted: Sun Feb 22, 2004 7:14 pm Post subject:

Thanks!!! Now we'll see who outbids me

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"Ya just can't have too many GVIIs"

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t.r.sanford · Posted: Sun Feb 22, 2004 7:22 pm Post subject:

You will observe that the seller does not know what the supplementary lens is used for. It is good to know that Tiffen made these things; I had not seen them in the company's product lists.

worldphoto · Posted: Sun Feb 22, 2004 8:41 pm Post subject:

Rich
If I had known you were interested I would of sent a PM. There shouldn't be too much interest, needless to say I'm passing it up.
Harry
tr
Now I have had to expand my search for what I need. The max I can use on my 360 is a minus 2.

[ This Message was edited by: worldphoto on 2004-02-22 13:18 ]

RichS · Posted: Sun Feb 22, 2004 11:03 pm Post subject:

I would love to have a full set of minus filter/lenses! I've passed on the seires 5 & 6 in the past because they're just too small. A 7 I would take

Now all I have to do is win it, and find the 1,2 and 3 to go with it

And I just had an odd thought. If a minus 'filter' makes the lens longer, why doesn't a plus 'filter' make the lens shorter (I know it's supposed to)? Has anyone tried to focus at infinity using a plus filter? I never thought of it before, but with a bellows camera, why not?

Just an oddball rambling while I'm making a strap handle...

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"Ya just can't have too many GVIIs"

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Henry · Posted: Sun Feb 22, 2004 11:15 pm Post subject:

Rich, t.r. explained this very nicely in topic 2309; see excerpt from his post below:

The basis of the calculation must be to convert the focal length of the prime lens into a diopter value. That value is obtained by dividing 1000 by the millimeter focal length -- that is, a 500mm. lens has a diopter focal length of +2, a 250mm. lens is +4 diopters, and so forth.
By the same token, a +1 close-up lens like the Kodak "Portra" has a focal length of 1000mm. A +3 has a focal length of 333.33mm. And a negative lens has a minus diopter value, e.g. a -2 "Telek" has a focal length of -500mm.
The advantage of the diopter system is that it's easy to determine the focal lengths that result from combining components. The difficulty is that the simple calculation assumes that both components are "thin" lenses and that there is no separation between them.
Thus, it's easy to figure out, very roughly, that a 127mm. lens is about +8 diopters (if it were a 125mm. lens, the FL would be +8 diopters exactly), and if it is combined with a -4 "Telek," the resulting system will have an effective focal length of something close to +4 diopters, or 250mm, or 10 inches.
In practice, the answer will be somewhat different because of the distance between the second Gauss points of the "Telek" (a genuine "thin lens") and of the prime lens (usually more or less in the plane of the diaphragm, but not so if the lens is a true telephoto).

t.r.sanford · Posted: Mon Feb 23, 2004 3:07 am Post subject:

A question that hasn't been addressed is whether shortening the effective focal length of a prime lens by adding a positive supplementary lens will widen the field. If it doesn't (and I can think of no reason why it should), then the technique would only be useful with a prime lens whose image circle is substantially greater in diameter than the diagonal of the film.

For example, if you attach a +2 "close-up" lens to a 135mm. prime lens, and the separation between the rear nodal point of the primary and the center of the supplementary is 15mm., you get a combination that I figure to be just under 109mm. focal length. You now slide the front standard rearwards to regain infinity focus. A sketch of the lens projecting a cone back onto the focal plane will show that the cone now is sectioned across a smaller diameter.

If the 135mm. lens in question forms a well-defined image circle just large enough to cover the diagonal of a 4x5 sheet, then its angle of coverage is just under 60 degrees. When it becomes a 109mm. lens, if the angle of coverage doesn't change, then its image circle shrinks to just under 125mm., and it will no longer cover 4x5 (or even 3-1/4x4-1/4).

The other difficulty, which has been discussed, is that lens aberrations tend to become worse as you move away from the axis. This suggests that using a minus lens (like a "Telek") to extend the focal length of the primary may cause less image degradation than you might expect, because you're narrowing the angle of coverage.

On the other hand, even if your primary has an image circle large enough to accommodate shortening the EFL by adding a plus lens, the effect of doing so may be to degrade the image severely at the edges.

Once again, all we can do is try it and see what happens.

RichS · Posted: Mon Feb 23, 2004 4:29 am Post subject:

I have a tendency to come up with odd questions, especially when I'm tired

I never heard of anyone ever trying to 'widen' a lens with a plus lens. I've used them for close-ups for years and just never thought of it. It's a "close-up lens" after all... It was that other discusion where it was mentioned that it really shortened the focal length that got me. I haven't had time to try anything yet. I look at it more like one of those fun things to do that probably has no useful purpose. But many things like that promote creativity. I could just imagine how bad the image would be in such a situation? But who knows?

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"Ya just can't have too many GVIIs"

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RichS · Posted: Mon Feb 23, 2004 4:33 am Post subject:

Thanks Henry. It was that discussion that got me thinking. I've never heard of anyone using the "close-up" lenses to actually shorten a focal length and use it at infinity. Actually, I've also never heard anyone mention that a close-up lens shortens the focal length! It's those kinds of things that spark my curiosity and make me ask dumb questions. When I get the free time, I'm going to play and see what ahppens...

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"Ya just can't have too many GVIIs"

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t.r.sanford · Posted: Mon Feb 23, 2004 4:37 pm Post subject:

In fact, I can think of a couple of reasons to do it. One would be to eke out the extra couple of degrees of horizontal coverage you might get from a lens delivering a generous image circle, if you could do that without making the image fall apart. Even if you could not, you might get some interesting effects: I can envision a vignetted image becoming increasingly distorted and blurred as it fades into black. There are occasional subjects for which something like this might be very effective, and usually attained by manipulating the image in the darkroom.

It took me 30 years to realize that a "close-up" lens shortens the focal length of the primary. Before that revelation, I simply had never thought about why the thing worked!

worldphoto · Posted: Mon Feb 23, 2004 4:49 pm Post subject:

Hi
Just a short note. I have emailed Mr. Robert Havira, the author of the article in the Nov./Dec. 2003 issue of View Camera that started this discussion. Perhaps, he might like to add to this thread?
Harry

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

RichS · Posted: Mon Feb 23, 2004 7:05 pm Post subject:

Yes, there's a lot of problems associated with 'coming up' from 35mm. Like thinking in only one kind of film. Forgetting movements, and having a heck of a time figuring them out in the first place

Like T.R., I never really wondered why a close-up lens worked and never thought of another use for them. Makes me wonder what else we're not 'seeing' here?

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"Ya just can't have too many GVIIs"

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t.r.sanford · Posted: Mon Feb 23, 2004 7:39 pm Post subject:

One sees what one expects to see, all right. I got my first "Graphic" when I was in college, barely five years after starting to learn the noble art with my father's scale-focusing 828 "Bantam," and I've used "Graphics" ever since, when I've needed their unique virtues.

One of those virtues is the bellows focusing system, which gives you the built-in ability to get to 1:1 with a normal lens, without ever worrying about close-up lenses, extension tubes, large and small bellows attachments, the amazing Ihagee "two-in-one" ring, and all the other paraphernalia. So I never thought about close-up lenses in a large format context at all.

I don't believe this was a result of my being trapped in a miniature-camera mindset, but rather, the consequence of having been freed from it at a relatively early age...

There's a lot to be said for keeping an open mind!

Dave · Joined: 05 Dec 2003 Posts: 78 Location: Canada