Graflex.org

[Micah in NC]

Hi folks,

I came across a Taylor Optical Co. (Made in Japan) lens the other day and picked it up for a paltry $7 on that famous internet auction site.

This lens is Series VI add-on "telephoto lens" and appears very clear and clean. Markings on the lens say something like "set focus to one-half distance except at infinity."

Anyone ever used such a beast on their Graflex?

--Micah in NC

[t.r.sanford]

This seems related to the recent discussion of "Varying the Focal Length of Large-Format Camera Lenses." I, for one, will be interested to learn how you fare with the attachment. Is it marked with a magnifying factor (e.g., 1.5X)?

The afocal supplementary lenses I've seen don't affect the focal length of the prime lens. The instruction to adjust the focus by scale therefore is curious -- of course, if you use the groundglass, you needn't worry about it.

I think a well-designed auxiliary Galilean lens that could (say) make an 8-inch lens act like a 12-inch one could be very useful under some circumstances. The inevitable image degradation gets worse as you move off axis, and in any case is lessened as you stop down. The thing might be a neat portrait tool.

[worldphoto]

I'm having a lot of fun using the single element supplementary in the positive and negative (diopter lens). But I have just bought the negative lenses several weeks ago off eBay and have not had time to test them. There is a good article in the November/December 2003 issue of View Camera on this very subject.
Harry
Yesterday I found out that my series 9 positive lenses will work behind the rear element of my 360mm prime lens. Too bad they don't make cheap series 9 lenses in that size for minus (telephoto) supplemaentary type lens.


[ This Message was edited by: worldphoto on 2004-02-13 10:18 ]

[t.r.sanford]

Many of us regret that Kodak did not make larger-diameter "Telek" negative supplementaries; that no one seems ever to have revived the idea in Series 8 or 9 (one might have hoped that Spiratone would, but I don't recall their ever doing it); and that there are so few large-diameter long focal length negative lenses on the surplus/salvage market.

I wonder whether one could induce a sympathetic optometrist to write a prescription for a -2 diopter lens with no "cylinder" correction, and then hunt up an optician with a display of large, round frames?

[worldphoto]

Tiffen may have some larger minus lenses. They still make the plus lenses but they are not cheap. I found some optical lenses on eBay that are made for magnifiers and telescopes that fit in series 7 holders (Sold by Macnan). They sell for less than five bucks each. I would sure like to turn that 360mm into about 600mm lens. A minus (-) 2 lens is about all I could use because the combined focal length would be 947mm. A minus (-) 1 lens would be combined 522mm.


[ This Message was edited by: worldphoto on 2004-02-20 23:11 ]

[t.r.sanford]

I haven't looked at Tiffen's product lists for awhile, but don't recall their making negative supplementary lenses in the past. They certainly could, and perhaps they do.

A rough calculation suggests that a lens of minus 1.1 diopter focal length would extend a 360mm. lens's EFL to around 600mm. At the same time, it would add about nine inches to the back focus.

Using a 1.5X "telephoto" attachment of the kind sold for digital cameras (and small movie cameras before them) would yield an image equivalent to that formed by a lens of 540mm. focal length, with little (if any) effect on the back focus or aperture.

I imagine someone would need to do some tests to find out which would have the worse effect on the corrections of the prime lens.

[worldphoto]

Did some calcs this afternoon using the info from that View Camera article. A +3 diopter lens attachment would turn that 360 into a 186mm wide angle for my 8x10. That's impressive! Now to get time to use it.
Harry
Using a minus 4 (Telek) diopter lens attachment behind my 152mm Ektar prime lens rear element would turn that into a 297mm (telephoto effect).

[ This Message was edited by: worldphoto on 2004-02-13 20:50 ]

[t.r.sanford]

It will be interesting to see what happens. Many, many years ago, I did a few very uncontrolled tests with a +1 on a 65mm. wide-angle "Raptar" and found that the image deteriorates very rapidly as you move off axis, but that was on a 2-1/4x3-1/4 camera (and with a lens which never impressed me with its sharpness, even unmodified). With a longer-than-normal lens on 8x10, you may get much better results.

Someone with ample time might try using two weaker supplementary lenses, one in front and one in back of the prime lens, and reversed. That is, you'd use a +1 before and a +1 behind, rather than a +2 alone. Intuition suggests that a symmetrical arrangement might have less effect on the corrections of the prime lens.

A useful thing that Spiratone used to offer was the "fractional-diopter" closeup lens. These came in +1/2 and +1/4 diopter focal lengths. Their intended use was on telephoto lenses for 35mm. cameras, which often had rather long minimum focusing distances (e.g., Enna's 240mm.). If still available, these might offer some interesting possibilities.

[worldphoto]

I have some dupe supplementary lenses so I could test on my 4x5 lenses, the 360 requires too large of a filter size on the front element.
It looks to me that a minus lens (having a telephoto effect) would work with a smaller diameter size because it reduces the field of view of the prime lens. The plus lens would require a larger diameter because it increases the prime lens field of view. Does that seem like a correct statement?

[ This Message was edited by: worldphoto on 2004-02-14 09:39 ]

[ This Message was edited by: worldphoto on 2004-02-14 09:42 ]

[t.r.sanford]

I rather think that the angular coverage of the prime lens, and the distance in front of or behind it at which the auxiliaries are positioned, will govern their minimum acceptable diameter. In other words, a wider field primary is likely to require larger-diameter supplementaries.

Many years ago, one of the photo magazines (I think "Modern") published a series of erudite letters from people arguing for and against the proposition that close-up lenses with a concavo-convex figure would cause less image deterioration than the plano-convex lenses commonly sold for the purpose. Somebody eventually went out and found some meniscus lenses, ran tests, and reported that the lens figure makes no detectable difference.

[Micah in NC]

Hi folks,

Hmmmm. The little Taylor lens generated a bunch of interest!

-----
T.R.: the Taylor isn't marked with a magnifying factor, unfortunately. If simply holding it up to my eye (haven't gotten around to putting it on the Graflex...yet) tells me anything, it is less than 2x, probably 1.5x or so.

------

I also have received a few Kodak Series 6 Telek lenses (1- and 4-) and also a 2- and a 3- but the 2- is SO nasty I can't use it. Looks like fungus has attacked it, big time. It is nearly opaque. The 3- is OK, I suppose, but has a faint haze on about 1/3 of it's area.

I also got a Portra 3+ lens in that set.

And I just won an auction (on you-know-what) for a Tiffen Split Field 1+ lens. I'm very excited about the possibilities on that!


So, now I have the capability to do some close-up stuff (Portra lenses) and try my hand at portraits or maybe landscapes with those Teleks. This will hopefully tide me over until I save some cash for lenses longer than my 15cm old Carl Zeiss lens and my 127mm Ektar.

-----

Harry: I don't have access to a copy of View Camera magazine to read about those calculations. What can I expect, focal length-wise, the 1- and 4- Teleks to do when used in front of my 127mm Ektar lens?

Thanks everybody, for all the comments!

--Micah in NC

[ This Message was edited by: Micah in NC on 2004-02-15 10:14 ]

[ This Message was edited by: Micah in NC on 2004-02-15 10:16 ]

[worldphoto]

I'll work out the answer on the 127mm very soon, I also have a 127mm Ektar. The article has a chart using a 135mm lens and for now: -1 = 151mm, -2 = 171mm, -3 = 197mm, -4 = 233mm.
Harry
The lenses should be clear with no coatings. Put them out in the sun for a few days and then use a glass cleaner on them. (Don't place them on anything that will burn. Remember the old magnifier trick to start a flame.)

[ This Message was edited by: worldphoto on 2004-02-15 11:38 ]

[ This Message was edited by: worldphoto on 2004-02-15 11:42 ]

[t.r.sanford]

I haven't seen the cited article, either. 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).

If the cited article provides a simple method for computing the effect of the separation of components on the effective focal length of the combination, this would be a very useful thing to know!

[worldphoto]

Following along on your thooughts tr, the formula does factor in the distance between lens centers even though it is just an estimate. The formula is:

Combined Focal Length = f x f '/ f '-f+d

f is the camera lens focal length
f ' is the negative diopter lens focal length
d is the distance between lens centers (estimated)

The f ' (focal length) must be longer than the prime lens focal length for the combination to focus. For instance, using a -4 lens the prime lens focal length must be less than 250mm or the combination will not focus.
The combined focal length for the 127mm (based on the above formula) is -4 = 208mm, -3 = 179mm, -2 = 158mm and -1 = 141mm.



[ This Message was edited by: worldphoto on 2004-02-15 16:48 ]

[t.r.sanford]

The same formula is provided by the "Focal Encyclopedia of Photography" (1969) under "Optical Calculations" --

F=(f1*f2)/f1+f2-S

where S (of course) is the Separation between the two elements -- the D in your statement.

I used the values 127 for f1, -250 for f2 (a -4 "Telek" lens), and 15mm. for the separation. The answer I got is +230mm., which seems to be in the ballpark.

The uncomplicated diopter addition seems to give us a pretty good idea of what to expect, and applying this formula no doubt gives us an even better idea -- but, in view of the unlikelihood that either lens works at its design focal length, the inconvenience of finding the second Gauss point of the primary, and the awkwardness of measuring the separation, I'd guess that the most practical procedure is to rough it in, then assemble the combination and see what happens!