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UltravioletPhotography

Helicoids


colinbm

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Helicoids can be used in lots of situations besides for focusing. They can be used in macro extension tubes to fine tune the tubes length, for magnification ratios. They can be used to set a lens at its Flange Focal Distance. What else can they be used for ?

I want to set a helicoid at a precise position & lock it there, is there anyway to do this Please ?

Cheers

Col

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There aren't any helicoids I've come across so far which have a locking screw or other locking mechanism.

 

But if you lock a helicoid, then you cannot focus any further with it.

So I'm not sure why you want to lock it?

Perhaps only to note the FFD for a particular lens?

 

If that is the case, then you could use some kind of marker on the extended barrel.

Or place a thick rubber band (assuming you could find one of the proper diameter).

 

Otherwise, strong duct tape wrapped around the extension area will hold it well enough.

Later you might have to clean off the tape residue.

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Never seen that TS before !

It is very long however - 51mm minimum.

My helical needs tend to fall between 12-30mm or so for photo lenses.

 

I hadn't realized the Baader version rotated. I had thought that was a push-pull.

It is very long also.

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enricosavazzi

I am aware of only one type of helicoids made for photography that can be locked with set screws or thumbscrew, the Schneider Unifocus. They have proprietary front and rear mounts and are intended for use with the Makro Apo Componon series of lenses. They are well built, but usually very expensive. See one example at http://savazzi.net/p...componon_60.htm

 

Edit - The pictures at the above URL actually don't show the helicoid. But it is designed for this type of lenses.

Edit2- It's Unifoc, not Unifocus.

 

There might be helicoids for telescope eyepieces equipped with a locking facility.

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Never seen that TS before !

It is very long however - 51mm minimum.

My helical needs tend to fall between 12-30mm or so for photo lenses.

 

I hadn't realized the Baader version rotated. I had thought that was a push-pull.

It is very long also.

Baader makes a shorter one also and there are others such as this Borg.

These are not really focusing helicoids but rather locking variable length extension tubes.

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Thanks everyone for the informative replies & the useful links, these are some nice helicoids.

In my case this time, I want to set the FFD of an older lens from an older MF folding camera.

I will see if I can take the Chinese helicoid apart & drill & tap a locking screw on the barrel.

Cheers

Col

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I just knew it was going to happen...........

I have now got a locking screw on the ring of the focus helicoid......but I can't get it back-together properly :)

I was careful to mark everything as it came apart, the 6 screws on the outside.....BUT....just when you are looking over at what to do next, it all falls apart. No problem, so I drilled & tapped the ring for a 2mm grub screw....easy.

Now to put it all back again....................hummm.....there are two little screw heads that have to slide in two slots, cut in the side of one of the rings ?

I have assembled it. but it is not quite right........instead of stopping at the end of the extension, it falls apart again, very frustrating.

Can anyone tell me the secret of putting this back the right way please.

I have noticed that the Chinese helicoids are the same as the Asahi Pentax Helicoids that Enrico has on his wonderful site http://www.savazzi.net/photography/focusing_helicoid.htm

I am able to use the helicoid & set my lens on it & adjust the infinity focus............but it will be nice to have it not fall apart when I inadvertently extend it past the end :(

Cheers

Col

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enricosavazzi

Some of the Chinese helicoids look like the old Pentax ones. I don't know whether they are built the same way.

 

I did not take apart one of these helicoids, but the problem you describe is usually one of the possible consequences of re-slotting the two spirally threaded parts together incorrectly. These are not like ordinary screw threads, which have just one thread. Instead, usually they have three or four parallel threads that start at regularly spaced intervals around the circumference. Rotate one of the two parts with respect to the other until it comes free from the other piece. Then rotate this part one direction (or the other) by 1/3 or 1/4 of turn (depending on the number of parallel threads) and re-insert it into the opposite threaded piece. If it still comes apart or stops turning too early, repeat until you have tested all possible thread combinations.

 

This is similar to the way the built-in focusing helicoids of lenses are made (some of them have many more parallel threads). This procedure can sometimes be used to adjust infinity focus, but often requires the additional tweaking of other retaining rings and set screws.

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Thanks Enrico, that is exactly the problem.

Most threads, like common nuts & bolts have a 'single start' thread. Some other types of threads have, double, triple or four start threads.

These helicoids have perhaps a twenty start thread, (I haven't counted them, just a guess from what I have seen).

Yes, my problem is just that, I need to move the start to one thread forwards of where I am now, but then it won't drop into the two grooves that the screw heads sit in, that stop everything from rotating independently.

I am not engineering dyslexic, but there must be a simple solution to this.....if I only knew how simple !

Cheers

Col

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PHEW........

That will be the first & hopefully the last time I take a helicoid apart...!

It is now back together & working as intended & with the addition of a locking screw :(

Don't ask me what I did...I just kept turning till each thread engaged & finally it dropped into the correct one & it fell together.....never to fall apart again !

 

What a day, first this mess, then a visit to the dentist, in the morning, all day with out being able to eat, getting annoyed with helicoids, finally I have eaten & got thr helicoid back properly & it is a hour before mid-night & I am ready for some sleep...without anything on my mind :)

Cheers

Col

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Just another little adventure in UV-world, Col !!! All's well that ends well, I hope. :)

 

*****

 

FWIW, I have had good luck so far with the various Chinese helicoids I've purchased on Ebay. Seem to be well made and sturdy. I also have one from Fotodiox which seems good - and was probably also made in China !!

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Thanks Andrea

Yes, tomorrow I'll probably find something else to exceed my abilities, & so the wheel goes around :)

More adventures in the wonderful world of UV :(

I can't criticize the Chinese helicoids, they are made quite well.

Cheers

Col

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Hi!

 

Instead of a helicoil I use the "Pentax Auto Bellows".

It has 4 separate handles to adjust focus and friction for lens and camera.

One can even block the sliders.

Unfortunately its minimum length is 40mm. Perhaps there are other types/brands of bellows that build shorter?

M42?

 

! da baffe

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I have an old Asahi Pentax M42 bellows which squishes down to about 30mm. But bellows probably are not made to be shorter because they are used for close work & magnification purposes ??

 

What camera are you using, Baffe?

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Depending on the lens, one can always try to mount it deeper in the bellows that it is originally intended. I have done this with El-Nikkor and Focotar enlarging lenses and with Kyoei Acall 35mm F/3.5 lens. It very much depends on the construction of the lens and bellows, and willingness to experiment.
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[[[off topic: Focotars are enlargers? I should add that to our lens info. Are they marked just "Leitz" or "Ernst Letiz Wetzlar"? Thx.]]]
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Yes, I know, I put them there. :D

But I'm wanting to know whether to mark them as ELs and what the branding is on the lens so that I can be accurate.

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Yes, I know, I put them there. :D

But I'm wanting to know whether to mark them as ELs and what the branding is on the lens so that I can be accurate.

 

As far as I have seen the "El-" designation was used by El-Nikkors and some rebranded lenses imported to USA with Omega enlargers.

 

Propoer inscriptions for Leitz enlarger lenses are listed here: http://www.l-camera-forum.com/leica-wiki.en/index.php/Enlargers_and_Film_Processing

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....using "EL" above as an abbreviation for declaring: "This is an enlarger lens with no helicoid."

So that readers will know additional equipment is needed should they decide to use such a lens.

 

As a child of the digital age, so to speak, it was not so very long ago that I myself was surprised to learn of such things as enlarger lenses which have no helicoids. I had no idea what an enlarger lens was or why it had no focusing mechanism. I've never seen a darkroom or an enlarger to this day. Now they are disappearing. So it goes..... :D

 

(Well, actually it has been a fairly long time. I began digital photography in the Year 2000 and ultraviolet photography in 2007. That's when I began to learn all kinds of cool things about filters, lenses, optics and light. Love this stuff !!)

 

Thank you for the link. That's exactly what I needed to know.

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enricosavazzi

[...]

(Well, actually it has been a fairly long time. I began digital photography in the Year 2000 and ultraviolet photography in 2007. That's when I began to learn all kinds of cool things about filters, lenses, optics and light. Love this stuff !!)

[...]

I started out in digital photography the same year, and probably UV photography in (or around) the same year too.

 

I did have a darkroom for several years in my "tweens", then moved around a lot and only used the darkrooms of the institutions where I was working, except a few years when I modified the bathroom of our apartment for this use (fairly easy since it did not have real windows, only a door to lightproof with a sliding curtain).

 

I initially modified the lens board of a cheap Meopta enlarger to mount a Panagor macro lens, which probably saved me from having to go through several iterations of cheap-to-expensive enlarger lenses until I found a sufficiently good one. I never owned an enlarger lens until about 1995, when I bought an old Leitz Focomat enlarger that came with its own Focotar. Sold the enlarger with lens for about 250$ a few years ago, before it became hopeless junk. Now that enlarger lenses and darkrooms have gone the way of Kodak and Polaroid (or perhaps vice versa), I have about three dozen enlarger lenses. Go figure.

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oh la !! That's how this UV obsession seems to work. We all wind up with bags full of interesting, strange lenses which we "repurpose" into the UV arena.

I think I have collected far too many at this point and need to begin to sell off some of them. Especially those which have not worked out so well as others.

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