M42 helicoid (macro tube) from hk300 and mflenses - a review

kds315* · Expire: 2021-03-09

This certainly depends on teh type of helicoid you are interested in.

1) you need to determine which total helicoid extension you need (maximum / minimum i.e. longest / shortest).

2) you need to select a suitable one in that range (usually a compromise needs to be accepted in terms of close focus, since infinity focus, or a bit more determines the shortest length = extension needed).

3) you can find out which total angle that selected helicoid needs from minimum extension to maximum extension (360 or 500 or 720 or whatever degree).

4) it is up to you to decide if that is fine enough or too course.

patrickh · Expire: 2011-11-18

Klaus

How can one calculate the size of helicoid needed for any given FL to achieve infinity? Is there a simple way to do it?

patrickh

kds315* · Expire: 2021-03-09

If you have the register length ("Auflagemass" in german) for a given length, yes, otherwise measurements or an approximation has to be used.

Denote:

RLL = Register Length of a Lens
RLC = Register Length of a camera (Nikon, Canon EOS, 4/3 - you name it)
HLI = Helicoid Length at Infinity
AL = Adaptor Length (usually a few millimeters thickness only)

then:

HLI = RLL - RLC - AL

that also means that HLI cannot be negative and has to be at least some 15mm or so (shortest Helicoid I know of). This also explains why with some lenses infinity focus cannot be reached.

If RLL is not know, the following procedure allows to measure it approximately:

take a white sheet of paper, a ruler and your lens, hold the lens in front of the white paper in a darkened room and point the lens front with fully open aperture to the outside to a bright object (can be the sun also, but be careful not to burn the paper) at least 100x further away then the focal length of that lens until you get a sharp image on that paper. Now measure the distance from that paper to the flange of the lens (end of the thread or mount (could be bajonet etc.) - not just the physical end of the lens!). This is approximately RLL.

If you want to use that lens for macro shooting, say at 1:1 magnification, then point the lens using the same procedure to a bright lamp (desktop tungsten works well) until you see an projected image which has the same size as the original lamp (us the visible lamp filament for instance (stepping down helps if the image is too bright). Keep that position and repeat the measurement at mentioned above). That gives you the approximation for RLL(1x) at magnification 1x.

Now we get

HL(1x) = RLL(1x) - RLC - AL

where HL(1x) denotes the needed maximum extension of your helicoid and

HR = HL(1x) - HLI is the range your helicoid has to cover when turning from infinity to 1x magnification (you can replace 1x with any wished factor of course). If HR is too long, it has to be replaced with a shorter helicoid and a tube of fixed length (say to reach only 0.5x for instance). [Example, if you would need HR = 50mm and the longest helicoid you can find is 25mm, then add a 25mm tube to reach 50mm]

YucatanPentax · Joined: 29 Dec 2009 Posts: 2 Location: Dallas / Yucatan

Wow, that's just excellent information to have. Amazing really the great things everyone shares here. I've been quietly reading and reading. I'm a little in awe after going through this thread.

Perhaps I'll post more soon. You all seem like a friendly lot... Smile

patrickh · Expire: 2011-11-18

Klaus

Belated thanks. Your depth of knowledge and ability to share are gratefully acknowledged

patrickh

kds315* · Expire: 2021-03-09

glad to be of help guys!

JohnBar · Joined: 21 Jun 2012 Posts: 581 Location: Liverpool

How stable are these at full extension with old metal heavy lenses?

Do they droop?
Do they wobble?

Do they shake rattle and roll? Smile

kds315* · Expire: 2021-03-09

Not sure what you are used to, but mine work pretty well and I use them all the time.

JohnBar · Joined: 21 Jun 2012 Posts: 581 Location: Liverpool

Thanks Klaus

One more question --- is the m52 size with filter thread pitch 0.75mm?

Presumably the M42 size is 1mm pitch

calvin83 · Joined: 12 Apr 2009 Posts: 7554 Location: Hong Kong

JohnBar · Joined: 21 Jun 2012 Posts: 581 Location: Liverpool

Thanks Calvin83

I must confess Ive never seen a M52/1

Anyway I just bought one so will see for sure

calvin83 · Joined: 12 Apr 2009 Posts: 7554 Location: Hong Kong

JohnBar · Joined: 21 Jun 2012 Posts: 581 Location: Liverpool

Well it has been dispatched already Smile

I had a look at photos of the same item from other sellers and the threads do look like .75

Anyway I need the girth - I have some big fat-ass lenses to try