mft custom made helicoids for lens conversions?

[kds315]

Some weeks ago I started a similar thread in another forum to make available custom made helicoids for easier lens conversions, which turned out positive.

Now I wondered if others here might be interested in such helicoids for mft cameras to easily adapt their manual lenses to? I would be willing to organize such a bulk order, as ususally 10-20 each have to be ordered before such a custom order will be accepted by manufacturers.

Available sizes as per today are:
a) short: approx. 13.5 - 20.5mm extension
b) middle: approx. 20.5 - 41.5mm extension
c) long: approx. 30.5 - 50.5mm extension
d) extra long: approx. 35.5 - 90.0mm extension

matte black or silver finish (if quantities are reached).

PM me or reply here to see if there would be some interest in that.

Estimated prices depend massively on the quantities we reach, I expect EUR80-100 each, but this can only be set after negotiations with the manufacturer(s).

This is how the custom made helicoids look like from that other project to have an idea about the quality to expect (bajonet rear mount, M42 front thread mount to attach any lens with suitable intermediate ring)

 

[Vivek]

Could you list the prices here please? Thanks!

What does the front end have?

 

[kds315]

Well, I expect inquiries how to determine the needed helicoid length. If you have the register *length ("Auflagemass" in german) for a given lens, it is quite easy, otherwise measurements or an approximation has to be used (as follows)

Denote:

RLL = Register Length of a Lens [length from rear flange to point of sharp focus if original is at infinity]
RLC = Register Length of a camera [mft = 19.6mm]
HLI = Helicoid Length at Infinity [measured front flange to rear flange]
AL = Adaptor Length (usually a few millimeters thickness only) [this can be set to zero if the helicoid has already mft mount]

then:

HLI = RLL - RLC - AL

that also means that HLI cannot be negative and has to be at least some 13mm or so (shortest Helicoid I know of). This also explains why with some lenses infinity focus cannot be reached.

If RLL is not known, 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.) towards the center of the lens- not 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 bulb has (use the visible lamp filament for focusing (stepping down a bit helps if the image of the bulb is too bright). Keep that position and repeat the measurement as mentioned above). That gives you an 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 may 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]

 

[kds315]

Could you list the prices here please? Thanks!

What does the front end have?

Price estimates given. Front as mentioned M42 x 1.0 thread mount. Leica thread mount (LTM, M39 x 26tpi) via adapter ring for EUR5 each possible.

 

[kds315]

A feedback I got from one of the participants, unedited as is:

Got mine today and I must say that look and feel is very impressive, there is no play in the focusing helicoils at all, the quality is similar to the best MF lenses I have seen. They mount perfectly on the camera mount, and wit the internal matte black baffle it all adds up to a perfect product!

 

[kds315]

Here my 90 seconds "conversion" of an older fine Schneider Xenon 2/40mm using such a helicoid (my working prototype). [the chrome part is an adapter ring I used between lens and helicoid]

Pics show the helicoid compressed and fully extended, it is type a). The helicoid front does not rotate, a big plus as it allows to arrange the lens markings upside (not yet done here).