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Custom Lens Mount Help Wanted
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PostPosted: Sun Jul 30, 2017 6:09 pm    Post subject: Custom Lens Mount Help Wanted Reply with quote

Hi! first off....I'm new here and thought I'd say hello!

I recently bought a used WWII made Kodak Aero Ektar 178mm F2.5. The lens came with a focusing helicoid with an Exakta mount. The helicoid is rather large and extends far beyond the lens itself. I believe the helicoid is made from aluminum. The lens screws into the helicoid and can be loosed by hand. I want to modify the helicoid adapter so I can mount it on a Pentax 645. I know there is a difference in flange depth between Exakta (44.70 mm) and Pentax 645 (70.87 mm). In order to reach infinity I will need to cut off 26.17mm??? from the end (plus some extra for the Pentax 645 mount). I am salvaging a well used Pentax 645 2X teleconverter and plan to use the male end mount to attach to the helicoid. In theory this should not be impossible, but how do I go about determining where to precisely cut the helicoid?

Note: I plan to find a local machine shop to machine the helicoid, I do not have the tools or experience in doing so precise. Does anyone know of a good machine shop in North Yorkshire, UK that does work on lenses?



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PostPosted: Sun Jul 30, 2017 6:43 pm    Post subject: Re: Custom Lens Mount Help Wanted Reply with quote

DonN wrote:
Hi! first off....I'm new here and thought I'd say hello!

I recently bought a used WWII made Kodak Aero Ektar 178mm F2.5. The lens came with a focusing helicoid with an Exakta mount. The helicoid is rather large and extends far beyond the lens itself. I believe the helicoid is made from aluminum. The lens screws into the helicoid and can be loosed by hand. I want to modify the helicoid adapter so I can mount it on a Pentax 645. I know there is a difference in flange depth between Exakta (44.70 mm) and Pentax 645 (70.87 mm). In order to reach infinity I will need to cut off 26.17mm??? from the end (plus some extra for the Pentax 645 mount). I am salvaging a well used Pentax 645 2X teleconverter and plan to use the male end mount to attach to the helicoid. In theory this should not be impossible, but how do I go about determining where to precisely cut the helicoid?

Note: I plan to find a local machine shop to machine the helicoid, I do not have the tools or experience in doing so precise. Does anyone know of a good machine shop in North Yorkshire, UK that does work on lenses?



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Welcome!
Your photos won't show in your first post (anti-spam measure).


PostPosted: Sun Jul 30, 2017 6:54 pm    Post subject: Reply with quote

Like 1

look this subject

http://www.ebay.com/itm/Kodak-Aero-Ektar-7-f2-5-Lens-Professionally-Machined-Mounted-for-Cine-C-Mount/142432304723?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41451%26meid%3D0483d010b68049ddb53dd241c059bbf4%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D282462770425


PostPosted: Sun Jul 30, 2017 7:25 pm    Post subject: Re: Custom Lens Mount Help Wanted Reply with quote

I have adapted some lenses to my former (now sold) Pentax 645N but I have always preferred to use the mount from some cheaper Pentax 645 adapters instead of the mount from P645 lenses.

In your case I think that first you have to check if the Exakta mount diameter and thickness (the large part with tripod mount on it) permits the Pentax mount screws to securely be screwed (has enough thickness to cover the Pentax mount screws holes).
If not you'll have to make a piece that screws inside the large (after cut) Exakta mount and offers thickness to permit screwing the Pentax mount screws. In order to do this you should make a lathe-made inner thread on the inside of the large Exakta mount (after cut). You should cut the Exakta mount a little shorter(~0,5-1mm.) than resulting from calculations because the linking piece will allow you to precisely get infinity for your lens (you unscrew it in the Exakta mount till you get infinity and cement it in place).

I don't know the exact dimensions (diameters) of your Exakta mount but it may be more simple to use a cheap Pentax 645 adapter mount instead of the 2x converter one.

The most simple way use the lens on your P645 should be with a Bellows unit (using only the Aero Ektar on it, without the Exakta mount helicoid) but I know that P645 Bellows are expensive and not easy to find. However, getting one will be helpful to adapt other lenses, too.
I preferred to change the mount of a Pentacon 6 Bellows unit to P645 for such tasks (much cheaper).


PostPosted: Sun Jul 30, 2017 8:16 pm    Post subject: Re: Custom Lens Mount Help Wanted Reply with quote

dan_ wrote:
I have adapted some lenses to my former (now sold) Pentax 645N but I have always preferred to use the mount from some cheaper Pentax 645 adapters instead of the mount from P645 lenses.

In your case I think that first you have to check if the Exakta mount diameter and thickness (the large part with tripod mount on it) permits the Pentax mount screws to securely be screwed (has enough thickness to cover the Pentax mount screws holes).
If not you'll have to make a piece that screws inside the large (after cut) Exakta mount and offers thickness to permit screwing the Pentax mount screws. In order to do this you should make a lathe-made inner thread on the inside of the large Exakta mount (after cut). You should cut the Exakta mount a little shorter(~0,5-1mm.) than resulting from calculations because the linking piece will allow you to precisely get infinity for your lens (you unscrew it in the Exakta mount till you get infinity and cement it in place).

I don't know the exact dimensions (diameters) of your Exakta mount but it may be more simple to use a cheap Pentax 645 adapter mount instead of the 2x converter one.

The most simple way use the lens on your P645 should be with a Bellows unit (using only the Aero Ektar on it, without the Exakta mount helicoid) but I know that P645 Bellows are expensive and not easy to find. However, getting one will be helpful to adapt other lenses, too.
I preferred to change the mount of a Pentacon 6 Bellows unit to P645 for such tasks (much cheaper).


This is a very wise message.


PostPosted: Sun Jul 30, 2017 9:11 pm    Post subject: Re: Custom Lens Mount Help Wanted Reply with quote

dan_ wrote:
I have adapted some lenses to my former (now sold) Pentax 645N but I have always preferred to use the mount from some cheaper Pentax 645 adapters instead of the mount from P645 lenses.

In your case I think that first you have to check if the Exakta mount diameter and thickness (the large part with tripod mount on it) permits the Pentax mount screws to securely be screwed (has enough thickness to cover the Pentax mount screws holes).
If not you'll have to make a piece that screws inside the large (after cut) Exakta mount and offers thickness to permit screwing the Pentax mount screws. In order to do this you should make a lathe-made inner thread on the inside of the large Exakta mount (after cut). You should cut the Exakta mount a little shorter(~0,5-1mm.) than resulting from calculations because the linking piece will allow you to precisely get infinity for your lens (you unscrew it in the Exakta mount till you get infinity and cement it in place).

I don't know the exact dimensions (diameters) of your Exakta mount but it may be more simple to use a cheap Pentax 645 adapter mount instead of the 2x converter one.

The most simple way use the lens on your P645 should be with a Bellows unit (using only the Aero Ektar on it, without the Exakta mount helicoid) but I know that P645 Bellows are expensive and not easy to find. However, getting one will be helpful to adapt other lenses, too.
I preferred to change the mount of a Pentacon 6 Bellows unit to P645 for such tasks (much cheaper).


Thanks for the advice. Here is a screen shot of the teleconverter, its made by Pentax. I'm waiting for it to arrive in the mail, but will check the diameter of the mount and determine where the screw holes for the mount line up. If needed I will have an inner collar/ring built for the mount. You also have some great advice about getting infinity, but I'm not very keen about using cement on the lens. I have a Pentacon-6 bellows/Pentax 645 adapter, but the lens doesn't fit into the exist opening, also I'm looking for something permanent.

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PostPosted: Sun Jul 30, 2017 10:00 pm    Post subject: Reply with quote

You're welcome!
One more thing - when ordering the collar/ring don't forget to design it in such a way that the Pentax mount will center properly(with an inner or outer rebord that wouldn't let the Pentax mount to be placed on it other than centered).


PostPosted: Sun Jul 30, 2017 10:05 pm    Post subject: Reply with quote

Perhaps the Kokak Aero Ektar has a special interest for you, but a more practical alternative would be to adapt a CZJ 180mm F2.8 lens, which is probably equal to or better than the Aero Ektar. There are many Pentacon Six to Pentax 645 adapter on the market, so you wouldn't need to do any surgery on the lens.


PostPosted: Sun Jul 30, 2017 10:28 pm    Post subject: Reply with quote

Gerald wrote:
Perhaps the Kokak Aero Ektar has a special interest for you, but a more practical alternative would be to adapt a CZJ 180mm F2.8 lens, which is probably equal to or better than the Aero Ektar. There are many Pentacon Six to Pentax 645 adapter on the market, so you wouldn't need to do any surgery on the lens.


Thank you - yes definitely a good alternative and a lot cheaper. I have a CZY 180mm 2.8, but to be honest I wanted the Ektar since its a bit faster/shallower depth of field. I also like the soft focus and the bokeh from the Ektar. I do not plan to do any surgery on the lens, only the helicoid which I think was made by a 2nd party. I know there are numerous other mounts for the Ektar and the ones I've seen on eBay are similar to the one I have.


PostPosted: Sun Jul 30, 2017 10:29 pm    Post subject: Reply with quote

The big deal about the Aero Ektar is it covers 4x5
There arent a lot of 4x5 lenses that fast.

The one you have looks like a late-40's or 1950's professional adaptation.
This was probably done when the Ektars were cheap surplus and similar lenses were hard to come by or expensive.

The adapter itself is an interesting vintage item, a pity to spoil it.


PostPosted: Mon Jul 31, 2017 6:26 pm    Post subject: Reply with quote

+1, pity to spoil a vintage helicoid for adaptation.


PostPosted: Mon Jul 31, 2017 9:57 pm    Post subject: Reply with quote

Just wondering if the Aero Ektar couldn't be adapted to the helicoid of the CZJ Sonnar 180mm...


PostPosted: Tue Aug 01, 2017 4:27 pm    Post subject: Reply with quote

Lightshow wrote:
+1, pity to spoil a vintage helicoid for adaptation.


I understand your concern, but if its properly modified to Pentax 645 mount it could be used on other cameras/mounts such as Canon, Nikon, Sony E-mount, Fuji, 4/3 mount, M42 mount cameras and lots more. Having a helicoid that I'm stuck using 35MM format only on a limited amount of cameras is useless to me.


PostPosted: Tue Aug 01, 2017 4:34 pm    Post subject: Reply with quote

Gerald wrote:
Just wondering if the Aero Ektar couldn't be adapted to the helicoid of the CZJ Sonnar 180mm...


Yes it can. Somebody else did a custom adaptation/hack.

https://www.facebook.com/thebokehfactory/photos/a.962403920524860.1073741864.341368619295063/962403937191525/?type=3

More Info here:
https://www.facebook.com/pg/thebokehfactory/photos/?tab=album&album_id=962403920524860

Don't get me wrong this is lens hack very impressive, but I do not have the desire to start making things more complicated for myself and buying more parts.


PostPosted: Wed Aug 02, 2017 2:38 pm    Post subject: Reply with quote

It's your lens, you can turn it into a flower vase if you wish. lol I just prefer not to see vintage equipment get irreversibly modified if at all possible, especially if it's rare or a significant piece.
If you get to use it how you want to, who cares what we think, right? Wink