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09-04-2019, 01:14 AM   #1
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K-mount/F-mount mechanical differences

Hi,

I need a custom made K-mount adapter to connect my K-1 to my telescope. There's a workshop in France that could do it for me but they only did adapters for Nikon F and Canon EF so far. I need to tell them precisely what to do.



I am aware that F-mounts and K-mounts are very similar, but what are precisely the mechanical differences ?


Throat diameter is the same (44mm) flange distance has a 1mm difference (45.5mm for Pentax vs. 46.5mm for Nikon). I don't know otherwise in which respect the bayonets differ from each other



thanks a lot !

Dan

09-04-2019, 01:53 AM - 1 Like   #2
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I'd have thought the best method would be to send them a mount from an old lens, along with the flange distance. This will be a lot more dependable than relying on you to specify all necessary differences between K and F mounts - and it puts the responsibility on the workshop to replicate what you've given them

An alternative would be to fit a good M42-to-K adapter to your K-1, and buy an M42 telescope adapter... Both of which you can obtain off-the-shelf without any concerns over bespoke manufacturing. Just a thought
09-04-2019, 02:28 AM   #3
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thanks for your message,


QuoteOriginally posted by BigMackCam Quote
I'd have thought the best method would be to send them a mount from an old lens, along with the flange distance.
I thought about this but they told me they don't want to waste to much time on this so they prefer to have the specs





QuoteOriginally posted by BigMackCam Quote
An alternative would be to fit a good M42-to-K adapter to your K-1, and buy an M42 telescope adapter... Both of which you can obtain off-the-shelf without any concerns over bespoke manufacturing. Just a thought
The problem is that it will create a bottleneck in the optical train so lot of vignetting...


best,

Dan
09-04-2019, 02:35 AM   #4
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QuoteOriginally posted by Dan Paris Quote
I thought about this but they told me they don't want to waste to much time on this so they prefer to have the specs
Fair enough. My concern stands, though... if you have to specify every single difference between Nikon F and K-mount, the responsibility is with you to get it absolutely spot-on - and if you don't, you'll get a product that might not fit properly. I'd also be a little concerned by their statement that they don't want to waste too much time on it, but maybe they didn't mean to be quite so off-hand

QuoteOriginally posted by Dan Paris Quote
The problem is that it will create a bottleneck in the optical train so lot of vignetting...
Ah, OK. What is the spec of the telescope mount your fitting to, or the eyepiece diameter? I'm surprised there isn't something already available off-the-shelf I'm sure you've researched it, of course...

09-04-2019, 03:24 AM   #5
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QuoteOriginally posted by Dan Paris Quote
thanks for your message,



I thought about this but they told me they don't want to waste to much time on this so they prefer to have the specs







The problem is that it will create a bottleneck in the optical train so lot of vignetting...


best,

Dan
Will this kind of thing work?
https://www.amazon.co.uk/Solomark-Telescope-Adapter-1-25inch-Cameras/dp/B016B3UJ8W

09-04-2019, 03:25 AM   #6
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But they must be able to do a T mount replacement for the eyepiece, right? That's a common standard in scopes.

Then you use this:

Bower T-Mount to Pentax K Mount Adapter ATPK B&H Photo Video
09-04-2019, 04:07 AM - 1 Like   #7
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What's different about your telescope that most of the "standard" telescope adapters won't work? The telescope is using "standard" eyepieces is it not?

If you need something custom try PreciseParts in Miami, FL in the US. They'll make just about any mount you can think of. Be prepared to pay at least $90.00 USD.

PreciseParts Build-An-Adapter

You might be better off having the adapter made for a T-mount in case you end up changing camera systems.

Note: They will even make lens to camera mount adapters Such as K-mount (lens) to M42 (camera).

Last edited by Not a Number; 09-04-2019 at 04:12 AM.
09-04-2019, 08:09 AM   #8
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Thanks all for your suggestions but I really need something custom.


Standard telescope adapters are too narrow (42mm) to get full illumination of the FF sensor. Also the length has to be very precise (half a milimeter accuracy) for good control of aberrations.

PreciseParts is a good idea (I've contacted them) but I would prefer a local solution



Dan

09-04-2019, 08:34 AM   #9
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QuoteOriginally posted by Dan Paris Quote
Thanks all for your suggestions but I really need something custom.


Standard telescope adapters are too narrow (42mm) to get full illumination of the FF sensor. Also the length has to be very precise (half a milimeter accuracy) for good control of aberrations.

PreciseParts is a good idea (I've contacted them) but I would prefer a local solution



Dan
Just did a bit of Googling and found this.
https://williamoptics.com/products/48mm-t-mount-for-pentax-k-red
If 48mm is enough.

09-04-2019, 06:20 PM   #10
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You could always send a K-mount lens to the French company to have the mount scanned. From that they can create a CNC template.

Otherwise maybe consider switching over to Nikon since a suitable solution is readily available. Seems like a lot less trouble if you don't want to go with an overseas company for the adapter.
09-04-2019, 09:45 PM   #11
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QuoteOriginally posted by Dan Paris Quote
Thanks all for your suggestions but I really need something custom.


Standard telescope adapters are too narrow (42mm) to get full illumination of the FF sensor. Also the length has to be very precise (half a milimeter accuracy) for good control of aberrations.

PreciseParts is a good idea (I've contacted them) but I would prefer a local solution
Dan, just to satisfy my curiosity, would you be able to provide a link to the French company's website and the specific Nikon adapter you're looking to have replicated for K-mount? Thanks in advance...
09-05-2019, 09:27 AM   #12
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It might help if we knew what telescope is in question too.

How about a direct 2" adapter? Comes in K-mount:
https://www.telescopeadapters.com/111-2-prime-focus-adapters-for-pentax

First Light Optics (UK) was offering a custom service too:
https://stargazerslounge.com/topic/171145-custom-made-astronomy-adapters-accessories/

https://www.firstlightoptics.com/

Last edited by Not a Number; 09-07-2019 at 07:35 AM.
09-05-2019, 10:09 PM   #13
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QuoteOriginally posted by Dan Paris Quote
Hi,

I need a custom made K-mount adapter to connect my K-1 to my telescope. There's a workshop in France that could do it for me but they only did adapters for Nikon F and Canon EF so far. I need to tell them precisely what to do.



I am aware that F-mounts and K-mounts are very similar, but what are precisely the mechanical differences ?


Throat diameter is the same (44mm) flange distance has a 1mm difference (45.5mm for Pentax vs. 46.5mm for Nikon). I don't know otherwise in which respect the bayonets differ from each other



thanks a lot !

Dan
Get the telescope mount information and send them to someone already making Pentax mount.
It sound easier for a lens adaptor maker to connect to a telescope than for a telescope maker to make a Pentax mount adapter.
The whole story sounds a little bit silly as many standards and adaptors exist. Who tried to invent his own standard.
09-07-2019, 05:12 AM   #14
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QuoteOriginally posted by Dan Paris Quote
Thanks all for your suggestions but I really need something custom.


Standard telescope adapters are too narrow (42mm) to get full illumination of the FF sensor. Also the length has to be very precise (half a milimeter accuracy) for good control of aberrations.

PreciseParts is a good idea (I've contacted them) but I would prefer a local solution



Dan

I have a t mount adaptor for my celestron C90 scope. Much smaller than the 43mm diagonal of the full frame image but there is no vignette game

I like others here is confused about the issue.

But if you insist on an adaptor take a flanged M42 adaptor to the shop to use.
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