How to use my Pentax K lenses

[sophiecentaur]

I just got my new ASI120 CMOS colour camera, basically for guiding and also for a start on planetary imaging. Now I have it (complete with a fisheye lens, thrown into the deal) It struck me that it could be interesting to use my existing Pentax camera lenses with it (as well as my 500mm ED80 OTA and guide scope). I have spent some time searching but all I seem to find is ways of connecting other lenses to my Pentax DSLR. That's the wrong way round.

You will all appreciate the possible fear of buying an adapter which works mechanically but has the wrong depth for focussing. The ASI120 has a2" spigot, an internal M42 thread and a M42 / 1.25" T adaptor.  I have written to the manufacturers of the camera but I have doubts whether they can actually help me. Has anyone else had a similar problem and solved it without buying stuff that they didn't actually need?

I'd really appreciate some pointers.

[Phil Fargaze]

Have you had a look at the camera adaptors from Modern Astronomy? see here. I wouldn`t know about the focusing though. You could ask Bernard at Modern Astronomy any questions, he is very helpful.

[Davey-T]

A lot of folk including me use the SMC Takumar M42 thread Pentax lenses with adapters, don't see why there shouldn't be adapters for "K" lenses but who knows.

The back focus on the M42 lenses can be adjusted don't know about the "K" lenses, maybe a bit of Googling will find something.

Dave

[Phil Fargaze]

Your original question made me realise I could try this out. I have a ASI120MC camera and a Pentax K adaptor plus Pentax K lenses. I put it together with the parts in the picture and got focus inside the room as well as on clouds, so I guess it is a viable option. That is, as long as this is what you are wanting to achieve. 

[sophiecentaur]

On 29/12/2017 at 13:19, Phil Fargaze said:

Your original question made me realise I could try this out. I have a ASI120MC camera and a Pentax K adaptor plus Pentax K lenses. I put it together with the parts in the picture and got focus inside the room as well as on clouds, so I guess it is a viable option. That is, as long as this is what you are wanting to achieve. 

Hi.

That looks to be just what I need. Have you a reference / model type so that I can try to source that adapter?

BTY I am a HAS member too. Perhaps we could what's app about this.

Andrew Lyner

[Phil Fargaze]

Hi Andrew! I could show you at the next meeting if you are going or wassap of course. The adaptor was from Modern Astronomy See here. I originally intended to use the Pentax lens with my low light video camera and I did give it a try and got some images if I remember correctly. I’ll have a look at finding the images soon when I get a chance. 

[sophiecentaur]

Philip. I looked around on Modern Astronomy but couldn't  find that but it seems to be what I need. The adapter in the picture seems to have a reasonable depth to it, which is certainly necessary because, focussing on the sensor must holding a pk lens in my hand seems to need the back face of the pk lens to be well above the face off the cmos camera. Not surprising as the pk lenses have to work with the SLR mirror between. 

I now realise my problem. I never bumped into the information that the camera has, in fact, a C mount thread. I was assuming that I would be using the 42mm thread on the actual body of the camera. That's the problem when trying to get into a new subject - so many names and numbers and not too much info to help the beginner. That's where HAS and AGL come in so handy.

Anyway, I plan to be at the next HAS meeting so we can chat about it then. There is no rush as I have a lot of things to try before that and not many suitable nights for doing it.

[Phil Fargaze]

Have you tried clicking on the words `see here` in my above post. That should take you direct to the part on the Modern Astronomy web page. Otherwise do a google search with the words "pentax k mount adapter modern astronomy" and that should get you there. I was in exactly he same situation as yourself, I was not familiar with c mounts,  t mounts and 42mm etc but I did a bit of looking about and question asking to arrive at what I have got now. I can bring the bits in then to the next meeting and show you how it all fits together.