How bring ASI174MM in focus with PST solar telescope

[Jordan Konisky]

My query relates to focusing my PST40 while using it with a ZWO ASI174mm video camera. To bring the system into focus I use a 2X Barlow lens (bottom only) screwed on to the nose of the camera. As discussed elsewhere in this forum, this solves the problem of bringing this camera into focus with the PST 40. While this works ok, I have found that to bring the solar edge into sharpest focus, requires that I rotate the focusing knob clockwise as far as it will go, that is, until it is tightened down all the way. I would prefer that the position of the knob at edge-focus would provide me flexibility on both the counterclockwise and clockwise sides of the focus point. The ability to move across the focus in both directions would give more confidence in establishing the best focus. Any suggestions on how I might further adapt my setup to address this issue would be greatly appreciated.

[marktownley]

Hi Jordan,

Get a shorter nosepiece for the camera.

Mark

[PDB]

Mark,

suppose you mean ZWO's low profile nosepiece. That is prohlematic on an ASI174. (seems then you need to remove the protective window)
ZWO says: "PS: this new cover can not hold the protect window of ASI174MM/MC, so you need an external 1.25″ filter"

Paul

[Rusted]

The filter problem with the ASI174 is discussed on the ASI website related to the low profile cover. "Adapter" would seem a better term.

https://astronomy-imaging-camera.com/pr ... file-cover

[PDB]

Yes, that is the one but as you can see on this image the protective window is in the back parts that you need to unscrew to place the part. (other cams have that over the sensor) So you need an extra filter at least for dust protection.

Capture.JPG (27.04 KiB) Viewed 1884 times

Paul

[marktownley]

Change the distance between the Barlow nosepiece and the camera, maybe put in 10 mm extension, should shift the focal position far enough to get away from the end stop of the thread. At the end stop the penta prism will be pushed off square which is why one edge of the disk is out of focus with respect to the other.