Focus issue: ASI174MM PST pairing: redux
Posted: Thu Dec 03, 2020 1:48 am
I have previously sought advice from members of Solar Chat on how best to bring my ASI174MM into focus with my PST40, a well-known and much discussed issue with this pairing. The consensus solution was to adapt the out-of-the-box camera with a low-profile nose piece and to add the bottom component of a 2X Barlow. To make everything fit, one must first remove the camera’s IR protective filter. Apparently, this solution works for many folks. No problem and that is what I did.
I thought all was going well, and my images (SharpCap, Autostakkert, Registax wavelets or ImPPG) seemed ok, although not great. Seemed not quite in focus, but I had never imaged the sun before. I attributed the lack of quality to a difficulty in focusing on a naked sun. The test came this past week when I tried to image sunspots 2785 and 2786. As I cranked the focusing knob clockwise the focus improved, yet never reached a crisp focus as the knob reached tightness at the end of its run. The sunspots were smudgy looking, out of focus. I tried the bottom component of both a GSO and Cemax 2X, but neither brought me to focus.
At that point, I brought out my ASI224MC, which out-of-the box with no modifications performed beautifully in easily reaching a crisp focus and a nice image. Interestingly enough, not at the clockwise end of the focusing knob, but rather closer to the counterclockwise end. So clearly the issue is with the ASI174MM.
Could it be that some Barlow will work, but not others? If a particular Barlow works for any of you using a PST AI174MM pair, I would appreciate knowing the exact Barlow make and model that you are using. Any other suggestions are most welcome.
I had the problem solved months ago by using the ZWO low profile nose in combination with the bottom component of a 2X Barlow, a solution that apparently works for many folks here
I thought all was going well, and my images (SharpCap, Autostakkert, Registax wavelets or ImPPG) seemed ok, although not great. Seemed not quite in focus, but I had never imaged the sun before. I attributed the lack of quality to a difficulty in focusing on a naked sun. The test came this past week when I tried to image sunspots 2785 and 2786. As I cranked the focusing knob clockwise the focus improved, yet never reached a crisp focus as the knob reached tightness at the end of its run. The sunspots were smudgy looking, out of focus. I tried the bottom component of both a GSO and Cemax 2X, but neither brought me to focus.
At that point, I brought out my ASI224MC, which out-of-the box with no modifications performed beautifully in easily reaching a crisp focus and a nice image. Interestingly enough, not at the clockwise end of the focusing knob, but rather closer to the counterclockwise end. So clearly the issue is with the ASI174MM.
Could it be that some Barlow will work, but not others? If a particular Barlow works for any of you using a PST AI174MM pair, I would appreciate knowing the exact Barlow make and model that you are using. Any other suggestions are most welcome.
I had the problem solved months ago by using the ZWO low profile nose in combination with the bottom component of a 2X Barlow, a solution that apparently works for many folks here