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PST Modders out there...a quick question..


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Hi all

I (finally) got some (quality?) time with my recently modded PST on Saturday - well, 2 hours in the dome but only about 20mins actually observing thanks to the big fluffy things in the sky!

Here's a pic, btw:

Its an Evostar90 with an AE supplied ERF&cell with a GSO(like) 2" crayford focuser holding the business end of a PST, at the appropriate point in the light cone. I'm (atm) using a MS LifecamHD, modded to fit into an EP draw tube as the imaging device.

I think the best I can say, so far, is that this setup has a load of potential. In the gaps between the clouds I managed to find 2 good looking prominances, as well as some surface detail on the Sun's disk. Twisting the PST tuning ring had an obvious and dramatic effect. Unfortunately, I had a lot of trouble focusing the system.

TBH, the seeing was lousey, which didn't help. Also, I found that adjusting the LifecamHD's brightness seemed to affect the 'apparent' focuas on screen. I found that adjusting the PST focusser way off, I got an obviously blurry image. As I homed in on focus, the image improved to a certain extent, before blurring again on the other side of focus.

I guess these are the variables in question:

  1. My limited experience of using the system.. need more practice!
  2. The etalon may not be perfectly at 200mm in from prime focus (I can understand how this could affect image quality, but not the focus).
  3. The seeing...not much I can do about this.. fingers X'd for a clear/steady sky this coming weekend.
  4. The imager...though it seems to behave well enough at night.
  5. Something else...?

I think #1 is the prime candidate. I just though I'd post and ask, in case there were something else I'd missed.



>>Edit: D'oh...I wrote this yesterday, and was slightly surprised that the thread never cropped up in the latest posts search... then I noticed I'd never actually posted it!...too many browser windows open...:D...the form seemes to have forgotten about the image in the intervening time...I won't post an image of the sun, becuase the only one I have look like strawberry blancmange pink and squidgey...<<


Edited by pauldaviesuk
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The image would help!

The focuser on the PST black box is not the easiest to use - try to fit a larger wooden/ plastic disk over the knob to give finer adjustement.

The AE ERF cell I believe has a built in tilt so ghosting should be minimised. If the original PST (etalon) gave good images, then you will get the same after the mod. The spacing of the etalon will affect the sweet spot etc.

No experience with the Lifecam, so can't help there...

More practise I think.


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TBK, Ken, I think you are exactly correct.. more practice!. I just wanted to be sure that was it, and not that I was missing something.. I get little enough Sun-time as it is, I don't want to waste to barking up the wrong tree...

I'm sure there are good images in there to be had - I got a couple of good promenances on Saturday, and some fairly significant 'motteling' on the Sun's surface, which I'm hoping will translate in to some good featrures, so I think the Etalon is doing its job. the problem is that I can't seem to get it to focus. Even if the Etalon were faulty, I'd still expect the Sun to show up as a crisp, if fearureless disk. I'm just getting a fizzy disk.


Edited by pauldaviesuk
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Paul - have you imaged with just the PST/ MS LifecamHD setup (before you modded it) ?

The reason I ask is that because I had to remove the extention adapter of the EP BF to get my DMK to come to focus because the prism didn't provide enough in-focus ?!


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