PST80 - AR1072 23rd May 2010

[pauldaviesuk]

Nick,

I've checked the inards of the PST, and it all looks OK. The top prism is perpendicular with the optical axis of the EP tube, but I did notice that at one extremity of its travel, the prism touched the top of the housing, skewing its alignment somewhat. I have a feeling that may be a big part of the problem.

I'll certainly take you up on your offer to have a look at my AE ERF, but I'd like to try to eliminate possible issues in the PST/scope first.. so let me do a little more experimenation first.

BTW, Nick, could you post a raw single frame from one of your captured movies to give me an idea of the level of image clarity I can expect to see on screen?

cheers

Paul

[NickH]

Paul, will do...remind me via PM tomorrow, and I will screen cap a frame from one of this weekend's runs...my hdd is in the office with avistack running a batch process

[pauldaviesuk]

Just come in from the obs. The OTA seems fine. I got some reasonable views of the moon, given the woeful seeing, as well as some pinpoint star images from Arcturus and Vega.

Interesting development, though. I was imaging at the weekend with my newly modded MS LifecamHD, which I started to use this evening. TBH the images of the moon were certainly better than the views of the Sun on the 23rd, but never the less, were rather disapointing, even given the poor seeing. However I switched to my Opticstar PL-130M (which I ditched indisgust as an autoguider earlier in the year) and got visibly better quality images - finer detail on the moon and smaller star images, too. The only drawback is that it doesn't seem to have as great a dynamic range as the LifecamHD.

cheers

Paul

[NickH]

Well that's one but of good news. For solar you really do need a mono camera, ICX098BL chipset ideally (or better) but the 098BL (DMK21 and mono modde3d webcams) has a good spectral response near to the 656nm area for H-A, and as that's monochromatic anyway...you get all the data

[NickH]

Paul, individual frame as promised. Out of the 1178 on this run this was a good average of the seeing/quality live view. A few people including Ken (Merlin66) have commented that I have a particularly good PST setup (took 4 attempts in the early days mind you).

[Merlin66]

I've been a bit busy assembling ( successfully!) the prototype Spectra-L200.....

Paul, if the penta-prism is properly aligned, when it travels towards the top inside surface of the black box it should be parallel to the surface. ( on some PST it can actually touch, which has be beneficial effect of squaring the prism:))

I'd put a plastic cap over the PST focusing knob ( Vegemite lid works well:D) this give that "extra fine" control.

The PST etalon is 20mm aperture for 200mm inside a f10 beam. The solar image at the etalon varies with the focal length of the scope, but in the original PST the size is 24mm - just larger than the etalon..this contributes towards the sweet spot. ( BTW when stopped down to 35mm the PST etalon is almost perfectly sized!)

It doesn't matter what the aperture is on a mod - just make sure you have a good ERF and IMHO watch the f ratio.

I've started a write-up on the Stage 1 and Stage 2 mods and will illustrate it with a conversion based on a "donor" 80mm f10, Baader ERF and a BF10.

Anyone who wants a copy of the "draft" as it currently stands just drop me a PM. ( Comments/ questions welcome).

I can also vouch for the quality of Nick's etalon - he's got a very good example!

Ken

[pauldaviesuk]

Thanks, Nick I'll use that as a 'standard candle' against which to compare my results

I've been thinking about a DMK21.. but getting my 350D modded is ahead of it in the queue

cheers

Paul