200PDS secondary central or offset?

[philhilo]

I have stripped, cleaned, flocked, masked the primary mirror clips, and put a new focuser on my SW 200PDS. Now I need to collimate (something I seemed to get away with before using a basic laser collimator), and the 1st step is ensuring I have the secondary in the right place - but where is the right place, central or offset? Astrobabys great instructions say consult the manufacturers instructions - there are instructions for the 200P - central, the Quattro - offset, but not the 200PDS which lies between the two in terms of aperture and focal length (Quattro fl 800 F4, PDS fl 900 f4.5, P fl 1000 F5). Any 200PDS users done a collimation from scratch?

[johninderby]

The secondary mirror is already mounted offset on the secondary holder so just center the secondary holder.

Edited November 10, 2020 by johninderby

[fozzybear]

55 minutes ago, philhilo said:

new focuser on my SW 200PDS

Is this in the same place? of care to share what focuser you now have?

[philhilo]

I have put on a Moonlite designed for 200mm Newts, seemed the way to go to reduce the diffraction spikes and better at holding my shiny new  mono cam and efw ... allegedly.

Edited November 10, 2020 by philhilo

[fozzybear]

so as per @johninderby quoted if nothing has changed then.

[philhilo]

But alas as part of the flocking process I had to remove the secondary, spider and all, unscrewing the tensioning bolts that position the mirror. Now when I come to put it back I need to figure out if it was central or offset, assuming this was originally achieved by adjusting the spider? What I should have done was measure the position of the secondary before I removed it, emphasis on should have done!

[Pixies]

It will be central. The mirror is offset in the holder.

As per the AB Guide, tighten the vane bolts so that the central secondary adjusting screw is dead centre.

[johninderby]

The seconday mirror is glued onto the holder off center so unless you removed the mirror from the holder no problem.

[Erling G-P]

The 200 PDS is 1000mm / F5, unless you use SW's 0.9 Coma Corrector (or a similar reducer), with which it technically becomes 900mm / F4.5, but would that affect how you collimate it ?

[philhilo]

Got it, the mirror is offset in the holder! Yes I left the mirror on the holder deliberately as I could clean it with it still attached (and more safely suspended in washing solution)  and it was one less variable to deal with later.

Thank you folks, hopefully ABs guide will get me through. Cheers.

[philhilo]

7 minutes ago, Erling G-P said:

The 200 PDS is 1000mm / F5, unless you use SW's 0.9 Coma Corrector (or a similar reducer), with which it technically becomes 900mm / F4.5, but would that affect how you collimate it ?

The 200PDS has the tube slightly shortened for astro imaging to bring the focal point further out (I think) - one of the drawbacks with the 200P where the focuser can't rack in far enough for prime focus. They didn't bother to change the stickers on the side of the OTA. Astrophotography tool gives me a calculated fl of 911.8mm from plate solving  images as I remember.

[Erling G-P]

Just now, philhilo said:

The 200PDS has the tube slightly shortened for astro imaging to bring the focal point further out (I think) - one of the drawbacks with the 200P where the focuser can't rack in far enough for prime focus. They didn't bother to change the stickers on the side of the OTA. Astrophotography tool gives me a calculated fl of 911.8mm from plate solving  images as I remember.

That's new to me - I just went with the sticker on mine.  That would seem to indicate that with the 0.9 CC, it then becomes 820mm and F4.1 ?

[philhilo]

Should be. I am using a generic coma corrector that doesn't act as a reducer, I figured it was fast enough and I wanted fl for galaxy imaging.

Erling, I was most impressed by your image of M33, especially with your 200PDS/HEQ5 Pro/DSLR set up, the same as me.  I thought Denmark was the land of eternal cloud, but I guess you at least have low light pollution unless you are in Copenhagen? Have you done any upgrades to your set up apart from the rowan belt mod?

I still think the 200PDS is under rated, and it's a huge step up in price to get the same fl in a refractor or SCT, which is why I am trying to hypertune mine (also need all the help I can get in bortle 8), however I have finally gone for a mono astro cam as I was sick of trying to remove epic noise, just hoping it is the right decision going mono rather than OSC. 

Here is my 5 hour Whirlpool which I think is OK for the budget OTA 200PDS and a DSLR (just need to get processing nailed).

M101final5hr.tiff

[Erling G-P]

Thanks Phil regarding M33.  Only other modification so far apart from the belt mod, is fitting a saddle from ADM, which provides a better grip on the dovetail.  I have flocking material at hand, but not yet gotten round to fitting it, so would be most interested in hearing about any percieved improvements once you get to try yours out.

We do have a lot of cloud here - I think our weather is about as bad as what you get in the UK.  Conditions for the M33 image weren't very good; lots of humidity, so would like to have another go at it some time.  I'm about 50km north of Copenhagen, in a small village. My sky is reasonably dark at Bortle 4.  My DSLR is cooled btw, which helps with the noise.

A nice M101, with lots of Ha visible.  Going mono should provide you with the most flexibility for sure. Personally I don't feel quite ready to tackle the added complexity of it just yet, but hope you'll have success with yours.

Maybe we should start a thread about 'Imaging with the (underrated) 200PDS'

Edited November 11, 2020 by Erling G-P