What's the singular of Pleiades?

[squeaky]

Using a 2x Barlow as I do at the moment to get a focus my 20 arc min FOV is way too tight to get them all.

A practice run last night - I managed to get 72 off subs at 30 secs on my dob and DSS stacked 48 of them. Amazing! Well, for me it's amazing - I was expecting it to stack less than half that many, Esp since I was looking fairly low through haze, not far from the Moon and over the top of a large town.

The upper brightest star is Taygeta and the lower one is Maia, with the faintest stars I'm sure of at about mag 15.2

Not much evidence of the nebulosity though.

Given that I can keep half (or better) of my subs at 30 secs and the 2x Barlow I'm going to have to get to work on getting a straightforward Prime Focus. Once I do, that should allow me to get 1 minute subs and keep half or more of them - and that "might" be worth a lot in terms of capturing nebulosity. Plus I'm running pretty much everything (camera, DSS etc) on defaults, more or less, so there's probably some fine tuning available as well.

[farunj]

That's awesome!!

[squeaky]

Hmm... thanks

The "awesome" bit, for me was getting usable 30 second subs on my dob - especially since the FOV is equivalent to using a 10mm EP (at approx x150) so as you can imagine - tracking has to be pretty fair, and rotation is a pain given that each 30 sec sub is actually taken about a minute and a half apart - so every ten subs I'd have to rotate the camera and tweak the framing to cover rotation and drift.

Also "awesome" was DSS stacking 2/3rds of them. Twice as many as the best I'd done to date!

The camera is set to take a "bias" after each sub, and I had long exposure noise reduction on which appears to be taking a dark after every sub before it then builds the output image.

What I don't know, YET... is how much nebulosity I'm losing to the noise reduction. Pretty much that entire field should be showing blue nebula. I'm going to have to do a trial with the noise reduction off next time I get a chance.

[Bizibilder]

If you turn the noise reduction off you double your imaging time!! Take twice as many subs and then take some darks (just put the lens cap on the camera) for the same exposure and temperature (+- 5°C will do) and save them for future use. There is no need to trake bias either as (if you use DSS) this data is not required - as it is already included in your darks (I think!).

If your object is more or less due south then rotation will be at a minimum for your Dob - you should find DSS will cope without you having to rotate the camera between frames.

[ollypenrice]

Well, the two you have are nice and round and nice and blue so that's a good sign!!!

Olly

[squeaky]

If you turn the noise reduction off you double your imaging time!! Take twice as many subs and then take some darks (just put the lens cap on the camera) for the same exposure and temperature (+- 5°C will do) and save them for future use. There is no need to trake bias either as (if you use DSS) this data is not required - as it is already included in your darks (I think!).

If your object is more or less due south then rotation will be at a minimum for your Dob - you should find DSS will cope without you having to rotate the camera between frames.

Aye! This is why my next trial will be with noise reduction within the camera switched off. I put it on this time because I'd been having so many problems with DSS and the Canon 550D's different version of CR2's. Having done a complete clear out of DSS and re-installed, plus pretty much going back to defaults on DSS and the camera and now getting "fair" results - it's clearly time to start trialling other options.

[squeaky]

Well, the two you have are nice and round and nice and blue so that's a good sign!!!

Olly

Wow! Damned by faint praise from the master himself

But true enough, mostly round stars with some blue colour... so I've got a decent starting point

Clearly lots to do yet before I get an image good enough for my scrap book

More to do on the scope and mount now too. I've got a light shroud and dew shield, plus a magnetic knife strip for balance weights - so I need to re-do the balance and clutch friction in ALT.

What I'm finding, now that my clutch friction is set in both axes to be just a bit more than the minimum necessary, is that I can minimise drift in ALT by shifting the balance weights, and I can, up to a point, reduce oval stars (but not overall drift) by deliberately adding a very small backlash adjustment. For this target I got my best result from 25 arc secs. I'm actually dead chuffed to get 30 sec subs at Prime Focus times two on a dob.

[squeaky]

Playtime. Stretched and curved to within an inch of its life I got some nebulosity - but at the expense of murdering the bright stars. One day I'll work out how to do it without killing them.

The only answer is going to be better data and lots more of it.

[squeaky]

Well.... all I can say is...

Woo Hoo !!!!

Having finally got achieving Prime Focus sorted (more on that below) I found that I didn't need to hit the ISO anything like as much as when using the 2x Barlow, and dealing with drift and rotation is far easier. So for the first time EVER (for me) instead of stacking a mere eight or nine minutes' worth of subs out of three hours work - here's a stack of 65 mins' worth out of only two hours work...

While it's still not good enough for my scrap album - I didn't cull the rubbish before handing to DSS (too eager to have a first look) - and I discovered at the end of shooting that I hadn't tightened the T2 adaptor and EP holder together enough so that when rotating the camera to keep the framing I was unscrewing it... and I need to do a bit more experimentation in adjusting for drift with balance weights (yes, even on on Dob ) and deliberate use of small amounts of backlash, and I forgot to collimate (muppet)... but I am so-o-o-o chuffed with this first real run and a quick look

BTW - the original image in the OP fits the top left corner of this one.

Prime Focus

=========

It was suggested in another thread a month or two ago that I try moving my trusses down a bit to get the secondary closer to the primary. And it worked. I've made a set of clip on collets (at 21mm length) out of some 25mm plastic conduit with a quarter of the arc cut out - so they sort of spring clip over the truss rod. They're a few thou out at the moment so I either need to put in some very fine work by hand or, better still, see if I can borrow a bit of lathe time somewhere and just part a set (or two) off.

So, after almost six months I'm finally approaching getting images that might be worth keeping

[acey]

Pleiad.