Thoughts on which imaging rigs to concentrate on

[RichLD]

Hi Gina, I can see from your signature that you already have lots of camera glass but how about looking for some cheap(ish) s/h medium format lenses, such as the Pentax 67's. They have a healthy 84.95mm register distance and are apparently really good for NB. Apologies in advance if you had already considered this and would rather not swell your lens collection any further 

All the best

Rich

[Gina]

Thanks rich   I did look at this idea a while back but not recently - sounds like quite a good idea for this new rig   I'll look into it.

This one looks a beauty but I'm rather reluctant to buy from the USA.   Maybe I don't need that much quality

I guess I don't really need a medium format lens, as you say I already have a lot of top quality glass.

[SilverAstro]

I have some genuine brass ex plate camera lenses somewhere, I think I ought to get a new cmos thingie and give them a surprise 

Good thinking Rich.

[Gina]

I've been looking further into using the Atik EFW2 plus OAG (FLO model) on the Esprit field flattener and I think I might be able to make it work.  The EFW2 has a rotating camera adapter and I might be able to turn a replacement with a female thread to replace the Atik one with a male thread.  That would enable me to use the 1600 camera straight on the FW saving 11mm.  The OAG is 18mm long leaving me with 7mm to find.  The adapter on the field flattener adds 10mm and I might be able to turn a shorter adapter for the FW. 

OTOH I'm not sure it's worth it - I could just use a guide scope on a dual mounting.  I already have the triple scope rig and could simply use one of the ST80s as guide scope and remove the other.  My lathe isn't really up to optical precision turning.

[RichLD]

13 minutes ago, Gina said:

This one looks a beauty but I'm rather reluctant to buy from the USA. 

Ooooh, that looks lush! Fast enough and a really nice focal length. I love old (or is that vintage?) MF lenses - I had a proper purchase binge on glass about 4 years ago and realised that I had become a hopeless collectaholic. Most of them got used a couple of times then sat in a drawer until I eventually caved in and put them back on fleabay, although I have to say I more or less broke even.

One of my favourites at the moment is an old Tamron 90 macro, lovely piece of engineering and sharp as a tack. 

[Gina]

My last post leads on to another thought.  I could use the triple scope rig mounting plate and put the WF rig where the second ST80 was then I could use the remaining ST80 for guiding.  This idea is fine while I'm using the EQ8.  That would give me medium FOV and wide FOV in one setup.  For smaller DSOs I would remove that rig and replace it with the MN190 scope with OAG.

Edited September 12, 2016 by Gina

[Gina]

I've ordered an OAG from ebay purporting to have an optical length of just 10mm.  This may work with the EFW2 for use with the Esprit.  I still prefer an OAG if possible.  I've also been thinking about the ZWO filter wheel with the possibility of taking the Astrodon filters out of their carriers and mounting them with the M2 screws and washers provided, as unmounted filters.  I think I will be returning the SX EFW+OAG as I don't think I can use it.

Edited September 13, 2016 by Gina

[Gina]

Installed PoleMaster driver and software on my observatory laptop in the hope of some clear sky tonight to check and correct my PA.

[Gina]

After umpteen attempts to install the PoleMaster driver I finally have it working   Now I just want the clouds to go away.  I have the Allen screws loosened ready to adjust the mount PA - the elevation locking wheels are still tight but they are handwheels so I can easily undo or tighten these in the dark.  I shall be interested to see how far my PA is out

The other thing I want to do tonight is RGB on M31 when it's high enough.  Really must try not to do too much or I'll only get confused   It's very warm again so I won't be able to get the imaging camera cool enough for short, high gain subs.

[Gina]

Sky around Polaris cleared for a few minutes and I was able to run PoleMaster for the first run.  The PA looks well out!  Now the clouds are back

 

[Gina]

Cloud beginning to break up.

[Gina]

Clearing now

[Gina]

Hmmm...  waiting...

[Gina]

Clear enough for a run - this shows the misalignment.

[Gina]

Adjusted both axes and onto the fine adjustment.  But I couldn't quite get the red and green circles exactly lined up.  As I got nearer and nearer I got to a point where the green circle started dancing all over the place.  I noticed that this corresponded to Polaris moving out of the green square.  Both axes needed altering to perform this alignment, particularly the Azimuth.  I just hope I've got the PA right and not totally undone the PA I got from AstroTortilla a couple of years ago!!.  I guess an imaging run will tell me!

Edited September 13, 2016 by Gina

[Gina]

I now have the rig pointing towards M31 - except that there's no sign of the galaxy!   Anyway, with zoom at 200 in SharpCap showing individual pixels I can see no star movement in five minutes which is an considerable improvement, so it seems the PA is definitely better   Best cooling temperature I can get is around -20°C so long subs at high gain are not on but I could reduce the gain.  Anyway, I'm doing what I said - M31.  When I find it

Edited September 13, 2016 by Gina

[Gina]

Found the galaxy   BUT the sky isn't very clear and the moon is giving a strong gradient so RGB imaging is not on.  I'll just have a little play with longer exposures and lower gain in Ha 3nm.

[Gina]

No joy with that - the mist has come in so I've packed up for the night.  Quite satisfied though - I've got the PA very much better   Not sure how long I could expose for without getting oval stars - I only went up to 5m and the movement was a pixel or less.  Looks like I won't need guiding with a lens of this FL or shorter.  I plan to do some even wider field covering something like 15° x 20° later on with a 55mm f1.8 lens.

[Demonperformer]

Yes, polemaster is brilliant - and I speak as someone who was faffing around for (literally) years with other ways and never getting anywhere near polar alignment. Can certainly do 5m subs with round stars (on an EQ6!) and was going to try and push it further the other night, but the cloud rolled in. I'm not sure I would recommend it as a mandatory purchase with an EQ mount (because of the price), but if anyone was having the least difficulty getting PA sorted, I would not hesitate to recommend (because it is so easy & accurate).

I have tended to pretty much ignore the final stage (from when you press 'Monitor'). As you say, it tends to dance around a lot, and I have also found that the adjustments can be so small that I can do more damage than good by trying to make them (also I get confused with translating up/down on the screen with which bolt to tighten/loosen on the mount, so am likely to go the wrong way anyway!).

[RichLD]

Nice one Gina - I love my Polemaster. It's the best bit of add on kit I've ever bought, well worth the money if only for saving my poor knees! 

Pity about the clouds and mist though - I'm sure they'll be plenty of clear nights coming up. Oh dear, I hope I haven't jinxed the weather by saying that...

Rich

[RichLD]

9 hours ago, Gina said:

As I got nearer and nearer I got to a point where the green circle started dancing all over the place.

Forgot to mention that I find that the "dancing circles" phenomenon is a good gauge of the seeing. If there significant atmospheric turbulence it can become nearly impossible to get the blighters lined up.

[Gina]

Thank you DP and Rich    When I used AstroTortilla I found results were not repeatable and it drove me up the wall!   What with repeated iterations of plate solving on a view to the east and then to the south, with adjusting the mount in between, and not really getting anywhere anyway, I just gave up having lost hours of clear sky I could have used for imaging!!   PoleMaster has saved my sanity and well worth the money

[Gina]

I've now realised why the DSOs were not appearing in the middle of the view when slewing to target from CdC - I think I must have moved the azimuth a couple of degrees or so when I adjusted the PA last night.  That means the Homed mount is no longer pointing due north after the azimuth adjustment so it's no longer star aligned.  AstroTortilla left me with an enormous PA error!   It's a wonder I could do much good imaging even with guiding!  I think the first thing to do tonight is to adjust the mount Home position to bring Polaris to the centre of the FOV.

And no!  I'm not using AstroTortilla to plate solve - I'm so disgusted, I've dumped it - I no longer have any confidence in it!   Maybe the new version has solved the problems but my confidence in it has been destroyed, and that's that I'm afraid.  I'll see how I feel when I go back to longer FL with telescopes but I hope to be using Linux by then.  I believe INDI or KStars or PixInsight or ekos or whatever has plate solving anyway.

[Gina]

The so-called 10mm optical length OAG has arrived but it isn't!   It's 19mm and exactly the same as the one FLO sell and the one I've got.  I did come with a whole heap of adapters and extension tubes of various lengths though which may be useful.  Don't think I can be bothered to send it back - it was half the price of the FLO one so I might be able to sell it at a profit

[Demonperformer]

Don't know if this would be of any use. I have one and the main body is genuinely 9mm. The threads on either side make the total 13, but the extra 4, of course, doubles up on whatever you attach to it. The catch is that, if you still need a filter wheel, that is likely to take you over the distance you have available!

There's nothing for it ... you are just going to have to design a combined FW/OAG that meets your exacting standards and get the 3D printer on the job. The only 'optical' bit (I think) would be the OAG prism - and as you have just bought an extra one that could be cannibalised ...