polarie, 300mm f4 and M31

[alocky]

While I was setting up for the meteors on Monday night I tried out a lens that Nikon Australia lent me. It's the 300mm f4 with the fancy new fresnel lens element. Although this isn't the finest Andromeda pic in existence, there's a few things that are worth noting:
It is a stack of 40 x 60 sec exposures off the polarie - no autoguiding mount, laptop or deep cycle batteries needed. Motorbike portable.
It was wide open at f4 - no visible field curvature or chromatic aberration; stars were good enough all the way to the edge for the tracking to be the limiting factor.

There was plenty of smoke from the Gidgegannup fires and it wasn't very high above the horizon, which is why there are some faint haloes around the brighter stars.
Fortunately for me I don't need this lens, but I believe it's a serious contender for AP. I have cropped the image to about 85% of the original but if anyone wants to see a corner crop I'm happy to put one up to show what this lens can do. No association with Nikon other than they give me stuff to play with now :-).
Higher res here- https://flic.kr/p/Bn3BCN
cheers,
Andrew.

[multiweb]

Wow! Impressive. 300mm would be a fair bit of weight on the old polarie no? :eyepop:

[alocky]

I knew there was something I forgot to mention! The lens weighs only 750g. Less than my 180mm f2.8. It also has VR and all sorts of other goodies you don't need for AP!
I've attached the corners from the uncropped image for the benefit of the pixel peepers amongst us!

[RickS]

That's a fine result, Andrew!

[topheart]

Thanks Andrew.....very amazing really what that lens can do....

Nikon will be pleased with that one!

Cheers,
Tim

[alocky]

Thanks Tim and Rick - they weren't so pleased that they were willing to give it away though :-)
I think one of these, an Astro-trac or similar heavy-duty tracker could keep me busy for a few years. And the portability is particularly attractive.

I'm trying to work out if the dark arcs in the haloes around the bright stars are related to the diffracting lens element.

Cheers,
Andrew.

[gregbradley]

That's impressive work for a Polarie. Your polar alignment must have been spot on.

Amazing really.

Greg.

[Ryderscope]

Isn't it great to see a lens that you can push to the edge like this. Very impressive.

[byronpaul]

Wow, impressive indeed !!!!

What tricks did you use to align your polarie :help:

Paul

[sn1987a]

Lots of expletives wasn't it Andrew?. :P

[DJDD]

impressive.
i must try my polarie out this holiday season.

my favourite part of your post, however, was this:

:D

[alocky]

Thanks Greg - if only the skies had been a bit clearer I think the result would have been even better. I have figured out a pretty neat way of polar aligning the thing.


Thanks Rodney - I'm very impressed with that lens, not the least because it is so light.


Hi Paul,
I've found the polar scope and a geared tripod head are absolutely essential. The polar scope is a swine of a thing to use owing to the non-illuminated reticle. Also, you need to pre-load the polarie on the tripod with the camera gear, or it will move when you put the camera on.
I used to use an old 2" eyepiece extension tube over the Polarie's drive ring so I could hang the camera and lens by its strap while doing the polar alignment - you can't use the polar alignment scope with the normal polarie mount in place. Then I very carefully took it apart, removed the scope, and attached the camera.
I have since built a little rig that replaces the camera mount with an aluminium cylinder, with a counterweight shaft on one side and the camera mounted on the other and a hole in the middle for the scope. This lets me set up, frame the shot, tweak the alignment again, and use an intervalometer to let the camera go by itself.
PM me if you want more detail.



You're thinking of the previous weekend Barry! This particular evening was expletive free.



Ha ha - yes, unfortunately my application for another focal length that was not more than 20% different to one I already own was rejected. So I took advantage of some fortuitous discounts, promotional offers and prizemoney to buy a 135mm Zeiss f2 instead :)

[Rigel003]

Hi Andrew. Missed this thread originally but it's a great M31 and the other Polarie images on your flickr site are terrific too. I've just bought a 2nd hand Astro-trac and refitted it with a Polarie polar finderscope (the original astro-trac one was crap). Reading your setup routine above, you might be interested in this Sky Watcher illuminator I found which fits over the end of the Polarie polar finder and illuminates the reticle. I bought one and it works well. It has really good control at minimum brightness levels so the stars aren't swamped. Quite pricey for a small plastic gizmo but it's worth it if you're using your polarscope regularly.
http://www.ebay.com.au/itm/Skywatcher-polar-illuminator-for-EQ3-2-EQ5-telescope-mounts-with-battery-Boxed-/161513537879?hash=item259af50157:g: UBEAAOSw7ThUhbns

[alocky]

Thanks for that! One is on it's way now...

[cazza132]

Very tight stars with that sort of load on the Polarie! Some nice detail in the dust lanes too.

With the AstroTrac, I don't even bother with the polar scope - tried once without success. Not enough bright stars at the south celestial pole.

Drift alignment has been the only way for me. Takes about 30-45min to get right though, but accurate. Yes, the payload does make a lot of difference though. I normally drift align using a 70-200 f2.8 (heavy lens) + 2xteleconverter and trying to minimize axial moment load, which affects the tracking rate. And, yes, having a heavy load will distort the whole system, so need to allow some small compensation (about 0.5deg) for north/south vertical alignment when a lighter lens is to be used.