#1  
Old 10-02-2017, 12:39 PM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Vixen Polarie Parameters

Hi guys , i've just joined up & wondering if anyone can give me some insight
about the VP set up.
Actually i am more of an amateur photographer than an astronomy guy
however the last few months i have been interested in astrophotos mostly
milky way shots.
My equipment is ( Canon 70D) , (Celestron Mak 90 cheapy) , (Tamron 70-300mm),(Canon 17-85mm),(Sigma 24mm 1.4),(Sigma 10-20mm 4-5.6)
(Samyang 14mm 2.8) , (Samyang 8mm 3.5 fisheye) lenses.
As you've guessed i like my wide angle lenses & i just recently purchased
most of the above for AP.
The first Q i need to ask is about accurate aligning of the VP to the SCP without having to get that expensive Vixen polar scope which i think is a bit of a rip off.I have the optional Polarie polar meter which i find to be precisely accurate so i have read some threads and apparently i need to
be aligned to true South rather than Magnetic South in which in my case
here at Cobram would be 11 degrees east ??? is this true.
Also i have on order an (digital box gauge angle protractor level inclinometer with light) to help with more precise longitudinal aligning.
Hopefully i have all the gear i need........only i need a little more insight from people with more knowledge than i have.............cheers Kev

Reply With Quote
  #2  
Old 10-02-2017, 06:08 PM
CapturingTheNight's Avatar
CapturingTheNight (Greg)
Registered User

CapturingTheNight is offline
 
Join Date: Jul 2011
Location: Holbrook, NSW
Posts: 1,230
Hello Kevin,

Welcome to IIS. The wider the lens you use on the vixen polarie the less accurate you need to be in terms of alignment. So for most of your lenses using the polar meter to line up with true south (Yes you need to offset the magnetic south and yes for Cobram that is 11 degrees East according to the magnetic declination map I looked up) and setting your longitude with your protractor/polar meter, will get you producing great long exposure wide field images of the night sky. If you want to use one of your lenses to zoom in on certain features you may find that your alignment might need a little tweaking depending on your exposure times.
One thing to keep in mind is the weight capacity of the polarie and the stability of your tripod. No amount of accurate alignment will make up for a flimsy tripod or a top heavy camera/lens combo.
From your current lens choices I assume that you are already doing fixed tripod astrophotography? When you start tracking the stars, also keep in mind that any terrestrial elements in your images will blur over the course of the exposure(s) so if you want to include crisp landscape features you will need to blend a static shot in later.
Looking forward to seeing what you come up with.

Kind Regards

Greg
Reply With Quote
  #3  
Old 11-02-2017, 08:25 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Thx Greg for the info.I was supposed to check out the local Photography
club last thursday at Thompsons beach for a night shoot but it was too
damn hot.I think they meet up every second thursday of the month so ill
check em out next time.You can see my first go at APs on Flikr below.
Cheers Mate...k
https://www.flickr.com/photos/146733...h/32369235296/
Reply With Quote
  #4  
Old 11-02-2017, 09:36 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Also Greg i forgot to mention i will mainly be concentrating on Milky Way
exposures without landscapes to start off with.Ive a fairly sturdy tripod
& i shorten the telescopic legs for more stability sometimes i shorten one leg
so the camera gear is well centered.Hopefully i can get a 5 to 8 minute
exposure without star trails.
Also on order i am getting an (anti vibration microphone clip holder mount
hot shoe adapter) to hold a powerful 50mw laser which i have access to
to pinpoint the SCP , i had a terrible time finding a gadget to hold a laser on
a dslr but this was the best i could find to do the job.
Cheers K

Reply With Quote
  #5  
Old 11-02-2017, 02:05 PM
CapturingTheNight's Avatar
CapturingTheNight (Greg)
Registered User

CapturingTheNight is offline
 
Join Date: Jul 2011
Location: Holbrook, NSW
Posts: 1,230
Sounds good Kevin and very nice first star images on your Flickr page. Wodonga might be a bit too far for you but if you want to pick the brains of some keen amateur astronomers/astrophotographers in person, the Astronomical Society of Albury Wodonga might be worth a visit one night (full disclosure- I am currently the Secretary). https://www.asaw.org.au/
Reply With Quote
  #6  
Old 11-02-2017, 04:31 PM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Okay , ill keep it in mind thx
Reply With Quote
  #7  
Old 11-02-2017, 06:11 PM
OzEclipse's Avatar
OzEclipse (Joe Cali)
Registered User

OzEclipse is offline
 
Join Date: Jun 2012
Location: Young Hilltops LGA, Australia
Posts: 1,177
The polarie contains magnets in it's motors. The internal compass is not great. Very hard to read. Use a non magnetic spacer - wood, foam, plastic about 300mm long with an orienteering compass on the far end of the spacer for magnetic setting of the polar axis.

Joe
Reply With Quote
  #8  
Old 12-02-2017, 06:01 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Thanks Joe, i have the optional Vixen hot shoe compass that sits a few inches away from the unit,sometimes the needle seems to wobble around a bit when pointed magnetic south but ill give the spacer a go if i have any issues.......cheers k

Last edited by kevino; 12-02-2017 at 06:14 AM.
Reply With Quote
  #9  
Old 13-02-2017, 08:48 AM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
The vixen hotshoe compass can still react to your camera/lens/tripod so test this i use a separate compass too to do a final comparison before leaving my setup to shoot. Getting the alignment right is critical if you are doing long exposures, but as others pointed out the wider the lens the less the problems manifest plus the vixen itself has accuracy limits (listed in its manual) which are hard (read impossible) to exceed. I use a compact zoom, not dslr on mine for weight at longer focal lengths (short exposures and stacking for my images).

One thing thats easy to overlook is that the polarie turns the camera. Depending on your camera/lense shape and how you mount it on the VP be mindful where the camera position limits are , ie where it will touch the VP body or something else. So on long exposures you might find the rig turns to a position where it makes contact with something, hindering rotation and straining the motors. Or Maybe you can always point your camera to all parts of the sky with ever contacting anything. But it needs to be considered. Likewise any cabling you have going to the camera rig could get twisted and caught on your tripod/VP too so consider that as well.
Reply With Quote
  #10  
Old 13-02-2017, 11:03 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Thanks Sil,I plan on (when conditions are right ) to orientate the camera
in line with the VP at the SCP as close as possible to avoid star trailing.
Correct me if i am wrong but ill start with the 300mm telephoto and over
time tapper down with my lenses to ultra wide using different time
exposures to test the limitations of the VP.
My objective at this stage is to shoot sky only without any landscape to
avoid complications in post processing.
Apparently the outer edges of the photos become more exagerated with
star trails so ill have to find a happy medium to get the crispest clearest
shots possible at all focal lengths of my lenses.
Phew !! what a learning process this is............cheers k
Reply With Quote
  #11  
Old 13-02-2017, 02:52 PM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
Use whatever process you feel makes sense and lets you repeat testing.
I don't know how you do your processing or how you want to work, there are an infinite variety of things you can do and "cheats" to get around some problems. For myself I have a recent physical disability that restricts what I can do and what of my equipment I can use, so I do things differently now to what I used to. 99% of my shooting is DSLR on tripod, 1% compact on polarie mount. So I guess the limitations I have there are things I overcome with processing. Eg I cant use my good tracking mount anymore to get long exposures so I instead take lots of subs to bring out the signal. I also have to use faster exposures to keep round(ish) stars.

All this is to say what I might suggest isn't going to be the only way to proceed and you can always try alternatives for yourself to achieve the same result.

First up zoom lenses are not as sharp as prime lenses and neither are at their best sharpness when wide open at fastest aperture. The optical elements get tested at the factory and need to be within a range of values. Parts with the best optical accuracy tend to end up in the more expensive faster lenses while those that aren't so good end up in the cheaper slower and kit lenses. A single lens will have around a dozen optical elements all with their own slight variations too. So each lens made gets tested too and must perform within a range of values. So no two lenses give the same sharpness and chromatic aberation figures. Even two of the "same" lens.
Because zoom lenses need to perform "acceptably" at all focal lengths the testing tolerances are much wider than for primes hence the generalisation that a prime lens is always better than a zoom but due to overlaps its possible for a particular zoom to outperform comparable primes.

Also apertures can be changed and likewise each lens needs to perform within a tolerance across a range of aperture settings. So a common photographic misconception is a fast prime is pin sharp at its fastest aperture when it won't be. You tend to need to stop down a little for the sweet spot. Then people complain because they bought an expensive lens expecting it would make them an instant famous photographer.

So when testing your lenses expect disappointments and surprises. During the day take shots on tripod at the sky through a neighbourhood leafless tree, fill the frame. This will give you a high contrast test across the whole frame of chromatic aberation performance. Fine dark random branches/twigs against a bright sky shows the colour fringing easily for all cameras/lenses. For astrophotgraphy this CA translates into an ugly colour edge around stars and you can see purplish looking stars in some people photos where CA was the problem. If you're using JPGs it tends to be worse but with raw you might be able to run through a raw converter and process most of it out .

Anyway, with zooms I stick to the extremes of its range, you always have to crop anyway when stacking subs. My main workhorse is a 70-200 f2.8 and its permanently set up at 200mm, fully focused and ready to take outside any time. So I suggest your 70-300 just keep it at 300 and test there. Being your longest lense you'll need to know how to use it for moon and planets , I guess your 17-85 @ 85 will be your most practical workhorse. When I started astrophotography I quickly found there is so much up there our eyes cant see but our cameras can quite easily so you can never have a too long focal length but remember you're trading off exposure time. Every photo I took I could see more interesting things like clusters and nebulosity so I started plate solving a good single and making an annotated reference of what else is in the shot I might like to go after the next night. Getting familiar with the constellations help your get framing good the next night.

During the day do a bunch of f-stop tests photographing street signs or shopfronts or print yourself a sharpness target so you can try to find your optimal aperture for sharpness on each lens at the preferred focal length.


For myself, my DSLR only ever gets used for astrophotography, I have other cameras for regular photography so I keep it set up on tripod with the 70-200 attached, it stays at 200mm and I have it prefocused since I never need to change focus and I'm careful to never touch or bump the lens as I spent several nights just taking test shots for focus and checking frames up close on computer until I was happy. You might be able to do something similar if you have lenses you dont use for regular photography but you find are good for your astrophotography. This also means I have my camera manually set ready to shoot. The goal was to not have to think about anything except dragging my stuff outside. But you may not be able to dedicate gear solely to astrophotography to have permanent settings. So I'd just a notebook you can keep your maximum and good settings in. By maximum and good , I've arrived at two settings for my targets I go after, "good" is where I want nice round stars so detail is sharpest, "maximum" is a slightly longer exposure time where I want to grab as much signal as possible but keep stars as close to round without obvious streaking. I keep ISO at one setting I am happy working with.

As I said at the start I work 99% dslr/tripod but all my above process works great for my compact polarie setup. When you push the weight and focal length recommendations of the polarie you start to get elongated stars. Its time consuming and boring to do lots of testing but it pays off. Then you can look at your processing, for myself I almost never look to get an image in camera, even solar and moon shots I often am looking to use several shots to stack. But its all up to you how and what you want to shoot and make sure you keep all your source files, in a year you will know so much more than now and will be able to make better use of the same shots. I'm in the process or reworking my workflow and looking forward to reprocessing some of my old photo sets.

Above all just enjoy it all and learn from, there are no set rules for anything, you can try different approaches and see how it works for you.
Reply With Quote
  #12  
Old 14-02-2017, 11:25 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Great Advice Sil

Thank you for the detailed help,i didnt realize i needed to stop down for
AP shots so i heeded your advice & took some shots of the moon this
morning and shot at varying F stops & to my surprise got a quite detailed
shot of the moon at F8.In post i cropped the imagewith a bit of sharpening &
contrast and i was rather pleased with the outcome shot at 300m,i also
took some star shots at 300mm and found that even a 5 second exposure
will produce some star trailing but only noticeable when zoomed in on my
pc software ( these shots were taken on a tripod with mirror lock & 10
second delay, without the VP attached).You can see the lunar shot @
https://www.flickr.com/photos/146733...h/32041996234/

Focusing on the stars was a bit tricky and with the Tamron 70-300mm
i found that manually adjusting not to infinity but creeping down to the L
was spot on.The other lenses i will have to experiment with in time.

I will look forward to shooting wide milky way shots without landscape
when conditions are right but i know its going to be a little tricky when
the VP is pointing to the SCP, im just thinking the sigma 24mm (38mm)
on my aps-c will be the best lens for this...............Thx Kev
Reply With Quote
  #13  
Old 15-02-2017, 03:22 PM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
Moon
Kevin, thats a good moon shot. perhaps a tiny bit oversharpened but most people do (including me). Don't ignore the moon during its various phases either, a common mistake is people think the full moon is what they should shoot, but as you can see on your shot the transition region where the moon goes from fully lit to in complete shadow you get the craters leaping out in great detail.


Focusing

This was another point I intended to mention but forgot. Camera lenses have a little bit of slack in their focusing mechanisms. Along with the variations in lens parameter I previously mentioned means they can not guarentee the lens focuses at infinity at its end stop point. Plus the contrast method for autofocusing they leave a little play beyond the infinity point for the lens to be out of focus measurably on either side. The slack in the mechanism means you can focus towards infinity by winding clockwise ONLY and if you notice/mark where the window on the lens indicates infinity. Then repeat by winding from the other direction and the indicator will be in a different position. Hope this makes sense. As a test try winding your focus all the way clockwise then autofocus on the moon, note the indicator location, now wind all the way anti-clockwise and autofocus again and the indicator will be different again.

As a photographer I got into the habit of always winding my lenses focus ring to beyond infinity to the stop point then winding it back slowly to get my focus particularly when I was shooting in tricky positions on tripod where I coulndt use the viewfinder and needed repeating shots at different focal points. I could mark my positions with a marker across the focus ring and the lens body so I could repeat my focus easily. I did the same when I started astrophotography to have a reliable infinity focus. I also use Lens Coats on my lenses which I think are great and you end up with an almost seamless transition across the lens rings making it ideal to use a fine point permanent mark to draw a line across I can use to line up focal reliably. Basically its a time saver if you can find a way to reliably set infinity on your lenses. If you are relying on a live view to set focus be aware there is a tiny delay between when you adjust focus and when the change is seen on the live view. For live view focusing point the camera first some bright stars, these will be easily picked up on the screen. now focus slowly pausing often to watch the screen and as you get the focus correct you'll notice slightly fainter stars "pop" onto the screen or off again as you go past the focus sweet spot. So the more of these fainter stars stay on screen when you stop touching the camera then your pretty good for focus. You can focus on any part of the sky, its all the same, so if possible do it early and leave it set, don't touch the lens again, do it on a sturdy tripod and put it on the polarie only when you're ready to shoot.


Lens creep

This bit me and might not even apply to you, but give it a test. I found that my sigma 150-500mm lens was so heavy, everytime I had it fully "out" at 500mm and pointed up at the sky it would slowly wind itsway back in towards 150mm under its own weight. So test your zooms but focusing at infinity, take a shot pointed straight up at stars and leave it sit on tripod for an hour and reshoot so you are confident its staying in position. My 70-200mm doesnt do this and yours probably won't be heavy enough, my sigma is a beast.


Astronomical Dark

If you are not stacking/processing shots where sky glow is easy to remove and you want a "black" background to your stars then look up when it'll be "astronomical dark" in your location. You'll still get light pollution in long exposures but the blackness of the sky will be at its blackest from that location. If you shoot before astronomical dark the sky in a long exposure can come out a shade of blue or even overexposed white depending how early. If it looks dark outside you're long exposures will tell you if you're right or wrong. Depending on the shot you want you may way to start shooting before full astro dark, its up to you but needs consideration.


Milky Way

You do have Stellarium on your computer or similar right? Use this to see where the milky way lies in the sky at the time you want to shoot. It might be nice and straight up across the sky or it could be wrapped around the horizon, or anywhere in between. So for a shot with interest take note of its position from your shooting location when choosing your composition.


Oh you mentioned slight trailing with 300mm, I think from memory if you check the vixen Polarie manual it's limit is 200mm focal length, anyway the table it had in mine I found to be pretty spot on for maximum exposure times for the focal lengths, just couldn't push it further. Of course I am happy to have less than perfectly round stars in my shots, especially if I put them online where they won't be noticed. Don't forget the Polarie has a half rate mode too for allowing nice milky way with landscape shots where technically everything will be streaked when pixel pepping but overall the whole shot will look sharp enough with good exposure.

Time for me to head home now, enjoy.
Reply With Quote
  #14  
Old 16-02-2017, 07:46 AM
kevino (Kevin)
Registered User

kevino is offline
 
Join Date: Feb 2017
Location: Australia
Posts: 8
Reply

Yes Sil I use Stellarium,my 8mm fisheye arrived yesterday & and i tested it
out ( daytime landscape shots) but obviously the barrel distortion was really
bad around the edges but not so bad in the center area so i cropped the
image with cinema scope (corel) and was quite pleased with the result being
a panned like image so ill try that out with Milky shots.
According to VPs manual 8mm is off the scale (8 minutes with a 15mm) so i
am guessing i might be able to push it out to 10 > 15 minutes.According to some online threads VP's recommended specs are very conservative at the
very least so ill try pushing it a bit.
As for manual focusing i was able adjust star sharpness @3oomm with live
view magnified x 10 but struggle with ultrawide lenses as their just way too small.
What do you think of the time consuming long exposure noise reduction
feature, i plan on using a iso between 400 & 800 for M W shots over
5 minutes.
Ill be trying my celestron mak 90 (1250mm) for my next moon shoot.
I have a backyard test shot on my flickr page i just put up if you want
to check out the detail of the scope on my old 30D.I can see a 8mm hex
nut @ 30 meters..........cheers next time
Reply With Quote
  #15  
Old 16-02-2017, 12:09 PM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,474
long exposure noise reduction

if you are looking to get a single shot in camera I would use a noise reduction tool later as it should be better than what is built into the camera. but do make sure it still takes its long exposure dark frame though, some cameras let you disable it, some dont.

if you intend to align and stack images then disable in camera noise reduction completely, the more subs you take the better the innate noise reduction becomes. you can never eliminate noise without damaging signal. this is pretty much exclusively how I work, i dont care much about exposure in camera except maybe moon.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:56 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement