Another night of imaging lost as I didn't Polar align early enough

[swag72]

Thanks for all of this so far guys. I have now got the scope running, so I'll see how tonight goes. Not sure why I was doing something so very different, and yet still getting alignment etc. I have learnt something new tonight - Cheers

[shaunster]

No, you need to polar align using the polar scope in the mount and not the imaging scope itself

You cannot achieve good enough polar alignment for long exposure imaging by just using the polar alignment scope.

Sorry Rob but Sara was asking a different question other than how to get long exposures. The question was how to polar align using the polar scope with the telescope already mounted...

I have found from experience the program polar finder good enough for 15 minutes at short focal lengths and I do not consider a drift alignment procedure practical on the short summer nights..

[MartinB]

It is a sweeping statement because it's correct. For long exposure imaging you need much more accurate alignment than can be achieved with a polar scope alone.

Rob.

Unless you have a Tak mount, you can then kiss goodbye to drift alignment. 2 minutes done, 30mis at 2000mm f/l with no field rotation. The vixen polar scopes are pretty accurate as well.

Sara, it sounds like you are mixing up polar and goto alignment. The goto alignment you do by using your finder scope is a seperate process to polar alignment. Polar alignment ensures your mount is correctly orientated so that stars stay in position as the mount tracks. Goto alignment enables the mount to find things. 2 entirely different processes.

[swag72]

Sorry guys, but I have sounded a complete numpty. The system I have used and been told about has worked for me for 8 months. Now I have to learn something different!!

I guess I have been confusing and I have managed very successfully to confuse myself and others too. So, here's to hoping that this is now sorted and I can continue without too many hiccups!

My difficulty in understanding is due to the fact that my mount stays put and doesn't move. So I was struggling to understand a couple of the steps as when I move my reticule Polaris is already set up and ready to go. So I guess I can just start from the home position - unless I move the mount.

[RobH]

Sorry Rob but Sara was asking a different question other than how to get long exposures. The question was how to polar align using the polar scope with the telescope already mounted...

I have found from experience the program polar finder good enough for 15 minutes at short focal lengths and I do not consider a drift alignment procedure practical on the short summer nights..

Apologies....I misunderstood

Martin....I have an HEQ5 and have no problem drift aligning it.

Glider....I've looked at some of your fine work....surely you don't get that level of accuracy simply by using the polarscope?

Cheers

Rob

[Beyond_Vision]

Rob I have never drift aligned my mount and it's on a permanent pier. Admitedly it's only using less than 620mm focal length. I have also had no problems with upto 15 minutes subs. Obviously for longer focal length or long narrowband exposure you would need to drift align

[carastro]

I never drift align either and do LX imaging. Polar alignment seems to work fine for me.

Carole

[RobH]

Well, as a whole bunch of you are doing LX imaging without drift aligning, I guess that's the proof of the pudding!!

BTW....I've never said that you can't do LX imaging without drift aligning, only that using the polar scope alone isn't up to it.

I've drift aligned all of the mounts that I've had, but as I tend to do medium to long FL imaging, it is neccesary, and simple polar alignment isn't good enough. I've refined my alignment over time, and the closer I've got to perfect alignment, the better the tracking accuracy and the fewer the guide commands issued. While it's not so crucial to have few guide commands issued in RA as I have my mount slightly east heavy to keep the gears meshed in the westerly direction, in DEC it's very important, as it's easy to run into backlash issues. Consequently, I'm a great believer in getting as good a polar alignment as possible, and not relying on the autoguiding system to compensaste for any innacuracies.

Cheers

Rob

[Zakalwe]

I'm a noob too, and have never drift aligned. My EQ6 is tripod mounted. I normally set it up with the scopes attached (1 x ED80, 1 80mm Equinox), get it balanced, then used EQMod to polar align. Yes, it's a bit awkward peering through the polarscope, but I'm a clumsy sort. If I PA without the scopes on, and then try to mount the kit, 9 times out of 10 I will knock the mount/tripod and put the alignment out.

Drift alignment is not essential for all long-exposure images, at least not at the focal lengths I use. Here's a 4 minute sub straight out of the camera.....looks good enough for my noob eyes. Yes, I have used a guidecam, but I can't see any evidence of field rotation, which I would expect to be thee is my PA was out?

[RobH]

No evidence of field rotation there, although you do have a little trailing, which is more likely to be from differential flexure than anything else.

To see field rotation on a 4 minute sub, you would need a polar alignment that is quite a long way out.

Nice very wide field BTW.

Cheers

Rob

[chrisshillito]

It is a sweeping statement because it's correct. For long exposure imaging you need much more accurate alignment than can be achieved with a polar scope alone.

Rob.

Sorry, it is a sweeping statement. Polar misalignment can certainly affect the quality of the image but by how much will depend on your target's position the sky, the focal length you're using, the pixel size of your sensor, the location of your guide star with respect to the target and the length of your exposure (when is an exposure considered long?)

Consider these factors carefully and you may just find that polar scope alignment is adequate for some objects and setups. Clearly doing drift alignment will guarantee the best possible results but that doesn't mean to say that folks cannot derive personal satisfaction from images taken without it (many do).

Chris.

[jgs001]

Rob, this was using 1370mm, 10 minute exposures, polar aligned only with the polar scope...

http://stargazerslounge.com/imaging-deep-sky/133998-m51-rc-repro.html

There are issues, focus, collimation and some sag as the camera fitting wasn't quite tight enough, but I didn't see any evidence of field rotation.

Sara, I use

1) Polar scope to align (if just my refractor pair, I leave them on) I used Astro_baby's tutorial to setup the polar scope in the first place, so just need to set the date and time on the setting circles.

2) Fit camera/RC etc...

3) set to home position (ish)

4) slew to a star near to target, use CdC and EQMod, sync the star, focus scopes etc

5) Use goto to target, and shoot test exposure, and adjust position if needed

6) setup PHD running, maybe adjust position of guidescope a little

And I'm off and running...

[chrisshillito]

Yes, it's a bit awkward peering through the polarscope, but I'm a clumsy sort.

To make things easier I slip a star diagonal with the barrel removed (so you can get your eye close to the mirror) over polar scope. I can then see enough of the reticule from a sitting position. The only trick is to remember the mirroring effect when setting the EQMOD polar scope start position!

Chris.

[malc-c]

Or use a web cam to see through the scope

[rfdesigner]

another vote for drift aligning here.. but that is because I learnt to take pics in the days of film and hand guiding.. 1 hour subs and an aching back.

One advantage of drift aligning is that it can be used on any mount what so ever, I used it successfully on my Tal1M.

You only really need to worry about alignment when the imaging time becomes long enough and you are have a larger area sensor. Focal length really doesn't matter that much, it's the ratio of star size to field of view that matters , so if using a DSLR you would need to care more than someone using a small area CCD... but if you're only at, say 5 to 10 minutes subs, a polar scope should be fine.

Derek (very thankful 1 hour subs are a thing of the past)

[RobH]

Rob, this was using 1370mm, 10 minute exposures, polar aligned only with the polar scope...

http://stargazerslounge.com/imaging-deep-sky/133998-m51-rc-repro.html

Wow!!!

I stand corrected John.....you can do LX imaging just using the polar scope

I'll do it when I'm next out in the field with the HEQ5, although as I said earlier, as near to perfect polar alignment as possible has certainly helped my tracking in that the guide commands are much less frequent, but if I can save half an hour in the field, great.

[jgs001]

I'm not sure what the numbers mean exactly, but the OSC index is normally between 0.3 and 0.5 on the PHD graph, if that helps any. If I had a permanent setup, then I'd spend the time to get it as spot on as I could, drift aligned the lot...

[johnb]

Wow what a thread - I used to be very confused about all this stuff until i had that lights on moment and i realised that I was polar Aglining the Mount and not the scope. So my order of event is as follows.

1 - I setup my mount and point it roughly in the right direction

I have previosul set the scales using the Astro Baby Guide - Astro Babys HEQ5 for Idiots Page

Make sure its LEVEL - it makes a huge diference.

2 - Now I aling the MOUNT so Polaris, again using an Astro Baby Guide which is here - Astro Babys HEQ5 for Idiots Page

Don't worry about the scope ( if its attached and now pointing in an odd direction - this is only to align the mount ).

3 - Set the Mount to the home postition Weights down etc

4 - Mount the scope, Balance etc

5 - I then undertake a 3 star alignment and im off

Using the above I can now get 10 Min exposures, I could probably extend that if I drift aligned etc.

Just my two penny worth

John B

[RobH]

I'm bowing out of this one.....when you're in a hole, don't keep digging :D

Rob

[swag72]

Seriously a big thanks to all who contributed to this thread - You can not beleive how I understand this now compared to last night!!

A big to you all, you are all fab!!

[ollypenrice]

A polar scope routine that does work is Takahashi's, where the bubble level goes on the RA axis after a time zone offset is applied to calibrate it. Brilliant. Getting mounts level takes a while. Getting the polar reticle calibrated this way via the RA axis is the work of two seconds. Thereafter you have, in effect, an accurate and calibrated planisphere in the polar viewfinder with the polaris position marked there.

You can do 30 minute subs straight from this routine.

Also not bad is iOptron's Polaris Position routine. Not as accurate but very fast and fine for mobile imaging.

Olly

[Zakalwe]

To make things easier I slip a star diagonal with the barrel removed (so you can get your eye close to the mirror) over polar scope. I can then see enough of the reticule from a sitting position. The only trick is to remember the mirroring effect when setting the EQMOD polar scope start position!

Chris.

That sounds like a plan.

And thank you for EQMod*.... what a cracking piece of software.

*Erm...you are the same Chris of the EQMod tutorial videos?

[JoLo]

First time post here...be gentle.

I think everyone has their own modifications to basic routines so they have a method they are comfortable with and accomplishes what they need. I basically follow Glider/Malcolms routines above, with a few mods I have incorporated.

* I do a quick home position check as a first step in setup. Move RA to balance position, place level on CW post and balance, set RA circle to 6 hr; Move dec to balance position, place level on DEC plate (or flat of mount) and balance, set DEC circle to your latitude. Now, when you reset both RA and DEC to "0", you have a very accurate home position which, I find, helps with both polar and GoTo alignments.

* I follow Rob's procedure when I am imaging above 500mm fl....go straight to the drift and get it right, cuz you gonna need it.

* I also image with a 400mm refractor, as well as 20 / 50 and 70-200 piggyback lenses; when using these, i find the polar alignment with the polar scope is good enough, I can guide out (I guide manually) any problems I run into, which are few below 400 mm focal length.

That's my 2 cents.....it accomplishes what I need, and I have it down to a routine that moves pretty quickly. When I am doing wide field, I can be up and imaging in 15 minutes....when using 800mm, takes about 45 min due to the drift aligment, but most of that time is spent letting the star drift anyway.

Joe

[chrisshillito]

*Erm...you are the same Chris of the EQMod tutorial videos?

Yes, that's me

Chris.

[Zakalwe]

Apologies to the OP for the thread kijack!

Yes, that's me

Chris.

Thanks for the work on EQMod. It's spot on:icon_salut: