Chris49

Hi Nigella,

This is my best effort from March 2017 - not an APOD 😉: EOS7D not modded, mounted on tracking A-VX, 70-300 at 280mm at f/8, best 12 out of 16 - 4min subs at ISO1600.  One dark and one bias, stacked in DSS.  I found stopping down the lens made a huge difference to the star roundness.

Chris

2 hours ago, cfpendock said:

It seems to me that your subs are quite short.

With longer than 90 sec subs, the stars start to become sausages.  This is I believe the result of flexure between the main and the guide scope.  I have now improved the guide scope rigidity by putting it in rings on top of the main scope, but I haven't had a chance to try this yet - part of the back garden was underwater this morning. 🙁

Your NGC891 is stunning - thanks for showing me what can be done.

Chris

2 hours ago, michael8554 said:

If your stars are smaller and round in the subs, then your guiding is "adequate", so isn't it your processing that is to blame for stars that are too big?

I see what you are getting at, but I come back to the HFR values that I get for the stars in the subs with Sequence Generator Pro - these range from 3.5 to 6.  When I watch videos of people using SGP, they get values as low as 1.2 so my stars are large at that stage.  I suspect they then get bigger still with my attempts at processing, probably because I have stretched them too much.

Your comments are certainly making me think!!

Thanks

Chris

9 hours ago, carastro said:

Chris, I have just given your image a quick run through the star reduction technique demonstrated in my video above.

This is the result.

I did watch your video last night and it looks very useful.  I'm such a novice with processing that I will need to follow it through step-by-step with an example of my own to understand it.

I have CS6 - yours may be a different version but I guess that won't matter.  Your star reduction certainly shows an improvement on my picture.

Thanks

Chris

10 hours ago, michael8554 said:

I don't believe that analysing a stack tells the real story. 

Are your stars that large in the subs?

You are right, they are not.  So I was just lucky they came out roughly round!

Back to improving the guiding!

Thanks

Chris

2 minutes ago, vlaiv said:

That setup has nowhere near needed precision to guide your setup for close in shots.

First "upgrade" would be switching to OAG.

You are right of course, but I think it is a case of "small steps" to make progress without getting discouraged.  I am a bit wary of the OAG because people say they are hard to use.  I hope to get there eventually!

Thanks for the advice.

Chris

10 hours ago, fireballxl5 said:

for star size comparison here's my shot of the same target from back in 2008

I'm not too far off then.

Thanks for posting your image.

Chris

11 hours ago, newbie alert said:

are you using a separate guide scope or oag?

The guide scope is the standard Celestron 50mm finder #51611 and holder that comes with the EdgeHD8 - not very satisfactory as it is not rigid.  Guide cam is SX Ultrastar.  I have since moved it to rings mounted on a Vixen dovetail on top of the main tube.  This is much more rigid and is symmetrical for balance so that should help.

11 hours ago, newbie alert said:

it's going to have to be a very good mount to do that comfortably..

Mount is iOptron GEM45 - just getting used to it, but I am impressed so far, way better than my A-VX which had so much Dec backlash that it never came back!

Thanks for the encouragement!

Chris

11 minutes ago, Davey-T said:

bear in mind that some "experts" spend tens of hours processing their images

There I was thinking 10 minutes processing was a bit excessive - I was hoping my subs were going to be nearly perfect straight out of the camera 😀.

Chris

6 minutes ago, Davey-T said:

You can "fix" eggy stars in P'Shop by copying the image onto itself and using blend mode darken nudge the layer with arrow keys to improve the stars.

That sounds a really clever technique.  There's a lot to this astro stuff when you get into it!

Thanks

Chris

5 minutes ago, JamesF said:

It's not clear from the specs for the camera on the SX site whether the optical window rejects IR/UV or not.  If it doesn't then it may be worth looking at how you might fit an IR/UV filter.  Or, if you're working in a fairly light-polluted area perhaps it is worth looking at an LP filter as has already been suggested.

I don't think it does reject UV, hence my worry that UV might be out of focus and lead to blobby stars.  I thought that was more a problem with refractors than reflectors though, although there is the corrector plate I suppose.

I do have an LP filter to try, but although Clear Outside says I have Bortle 4, I find that hard to believe!

I will search for PS star reduction as you suggest.

Thanks

Chris

6 minutes ago, carastro said:

OK, in Photoshop. in levels, you have a black point, a grey point and a white point.  I never move the white point, it just causes enlarged burnt out stars.  Even the grey slider can enlarge the stars a bit, so need to use that carefully.

If you are using curves, I always anchor the white point down (on the diagonal line = click on the white stars and watch where the mini box pops up and then click on that spot) then when you stretch in Curves it will help stop the white being stretched.

Thank you Carole.  I will be more careful next time.  So far I have had very little idea what I am trying to do and even less about how to do it!  It's all part of the learning curve. 

Chris

5 minutes ago, vlaiv said:

Well - you want to do two things, and wait for third - as there is noting you can do about it, except moving to Atacama or similar.

Do whatever it takes to get your guiding sorted and that means guide RMS at 0.5" or below. Make your sampling rate somewhere between 1 and 1.2"/px and of course - wait for night of good seeing. Actually that last one can be helped - avoid anything that can mess up seeing locally (read on how to optimize planetary viewing) and work on targets when they are highest in the sky and / or best positioned.

In order to get to certain resolution with EdgeHd8" and that color camera, you need to do two things - add reducer and debayer using super pixel mode. That will put you in 1.32"/px and that is quite ok to start with for high resolution work.

Thanks Vlaiv, that's very helpful. I guess I have been unrealistic up to now.  I will work towards what you suggest.

Chris

3 minutes ago, carastro said:

What software are you using for post-processing?

Stacked in DSS, stretched a bit in Photoshop - I may well have clipped off the brighter stars.

Chris

9 minutes ago, vlaiv said:

it is down to matching pixel scale, guide performance and seeing conditions

A lot to think about here.  Clearly I will try to find a place to put the filter and concentrate on improving the guiding.  Also maybe I should include the #94242 0.7x reducer - I was trying without because it is the tiny galaxies that I'm really after.

Thank you for your advice.

Chris

3 minutes ago, Star101 said:

Check the subs and remove any that don't have perfect round stars. Taking a closer look, I feel this image was taken on a windy night.

This was 19 out of 30, so a lot were thrown away.  I haven't splashed out on Pixinsight yet, I am trying to get something worth processing first!

I have made big changes to the setup - moving the #51611 guide scope on to a top bar from the normal finderscope position.  That should help balance.  Waiting for it to stop raining here!

Thanks for your thoughts.

Chris

6 minutes ago, Star101 said:

They are not too bad looking at my image taken about a year ago.

Thanks Dave.

Presumably that is with your C11?  I've never used a refractor, but people seem to get HFR of ~1.2 with those.  Is 3.5 to 6 all I can expect with a reflector?

10 minutes ago, Davey-T said:

Stars look slightly misshapen, may be flexure as you say, also a few hot pixels, if this is straight out of DSS it's not bad, stars look a bit over exposed but lots can be done in processing to correct  stuff.

Thanks Dave, I did give it a bit of curves stretching in Photoshop and I had to suppress the hot pixels by hand - no dark frames - clearly I missed a few.

Any thoughts on the need for a filter?

Chris

This is NGC891 taken as 19 subs of 90sec on 3rd Dec. using EdgeHD8 at 2032mm attached through the #93644 T adaptor to an SX694C Pro OSC, then stacked in DSS.

Why are the stars so big? SG Pro gives the HFR values between 3.5 and 6 - I've tried improving focus, but can't get it better.  I've used a Bahtinov mask and I've used the autofocus routine in SG Pro, but to no avail.

Is it that I need a UV/IR filter?  If so, where in the image chain can I mount it - there don't seem to be any convenient 1.25" or 2" threads to mount it with my setup.

Guiding with PHD2 gives me about 1 arcsec or better, but I have some flexure issues.

As you will have noted, I have minimal skill at processing!

I would be very pleased for any pointers as to what is happening here - don't hold back to spare my feelings, I know there is a long way to go!

Many thanks

Chris

Just got the chance to try the calibration again.  This time, I moved the counterweight bar to horizontal, then clicked on Confirm position 1.  It said to slew the RA more than 45 degrees from previous positions, which I did and it then said it had auto-confirmed position 2 and that all positions were confirmed.  This gave X=462.1 and Y=665.2 so very close to what I had before.

It seems they have made the software even more automatic than in the manual and it knows when it has moved enough to make the calculation.

Unfortunately the clouds rolled in again and I wasn't able to check the polar alignment accuracy in PHD2, but I think the calibration has done the right thing now - so a small step forward!

Chris

My GEM45 has similar problems with setting up the iPolar - I've started by moving the counterweight bar to horizontal and it doesn't wait for you to press the Confirm Position 1 - it has already pressed it and moved on to Position 2.  You start slewing the RA back so that the counterweight bar is pointing down and before you've got there it says "All position confirmed".  It seems to give sensible values for the Center of Camera X=461.8 and Y=664.2.

I then centered the cross on the dot successfully, but when I checked the polar alignment error in PHD2 it said 37.7 arc-min!

I think I have been starting with scope east/ counterweight west, but if we get to see some stars soon, I will try it the other way round - thanks for the suggestion.

Chris

50 minutes ago, michael8554 said:

Search Zero Position - if you are unable to be physically present to return the mount to the correct Zero Position as above, this will search for and return the mount to the correct position. 

Michael 

I found a thread on cloudy nights https://www.cloudynights.com/topic/513870-cem60-search-for-zero-and-other-stuff/ in which someone took his CEM60 apart and found a combination of pins and Hall Effect sensors that control the Search Zero process.  Presumably that is more accurate for setting the zero than doing it by adjusting the clutches by hand and eye, whether you can be present or not.

Thank you for your efforts to help.

Chris

12 hours ago, Davey-T said:

With my old iEQ45 I just scroll down to zero position press enter and it wanders off to some arbitrary point I then loosen the clutches and set it to up / north so it knows where it's at, as said the latest software helps to find the place for you.

Dave

I don't know if iEQ45 has through-the-mount cabling, but I will try your approach and see how i get on.

Thanks

Chris

11 hours ago, michael8554 said:

Never hurts to read the Instruction Manual...........

 

I had read it, but sadly I hadn't understood it - hence the request for guidance.

My anxiety was that you could tangle up the through-the-mount cabling by moving the Zero Position.

The Goto Zero Position takes you to where the mount thinks is Up and North, but not if the clutches have moved.  The Search Zero command (by some clever method that I do not understand) sets the mount to Up and North even if the clutches have moved.  But doesn't this mean that the wiring risks getting wound up?  Apparently not.

I think I now know what to do but without understanding why.

Chris

I have recently bought an iOptron GEM45 (from FLO) and I am a bit mystified by the Zero Position.  The hand control gives you the options of "Goto Zero Position" and also "Search Zero Position", but they appear to do the same thing!

Does the mount have sensors like the Home position of a Paramount, which sets the axes to an exact hardware position, or is it something else?

I guess this is the same for other iOptron EQ mounts so maybe a skilled user can enligten me.

Many thanks

Chris