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Tommohawk

NGC4490 Interacting galaxies

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Was trying to find a nice galaxy target somewhere other than Virgo cos I cant see to  the South-East.. .and I have to sleep at night so can't wit til after the meridian! So whilst searching through the DSOs on Stellarium I found this chap - or pair of chaps as is turns out. Apparently 25 million light years away or 40-50 million light years depending on who you ask - I won't just copy and paste info from Wiki - it might almost look like I know what I'm talking about! Anyhow it's two galaxies which collided some time back and are a long way away!

I don't really have a proper galaxy scope - only the old faithful 200 PDS, so dusted it off and hooked it up. I need to get a secondary heater on the Quattro, although as it turns out there was little condensation until I packed up at about 11.30pm.

Done over a couple of nights - and everything went without a hitch. Guiding, focusing, heaters all working lovely. I didnt use the 0.9 coma corrector cos I knew I was going to crop big time, and didn't want any image size reduction.

So - HEQ5, SW200PDS, ASI1600MM at -15degC, 141 x 60s L, and about 50x60s each of RGB, no binning, DSS and PS. 

Bit of grief with  gradients - my fault because I rotated the camera by 180deg on the second run. I tried a reversed masterflat but that didn't seem to work. Also I only used light flats, no dark flats. Need to get my calibration sorted!!

Hope you like it - happy for comment!

 

 

crop.png

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Ohh  meant to also add - I notice the stars have a slight inverted heart shape. I seem to get this with my two different scopes currently so I think its something non-optical - maybe a guiding artifact? Although I was running consistently at only 0.8" total RMS error.  

Any ideas?

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Very nice Tom, I've been hopping around imaging a few galaxies up in that area, will add that one to my list.

I have to stop when they cross the meridian as they head into too much S. London light pollution.

No idea about the stars.

Dave

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10 hours ago, Davey-T said:

Very nice Tom, I've been hopping around imaging a few galaxies up in that area, will add that one to my list.

I have to stop when they cross the meridian as they head into too much S. London light pollution.

No idea about the stars.

Dave

Thanks Dave.

anyone else any ideas about the star shapes?

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4 hours ago, Tommohawk said:

Thanks Dave.

anyone else any ideas about the star shapes?

Looks like coma / poor colimation to me. Are you using a corrector?

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3 minutes ago, Adam J said:

Looks like coma / poor colimation to me. Are you using a corrector?

Hi  Adam. This is with a Newt and no coma corrector - but to my eye is looks different to coma I think and anyhow I get exactly the same issue with my refractor, same odd shape, same orientation.

 

 

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6 minutes ago, Tommohawk said:

Hi  Adam. This is with a Newt and no coma corrector - but to my eye is looks different to coma I think and anyhow I get exactly the same issue with my refractor, same odd shape, same orientation.

 

 

If it looks the same with the refactor in the same direction then its is sensor tilt. 

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Hmmm, I was fighting with the spacing of my 130PDS and SW CC + OAG for some time, 

And I can assure, nothing like this showed up in the central area of the image with incorrect spacings with/without CC during my tests...

How do you attach camera to the Focuser without the CC? Tilt maybe?

Edited by RolandKol

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2 hours ago, RolandKol said:

Hmmm, I was fighting with the spacing of my 130PDS and SW CC + OAG for some time, 

And I can assure, nothing like this showed up in the central area of the image with incorrect spacings with/without CC during my tests...

How do you attach camera to the Focuser without the CC? Tilt maybe?

Hi Roland. With this set up I screw a short spacer into the efw and clamp that into the 2" ep holder. The cc would give a better connection for sure because it sits deep in the focuser tube. So that's my next experiment.

With my refractor I also clamp into the ep holder. Maybe the camera does sag a bit. I'll see if there's a better way to connect with the refractor, but no obvious screw together option. 

 

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Yeep... Probably Tilt.. These SW focusers are really lousy...  
I think of some kind 2" EP lock like Baader ClickClock, which, unfortunately, is a bit too larger and PDS wount focus with it....

The image is really nice!

Dancing galaxies are my favorite! :)

Unfortunately, I still have not learned how to image any of them from London, except M51 probably... A bit too bright here...

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I sometimes get stars like that when I have not switched on my cooling fan in the Newt - tube currents......

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On ‎02‎/‎04‎/‎2019 at 20:39, blinky said:

I sometimes get stars like that when I have not switched on my cooling fan in the Newt - tube currents......

OK that's interesting - but I thinks its the same with the refractor, and also the heart shape is that same orientation even with the camera rotated 180 degrees. I need to have a more detailed look at my subs.

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3 minutes ago, Tommohawk said:

OK that's interesting - but I thinks its the same with the refractor, and also the heart shape is that same orientation even with the camera rotated 180 degrees. I need to have a more detailed look at my subs.

As above if what you say is accurate it can only be sensor tilt.

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12 minutes ago, Adam J said:

As above if what you say is accurate it can only be sensor tilt.

Well it looks that way. One odd thing though - I've used this camera with the same filter wheel for some time and never noticed this before. I've just been looking at some subs taken with my old camera lens and I really cant see this at all. the camera hasn't suffered any mishap so now I'm wondering of its just more apparent with longer FL, or maybe I'm being more fussy. 

I know this is all a bit subjective, but does it look like a big problem to you - am I just being too picky?

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Not sure about focal length but it will be more apparent at faster F-ratios.

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First off, thanks for all the likes!

22 hours ago, Adam J said:

Not sure about focal length but it will be more apparent at faster F-ratios.

OK I guess that figures - though I seemed to have least problem when using my camera lens at F4, which  is the fastest of all the options I've used.

I've just been having a play with a trial version of CCD inspector - and there doesn't seem to be any pattern to the tilt at all. It's very odd! Most particularly the direction of tilt varies all round the clock. The CCD inspector results do look pretty consistent for a given set up however.  Eg with the Camera lens, possible slight flexure over time:

  image.png.c78db51e85d511ed96b0e9329fa8f8d7.png

Part of the problem is that I've used several different scopes/optical trains and limited runs with each version. Tamron 300mm lens, TS optics scope (with reducer spacing not fully sorted - yet another issue I'm trying to resolve!), Quattro with no coma corrector - still in evaluation stage, and the trusty 200PDS.

So I'm now wondering if there is some variable flexure.

With the camera lens the EOS adapter was never rock solid (though that shows the least issue!) 

With the 200PDS the EFW was screwed to the adapter via a screwed spacer - although this was only clamped into the 2" EP holder with the basic SW clamp screws.

With the TS72 F6 the connection should be strongest of all - the reduced is screwed to the EFW and then held in a pretty decent and deep 2" EP clamp. Of course there is the possibility of tilt in the reducer!

I've tightened the front plate of the EFW in case theres any play there, and I think I'll try removing the reducer to see what happens then - I wont have a flat field, but I should have the least variables.

Always need more time for experimentation!

BTW what do you think is an acceptable level of tilt?

 

Edited by Tommohawk

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28 minutes ago, Tommohawk said:

First off, thanks for all the likes!

OK I guess that figures - though I seemed to have least problem when using my camera lens at F4, which  is the fastest of all the options I've used.

I've just been having a play with a trial version of CCD inspector - and there doesn't seem to be any pattern to the tilt at all. It's very odd! Most particularly the direction of tilt varies all round the clock. The CCD inspector results do look pretty consistent for a given set up however.  Eg with the Camera lens, possible slight flexure over time:

  image.png.c78db51e85d511ed96b0e9329fa8f8d7.png

Part of the problem is that I've used several different scopes/optical trains and limited runs with each version. Tamron 300mm lens, TS optics scope (with reducer spacing not fully sorted - yet another issue I'm trying to resolve!), Quattro with no coma corrector - still in evaluation stage, and the trusty 200PDS.

So I'm now wondering if there is some variable flexure.

With the camera lens the EOS adapter was never rock solid (though that shows the least issue!) 

With the 200PDS the EFW was screwed to the adapter via a screwed spacer - although this was only clamped into the 2" EP holder with the basic SW clamp screws.

With the TS72 F6 the connection should be strongest of all - the reduced is screwed to the EFW and then held in a pretty decent and deep 2" EP clamp. Of course there is the possibility of tilt in the reducer!

I've tightened the front plate of the EFW in case theres any play there, and I think I'll try removing the reducer to see what happens then - I wont have a flat field, but I should have the least variables.

Always need more time for experimentation!

BTW what do you think is an acceptable level of tilt?

 

Ok but I guess despite being at F4 you are very under-sampled as that lens will be very short focal length. As such you may not be sampling the distorted airy disk to the required level to detect a distortion. So I guess that it will be less obvious with shorter focal lenght and slower F-ratio.

As for CCD inspector that is a complete mystery to me as I cant find any documentation to say what those measures actually mean. So who knows if that is good or bad lol

Edited by Adam J

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