What is this image telling me?

[philhilo]

So I finally have a reasonable image after probably 10 sessions of adding kit and general learning, and I was hoping folks could help me understand what I can do (technique, session craft, adjustments etc) and can't do (due to kit limitations) to improve.

The image is M45, taken through a SW 200PDS with the SW coma corrector and no additional filtering using a Canon D700 in a bortle 8+ area. The image is composed of 29 x 60 secs subs at ISO 800 controlled by APT and guided using PHD2 . These were stacked in DSS and edited (very quickly and badly) in Gimp.

I would love to think I was seeing the reflection nebula around the stars, however I don't think I am. I guess the fact that it is a Newt is giving me the diffraction spikes around the brightest stars, these appear to be slightly off to the bottom left - is that a collimation issue (I use a laser collimator but it doesn't sit flush to the OTA aperture so making a bit of a nonsense of the process!)? Then there are the halo's - is this an unavoidable feature of the Newt or some other issue? On the good side the stars are reasonably round right out to the edge so the guiding appears to be OK, and the coma corrector is doing its job.

Thanks in advance for any feedback.

 

[philhilo]

Further thoughts, I guess more integration time and less aggressive editing would be good for the image, would it turn the halos into nebulosity or would that just get me brighter halos with a hint of nebulosity?

[ebdons]

Hi could be some condensation trapped somewhere it just needs a bit even difficult to see on a newt and M45 is very bright on the main stars? don't think the CC is quite right yet needs a bit of fine tuning, I have a f3,9 newt and I found it a hard learning curve to get everything adjusted right. could be something in the cam or just some issue with the sensor cleanliness. check it out and see? ton

[symmetal]

The halos and multiple diffraction spikes are unfortunately due to condensation, possibly on the main mirror. The star shapes as you say look pretty good. Very slight elongation but not enough to worry about at the moment. There is possibly slight coma on the bright corner stars but this may be just due to the condensation.

In your processing you've black clipped the background so have probably lost any nebulosity which was present, though it was probably masked by the condensation artefacts anyway.

Good start anyway. 

Alan

Edited October 15, 2019 by symmetal

[JamesF]

I favour condensation as the explanation for the halos too.

James

[Adam J]

3 hours ago, philhilo said:

So I finally have a reasonable image after probably 10 sessions of adding kit and general learning, and I was hoping folks could help me understand what I can do (technique, session craft, adjustments etc) and can't do (due to kit limitations) to improve.

The image is M45, taken through a SW 200PDS with the SW coma corrector and no additional filtering using a Canon D700 in a bortle 8+ area. The image is composed of 29 x 60 secs subs at ISO 800 controlled by APT and guided using PHD2 . These were stacked in DSS and edited (very quickly and badly) in Gimp.

I would love to think I was seeing the reflection nebula around the stars, however I don't think I am. I guess the fact that it is a Newt is giving me the diffraction spikes around the brightest stars, these appear to be slightly off to the bottom left - is that a collimation issue (I use a laser collimator but it doesn't sit flush to the OTA aperture so making a bit of a nonsense of the process!)? Then there are the halo's - is this an unavoidable feature of the Newt or some other issue? On the good side the stars are reasonably round right out to the edge so the guiding appears to be OK, and the coma corrector is doing its job.

Thanks in advance for any feedback.

 

vance

Looks like an image taken through either dew on optics or high altitude cloud to me. 

[bottletopburly]

I’ve had that on my 200pd before put it down to moisture in atmosphere 

[philhilo]

Thank you everyone for the feedback, that is very useful in pointing me in the right direction. Seems like 2 possible explanations for the excessive coronas/diff spikes - moisture on the optics, or moisture in the air. As I remember the target was pretty low to middling so I doubt it was a dew issue (and am I correct in figuring Newts don't tend to get dew issues as much due to the optics being way down out of the way), so most likely problem was the seeing.  That's good news, one to check for in a test image. 

On the processing side I will have more time over the winter (hopefully) to get deeper into that, I might get pixinsight. 

Collimation, I have yet to try the collimation tool on APT so that's got potential over my current vexing collimator issue (and I can't figure out what surface isn't flat that is causing the wobble between collimator and OTA).

I know the 200PDS is the 'wrong' OTA to be starting with but its what a lot of folk get before they get sucked into imaging. However it is also great to see lots of you using them and the images are inspiring.  I am looking at a TS Optics 90/600 triplet on ebay, which would I think be better for some of the bigger objects (like M31) and be a little kinder on my mount. Fingers crossed for the bidding on that one.

So thanks again folks, I will be back.

[almcl]

9 minutes ago, philhilo said:

am I correct in figuring Newts don't tend to get dew issues as much due to the optics being way down out of the way

If only that were the case!

My SW200P has had several cases of dew on the secondary and some of dew on the primary - this seems particularly the case when we have a clearance in the evening after a day of rain.  The outside of the OTA is often running with water by the end of an imaging session. 

The angle of the target doesn't seem to make much difference. 

I now use a dew shield on the front end which has helped somewhat (it also improves stray light rejection) but on occasions have had to resort to a heat gun on low power to clear the mirrors.  This approach carries a bit of a risk so if you discover you need to adopt it, take care!

[Adam J]

41 minutes ago, philhilo said:

 (and am I correct in figuring Newts don't tend to get dew issues as much due to the optics being way down out of the way)

No the Primary is all the say down the tube the Secondary however is very given to collecting dew.

Edited October 15, 2019 by Adam J

[ebdons]

 Dew can occur quite quickly even on the primary and more on the secondary, fit a brushless pc fan on the rear end to either blow air up the tube or a fan to draw air down and have a secondary mirror heater, as I find that dew forms quickly on even my primary without the fan running and normally any dew% above 95% on the scale has a massive effect in ruining any images I get. but it's part of the newt learning process. my sct suffers even more than that tho. Ton

[philhilo]

Dang, so could well be soggy optics. I think most of my recent sessions have been after rain - its autumn. I was just hoping there was an upside to Newts. I don't think I could possibly ask my overloaded HEQ5Pro to cope with any more load, fans, dew heaters etc. I say thank you when she is tracking well - thankfully at home I can put the rig in a sheltered spot however the 2 weights are already sitting on the stop on the bar to achieve balance, and although I have two more weights it just isn't designed to take the load so I am reluctant to add more. Hairdryer or bust! Thus I was thinking get a decent 80/90 refractor, then later upgrade to an EQ6 (if I don't get sucked into a dedicated cooled camera). Trouble is I really like imaging galaxies so I like the power of the 200PDS (and I couldn't swallow the cost of comparable refractor....yet).

[ebdons]

yep dew is also dependent on what ground surface you have, chalk base is better than my heavy clay as the clay traps the moisture and releases it in the night? anyway get the EQ6 pro and that will do you for years, it has it's limitations but it's not silly money and a few mods can be done like belt drive and better bearings and grease etc. I have one for a few years and it could even take a 12" short tube newt if it's balanced right. mainly galaxies and nebs for me so a newt is good for the HD small scale stuff and a 80 or 120 mm frac for the widefield nebs or galaxy groups. just need clear skies now haven't seen the moon for either for a week or more! Ton

 

[Erling G-P]

I've had very similar images of M45 from my 200PDS and it was dew on the secondary.   Are now using it with a dew shield which helps quite a lot, but unfortunately makes the scope more nose heavy.  To compensate, I've had to move the OTA rearwards, which makes it more susceptible to run into the legs.

Am on a HEQ5Pro as well.  One little tip regarding balance, if you haven't done so already, is to rotate the OTA, so your camera is on the 'inside', towards the mount.  It reduces the needed counter weight some, and in my case meant I could make do with just the two supplied 5 kg weights.

[ollypenrice]

I think that the best thing - and it's a very important thing - is that you've critically appraised the image and doubted that you have the nebulosity in it. The most important thing any imager needs is the ability to study an image to see what's good and bad about it, at every step of the way.  You've done that. 

Olly