Help using barlow for planetary imaging

[Alastro]

I’m trying to improve imaging of Jupiter, Saturn, etc. I’m using a ZWO-120 webcam mounted straight to the visual back of CGEM 9.25 with a 2” adapter.  I have recorded with and without a Celestron Luminos 2,5 barlow, see [pictures below. The images taken without the barlow turn out to be fairly decent, given the conditions. However, images taken with the barlow are much more washed out than I would imagine. I realize that exposure time will go up, image quality will go down to some degree, etc, but the difference in quality is so drastic that it really makes no sense at all to use the barlow.

I see images taken with smaller telescopes that are much better in quality and in image size. Is it the barlow that I’m using? What am I doing wrong?

[CraigT82]

Could be either poor conditions/seeing, poor collimation or poor focus. Cant do much about the first but the others you can!  Did you check collimation when you set up? What technique are you using to get focus? Likely that conditions just weren't good enough for the 2.5x barlow on an already long FL scope

[Alastro]

I have never looked into collimation as it appears to be fine. Wouldn't a poor collimation have an impacted on focusing with and without barlow? Finding the right focus is of course not easy due to the mirror shift and I have not invested yet into a remote fine focuser.

[CraigT82]

  In your first post you mention "given the conditions', implying they were poor? Putting a 2.5x barlow in in poor conditions is going to make things worse.  

You say collimation appears to be fine, have you done a star test to confirm?

[Alastro]

Just now, CraigT82 said:

  In your first post you mention "given the conditions', implying they were poor? Putting a 2.5x barlow in in poor conditions is going to make things worse.  

You say collimation appears to be fine, have you done a star test to confirm?

Well, under "condition" I mean mainly living only an hour out of NYC with a great deal of light pollution. The pictures were taken yesterday with pretty high temperatures. At any rate, these conditions were the same when imaging with and without barlow.   So why does the barlow have such negative impact?  

I have never collimated nor have is ever checked the collimation as I read that collimation for a SCT is pretty stable. I guess I would have to do that just to be certain.

[Stargazer33]

A lower magnification will always look cleaner. Any vibration due to wind, traffic if you are near a road (a metal wall decoration in our conservatory rings when a large lorry goes past our home!), or even just walking around if your 'scope is on concrete will cause the image to move. If you have put a 2.5x Barlow into your imaging train then that movement will be magnified 2.5x also.

[CraigT82]

The Barlowed image is worse because it's amplifying the poor conditions buy 2.5x. 

Yoi should really check the collimation, SCTs do hold it well but they can go out if knocked about. 

[Alastro]

9 minutes ago, southerndiver357 said:

A lower magnification will always look cleaner. Any vibration due to wind, traffic if you are near a road (a metal wall decoration in our conservatory rings when a large lorry goes past our home!), or even just walking around if your 'scope is on concrete will cause the image to move. If you have put a 2.5x Barlow into your imaging train then that movement will be magnified 2.5x also.

I do reallize that a barlow has an impact and that it magnifies the ambient conditions, and that it requires a larger exposure time, etc.  Maybe I do not quite understand the principle of the mechanics of the optics ... but if the barlow magnifies the image, wouldn't it than also be true that, as telescopes become larger that the image quality would go down as well? Beside the fact that a larger telescopes gazers more light, which should reduce the exposure time, making for a better image again.

At any rate, it appears that a low exposure time is the main factor for better images. Or near perfect conditions are required when using a barlow. Maybe have to setup the scope on the top of a mountain in Andes

 

[riklaunim]

f/25 can also be bit to much for 3,75 pixels of ASI120MM. Try staying by f/20 for most of planetary imaging. At max telescope resolution collimation must be good, the telescope must be at ambient temperature (the bigger the SCT OTA the more likely is that will start lagging behind and will be useless). Focus - best set with a motocryford - is also essential. Small misfocus and the image will be failed.

[Alastro]

1 hour ago, riklaunim said:

f/25 can also be bit to much for 3,75 pixels of ASI120MM. Try staying by f/20 for most of planetary imaging. At max telescope resolution collimation must be good, the telescope must be at ambient temperature (the bigger the SCT OTA the more likely is that will start lagging behind and will be useless). Focus - best set with a motocryford - is also essential. Small misfocus and the image will be failed.

Thanks for advice.