Barlow + ZWO ASI120MC-S Focusing problem

[Yogesh]

Hi 

I have a Skywatcher 200PDS. I managed to get images of saturn, jupiter with the telescope and the ASI120MC-S camera. However, to get a bit more magnified image of these planets I got myself a Barlow Tele Vue 3x and Revelation 5x. I am having trouble with this setup and really disappointed now. I am not able to achieve focus with any of these barlows using my planetary camera. I have added extension etc. but no luck whatsover. I just see a blank black video preview in SharpCap. I have seen people using the same setup and getting good images out of those. Any help highly appreciated.

Thanks and Regards,

Yogesh

[Owmuchonomy]

Do you have an out of focus image or no image at all? If it is the latter then the problem could easily be that your object is not centred on your chip. As you add magnification in the form of a Barlow it becomes much more challenging to centre your object.  Try increasing the gain on your image capture to see if part of the fov is brighter, then slew towards this and centre the object. Remember to re adjust your gain before capture.

[Yogesh]

1 hour ago, Owmuchonomy said:

Do you have an out of focus image or no image at all? If it is the latter then the problem could easily be that your object is not centred on your chip. As you add magnification in the form of a Barlow it becomes much more challenging to centre your object.  Try increasing the gain on your image capture to see if part of the fov is brighter, then slew towards this and centre the object. Remember to re adjust your gain before capture.

Hi 

Thanks for your reply. What I did was to get the image focused on the chip with out using any barlow and then simply insert the barlow and then tried to focus again. I must mention that I am using HEQ5 pro for tracking. 

Thanks and Regards,

Yogesh

 

 

[Cosmic Geoff]

I have found that with planetary cameras, unless the image of a planet is almost in focus, you can't see anything at all.  I had some trouble till I worked out ways of pre-focusing the system so that the camera would be near focus when I dropped it in.  (I focus my Mak and SCT with the eyepiece held about 6mm out of its normal position, then drop in the camera.) 

It is also possible that with the Barlow in place, your system is not capable of reaching focus - something you can most readily test on the edge of the Moon or a distant terrestrial target.

[Stub Mandrel]

1 hour ago, Yogesh said:

Thanks for your reply. What I did was to get the image focused on the chip with out using any barlow and then simply insert the barlow and then tried to focus again. I must mention that I am using HEQ5 pro for tracking.

I use an x3 barlow with a 1200mm scope and an ASI120MC which has the same size chip

My experience is that there's no guarantee this will work, especially with stronger barlows.

I setup using the moon as a target, and get my finderscope VERY accurately aligned using an obvious crater, and tweak once you have a planet in view. I find it is still unlikely that a planet will be on the chip after putting the scope away and getting it out again.

With an x5 barlow, it will be exceptionally demanding to find the planet and exceptional difficult to focus accurately. The action of focusing will probably send the planet out of the field of view until you develop a very delicate touch.

Another trick (if the moon is hidden) is to defocus and use a very long exposure (about a second) and use a bright star (or jupiter/mars) as a target as they  will show a halo even if outside the frame.

The HEQ5 goto will struggle to accurately target planets at that focal length, so setting the finder is a challenge and it must be used. I set the planet in one of the 'corners' of the crosshair's x as when it is hidden by the X it can actually be slightly off centre and the cameras Field of view isn't much bigger than where the crosshairs cross!

[Owmuchonomy]

19 hours ago, Yogesh said:

Hi 

Thanks for your reply. What I did was to get the image focused on the chip with out using any barlow and then simply insert the barlow and then tried to focus again. I must mention that I am using HEQ5 pro for tracking. 

Thanks and Regards,

Yogesh

 

 

That method is unreliable because the action of placing the Barlow in the image train moves the previously centred image away from the chip. You need to recentre once the Barlow is in place using the method I describe.

[newbie alert]

I've found that the seeing conditions have never been good enough or steady enough for my x3 Barlow.. it's never been a better image than without it..see it as a waste of time.. Maybe a x2 would be better for me but I'm not going to waste my money trying with a average costing Barlow.i will get a powermate one day.. I see a Barlow as like a high strength ep..as a e.g. a 25mm is going to give you the best views so why try try a 5mm

[Yogesh]

19 hours ago, Stub Mandrel said:

I use an x3 barlow with a 1200mm scope and an ASI120MC which has the same size chip

My experience is that there's no guarantee this will work, especially with stronger barlows.

I setup using the moon as a target, and get my finderscope VERY accurately aligned using an obvious crater, and tweak once you have a planet in view. I find it is still unlikely that a planet will be on the chip after putting the scope away and getting it out again.

With an x5 barlow, it will be exceptionally demanding to find the planet and exceptional difficult to focus accurately. The action of focusing will probably send the planet out of the field of view until you develop a very delicate touch.

Another trick (if the moon is hidden) is to defocus and use a very long exposure (about a second) and use a bright star (or jupiter/mars) as a target as they  will show a halo even if outside the frame.

The HEQ5 goto will struggle to accurately target planets at that focal length, so setting the finder is a challenge and it must be used. I set the planet in one of the 'corners' of the crosshair's x as when it is hidden by the X it can actually be slightly off centre and the cameras Field of view isn't much bigger than where the crosshairs cross!

Hi 

 

Thanks a lot for your reply. That is some good tip. I did not really realize untill you mentioned that the fov is that small. I suppose I was taking some things for granted in my head. Thanks! I will try it on the moon to start with next time. 

Thanks and Regards,

Yogesh 

[Yogesh]

1 hour ago, Owmuchonomy said:

That method is unreliable because the action of placing the Barlow in the image train moves the previously centred image away from the chip. You need to recentre once the Barlow is in place using the method I describe.

Thanks again. I really appreciate you replying back. I am definitely going to try what you suggested , increasing the gain and re-centering next time. I will keep this thread updated if i manage to succeed or not . 

Thanks and Regards,

Yogesh

 

[Yogesh]

1 hour ago, newbie alert said:

I've found that the seeing conditions have never been good enough or steady enough for my x3 Barlow.. it's never been a better image than without it..see it as a waste of time.. Maybe a x2 would be better for me but I'm not going to waste my money trying with a average costing Barlow.i will get a powermate one day.. I see a Barlow as like a high strength ep..as a e.g. a 25mm is going to give you the best views so why try try a 5mm

Hi 

Thanks for your reply. What is the difference between a barlow and a powermate ? Are you suggesting that in the long run it would be good to get a powermate ? Do you recommend any ?

Thanks and Regards,

Yogesh

[newbie alert]

Powermate are made by televue..but they also do barlows ..what the difference is I'm not sure..but all  serious  planetary imagers use them..

[Stub Mandrel]

A barlow spreads the light rays out wider. A powermate magnifies without doing this. This makes it less sensitive to spacing (barlows get more powerful as you increase the spacing) 

Lots of planetary imagers use them because of the quality, but the practical advantages are actually greater for visual astronomers (things like exit pupil size that are irrelevant to imagers).

http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app

I wouldn't get too hung up on what to use as even mid-price barlows are very good because they are optically pretty straightforward. I'm only just gettin g to eth point where I'm thinking a better barlow or powermate could improve my planetary imaging.