I was forced to image planets with a short tube achromat, and was pleasantly surprised.

[Chris]

Saturn and Jupiter were positions above the 'big gap' to the front of our house about midnight, so having just bought a ZWO385mc I was keen to try it out for planetary imaging. I looked at my scopes all sitting in the corner and picked out the Heritage 150p as my best hope. It has the relatively big 6" mirror and no chromatic aberration to worry about, so I fitted the 150p optical tube to my motor driven Starquest mount and all seemed well until!... I could not get focus! Not even with the Barlow lens!

I was then faced with two options, switch the Heritage 150p for the Meg72 or my the really wild card, my 102mm f/5 achromat. I very nearly went for the meg72 but decided on the short f/5 Achromat in full knowledge that I was using a low power wide field scope to try and image the planets. My expectations were low, especially as the seeing was quite poor. 

However, I was quite surprised by the stacked images after processing. The 2.5x Barlow really helped.

 

[happy-kat]

But that was the heritage 150p why not just drop the trusses about an inch for focus.

[happy-kat]

Nice to show the video and the image taken with that. Where your videos very long or around a minute or so each?

[Chris]

8 hours ago, happy-kat said:

But that was the heritage 150p why not just drop the trusses about an inch for focus.

You know what, I didn't remember to do that until I was trying to get sleep that night, doh! lol 

I'll drop the truss rods for planetary imaging round two  

Edited July 24, 2020 by Lockie

[Chris]

24 minutes ago, happy-kat said:

Nice to show the video and the image taken with that. Where your videos very long or around a minute or so each?

I took about 1000 frames for each run, so yeah around a minute because the frame rate wasn't particularly high. 

[RobertI]

Pretty good Chris! Some surprising detail on Jupiter. Is the yellow cast due to the achromat or is that a fairly accurate colour rendition?

On the subject of dropping the trusses, presumably this would cut off some of the light cone? I'm assming it would not have much effect if dropping by one inch, but say you dropped by six inches, would this theoretically reduce the resolution or just the image brightness (or both)?

[Chris]

46 minutes ago, RobertI said:

Pretty good Chris! Some surprising detail on Jupiter. Is the yellow cast due to the achromat or is that a fairly accurate colour rendition?

On the subject of dropping the trusses, presumably this would cut off some of the light cone? I'm assming it would not have much effect if dropping by one inch, but say you dropped by six inches, would this theoretically reduce the resolution or just the image brightness (or both)?

Thanks Rob, I did think they were a touch too yellow. I'm guessing this is an achromat thing? unless it was the Baader IR cut filter screwed onto the camera? 

My thinking is that you would need to drop the trusses down as little as possible to avoid losing light, but it would be good to hear from someone more in the know about this. My educated guess would be that moving the secondary down the tube too far would mean that some of the reflected light from the primary would miss the secondary because as you move down the tube the path of reflected light from the primary gets wider. Does that make sense? What do you think Rob? 

[RobertI]

59 minutes ago, Lockie said:

What do you think Rob? 

I agree with your logic Chris. So say the secondary ends up getting only 80% of the width of the full light cone, then I guess you have suddenly got an 80mm refractor with the same focal length (so F5 becomes F6.4), which is photographically slower, and visually has less resolving power? My best guess! 

Edited July 24, 2020 by RobertI

[Pete Presland]

Very nice