Second attempt at planetary!

[CraigT82]

Hi all, Thanks for all the positive comments on my previous post (First attempts at planetary). I had another go last night, this time I felt a bit crazy and put the 200mm skyliner tube on the CG-5.  I wouldn't normally do this but there wasn't a hint of wind so I thought I could get away with it.  Actually it went quite well!

Below is an image I got of jupiter using a DFK21au04 colour with a Baader 2.25x barlow for a focal length of 2700mm (f13.5).  After looking at the tiff and calculating the pixels the width of the planet was occupying, I calculated I was sampling at 0.4" per pixel. So it looks like the focal length was actually around 2875mm.  

Capture info: oacapture on a macbook pro.  Exposure 10ms, gain 866 , 60 fps.

Pre processed in PIPP, stacked in AS!2, wavelets in Registax.  Final tweaking in Pixelmator.

I think I need to increase my sampling to around the 0.25" pp mark to pick up some finer detail...I've seen other peoples images through a 200p and 2x barlow which have got tonnes of fine detail (SGL user Catman161 used to own this very OTA and his images with an ASI120mc and 2x powermate are crackers) which means I'm gonna have to get a camera with smaller pixels as I think extending the FL even further isn't a real option with this mount.  Damn this imaging lark is addictive (and expensive!)

Thanks for looking, any and all criticism greatly received!

 

[michael.h.f.wilkinson]

Some nice detail captured. Before rushing off to get another camera, perhaps consider that the use of a longer focal length, and the use of smaller pixels are precisely equivalent, both in terms of imaging and tracking. It is simply the number of arcseconds per pixel that counts.

[Grotemobile]

Are U using one of these.https://www.firstlightoptics.com/uv-ir-filters/celestron-skyris-ir-block-filter.html

That is what I use on Jupiter. I think it is a very good  picture.

[CraigT82]

2 hours ago, michael.h.f.wilkinson said:

Some nice detail captured. Before rushing off to get another camera, perhaps consider that the use of a longer focal length, and the use of smaller pixels are precisely equivalent, both in terms of imaging and tracking. It is simply the number of arcseconds per pixel that counts.

I *think* I understand! Basically I think I'm under sampling with my current set up. In order to correct that I can either increase FL or reduce pixel size. My issue is that my scope is under mounted as it is so I think the easy option is rather than increase FL I will reduce pixel size, with the aim of increasing fine detail at the same image scale. 

I would like to keep this camera and just increase FL (probably with just an extension tube) but I think I will struggle to keep the planet on the chip. 

Does that make sense or am I barking up the wrong tree?! 

Of course I should just upgrade my mount but that's not happening in the near future! 

[CraigT82]

2 hours ago, Grotemobile said:

Are U using one of these.https://www.firstlightoptics.com/uv-ir-filters/celestron-skyris-ir-block-filter.html

That is what I use on Jupiter. I think it is a very good  picture.

No I'm not using any IR cut filter, I was under the impression the DFK has an IR cut optical window but not sure it has to be honest. There seems to be a red tinted window over the chip!   Do you think the image is suffering form IR blurring?

[michael.h.f.wilkinson]

11 minutes ago, CraigT82 said:

I *think* I understand! Basically I think I'm under sampling with my current set up. In order to correct that I can either increase FL or reduce pixel size. My issue is that my scope is under mounted as it is so I think the easy option is rather than increase FL I will reduce pixel size, with the aim of increasing fine detail at the same image scale. 

I would like to keep this camera and just increase FL (probably with just an extension tube) but I think I will struggle to keep the planet on the chip. 

Does that make sense or am I barking up the wrong tree?! 

Of course I should just upgrade my mount but that's not happening in the near future! 

Actually, it makes no difference whether you change camera or increase focal length. If you mount wobbles by 2 arcsec, and your image scale is 0.5 arcsec per pixel (for the sake of an argument) the wobble will be 4 pixels, regardless of how the image scale is obtained. What does matter is the physical length of the scope. A CG-5 is roughly the same as my Vixen Great Polaris, and my C8 has the same aperture as the SW 200P. When I used a DMK21 (same pixel size as your DFK21) I used F/25 to F/30 on Jupiter. This would also be optimal in your case. We should therefore be working at the same focal length. The reason the SCT has a slight edge here is that its short build means it puts less torque on the mount, reducing wobble. Vixen didn't like to mention a maximum payload in terms of weight, but instead specified the GP mount was suitable for a 4" refractor (usually very long and slow affairs in those days, F/12-F/15), a 6" Newt (typically F/8) or an 8" SCT.

[CraigT82]

Thanks Michael! I understand and the wobble covering the same amount of pixels, however it was my belief that for fast frame lucky imaging, wobble of the subject on the chip isn't so much of an issue.  Or am i misunderstanding this? If I extend the FL I'm worried I'll be unable to even get it on the chip! 

My thoughts are to switch to a camera with 3.75 micron pixels thereby achieving correct sampling (with my 2.25x Barlow) with the same amount of scope/chip wobble as I have currently. I appreciate I'll have to shoot at a larger ROI than the 640x480 of my current DFK, in order to keep the chip area the same, hopefully I'll still get a decent frame rate ( or maybe reduce exposure and add some gain to compensate)

[rodrigol]

Awesome! Lots of detail and I love the fact you did not overdo the processing too much ;-)