Star Adventurer + 400mm lens test

[fwm891]

I decided last night to try my S.A. with an old 400mm Tokina 400mm f5.6 lens on a Nikon D5100 mono modified body. Although I have the Pro version of the mount I decided to just mount the camera/lens on a ball head rather than the the dec shaft and counter weight.

I pointed the lens at M51, focused by zooming the image on the camera's live-view screen. I set the iso at 1600, shutter to bulb, connected a shutter release cable to the 'snap' socket on the mount which gave me circa 100s sub frames. There is a firmware update which allows other variations but I'm using as supplied at present.

The image is a central crop of the frame. 45 frames were shot and 34 selected via PI's blink viewer taking out frames with aircraft/satellites etc.

No darks, bias or flats have been added. No DBE to even the background. Frames integrated and histogram adjusted.

Will try again with the lens/camera mounted on the dec shaft with everything balanced out.

 

Edited March 28, 2019 by fwm891
Wrong image added first off

[groberts]

That looks like a very successful test. 

Just to complete the picture (no pun intended), what exposure time did you use?

Graham  

[fwm891]

22 minutes ago, groberts said:

That looks like a very successful test. 

Just to complete the picture (no pun intended), what exposure time did you use?

Graham  

Hi Graham,

The subs were circa 100s, that's determined by the mount's firmware. I'm using the original firmware which when I connect the camera to the 'snap' socket on the mount gives - fits header says 99.4s.

Note: the bloating round the stars is caused by primarily two things: the condition of the lens and the full spectrum mod on the camera making it more sensitive to IR/UV which doesn't focus to the same point as the visual spectrum.

[Bobby1970]

How did you polar align the Star Adventurer? Just using the polar scope?

 

 

 

[tooth_dr]

This is really great Francis! I'm debating whether to get me SA out tonight, and try it with a 180mm lens also on a Nikon body, this is convincing me to try it!

[fwm891]

1 hour ago, Bobby1970 said:

How did you polar align the Star Adventurer? Just using the polar scope?

 

 

 

Yes, just the polar scope. Used a phone app to locate where Polaris should be and set the mount accordingly.

[Bobby1970]

20 minutes ago, fwm891 said:

Yes, just the polar scope. Used a phone app to locate where Polaris should be and set the mount accordingly.

I think you have done amazingly well with that focal length just by using the polar scope. Well done. I think it must be my eyes that are letting me down when just using the polar scope. I have had really good alignment when using sharpcap to polar align. But nothing like you have achieved at that focal length using just the polar scope. 

[Davey-T]

22 minutes ago, Bobby1970 said:

I have had really good alignment when using sharpcap to polar align. But nothing like you have achieved at that focal length using just the polar scope. 

As is the way with mass produced stuff SWSA are very variable, I've had a couple and one was rubbish and the other excellent.

On the PA question as long as the polar scope is aligned with the mount axis it's pretty easy to just check as you're imaging and tweak it to keep Polaris tracking round the circle, this will also give you an indication of how good your PA is, if it wanders off immediately you know it's not good.

I' it tracks round the circle and your images are still not great then it's more likely mechanical.

Dave

[fwm891]

I did spend quite some time after getting the SA aligning the reticule on as distant an object as I could. Took quite a lot of very small adjustments before I was happy that rotating the mount whilst looking through the polar scope showed absolute minimal movement of the central cross hair.

If your using a phone app to locate where Polaris should be placed make sure you have the correct settings in the app. Mine has a visual setting and a telescope setting - one being 180° from the other.

[Eta Carina fan]

I live in Santiago, Chile. The SA little polar scope is useless here. I use a phone app and take a number of 30 to 40 seconds test shots to tweak my settings. Under 400 mms it works pretty well.

 

[Astrofriend]

Hi,

I live at 60 degree and the polarscope is not so easy to use. Now I have added a 90 degree finder. It's like a dream:

http://www.astrofriend.eu/astronomy/projects/project-star-adventurer-angled-viewfinder/project-star-adventurer-angled-viewfinder.html

Now I can easilly track with my 150 mm lens. Lately I bought a 300 mm lens, to get better tracking and more portable I have built a new tripod from a Manfrotto. Shorter legs, no centerpillar.

http://www.astrofriend.eu/astronomy/projects/project-star-adventurer-tripod/01-project-star-adventurer-tripod.html

I have also made some modification to the wedge to get it more stable:

http://www.astrofriend.eu/astronomy/projects/project-star-adventurer-modify-wedge/project-star-adventurer-modify-wedge.html

 

I have sometimes used a big ballhead, but to weak in combination with the 300 mm lens. I will built something else to replace it later. Maybe something I can do with the 3D printer I have ordered.

/Lars