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Old 18-05-2015, 09:37 AM
algwat (Alan)
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Seeing Red

Gidday All,
this may have been seen before....

I have an EON80mm Orion and Canon 450d unmodded.

When I use this combo I get rather red backgrounds from my suburban back yard. At ISO 1600 for 45 sec's , always guaranteed.

So, I tried to resurrect an old MEADE ETX90 on my EQ6 and with the same camera. I don't see the red background, my be just a very little at ISO 1600 and 45 sec's subs. I took it upto 2 min's and the red back ground was still barely noticeable. A good option for me if i can lock it on to my rig correctly. May be to make it a spectrscope, with SA100.

The question is, What is changing the red character of the background?
Am I seeing warm air trapped in the EON80? Perhaps the glass characteristics? Or the cold mass of the ETX90 mirror?

If this change of optics rig makes for better backgrounds, then coolling a dslr seems a bit dramatic?

I'll added a few picture shortly.

regards, Alan.
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  #2  
Old 18-05-2015, 12:47 PM
algwat (Alan)
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Added image, last two are of comet master.

All unmodded 450D at iso 1600 45 sec single frame.

Left Sanyang 500 mm lens, middle EON 80 mm Orion, right ETX 90 at prime focus inline.

Sanyang look best but has sloppy focus.

Any thoughts most welcome..

rgds, Alan.
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  #3  
Old 18-05-2015, 01:29 PM
DJT (David)
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Hi

The ED80 has a focal length of 7.5 (faster), the ETX90 has 13.5 (slower).

The ED80 is gathering photons much faster than the EDX which basically means you are hoovering up all that lovely light pollution (the red stuff) far more efficiently than you would with the ETX. Always gonna get you from suberbia.

Buy an LP filter, a clip in for the camera could be the way to go, if you are going for deep sky objects with the 80 but you will see an immediate difference.
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  #4  
Old 19-05-2015, 08:39 AM
algwat (Alan)
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Ah, thanks david.

I'll concentrate on the Orion with shorter but more subs. Which will help as my rig is not guided and not totally aligned up.

Or if that fails, move to a darker sky.... 8)

regards, Alan.
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