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petemumbower
Pooh-Bah
Reged: 07/12/09
Loc: West Michigan
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Photometry w/ reflector
#5288141 - 06/25/12 10:02 AM
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Hello again, another question from my beginner mind. I am needing to send in my FR for collimation and the FOV w/ my c9.25 & ST-7E is quite small at f/10. So I am considering mounting my 8"f/4 newt and do work with that. But I am wondering if the diffraction spikes will cause any issues when getting the data. I suppose that I will not expose deep enough on a target/companion star to cause this. But can this effect the precision obtainable?
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brianb11213
Postmaster
Reged: 02/25/09
Loc: 55.215N 6.554W
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Re: Photometry w/ reflector
[Re: petemumbower]
#5288284 - 06/25/12 11:27 AM
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The diffraction pattern is the same shape irrespective of the brightness of the star. So it shouldn't affect the precision of measurement.
Most measurement programs will ignore the brightest 20% or so of pixels in the "dark" annulus to avoid background stars affecting the measurement, this will tend to wipe out diffraction spikes unless they're very bright (from bright field stars rather than the objects you're trying to measure).
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gavinm
Carpal Tunnel
Reged: 08/26/05
Loc: Auckland New Zealand
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Re: Photometry w/ reflector
[Re: brianb11213]
#5288979 - 06/25/12 07:26 PM
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or you could get a focal reducer
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Hubert
sage
Reged: 09/26/06
Loc: Belgium
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Re: Photometry w/ reflector
[Re: gavinm]
#5289638 - 06/26/12 07:39 AM
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I do my photometry with a C8 and 6.3 focal reducer. That gives with my ST7 a FOV of 18.5' and 1.4'.
No problem for most of the variables.
cheers, Hubert
http://www.vvs.be/werkgroepen/werkgroep-veranderlijke-sterren
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Hubert
sage
Reged: 09/26/06
Loc: Belgium
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Re: Photometry w/ reflector
[Re: Hubert]
#5289641 - 06/26/12 07:41 AM
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This must be:
A FOV of 18.5' and 12.4'. <-----------------
No problem for most of the variables.
cheers, Hubert
http://www.vvs.be/werkgroepen/werkgroep-veranderlijke-sterren
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petemumbower
Pooh-Bah
Reged: 07/12/09
Loc: West Michigan
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Re: Photometry w/ reflector
[Re: Hubert]
#5289833 - 06/26/12 10:04 AM
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As a clarification, I do have a focal reducer...but I need to send it in to Celestron to fix it. The rear lens is loose and my star shapes are messed up when I use it. The said it might be 3-4 months(yeah really). So I thought to use my reflector for photometry in the meantime. Or pick variables with close companions and check stars.
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NJScope
sage
Reged: 03/08/04
Loc: NJ
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Re: Photometry w/ reflector
[Re: petemumbower]
#5292439 - 06/27/12 10:55 PM
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Peter
Diffraction spikes should not be a problem. I regularly use a VC200L for photometry without negatively effecting precision compared to an 8" SCT.
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