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Old 15-09-2012, 10:06 AM
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OneCosmos (Chris)
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Flattener vs Flattener/Reducer

Hi all,

I am finally about to bring out my TMB/APM 152mm from the UK - about time after three Astrofests using the humble but capable Meade 80mm.

I don't currently have a field flattener for the 152mm and so am looking at options. APM sell a Riccardi 0.75 flattener/reducer for my specific scope and they also sell a dedicated flattener for the LZOS Triplet I have. I will be using the QHY12 camera.

Of course I understand the advantages of f6 over f8 and also the advantages of 1200mm focal length of 900mm but I am wondering if anyone has any thoughts on which is the best way to go? For example would I actually get better results with the flattener notwithstanding the longer exposures required? Is a reduced image size really the only downsize to the reducer?

Thanks,

Chris
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Old 18-09-2012, 07:43 AM
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OneCosmos (Chris)
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Ok, so no takers on this topic? Perhaps let me phrase the problem in a different way.

If the flattener produced f/6 and the flattener/reducer produced f/4 I think I'd be inclined to just use the flattener on the grounds that f/6 is still fast and it would maximise the image size.

The actual scenario though is a difference between f/8 and f/6 and 1200mm vs 900mm focal length. F/8 seems just very slow and I'm wondering if I would regret that decision.

Is there anyone imaging at speeds as slow as f/8 for deep sky subjects and if so, is it a real problem?

Chris
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Old 18-09-2012, 09:27 AM
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Is there anyone imaging at speeds as slow as f/8 for deep sky subjects and if so, is it a real problem?
Chris,

I did some galaxy imaging at f/8 with my RC10 and SX camera (KAF8300 sensor). I found I needed 8 hours of data to get a decent result and more would have been better. Brighter targets would be better, of course.

Cheers,
Rick.
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Old 18-09-2012, 11:01 AM
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OneCosmos (Chris)
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hmm, it sounds like the reducer will be the way to go after all.

Thanks,

Chris
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Old 18-09-2012, 02:11 PM
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hmm, it sounds like the reducer will be the way to go after all.

Thanks,

Chris
Chris, I would also go the reducer way as it will give the scope a new perspective in wider field while still flattening and this will gather data quicker.
Allan
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Old 18-09-2012, 02:47 PM
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It does depend on the size of the pixels in your camera. If you end up undersampling with the shorter focal length you will have a bright but tiny image of whatever you are imaging. If the shorter FL still gives you well sampled images then you can use the reducer with no loss of resolution.
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