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ngc 891


alacant

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Hi everyone

I'm trying to convince myself I don't need an OAG. There's star elongation -I think- this may be due in part at least to the PHD2 error corrections being greater in RA than in DEC. The PHD2 gurus suggested that dither may also be a factor, so half the frames here are not dithered. They also suggested the near impossibility of being able to guide a 6" f8 Newtonian without an OAG.

Anyway, 2 nights of experimentation with and without dither, breaking down and tightening with proper screws, neoprene shims to stop the mirror moving, springs over the primary lock screws, llaves allen y inglesas... Do you notice the elongation?

Thanks for looking and clear skies.

700d + nt150l; 3 hours frames of different lengths 30s to 6m

891phd2trial.thumb.jpg.bea5d2c0c037eecb2b95f32cbea428e1.jpg

 

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Not at 100% full size so I wouldn't worry about it.

Very nice image, just taking some flats to see how my version has come out so far, if it's anywhere near as good as yours I'll be well pleased.

I should think an OAG on a Newt' would cause problems anyway with focus travel and balance.

Dave

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Nice one, dust lane detail is there, not enough star elongation to detract from the end result in my humble opinion.

I’m currently working on a wider field image which will include the galaxy cluster Abell 347, assuming they’ll be visible in my final image.

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13 hours ago, tomato said:

wider field image which will include the galaxy cluster Abell 347

That's an interesting project. Just had a quick look in CDC. It looks as if 750mm will fit in both 891 and a lot of the little galaxies. Do you have enough frames for an interim view yet? 

Cheers and clear skies.

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14 hours ago, Davey-T said:

an OAG on a Newt' would cause problems anyway with focus travel and balance

Hadn't thought of that. I've about 25mm inward focus left and at f8, there's no corrector to have to worry about, but yeah, the extra weight would probably be difficult to balance. Are there OAGs designed for Newtonians I wonder, or are they for refractors only?

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The OAG is primarily a tool for reflectors because of the issue of mirror flop which the guidescope doesn't 'see.' I've never used one on a refractor, though you can. If you have the back focus I'd go for it.

I'd be very reluctant to give up dither with a DSLR, too.

Olly

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12 minutes ago, jjosefsen said:

the dust lane

Yeah, I'm trying to picture what's happening. If we're seeing it edge on, then the dust lane must divide the galaxy into 3 layers, stars:dust:stars maybe? Or could it be there's dust only at the side toward us but outside the galaxy?

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2 hours ago, alacant said:

Yeah, I'm trying to picture what's happening. If we're seeing it edge on, then the dust lane must divide the galaxy into 3 layers, stars:dust:stars maybe? Or could it be there's dust only at the side toward us but outside the galaxy?

Makes sense that the dust is in the middle of the galaxy when edge on, as it is also affected by the spin of the core. In my mind atleast.. ☺️

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