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alacant

auriga nebulae

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Hi everyone

Slowly coming to terms with wide field processing and am pleased with the €60 Takumar of 1972 vintage. Modern lenses seem far less sharp and seem poorly corrected by comparison. Or maybe I've only tried bad ones. I get the feeling I'd have to spend €silly to get anywhere near Asahi quality...

Anyway, coming from -relatively huge- reflectors, you notice the acute lack of aperture. I suppose at most you have around 40mm, so even 5 minute exposures get you nowhere. This was close on 4 hours, all perfectly executed from guiding and alignment, through meridian flip and realignment to the not-a-single-dropped-frame capture via the EKOS scheduler; all I did was hit start and left for the new year celebrations. Linux reliability par excellence:)

Don't like the bright stars. I think this is due the lens diaphragm. Anyway, thanks for looking and any suggestions for technique improvement most welcome.

700d + takumar 200mm

855097647_auriga(copy).thumb.jpg.0ddd40fca86c8fcc08a184c6733fdac4.jpg

Edited by alacant
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Nice image.

I've been thinking about these aperture blade defraction spikes. Would it be possible to use various sized rings, cut from card or preferably plastic, that you could mount into a filter holder to get the same stop down, but without the little angles where the aperture blades cross that cause the defraction spikes?

Not sure if the stop down needs to be inside the lens rather than outside at the front!

Edited by Stargazer33
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Beautiful view of a number of bright nebulae in Auriga.  However, I would also be interested in your imaging of the fainter Sh2-224 some 7 degrees north and Simeis 147 some 5 degrees south since they would show nicely in such a field of view.  nebulaeman

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Wow that’s beautiful, worthy of framing.

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Given how easy it is to make a front aperture mask I'd say it might be worth a try.

APERTURE%20MASK-M.jpg

Olly

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Some of those early Takumars are very sharp. I have a 35mm f/2.0 you could shave with. Only problem, the thorium glass in the last element. I've measured alpha, beta, and gamma from that lens.

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Very nice!

Why did you not use the lens at full opening? Then you would not have had those star spikes created by the iris blades moving into the optical path. If the lens does not perform well at full opening (odd looking stars in the corners) then you should stop it down with aperture rings. You could cut them from cardboard but step-down filter rings cost almost nothing on ebay (where I got mine). Made a quick search and found these:

https://www.ebay.co.uk/itm/Lens-Filter-Step-up-Step-down-Rings-set-18pcs-37mm-82mm-82mm-37mm-as-hood-fr/161886367752?hash=item25b12df008:g:nbYAAOxyOlhSs7Xp:rk:1:pf:0

Edited by gorann
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21 hours ago, gorann said:

Made a quick search and found these:

Yes, of course. Thanks. I already have some. Looks as though I'm gonna need 58mm (the takumar filter thread) down to... Any idea for f5.6?

Cheers and clear skies.

Edited by alacant

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6 minutes ago, alacant said:

Yes, of course. Thanks. I already have some. Looks as though I'm gonna need 58mm down to... Any idea for f5.6?

Cheers and clear skies.

To calculate your f number I need to know what Takumar you have (FL and f number). If it is a 200 mm f/4, that means that your aperture (=front lens diameter) is 200 / 4 = 50mm. So to get f/5.6 you need to stop it down to 200 / 5.6 = 36 mm.

So, f number = focal length / aperture

Edited by gorann

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1 hour ago, gorann said:

So to get f/5.6 you need to stop it down to 200 / 5.6 = 36 mm.

Yes. It's the 200f4 so perfect. I'm on it. Cheers.

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6 minutes ago, alacant said:

Yes. It's the 200f4 so perfect. I'm on it. Cheers.

Yes, though there will be some inaccuracy deriving from the precise positioning of the front mask. You could plate solve an image to find out the effective focal length of the system.

Olly 

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1 hour ago, ollypenrice said:

Yes, though there will be some inaccuracy deriving from the precise positioning of the front mask. You could plate solve an image to find out the effective focal length of the system.

Olly 

That comment made me a bit confused Olly. How could stopping it down affect the focal length? I though it would only reduce aperture and thereby focal ratio.

Edited by gorann

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19 minutes ago, gorann said:

That comment made me a bit confused Olly. How could stopping it down affec the focal length? I though it would only reduce aperture and thereby focal ratio.

You're right, Goran. I've spent over four hours today lying on concrete in the freezing cold unplugging and replugging ethernet cables in our robotic shed at the behest of the owners and my will to live is at an all time low! It is the precise F ratio will which will be hard to define. Humble apologies!

Olly

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31 minutes ago, ollypenrice said:

You're right, Goran. I've spent over four hours today lying on concrete in the freezing cold unplugging and replugging ethernet cables in our robotic shed at the behest of the owners and my will to live is at an all time low! It is the precise F ratio will which will be hard to define. Humble apologies!

Olly

You are very much excused!?

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Can't fault your capture, that's a cracker of the area.Mark

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