Holiday pics

[Graeme Coates]

We're on hols at the moment in France, in the Dordogne region - last year I didn't bring astro kit, but this year didn't make same mistake.

Couple of shots - first of the Scutum star cloud and M11 through a Canon 85mm lens at f3.5 - 6*180sec. Second is a wide field of Cygnus and the Summer Triangle through a Samyang 14mm at f2.8 (12*5min). I think I have issues with the lens (decentralised) so may return it for exchange when home.

V dark here - moon starting to interfere though!

GC

[trevsie7 .]

Very nice.  It just shows how important dark skies are for good imaging.

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[Mike Maunder]

Hi, all.

I'm very interested in comparing cameras and sky conditions after what's been seen here, so here goes.

Just before the clouds and fog bank rolled in on morning of July 21st on Alderney, decided too good a sky to miss, as usual stars not twinkling and Milky Way & stars right down to horizon.

My camera is medium format - Pentax 645Z - with the standard lens of 55mm fl, f2.8.

I set the camera on my bedroom window ledge, set the lens as best I could in dark to infinity and shot away on an undriven bipod, one I use for shooting at Bisley. The most stable of all for camera just a couple of hand spans above the ledge.

I stopped down to f3.2 and gave 20sec exposures at ISO 400. All I've done (same effect in jpg or RAW, can do both on 2 cards) in Photoshop is to correct the colour balance that has the magic effect of appearing to increase exposure several stops.

I'd be interested to know what you make the limiting magnitude when not fully in focus and undriven. The clouds and beginning of sea mist make a nice artistic effect…

The theoretical diameter for the Pentax lens is~19.6mm, but medium format design allows much larger and simpler optics. Thus, the Pentax lens aperture is 47mm almost identical with my 35mm Canon 50mm f1.4 @ 46.7. The light bucket effect seems proved here.

The sensor is CMOS 51Mpix, yielding Jpgs ~ 28Mb or RAW around 58 here.

The image here has been converted "for web' but even then is over 6Mb.

Try enlarging the image ~12-15fold and let me know limiting mag on 20sec exp.

Mike

Incidentally, CMOS is now being produced in curved sheets, opening the way to some amazing future Mak and other telescope designs.

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Mike

Today's thought

"We don't rise to the level of our abilities, we fall to the level of our excuses."

Peter James in his book "Dead Simple"

[J R]

Mike 

That is a spectacular image of a spectacular view.  I don't know about magnitudes but a bit of tweaking here produces what Turner would have killed for.

A curved sensor seems to be the next thing then.  Another reason to put off buying a cooled camera!

James

Sent from my iPad

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<Scutum 2017. 7.21.01.23UT.jpg>

<Curved CMOS Electoptics 2017 July p42.pdf>

[Graeme Coates]

Hi Mike,

 

Really good shot – I suspect you have a much better horizon than we had in France! I’ve got quite some other undriven images to deal with at some point, with quite some gradients to remove – I’ll try and post them when I have them done.

 

I suspect (actually, sure!) that more modern CMOS cameras than the 350d will perform better – amp glow is prevalent on the 350d (but this is now not an issue on more modern cams), and needs effective dark reduction, etc.  Long term, I’d like a larger format cooled CCD to use with longer camera lenses (KAF8300 + 85mm/200mm makes for a powerful combo – especially since widefield narrowband becomes an option).

 

With medium format, you have the advantage of flatter fields (using longer FL lenses which are easier to make – of course, this was always the case, prior to digital). Focusing is tricky, though I have made an ASCOM compatible stepper motor focuser which belt drives the lens so I can focus using the FWHM readings direct from the camera. Liveview would be much better here I have to say! Replacement 14mm Samyang has arrived, so hopefully a better quality example with me now…

 

Graeme

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Mike

 

Today's thought

 

"We don't rise to the level of our abilities, we fall to the level of our excuses."

Peter James in his book "Dead Simple"

 

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