Archive for the “Writing” Category

I recently discovered that Takahashi have discontinued making the Sky 90 – mad decision IMO.  And this comes at a time when I was looking to replace the TS80 with a Sky 90 giving me a mini-WASP array with 3 x Sky 90 refractors and a 200mm lens – all with M26C OSC CCD cameras.  By sheer coincidence an astronomer colleague found himself with a mint Sky 90 (collimatable version!!) for sale.  Needless to say I have bought this together with the camera angle adjuster and the f#4.5 reducer corrector.

So the new mini-WASP configuration will be 3 x Sky 90 refractors and a Canon 200mm lens for imaging, and a Megrez 80mm guide scope.

I have this terrible niggle to put a 4th Sky 90 in the frame and use off axis guiding on one of the Sky 9os, but I know that I will become severely cheesed off with the limitations that this sort of guiding will bring.  So at all costs I must resist!!

The new Sky 90 has come along just in time for the longer nights and all the Winter goodies – now all we need are the clear Moonless skies – something that was totally missing last Winter :(

 

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I am in the final stages of setting up a new imaging system based on a Canon 200mm prime lens with M25C OSC imager and a 52 mm IDAS filter on the front of the lens giving me f#3.85 and spikeless images :)  As it is that time of the year an obvious target for testing out the star imaging qualities of the rig is the Double Cluster.  With a horrendous sampling of 7.97 arcseconds per pixel it makes you wonder how it can even resolve stars – but clearly it does :)  Above the Double Cluster we see the rarely images Stock 2 open cluster, which looks like a stick man on his side.  And at the very top/left you can just see the edges of the Heart & Soul nebulae.

Only 16 x 5-minute subs for this one, and very misty conditions too, a LOT of water vapour in the air – however, as a bonus, there was no Moon.

I think this is going to make a good rig for those BIG winter nebulae.  It is NOT a good rig for those single bright star shots as there are terrible ghost flares from very bright stars, probably resulting from all that glass in the 200mm lens.  Well you can’t have it all I guess.

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Put the 5D MkII on the back of a TS80 refractor together with a 5X Barlow (not really called a Barlow then, but the name sticks).

Took 17 subs at 1/200th second and ISO800 which I stacked in Maxim.  This is the result.

See in higher resolution here https://flic.kr/p/oSq5uA

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Managed to capture a few 5-minute subs of comet Jacques when it was close to Epsilon Cassiopeiae on the evening of 22nd August 2014.

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Second upgrade for the week that required the earlier upgrade to go ahead :)

This time the in-storage Sky 90 and filter-wheel have gone back on.  It was taken off over a year ago as I got terrible star shapes with the M26C camera and I put this down to collimation being way out.  Realised later that it was the camera flatness that was way out, but I left the (flattened) camera on the TS80 and worked with that.  Checked the Sky 90 collimation while it was off the array and it looked alright to me.  So now need to see if it is indeed alright next imaging session.  Problem is, the computer that drives this imager decided at this very instant to pop its clogs – there’s always something!!!

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A small upgrade was made to the mini-WASP array this week – can you spot it??

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This is a Solstice-to-Solstice solargraph taken at the New Forest Observatory using the REALLY BIG pinhole camera.

You can clearly see the two New Forest Observatory domes, and the oval-shaped object in the middle foreground is the top of a Teak garden table.

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A friend on one of the astronomy forums asked me if these would be any good for taking flats:

Any good?  They are utterly superb!!!!!!!!!!!!  AND they are cheap!!!!!!!!!!!!!!!!!!  AND you can get an A3 or even an A2 panel (also CHEAP) if you have a large aperture scope.

I think these guys may find they have an unknown market out there for their drawing light boxes :)

 

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I am getting all the bits together to be able to put another Canon 200mm prime lens on the mini-WASP top plate.  I will use an M26C camera from the top TS80 scope and will put an eyepiece (shock-horror) into the TS80.  I haven’t actually looked through an eyepiece in years.

Goods that have arrived so far:

1)  Canon 200mm f#2.8 prime lens.

2)  Set of beefy scope rings to hold the lens and camera.

3)  Several 72mm – 52mm step-down rings to hold a 52mm IDAS filter in front of the 200mm lens.

4)  A 52mm IDAS filter.

5)  A Geoptik adapter for fitting the 200mm lens to an M26C OSC.

I am making up a pair of Aluminium mounting blocks that go between the scope rings and the top plate.  I will put two mounting holes into the scope rings to prevent twist – they only come with one tapped hole.

I am awaiting delivery of a 4th Paramount counterweight as the 3 that are already on there are right at the bottom of the counterweight shaft, i.e. I can’t put any more weight on top until I get the extra counterweight.

I am also awaiting delivery of a whole bunch of Allen bolts for the scope ring mountings.

So it’s all slowly coming together.  I will also put the Robofocus from the TS80 onto the 200mm lens and see if I can get it autofocusing (I know this is a non-trivial exercise).

As it looks like it will be clear tonight, I have put the 72mm – 52mm step-down adapter on the original 200mm lens and fitted a 52mm IDAS filter.  I set the lens to f#2.8 (i.e. wide open) and I will check yo see if there are any diffraction spikes or not.  If there are still spikes I will put an aperture in the Geoptik to cover whatever part of the lens iris is showing.

Busy, busy :) :)

 

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Sergi Verdugo is a very clever chap http://astrophoto-sv.com/index.php?p=1_78 :)

I have been thinking today about setting up a second Canon 200mm lens on the mini-WASP array for the wide field work.  To this end I was looking for 72mm HUTECH IDAS light pollution filters (I have one of these on the Canon 200mm lens I am currently using) and was drawing a blank.  Searching for HUTECH IDAS filters I came across Sergi’s (very nice!) work and found his ingenious solution.

First let’s go to basics and what I did.  I put a 72mm LP filter on the front of the Canon 200mm lens and stopped the lens down (using its internal diaphragm) to f#4.5.  Why did I stop it down?  Two reasons: one so that the filter will work (it is not designed for f#2.8 which is the lens wide open) and secondly so that I get good quality stars across the whole APS-C size sensor.  I also get the 8 highly annoying diffraction spikes around bright stars from the diaphragm thrown in for good measure.

Here comes Sergi’s solution.  Fit a 72mm – 48mm step down adapter to the front of the Canon 200mm lens and put a 48mm IDAS filter in that.  You automatically stop down your lens to f#4 where the filter will work and you will get good star shapes.  In addition you can now work with the diaphragm wide open – so no diffraction spikes – how brilliant is that then?

I bought the 52mm IDAS filter instead of the 48mm, so I get a tiny bit more speed out of the lens, and I bought a 72mm – 52mm step-down adapter from e-Bay.  I already have a 52mm – 48mm step-down adapter, so I can put in my 48mm narrowband filters when I want to do some narrowband work – and all with no diffraction spikes.  How cool is that then?

Thank you very much Sergi, a great solution – and one that I should have come up with years ago – and didn’t.  I guess I’m getting old.

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