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M31, WO Star 71, DSLR

lensman57

By lensman57
in Imaging - Deep Sky

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lensman57

lensman57

Posted
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Hi,

I got home from work last night , early this morning infact and about 1.00 am the clouds vanished. Even though I was tired and hungry I set the mount and the scope out and went for M31 using my Baader modded Canon 1100d witha dirty CLS clip filter as I have not used the DSLR for a long while and i was not in the mood ot give the pre imaging clean up at 2 am, I just wanted to make use of the clear spell. As it happenes quite a few gremlins were at work last night including the APT refusing to operate the shutter on the 1100d even though the livview work work so in the end I used Nebulasity 3 for capture. to top it all up the flats have not worked either so I am glad that i could get this out of the session.

21 X 360s @ iso 1600 with 101 Bias, 35 Darks and 31 ( useless ) Flats, stacked and processed in PI and PS.  The image has had a bit of cropping off the edges but in the original image the stars are tack sharp and perfectly round  right to the edges of the DSLR sensor so William Optics claim of the scope having a 45mm image circle is verified and am I glad about it. I also apologise for  having dirt on the sensor and allowing a couple of the stars to get out of hand during the many masking operations. I put it down to tiredness.

Many thanks for looking.

Regards,

A.G

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lensman57

lensman57

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very nice - tack sharp all the way to the corners  :D

And depite the tiredness and issues, a cracking image to boot.

John

Thanks to both John and Anthony,

I am very happy with the scope. The colour correction compared to my Ascension Apo Triplet is superior and the field is flat as in the image. There are a few niggly bits. The scope seems to have been designed with DSLR in mind ( 55 mm back focus again ) with the draw tube terminating with a M48 thread so unless you have a filter box or wheel a 2" filter can't be used or I have not found how as yet. The shade is too short with an extension of 1.5" which is not adequate even though the scope is short and wide but still a longer hood would have been desirable. I also had a bit of a worry about the star shapes in my first two tests M33 and NGC 6820, I even emailed Ian King. To me they looked sort of pinched. For this one I loosened the rings a little and moved up about 1/2" now the stars are tack sharp and round. I may have over tightened the rings over the location of the rear elements perhaps causing stress. The scope will not accept a conventional diagonal either. I have a Baader T- 1.25" mini helical focuser that I have attached to the scope using a low profile M48-T adapter and this allows me to put the EP through for alignment. The focuser is brilliant with only a short throw to ensure rigidity and orthogonality with heavy imaging gear and the action if firm but smooth, I think for once calling a scope an Astrograph  is justified.

Regards,

A.G

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lensman57

lensman57

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Thank you Lee, Gav and Guy. Your kind words are much appreciated. I afor got to mention that although the image had a very mild Deapplied to it during the linear stage of the processing I did not use any Morphologcal itransformation to reduce the stars so the star shapes are as were in the original subs but the effect of stretching.

Regards,

A.G

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lensman57

lensman57

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Nice...How do you decide how many bias, flats, and darks you will use?

Hi,

The number of the calibration frames were dudcted from reading various tests and analysis done by people who know beter than me both for DSLR and Cooled CCDs. It appears that above 70 or 80 bias frames ( in particular For a Cooled CCD ) will yeild a Clean Master Bias virtually free from random noise. I use 101 Bias frames for the master and the one for the image had a Super Bias routine applied in PI to smooth the master out even further, similarly above 30 Darks were found to give a Master with a more representative Thermal noise average. I use between 30 and 50 Flats but some people are happy with just 20 , I guess that it just depends on the camera. scope and filter combination. I do not use any Darks when I use a cooled CCD if the sub length is below 1800s even for my old QHY8, the new Sony sensors are very clean and using 101 Bias with the Super Bias applied and High Dithering in PHD- Nebulasity usually does the trick. A DSLR is a slightly noisier proposition and does require Dark frame subtraction as does a CCD with a Kodak chip.

Regards,

A.G

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NorrinRadd

NorrinRadd

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Superb and thank you for sharing your in depth review on the Star 71. I need a small refractor and I've been anxiously waiting to see what it's capable of.

Really like the core detail you have which is always blown out on a lot of pics. Superb, really nice image.

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