My M22 from Jun 22nd

[LT_Ng]

Hi Everyone,

Seldom to post my deep sky images here. Attached is my lastest one taken at the midnight of Jun 22nd in Hong Kong.

That is a test to see how accurate of SX-D in unguided tracking.

6" F5 Newtonian + MPCC + unmodified EOS350D @ iso800 RAW w/internal NR OFF, unguided. 11 x 30s stacked in DeepSkyStacker, ~95% cropping and pro-processed and resized in PS.

Larger size at http://www.astrofarm.net/dbphoto/loadimg.php?id=12840

Seemed not too bad.

LT

[iceman (Mike)]

A nice, widefield image, William. Great job.

Why is it the brighter stars are now square?

[h0ughy (David)]

same question as Mike, why the square stars?

[Garyh]

Nice job LT. I like it!!!
cheers

[LT_Ng]

Thanks for the kind words from all of you.

I am not sure what causes the bright stars being in square shape. I was guessing that is resulted from the strong diffraction effect on bright stars by the 4mm thick spider rods.

LT

[Dr Nick (Nick)]

Nice image, I love it!

[[1ponders] (Paul)]

Nice image William.

You will find a possible answer to the square star problem here in the second paragraph http://www.ccd.com/ccd113.html though undersampling is unlikely to be the cause in this case. Your telescope and camera are a pretty good match.

(btw its a great site if you like to learn about CCDs)

Another reason is possibly from jpeg comression before uploading.

[LT_Ng]

Thank you for the link.

I think the reason why the bright stars became "square" in shape after PS was not due to the jpeg compression. Because the effect was still there before uploading.

My first explanation is the spider rod too thick and the CO percentage too much. This 6" newtonian was originally designed for deep sky shooting with 35mm film w/full frame illumination. So, the secondary mirror is oversized. Those result more amount of diffraction by the spider rod and the CO. I had obtained similar effect w/VC200L. But with your link, I think my guess might be wrong and have to think about it in more depth.

I know you have placed an order for one TVGuider. I am interested in it too. So, once you get it and test it, could you email me of your opinion/comment on it? If it works very similar with some kinds of CCD autoguider such as ST-4, STV, etc., I will replace my AGA-1 with it.

Look forward to hearing your report.

Clear skies,

LT

Originally Posted by [1ponders]

Nice image William.

You will find a possible answer to the square star problem here in the second paragraph http://www.ccd.com/ccd113.html though undersampling is unlikely to be the cause in this case. Your telescope and camera are a pretty good match.

(btw its a great site if you like to learn about CCDs)

Another reason is possibly from jpeg comression before uploading.