Comet Holmes, complimentary to Jiahao's pictures

[weixing]

Hi,
WOW!! Excellent shot...

Hmm... Just wonder why you choose to take so many frames at 45s exposure ISO800 instead of fewer frames, but longer exposure each?? Your mount should be able to take longer exposure at such short focal length. Is it because the comet is moving very fast, such that without guiding on the comet, the comet in the image will be blur?? Or because of the light pollution causing the image to saturate at longer exposure?? Or the comet is too bright that longer exposure is not necessary??

Anyway, do you think it is ok to take longer exposure without guiding on the comet?? I'll try to image the comet using the Vixen R135 during the weekend if the weather is clear. Since the focal length is quite short, I should be able to get a longer exposure (if I do a good drift alignment), so that I can image the comet at lower ISO to reduce noise, but worry that the comet will move (not doing any guiding on the comet) during the exposure if the exposure is too long causing blurring of the comet in the image.

Hope to hear more advices from all the experts.

Have a nice day.

[Airconvent]

Beautiful! ...its amazing that occupies the same size as our sun..

[VinSnr]

Hi thanks for all the replies, before more questions pop up, I better admit to several mistakes I made in the picture:

1) Its an average of 53 frames of 45 secs each
2) Shot from NUS rooftop, so there is severe light pollution, I used Orion LPR filter. Looks like IDAS LPS is the next item to order. Hehe
3) In a desperate attempt to save the colour distortion due to LPR filter used and its a modfied camera, I roughly white balance it using a Macbeth card shot under flourescent light with the filter on.
4) In the end, I decided to colour balance with a bit of green tone in the picture.
5) To make the focal ratio small, I used a SCT reducer on the Megrez 80, so you can see severe distortions of stars 50% out the field, I cropped and downsampled to make it less visible.

hope all of you learn from the errors I made. Nevertheless enjoy the beauty of the comet.

The photo is incredible considering you took it from NUS rooftop. Look like the filter did work well? Never mind all the "tweaking", since it is understandable. Infact, it was great that you use your own tweaking methods to get the picture right.

Great work.

[Meng Lee]

Hi,
WOW!! Excellent shot...

Hmm... Just wonder why you choose to take so many frames at 45s exposure ISO800 instead of fewer frames, but longer exposure each?? Your mount should be able to take longer exposure at such short focal length. Is it because the comet is moving very fast, such that without guiding on the comet, the comet in the image will be blur?? Or because of the light pollution causing the image to saturate at longer exposure?? Or the comet is too bright that longer exposure is not necessary??

Anyway, do you think it is ok to take longer exposure without guiding on the comet?? I'll try to image the comet using the Vixen R135 during the weekend if the weather is clear. Since the focal length is quite short, I should be able to get a longer exposure (if I do a good drift alignment), so that I can image the comet at lower ISO to reduce noise, but worry that the comet will move (not doing any guiding on the comet) during the exposure if the exposure is too long causing blurring of the comet in the image.

Hope to hear more advices from all the experts.

Have a nice day.

My setup is roughly 350mm at f/4, and if I do not put the LPR, I will reach saturation at 30s at ISO 800. So my reason for short exposures is mostly light pollution. I think the comet should be far enough that minutes of exposures shouldnt smear (not too sure about that).

I think for DSLR, there is usually a certain ISO range that is optimum. For my 350D, i think it is at 400 or 800. Don't image at too low ISO, because the shadow areas (faint coma areas) are given too little tonal steps, then during the non-linear stretch stage, the shadow areas will posterise. ISO 200-800 should be a typical value for most cameras.

I chose 800 because I am scared of comet smearing also. Then all the 53 frames are stacked on the comet nucleus. But come to think of it now, 53 x 45s = 40mins and the stars hardly trailed. So it seems like that the comet is really far enough, that minutes of exposure will not cause smearing of the comet.

Haha, using the LPR really mess up all the colour balancing! Sigh, now I will need Hutech IDAS LPS filter because its colour balance is much better.

I am no expert, but I hope you can gain from my experience and take better shots.

[Meng Lee]

gosh i hope someone can teach me take this kind of photos

but it sounds like an expensive hobby to pick up!!

If you want, I can give you all the technical details, requirements and specifications on how to carry out astrophotography. I am conducting workshops for schools anyway.

my own opinion is that, indeed it is a very expensive hobby to pick up once you want to do astrophotography. Thats my personal view.

[Razsky]

That is so cool.

[weixing]

Hi,

I will need Hutech IDAS LPS filter because its colour balance is much better.

The IDAS LPS produce good colour balance, but I think it'll also block IR from your modified camera.

Have a nice day.

[Meng Lee]

Oh if it blocks IR also, then that will be good !!! (because save money on another filter). Also, the modified camera will have already caused the red histogram to be shifted widely from the blue and green ones, then if the Light Pollution causes even more shift, then there is a very high chance of overexposing the red channel and underexposing the blue and green channels. So if the filter is already quite well balanced, then it reduces the chance for such problems.

Now everything boils down to $$$$$$$$

[aquillae]

wow, nice comet Holmes pic.

i haven't even had the chance to look at it

[cataclysm]

[quote]The IDAS LPS produce good colour balance, but I think it'll also block IR from your modified camera. [/qu
Imo, Hutech IDAS is not strong enough filter for our highly light polluted sky. For deep sky objects, you have to go with a narrower filter like the Astronomik UHC.