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Hi Sheridan,
It is true that a ratty dark frame will add noise to the output image but you don’t use ratty dark frames. Since darks are much easier to obtain than light frames you can collect hundreds of them when it is cloudy and median stack them. You then use the clean dark in your calibration process. The same applies to flats and biases. With a DSLR flats are very easy to obtain since you can use short exposures on a bright sky, I even do them in daylight. It is true that if you median clip stack dithered images you can get away without darks but you still need to calibrate the light frame so that you can properly apply the flat. If you don’t you can get significant zero point errors, particularly if you are stacking a lot of short exposures. You can possibly get away without using a flat in dark locations but not where I live.
All of this may be too much for beginners, although programs such as Deep Sky Stacker make it easy to do, but my problem with Graham’s website is that he appears to dismiss calibration altogether and I think that is wrong.
Going back to the original subject I have read David’s review again and it seems perfectly reasonable to me. A book review will always involve some degree of personal opinion and the Journal would be a much worse place if we only ever published positive ones.
Doing anything generally lends to the risk of criticism. That is part of life and it is something that you get used to.
Nick.
Hi James,
The reason for the magnitude limit is that this is roughly the detection limit of my TV system (Watec 902H2 Ultimate + 3.8mm, f/0.8 lens) in individual video frames. Deeper limits are possible with TV systems using longer focal lengths but you then get smaller fields of view.
The frames are analysed using a program called UFO Analyser. This matches stars in the image with a catalogue (see the image below) and then uses this to estimate the magnitude of the meteor throughout its path. The magnitude quoted is the maximum magnitude but the advantage of a TV system is that you can get a magnitude profile sampled 25 times a second.
Nick.
Denis,
That’s a great video. Amazing what Bill managed with such simple equipment and a lot of dedication.
Nick.
Peter,
That is a classic observation but perhaps doesn’t conform to the Meteor Section’s rules!
Pete Lawrence also got it from Selsey and his excellent image is on the spaceweather.com front page today. This has allowed us to confirm that the track started at the Orwell Estuary and ended somewhere around Bradwell on the Dengie so it would have been to the north of you. From comparison with the Moon the terminal burst was brighter than mag -12 for around 80ms or so.
Nick.
Hi Sheridan,
I think there is certainly a debate to be had and you can make the case that mentioning the use of calibration frames can be offputting to beginners. As I said, I haven’t seen the book that was the subject of David’s review, but I have seen Graham’s website here and that appears to go much further in that it says: “This page explains why they are not important – unless you wish to do photometry” and “We have seen that bias frames are absolutely not needed for DSLR work”. I think that is plain wrong, particularly if you live in areas of the country, as many of us do, where the sky is reasonably bright.
By all means tell beginners that they don’t need to use cal frames when they start but don’t dismiss the process entirely. If those beginners are using high-end DSLRs they will ultimately want to get the best out of their equipment and good calibration is required to do that. It really isn’t that hard if explained clearly.
Whenever you publish anything on a subject where there are a range of opinions you need to be ready to take criticism and respond appropriately. Such is life!
Nick.
I met Dame K several times and she was a great character with an amazingly varied set of interests and many fascinating stories. She really hit it off with Patrick and they were very similar characters. Listening to a conversation between the two of them was great fun.
I visited her Coniston observatory but it was chucking it down at the time so it was rather hard to judge the potential sky conditions…
Nick.
Hi Sheridan,
One of the things that you quickly have to gain as an author is a thick skin. Bad reviews are par for the course and, if you think that the criticism is unwarranted, the appropriate action is to send a letter of rebuttal and hope to get it published. I would welcome the return of fiery debate in the letters column of the JBAA as authors (often Patrick) slugged it out with reviewers. Perhaps the modern equivalent is this forum.
In this case I have not read the book and so cannot comment directly but David is one of our best imagers and he is well placed to provide a review. I certainly think that some of his criticism is valid (Graham’s views on the non-use of calibration frames in particular) so there are questions to answer. Let’s have the debate!
Nick.
Quite a few nice Perseids last night. Despite some drifting cloud and a bright Moon I caught 86 Perseids out of a total of 123 meteors on the two cameras. The attached pic shows a nice mag -2.8 Perseid at 00:33:33. You can browse through the other confirmed meteors here.
The current forecast for here tonight looks reasonable too so keep an eye on the live page.
It could have been the lion that was spotted a few years ago but which was never traced. The police deployed many resources including the helicopter to find that.
Anyway, much clearer tonight so some real meteors showing up in the images.
Paul,
Thanks for the visual report. It was also seen from Portsmouth and another NEMETODE camera at the South Downs Planetarium which is operated by John Mason and Russ Slater. William Stewart and Alex Pratt analyzed the SDP data and we have produced a ground track that show that the concrete cows in Milton Keynes should have had a very good view as it went overhead. The original orbit was cometary with e=0.91, i=80, q=0.97au.
Nick.
Gary, Can you download one of the MP4 movies and then just play it in Windows Media Player on your Win 8 machine. The coding of these videos is nothing special and they should play on any modern system, even Windows 8. If still no joy with WMP then contact me offline and we can try to investigate further.
Alex,
I’ve just downloaded the MP4 of Lyn’s talk and it plays OK for me (Windows Media Player under Win 7/64). The downloaded filesize is 65,875,977 bytes. It is possible that it is stuck in a cache somewhere so that your repeated attempts to download it keep giving you the same result. Hopefully time will fix this if you are patient!
Nick.
The meeting videos are nearly done and they should be up on the site early this coming week. I’ll post an announcement here when they are up.
If anyone has any good photos or video clips from Saturday and would be willing to (potentially) have them included in the meeting video please send them to me on ndj@nickdjames.com.
It would be good to see a few thumbnails posted here too. I’ll start the ball rolling with the attached.
Nick.
Alex,
The audio and slides are loaded on my PC so the recording should be up on the site in the next few weeks or so. All the talks were very good but Allan’s stood out as he put Patrick’s life in the context of other astronomy popularisers of the past. He also did a good job of putting some of Patrick’s taller stories in context. Patrick was in a good company since apparently Galileo and Newton did the same thing…
Nick.
Those were the days when comets were real comets not the puny little fuzzballs that we have to put up with now!
Here’s a direct link to the Youtube Vid that Bill mentions. Nice NLC. I haven’t seen any myself so far this year.
Nick.
