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Great new book

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Sheridan's picture
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Great new book

The Dark Skies of the North Pennines: An amateur photographer's delight
by Graham Relf FRAS

This book was reviewed in the August 2014 Journal by David Arditti, who was very critical of the style and content. In my view this book is aimed perfectly at those who want to get into astro-imaging anywhere in the world, not just the North Penines. Indeed Graham is able to identify what the beginner needs and how to achieve it, better than David who is uses expensive equipment and techniques out of the beginners' league. If you like a didactic style, and in this instance it is the best approach, then I would thoroughly recommend it. Ignore David's other criticism about the need for dark and flat frames and auto-guiding, as this simply complicates it for beginners. The general consensus of David's review was that it was "a little mean-spirited".

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Hi Sheridan,

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.

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Calibration frames

Surely the quickest way to put an absolute beginner is to say that calibration frames are essential. Once the beginner has mastered the basics, then they should be encouraged to look into ways of improving their images.

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Hi Sheridan,

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.

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To calibrate or not to calibrate

Hah! The old “to calibrate or not to calibrate” debate! My view: calibration is needed on scientific images, where one intends to extract data, such as photometry. But if it’s purely for images, then the choice is yours. The proof of pudding is in the eye of the beholder (to mix two sayings). I have seen many wonderful images which were not calibrated, which also convey the beauty of the night sky. I also think that for beginners, who may be keen to get their first results, then there is no real issue in not calibrating - they can move onto that later.

A similar debate has run in CCD photometry on the use of photometric filters (he ventures, not really wishing to trigger another subject of debate). There is certainly a place for using these, depending on the objective of the work. But I have noticed that some beginners have been put off even starting CCD photometry because they are worried about getting V filters etc. I say: have a go unfiltered to start with and select you targets with that in mind. If you find you like the work, then by all means invest in filters later.

Go well!
Jeremy

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David Arditti's review is

David Arditti's review is well-constructed and not quite as negative as Sheridan's words make out. Looking at other comments about the book on the Web, it is clear that Graham has several objectives in writing/producing the book and so it will definitel;y appeal to several audiences. How well it satisfies the budding astrophotographer is possibly a bit like asking the proverbial 'length of string' question. Maybe David is indeed expecting too much of an in-depth approach. I see that Graham is a member of the Tynemouth Photographic Society and I can imagine it could have a strong appeal amongst amateur photographers especially if they can exploit local dark skies.

Richard

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P.S.

Back in April, Graham e-mailed a number of BAA folk, but which did not include David A., the following: "The astronomy content is at a very introductory level. One aim is to get existing photographers out there to be as amazed as I have been in recent years by what can be done with ordinary digital cameras as long as you get away from the light polluted towns. The book should also be useful to those who are already astronomers but have not yet tried photography (Part 3 is about practical techniques and every photo in the book has full details of how it was taken).

Another aim is to get youngsters interested in something technical. The book is intended to be suitable for school pupils.

Hopefully this puts the book more in perspective.

Richard 

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Target audience

I think we ought to go back to the subtitle, which explains what the book is about. David says "But I disliked the didactic style and felt the author had not thought-through at what audience it was aimed" both Graham and I were definite about the target audience as the subtitle says. Personally I prefer a didactic style, and obviously Graham does too, saying you dislike the didactic style is like saying you didn't like the font or size of the book. Many people I have spoken to say they thought the review a bit nit-picking. The review will inevitably result in a loss of sales so Graham feels he will be out of pocket on his first self-publishing venture and we have lost his goodwill and membership.

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Callibration vs camera budget

I'd be curious to know how many widefield DSLR astrophotographers do or don't callibrate their frames. I think a lot comes down to what camera you're using.

About 10 years ago, I started out (I would imagine like many beginners) doing astrophotography with a very low-end camera. I found a compact Canon Powershot can get you nice pictures of M31, M42, etc, but I absolutely had to callibrate those frames because the sensor was rubbish. The same seems to be true of low-end DSLRs, e.g. a Canon EOS 1000D produces rather scratty frames at ISO 800 or 1600, yet I've seen many astrophotos in online forums taken with it. Yes, you can get impressive images without callibration, but you can do a lot better with.

I don't doubt that if you use a Canon EOS 5D (I think the camera Graham uses?), you can push it to a very high ISO setting and still get nice clean images. But I wonder how many beginners are willing to splash out on such an expensive camera?

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Wide field imaging & calibration

Most of my experiments with a DSLR were with camera lenses on an old Canon 300d - so widefield mainly using fixed focus lenses - 8mm, 50mm and 85mm.

I found images were always better with dark frame subtraction.

I was never really sure how to do flat fields for 'wide-field' lenses - so never did.
I did use processing techniques for 'synthetic' flats, though, using IRIS.

I have a new camera, Canon 600d, now, but not done much with it so far. 
I expect it has much lower noise that the 300d, but whether it is neglible in exposures from 5s to 10s I have yet to measure.

Callum.

 

 

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We all have to start

We all have to start somewhere, from 'getting our eye in' on the planets, discerning faint detail in comets and galaxies, getting fine resolution on double stars, and making judgements on intermediate magnitudes compared with reference stars for the variables. So not surprisingly digital users also have to start somewhere.

Whilst I've not read the book either, it seems a wider readership is served by starting with basics (which experienced, almost professional, observers can skip or disagree with), though to some pretty detailed material in an appropriate context for advanced amateurs.

It would be interesting, for instance, to know about Damian Peach's first/early efforts in order to attain Hubble quality images nowadays. Would he have been overawed by talk of calibrations?

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Why calibration is NOT needed for beginners

If you subtract a dark frame you are ADDING more random (thermal) noise, just as much as if you add a real data frame to the stack. If you add enough frames the random noise eventually smoothes out, and this happens whether they are dark frames or data frames. But with dark frames you are adding only noise, not signal. Therefore it is better to stack as many real data frames as you can. There is no problem using 100 data frames! Mechanical shutters in DSLRs are rated at well over 100,000 operations (MTBF) and in compact cameras the "shutter" is electronic and so should have no practical limit (something else will fail first).

So the key is to use MANY exposures and appropriate stacking software. (Fixed-pattern noise and bad pixels are smoothed out by the fact that images taken on fixed tripods or unguided EQ mounts are all shifted in relation to each other, which the stacking process addresses.)

As to the idea that you cannot use bottom-of-the-range cameras, that is also wrong.

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Calibration frames

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.

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Loss to the BAA

The trouble is that as a result of David's (over-critical in many people's opinion) review we have lost an extremely valuable member of the Association and section webmaster. The Computing section's future is in jeopardy as the workload has increased to a level that I'm not happy to bear without such a skilled and knowledgeable webmaster.

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Loss to the BAA

Hi Sheridan,

I am very sorry to hear that Graham has left the Association. He contributed a great deal to the Computing Section, for the benefit of all.

As mentioned by Nick, the Letters column in the Journal gives recourse to reply to any comments about a paper, review or observation. Graham could take this route to support his book and his imaging techniques.

In the latest 'Sky at Night' Pete Lawrence demonstrated how beginners can take aesthetically pleasing images of the night sky with a 'standard' camera. Oh dear, but he didn't explain how to take and apply dark frames and flat fields, etc. Should those scenes be re-shot with this vital information? Of course not!

We all started on that path, were pleased with our results, then found out that we could improve our images by stacking them, applying calibration, etc.

I hope Graham stays with us.

Clear skies,

     Alex.

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Loss to the BAA

Alex, I'm afraid that Graham has gone for good as a result of David's unfair review. What of the future for the computing section? I wonder why David has not defended his review in public?

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Calibration frames

All
I have imaged with various Canon DSLR's over the past few years I have had to rely upon software to fix as far as possible any defects in my images, hot pixels & amplifier glow on the older cameras especially. I have now started to use calibration frames and to be honest there are more benefits than disincentives in my opinion even though my latest camera has the best sensor from a technical point of view
I did a quick poll at my Astronomy club tonight amongst the DSLR users, most did not use calibration frames, but acknowledged they need to get into the habit of calibrating their data to get the best results. There is nothing difficult about calibration frames compared to focussing on a subject you cannot see in the viewfinder or looks grim on the rear screen. Calibration frames are easy especially with the DSLR control programmes now available.

Tony

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End of discussion

Please let's end this discussion. There have been some very good postings, but I still think that the absolute beginner should experiment with simple images, and only then graduate to using calibration frames. Graham's book is aimed at absolute beginners and should have been reviewed as such.