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  #41  
Old 22-03-2016, 03:52 PM
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Originally Posted by rustigsmed View Post
if the moon was lowish in the sky it could be some atmospheric dispersion rather than the scope. if you put the photo into RegiStax and choose RGB align (from memory) it can often offer some improvement.
I think you may have nailed it. With that telescope the resolution of the camera's sensor works out at about 0.5 arc second per pixel, so atmospherics would be a likely culprit. I thought of aligning RGB but looking at the channels separately (with the G channel showing more detail) and the overall relatively poor quality of the image I did not think it worth the bother.

Easy way to settle it is to take more shots with the Moon nearer to zenith, which I will certainly do.

PS. I don't even need to do that. Closer look at the photo reveals colour shifted uniformly across the whole photo: up for the blue end and down for the red end of the spectrum. It could still be miscollimation but it would be a little bit of an unlucky coincidence if the miscollimation matches up with the up-down direction in the sky.

Last edited by janoskiss; 22-03-2016 at 04:06 PM.
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  #42  
Old 22-03-2016, 06:09 PM
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I had another look at your image after my last post, and realised that it
couldn't be CA because I could see yellow as well as violet in and around the craters. The violet was also too intense. So I came to the same conclusion, but Russ beat me to it.
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  #43  
Old 23-03-2016, 01:51 AM
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You were right raymo (& Russ), there is no CA from this scope even at the edge of frame. Here are a couple of the Moon in RGB through thin clouds at around 70 degree altitude (with a counterweighted and roughly SCP aligned mount with tracking on).
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  #44  
Old 23-03-2016, 08:42 AM
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Quote:
Originally Posted by janoskiss View Post
You were right raymo (& Russ), there is no CA from this scope even at the edge of frame. Here are a couple of the Moon in RGB through thin clouds at around 70 degree altitude (with a counterweighted and roughly SCP aligned mount with tracking on).
that's good news
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  #45  
Old 23-03-2016, 10:47 AM
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  #46  
Old 23-03-2016, 03:37 PM
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Keen to hear your thoughts on the D3300. I just ordered one purely for AP - figured it was better to stick with Nikon, for which we have about $8000 worth of lenses, rather than needlessly start down the Canon path. It worries me slightly how very cheap it is; is it okay?
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  #47  
Old 23-03-2016, 04:10 PM
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You have nothing to fear but fear itself. The camera is fantastic value for money. It's classed as a "beginner's" DSLR because it's lacking fancy features and "only" has 11 AF zones. (First thing I do with any camera for normal use is change AF to centre only; almost always shoot by aiming at what I want in focus first and getting AF to lock in on it.)

The "Effects" mode and all the effects therein are very gimmicky (childishly so) and just removing that from the dial altogether would already make the camera seem more professional. But who cares! The other thing about the whole beginner vs pro camera thing is that you have to go into the menu to change things that on more expensive cameras are more immediately accessible. But again for astrophotography, for the most part, who cares!

As far as the performance of the sensor goes it's only within a couple of f-stops (2-4x ISO) of some fairly recent pro cameras costing several $1000. It's within about one f-stop / 2x ISO of the Canon 5D Mk II & III in terms of low light performance and noise. At least they're my initial impressions (friend of mine has a 5D Mk II). But maybe on long exposures the thermal noise will get worse with the smaller DX sensor. But still, for <$300 one can't complain. And it's great that you don't need to be so precious about it because it's inexpensive. It's small and light as well.

For the money, you cannot go wrong; in fact you could do a lot worse for a lot more. But you really should be asking these questions before buying the camera.

If you already have so many lenses then it's a no brainer. Even if you don't the F-mount is probably the most backward compatible mount ever made. There are tonnes of decent old film camera lenses available on the cheap. The DX sensor format is especially kind to lenses designed for 35mm film.

Last edited by janoskiss; 23-03-2016 at 04:31 PM.
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  #48  
Old 23-03-2016, 07:50 PM
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Glad to hear it!

I guess I worry about noise. We had a D7000 years ago and I was fairly unimpressed with its low light ability; I expect the D3300 to be less adept, being significantly cheaper. But then I know how remarkably far cameras have come in the past five years, so maybe it'll be better. DxO Mark suggests it is, though I always take DxO with a grain of salt.

Yeah, even the D750 has the gimmick modes in there - Sketch Mode, Miniature Mode... what on earth were Nikon thinking? Who is there spending $2k on a body who wants that nonsense? Our cameras have never been off Manual mode shooting RAW anyway. And I'm with you on the focus points, I switch all ours to 11 points regardless of how many they come with.

Either way, it'll be fun to have a little DX again - and this way I avoid having to learn my way around a Canon for a while longer...
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  #49  
Old 24-03-2016, 12:30 AM
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You can check out the very non-astro comparisons between the D3300 and D7000 yourself: http://www.dpreview.com/reviews/nikon-d3300/11

It looks like the D3300 has a tad more noise but it's spread over more pixels and overall there is nothing in it really. I read and watched a lot of reviews before buying it and the consensus seemed to be that the D3300 offers the same raw performance as the D7200 but it's not as feature packed.

But features are lost on me. Just give me a sensor, exposure, aperture, focus and maybe a light meter (what luxury!). Then get out of my way and let me drive my own camera while I collect some photons. Basically I'd be more than happy with a decent Praktica that has a CCD in place of where the film used to go.

I do understand the need for more features for pro photographers who need to be on and always ready to shoot, but I don't like how the industry uses that to manipulate public perception and sell the same gear at hugely inflated prices. Case in point: D3300 body going for around $300; D7200 for $1200. It's basically the same camera apart from the window dressing! But maybe I'm wrong and someone more knowledgeable will put me in my place. I'm all ears. Don't hold back folks. It's the only way I'll learn.
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Old 24-03-2016, 11:26 AM
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Well... most recent models (the D5500, D7100, D7200, D750, D810) are ISO invariant, which is a fairly big deal and worth paying considerably more for - particularly when it comes to low light photography.

Some of the other features are worth having, too. The higher quality LCD display is one. The major lack of controls on the D3300 is going to be very hard to get used to. No aperture preview is a bit annoying. And no ISO button!! Argh!! I know I can assign the Fn button, but I usually use that for spot metering for (I do a lot of stage & live performance photography; admittedly I'm not planning to with this camera, but the lack of proper controls is a definite drawback).

Then there's the fact it's 12 bit instead of 14. The smaller battery & shorter life. The single SD card slot. Etc etc. All this in addition to a clearly inferior sensor - seriously, the sensor in the D750 is insanely good; I wouldn't be surprised if the D750 at ISO 12,800 is better than the D3300 at ISO 3200.

On the other hand, I don't care about the lack of AF motor - I don't own vintage lenses or ever plan to. I look forward to the small size and light weight. It's got the nice new processor and all the video capability of its bigger brothers. Its sensor should (hopefully) do the job. Most of all, the thing costs so little, there's really no right to complain - of course it'll come up short when compared to cameras costing five times as much!!

Anyway. Looking forward to using it, and to seeing some more of your results! Hopefully you're getting clearer skies down there than we are in Sydney...
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  #51  
Old 24-03-2016, 11:48 AM
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Thanks, you make good points.

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Well... most recent models (the D5500, D7100, D7200, D750, D810) are ISO invariant
Can you briefly explain what "ISO invariant" means?
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  #52  
Old 24-03-2016, 12:01 PM
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Okay Chris, ISO invariance is most definitely not a big deal; noise is the
astrophotographer's biggest enemy, and invariance has no effect on that,
and even causes a slight loss of detail in the shadows[with the 750D]. As far as astro imaging goes, all the user reviews show it as pretty much a non event. As far as battery life is concerned, less than $20 buys a 240v adaptor, eliminating the need for a battery. Why would you need more than one SD slot for astro imaging? What does a higher quality LCD screen do for astro imaging? it has zero effect on the images you produce.
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  #53  
Old 24-03-2016, 12:11 PM
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I'd still like to know what "ISO invariant" means.

The battery life of the D3300 is supposed to be exceptionally good (one of the claimed main improvements over the D3200). This guy reckons it "lasts for ever": https://www.youtube.com/watch?v=r8Ksuc7T-VQ --- claims 700 x 20s shots. I have not used it enough to have anything more to say about it. But in any case I would definitely like to get a spare battery to have on standby.
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  #54  
Old 24-03-2016, 12:29 PM
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I read this article on ISO invariance: http://improvephotography.com/34818/iso-invariance/

I get it but it would seem you'd need a lot more than 14 or even 16 bit resolution in RAW. Basically each ISO step (e.g. ISO 1600 to 3200) needs an extra bit (because you're halving the intensity or photon count, if you like, going from 3200 to 1600). So if you want to shoot at ISO 100 and then boost it to ISO 6400 in post-processing and still want say 12-bit colour at ISO 6400, then you'll need 12 + log_base2(6400/100) = 12 + 6 = 18 bit colour.

It's the same as if you want to record audio but don't want to worry about levels. You record in 24-bit to capture quite (-45dB) signals at 16-bits for the final master.

So I don't see how this ISO invariance could work as well as amplifying the signal as it's collected at the sensor.
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Old 24-03-2016, 12:31 PM
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Raymo, I'm not talking specifically about AP here. I'm talking about the differences between the absolute entry-level DSLRs and the pro models, which is what Steve and I were discussing. Surely we all agree that DSLRs and the comparisons between them are meaningless when compared to purpose-designed CCDs. We're talking about what you get for your money when you go beyond the absolute cheapest DSLRs on the market.

ISO invariance, to summarise, basically means that you can underexpose a shot by several stops and not lose any detail (how many stops largely depends on the bitrate). It's explained reasonably well here:

http://improvephotography.com/34818/iso-invariance/

Raymo I know you're a big fan of the entry-level Canons, but I'm gonna just go ahead and disagree with you on their superiority over the ISO invariant Nikons. There's simply no way they can compete with the likes of the D750, or even come close.
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Old 24-03-2016, 12:43 PM
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Steve - yes, it's similar to headroom in digital recording. That's precisely why studios do record in 24 bits in preparation for mastering in 16 bits. It's a good idea.

I actually don't know how it transfers to usage in AP to be honest. Haven't tried it yet, I'm waiting on scope and mount to arrive. But I've used both types extensively in regular photography and I can say it's a relief to be able to deliberately underexpose shots with the knowledge that detail isn't actually lost.

But claiming that battery life doesn't matter because you can just plug it in... yeah I totally and utterly disagree there.

Anyway. Raymo and I probably aren't destined to agree on this. My own experience and reading leads me to different conclusions than his experience and reading has. What's more, it's all beside the point! We're all shooting with entry-level DSLRs. We should be united in fist-pumps for the little guys of the camera world.
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  #57  
Old 24-03-2016, 12:45 PM
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Quote:
Originally Posted by thegableguy View Post
ISO invariance, to summarise, basically means that you can underexpose a shot by several stops and not lose any detail (how many stops largely depends on the bitrate). It's explained reasonably well here:

http://improvephotography.com/34818/iso-invariance/
You must have been typing your message while I posted mine. Yes I've read the article but I'm skeptical for reasons I stated in the above post. I can already do this anyway if I'm happy with 8-bit colour. Shooting at ISO 200 and then upping the gain in post processing by a factor of 8 will give me a virtually identical result to shooting at ISO 1600 = 8 * 200. (I don't actually use a "factor of 8" in practice; that's just theoretical; I just contrast-stretch/normalise each photo.) And that works because I have 4-bits to spare between 12-bit RAW and 8-bit final. So I could even go as high as ISO-3200-equivalent from ISO 200.
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Old 24-03-2016, 12:47 PM
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We're posting out-of sync. Thanks for the feedback anyway. Being new to DSLRs I have much to learn. I'll read your last response now.
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Old 24-03-2016, 01:00 PM
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Quote:
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But claiming that battery life doesn't matter because you can just plug it in... yeah I totally and utterly disagree there.
Yeah, I have no experience but I'd be worried about electronic noise and heat interfering with the sensor.

Quote:
We're all shooting with entry-level DSLRs. We should be united in fist-pumps for the little guys of the camera world.
I like the idea of pushing the limits on a budget and working on things that make the hobby and even some of the science accessible to more people. I found glend's recent posts on de-Bayering and how old cheap DSLRs can be turned into high-performance astro-cameras most interesting:
http://www.iceinspace.com.au/forum/s...d.php?t=139719
http://www.iceinspace.com.au/forum/s...d.php?t=144032
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Old 24-03-2016, 01:41 PM
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Re the last post, batteries do produce heat as they are used and their presence inside the camera contributes to heat build up. If you are shooting a series of long subs, you can feel the warmth in a battery when you remove it as it gets down to lower power after some time at imaging. It is better imho to use a battery eliminator (like the Orion ones), as it does not create heat nor hold it inside the camera. It also makes cooling and sealing a camera much easier as you don't have to open it to change batteries. In my experience heat build up comes not just from the sensor itself but as much from the camera processor. The more 'work' being done by the image processor the more heat it generates. By processing work I am referring to is any programmed feature such as internal dark generation for each image, internal noise reduction, video processing is perhaps the worse, etc etc. Setup for astro imaging varies by camera make and model but you want to minimise the camera doing work that you intend to do in post-processing and through dark, Bias, flat capture. Also watch out for EXIF temperature data that is included in RAW file data, as it is not the sensor temperature itself but is actually captured at the processor. Some modern DSLRs actually have muliple processors, and these generate more heat than single processor cameras. I cannot comment on Nikons or Sony's as I have no experience with them.
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