Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #61  
Old 29-06-2010, 08:11 AM
sejanus's Avatar
sejanus (Gavin)
Registered User

sejanus is offline
 
Join Date: Sep 2006
Location: Sydney, Southern suburbs
Posts: 683
What you are saying still doesn't ring true or I'm being a complete man-bimbo.

I do expose to the right but iso 100 *does* have less noise than the other iso's regardless of shutter speed etc.

Mind you I'm a high iso guy - I do most weddings at 800-3200 iso but the lower iso's definitely have less noise.
Reply With Quote
  #62  
Old 29-06-2010, 08:47 AM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
If you compare a 1 sec exposure at 100 ISO and a 1 sec exposure at 800 ISO then the second will have more noise. But what about comparing an 8 sec exposure at 100 ISO with a 1 sec exposure at 800 ISO. Both exposures capture the same quantity of photons and Luigi is asserting that you will get less noise in the second case. This seems plausible to me since thermal noise builds up over time.
Reply With Quote
  #63  
Old 29-06-2010, 08:52 AM
sejanus's Avatar
sejanus (Gavin)
Registered User

sejanus is offline
 
Join Date: Sep 2006
Location: Sydney, Southern suburbs
Posts: 683
Quote:
Originally Posted by RickS View Post
If you compare a 1 sec exposure at 100 ISO and a 1 sec exposure at 800 ISO then the second will have more noise. But what about comparing an 8 sec exposure at 100 ISO with a 1 sec exposure at 800 ISO. Both exposures capture the same quantity of photons and Luigi is asserting that you will get less noise in the second case. This seems plausible to me since thermal noise builds up over time.
Ahh, that makes sense now. Thanks.
Reply With Quote
  #64  
Old 29-06-2010, 01:47 PM
Ross G
Registered User

Ross G is offline
 
Join Date: Apr 2007
Location: Cherrybrook, NSW
Posts: 4,996
Hi,

But....would an 8 sec exposure at 800asa have more noise than an 8sec exposure at 100asa?

Ross
Reply With Quote
  #65  
Old 29-06-2010, 01:51 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Quote:
Originally Posted by RickS View Post
If you compare a 1 sec exposure at 100 ISO and a 1 sec exposure at 800 ISO then the second will have more noise. But what about comparing an 8 sec exposure at 100 ISO with a 1 sec exposure at 800 ISO. Both exposures capture the same quantity of photons and Luigi is asserting that you will get less noise in the second case. This seems plausible to me since thermal noise builds up over time.
Sorry, the comment about capturing the same number of photons in 8 secs @ 100 ISO and 1 sec @ 800 ISO is bogus. You will, of course, capture more photons in 8 seconds. I meant that the exposures are equivalent, at least in the traditional photographic sense.

I think I need to go do some research on how image sensors work and think about this some more...
Reply With Quote
  #66  
Old 29-06-2010, 03:57 PM
sejanus's Avatar
sejanus (Gavin)
Registered User

sejanus is offline
 
Join Date: Sep 2006
Location: Sydney, Southern suburbs
Posts: 683
I think I need to do some testing! I don't do long exposure AP when I shoot weddings
Reply With Quote
  #67  
Old 29-06-2010, 10:08 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Quote:
Originally Posted by RickS View Post
I think I need to go do some research on how image sensors work and think about this some more...
OK, I did a bit of reading. There are several sources of noise, but there are effectively two types:
- noise independent of exposure time (e.g. readout noise generated when the pixel values are read from the sensor, amplified and converted from analog to digital). Let's call this NI.
- noise dependent on exposure time (e.g. thermal noise aka dark current). Let's call this ND.

We also need to know that the ISO value doesn't affect the image sensor at all - it determines the amplification used when the data is read from the sensor (and amplifies noise as well as signal).

The reason that a higher ISO in conventional DSLR photography is more noisy is because of NI noise. As an example, let's say this noise is 10 electrons per pixel. If a pixel in the sensor is receiving 100 photons a second and we assume 100% efficiency:
- an exposure of 8 seconds at ISO 100 results in 800 photons being collected and 800 electrons being generated. The signal to noise ratio is 800:10 or 80:1.
- an exposure of 1 second at ISO 800 results in 100 photons being collected. The signal to noise ratio is 100:10 or 10:1.
In the second case the output is amplified 8 times more to give the same exposure, but the noise is a much higher proportion of the result.

The longer the exposure the smaller the impact of NI. I believe that's why Luigi suggested exposing for as long as possible.

Assuming that ND increases linearly (which appears to be approximately correct) exposure time won't affect it's contribution to the signal to noise ratio.

Does that all make sense? I've used a very simple model and the real world is more complicated, but I think this offers a useful insight. I'm also happy to be corrected if somebody more knowledgeable comes along!

Quote:
But....would an 8 sec exposure at 800asa have more noise than an 8sec exposure at 100asa?
The sensor would produce exactly the same data. The only difference is that for ISO 800 the camera would amplify the data by 8 times more which would increase both the signal and the noise by the same amount. The signal to noise ratio would be the same. Of course, in practice this might cause a digital overflow/overexposure, but we all know how to avoid that

Cheers,
Rick.
Reply With Quote
  #68  
Old 29-06-2010, 10:17 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Oh, and another little tidbit...

NI is why bias frames are used. Taking a dark frame with as short an exposure as possible captures a snapshot of this noise by minimizing ND.

ND is why dark frames are used and why you take darks with the same exposure time as lights (keeping the temperature the same is done to keep thermal noise at the same level).
Reply With Quote
  #69  
Old 29-06-2010, 10:27 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Whoa! This thread of mine has really speared off in another direction!

"Widest and fastest lens without curvature" is now a very interesting topic about ISO settings.

It's great info folks, and I thank you very much for it. I think it deserves a thread more correctly titled, so that others can benefit from it.

How about I go create one here?

Baz.
Reply With Quote
  #70  
Old 29-06-2010, 11:56 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
Rick,

The bias is included in the darks and therefore when subtracting darks from lights, the bias is removed automatically.

H
Reply With Quote
  #71  
Old 30-06-2010, 08:10 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Quote:
Originally Posted by Octane View Post
Rick,

The bias is included in the darks and therefore when subtracting darks from lights, the bias is removed automatically.

H
Yep, I see that thanks, H. I understand there is some debate about the value of separate bias frames. I haven't formed my own opinion yet. Maybe once I've finished reading the Handbook of Astronomical Image Processing...

Baz: sorry to derail your thread again. I'll move any further comments to the new thread you created.

Just to add a slight on-topic note: the Image Trends Fisheye-Hemi plugins do a good job of correcting fisheye distortion (IMHO).

Cheers,
Rick.
Reply With Quote
  #72  
Old 01-07-2010, 06:42 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
I'm really starting to think the Canon EF 14mm f2.8L II USM Lens might be the way to go now....grrrrrr.... I hate thinking....

TEDS is selling it for $3200!!! That's dearer than the camera!!
Reply With Quote
  #73  
Old 01-07-2010, 09:12 PM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,827
Baz - these guys are consistently the cheapest I've found in Aus, esp since they opened a store here in Brisbane. Even where you are, it's probably only $25 or so delivered.

http://d-d-photographics.com.au/canonlenses.htm#14

Thoroughly recommend them. I just bought several grand worth of gear from them. No worries. Don't let my wife read this. Don't let my wife read this. Don't...
Reply With Quote
  #74  
Old 01-07-2010, 09:24 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
Yep, I do my shopping there, too.

Great service. If going in, you need to order a couple of days in advance, otherwise you might be in for a shock if you go in and ask to buy stuff over the counter. I drove over 3 hours there to be told they don't usually keep big ticket items in stock. Epic fail.

H
Reply With Quote
  #75  
Old 01-07-2010, 10:28 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
$2389...is that before or after GST? Are there any hidden costs or is that it plus freight?
Reply With Quote
  #76  
Old 01-07-2010, 10:41 PM
luigi
Registered User

luigi is offline
 
Join Date: Jun 2010
Posts: 438
Careful the 14II is a great lens but doesn't have a good reputation wide open. The Nikkon 14-24 F2.8 is much much better. You just need a Nikkon 2 Eos adapter.
Many Canon photographers use the Nikon 14-24 because it's excellent.
Google Nikkon to EOS adapter they are quite easy to find.

At a lower cost you get a 14-24 zoom instead of a 14mm prime and better image quality.


Quote:
Originally Posted by bloodhound31 View Post
I'm really starting to think the Canon EF 14mm f2.8L II USM Lens might be the way to go now....grrrrrr.... I hate thinking....

TEDS is selling it for $3200!!! That's dearer than the camera!!
Reply With Quote
  #77  
Old 01-07-2010, 11:11 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
That's it, plus freight.

Note, it's grey import. No Canon-backed warranty. If your lens screws up, the store will honour your warranty. That is, you don't know who is doing what to your gear. If you're willing to take that risk, then, you save a motza.

H
Reply With Quote
  #78  
Old 04-07-2010, 01:01 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
I hear the stigma around "Grey import" a lot!

From what I understand, the Canon factory in Japan supplies distributors such as Canon China, Canon USA, Canon Australia etc, and from there the online, commercial and shop-front distributors on-sell them.

At the end of the day, all the camera's and all the lenses still initially come from Canon factory in Japan?

So, what does "Grey import" really mean? Why is it so bad?

From what I read on the DDP and DWI websites, they seem pretty legitimate. "Grey import" seems to suggest a degree of shadiness or unreliability. Does this mean they can't be trusted?

Admittedly, DWI and DDP aren't as clear as to whether their prices include GST or not. (I can't seem to find it), so one has to be careful that they are comparing apples to apples with the advertised online prices. I sent an e-mail to DWI to get an answer that they are a Hong Kong based company and if the purchase is over $1000, then you would be chareged a 10% GST on top of their online price.

Surely if you buy a camera from a shop, you take it back with your receipt if you think there is something wrong with it and they take care of it.

Surely if you buy from an online store the same thing would apply?

Or not?

Baz.
Reply With Quote
  #79  
Old 04-07-2010, 01:24 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
The issue with grey market gear is whether the manufacturer will offer local support, warranty and repairs. The grey market retailer may take longer to fix a product you return (e.g. might send it back to Hong Kong) or repair it to a lower standard. They might go out of business too...

Gear with an international warranty (most lenses?) should be cool but camera bodies are a bit more risky to buy grey market.

Cheers,
Rick.
Reply With Quote
  #80  
Old 04-07-2010, 02:59 PM
sejanus's Avatar
sejanus (Gavin)
Registered User

sejanus is offline
 
Join Date: Sep 2006
Location: Sydney, Southern suburbs
Posts: 683
Lenses are covered internationally, so buy them wherever the cheapest is. I get a lot of my gear from adorama.com for example

camera bodies are not covered locally by warranty, so you need to send them back to the country of origin. If you deal with a local importer like DD they will do all that for you.

Given how utterly incompetent canons repair area can be, chances are it'll be returned in about the same amount of time.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 11:45 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
Meade Australia
Advertisement
Lunatico Astronomical
Advertisement
Celestron Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
SkyWatcher Australia
Advertisement
Astronomy and Electronics Centre
Advertisement