#1  
Old 30-01-2019, 05:14 AM
Ukastronomer (Jeremy)
Feel free to edit my imag

Ukastronomer is offline
 
Join Date: Jan 2019
Location: Llandysul, WALES, UK
Posts: 1,220
Is there any benefit is capturing in low res

As a photographer unless I am sending proofs to a magazine I rarely use low resolution, when shooting sports I always use 36Mp, therefore I was wondering

I have so far only used either my D810 or D4s for imaging, why do dedicated cameras such as the ASI 178MM which IF we EVER get any Sun, I will use for Ha, in programs such as sharpcap offer maximum down to 320x240

Not talking sensor size here just image size


Thanks
Reply With Quote
  #2  
Old 30-01-2019, 07:16 AM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 2,140
Usually those smaller images sizes will be down to “region of interest”

Basically if you are doing lucky imaging and the target only occupies a small portion of the sensor you can increase the frame rate and reduce file size by only reading the data off a small portion of the sensor.

The resolution is the same by way of angular size per pixel. I know you said above that you are not talking sensor size, rather image size, but essentially you ARE talking sensor size in this context.
Reply With Quote
  #3  
Old 30-01-2019, 07:13 PM
Ukastronomer (Jeremy)
Feel free to edit my imag

Ukastronomer is offline
 
Join Date: Jan 2019
Location: Llandysul, WALES, UK
Posts: 1,220
Ah, thanks
Reply With Quote
  #4  
Old 01-02-2019, 09:29 AM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,402
You're really talking data rate. Sensor size and resolution are irrelevant. Colour you capture at least 8bit depth usually more. thats 8 bits per pixel which is a quantity of data size. Multiply by three for the separate R, G and B values to make a 24bit colour image from. This is now 24bits for each pixel or 3 bytes of data. Multiply by the megapixel value in full numeric form to get number of bytes to make up one image. There is a limit to how much total data that can be captured and sent to storage (bandwidth of serial communications, which you'll notice is given usually in Mbps (mega bits per second) again a data size or bandwidth per second. Storage media have there own write rates again in bits per second (notice the pattern yet?). Its a matter of doing the maths, multiplying numbers and you get a huge number in bits to divide by 8 for bytes then divide recursively by 1,024 for kilobytes, megabytes etc. So yes a 36 megapixel image gives you lots of detail but when you're only interested in a small portion you are wasting most of the bandwidth, so capturing at a reduced resolution as Paul mentioned lets you capture more frames in the same amount of time as its making more effective use of the bandwidth of how much data can be transferred from the camera and written to storage media. Slow storage means loss of data due to the writing bandwidth bottleneck.
Reply With Quote
  #5  
Old 05-02-2019, 09:03 AM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 2,140
An obvious example was me playing with my new camera (ASI294) it is not really set up for planetary imaging but I will be giving it a shot anyway.

Using the ASICAP software as APT does not seem to recognise this one for capturing multiple frames, if I let it produce video and run it in full resolution it produces a couple of frames a second due to the read time, where if I pulled it down to 1/16 of the sensor it jumped up to near 200fps.

I did not investigate further at the time but that may or may not have been limited by my exposure settings. Obviously if you are exposing for a hundredth of a second then the best frame rate you will be able to get will be somewhere slightly below 100 frames per second.

Again, it is not "Low res" as such, just reduced area on the chip. The software even calls it basically that, "Region of interest"
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 09:39 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
EQ8-R
Advertisement
Lunatico Astronomical
Advertisement
Star Adventurer
Advertisement
Celestron RASA
Advertisement
Astromechanics
Advertisement
Bintel
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement