Question regarding imaging OII/Ha etc

[Eri]

Ok so i've been here for a while now lurking alot, reading more, posting a bit and I think that i've come to the conclusion that my current imaging of just slap the camera to the scope while works for alot of the DSO's i've gone for so far could be improved by the use of filters (now you're all most likely politely thinking Duh of course    )

My questions i suppose are:

0. is there a QSG post/website that explains the following questions?

1. what do the filters do? i suspect they block or certain wavelengths and allow others?

2. what filters are needed for a "whole" colour picture?

3. How do you take the images? is it a case of e.g. 1 hour with OII 1 hour with Ha etc using a set exposure time say 30*2mins ? or do certain filters give better results with different exposures OII =  30*2min Ha = 30*3mins

4. How would I fit the filters for my camera (Canon EOS 700D) I've seen an astropix? filter item that fits infront of the sensor in the body but I've also seen filters on FLO which are too big for that but too small for the 2" adaptor

*edit*

also I see mosaic mentioned what/how are those done? are these an image of one section of say M42 then move to the running man and image that and stitch together in DSS or something?

[Joel Shepherd]

Answers to some of your questions ... also, I'm no expert and others may fill in or correct.

* Filters effectively block most wavelengths of light and only allow through light in certain specific frequency ranges. An appropriate filter can dramatically increase contrast and greatly reduce the effects of many types of light pollution and moonlight (e.g., a hydrogen-alpha -- Ha -- filter on an emission nebula).

* Depends. There are many ways of combining "colors" from different filter types. Typically lights from Ha, O-III and S-II filters will be combined, but depending on the effect you want there are different strategies for assigning colors to the light captured with each different filter type. Google it. :-)

* Folks tend to take the same number of lights with the same exposure time for each type. More Ha may be collected as it is used for luminance/brightness as well as (typically) red.

[Thalestris24]

Hi

With a dslr you've got a built-in colour filter called the Bayer Matrix which is bonded to the sensor (it can be removed, but...). There are a couple of others that you might be able to use with advantage e.g. 1) a light pollution filter 2) a uhc filter. The other filters you mention are narrowband filters which are best used with a mono camera and which only pass a very narrow range of light wavelengths. There are also (l)rgb filters which enable monochrome cameras to create colour images by combining separate red, green and blue exposures (plus luminance). Some people have used a h-alpha narrowband filter to enhance emission nebula images (using a astro modded dslr). Narrowband filters are quite expensive, can be awkward to focus and require long exposures (20min+ ).

Hope that helps

Louise

ps you seem to have managed to take some decent images with your 700d

[Eri]

thanks for the replies guys, I'll stick with the current 700D for now and look at getting a CCD at some point later on when I'm happier in my processing

[swag72]

I'd be careful at this stage what filters you even both with ........ a LP filter would be good (if you live in a place with LP!) and the Astronomiks clip range works well with a DSLR.

[wxsatuser]

Quite honestly,  forget the filters with a dslr, it's one shot colour.

Settle for that or spend out on a mono CCD.

Apart from the LP filter, if you have LP, is most likely all you need.

[ollypenrice]

To answer your question on mosaics, you simply take a series of pictures which have a decent overlap with their neighbours. Beginners should start with a generous overlap of 15 to 20%.

These are then combined in the software of your choice. Microsoft ICE is free, Autopano Pro is a sophisticated package for daytime and nighttime pictures, Registar and Pixinsight are dedicated astronomy packages.

The greater the number of panels, the harder it is. Gradual changes in colour balance and brightness build up, as do distortions due to field curvature. 

Olly

[swag72]

I've got a little bit on my website specifically about mosaics http://swagastro.weebly.com/building-a-mosaic.html.... That puts in pictures what Olly has just said, maybe easier to visualise.

[Eri]

thanks for the replies regarding mosaics olly and Sara, that helps alot and I've bookmarked your website for future reading, I have an idea on a mosaic i'd like to create now but i'll keep it as a hopefully nice surprise be a nice project for this year