full spectrum camera and filters

[mislav]

hi, i am going to try full spectrum astrophoto... i am waiting my full spectrum NEX 5n camera to come... i have star discovery 150p scope.. i was wondering- do i have to have some extra filters that i can image with this camera?? (with scope and prine focus)... i found somewhere that all will be blured... what i have to do??? (exposures will be about 30sex, no more because of alt/azt mount).. i kbow that i have to buy uv/ir filter for lens if i want to use it for normal terestial imaging...but what for telescope? what for nebulas? etc... i am little bit confused now...i tought that full spectrum camera and scope is enough...

[Handy_Andy]

Will full spectrum cameras you can't achieve focus without some sort of filter, the spectrum is too broad. If violet is in focus the far red shifts out of focus due to the difference in wavelengths. The UV/Ir filter is so that you can achieve focus on nighttime targets such as nebula, you can use it during the day but images will appear to have a red tint as the camera is more sensitive to red then it used to be. The full spectrum mod removes the Ir cut filters which are less selective than astronomy filters and remove somewhere like 70% of light emitted in H-alpha which is what many nebulae are. The infra-red is useful for lunar and planetary shots using either an Ir pass filter or a long-pass red filter, these cut the blue end of the spectrum so that you can still achieve focus. Just note that for pictures taken with an Ir pass filter you won't be able to focus though the viewfinder but you can through a screen.

To use your camera as normal during the day you would use an original white balance filter (OWB), or you can reduce the red during processing of images in Photoshop or the like so long as you take your pictures in raw mode.

 

[drjolo]

If you do not have refractive optics in the optical train, you do not need to use any filters. So for pure newtonian (without any coma corrector), or for example RC telescope you can just start imaging. Once you put any refracting element to the optical train (barlow, reducer, corrector), then image may become blurred and you need to use filters, like Handy_Andy described. 

[mislav]

what is OWB (original white blance filter??? where i can buy that? i cant find it on ebay...so i can start imaging with my 150p...but if i put barlow i have to put uv/ir filter?i have this cheap svbony uv/ir filter...will it do the yob? also have their uhc filter....

[mislav]

will polarasing filter do? or its not enough for white balancing?

[Handy_Andy]

OWB filters take away some of the red like the camera's original filters did, Astronomik do clip in filters for different cameras.

You could set a custom white balance to correct for the red tint if that's available for daytime shots and switch back to normal for astro work, you need to experiment to find out how with your Sony as I'm only familiar with canon.

The uv/ir filter will be fine for the present whilst your still getting to grips with your equipment.

[Merlin66]

Andy,

I need to correct you...

Quote:

""Will full spectrum cameras you can't achieve focus without some sort of filter, the spectrum is too broad. If violet is in focus the far red shifts out of focus due to the difference in wavelengths.""

The optics of the telescope lenses dictate the focus - the camera sensor has no impact on the focus.

I don't know about the Sony, but the Canon, after the mod still has a UV-IR cut capability based on the remaining filter element.

Using standard photographic lenses can be an issue - not so when used with a telescope.

 

 

[Thalestris24]

2 hours ago, Merlin66 said:

Andy,

I need to correct you...

Quote:

""Will full spectrum cameras you can't achieve focus without some sort of filter, the spectrum is too broad. If violet is in focus the far red shifts out of focus due to the difference in wavelengths.""

The optics of the telescope lenses dictate the focus - the camera sensor has no impact on the focus.

I don't know about the Sony, but the Canon, after the mod still has a UV-IR cut capability based on the remaining filter element.

Using standard photographic lenses can be an issue - not so when used with a telescope.

 

 

But without a filter the full-spectrum sensor is sensitive to wavelengths which might not be in focus - more of a potential problem with refractors. Infra red sensitivity can also cause bloating. On the other hand, imaging with an IR-pass filter can cut down lp, at the expense of loss of colour.

Louise

[Merlin66]

No difference to imaging with a Mono or one-shot colour CCD.

The ability to bring varying wavelengths to the same focus comes down to the type and design of the optical system.

 

[rigradio]

I have a full spectrum Canon 60D, and here are the filters I used to:
- Astronomik Ha 12nm for astrophotography
- Astronomik UV/IR clip in for astrophotography & normal photography (CWB required)
- IDAS LPS D1 for astrophotography
- Kolari vision 590nm & Kenko R1 for IR photography

Ketut