Astronomics 840nm IR pass filter ?

[todd8137]

Hi all being a keen moon imager and all round moon freak,as any one used /have this filter ,Now i no its a deep ir cut at 840nm so any advice help before a purchase ? I already have the baader one ,and the astronomics 742nm ,but would like the 840 nm,any planetry imagers have any planet or moon images please post or link to i have a hole burning in my pocket

Pat

[riklaunim]

No point in getting such deep IR filter, except maybe Venus as it might show more IR detail than 742. For Moon the Baader should be optimal, 742 if the seeing isn't very bad. For dim planets Baader IR-Pass, for Jupiter 742 if you have to... but if the seeing is good use as broad filter as possible (allows lower gain = less grainy noise, bit shorter exposures, and less resolution loss due to longer wavelengths).

I used ProPlanet 742 a lot, but I switched to broad red/orange/yellow visual filters. They work like IR-Pass/ProPlanet but they pass more visible light. The broader they are they need better seeing (and the object can't be low on the sky due to dispersion - unless you have corrector for that), but they give brighter and better luminance channels of planets (thats easily noticeable on Jupiter). For Moon I usually use the red visual or sometimes ProPlanet 742.

[todd8137]

Hi and thanks for the info all is welcome i do have a set of rgbl and filter wheel for planets but the moon was the main aim all advice taken on board heres a moon image from the 26th of August with the 742

pat

[riklaunim]

Longer wavelengths won't make it better (you will even get lower resolution). Usually Moon is photographed at faster f-ratio than planets to avoid noticeable light diffraction (as Moon has many edges). That + any of good infraredish filter and it works. With SCT I use f/10 and not /f20 for the Moon. f/20 needs very good conditions to work out without diffraction + seeing spoiling it.

[todd8137]

Yes i agree with what you saying i have been at this ifor 3 years now with the moon i do disagree with longer wave lenghts giving lower res as i have some hi res shots of the moon with the 742 filter

that a side i found your web site of great interest to me and it proves we all have diferent styles ,i only have a moddest c9.25 unlike your beast of a sct same with planets i seem to get decent res ect so i lokk forward to your site updates and. Images

Pat

[riklaunim]

As the wavelength increases your telescope achievable resolution decreases. It's a law, not a theory or something. Check http://www.planetary-astronomy-and-imaging.com/en/optical-resolution-and-the-wavelength/

You can put a 5x Barlow to get f/50 but that doesn't mean you will get 5x the resolution. You can get only to some X arcsec/pixel of real detail and that X increases with longer wavelengths.