One filter to rule them all!

[AJSullivan]

Hi guys

Recently bought a DSLR for astro as well as normal photography. I was just wondering if their is one particular filter that i should invest in before i start atempting some astro shots? I dont think I can afford to change the filters on the SLR, im also not sure if they do it for my camera (K10D Pentax).

I have a moon filter which gets little use, and i think i have a cheap IR filter somewhere. I get some fringing when i view Venus through my scope though not noticed this on the moon oddly enough.

Any help would be appreciated!

Alex

[russ]

Hi Alex,

Do you have any idea how you want to use the DSLR? For instance, just on a camera tripod for short images of the constellations. Or on a tracking platform for long exposures but still with the camera lens. Or finally hooked up to the telescope?

For constellation shots you probably won't need a filter.

If you want to put a filter on the camera lens you'll need a step down ring. For instance, a lens with a filter thread of 58mm will need a 58-48 step down ring to use a 2" astro filter.

A good filter is the Astronomics CLS 2" filter but it isn't cheap. They do a clip-on filter for Canon DSLR's but i don't think they do one to fit other brands, not even Nikon.

Russ

[AJSullivan]

Well my 80m Refractor is on a AZ Goto, so as long as what I am imaging is high in the sky I should get a few minutes exposure time (i am lead to believe?).

As for the number you through at me, I was a little lost their.

I have bought a T ring and the adapter is winging its way to me, so I can attach it to my scope. If I want to image something such as M45 which is a nice easy one to find (in my relatively light polluted skies anyways), and maybe even the one below orions belt (whose name has escaped me for a moment), which filter will I be able to attach to get the best shots?

Alex

Edit: I was thinking of M42, Orion Nebulae i believe.

[russ]

Ah so you have the bits to attach to the scope. I'm guessing you bought the 1.25" adapter?

For me the Astronomics CLS was too harsh for shorter exposures (2 mins or less) and i ended up capturing nothing with it. I found one of the Neodymium filters a much better bet for shorter exposures. And they are cheap. The Neodymium will only cost £20 in 1.25" form, so nothing really lost if it doesn't pan out. The CLS costs £80 and that's a lot to lose if it doesn't work out.

[russ]

well what do you know, someone has just posted a secondhand CLS in the For Sale section for £45. I still think it blocks too much light for short exposures in a small aperture scope but it maybe worth a punt for that money. It's certainly the right filter for later down the road should the imaging take off.

[jgs001]

Well my 80m Refractor is on a AZ Goto, so as long as what I am imaging is high in the sky I should get a few minutes exposure time (i am lead to believe?).

As for the number you through at me, I was a little lost their.

I have bought a T ring and the adapter is winging its way to me, so I can attach it to my scope. If I want to image something such as M45 which is a nice easy one to find (in my relatively light polluted skies anyways), and maybe even the one below orions belt (whose name has escaped me for a moment), which filter will I be able to attach to get the best shots?

Alex

Edit: I was thinking of M42, Orion Nebulae i believe.

I use the Astronomik CLS on my 80mm AltAz Goto (I assume that's what you mean by AZ). You need to be aiming low in the east or west to get exposures of a couple of minutes. As you get higher in the sky, or further north/south, the exposure times drop before trailing becomes evident. this image was shot with my ST80 equivalent scope with the CLS filter on my AltAz goto as an example.

[russ]

Well i stand corrected.....nice image John

[AJSullivan]

Thanks for the help guys. I am actually ordering a 2" adapter. I hope this is correct. once i take the diagonal out of the scope it is a 2" fitting. I think I am correct in taking out the diagonal? I have a webcam adapter though this couldnt be attached to the T ring of my camera.

As for the filters, the image you posted was pretty good! You used a CLS filter, what do you think of the neo one Rus just mentioned?

Also AZ did mean Alt Az.

Alex

[jgs001]

Cheers Russ , I'm trying hard to break as many rules as I can .

Sorry Alex, not a clue about the Neo filters. I also used a Baader Semi Apo filter on that image to reduce the CA fringing, and I believe that's neo based, but I could be wrong. My filter collection is not extensive. the CLS, Semi Apo, Fringe Killer and Contrast Booster.

[russ]

2" adapter....excellent I didn't want to say anything just in case you had ordered the 1.25". But the 2" is definitely the way to go if you can.

The 2" CLS is not cheap, something like £130. But it is the filter of choice for most poeple.

I loved my Baader Neodymium because it worked a treat at the shorter exposures. But as John has shown the CLS also works really well on shorter exp and that's a filter for the long term. The Neo costs £40 for the 2", so it is cheap. There also a Skywatcher version which is cheaper still.