200mm h-alpha Triplet

[Peter Ward]

First (astronomical) light of my Canon 200mm F2.0 proved challenging.... being F2.0 it's quite difficult to nail the focus plus remove camera tilt due the modest weight of the CFW+ CCD....I suspect I'll need some sort of bracket to further support the camera.

Anyway enough waffle..

initial results here (http://www.atscope.com.au/BRO/gallery257.html)

[Larryp]

Showing a lot of promise, Peter. Detail is excellent.

[h0ughy]

wonderful field of view - a lot of data there

[Peter Ward]

Ta Dave. Not sure where next with this lens. I suspect it may go well with the 60da...and Comet Ison ;)

[Bassnut]

mmm, blown to hell, and I think your RCOS hates you now.

[gregbradley]

Looks very promising as you'd hope for a $6,000 + lens. The acid test of a fast lens is chromatic aberration wide open or coma in the corners wide open. Looking good on the coma aspect.

Greg.

[Paul Haese]

Good field of view. What was the sub length? 10 minutes? Or 5?

Center of field looks good but the corners look odd in the provided image. Is the stars in the top right elongated? Then what looks like field rotation in the other corners. I know this would not be the case but is there some tilt of something going on there? I suppose that is the reason for your comment about the bracket. Good potential but what about imaging with that AP RH?

[Peter Ward]

Thanks Paul... So many questions... :)

10 minute subs. The lens/camera simply wouldn't sit flush on the EOS adapter, as there was some slight but ever present play with the bayonet fitting- hence all sorts of tilts were probably going on.....which is a shame as this lens seems to be very well behaved, with minimal aberrations...rare properties for camera lenses.

I'm not really sure how to fix this, but suspect a thin shim might take out any movement. :question:

The weather in Sydney has been appalling of late...in fact the test data was taken with thin cloud and a partial moon...

Despite its sublime performance, I've simply not been able to use the Honders due nil opportunity to get any run of serious data....plus with over 5x the focal length of the 200mm, the field coverage is quite a bit more narrow ;)

[Paul Haese]

I know what you mean about camera adapters. The Nikon one for the QSI has just a tiny bit of slop in it and that makes for some unpredictable tip and tilt. I think a circular shim would fix the problem. Maybe get one made of plastic so it will not come into contact with the points on the lens.

[DavidTrap]

Looks impressive Peter - far better results than I had with a 70-200mm lens on my QSI.

Any chance of a pic of your setup on your mount (I'm after a bit more than your pic posted on the 12th June). I'm interested in how you have cobbled everything together as I'm planning some brackets for my QSI and short focal length lenses. I have a belt driven focuser to add into the mix as well.

ta
DT

[Peter Ward]

No problemo...I'm taking a few days off in the Hunter valley but will post a few pics when I get back :thumbsup:

[DavidTrap]

Ta
DT

[dvj]

F/2 would have little to no acceptance of mechanical tilt. But even more critical is the bandwidth of the Ha filter and its behavior at f/2. I've been testing the AD 3nm Ha filter on my RH200 F/3 with poor transmission results. 5nm seems OK.

Still, this looks like a great combination with the 8300 array.

[Stevec35]

Looks pretty good to me

Steve

[Peter Ward]

As promised.... It was bucketing down outside, so I couldn't open the dome slit for more light without getting everything saturated.

[DavidTrap]

Thanks Peter,

Couple of questions:

Is your camera supported, or does it hang off the lens? I had mine hanging from a 70-200mm lens and I think that is where I got some flexure.

How are you focusing?? Manually twisting the focus ring??

DT

[Peter Ward]

David... the camera is fixed only by its EOS adapter at the moment. The fitting is snug, but does have flexure.

I'm looking at sliding a Losmandy DA under the camera with some sort of thread or cradle to give it more support in round 2.

Focus is by hairy hand and eyeball... not as dodgy as it sounds.. as the STT8300 updates almost in real-time and only takes a few iterations to get it right.

[DavidTrap]

Sounds like we've got something similar in mind. Will hopefully get a chance to do that this week.

Are you focusing by numbers or with a bahtinov mask?

DT

[Peter Ward]

I use the numbers :thumbsup: