Initial Test Images

[Chuck]

Finally got out last week to get some initial test images using a Canon 7D Mark II DSLR with my Meade 8" SCT OTA on a Celestron Advanced VX mount. I wanted to see how the setup process for taking images at a remote site was going to go versus a normal visual session. I then wanted to get some quick test shots of the Ring Nebula, Albireo and the moon.

The setup process wasn't too bad but I do have to be more organized, which will come with time. I went to Pardon Gray Preserve in Tiverton due to the good weather forecast and good unobstructed views, especially North, East and South from where I parked. First, as usual, the forecast was wrong and the skies didn't really clear till almost 11PM. Even then, there was high level clouds and a lot of turbulence. Second, the mosquitoes were out in force already. I brought spray just in case and glad I did. Lastly, when packing it in about 12:30AM, the coyotes were out, howling at the moon.

From the few test shots, I was pleased though I need to get the focusing in control. Looks like I really need to invest in a better focuser, so I'll start checking into that soon. Right now I just have the stock focuser on the SCT itself and an old JMI Motofocus which was okay for visual use but won't cut it for AP. I was also having trouble with the focus mode in Backyard EOS as the FWHM values were jumping around quite a bit. Not sure how much was due to the focuser and not so good seeing.

Below are the three test images:

1. Albireo



2. Ring Nebula



3. Moon

[bluemax]

Chuck, how was the DSLR connected to the SCT? Guess these shots were all at F10 or so. I have an Edge 8" SCT and have an adapter which allows use of a DSLR and is F7. Haven't used it yet though. So am curious what you used for these shots. Thanks for sharing your images!

[Bruce D]

Awesome Chuck, that is a very nice image of M57!

[Chuck]

Thanks Frank and Bruce. For quick test shots, I was happy with the results. Just need to be more organized and get a handle on focusing.

@ Frank: With regard to your question on connecting my DSLR to the Meade, I used a Hotech SCA T-adapter and T-ring for my Canon EOS. For the Edge, I think Celestron has a specific T-adapter which sounds like you already have. I'm thinking you just need the appropriate T-ring for your camera though I'm not sure.

I know Ron B. recently purchased an Edge and has mentioned it requires a specific back focus for the best results. Hopefully he'll see this and can answer this best for you.

---- Chuck

[AndyG]

Chuck, excellent, you're off to a great start. A lot has to come together to get to that point, so congrats.

[Chuck]

Thanks, Andy. The 'Imager's Studio' on this board has been a real inspiration on what can be achieved in this field. Clear skies.

----- Chuck

[rjbokleman]

Chuck,

It's great to see that you're now up and running! Looking forward to see more! I can see the color on Albireo too.

BYE and FWHM: The FWHM with Live View on your Canon will indeed jump around due to the seeing. Quite normal behavior actually.

What I do is pick one of our brightest stars in the sky for the season. Right now that could be Vega (East) or Arcturus (Zenith-->West) depending upon what time it is and your East <-- > West preference.

I then slew there using the HC or Stellarium and use my red dot to get the star centered.

Ensure that the Canon is in Manual mode 'M'.

Fire up BYE, connect to the Canon via USB.

Switch to BYE Frame & Focus mode.

Use BYE to set the Canon in 20-30 second exposure mode @ ISO ~800. You can go higher or lower as you prefer.

Initially the star will be very large and out of focus and the FWHM might not even register.

As you turn your scopes focus knob you'll see it getting bigger or smaller...obviously you want to head toward the smaller side ( ) and just ignore the FWHM values until you can visually see it nearly focused with just your eyes in BYE/Live View.

Once you get to that point...now pay attention to the FWHM values as they climb up and down. Let it settle for 10-15 seconds and see what the rough average value being displayed comes out to..say it's 5.0, but jumps up and down between 5.4 and 4.7.

Turn the focus knob clockwise just a hair and then let the FWHM settle again. Are you now above 5.0 average? Another words is FWHM now bouncing between 5.8 and 5.4? If so, we went too far clockwise and you then want to carefully go counterclockwise this time.

Does FWHM jump up and down now between say 5.2 and 4.8? You're now closer and have better focus. The idea is to get the lowest possible average you can making extremely small adjustments remembering, of course, whether you went clockwise or counterclockwise. BTW, I've seen folks recommend using an old clothespin or something similar to make those small adjustments on standard SCT focus knobs.

Things that can mess this up during a nights imaging run are things like temperature (somewhat scope and weather dependent) as well as seeing conditions. However, for most of my work over 2-4 hours all my scopes hold well enough that once I get locked on a star things are pretty good for that night at least.

[rjbokleman]

Focus on an SCT

This brings up a very good side conversation on focusing an SCT for AP. I've been struggling with FWHM (or in Sequence Generator Pro - Half Flux Radius/Diameter (HFR)) on my new C8 EdgeHD. The reason is...focal length..and the extremely tight tolerance in achieving focus. Despite what I just posted about FWHM for Chuck...getting an SCT in focus can be a real challenge.

@ 2032mm (or @ 1422mm with the focal reducer) these scopes can be a bit more challenging to get focus - with a DSLR or CMOS/CCD camera than say something between 420mm-900mm. It seems like when you cross that 1000mm line, it gets more difficult. Not to mention the back focus issues already mentioned by Bill L. That's another whole topic...

I'd been having just this same conversation with Andy G. last week in fact. I'd ignored using a Batinov mask previously since I was having such good luck with FWHM on my scopes 900mm or less. Andy suggested that I revisit that and I finally bought one for the C8 EdgeHD after several out of focus and focus frustrating nights.

Tried it last night for the first time. Used Vega as the target. Took 5 minutes. Bang spot on. If you don't have all the cool auto-focus gear (like me) and are doing this manually a simple Batinov mask for your scope will certainly do the trick. http://www.farpointastro.com/bmask/bmask.php

[Chuck]

Ron, thanks for the info. Actually, after some research, I did purchase a Bahtinov mask that I received yesterday. I'm eager to try it out but I've got to kick this terrible summer cold that has had me laid-up for almost a week. Can't remember when I've had one this bad.

---- Chuck

[Chuck]

Looks like I'm going to be sidelined for a bit longer. My cold finally started clearing up then I was hit with bronchitis and allergies. I had this happen one other time in the 90's. Not fun and takes time to finally clear up. Besides that, I was in the middle of a major master bathroom remodel, when all this started, so I'll need to also finish that up. When it rains it pours. Stay healthy everyone.

---- Chuck